In the early years of the universe, many galaxies formed in a short time, astronomers suspect. But galaxies can’t move through space at the speed of light, can they? Because not only does the momentum increase with the speed, but also the relativistic mass m(v). How can there be galaxies 12 to 13 billion years away from us? Then the universe must be much older, if the furthest light of these masses at 13.7 billion years only now reaches us?
Answer
Hi Dave,
This apparent paradox arises from the special structure of our universe. You are probably inclined to think that our universe is an infinite Euclidean space with three space dimensions and one time dimension, in which matter spread out from a center after the Big Bang. The structure of our universe can be explained much better in a model with three space dimensions that are curved in a fourth space dimension. To be able to grasp this, it is best to think away a dimension and reason as if we were flat 2-dimensional figures that lived in a plane. We would then be inclined to think that we lived in an infinite two-dimensional Euclidean plane in which matter would spread out from a center into an ever-expanding disk.
However, you have to consider that it is just as possible that we did not live in a plane, but on the surface of a large sphere (ie a two-dimensional surface curved in a third dimension). The big bang is not the spreading of matter, but the expansion of space itself! With one dimension removed, space then looks like the surface of a small sphere that rapidly expands to the surface of an ever-expanding sphere. No point on the spherical surface is in ‘the center’, but everything moves away from each other.
There is no limit to the rate at which space itself can expand. The speed of light is a limitation that light and matter has moving in space. So it is possible that space has become much larger than the 13.7 billion light-years we see. During the inflationary expansion in the early stages of the Big Bang, light simply fell behind the size of space. We can only see 13.7 billion light years away, but every day we see a little further. What we see there is not what is there now, but the light that started traveling to us from that direction just after the big bang.
This is just a theoretical model. If ‘light lags behind’ to space, that means causality also lags behind. We don’t have any causal relationship with space beyond 13.7 billion light-years, so models that assume that space doesn’t exist (yet) may be more correct.
Hopefully this will shed some light on this complex matter.
regards,
Ward
Answered by
Dr. Ir. Ward Blondé
Physics Bioinformatics
http://www.ugent.be
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