Ok, quick question, kinda in refernce to the other post about the end of the universe.
If the universe is explanding, this means that it was once one size, and now is another. This is what it means to expand. That being said, the universe could be “measured”. Something without a “size” cannot expand. You cannot try to say that it is now larger than it used to be, say, 2 billion years ago, without out it having had a “size” then, and a “size” now.
This means there would be and “end” to the universe. Even throwing away the fact that it is expanding… assuming you had a spacecraft that ran off it’s own fuel, or infinite energy, or something of the like, and could travel forever. SOMETHING would have to happen eventually if you took off from earth and followed a straight line. It’s not like it would just go on forever, that is impossible. What would you reach?
Someone in the other thread explain the universe as more like the surface of a balloon, as opposed to the surface. Assuming that is indeed true, and we’re on a 2d plan, so to speak… eventually you’d reach the begining again, if it is indeed a sphere. Would you loop, and run into earth again?
I also don’t understand the 2d theory entirely. Assuming we’re on the surface… how can we move in 3 dimensions without leaving the surface?
“Someone in the other thread explain the universe as more like the surface of a balloon, as opposed to the surface. Assuming that is indeed true, and we’re on a 2d plan, so to speak… eventually you’d reach the begining again, if it is indeed a sphere. Would you loop, and run into earth again?”
That’s the idea. Look at it this way: you exist in four dimensions, not just three. In the early days, when people believed the earth was flat, one was they could (but didn’t) discover otherwise would be to travel around it. Although we have no practical access to this fourth dimension yet, the simplest answer to “what is at the edge of the universe” is nothing; thus, the universe doesn’t end, it doubles back on itself in a dimension that the mind simply cannot appreciate. Think of it as a “hypersphere”, if a sphere were called a “hypercircle”. (thanks to Iain Banks for those terms.)
No, that’s incorrect. You and I exist in just three spatial dimensions. Unless you count time as a dimension, then you can say we exist in four spacetime dimensions. Any additional spatial dimensions (required by superstring and M-theory) are thought to be tightly curled up on a scale smaller than the Planck length, so that we can never observe them directly.
The two-dimensional balloon universe analogy is just that: an analogy in two dimensions for what is really happening in three. Only two-dimensional beings could exist in the balloon-surfance universe, since in that universe there is no third spatial dimension. The ballon itself is threedimensional, but we are only talking about its surface. Nothing else exists in that analogy.
Unfortunately, you would never reach the most distant galaxies we can see now-
they are expanding away from you all the time, getting faster and faster as they get further away - so you would never reach the most distant galaxies within the observable universe.
And the balloon analogy is only a 2D representation- you have to imagine that skin of the balloon as a three dimensional expanding space rather than a skin.
Difficult to do, but there it is.
Yes, it appears that the universe was once one size and is now another. And is growing. And recent data from looking at distant (and therefore ancient) supernovas seem to prove that the rate of expansion is itself increasing. So why must this stop. Will the baloon burst? There is nothing to suggest it will. The universe will expand and in something on the order of 10^150 years all the protons will have decayed, all the black holes will have evaporated (yes, black holes do evaporate, very slowly when they are large, more quickly when small) and we will be left with an extremely thin soup of photons, neutrinos and electrons. At least that is what the standard model predicts.
Ok, but I’m assuming we can somehow. I mean, there are THINGS out there somewhere. Assume that instead of where we are, earth is quite close to the “edge” of the universe. You would have to hit something eventually, or loops around to the other side of the universe (freaky).
Assuming the baloon surface it more like a second chamber surrounding the baloon, the chamber itself having 3 dimensions, you would indeed loop around and reach earth again.
Also, just thinking about the chamber thing… is the universe expanding in all directions? If so, you’d eventually run out of space in the center of the baloon, for the chamber to fill.
Maybe I’mw ay off… but I’m bored, and this stuff will keep my mind busy forever.
Red shift shows that astronomical artifacts (e.g., galaxies) are moving away from us in all directions.
The balloon analogy is simplistic, but there are two ways to look at it:
The wrong way: Take a deflated balloon and paint dots on it to represent galaxies. Blow it up. The galaxies expand along with the space between them.
The right way: Take a deflated balloon and paste dots on it. Blow it up. The galaxies do not expand but the space between them gets larger.
Galaxies are “gravity wells.” They resist being pulled apart. The space between them grows bigger. That’s why most everything is red-shifted, indicating that they’re moving away from us.
What has always confuzzled me is the statement that the farther away we look (in the universe), the farther back in time we are seeing because it takes time for light to travel. My question has always been - if we could look far enough away, would we see the big bang? Wouldn’t that be a conundrum?
NO, Cillasi, there is a definite limit on how far we can see back. The furthest away (in time) radiation we can see is the cosmic background radiation which is an articfact of the decoupling era, 300,000 years after the big bang. We cannot see any further than this because before this era the density was so high that any photon was instantly absorbed by matter when it was emitted.
A fundamental misconception in the OP: Saying that the Universe is expanding does not imply that the Universe has a size. Picture an infinite sheet of graph paper, ruled at 5 squares per inch. Since it’s infinite, it does not have a size, nor can you measure the size of the whole piece of graph paper. But you could stretch the paper uniformly, such that the squares are now a quarter of an inch. The whole paper is still unmeasureable, but you could say that it’s expanded by 25%.
And one can argue that, when you look at the cosmic microwave background, you are in fact “seeing the big bang”. It’s not a conundrum at all.
Chronos, I don’t see how you could argue that observing the CMBR is observing the big bang. For example if your measuring athe isotropy of the CMBR you’re not measuring the isotropy of anything earlier than the decoupling era, when the radiation was emitted (of course you can infer and put limits on earlier isotropy from this information, but it’s not a direct observation). In fact the people involved in scanning CMBR usually say (i.e. WMAP): “this is the universe at 0300,000 years old” when relesing their results to the public.