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Comment by cgriswald | Hacker News Reader

> On the traditional balloon model, the surface of the balloon represents space itself...

For any still confused, there is also a 'raisin bread' model (which I prefer because it's 3D, unlike the surface of a balloon). The raisins are galaxies, and the bread is the space between them. As it bakes, the raisins get further apart, even though the raisins aren't moving through the dough.

(Although galaxies also have movement through space, this isn't what is causing them to get further apart.)

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Omg, thank you for this! The balloon model always confused me because I could never understand what was in the middle of the balloon, and why we were on top of it. It's an odd 2d example using an object that is 3d, the balloon.

Raisin bread, oh I love thee even more today.

The raisin bread is a 3D expansion in 3D space. So from the viewpoint of a specific raisin the others are moving differently depending on what direction you look and you can use that to determine where the center of the bread is.

The balloon is a 2D expansion in 3D space, which is a better analogy for our 3D universe expanding in 4D space. From the viewpoint of a particular dot you see the exact same thing no matter what 2D direction you look. There is no center.

I agree that the balloon is more confusing, but it is more correct in that it doesn't lead to ideas like "the point where the big bang happened".

Your last point resonates with me. I had neither previously considered where the big bang might have taken place, nor that this would somehow be an erroneous concept. I scrolled through a bunch of disjointed answers on Quora that left me more confused than before. Could you point me to some good resource on that topic?

Is the a term for the 4-dimensional coordinate of the 'inflationary center', like there a 3d coordinate for the center of the balloon (inaccessible from the flat universe on its surface)?

Imagine that the balloon is actually completely flat and (to all intents and purposes) stretches infinitely in X and Y directions without wrapping around. As I understand it, we currently believe we're in a 3D version of that:

https://en.wikipedia.org/wiki/Shape_of_the_universe

Why not chocolate chip bread? I suppose raisins more closely represent galaxies.

Is that a real thing? You can buy raisin bread at any grocery store... I've never even heard of chocolate chip bread.

It's definitely a thing. And yes, I've bought it in stores, not just made it.

I wanted to propose bread with sunflower seeds, because raisins are gross. But now I'm intrigued: wouldn't chocolate melt when the bread is baked? Is it effectively ‘chocolate blob’ bread?

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