Referring the universe as a balloon ?

Question

This is confusing ! when questioning an expanding universe, many people say "think about it as a balloon filling up with air". Ok fine. Question..are we inside the balloon or on the balloon ?

Answer 1

It's a 2-D model where you and everything else are embedded in the surface. It is a trick when you just draw dots on it and say that as you blow it up the 2-D "stars" then expand apart. Better to draw a 2-D man separated by another 2-D man by a certain distance. Draw their little circular eyes. Draw a "ruler" between them and even mark it with rulings and numbers. Below the ruler draw a sinusoidal wave between them. As you blow it up, the men stretch, the ruler and its markings stretch, the sinusoidal wave stretches, and even their little 2-D eyes with their little retinas have stretched. Notice that though the expansion has taken place the ruler still reads the same number and is still between. There is no way for anyone to actually if they are expanding because everything would stretch- ALL SPACE! But according to Big Bang theory, the object's dimesions don't strecth and mundane spaces like planetary orbits and atomic orbitals don't stretch. Just magical, large scale cosmological space expands somehow. So according to Big Bang theory there are different types of space. I say space is space and this theory is wrong! Also you can see that the ballon would have positively curved space, but our universe has zero curvature. They say maybe its so big it just looks like zero curvature but if that was so then the expansion would barely be noticed as well.  

Answer 2

We're on the surface of the balloon.  The point is that every point on the balloon is getting farther from every other point, and there is no center.

I like the raisin bread rising in the oven analogy better.  All the raisins are getting farther from each other.  The loaf is infinite in size.  Yum!

But all analogies break down somewhere.  If they didn't, they wouldn't be analogies, they'd be the thing you're talking about.

Answer 3

The reference to balloon is only an analogy, you don't take it totally literally.

First you need to get rid of the notion of balloon surface, the universe fills the entire volume (up to the surface) of the balloon and this volume is expanding, in 3D similarly as you can see the balloon surface expand - except it's only in 2D (as the analogy goes).

Answer 4

The Universe is always expanding.  The analogy refers to galaxies moving within the Universe.  the further away the galaxy (in this case, from Earth), the faster it's moving.  

Where the balloon fits in: if you take a deflated balloon and draw a bunch of dots on it, designating one as 'Earth'.  Then blow up the balloon.  The dots (galaxies) that are further away moved faster in the same amount of time (when you blew up the balloon) as the closer dots.

Answer 5

The balloon analogy is a little confusing because it in fact does not include the inside of the ballon. Instead, it pictures our universe as a two-dimensional surface that inhabits the outer surface of the ballon. The residents of this 2 dimensional surface have no sense of the inside or the outside of the ballon; they can perceive only the two-dimensional surface of the outer skin. So, if there are several dots on the balloon representing galaxies, then the residents of those galaxies look out along the curved surface as the balloon expands and they notice that all of the other dots (galaxies) are receding away from them. They cannot see the center of the balloon, (they can only sense two dimensions) so they cannot see the origin or the central reference point for the expansion. They can only see that all galaxies are receding in all directions.

Now, take this analogy and apply it to a 3 dimensional universe - and you can perhaps begin to picture why we see all galaxies receding from us in all directions, with no identifiable center or starting point.

ADDED: The point of the analogy is this: The balloon represents a thin sheet ( a 2 dimensional surface) that is warped into the third dimension to create a sphere. However, if there were two dimensional inhabitants of that surface (like the classic Flatland story), they would not be able to see that curvature - they could only look straight out along the surface. As they do, their vision curves with the surface, so they can see the other dots on the surface, but they cannot see outside or inside the surface - and they in fact have no concept of "inside" or "outside."

Now imagine a 3 dimensional universe, like ours - (actually, it's four dimensions if you consider time, but I am talking about spatial or geometric dimensions) - that is warped into an additional dimension that we cannot see because we are three dimensional creatures. The universe is expanding in all dimensions, including that extra one, and that's why we cannot see the center of expansion.

Answer 6

someone recently made it make more sense to me by using the balloon in a different way.... he said the balloon contained molecules of air (galaxies) and that if we took it up into the upper atmosphere, the balloon and it's contents would expand, tho nothing had been done to add to it....every molecule would be farther away from every other molecule in the expansion, tho there were no more than there were at the start....

for me, to make that 'dots on a balloon' thing work, I have to see an infinite number of balloons inside each other, all expanding at the same time, 'taking up space' .....they'd all be expanding at about the same rate, but the one on the outside would have to be expanding faster than the ones on the inside, to make room for the expansion of the interior ones................but visualizing infinite numbers of balloons inside each other is tough for me..... so the atmospheric pressure balloon works better to my little brain!....