The universe and eternity

[Alex K]

I saw a link or two on these forums about an eternal universe.  (If anyone has any more studies or articles -- especially ones easy to read for someone who is not well versed in science -- I'd appreciate some links!)  Is it widespread for scientists and physicists to regard the cosmos or at least the energy of which it is composed as eternal?  What is your opinion on this matter?

I tend to think the energy itself has always been here.  I don't see how it could be otherwise and haven't found any reason to believe it was created or generated from nothing.

As you probably know, according to the well-established theory of General Relativity, matter and energy curve space and time, and gravity is then caused by this curvature of space and time. In General Relativity, time and space are - up to rare singular points or surfaces such as black holes - smooth things. However, this view does not take into account what we know about quantum theory. In extreme conditions such as near the "big bang", the usual General Relativity stops being valid because the quantum uncertainties in space and time themselves become relevant, and we do not currently understand with any certainty what happens at this point.

This means that the concept of time itself becomes problematic in very extreme conditions - it might not be the linear and smooth thing that you are used to from everyday experience - in fact, it seems very unlikely that it will still have much in common with what you and I perceive as time in our daily lives. It could be a fragmented, many-fingered, fuzzy thing that branches out in many different directions when we reach a point near the big bang where the quantum nature of space and time become dominant. We do not understand what happens there, and there is no good justification to simply assume a sharp beginning of time in our past just because an incomplete theory (General Relativity) runs into initial singularities in some scenarios. When cosmologists talk about the universe being 13.8 billion years old, they do not mean that there is an absolute sharp singular stopping point there - they don't know that! - this number is the time you can go back before the universe becomes a dense hot soup in which the particles we are made of came to be.

But even if there were a sharp beginning, this would mean that our time line would end there - there is no before in the sense we use the word, and this also means that the universe and time itself cannot have been created, whatever that means - because creation as it is used by virtually everyone is a temporal process, and if there is no time, the word is meaningless.

The conservation of Energy is something we intuitively take for granted because it holds to a super-precise degree at human scales. But when looking at cosmology, you have to be careful when carrying such intuitions into your arguments. To give you an example why Energy in the Universe is not conserved: if you send a bunch of photons (a beam of light) to a far away star, when it arrives there space will have expanded because of cosmic expansion, and your photons will have been redshifted, i.e. they will have lower energy! That's an observational fact - we see light redshifted that has travelled through space for a while, and hence we know that radiation energy contained in the Universe is not conserved but can generally be lost.

Now, one can rescue to principle of energy conservation by assigning energy to the curvature of space and time themselves - a very subtle mathematical endeavour where the expansion of space itself is a reservoir for energy compensating for the red shift of stuff within it. Doing that, one can come to the conclusion that the total energy of what's in the universe, and of space, might be zero! Therefore, the universe might have no net energy. This is just to illustrate that you have to be careful when applying everyday intuitions to the universe as a whole.