Podcast: Questions about the Size, Shape and Centre of the Universe
Written by Fraser Cain
As predicted, we had a huge number of listener questions after our puzzling trilogy about the nature of space itself. Is the Universe really a big donut? Could you see the same star in all directions? If the Universe is expanding, there must be an edge? Right? Listen in as we decrease the number of headaches by 5, and get a special bonus explanation you can use on the dark matter deniers in your life.
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Questions about the Size, Shape and Centre of the Universe – Show notes and transcript
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March 27th, 2008 at 3:33 pm
One question i have about all this is the balloon analogy
I can imagine that if you are sat on the surface of the balloon and travel along the x axis (west or east) and y axis (north or south) you will come back to where you started.
Great,
But thats only two dimensions, right? what about if i travel the zaxis (up or down)? i would come to the edge..
So i can understand this if we were talking about a 2d universe wrapped around a 3d balloon universe
But i stuggle to see how this applys to the 3rd dimension
March 28th, 2008 at 8:05 am
Once you have a good handle on how it works in two dimensions, mentally change the balloon to a lump of dough with raisins inside. Put the dough in the oven. As the dough rises, gets larger, the rasin that was in the center stayed there. However, the second raisin that was an inch above the first is now two inches higher. The third raisin started out an inch above the second raisin and therefore two inches above the first.
Now the third raisin is two inches above the second. However, it is four inches above the first. The thinking process is the same as the expanding balloon, but now the expansion also happens in the third dimension.