Seeing the Big Bang

[M.Talkingsworth]

Hello,

I have read that if one were able to "see" far enough into space, one would be able to observe the Big Bang. This idea comes from Stephen Hawkings' book, The universe in a Nutshell. I am somewhat confused by this idea as it seems that the big bang was a single event and is not continuously eminating light which could still be observed. Is it not possible that all the light released from it has already passed us by rendering it non-observable?

Cheers,

matt

[premjan]

Some parts of the universe are expanding faster than the speed of light relative to us. Presuming that this was true right around the big bang as well, then there are probably some photons that never reached us from the big bang. There are probably some preconditions, but some of those photons may be able to reach us today, if we had very sensitive detectors.

[ZikZak]

The big bang was not an explosion that happened "somewhere over there" that you can point to in space. It was not an explosion. There is no center of everything out of which galaxies are streaming.

The universe is more or less uniformly filled with galaxies everywhere, and they are not streaming out from any central region out into a void space. In fact, the galaxies are more or less where they have always been for all time, but the space between them is stretching. A few billion years ago, the galaxies were STILL found uniformly everywhere in space, pretty much where they've always been, but there was less space between them. 13.7 billion years ago, there was very little space indeed, and the universe was very small and very hot.

The ENTIRE universe was very small and hot. Not a part of the universe, not a ball-o'-stuff in the universe, THE UNIVERSE was small and hot. The galaxies (or, rather, the energy that would become the galaxies) was still distributed uniformly everywhere in space, although "everywhere in space" would have been a very small amount of real estate. Nevertheless, all of space, absolutely everywhere, was dense and hot.

So if you look 13.7 billion light years away, you are seeing photons that are 13.7 billion years old, because that's how long they take to get to your telescope. Those are photons that were generated when the universe was very small, dense, and hot. And thus you directly observe the big bang.

In reality, we do not directly observe the big bang itself, becuase before the universe was 100,000 years old or so, the gas in it was opaque. What you do see if you look 13.7 Gly away is the hot, opaque gas that formed the universe when it was about 100,000 years old, and you see this everywhere, in every direction, because the universe was hot and dense everywhere. We call this the Cosmic Microwave Background. If that gas were not opaque, we would be able to see an additional 100,000 light years past it to time t=0 itself. As far as I am concerned though, the ability to directly observe the CMB on a daily basis is a pretty damn direct observation of the Big Bang.

Note that if only we could see through the hot opaque gas that filled the universe until t=100,000 years, we would indeed directly observe the Big Bang. Well, the early universe was not opaque to absolutely every kind of radiation imaginable: if we could detect primordial neutrino radiation, we would be receiving it directly from a time when the universe was a very tiny fraction of a second old, as most of the early universe is transparent to them. Alas, that is a bit difficult.... for now.