Question: What is expanding when we say the universe is expanding? Light from distant stars have not even reached our earth which means it is much much much much..........distant to earth. If that is the case then universe should have expanded at a speed much greater than the speed of light. So the thing that is expanding when we say the universe is expanding should have travelled at a speed much greater than the speed of light during the period of inflation. This would mean that something would travel at a speed greater than the speed of light if much much much energy is provided. So, why is speed of light considered as the ultimate speed limit?(do correct me if I'm thinking wrong)

David Freeborn answered on 22 Jun 2013:

Hi rajathjackson,

As Chris says, the thing that is expanding is space itself. Nothing in the Universe is actually “moving” anywhere when space expands, it’s more accurate to just say that the “distance” between every object is increasing.

This is why I don’t like it when some people compare the expanding Universe to an expanding balloon. When you blow up a balloon, all the parts of the balloon are moving, as the balloon is stretched. That’s not what is happening when the Universe expands, nothing in the Universe is moving. It’s the properties of space that are changing, to make every distance between any two objects in the Universe longer.

As Chris says, this doesn’t transfer any information. Indeed, nothing is really being transferred at all, because nothing is moving. What’s happening is that distances themselves are just increasing.

That’s a really difficult concept to grasp, so I hope it’s clear!

(you can read a bit more about the concept here: https://en.wikipedia.org/wiki/Metric_expansion_of_space)