What an Expanding Universe Looks Like

[FeDeX_LaTeX]

Hello;

Please forgive me if this is a silly question, or if it's been answered before. I have tried googling this, but I can't find the information I need, I've probably overlooked it, but I can't find it.

I recall a quotation by Lawrence Krauss who said in a talk that "from the inside, the universe would look like it was expanding, but from the outside, it would look like it was contracting". Can somebody please explain this? I will try to find the video in which this was said.

Thanks.

 

[marcus]

Without a link I can only speculate. It sounds to me as if he is talking about an alternative explanation of the observed accelerated expansion that was put forward by David Wiltshire but did not catch on with the community. The idea has some problems since it depends on our galaxy being in a somewhat special location and on the universe having uneven density in a special way. But that said the idea makes sense on a certain level.

Call it the big void explanation. Suppose we are in the middle of a huge region of below average density. Then the galaxies around us would be attracted away by the outer region of higher density. So they would accelerate away.

This accelerated expansion is what has been inferred from observation. The simpler explanation is just to assign a small positive value to a constant called Lambda which appears in the Einstein equation that standard cosmology is based on.

However I am not sure that Wiltshire's void idea was what Larry Krauss was talking about on that occasion. This is only my best guess.