Is it possible to have chance happenings, true randomness?

[mowgli]

My question is 'Do we call something random because we don't (yet) have the knowledge to predict the result accurately?'

Lets take the standard example of tossing a coin with our thumb. Lets suppose that we are precisely able to calculate or have knowledge of these values when the coin is tossed:

1. All the physical properties of the coin, like weight, shape, structure etc. that can affect the result of the toss.
2. All the properties in the environment, like graviational force, air resistance, wind in the room, any magnetic forces acting, the hardness of the floor/carpet and other properties that may influence the toss.
3. the magnitude and direction of the force applied to the coin by the thumb
4. The initial position and orientation of the coin and its height from the floor

Using 1,2,3 and 4 (or maybe other pertinent attributes) i think it would be easy to calculate exactly whether the result would be heads or tails, based on the laws of physics.

Or, conversely, an extremely talented person could take such factors into account and always, for example, toss a coin in such a way that only it shows up heads.

A similar argument can be made for the rolling of dice, the functioning of casino machines, every card game(of course,atleast those not involving interaction and thus the free will, of the players) or indeed any other thing that we say happened by 'chance'.

It seems to me that 'happened by chance', 'was a coincidence' just indicate incomplete knowledge. For example, if you and your colleague meet your boss at a wedding, and you didn't know he would be coming to the wedding but your colleague did, you would say you met him by chance, but your colleague would say that he just met him.

In order to avoid these scenarios, in the study of probability, the notion of a fair coin is used. But my question is, is a fair coin only an ideal theoretical construct or can it practically exist? Doesn't every coin toss depend on the force applied to it while being tossed by the person(of course, an infinitesmal change in this force can change the result, so its very difficult to control it). So how can things be random?

Also, as far i understand chaos theory, it says that very small changes in a large system can result in very large changes. For example, a butterfly fluttering its wings in Sri Lanka can lead to a hurricane in the atlantic. So its still possible, however complex it maybe, to model the effects of the butterfly on our atmosphere.

Suppose we can somehow model the universe on a extremely powerful computer and somehow manage to program all the causes, effects and laws of physics, won't it able to predict each and every seemingly 'random' occurrence with extreme accuracy? (please ignore the effects of beings with Free Will, i.e just suppose that we are modeling a part of the universe with no Free Will entities).

How does all this fit in with probability theory which says that the chance of the head turning up in a fair coin toss is 0.5 ? Do we attribute something to chance or randomness when we have incomplete knowledge of it.

[mowgli]

Also, there is an extremely interesting way of calculating the value of pi from randomness. Take a square and draw a circle inside it. Now, randomly choose , say, a 1000 points in the square. Now, count the number of points that are inside the circle and label it as nc. Let the radius the circle be r, and the length of the side of the square be s. Thus the area of the square is s*s and the are of the circle is pi*r*r. Since the chance of the points falling into the circle is directly proportional to the area of the circle we have the following equation
(pi*r*r)/(s*s) = n/1000
Knowing the values of r, s and n, we can calculate the value of pi. Of course, the more points that we randomly choose inside the square(we chose 1000, in this example), the better estimate we get. Pi has actually been calculated using this method to a high degree of accuracy but the quality of the result depends on the random choosing of points to be truly random.

[Godless Wonder]

Pi has actually been calculated using this method to a high degree of accuracy but the quality of the result depends on the random choosing of points to be truly random. Does this not answer the question in the OP? To how many significant figures would have you to figure the value of pi before you would decide to call your source of random data "truly" random? Finite? or infinite? If you did have a truly random source of data, how would you verify this?

Seems like the Heisenberg uncertainty principle might be something worth looking into wrt "true" randomness.

[Mallow o' the Marsh]

My question is 'Do we call something random because we don't (yet) have the knowledge to predict the result accurately?'

Good question. :thumbs:

I think, as you said, that randomness is in he eye of the beholder. When something is known (the outcome of the coin flip, for instance), there is no randomness. When it can't, there is.

Of course, this seems to conclude that there is no absolute randomness, which is kind of sad to think about (no free will).

Currently, there are some phenomena in quantum mechanics that appear to be truly random (spontaneous creation of particle pairs, quantum tunneling, exact location of a particle, etc). Who knows whether or not we will find a cause for these.

[Loren Pechtel]

At the most basic level randomness will come from quantum uncertainty.

[mowgli]

If you did have a truly random source of data, how would you verify this?


There are some statistical tests that determine the quality of random numbers, here is a
link (http://burtleburtle.net/bob/rand/testsfor.html)

Note that generation of random numbers is very important in a number of fields, especially cryptography(to chose keys etc.).

So are you saying that its impossible to know whether a source of data is truly random or that there is no truly random source of data?

Good question. :thumbs:

I think, as you said, that randomness is in he eye of the beholder. When something is known (the outcome of the coin flip, for instance), there is no randomness. When it can't, there is.

Of course, this seems to conclude that there is no absolute randomness, which is kind of sad to think about (no free will).

Thanks!
But the question of free will is a different one.

Lets suppose we have an all knowing computer, which predicts which number you can choose. But if you have the knowledge of the computer saying that you will choose a 9, you can choose a 6 to spite it. In this case, the computer has to be updated with the new state of your mind i.e of you knowing of the computer's earlier prediction. Now the computer will make a new prediction of you choosing 6 and the process can continue forever.

So, to get around this, you must not have any direct or indirect contact with the said computer, or, the computer can only make the same decisions/choices as you, simultaneously as you do. That would equivalent of replicating your mind. There are no laws that predict the behaviour of the mind, (for example, which number you choose at a particular time) unlike laws of physics which are pretty well understood.

At the most basic level randomness will come from quantum uncertainty.

Has quantum uncertainity proven to be unmodelable? Or are we brushing the issue under the carpet of quantum mechanics because we don't understand it well right now? Can't we in the future (atleast theoretically) model the quantum states accurately enough to predict them? Is there something fundamentally stopping us from doing so?

I am interested in this quantum randomness. Please provide some good material if you know any.

[Loren Pechtel]

Has quantum uncertainity proven to be unmodelable? Or are we brushing the issue under the carpet of quantum mechanics because we don't understand it well right now? Can't we in the future (atleast theoretically) model the quantum states accurately enough to predict them? Is there something fundamentally stopping us from doing so?

I am interested in this quantum randomness. Please provide some good material if you know any.

If someone succeeds in modelling it so it's not so uncertain anymore a *LOT* of physics goes down the tube.

[premjan]

I don't think quantum has to be invoked, there are the statistical Bell Curve laws (the laws of large numbers) that can be empirically tested for any given random distribution generated by various physical systems.

[Mallow o' the Marsh]

Thanks!
But the question of free will is a different one.
No randomness = no free will. If there is no randomness, there can be no choice, no "fork in the road", so to speak. Everything is predetermined, everything has a cause. Ergo no free will.



Lets suppose we have an all knowing computer, which predicts which number you can choose. But if you have the knowledge of the computer saying that you will choose a 9, you can choose a 6 to spite it.
Then the computer would not be all knowing.



That would equivalent of replicating your mind. There are no laws that predict the behaviour of the mind, (for example, which number you choose at a particular time) unlike laws of physics which are pretty well understood.

If you believe the mind is just a series of electrochemical interactions (no soul or other metaphysical part), then there are laws that govern it completely. The human mind is incredibly complex, making any attempt at modelling or predicting it unfeasible - for now at least. I have no doubt that one day scientists will be able to plug a person into a machine and predict what he will be thinking based on sensory input and past experiences. Just like the Butterfly effect, if you have enough data and measurements, you can determine things that otherwise seem random.

[mowgli]

Then the computer would not be all knowing.



I think such an all knowing computer is logically impossible to construct.
Look here for a very good discussion on Newcomb's paradox (http://en.wikipedia.org/wiki/Newcomb's_paradox) which precisely discusses this very point.

On the other hand, a computer, which, when given a current state of mind and its inputs, predicts the next state of mind is certainly plausible. What I meant was, the computer does not factor in, initially that you will be knowing what the computer predicted. I wasn't talking about an all knowing computer but a all-calculating computer used to predict the future. If it does only that, then it might guess that you will choose a 6 with the updated knowledge that it now has.


If you believe the mind is just a series of electrochemical interactions (no soul or other metaphysical part), then there are laws that govern it completely. The human mind is incredibly complex, making any attempt at modelling or predicting it unfeasible - for now at least. I have no doubt that one day scientists will be able to plug a person into a machine and predict what he will be thinking based on sensory input and past experiences. Just like the Butterfly effect, if you have enough data and measurements, you can determine things that otherwise seem random.

I am with you there but have a few questions.
Will that machine be conscious? Do you think scientists will ever be able to make a conscious machine? and how would we test for it?
And what would be the differences between such a machine and a completely genetically engineered thinking being?

[mowgli]

If someone succeeds in modelling it so it's not so uncertain anymore a *LOT* of physics goes down the tube.

Well, my main query was, does such a modeling have a logical barrier against it? In other words, has it been proven to be impossible to model? Or is it possible but we don't know how do it yet?

[Godless Wonder]

No randomness = no free will. If there is no randomness, there can be no choice, no "fork in the road", so to speak. Everything is predetermined, everything has a cause. Ergo no free will.
You make a mistake if you think that randomness gets you free will. (Something which you haven't said, I realize.) Suppose you have a deterministic system and you interject random perturbances from the outside. These random perturbances do not magically enable the beings inside this mostly deterministic system to have more free will than beings in an equivalent deterministic system without those random perturbances. It just means those beings are unpredictable, since they get influenced by random perturbances.

[Dark Knight Bob]

Statistical chance has a lot (well everything really) to do with chaos theory. I.e there are VERY few deterministic systems (and none at all when you learn about quantum theory) that exist. Newton discovered some with his laws of motion but it became apparent that they only work for 2 bodies. Once you introduce a third the rules 'break. The system is chaotic. As it happened during newtons era people were only looking for deterministic systems. Physicists couldn't give a hoot about non-linear systems that couldn't be predicted.

For instance a simple harmonic oscillator doesn't exist. It's used to predict oscillations of small angles but mathematically if you extend that to large angles it no longer works. So it was a sort of 'fix' to do physics with.

So in order to deal with chaotic systems where you cannot find true determinism you use statisitics to find patterns within the chaos on which to draw out elements of the whole. This is why scientists don't get 100% accurate experiments. If something is 99.99% accruate however it can be assumed that the 0.01% error was due to other unknown factors that can't either be measured or have yet to be investigated. historically this leads onto quantum physics where it turns out there is no truely deterministic system because a system cannot be consistent if it is able to measure itself. We're part of the universe so whilst determinism exists from outside the universe we can never 100% measure it.

When you flip a coin you have 2 possible outcomes. now that doesn't mean you would get heads and tails one after the other each time because then you would have a 100% certainty of what was going to happen. Each flip is independant of the last but because there is a major factor involved (it has to land either head or tails up) it will tend towards a 50/50 split over time. What influences the differance is due to differing initial conditions and subtle influences in the environment. If these influences were large enough then the odds would tend away from being 50/50 towards mabye 40/60 (certain american coins do this due to angled edges).

But as these influences within the state of the system are small and random (random in the sense that they are not the same each time. The only constants are the size and shape of the coin) over a long enough time period you would get the majority of results being a 50/50

An interesting effect known as the random walk would mean however that even the most microscopic flaw in the coin could bias it. 50.000001% chance of losing would mean that given enough time you would eventualy lose more than you'd win. This is how casinos also win even when the odds seem even. The roullete table wins evn on red + black because of the green 0. The more you play the more likely it is you'll lose.

If you ever want to win on a roulette table, put ALL your money on red or black doesn't matter which and play ONE round only. This gives you the greatest chance of winning.

If you could calculate the small factors such as air resistance etc you would be able to get a more accurate distirbution of tosses. Your odds would increase. But doing so is extremely difficult due to the nature of chaotic behaviour.

So basically it is determined but there is no way to know for 100% how everything works so in that sense random behaviour exists.

Chaos is really more to do with unpredictability rather than a butterfly causing a hurricane. The hurriacane would most likely still occour if it was only the butterfly that influenced it because of other thresholds that simply over power the butterfly's effect.

In mathematical terms it is more to do with non-linear systems. Everything to do with calculus is to do with determining if a system is linear or not.

The problem is that there are infinitiely more non-linear systems than linear. This is where statistics can come in to reduce it down to it's components

Suppose we can somehow model the universe on a extremely powerful computer and somehow manage to program all the causes, effects and laws of physics, won't it able to predict each and every seemingly 'random' occurrence with extreme accuracy? (please ignore the effects of beings with Free Will, i.e just suppose that we are modeling a part of the universe with no Free Will entities).


The short answer is no. Not for a 100% accuracy. The more you knew the more accurate it would be but the further forward in time you go and the smaller the error you want the more exponential amount of data you need.

fortunately for cosmology we don't need to know how each atom is moving to predict how galaxies work (to some degree) because they are so large. We can use the laws of averages to show that whilst there is random behaviour within a system on average it produces a bias in one direction.

Boyles law works on this prinicple. There are a few VERY high energy particles in system whizzing about and a few very low energy particles but the majority are of the same temperature. So a temperature of a gas is the average temperature but you can be certain that the majority are acting in that way. In fact you can tell just how many within a system are of that temperature though you will not be able to pick out any individual one.

I've listed more examples than explanations here but as with anything statistically if you average enough together you'll get the big picture :D

Ok i see i'm the only one laughing... :banghead:

[epepke]

Well, my main query was, does such a modeling have a logical barrier against it? In other words, has it been proven to be impossible to model? Or is it possible but we don't know how do it yet?

I'm going to try to answer this.

You were quite correct in your original posting in that if you knew everything about a system that was sufficiently classical (a coin toss, say) that you could predict it exactly. Chaos theory suggests that if you don't know everything exactly, then a better measurement is not guaranteed to bring you closer to the result.

Now, quantum uncertainty is something that everybody wonders about, and your question is one that most people come up with. It's natural to think that, if the instruments were just a bit more sensitive, that we could detect causality.

There are a couple of problems with this. The first is that the reason to think in terms of quantum uncertainty in the first place was that, eighty years or so ago, out instruments got so precise that they would have been able to detect classical behavior. Of course, they've gotten way, way more sensitive since then. So if there were a way of making it all classical, we would probably have been able to detect it right now.

However, there's a much stronger reason. In QM, pairs of particles can be coupled, so that with two particles that are even very far away, taking a measurement of one seems to have an effect on taking a measurement of the other. This has been detected on experiments up to a few kilometers big. This is a problem, because according to relativity, it should not be possible to send a signal faster than c.

It seems that it isn't. Nobody has ever succeeded in sending a signal faster than c. It's only when the signals from the detectors are brought back together that the coupling is apparent.

So, nature does seem to have this coupling, and it also seems to have a limit of c for sending a signal at once. The only way for this to work is if there is a truly, unbeatably random component to the process, one that cannot be predicted. If it were possible to predict it, even slightly, then the people on the ends of the communication system could use it as sort of a code book and send signals to each other faster than light.

[Loren Pechtel]

Well, my main query was, does such a modeling have a logical barrier against it? In other words, has it been proven to be impossible to model? Or is it possible but we don't know how do it yet?

If you can model it, down goes the Heisenberg Uncertainty Principle. And with it goes a lot of physics.

[Mallow o' the Marsh]

I think such an all knowing computer is logically impossible to construct.
I think so too. Certainly impossible for me :) However, see below.


On the other hand, a computer, which, when given a current state of mind and its inputs, predicts the next state of mind is certainly plausible. What I meant was, the computer does not factor in, initially that you will be knowing what the computer predicted. I wasn't talking about an all knowing computer but a all-calculating computer used to predict the future. If it does only that, then it might guess that you will choose a 6 with the updated knowledge that it now has.
I thought about this for awhile, and I think this is, as you said, a logical paradox. Since the person will not pick whatever number is displayed, it is logically impossible to display the correct number. It should be possible for the computer to display a number, determine if the person will reject it or not, and determine the correct number the person will pick, but not display it.



I am with you there but have a few questions.
Will that machine be conscious?
Not necessarily. It could just be a humonguous calculator. Intelligence is not required to model things.


Do you think scientists will ever be able to make a conscious machine?
Absolutely. Animals have been cloned, although that is probably not what you were thinking of. Certain levels of consciousness (although not up to our level) have allready been "built" in the classical sense; i.e. neurons on an electrical grid connected to sensors and stimulators.



and how would we test for it?
The classic test is the Turing test, of course, but that uses a very narrow definition of consciousness. No one really agrees on what consciousness really is, which makes it pretty hard to test for.


And what would be the differences between such a machine and a completely genetically engineered thinking being?
Assuming the same physical "specs" between both of them, nothing I would say.

[Mallow o' the Marsh]

You make a mistake if you think that randomness gets you free will. (Something which you haven't said, I realize.) Suppose you have a deterministic system and you interject random perturbances from the outside. These random perturbances do not magically enable the beings inside this mostly deterministic system to have more free will than beings in an equivalent deterministic system without those random perturbances. It just means those beings are unpredictable, since they get influenced by random perturbances.

I agree. Randomness does not cause free will, but it is a requirement. Good point, I had not thought of that.

[Mallow o' the Marsh]

I think we all agree that, as far as we know now, there are certain principles in quantum mechanics that are random. However, many things seem random, but as we learn more about the universe, we learn they have causes behind them. What if these phenomena have causes that we don't yet know about, something that makes them nonrandom? Couldn't we then model them, and the rest of the universe, with a sufficiently powerful computer?

Admittedly, for this to work the universe must be nonrandom. If they aren't, then all bets are off and, as you say, we can at best model classical phenomena to a certain degree of accuracy.

[Schneibster]

Edward Lorentz proved in 1963 that you can generate stochastic results on a computer. Chaos is not a matter of not knowing enough to predict the outcome; it is a matter of not ever being able to know enough to set the initial conditions.

You can run a computer program that draws a mandelbrot figure; but there is no mathematical procedure that is simpler than the computer program that can predict where the next dot will go.

And yes, the uncertainty principle underlies it.

[epepke]

I think we all agree that, as far as we know now, there are certain principles in quantum mechanics that are random. However, many things seem random, but as we learn more about the universe, we learn they have causes behind them. What if these phenomena have causes that we don't yet know about, something that makes them nonrandom? Couldn't we then model them, and the rest of the universe, with a sufficiently powerful computer?

That's why I said that I would try to explain this. It's difficult to do so. To discover that there is no randomness in QM wouldn't simply be a process of getting better at investigating. It would necessarily mean that Relativity is just totally fucked. And then someone would have to come up with a different theory\'

[epepke]

I think we all agree that, as far as we know now, there are certain principles in quantum mechanics that are random. However, many things seem random, but as we learn more about the universe, we learn they have causes behind them. What if these phenomena have causes that we don't yet know about, something that makes them nonrandom? Couldn't we then model them, and the rest of the universe, with a sufficiently powerful computer?

That's why I said that I would try to explain this. It's difficult to do so. To discover that there is no randomness in QM wouldn't simply be a process of getting better at investigating. It would necessarily mean that Relativity is just totally fucked. And then someone would have to come up with a different theory\'

[B_Sharp]

If you practise long enough, you can flip a coin consistantly. Magicians practise tricks like that for long hours.

[Sven]

I think we all agree that, as far as we know now, there are certain principles in quantum mechanics that are random. However, many things seem random, but as we learn more about the universe, we learn they have causes behind them. What if these phenomena have causes that we don't yet know about, something that makes them nonrandom? Couldn't we then model them, and the rest of the universe, with a sufficiently powerful computer?
What you are looking for are Bohmian interpretations of QM (just google). They in essence say that QM is not random, but depends on some "hidden" variables - but which are impossible to detect (thus "hidden")!
But there's Bell's theorem (just google) which in essence says: either QM is random, or if it's not random, than communication faster than light is possible (contradicting relativity).

In the end we have to choose between two possibilities (randomness vs. faster than light) which make us both uncomfortable. That's life. :p

[Mallow o' the Marsh]

To discover that there is no randomness in QM wouldn't simply be a process of getting better at investigating.
Isn't this how science progresses? Science investigates something, and comes up with a theory describing how things work. Then they do more/better investigation, and come up with a better theory.


It would necessarily mean that Relativity is just totally fucked. And then someone would have to come up with a different theory\'
You are probably right. I don't have a better theory. I don't even have a better idea. I am saying that, if there turns out to be no randomness in quantum mechanics (which is this last place where we see randomness, as far as I know), then there would be no randomness in the universe. All of my other speculations follow this.

[Mallow o' the Marsh]

But there's Bell's theorem (just google) which in essence says: either QM is random, or if it's not random, than communication faster than light is possible (contradicting relativity).
You probably have a better understanding of this than me, but how does quantum tunneling fit into the picture. The last I heard (I can't find the link), some scientists at the university used it to transfer one of Mozart's symphonys across a barrier at FTL "speeds".

[ueit]

First of all I’d like to say Hello to everybody, it’s my first post here.

There are a few problems IMO about the uncertainty principle. Let’s consider the position – speed pair. Now, what is speed? A change in position. What is the logic of asking what is the change in position at a specific position? You just cannot logically define speed if you don’t have at least two points. If you have one point, the particle “rests� at that point, if you have two, you can speak about speed but you don’t have a precise position anymore. Now, in classical physics you can make the distance between two points as close to zero as you like. It seems to me that QM tells us that in reality you cannot. Perhaps the nature tells us not that there is true randomness but that we ask the wrong questions. If the space itself is quantified there is no mystery why you cannot know both speed and position with 0 error.

Let’s think about other such parameters, energy and time. The energy can be considered to be a change in shape. What is the logic in asking how the shape changes in one moment? If dt is 0 you don’t have change, if it’s not 0 you have change (so you have energy) but you have not one moment in time, but a time interval. The conclusion could be that time is quantified and you cannot make dt smaller than a certain value.

I don’t know what to say about the spin around more axes. I’d appreciate if someone with more knowledge in QM than me (not at all hard to find here) could point me in the right direction.

P.S.
Please excuse me for the bad English, it’s not my native language.

[Sven]

First of all I’d like to say Hello to everybody, it’s my first post here.
Welcome! :wave:

There are a few problems IMO about the uncertainty principle. Let’s consider the position – speed pair. Now, what is speed? A change in position. What is the logic of asking what is the change in position at a specific position? You just cannot logically define speed if you don’t have at least two points. If you have one point, the particle “rests� at that point, if you have two, you can speak about speed but you don’t have a precise position anymore.
What you of course ignore is that speed can not only be quantified as time for travel between two points, but also as kinetic energy. Measuring the energy of a (free) particle means determining its speed - no need for two positions. One can define speed without them.

Now, in classical physics you can make the distance between two points as close to zero as you like. It seems to me that QM tells us that in reality you cannot.
QM tells no such thing. Every intergral in QM is solved over continous space, it is not a sum over a discrete space.

Perhaps the nature tells us not that there is true randomness but that we ask the wrong questions. If the space itself is quantified there is no mystery why you cannot know both speed and position with 0 error.
I have no idea how this follows.

Let’s think about other such parameters, energy and time. The energy can be considered to be a change in shape.

WTF? Do you have any idea what energy is?

What is the logic in asking how the shape changes in one moment?
Since no one asks things like this, this is a red herring based on your misunderstanding of physics.

If dt is 0 you don’t have change, if it’s not 0 you have change
Nonsense. What you mean is not dt, but dE/dt.

but you have not one moment in time, but a time interval.
If you talk about dt, you have an infinitesimally small time interval - in other words, a moment in time.

The conclusion could be that time is quantified and you cannot make dt smaller than a certain value.
Even if you were right above, I still don't see how this follows.

I don’t know what to say about the spin around more axes. I’d appreciate if someone with more knowledge in QM than me (not at all hard to find here) could point me in the right direction.
Are you talking about the uncertainty principe for angle and angular momentum?

P.S.
Please excuse me for the bad English, it’s not my native language.
It's at least as good as mine - and I'm also no native speaker. :)

[Sven]

You probably have a better understanding of this than me, but how does quantum tunneling fit into the picture. The last I heard (I can't find the link), some scientists at the university used it to transfer one of Mozart's symphonys across a barrier at FTL "speeds".
Sorry, I don't now much about this, but as far as I know this is mainly a problem of defining the speed of the signal. Waves have a phase speed and a group speed; there's also something called the front speed (and probably a few others). I've no idea which of these speeds is actually faster than light in the experiments, and which of these speeds represents the "speed of information".
You could write Jesse a PM about this and invite him here, he's a real relativity crack.

[Dark Knight Bob]

Now, in classical physics you can make the distance between two points as close to zero as you like.

But how do you measure those points beyond the theoretical?

If you can only measure how fast a tennis ball is travelling by firing a tennis ball into it you change the velocity it was travelling at (because they weight about the same so it will cause it to bounce in a different direction). "But why not just look at where the tennis ball you threw at it went" you might ask. well the only way to see THAT tennis ball is to throw another tennis ball at it. And you need a nother tennis ball to see that one too etc etc.

Now in QM the problem is that when you go small enough you can't go any smaller so there is no way to make the object doing the measuring (i.e light) go any smaller so that whatever impact it makes is negligible.

Classical physics assumed an infinitely reducible mass (it also assumed made some assumptions about light itself that turned out to be wrong)

Now where chaos comes into it is because you can't use a large motion to extrapolate an inifitely long motion without knowing EXACTLY the initial conditions.

You can reduce it somewhat by making the motion extremely simple but it is impossible except in very few instances mathemtaically (i.e calculus) to tell if the motion will remain stable or chaotic. Even with the orbit of planets etc. You could get a limit within a finite amount of time but even then only to a degree of accuracy. Not an absolute. It is impossible for instance to calculate whether our planet will one day develop an expontential chaotic motion and fling itself into the sun or out into the universe.

Again this all makes a lot of sense when you realise that everything is physically linked to everything else and all it's forces work relative to each other. Even a grain of dust on the outskirts of the solar system affects our planets orbit. It doens't affect it much and on it's own the universe will probably end before it can affect the earths orbit but it is a component that makes it impossible to deterministically calculate the earths exact orbit. We can only rely on statistical extrapolation whereby we look at the average amount of dust and it's density in regard to it's radius from the sun and make a reasonable estimation (we can do this to a high degree of accuract that is relative to a point where it won't affect any other calculations we make for say the next billion years of so) but it will still be an unknown chaotic component.

[ueit]

Sven,
Thank you for your answer. I’ll try to explain my previous statements.

I said that the energy could be considered as a change in shape. I had in mind the concept of mass in superstring theory. In “The Elegant Universe� Brian Green says:

According to string theory, the properties of an elementary "particle"—its mass and its various force charges—are determined by the precise resonant pattern of vibration that its internal string executes.

We know that mass and energy are equivalent, so we can say that a particle energy is given by the vibration of its “internal� string (the change in shape of the string).

I do not know how to think of mass in QM. AFAIK it says that the particles exchange with the vacuum some yet undiscovered bosons (higgs). If this is true then the mass (energy) of a particle will be given by the average number of collisions between it and the surrounding higgs bosons. If the time interval in which you measure the energy is close to 0 you could find a very high energy (in the moment of collision with the higgs) or a 0 energy (between collisions).

I was wrong writing dt, I wanted to say a delta t, a time interval, but I didn’t have the right letter. Sorry for confusion.

Quote:
The conclusion could be that time is quantified and you cannot make dt smaller than a certain value.

Even if you were right above, I still don't see how this follows.

If the time is not quantified you could say that no matter how small your time interval is, there is enough time for the string to vibrate, or for a big enough number of higgs bosons to collide with your particle in order to get you a well defined energy. However, the HUP shows us that this is not the case. One possible explanation for this could be that you cannot make your time interval too small, or in other words, the time is quantified.

What you of course ignore is that speed can not only be quantified as time for travel between two points, but also as kinetic energy. Measuring the energy of a (free) particle means determining its speed - no need for two positions. One can define speed without them.

Now, if you cannot ask what the energy is at a specific time it’s of no use to replace the speed with kinetic energy. You will need some time to determine the energy (by counting the collisions with higgs or studying the change of the shape of the string) and when you finish the particle will not be at that position anymore. It still seems to me that it is not logical to ask what the speed (or, if you want, kinetic energy) is at a specific point in space.

Quote:
Now, in classical physics you can make the distance between two points as close to zero as you like. It seems to me that QM tells us that in reality you cannot.

QM tells no such thing. Every integral in QM is solved over continuous space, it is not a sum over a discrete space.

I didn’t want to say that space is quantified in QM but that we could interpret the HUP as evidence for a quantified space and not for the existence of true randomness. If space is quantified the HUP is a logical consequence. There is no such position, let’s say c5.676 on a chessboard. It can be c5 or c6. Asking for a more precise answer is absurd.

Are you talking about the uncertainty principle for angle and angular momentum?

Yes, but I think that angular momentum is more an analogy than a correct definition of spin.

[Mallow o' the Marsh]

Sorry, I don't now much about this, but as far as I know this is mainly a problem of defining the speed of the signal. Waves have a phase speed and a group speed; there's also something called the front speed (and probably a few others). I've no idea which of these speeds is actually faster than light in the experiments, and which of these speeds represents the "speed of information".
You could write Jesse a PM about this and invite him here, he's a real relativity crack.

From this (http://www.aei-potsdam.mpg.de/~mpoessel/Physik/FTL/tunnelingftl.html) link (a brief overview of the experiment I was referring to, but with a bunch of references): "in special relativity neither information nor energy are allowed to be transmitted faster than light, but that certain velocities in connection with the phenomena of wave transmission may well excede light speed."

Going back and reading some more about it, the experiment I mentioned doesn't necessarily contradict special relativity. I was getting a bit far afield of the OP anyway :)



First of all I’d like to say Hello to everybody, it’s my first post here.

:wave:

[Sven]

I said that the energy could be considered as a change in shape. I had in mind the concept of mass in superstring theory. In “The Elegant Universe� Brian Green says:
[snip]
We know that mass and energy are equivalent, so we can say that a particle energy is given by the vibration of its “internal� string (the change in shape of the string).
(1) I'm quite sure that Green is talking about the rest mass here, since he also mentions charge, which is an intrinsic property of the particle. Another argument that he means the rest mass is that the "relativistic mass" (it's energy) is not defined without a reference point in relation to which the speed of the particle is measured.
So the kinetic energy which manifests itself as part of the relativistic mass simple isn't one of the things which changes the vibration of the "internal strings."
(2) Change of vibration is not change in shape.

I do not know how to think of mass in QM. AFAIK it says that the particles exchange with the vacuum some yet undiscovered bosons (higgs). If this is true then the mass (energy) of a particle will be given by the average number of collisions between it and the surrounding higgs bosons. If the time interval in which you measure the energy is close to 0 you could find a very high energy (in the moment of collision with the higgs) or a 0 energy (between collisions).
I think you overemphasize the particle concept of Higgs bosons here. Remember, we always have the wave-particle-duality, I'm really not sure if this gedankenexperiment makes sense. AFAIK, collisions with Higgs bosons is more of a model explanation that the "real thing". But I'm sure that others with more knowledge of quantum physics will comment on this.

I was wrong writing dt, I wanted to say a delta t, a time interval, but I didn’t have the right letter. Sorry for confusion.
OK. But it's still delta E / delta t what you were talking about.

If the time is not quantified you could say that no matter how small your time interval is, there is enough time for the string to vibrate, or for a big enough number of higgs bosons to collide with your particle in order to get you a well defined energy. However, the HUP shows us that this is not the case. One possible explanation for this could be that you cannot make your time interval too small, or in other words, the time is quantified.
As I said above, the kinetic energy of a particle does not manifest itself in vibration of strings. And the collisions with Higgs bosons is (probably) too much classical thinking. So your conclusion is likely based on faulty premises.
Apart from this, (as far as I know) the HUP for time and energy is fundamentally different than the HUP for position and momentum / angle and angular momentum / etc. since it can not be derived the same way.

Now, if you cannot ask what the energy is at a specific time it’s of no use to replace the speed with kinetic energy.
But you can ask this at any specific time by simply collinding the particle with another of known energy and observing the scattering.

You will need some time to determine the energy (by counting the collisions with higgs or studying the change of the shape of the string)
No. The collison is instantly. The interpretation of the collision is of course not, but that's irrelevant.

and when you finish the particle will not be at that position anymore.
Yes. So what? At the moment of collision, it is at a specific position.

It still seems to me that it is not logical to ask what the speed (or, if you want, kinetic energy) is at a specific point in space.
What's the problem? :huh:

I didn’t want to say that space is quantified in QM but that we could interpret the HUP as evidence for a quantified space and not for the existence of true randomness.
OK, misunderstood you in some way. Sorry.
Your argument in the OP has another problem: The HUP says that the product of the uncertainties is a certain value (h-bar/(2*pi)) - how does this follow form quantified space?

And let us think this through. If space is quantified, then a particle has to "hop" from one position to another. Thus its position is determined exactly at each time. Following the HUP, it's speed is thus entirely undetermined.
But if the position of the particle is determined exactly at each time, we can detect the particle at two different times at two different positions and thus determine its speed. Since the quantisation of space has no influence on the detection (as far as I see it), we would get the same result every time we measure the speed. So we would also get a definite speed - in violation of the HUP.
So quantisation of space does in effect [b]nothing[/n] to explain the HUP.

If space is quantified the HUP is a logical consequence. There is no such position, let’s say c5.676 on a chessboard. It can be c5 or c6. Asking for a more precise answer is absurd.
As I demonstrated above, there's no reason why the HUP should be a logical consequence.


Yes, but I think that angular momentum is more an analogy than a correct definition of spin.
Are we talking about the spin of a single particle (for which angular momentum is not an analogy, only looking at the spin itself as an rotation is), or the rotation of an entire molecule? For the latter, I think the classical notion still makes sense (at least in a way), especially for high rotational excitation.
On the other hand, one could also say that position/momentum (i.e. travel on a straight line) is more an analogy if we talk about the quantum world (just think about particle-in-a-box).

[Schneibster]

First of all I’d like to say Hello to everybody, it’s my first post here.Hi! And welcome.

There are a few problems IMO about the uncertainty principle. Let’s consider the position – speed pair. Errrrmmmm, it's position/momentum, not position/speed.

Now, what is speed? A change in position. What is the logic of asking what is the change in position at a specific position? You just cannot logically define speed if you don’t have at least two points. If you have one point, the particle “rests� at that point, if you have two, you can speak about speed but you don’t have a precise position anymore. Have you ever heard of calculus? The meaning of the scalar speed component of momentum is the infinitesimal change in position over an infinitesimal time: dx/dt. Calculus is math for determining the exact meaning of this given some observations.

Now, in classical physics you can make the distance between two points as close to zero as you like. It seems to me that QM tells us that in reality you cannot. Perhaps the nature tells us not that there is true randomness but that we ask the wrong questions. If the space itself is quantified there is no mystery why you cannot know both speed and position with 0 error.I'm not sure why you think either that QM says you cannot make the distance between two points arbitrarily close to zero, or why you say that quantification of spacetime (according to SRT there is no separate space and time, only the one thing) would make it clear why you cannot know position and momentum with arbitrary accuracy. I'm not saying you're wrong, but that I'd like to know your thought process that leads to these assertions before I comment.

Let’s think about other such parameters, energy and time. The energy can be considered to be a change in shape. This I do not follow at all.

[epepke]

Isn't this how science progresses? Science investigates something, and comes up with a theory describing how things work. Then they do more/better investigation, and come up with a better theory.

I should probably have written "better at measuring." We're way good at measuring. There are several commercial quantum cryptography systems that work at up to 100 km. That should give an idea of how good we are at measuring quantum stuff. This is not your great-grandfather's double-slit experiment.

As for how science progresses, that's a difficult question with a difficult answer. I think Isaac Asimov said it best. The most important words in science are not "Eureka!" but "Hmm... that's funny." Really new theories come across when there's a smoking gun. There are a few things that are maybe smoking derringers out there, but QM and SR/GR were based on smoking cannon.

You are probably right. I don't have a better theory. I don't even have a better idea. I am saying that, if there turns out to be no randomness in quantum mechanics (which is this last place where we see randomness, as far as I know), then there would be no randomness in the universe. All of my other speculations follow this.

What I was trying to show was that there are a vast number of observations, consistent with existing theory, that show good reason to believe that there must be randomness in QM, with a minor proviso: that we want to believe that there are events that do or do not happen. At the very least, however, deterministic classical thought seems doomed no matter which way we go. Either we have to accept randomness, or we have to stop thinking in terms of events that do or do not happen.

As for QM, it means little to say that QM is the last place, because QM is everything. You are seeing these words because of QM. It's built in a macroscopically-effective way into your very retina, which would not work without QM. If you read this paragraph, and you remember what it says, that's all due to QM.

It's just that, in a large number of situations, so much of the QM weirdness cancels out, so that we can look at things classically, with negligible chance of ever coming to the wrong conclusion. Still, there's always a probability, which can be calculated, that a classical approximation won't work. When the mean time between violations is something like a googelplex times the age of the universe, we tend to lose interest. But there's really no magical scale at which the universe ceases to become quantum. The fact that the light from the most distant galaxies reaches us is, every bit of the way, determined by quantum behavior. Even the fact that light travels in a straight line (actually a geodesic) is determined by quantum behavior.

[Dark Knight Bob]

Richard Feynman once tried to put the accuracy of QM into perspective as having the same accuracy of measuring the distance from london to new york to within an accuracy of a hair's width.

Being uncertain doesn't mean you can't do anything with it or that it's somehow the end of the line.

[ueit]

Dark Knight Bob:
If you can only measure how fast a tennis ball is traveling by firing a tennis ball into it you change the velocity it was traveling at (because they weight about the same so it will cause it to bounce in a different direction).
I am aware of Heisenberg’s gedankenexperiment (gamma-ray microscope). However, I think that there is more to HUP than only the lack of a delicate-enough “tennis ball�. I’m thinking at double-split or Aspect experiments. I think that HUP shows us something fundamental about the universe we live in, but the question is “what?�. Some say that there is true randomness. I’m trying to figure-out if this randomness is not a consequence of a misunderstanding of reality.
Sven:
(1) I'm quite sure that Green is talking about the rest mass here, since he also mentions charge, which is an intrinsic property of the particle.
I think you are right, my mistake.
So the kinetic energy which manifests itself as part of the relativistic mass simple isn't one of the things which changes the vibration of the "internal strings."
It’s not really important for my point but could be possible that the relativistic effects change the string vibration in the observer reference frame?
Change of vibration is not change in shape.
If time is quantified, “during� a time quanta there is no vibration. The string just stays still in a certain shape. The next time quanta it will be in another shape. Over a big-enough time interval this series of shapes give you the illusion of vibration.
As I said above, the kinetic energy of a particle does not manifest itself in vibration of strings. And the collisions with Higgs bosons is (probably) too much classical thinking. So your conclusion is likely based on faulty premises.
OK, I agree the rest mass is not relevant to our discussion. But I think my conclusion could still be true. Let’s suppose you could “see� the particle moving without disturbing it. And let’s assume that time is quantified. What will you see? At moment t0 the particle will stay at a precise position (during a time-quanta it cannot move). Its kinetic energy will be therefore 0. No movement, no vibration, only position. At moment t1 the particle will appear in other position. There is no time between t0 and t1, so, its kinetic energy will appear to be infinite. This is the reason why, if we try to determine the value of the energy in a very short time interval its value will be indeterminate. If you allow enough time for your measurement you will get a reliable value (the average kinetic energy).
Quote:
It still seems to me that it is not logical to ask what the speed (or, if you want, kinetic energy) is at a specific point in space.
What's the problem?
Because there is no speed in reality, what we call speed is an average number. It does not describe what is happening on distances comparable with the space quanta. What is the speed of a car in a single movie frame?
And let us think this through. If space is quantified, then a particle has to "hop" from one position to another. Thus its position is determined exactly at each time. Following the HUP, it's speed is thus entirely undetermined.
This is true. As I said, not only its speed is undetermined but it is not a meaningful concept at very small distances.
But if the position of the particle is determined exactly at each time, we can detect the particle at two different times at two different positions and thus determine its speed. But if the position of the particle is determined exactly at each time, we can detect the particle at two different times at two different positions and thus determine its speed. Since the quantization of space has no influence on the detection (as far as I see it), we would get the same result every time we measure the speed. So we would also get a definite speed - in violation of the HUP.
So quantization of space does in effect [b]nothing[/n] to explain the HUP.
If the two points you use for your measurement are far apart you will get the same value for the speed, but it will be an average value. If your points are very close you will get any speed between 0 and infinity.
I tried to find some information about my idea and I found these articles:

http://www.icmp.lviv.ua/journal/zbirnyk.35/001/art01.pdf

We first consider the case of a point particle of mass m. We assume that m induces a discrete structure in space and time. As discussed in the Introduction, this means that the space-time is formed by a set of points (xi; ti). In this first attempt, in order to be illustrative we assume that the points are located on the sites of a regular lattice. Moreover, we assume that the lattice spacings delta x for the spatial coordinates and delta t for the time axis are not independent. At this level of description the only relation that we can find between delta x and delta t is (delta x)^2/delta t = h-bar/m.
Whatever the values of delta x and delta t we immediately have
delta x*delta p = h-bar and delta t*delta E = h-bar/2 (1)
provided we use delta p = m(delta x/delta t) and delta E = (1/2)m(delta x/delta t)^2. The relations (1) mimic the Heisenberg uncertainty relations but they result from the discreteness of the space-time. Note that these two relations appear here on the same footing as the consequence of (delta x)^2/ delta t = h-bar /m. In standard quantum mechanics the position-momentum and the time-energy uncertainty relations are not of the same nature since the second one is not connected with the non-commutation of two operators [12].
http://www.arxiv.org/PS_cache/quant-ph/pdf/0203/0203009.pdf
In this note we demonstrate that a quantum-like interference picture could appear as a statistical effect of interference of deterministic particles, i.e. particles that have trajectories and obey deterministic equations, if one introduces a discrete time.
http://www.phys.psu.edu/~scalise/misc/crackpot/tousson.pdf
The discreteness of space and time, which requires modifications of our conservation laws, appears to give rise to the Heisenberg-Uncertainty behavior of nature, as corrections to the conservation laws of the continuous description of space and time.
Are we talking about the spin of a single particle (for which angular momentum is not an analogy, only looking at the spin itself as an rotation is), or the rotation of an entire molecule?
I’m interested in the spin of a single particle. I’m trying to understand if the Aspect experiment could make more sense in a quantified space or space-time.

Originally Posted by Schneibster
Errrrmmmm, it's position/momentum, not position/speed.
This is true, but for a simple case of a particle moving in straight line its mass is constant.
Have you ever heard of calculus? The meaning of the scalar speed component of momentum is the infinitesimal change in position over an infinitesimal time: dx/dt. Calculus is math for determining the exact meaning of this given some observations.
But if in reality there is no such thing as an “infinitesimal change in position� or “infinitesimal time� your results will not give you the right answer. You can, of course, calculate the speed of your mouse pointer over the screen and you could find that 2 seconds from now it will be in the 12.12364 X 55.2323 pixel. I’d bet that the real position will be 12 X 55.
I'm not sure why you think either that QM says you cannot make the distance between two points arbitrarily close to zero, or why you say that quantification of spacetime (according to SRT there is no separate space and time, only the one thing) would make it clear why you cannot know position and momentum with arbitrary accuracy. I'm not saying you're wrong, but that I'd like to know your thought process that leads to these assertions before I comment.
This I do not follow at all.
I tried to answer that in the first part of my post.

[epepke]

Some say that there is true randomness. I’m trying to figure-out if this randomness is not a consequence of a misunderstanding of reality.

What I try to get across is this:

What the experiments with QM have shown is that, in order to understand quantum behavior, you have to give up something that is part of common sense and that people don't like to give up.

There's a certain amount of variation in which of the common-sense things you have to give up, and largely, the interpretations of QM are about this.

I'm guessing that there probably are misunderstandings of reality going around and that nobody has yet come up with a better one. Intuitively, I'm nearly certain that this is the case.

However, the evidence strongly suggests that it isn't possible, at all, for there to be a better understanding that just makes all of the unsettling and non-common-sensical things go away. It's not going to happen. It's like trying to get rid of a glob of mercury with a hammer. If you mash it down in one place, it's going to blob up in another.

So, if you want to keep the notion that the universe is deterministic, then you have to give up something else, and the question is, whether it is worth it? I think the thing you have to give up is the notion that any part of the universe ever exists in any definite state.

Personally, I don't have a problem with this. I don't mind saying that I can't tell for sure if the cat is alive or dead even after opening the box, only that my brain has become entangled with the cat. I could even point out that if the universe were such that the cat changed back and forth between alive and dead every millisecond, but my brain also changed, I wouldn't be able to tell the difference. But that's because I'm weird. More normal people would have problems with that.

Now, there may be some other notion that you could give up that I just haven't thought up. I can't say that it isn't. But I am pretty sure that it's going to be something that you don't want to give up either.

[Dark Knight Bob]

To be honest I don't care either way. As long as I can still do science it's all good. Whatever it ends up being.

[epepke]

To be honest I don't care either way. As long as I can still do science it's all good. Whatever it ends up being.

That's my opinion as well. Whatever nature looks like, well, that's what it looks like. If you don't like it, tough. Move somewhere else, like a nice classical universe. But don't call me if your eyes don't work any more. (And you probably can't, because your cell phone won't work either.) As for my part, I like it, because it means more fun for me.

However, this is a mixed group, and I think it's important to point out that there are really good reasons to support acquiescence to the Dirac equation and stuff like that. It's not because we're stupid and our meters aren't good enough, and some idea from philosophy could just make everything all better and all classical. We may to some degree be stupid, and our meters might be better, but it just ain't gonna happen.

We've long gone beyond the point of common-sense complacency. The Universe is weird. Deal.

[Sven]

kIt’s not really important for my point but could be possible that the relativistic effects change the string vibration in the observer reference frame?
I know next to nothing about string theory - but one thing I do know: That it's yet a hypotheses, not established to be "true".
Apart from this, since time dilation is a relativistic effect, I think it's possible that an observer observes (what else? :p ) different vibration frequencies, depending on his relative speed to the particle.

If time is quantified, “during� a time quanta there is no vibration. The string just stays still in a certain shape. The next time quanta it will be in another shape. Over a big-enough time interval this series of shapes give you the illusion of vibration.
OK, now I understand your reasoning. This (perhaps!!) works for kinetic energy (see above) - but how do you explain the broadening of signals in a spectrum, depending on the time of measurement?

OK, I agree the rest mass is not relevant to our discussion. But I think my conclusion could still be true. Let’s suppose you could “see� the particle moving without disturbing it. And let’s assume that time is quantified. What will you see? At moment t0 the particle will stay at a precise position (during a time-quanta it cannot move). Its kinetic energy will be therefore 0.
No. This does not follow. You simply can not say anything about the speed of a particle by looking at a single position. On the other hand, if you made the particle collide with one another at a single position, you would observe that it's kinetic energy (and thus it speeds) is far from being 0.
Apart from this: You again violate the HUP yourself. You say that the position is determined exactly, but you also say that the kinetic energy (and thus its speed and momentum) is determined exactly. This is not possible according to the HUP.

At moment t1 the particle will appear in other position. There is no time between t0 and t1, so, its kinetic energy will appear to be infinite.
Why is there no time between t0 and t1?
Do you think that every particle hops instantly from one position to the next? This would of course mean that every particle moved infinitely fast - obviously wrong.

This is the reason why, if we try to determine the value of the energy in a very short time interval its value will be indeterminate.
No. No quantisation of space is necessary to see that we can not determine the speed of the particle by only looking at it at a single position. But with a collision, we can.

If you allow enough time for your measurement you will get a reliable value (the average kinetic energy).
How on Earth does this follow from your reasoning above?

Because there is no speed in reality, what we call speed is an average number.
Speed is an average speed, following your words. So there is speed.

[snip]

This is true. As I said, not only its speed is undetermined but it is not a meaningful concept at very small distances.
As I explained, speed is always a meaningful concept - as soon as you stop to define it only your way.

If the two points you use for your measurement are far apart you will get the same value for the speed, but it will be an average value.
Averaged over what? The speed between every two pairs of distinct positions in space?

If your points are very close you will get any speed between 0 and infinity.
Why? This is - I think - the key question you need to address.

I tried to find some information about my idea and I found these articles:http://www.icmp.lviv.ua/journal/zbirnyk.35/001/art01.pdf
[snip quote]
(1) He assumes that delta x and delta t depend on each other - something you had not introduced up to now.
(2) He comes up with (delta x)^2/delta t = h-bar/m., but I have no idea how he got this equation.

http://www.arxiv.org/PS_cache/quant-ph/pdf/0203/0203009.pdf
This apparently says that only discrete time is necessary. Another quote from the article which made me suspicious of the quality of scholarship employed here:
However, by [sic] some reasons Bohmian theory is commonly considered as unacceptable
It's not "some" reasons - the reasons are quite clear, one of them being that Bohmian theories violate Relativity (faster than light communication).

http://www.phys.psu.edu/~scalise/misc/crackpot/tousson.pdf

This is over my head, since he (?) used 4D space, and I'm no accustomed to Relativity.

I’m interested in the spin of a single particle.
If space is quantified, this certainly should have an effect on the rotation of molecules, too.

I’m trying to understand if the Aspect experiment could make more sense in a quantified space or space-time.
I can not help you here.

[mowgli]

wow, I guess I really asked for all this QM stuff when I started this thread. Great going guys!
:notworthy

Examples of things used for randomness in the generators are radioactivity, thermal noise in a resistor, the photo electric effect etc.

For a nice link on this subject, lets go to wikepedia (http://en.wikipedia.org/wiki/Hardware_random-number_generator)

And if you scroll down below, you will find the different physical phenomena used in the h/w generators here (http://en.wikipedia.org/wiki/Hardware_random-number_generator#Physical_phenomena_used_for_random_number_generation)

How does this fit in with all the discussion that we had on this thread? How do the quantum effects manifest themselves in radioactive decay, for example?

[mowgli]

To be honest I don't care either way. As long as I can still do science it's all good. Whatever it ends up being.

uh oh

Apathy is the nemesis of science. Curiosity fuels it.

Let me ask you a question to keep this going, lets say we somehow make an exact copy of planet mars (lets assume no life forms exist there to avoid the icky problem of free will)

Lets assume we somehow manage to place our copy of mars in an external enviroment exactly matching the external enviroment of the original mars(along with all the comets, light, etc falling on it, effects of the planets, sun and what have you).

My question is, after ,say, one year has elapsed, will they be indistinguishable from each other, or will the QM randomness take over and they become different? Of course this begs the question, is it possible to make an exact physical copy of something(ignore lifeforms)?

[SLUGFly]

Wow... this one's good and the OP made an excellent point.

Rosencratz and Guildenstern are Dead. They open the movie flipping a coin, heads. Flip it again, heads. Again, heads. An hour into the movie they are still flipping the coin and still coming up heads... a very cool debate about 50% odds is woven through it, 50% odds should say that two times should produce 2 results, but it's a new 50% odds each time, so each time is seperate from the previous and new odds are counted. If we were to calculate the endless list of variables in the simple act of tossing a coin (including the EXACT amount of pressure to apply to your thumb on the flick and the EXACT height of your catching hand) then perhaps we could eliminate chance. Hey we killed god, surely the fates (and hopefully, eventually the Erinyes) could be killed too.

So let's shoot into the future here, say about 10,000 years. If our current rate of intellectual evolution continues steadily (let's pretend) then surely by the end of the next 10,000 years we'll have completely mapped every known variable in human consciousness.

We are preprogrammed to carry out certain acts, to desire certain things, to need stimulus. This is modified by our upbringing (nature and nurture). So it's possible that by the end of 10,2005 we'll have eliminated chance even to the point of knowing whose children will grow up to murder someone in a drunken fight on the corner of 34th and main at 11:00 at night, while the child is still in the womb.

But... our knowledge is on paper. One person can only know so many things, when we focus on one thing other things get pushed to the back and often times forgotten. We remember what's important. So the general public, not being able to grasp entirely how the future can be completely (not just accurately) predicted will not believe it (this will be predicted) and will rebel against the "pre-crime" police (courtesy of Minority Report) which will also have been predicted. In the end, only the elite (politicians and advertising execs) will be monitoring these things and the general public will still cling to the realm of free-will.

As an additive, the elite will likely NOT want to expose their knowledge of free-will since this would give people a way to nullify their punishments in vicious crimes... "I had no choice, I didn't want to but it was -destiny-"

Myself, I prefer the idea that there will always be chance, randomness and chaos. If I do not have complete control over my own actions then that means that I do not have any control, since for one thing in my life to be predetermined, everything leading up to it must be predetermined. No babies aborted because of a drunken brawl in their future for me.

[ueit]

Quote:
If your points are very close you will get any speed between 0 and infinity.

Why? This is - I think - the key question you need to address.
OK, I’ll start with this thought experiment. Let’s assume that our particle is one black dot, a pixel wide on a white monitor. It “moves� in the following way: 10s (I take this as time quanta) will stay in the first pixel, then it will be in the 2nd pixel for another 10s and so on. There is no time “between�. After 10s it simply ceases to exist in pixel 1 (px1) and appears in px2. Suppose you can investigate the particle by looking instantly at the screen (you assume a continuum time), note its position, then look again, see its new position and, using a “continuum-time� clock in the lab, write down the time. What values can you get for speed if delta x is 1 pixel? You will get any value between 1px/20s (if you manage to measure two full time quanta) and infinity (if you measure very quickly and the transition take place during that time interval). So, for a precision of 1 space quanta your speed is entirely undetermined. For delta x = 2 you get a speed between 2px/10s (0.2) and 2px/30s (0.06), for delta x=3 between 3px/20s (0.15) and 3px/40s (0.075) and, for delta x = 100, between 100px/990 (0.101) and 100px/1010 (0.099). It’s easy to see that the bigger delta x is, the closer you are to the “real� value for speed of 0.1 px/s. As the measurement time (delta t) increases in the same way as delta x, and the kinetic energy is given by the measured speed the conclusion holds true for this pair as well.
Apart from this, since time dilation is a relativistic effect, I think it's possible that an observer observes (what else? ) different vibration frequencies, depending on his relative speed to the particle.
So it could be possible that the relativistic mass can be “seen� in the string vibrations as well.
Quote:
OK, I agree the rest mass is not relevant to our discussion. But I think my conclusion could still be true. Let’s suppose you could “see� the particle moving without disturbing it. And let’s assume that time is quantified. What will you see? At moment t0 the particle will stay at a precise position (during a time-quanta it cannot move). Its kinetic energy will be therefore 0.
No. This does not follow. You simply can not say anything about the speed of a particle by looking at a single position.
If you assume continuous time you can (in theory) look twice at the particle during a single time quanta. So, given that assumption, you are sure that you measured a null speed.
On the other hand, if you made the particle collide with one another at a single position, you would observe that it's kinetic energy (and thus it speeds) is far from being 0.
I do not know what a collision is in a quantified space, I don’t have a full developed theory, only an idea. IMO “energy� does not exist in reality. If you are working with integers you cannot use derivatives.
Apart from this: You again violate the HUP yourself. You say that the position is determined exactly, but you also say that the kinetic energy (and thus its speed and momentum) is determined exactly. This is not possible according to the HUP.
HUP appears as a consequence of trying to use real numbers when we should use integers. There is no HUP at the fundamental level.
Why is there no time between t0 and t1?
Do you think that every particle hops instantly from one position to the next? This would of course mean that every particle moved infinitely fast - obviously wrong.
A time quanta has a finite, nonzero value. There is no time “between� two quanta.
No. No quantisation of space is necessary to see that we can not determine the speed of the particle by only looking at it at a single position.
It is, otherwise the particle will never be truly at rest. In a continuum space-time, the particle is never at “a single position�.
Quote:
If you allow enough time for your measurement you will get a reliable value (the average kinetic energy).
How on Earth does this follow from your reasoning above?
I think I’ve answered to this in the beginning of my post.
Quote:
Because there is no speed in reality, what we call speed is an average number.
Speed is an average speed, following your words. So there is speed.
You can say that speed is delta x/ delta t. Speed in classical sense, dx/dt does not exist, or, if you like, is always 0.
(2) He comes up with (delta x)^2/delta t = h-bar/m., but I have no idea how he got this equation.
I think he choose it to be that way. If the space and time are quantified like that you have the HUP for position/impulse and time/energy.
This apparently says that only discrete time is necessary.
I’m not interested in finding proofs for my theory because I know it is extremely simplistic. It’s highly unlikely that the universe resembles a regular lattice. I think loop quantum gravity theory has a discrete spacetime organized as a “spin network�, but my math is too bad to even try to understand it.
I found this article interesting because they claim that classical charged spheres could give you an interference pattern if you assume a quantified time. No need for probability waves.
It's not "some" reasons - the reasons are quite clear, one of them being that Bohmian theories violate Relativity (faster than light communication).
I do not know almost anything about Bohm’s theory, but how can the orthodox interpretation explain the wave collapse without faster than light communication?

P.S.
Does anybody know something about Paul Marmet? His site (http://www.newtonphysics.on.ca/HEISENBERG/index.html) resembles an ID-type one but I think it’s not completely without merit. And there is a lot of math in there to support his assertions.

[Dark Knight Bob]

uh oh

Apathy is the nemesis of science. Curiosity fuels it.

I think I get to chose when to worry about the implications of QM. Please don't impose your ideas of what I think about this as some sort of apathy. I just don't see a problem with accepting that the universe might be weird. I was merely trying to answer the question with regards to randomness.

I believe yet cannot prove that there is inherent determinism, but that our current understanding of it may mean that like relativity destorying the assumption that time is constant that determinism doesn't quite work in the way we think it does.

For the moment it seems that QM works purely on the statistical but again there is the problem of hidden variables and such.

If anything my 'apathy' is not about caring. It is about not being so zealous about a certain theory as to blind myself to the other possibilites. Like I said. I would quite like the universe to be deterministic but the creation of the universe might require this not to be so... if that's the case.. then 'meh'. I enjoy science because I can explain a lot during my lifetime. I think anyone that expects to find the final answer before they die and to have all the ends rounded off is more of a fool than someone who just is content with finding out what he can and enjoy's the means not the end.

My question is, after ,say, one year has elapsed, will they be indistinguishable from each other, or will the QM randomness take over and they become different?

QM doesn't 'take over' it is always there. It is just we don't experience it on a large scale due to it being only 'apparent' on extremely small scales.

Of course this begs the question, is it possible to make an exact physical copy of something(ignore lifeforms)?

According to current theory. No. In both deterministic and statistical. In the former you would have to be external to the universe to do so and have some unknown way of measuring matter wihtout interferance. In a statistical universe you could only have a probabilty not a definite.

[ueit]

epepke:
What the experiments with QM have shown is that, in order to understand quantum behavior, you have to give up something that is part of common sense and that people don't like to give up.
I think we have to keep in mind that QM is an incomplete theory. It doesn't say anything about gravity, it brakes down if this force becomes important. As we know, gravity is related with space and time so, we just cannot take QM's word for the reality we live in. I agree that we will have to give up something, but we have to be careful.
So, if you want to keep the notion that the universe is deterministic, then you have to give up something else, and the question is, whether it is worth it?
I think that causality should be the last thing to give up. It takes our logic down with it.
I think the thing you have to give up is the notion that any part of the universe ever exists in any definite state.
Why is that?
Now, there may be some other notion that you could give up that I just haven't thought up. I can't say that it isn't. But I am pretty sure that it's going to be something that you don't want to give up either.
Until we have a TOE it's impossible to say what.

[Sven]

OK, I’ll start with this thought experiment. Let’s assume that our particle is one black dot, a pixel wide on a white monitor. It “moves� in the following way: 10s (I take this as time quanta) will stay in the first pixel, then it will be in the 2nd pixel for another 10s and so on. There is no time “between�. After 10s it simply ceases to exist in pixel 1 (px1) and appears in px2. Suppose you can investigate the particle by looking instantly at the screen (you assume a continuum time), note its position, then look again, see its new position and, using a “continuum-time� clock in the lab, write down the time. What values can you get for speed if delta x is 1 pixel? You will get any value between 1px/20s (if you manage to measure two full time quanta) and infinity (if you measure very quickly and the transition take place during that time interval). So, for a precision of 1 space quanta your speed is entirely undetermined. For delta x = 2 you get a speed between 2px/10s (0.2) and 2px/30s (0.06), for delta x=3 between 3px/20s (0.15) and 3px/40s (0.075) and, for delta x = 100, between 100px/990 (0.101) and 100px/1010 (0.099). It’s easy to see that the bigger delta x is, the closer you are to the “real� value for speed of 0.1 px/s. As the measurement time (delta t) increases in the same way as delta x, and the kinetic energy is given by the measured speed the conclusion holds true for this pair as well.
Thanks! I now understand your point better. But suppose we really measure the particles very quickly a lot of times at the two different positions. Then we would see that it simply rests there for a time and then changes place etc. The speed would be determined exactly then, and the position too - violating the HUP.

So it could be possible that the relativistic mass can be “seen� in the string vibrations as well.
It could. And it would depend on the observer - other observers with different speeds relative to the particles would see a different pattern. I don't think that this is what you need.

If you assume continuous time you can (in theory) look twice at the particle during a single time quanta. So, given that assumption, you are sure that you measured a null speed.
But nobody would look at a single position to determine its speed - because as you yourself argued this does not make sense. And if I collided the particle at this position with another, I would see very well that it is not at rest.

I do not know what a collision is in a quantified space, I don’t have a full developed theory, only an idea. IMO “energy� does not exist in reality.
Energy exists just in the same way as mass or charge exists - it's a description of the behaviour of particles. And if your idea can not deal with collisions up to now - well, then go back to the drawing board and present it again when it can.

If you are working with integers you cannot use derivatives.
Yes. If.

Apart from this: You again violate the HUP yourself. You say that the position is determined exactly, but you also say that the kinetic energy (and thus its speed and momentum) is determined exactly. This is not possible according to the HUP.
HUP appears as a consequence of trying to use real numbers when we should use integers. There is no HUP at the fundamental level.
What? :huh: You try to explain the HUP and then claim that it doesn't exist?

No. No quantisation of space is necessary to see that we can not determine the speed of the particle by only looking at it at a single position.
It is, otherwise the particle will never be truly at rest. In a continuum space-time, the particle is never at “a single position�.
Why?

You can say that speed is delta x/ delta t. Speed in classical sense, dx/dt does not exist, or, if you like, is always 0.
OK. Your statement "there is no speed in reality" was meant as "there is no speed according to the classical definition in reality".

(2) He comes up with (delta x)^2/delta t = h-bar/m., but I have no idea how he got this equation.
I think he choose it to be that way.
The article rather sounds like as if this can be derived.

If the space and time are quantified like that you have the HUP for position/impulse and time/energy.
May be. But again, apparently a relation between time and space quantization is necessary, something which you don't use.

I think loop quantum gravity theory has a discrete spacetime organized as a “spin network�
Do you have a reference?

I found this article interesting because they claim that classical charged spheres could give you an interference pattern if you assume a quantified time. No need for probability waves.
I wonder if this also explains experiments in which
(1) the interfering particles were detected in the slits, leading to no interference pattern
(2) the particles were sent one at a time through the slits

I do not know almost anything about Bohm’s theory, but how can the orthodox interpretation explain the wave collapse without faster than light communication?
Are you talking about the EPR-paradoxon or what?

Does anybody know something about Paul Marmet?
Never heard about him.

[ueit]

But suppose we really measure the particles very quickly a lot of times at the two different positions. Then we would see that it simply rests there for a time and then changes place etc. The speed would be determined exactly then, and the position too - violating the HUP.
In reality you cannot even make two measurements so you cannot violate HUP. However, if a new theory describing the reality at a very small scale (a unified quantum theory including gravity) appears, I think HUP will remain only a limit for practical measurements (involving direct detection of a particle using another particle), not a description of the internal workings of our universe.
It could. And it would depend on the observer - other observers with different speeds relative to the particles would see a different pattern. I don't think that this is what you need.
It’s exactly what I need. Different observers will measure different masses in accordance with special relativity; different masses – different velocities. I don’t see the problem here.

I don’t really understand what you want to prove with the particle collisions. If the space (spacetime) is quantified everything moves in accordance with some laws we do not know yet (we don’t have a quantum theory of gravity), including the particle you use for detection. You will not SEE that the particle is at rest or not. You will just interpret what you see on the photographic plate in accordance with the approximate equations given by QM and you will happily say that the particle have some speed plus or minus the quantity required by HUP.
Energy exists just in the same way as mass or charge exists - it's a description of the behavior of particles.
We do not know WHAT is this energy, mass or charge. We ASSUME that these parameters describe correctly the reality. IMO they are for particles what temperature or pressure are for macroscopic objects. We can use them for measurements on a large enough scale but not at the level where the discontinuities become evident.
Quote:
HUP appears as a consequence of trying to use real numbers when we should use integers. There is no HUP at the fundamental level.
What? You try to explain the HUP and then claim that it doesn't exist?
We can calculate a kind of “HUP� for temperature measurements. No matter how good your thermometer is you will find large variations when you use a very small time interval for your measurement. When you will not register a molecular collision the temperature is 0, otherwise you will find different temperatures given by the speed of the molecules hitting the thermometer. This proves the fundamental fact that the objects are not smooth but granular and the temperature is not a good parameter for describing reality on small scales. Likewise HUP shows us the fundamental fact that “energy� and “speed� are not good for describing reality on microscopic scales. If you know the structure of the macroscopic objects the variations in temperature will not be a mystery anymore. But they will continue to exist. This is why I said HUP shows us something fundamental about our universe but when (or if) a correct theory of space (spacetime) will be available it will cease to exist as a fundamental limitation of our knowledge.
OK. Your statement "there is no speed in reality" was meant as "there is no speed according to the classical definition in reality".
I never encounter in physics other definition for speed than ds/dt. But I agree.
I think loop quantum gravity theory has a discrete spacetime organized as a “spin network�
Do you have a reference?
You can find a book written by Carlo Rovelli, a leading researcher in LQC, here:
Quantum Gravity (http://www.cpt.univ-mrs.fr/~rovelli/book.pdf)
At page 14 we find:
The fact that spin networks do not live in space, but rather are space, has long ranging consequences. Space itself turns out to have a discrete and combinatorial character. Notice that this is not imposed on the theory, or assumed. It is the result of a completely conventional quantum mechanical calculation of the spectrum of the physical quantities that describe the geometry of space. Since there is no spatial continuity at small scale, there is (literally!) no room in the theory for ultraviolet divergencies. The theory effectively cuts itself off at the Planck scale. Space is effectively granular at the Planck scale, and there is no ultraviolet limit.
I wonder if this also explains experiments in which
(1) the interfering particles were detected in the slits, leading to no interference pattern
(2) the particles were sent one at a time through the slits
I think the particles were sent one by one but he studied diffraction on a single slit, so, he doesn’t reproduce the “two slits experiment�. However, he proves that you can have interference fringes without waves, only with a discrete time.
Are you talking about the EPR-paradox or what?
Not only. Isn’t the instantaneous wave collapse in the entire universe following any measurement?

[Sven]

In reality you cannot even make two measurements so you cannot violate HUP.
One can indeed measure without interaction in QM. Look it up.

However, if a new theory describing the reality at a very small scale (a unified quantum theory including gravity) appears, I think HUP will remain only a limit for practical measurements (involving direct detection of a particle using another particle), not a description of the internal workings of our universe.
Perhaps.

It’s exactly what I need. Different observers will measure different masses in accordance with special relativity; different masses – different velocities. I don’t see the problem here.
The problem is that you have yet to establish a functional relationship between these measurements; simply hand-waving won't do. Another problem is that we have no idea if string theory is indeed right; that we have no idea if these vibrations can be and are indeed observed differently by different observers, etc. In short, too many unknowns to base any idea on.

I don’t really understand what you want to prove with the particle collisions.
With a particle collision, I can determine the speed of a particle at a specific place - something what you claim is not possible, you continue to claim that we need to positions.

If the space (spacetime) is quantified everything moves in accordance with some laws we do not know yet (we don’t have a quantum theory of gravity)
So when we don't know the laws yet, it does not make any sense to speculate on if they could explain the HUP. This statement made your OP obsolete.

You will not SEE that the particle is at rest or not. You will just interpret what you see on the photographic plate in accordance with the approximate equations given by QM and you will happily say that the particle have some speed plus or minus the quantity required by HUP.
Yes. But since you talked about classical/QM laws all the time and used them for your idea, that's all what I need.

We do not know WHAT is this energy, mass or charge.
Right. Their are properties we atrribute to particles to describe their behavior. That's all.

We ASSUME that these parameters describe correctly the reality.
We only assume that these parameters describe their behavior correctly, not that these parameters necessarily represent reality themselves. And the former is certainly justified, since we specifically chose those parameters so that their behavior is described correctly.

IMO they are for particles what temperature or pressure are for macroscopic objects. We can use them for measurements on a large enough scale but not at the level where the discontinuities become evident.
Then I'm really curious why spectroscopy works. For instance, we get 13.6 eV for the ionization of H atoms every time we do the measurement, regardless if we take a bunch of atoms or single atoms.

Likewise HUP shows us the fundamental fact that “energy� and “speed� are not good for describing reality on microscopic scales.
Energy seems to be no problem. See above.

This is why I said HUP shows us something fundamental about our universe but when (or if) a correct theory of space (spacetime) will be available it will cease to exist as a fundamental limitation of our knowledge.
Possible. But your ideas alone don't work. Let's wait and see.

You can find a book written by Carlo Rovelli, a leading researcher in LQC, here:
Quantum Gravity (http://www.cpt.univ-mrs.fr/~rovelli/book.pdf)
At page 14 we find:
[snip]

Thanks! Very interesting!

I think the particles were sent one by one but he studied diffraction on a single slit, so, he doesn’t reproduce the “two slits experiment�. However, he proves that you can have interference fringes without waves, only with a discrete time.
This, presumably, answers my second point, thanks. Do you also have any information on my first point:
I wonder if this also explains experiments in which (1) the interfering particles were detected in the slits, leading to no interference pattern
?

Not only. Isn’t the instantaneous wave collapse in the entire universe following any measurement?
Hmm. Good point. But I wonder if this is really faster than light communication (transfer of information). Sorry, I'm bad at Relativity, perhaps you could write Jesse and/or Schneibster a PM about this.

[ueit]

Originally Posted by Sven
One can indeed measure without interaction in QM. Look it up.

Give me an example in which you measure two times the position of the same particle without disturbing it.

Another problem is that we have no idea if string theory is indeed right; that we have no idea if these vibrations can be and are indeed observed differently by different observers, etc. In short, too many unknowns to base any idea on.I agree, it's pure speculation. And I don't base my idea on it. With a particle collision, I can determine the speed of a particle at a specific place - something what you claim is not possible, you continue to claim that we need to positions.Prove me that a collision takes place on a distance smaller than, let's say, Planck length and in a time interval of less than Planck time. Otherwise you cannot claim that a collision can give you both the speed and position anymore. And HUP doesn’t agree with you.Quote: If the space (spacetime) is quantified everything moves in accordance with some laws we do not know yet (we don’t have a quantum theory of gravity)
So when we don't know the laws yet, it does not make any sense to speculate on if they could explain the HUP. This statement made your OP obsolete.Are you saying that we shouldn't try to find out how our universe works just because we do not know yet how it works? I said that a quantum space (spacetime) could explain HUP and I think it does. However, in order to have a coherent theory we need much more than that.Quote:
You will not SEE that the particle is at rest or not. You will just interpret what you see on the photographic plate in accordance with the approximate equations given by QM and you will happily say that the particle have some speed plus or minus the quantity required by HUP.

Yes. But since you talked about classical/QM laws all the time and used them for your idea, that's all what I need.If your assumption that the collisions are instantaneous is wrong you just cannot use collisions for probing very small distances, so you cannot see how exactly the particle moves.We only assume that these parameters describe their behavior correctly, not that these parameters necessarily represent reality themselves. And the former is certainly justified, since we specifically chose those parameters so that their behavior is described correctly.The particle behavior is NOT described correctly, otherwise we wouldn't have uncertainties. Therefore I say that the parameters are not well chosen. How can you say that position and impulse describe correctly the reality when you cannot measure them both? At least one of them is not good.Then I'm really curious why spectroscopy works. For instance, we get 13.6 eV for the ionization of H atoms every time we do the measurement, regardless if we take a bunch of atoms or single atoms.I didn't say that the energy of a particle is given by the average energy of many other particles. Remember the black dot on the screen. Its kinetic energy is given by the average change in its position over time. Therefore kinetic energy is a statistical parameter, not a constant property of the particle.Energy seems to be no problem. See above.So, you deny HUP? It says that there is a problem. I've never heard of a spectra taken instantly.I wonder if this also explains experiments in which (1) the interfering particles were detected in the slits, leading to no interference patternSorry, I have no idea. Perhaps some calculations could be done but not by me, for sure.

[Sven]

Give me an example in which you measure two times the position of the same particle without disturbing it.
Here is a decription (http://www.fortunecity.com/emachines/e11/86/seedark.html) of an experiment which shows measurement without interaction. I'm not sure if this could indeed be used for measuring "two times the position of the same particle without disturbing it", but I see no principal reason against it.

Prove me that a collision takes place on a distance smaller than, let's say, Planck length and in a time interval of less than Planck time. Otherwise you cannot claim that a collision can give you both the speed and position anymore. And HUP doesn’t agree with you.
Touche. :)
Seems my picture of the collision process is too classical.

Are you saying that we shouldn't try to find out how our universe works just because we do not know yet how it works?
Of course not. But it does not make any sense too speculate on the effects of quantified space-time when at the same time believing that different laws hold in this case. Only experiments can help one here, speculations don't.

I said that a quantum space (spacetime) could explain HUP and I think it does.
Judging from the article you linked, it indeed looks like as if there were something to it. But as I said, apparenly a causal relationship between the "smallest time" and the "smallest space" is necessary.

However, in order to have a coherent theory we need much more than that.
Indeed.

If your assumption that the collisions are instantaneous is wrong you just cannot use collisions for probing very small distances
I don't think that the "instantaneous" part is wrong. I'm not sure what exactly is wrong in my picture, but that's not it.

Therefore I say that the parameters are not well chosen. How can you say that position and impulse describe correctly the reality when you cannot measure them both? At least one of them is not good
Hmm. Good point (BTW, I think it's "momentum"). But remember that there always are some characteristics of a particle which can be measured exactly. So the "correct" parameters are simply not universal, but depend on the kind of experiment.

Remember the black dot on the screen. Its kinetic energy is given by the average change in its position over time. Therefore kinetic energy is a statistical parameter, not a constant property of the particle.
If space is quantified, yes.

So, you deny HUP? It says that there is a problem. I've never heard of a spectra taken instantly.
Again: Touche. I should think a bit more before I post. :o

Looks like as if we agreed after all about most points :)
- and it was me who had to give up his position. That's life. :cool:

[Schneibster]

Let’s assume that our particle is one black dot, a pixel wide on a white monitor. It “moves� in the following way: 10s (I take this as time quanta) will stay in the first pixel, then it will be in the 2nd pixel for another 10s and so on... It’s easy to see that the bigger delta x is, the closer you are to the “real� value for speed of 0.1 px/s. As the measurement time (delta t) increases in the same way as delta x, and the kinetic energy is given by the measured speed the conclusion holds true for this pair as well.But suppose we really measure the particles very quickly a lot of times at the two different positions. Then we would see that it simply rests there for a time and then changes place etc. The speed would be determined exactly then, and the position too - violating the HUP.In reality you cannot even make two measurements so you cannot violate HUP. Why not?

However, if a new theory describing the reality at a very small scale (a unified quantum theory including gravity) appears, I think HUP will remain only a limit for practical measurements (involving direct detection of a particle using another particle), not a description of the internal workings of our universe.This would be true if your assumption of quantization of space and time turned out to be true; however, there is no evidence to support it. In fact, violation of the uncertainty principle would have some very noticeable effects at the macro scale; for starters, atoms could not exist because the nucleons could not exchange pions (or, if you prefer, the quarks in the nucleus could not exchange gluons) without it. Remember, the uncertainty covers many more pairs of conjugate variables than position and momentum; energy and time, and spin in different planes of polarization, are also conjugate. There would be a very large number of effects that we can measure that would not occur in the absence of uncertainty.

We know that mass and energy are equivalent, so we can say that a particle energy is given by the vibration of its “internal� string (the change in shape of the string).So the kinetic energy which manifests itself as part of the relativistic mass simple isn't one of the things which changes the vibration of the "internal strings."It’s not really important for my point but could be possible that the relativistic effects change the string vibration in the observer reference frame?Apart from this, since time dilation is a relativistic effect, I think it's possible that an observer observes (what else? ) different vibration frequencies, depending on his relative speed to the particle. So it could be possible that the relativistic mass can be “seen� in the string vibrations as well.It could. And it would depend on the observer - other observers with different speeds relative to the particles would see a different pattern. I don't think that this is what you need.It’s exactly what I need. Different observers will measure different masses in accordance with special relativity; different masses – different velocities. I don’t see the problem here.Hmmmm. I don't think so. String physics are explicitly relativistic, and the vibration modes are described in terms of the world sheet, which means that they are unaffected by relativistic mass changes. The mass increase is not the result of a change in vibration frequency; the vibration frequency is not an observable. I am asking right now on a physics forum what the effects are of the Lorentz transform on the equation of motion of the relativistic string, and if I get an answer (the original person who asked the question didn't) I'll post it here. But I expect it will affect another parameter of the string (perhaps the tension) instead of the vibration modes.

I don’t really understand what you want to prove with the particle collisions. If the space (spacetime) is quantified everything moves in accordance with some laws we do not know yet (we don’t have a quantum theory of gravity), including the particle you use for detection. You will not SEE that the particle is at rest or not. You will just interpret what you see on the photographic plate in accordance with the approximate equations given by QM and you will happily say that the particle have some speed plus or minus the quantity required by HUP.You may not know about bubble chambers, and you certainly have not understood the degree to which various properties are dependent on uncertainty. In order for your idea of quantized space and time to be viable, it needs considerably more thought. Let's examine the most obvious consequences.

A particle will have to jump to the "next" quantum that has the same space co-ordinates but the "next" time ordinate whenever a quantum of time has passed, if the particle's cumulative uncertainty has not become high enough to require it to move to new space co-ordinates. It therefore is theoretically possible to determine the particle's space co-ordinates at two successive time ordinates, and the fact that its space co-ordinates are unchanged would mean that its momentum is zero- and that means that you would know both position and momentum simultaneously with unlimited precision, which is impossible under uncertainty. I have to mention here in passing, as I did above, that without uncertainty, atoms cannot exist, and that is merely the tip of the iceberg.

In order to get around this, you would have to posit that a particle cannot occupy the same position in successive time quanta. However, the uncertainty relation is quite exact, and while it is never violated, the uncertainties in time and energy are pushed absolutely to the limit to determine the probabilities of various interactions; as a result, particles with different masses would have to have different sized quanta of time! This would so complicate matters that it is nearly impossible to imagine that physics could ever be so complex, and would also result in paradoxes that would make themselves felt at our level of reality. Thus, most physicists do not believe that time or space are quantized, but that they are a continuum as the postulates of relativity require.

We do not know WHAT is this energy, mass or charge. We ASSUME that these parameters describe correctly the reality. IMO they are for particles what temperature or pressure are for macroscopic objects. We can use them for measurements on a large enough scale but not at the level where the discontinuities become evident.No. We know that energy and time are intimately associated; we know that momentum (of which mass is a crucial part) and space are intimately associated; and we know that mass and energy are intimately associated. The first two are by Noether's theorem, which states that for every symmetry there is an associated conservation law; the symmetry of experimental results over time (I'll get the same results tomorrow as I did today) is associated with the conservation of energy. The symmetry of results over space (I'll get the same results over here as over there) is associated with the conservation of momentum. The association of mass and energy is by SRT; the famous E=mc^2.

Charge is a conserved quantity; the associated symmetry is called U(1). It is the unitary symmetry group of dimension one, a mathematical object that describes the operations that can be applied to the electromagnetic force. This U(1) symmetry is intimately associated with Maxwell's equations, which completely describe the electric and magnetic fields and their relationship to one another, and also to Quantum Electrodynamics, which is the quantum field theory of the electromagnetic interaction.

So you can see that there are deep associations among the forces and the dimensions, and that there are many different areas of physics tied all together to yield what we can observe. When you say that we don't know what mass is, and that it is a composite, statistical entity of some underlying reality like pressure and temperature are, you are saying in effect that space and time are also such composite, statistical entities; while this may be true, it is certain that if they are, it is nothing so simple as a quantization of spacetime.

Isn’t the instantaneous wave collapse in the entire universe following any measurement?That is a misunderstanding. These are correlated events, not cause-and-effect. What you are referring to is that when a particle is measured at one particular location, it is simultaneously not present at all other locations; this is the "collapse of the wave function." However, viewed from the correct perspective, both the detection of the particle at one particular location, and the non-detection at all other locations, are both effects of the same cause: the particle's trajectory. And that is an effect of many causes; but that's not important. What is important is the relationship between the detection and non-detection. There is no "collapse of the wave function." You'll want to go back now and have another look at the Aspect EPR experiment.

[dannyk]

That's my opinion as well. Whatever nature looks like, well, that's what it looks like. If you don't like it, tough. Move somewhere else, like a nice classical universe.

Shouldn't you be giving credit to Mr Feynman for that quote :wave:

Tis a great quote though. :notworthy

Graeme

[dannyk]

What he actually said was ...

"It's the way nature works. If you want to know the way nature works...we looked at it ..carefully.. Thats the way it looks.... If you don't like it go somewhere else. To another universe where the rules are simpler......Philosophically more pleasing.....More psychologically more easy....I can't help it ! ............OK"

Graeme

[ueit]

Originally Posted by Sven
Here is a description of an experiment which shows measurement without interaction. Thanks, I’ll need some time to understand the implications of this experiment. However, on order to measure the exact location of a particle you need to know exactly the photon path. And I think you cannot know that.I don't think that the "instantaneous" part is wrong. I'm not sure what exactly is wrong in my picture, but that's not it. I have to say that I know nothing about how the collisions are described in QM. I cannot even imagine how two 0-D point particles could ever collide. I tried to find something on Google but no success until now.
But remember that there always are some characteristics of a particle which can be measured exactly. So the "correct" parameters are simply not universal, but depend on the kind of experiment. It seems to me that in fact you cannot measure any property with great precision. Heisenberg said that you could determine the exact position of a particle using a high energy photon. However, you need to assume that the photon travels in straight line, and you have to know exactly its path, both banned by HUP.Looks like as if we agreed after all about most points
- and it was me who had to give up his position.
Sadly, this doesn’t prove that I’m right and you – wrong.
That's life. Yeah, I know. I was just wondering how smart I am, dreaming to the Nobel price I rightfully deserve, when, imagine, I saw Schneibster’s post.

[Sven]

However, on order to measure the exact location of a particle you need to know exactly the photon path. And I think you cannot know that.
Hmm, you might have a point.

I have to say that I know nothing about how the collisions are described in QM. I cannot even imagine how two 0-D point particles could ever collide. I tried to find something on Google but no success until now.
Try "quantum scattering theory" :)

It seems to me that in fact you cannot measure any property with great precision. Heisenberg said that you could determine the exact position of a particle using a high energy photon. However, you need to assume that the photon travels in straight line, and you have to know exactly its path, both banned by HUP.
I'm not sure about this. Maybe an uncertainty of 0 is really an overidealized case. But in gedankenexperiments, some properties are indeed determined exactly - for example the momentum in the famous particle-in-the-box.


Yeah, I know. I was just wondering how smart I am, dreaming to the Nobel price I rightfully deserve, when, imagine, I saw Schneibster’s post.
If it makes you feel better, I could try to nominate you for the Nobel price. :p

[ueit]

Quote:
Originally Posted by ueit
In reality you cannot even make two measurements so you cannot violate HUP.
Why not?
In my hypothetical experiment I assumed that you could “see� a particle without disturbing it. I’ve shown that even in this case the incompatibility position-momentum and time-energy arises if one assumes a quantified space and time. If such an experiment could be done I think that you could “see� the particle staying for some time at a single position. In real life the first measurement will alter the particle properties, so, even if you manage to do the second one it will be meaningless.Originally Posted by ueit
However, if a new theory describing the reality at a very small scale (a unified quantum theory including gravity) appears, I think HUP will remain only a limit for practical measurements (involving direct detection of a particle using another particle), not a description of the internal workings of our universe.
This would be true if your assumption of quantization of space and time turned out to be true; however, there is no evidence to support it.
I think there is some evidence for a quantified spacetime. It is clear that QM cannot tell us anything about space and time (only assumes them to b