The January 2008 Popular Astronomy carried a project in which you mark a balloon with galaxies, then blow up the balloon so that the galaxies expand away from each other, just as in the expanding Universe. It posed some questions at the end – and if you’ve come here, you probably want to know more.
So here are ten top questions about the expanding Universe, answered for us by Dr Francisco Diego of University College, London.
Q How do we know the Universe is expanding?
A Because we can measure the velocities of all the clusters of galaxies and all of them are going away from us
Q When did it start to expand?
A The latest calculations give 13.7 thousand million years ago
Q What was there before it began?
A Absolute nothing. There was no before because time itself did not exist (not that anybody really understands this, but we have to accept it)
Q What is it expanding into?
A Into nothing. Space itself is expanding as part of the Universe (again, nobody understands this)
Q Where is the middle of the Universe?
A Everywhere and nowhere. Using the balloon as an example, space is the surface of the balloon, and there is no centre to its surface. The centre of the balloon is outside the Universe and that place does not exist.
Q Will it go on expanding for ever?
A It looks like it will
Q How far is it to the edge of the Universe?
A There is no edge on the surface of the balloon!
Q Are there other Universes?
A Nobody knows, but we can’t say no
Q How far can we see towards the edge of the Universe?
A Our technology reaches objects as far as 13 thousand million light years or something like that.
Q How loud was the Big Bang?
A Although TV documentaries like to have a sound to it, and show it from outside, there was no air surrounding it so there couldn’t have been any sound, and there was nothing outside it so no-one could have seen it happen. In space, no-one can hear you scream, remember?!
Now the answers to the questions in the Very Challenging part of the project:
Q Think about how you can use your answers to work out the age of your balloon Universe. How do you think the results would change if you used a different galaxy to measure from?
A The age of the Universe was measured directly during the experiment – the time you took to blow up the balloon. But if you were on a galaxy and saw the others moving away from you at a given rate, you could work out how long it had been since all the galaxies were next to each other. It would not matter which galaxy you chose, anywhere on the balloon – the rate of expansion is the same for all.