I just do not understand this concept of metric expansion of space. Shouldn't the galaxies move away from each other. How can the space between them expand if the galaxies are not moving away from each other. I do not want an analogy of a balloon or something like that. I just want a real answer and if possible the reason behind it. There maybe something that is causing this expansion. I just can't understand how space can expand.
Asked
Active
Viewed 1,342 times
2 Answers
2
This isn't an answer, because I don't think your question has an answer, but it got too long to put in a comment.
Anyhow, when physicists try to describe the universe we do it by constructing mathetical models. Then we use these models to calculate what will happen and do experiments to see if we we correct. If we got the correct answer it means our model is a good one, but whether the model is really what happens is a question we leave to the philosophers.
General Relativity is a mathematical model developed by Einstein to describe gravity, and it gives an excellent description of the universe around us - so good in fact that no experiment has even been done that contradicted GR. It is a feature of GR that spacetime is a dynamic object and can and does change with time. The expansion of the universe is an example of this. It's a result of the solution we get to Einstein's equation when we make a few plausible approximations like the universe is basically the same everywhere.
So when you ask how space can expand the answer is that if Einstein's equation is correct this is an inevitable consequence of a universe where the density of matter is the same everywhere. The answer is that given our initial conditions space must expand (or contract if the density is high enough).
I think you're right to dismiss analogies like the rubber balloon because they are misleading. In the case of the balloon its skin expands because someone is pumping air into it. Nothing like this is happening in the universe - there is no outside cause of the expansion - the expansion is an intrinsic property of uniform distributions of matter.
If you are interested to try and get some understanding of how the expansion arises, and what it means, try Googling for the FLRW metric or indeed searching this site will find lots of related questions. For example my answer to Does time expand with space? (or contract) is an attempt to explain some of the ideas at a popular science level.
John Rennie
- 367,598
1
The galaxies and (and binded objects) are maintained by gravity. The rest is explained here, Whats left at the center of the Universe after Big bang?
