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You have to ignore the air inside and outside of the balloon as having any importance. And that's the bit of mental acrobatics that makes the metaphor break do

You have to ignore the air inside and outside of the balloon as having any importance. And that's the bit of mental acrobatics that makes the metaphor break down. Which is why the advice above ("Don't believe the metaphors") is relevant.

ErrantX 17y ago
I don't know - as long as you say, during the explanation, that the air inside/outside is irrelevant then it's a good demonstration of expansion!
- michael_dorfman 17y ago
  Umm, no. When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. When the universe expands, the volume of matter remains the same, but the area.....um, what? Expands into open space? That can't be right. So, if the universe is getting larger, like a balloon, where is it going? Oh, so it's not really like a balloon, then.
  - ErrantX 17y ago
    > When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. Well, actually you're considering the air there - so it doesn't work. Ignore the air and think about how the balloon skin moves through the medium. In fact the balloon can be considered as not expanding into open air; simply more air is inside it than before - equally a little less air is outside it than there was before (ignoring pressure differences for the moment). Imagine if the skin was perfectly flat and was stretched. The air "moves" around it but is irrelevant to the expansion (and thinning) of the skin. The example only demonstrates how an object can have a larger area without changing volume. Same principle - but in the balloon it is easier to demonstrate relative movement. Im only basing this on my own experience but anyone I've ever given the proper explanation too has gone "oh yeh, I see" (or something the that effect).
  - stcredzero 17y ago
    So, if the universe is getting larger, like a balloon, where is it going? In a way, it's like all of the light waves are shrinking locally, and only the ones traveling the distance between galaxies are staying the same. (Which is not what's really happening either.)
stcredzero 17y ago
If any given model of the universe involves n dimensions, why can't we simply have it expand into the n+1 dimension? When you inflate a balloon, it's 2d area is increasing by the balloon expanding into the 3rd dimension. In any model of the universe as a brane of n dimension, its expansion can be modeled as expansion in the n+1 dimension. Perhaps "universe" is a paradoxical word that cannot have a meaning? It's hard to imagine a world of infinite dimension.
- sp332 17y ago
  It doesn't work. Time & space - all the dimensions that exist - exist inside the universe. There is no "space" out there to expand into.
  - stcredzero 17y ago
    So you posit a universe of an infinite number of dimensions? That's nonsense. Just because there's nothing in dimension n+1 doesn't mean it's not part of the universe. It would also allow expansion of the n-dimension brane. Do you know of cosmological models proposing an infinite number of spatial dimensions? EDIT: Note that the "expansion of the universe" is really only "expansion we observe through telescopes." I've never heard anything about astronomical observations concerning dimensions S, 6, or others. 3D space can easily expand without the need for anything outside the universe, in a universe of more than 3 dimensions.
    - sp332 17y ago
      I'm saying that there are a finite number of dimensions - maybe a dozen or less. They all exist inside the universe. "Outside" the universe, there are no dimensions. There is no space or time. There is actually no "place" for you to "go" outside the universe. It only makes sense to say that the universe is expanding by measuring the space and matter in it. There is no measuring stick outside to hold the universe up to.
      - stcredzero 17y ago

ErrantX 17y ago

I don't know - as long as you say, during the explanation, that the air inside/outside is irrelevant then it's a good demonstration of expansion!

michael_dorfman 17y ago
Umm, no. When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. When the universe expands, the volume of matter remains the same, but the area.....um, what? Expands into open space? That can't be right. So, if the universe is getting larger, like a balloon, where is it going? Oh, so it's not really like a balloon, then.
- ErrantX 17y ago
  > When you blow up a balloon, the volume of rubber remains the same, but the area gets larger-- because it expands into open space. Well, actually you're considering the air there - so it doesn't work. Ignore the air and think about how the balloon skin moves through the medium. In fact the balloon can be considered as not expanding into open air; simply more air is inside it than before - equally a little less air is outside it than there was before (ignoring pressure differences for the moment). Imagine if the skin was perfectly flat and was stretched. The air "moves" around it but is irrelevant to the expansion (and thinning) of the skin. The example only demonstrates how an object can have a larger area without changing volume. Same principle - but in the balloon it is easier to demonstrate relative movement. Im only basing this on my own experience but anyone I've ever given the proper explanation too has gone "oh yeh, I see" (or something the that effect).
- stcredzero 17y ago
  So, if the universe is getting larger, like a balloon, where is it going? In a way, it's like all of the light waves are shrinking locally, and only the ones traveling the distance between galaxies are staying the same. (Which is not what's really happening either.)

stcredzero 17y ago

If any given model of the universe involves n dimensions, why can't we simply have it expand into the n+1 dimension? When you inflate a balloon, it's 2d area is increasing by the balloon expanding into the 3rd dimension. In any model of the universe as a brane of n dimension, its expansion can be modeled as expansion in the n+1 dimension. Perhaps "universe" is a paradoxical word that cannot have a meaning? It's hard to imagine a world of infinite dimension.

sp332 17y ago
It doesn't work. Time & space - all the dimensions that exist - exist inside the universe. There is no "space" out there to expand into.
- stcredzero 17y ago
  So you posit a universe of an infinite number of dimensions? That's nonsense. Just because there's nothing in dimension n+1 doesn't mean it's not part of the universe. It would also allow expansion of the n-dimension brane. Do you know of cosmological models proposing an infinite number of spatial dimensions? EDIT: Note that the "expansion of the universe" is really only "expansion we observe through telescopes." I've never heard anything about astronomical observations concerning dimensions S, 6, or others. 3D space can easily expand without the need for anything outside the universe, in a universe of more than 3 dimensions.
  - sp332 17y ago
    I'm saying that there are a finite number of dimensions - maybe a dozen or less. They all exist inside the universe. "Outside" the universe, there are no dimensions. There is no space or time. There is actually no "place" for you to "go" outside the universe. It only makes sense to say that the universe is expanding by measuring the space and matter in it. There is no measuring stick outside to hold the universe up to.
    - stcredzero 17y ago