Staffan Lincoln asked:
If you pop a balloon in space, would the vaccuum cause the gas to expand at an ever increasing rate?
We put Staffan's question to Caroline Steel...
Caroline - So firstly, unfortunately, you couldn’t pop a balloon in space because as soon as you got the balloon into space it would split. And that’s because, as the questioner said, there’s more gas inside the balloon and there’s less gas outside the balloon in the vacuum of space. So the balloon would expand as the gas inside it would want to move towards the area of no gas. So if you could video it and play it in slow mo you could see the balloon expand and then probably split down one side.
Unfortunately, you wouldn’t even be able to hear this sort of ‘pop’ as there’s no molecules to take the sound to your ears so you wouldn’t hear it. And then once the balloon has split the molecules from inside the balloon would travel off into the vastness of space never to be seen again.
The first thing to say is that a vacuum doesn't suck - it is the pressure of the gas in the balloon that blows.
It's also worth noting that, while it is true that the molecules will slow down, they won't slow down much. The attractive forces are small and they fall off very quickly as the molecules get further apart. Bored chemist, Fri, 23rd Sep 2016
Thanks evan_au. Your answer completely changed my mental model of gas and vacuum. I thought of gas and vacuum as two variants of filled space. One with high density and one with 0 density. I also thought of the air as being completely still within the balloon. And since I've seen lots of science fiction scenes where the air rushes out of a breach in the hull of a space ship, I thought it was the low pressure that somehow pulled the air out of the ship. Since space is largely empty, I imagined this pulling effect would perhaps account for the increased rate of expansion of the universe. From your answer, I now imagine the air molecules as lots of rapidly moving pool balls, who are trapped by a rubber barrier. Staffan Lincoln, Wed, 5th Oct 2016