[Patrick Poisson]

Patrick Poisson  asked the Naked Scientists:
   
Chris,

Doesn't it stand to reason that if the universe is made of matter and energy, all of which is limited to the speed of light or less, that the largest that the universe could be is a sphere no bigger than 27.4 billion light years in diameter? However I've read that the universe is estimated to be some 140 billion lightyears across?

What do you think?

[DoctorBeaver]

Here's a reply I posted to this question a while back in another thread:-

Some estimates put the size of the universe at 125 billion light years across. A lot of people have trouble understanding how that can be if the universe is only 13.5 billion years old and nothing can travel faster than light - I didn't get it at first either. The obvious assumption is that the universe cannot be more than 27 billion light years across (13.5 billion years expanding in all directions). This, however, is not what happened.

"Things" are not moving apart due to their own movement; space itself is expanding. In the very early universe (10^-35 to 10^-33 seconds) this expansion caused a 100-fold increase in size. This brief event is known as "inflation". Nothing was actually moving through the universe (not even light), so the universal speed limit of light was not violated.

Nobody is entirely sure what happened at 10^-35 seconds to start inflation, or at 10^-33 seconds to stop it. There are various theories, but as far as I am aware each has holes in it (maybe someone has more knowledge of some of those theories and can respond). The driving force behind inflation may have been the same force that is now causing the acceleration in the rate of expansion of the universe, or it may have been something totally different.

It has to be said, though, that some physicists do not go along with the inflation theory. There are certainly problems associated with it. and scientists such as Martin Bojowald are investigating other theories.

I've just realised a mistake in my reply. I said that inflation caused a 100-fold increase in size. I should have said an increase in size of 100 orders of magnitude. My apologies.  [:I]

HERE is a link to that other thread.