I am not an expert at all in cosmology, and I was always puzzled by the following question. To my knowledge, everything started from a singularity (Big-Bang), then inflation followed, then space continued to expand. However, after the end of inflation, it is now believed the whole universe was of the scale of centi-meters (still infinitely large than a single point). The question I have is this: suppose at the end of the inflationary period (i.e. ~10^-32s after Big-Bang), one shines a photon. What will happen with it? Will it encounter a "boundary" of space? Or is the space still expanding faster than the speed of light and the question is meaningless? And, finally, can we say that the universe itself had a finite volume?
Thanks!
Dear Vlad, your question is interesting, although can be analysed further. I will not give a direct answer, but I will try to help you find it by yourself. Let's start:
"To my knowledge, everything started...", be careful: what is time? see my suggestion here: https://www.researchgate.net/publication/263104630 and you will realize that such a formulation is meaningless
"...then inflation followed, then space continued to expand": for inflation and cosmology see more here: https://www.researchgate.net/publication/264537258 , you will find that it is not necessary to create space (expansion) at all and inflation is incompatible with the postulate that speed of light=upper limit.
My brief opinion is that most of the questions that involve a concept of point singularity universe creation are just a measure of our ignorance.
If you want a precise answer, no expansion took place at all, since it is more reasonable to accept the existence of infinite 'local universes (with unknown cardinality and unknown creation process...)
Article A simple definition of Time
Article A new cosmological paradigm: universal locality
Dear Vlad, your question is interesting, although can be analysed further. I will not give a direct answer, but I will try to help you find it by yourself. Let's start:
"To my knowledge, everything started...", be careful: what is time? see my suggestion here: https://www.researchgate.net/publication/263104630 and you will realize that such a formulation is meaningless
"...then inflation followed, then space continued to expand": for inflation and cosmology see more here: https://www.researchgate.net/publication/264537258 , you will find that it is not necessary to create space (expansion) at all and inflation is incompatible with the postulate that speed of light=upper limit.
My brief opinion is that most of the questions that involve a concept of point singularity universe creation are just a measure of our ignorance.
If you want a precise answer, no expansion took place at all, since it is more reasonable to accept the existence of infinite 'local universes (with unknown cardinality and unknown creation process...)
Article A simple definition of Time
Article A new cosmological paradigm: universal locality
@Demetris, thanks for your answer. I thought space itself can expand faster than the speed of light, but again may be wrong :)
@Vlad. I like to answer your question with another question.
Did geometry exist prior to creation? Is geometry part of the creation or above the creation? My own view is that the fundamental substance of the creation from which the universe emerged did not have any geometry. This means that it did not have any boundary. This substance was a unified whole without any motion and did not interact with anything else so it has the same property like the empty space. When this substance begins to move, it splits up into particle anti-particle pairs and this gives birth to geometry and boundary etc.
See this article:
doi:10.1038/nature13674
http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html
Don't forget to watch the submitted to Nature video:
http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html#videos
http://bcove.me/9kbck303
and watch this video:
http://www.youtube.com/watch?v=rENyyRwxpHo
You will realise our so preliminary knowledge about universe...
Vlad, inflation is not incompatible with any postulate of relativity.
The basic answer is that (a) the observable universe was of order centimeters in size, but the entire universe was much much larger, by at least two orders of magnitude; and (b) the best guess is that the universe is actually infinite in size, although we don't know for sure.
If the universe is finite in size, then there are some regions where photons have gotten to but no matter has gotten to. If it's infinite, then the basic character of most patches the size of our observable portion is probably pretty similar to the character of ours.
Vlad: Initially one way to avoid the horizon problem ( the problem to explain how opposite parts of the universe, never in contact, have the same physical property like temperature), apart from inflation, is to deal with a time varying speed of light. And decreasing with expansion. With this approach it turns out that the initial speed of light, much much higher than its present value, must be identical to the initial velocity of expansion of the universe. Then you solve the horizon problem and your photon just rides with the expanding universe.
@Antonio, is there any experimental support for such a theory? As I believe nowadays the space-like separated correlations in the CMB radiation are attributed to inflation. Thanks for your answer!
The recently reported observation of the CMB proposed to be related to the inflation theory are in doubt. Apparently it is not clear if the effect of dust in our galaxy has been taken into account correctly. As far as I know the only evidence that supports the inflation theory is the observed flatness of the universe, a property implied in the inflation theory.
On the other hand, as far as the speed of light decreasing with the expansion of the universe, there are some observations that favour this idea, like works by Paul Smeulders, and australian astronomers in the team of Paul Davies. If you are interested I can recollect this evidence in the near future.
Dear Vlad, the radius of the observable universe is approximately 4.2 Gpc (its age 13.75 Giga-years multiplied by the speed of light). The whole universe can be much bigger, but we can not observe more than this. Inflation solves the horizon problem, the flatness problem (and the magnetic monopol problem).
I think your photon will not encounter a space boundary: Imagine a particle, moving on the 2-dimensional surface of a balloon, which is blown up. The particle can not encounter a space boundary. Same holds for the photon in the expanding universe, but with 4 dimensions.
Dear all: May be what I am about to say will give some new light to the whole problem of the initial stages of the universe. I am finalizing a paper on this and hope to get it published soon. The point is that in this new approach I found that the initial speed of expansion of the universe was identical to the speed of light, and the content of the universe was radiation, with the corresponding equation of state p = 1/3 E/V i.e. the parameter w = 1/3. Then it seems that this model predicts an initial expansion of a quantum black hole (the Planck´s quantum black hole used as a natural system of units out of the three G,c and h). Hence the picture is quite simple, an initial expanding quantum black hole at the speed of light. There is no horizon problem in this model.
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