Is the universe a bubble or balloon?

Discovering the limits of our universe

The concept of space going on forever is a mind-boggling one, not least because our brains aren’t designed to cope with concepts such as infinity. But perhaps, because it’s forever expanding, it only appears to be infinite? This is one theory that physicists and planetary experts have put forward.

The universe is around 13.8 to 14 billion years old, but in actuality we can see for 46 million light years in all directions because of its constant expansion. So if you were to stop time, and therefore stop the expansion, the universe would then have a reachable end point or edge. One way to picture this concept is to think of a ballon, as teacher, presenter and planetary scientist Dr Sheila Kanani explains. Picture yourself inside this balloon, living on its interior surface in a two-dimensional space. The balloon is the universe, and as more air is blown into it, you would see the space or surface area of the universe expanding and every point on its surface getting further and further away from one other.

This poses a further question: what will happen to our universe when this expansion stops? Many theoretical physicists believe that the universe could come to an end somewhere between 2.8 and 22 billion years from now – so we probably won’t be around to find out what happens. The idea of a ‘Big Crunch’ is one of several possible fates awaiting our universe. In reversal of the Big Bang, a Big Crunch may cause matter and space-time to collapse in on themselves, creating a singularity – an infinitely dense point similar to that from which the universe came into being in the first place.

It’s been suggested that this idea ties into the likely existence of multiverses, or multiple universes. Perhaps our own universe will expand and then contract into a big crunch, and this will cause a new Big Bang and a new universe will be created. Imagine a glass of fizzy water – there’s nothing in the water except for the water, but suddenly a bubble appears. Equally as suddenly the bubble pops, and more and more bubbles in the water appear and do the same: each of the bubbles is created from a bang and disappears after a crunch. So maybe in space our universe and other universes aren’t created from and expanding into nothing, and perhaps there’s something else present that universes are created in, and we simply haven’t learned what that is yet. Is your head spinning?

These concepts are very difficult for us to get to grips with – which is why many scientists talk about balloons and fizzy water to help us understand them. And as soon as we answer one question it leads to many more that we have yet to answer – a little bit like those bubbles in that water. The universe may go on and on and on, but hopefully one day our questions about it won’t.

Suorce: BBC UK