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The Raisin Bread Analogy Question

  1. Oct 5, 2011 #1
    read analogy here:


    Less like an explosion and more like raisins baking in raisin bread. No matter from which raisin you look, all other raisins appear to be moving away.

    the question:

    The universe is the very boundary of space time, so it isn't expanding into anything or is it? It is just expanding.

    What does the "dough" in the analogy expand into?
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Oct 5, 2011 #2


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    It is expanding into nothing - literally. 'Outside' the universe does not exist. The universe is not embedded in some pre-existing infinite emptiness. The raisin bread analogy fails when you observe it from outside the dough [you cannot observe the universe from 'outside' the universe]. It is only good so long as you are inside the dough. The only way you can tell the dough is expanding is by watching the raisins.
  4. Oct 5, 2011 #3
    Nothing? That does not seem logical. You might as well have said that a perpetual motion machine is possible. Something cannot expand into "Nothing".

    My thought is that our universe is just one bubble amongst many bubbles within an ocean of something...something that is not "nothing".
  5. Oct 5, 2011 #4


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    If you are looking for things to be intuitively "logical" in cosmology and/or quantum mechanics, you are in for some rude disappointments.

    And you could well be right but this is at preset a theological statement (not falsifiable) and an opinion, not science.

    Certainly there are theories along those lines but their validity as theories is not on a par with the theory of relativity or the theory of evolution.
  6. Oct 5, 2011 #5
    yes indeed I'm afraid it will quite possibly always remain a theological statement (not falsifiable), however if we deal in probabilities I can say that something expanding into nothing is less probable than something expanding into something correct?
  7. Oct 5, 2011 #6
    Yes, however there is no evidence to support the idea that there is something 'outside' of our universe. And while it can be intellectually stimulating to think about it, because there is no evidence (or way to find evidence), it makes more sense to assume that there is nothing outside of our universe and go from there, because if we can't detect/measure/interact with it, it mine as well not exist.
  8. Oct 5, 2011 #7
    Vorde, there will probably NEVER be evidence to support my idea. However the idea that there is "nothing" outside our universe seems a bit childish to me. You might as well tell me that there is a hidden realm called heaven and hell :)
  9. Oct 5, 2011 #8


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    Just realize that current models of the universe never say there is nothing, they simply don't require that there be anything to expand into. (As far as I know at least) Also, you may be unaware that a simple 3d volume is not sufficient to describe the universe, so an analogy or thinking about it that way will ultimately fail. Models of the universe take into account spacetime, not just space. When you get down to the details, there is no way to visualize what is happening since it is primarily described through math where the results on non-intuitive and not through something like a picture. This is similar to Quantum Mechanics, in that QM is also described using complex math and any attempt to visualize what is "really" happening is futile.

    Edit: Also, is thinking that there is "nothing" really any different than considering the universe infinite, being in a multiverse, or being finite? Not in my opinion.
    Last edited: Oct 5, 2011
  10. Oct 5, 2011 #9
    The problem with your thought (at least in my view, there are definitely people out there who would disagree with this) is not your idea, but the concept of an area outside of our universe in the first place.

    Any point in our universe can be represented by 4 coordinates: x,y,z,t (lets ignore higher dimensions for now because they don't change the problem). Now you can locate any point in the universe like that. So when someone says "outside our universe", they are referring to a point, which by definition cannot be located using that coordinate system. The question is, it is even meaningful to talk about an area that cannot be mathematically located?

    EDIT: I didn't see the Drakkith post, he summed it up better than I did.
    Last edited: Oct 5, 2011
  11. Oct 5, 2011 #10
    Meaningful? Interesting choice of words. Is it meaningful to imagine a creator that gets angry? I wonder.... However if the analogy of the raisin bread, which is taught at Berkeley (where I first heard it) is propagated then the logical question must be pondered: what does the dough expand into? It may not be meaningful, however the question must be asked. Dwell on it... for it is all we can do.
  12. Oct 5, 2011 #11
    It doesn't have to be asked however. Imagine this:

    You are in a two dimensional universe that is governed only by the following rules:
    -There are no deformities in the smoothness of the plane in all directions.
    -There are only 2 dimensions of movement (and therefore of location), Up/down and left/right.

    Now there are 2D people in this universe, and an adventurous 2D object decides to go as far 'left' as he can. Eventually he finds that he returned to the place he started. This is done many times, and each time the same thing happens. Now the scientists of this world analyze this, and come to the conclusion that this is proof they lived in a curved universe.

    Now as 3 dimensional people, we look at that and we can easily imagine it as a surface of a sphere, you go in one direction far enough and you come around to the other side. And looking at that, you may be tempted to ask, well whats outside of the sphere? What happens when you lift up from the sphere?

    However it is not a meaningful question, you simply cannot do that. This universe is defined only having those two dimensions, so outside of the surface of this 'sphere' (or inside for this matter) is simply not a place.

    Do you see why when applied to our universe this prevents the exterior of the universe from being a meaningful place, even if we can't picture it as well?
  13. Oct 5, 2011 #12


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    There's nothing wrong with the question. The raisins in dough is an analogy, a way of visualizing it, nothing more. When you ask about the crust and what the dough is expanding into, then the answer you get is that the universe has no crust and is not expanding into anything according to current knowledge. The raisin bread isn't going to be 100% correct because it is JUST a way of teaching the subject, of making people understand it. It is not the model itself.

    To take the question further, the answer to what's beyond the universe, or if there is an edge or beyond to the universe, the answer you get is "we don't know, but our models don't need one to work". That's all.
  14. Oct 5, 2011 #13
    great answer and of course the correct one for now. We simply don't know. To say it's "nothing" is wrong. The answer is: We don't know. Period. However if we do KNOW that the universe is expanding then it is more probable it is expanding into SOMETHING rather than NOTHING. That's my point. Thanks guys for the great discussion!
  15. Oct 5, 2011 #14


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    You have no way of knowing that, nor do you understand what is meant by "expansion". Science has shown that on the scale of the very large and the very small things do NOT work as we think they should. I see no reason to say that it is more probable for the universe to be expanding into anything. In fact, I would say that there is more reason to believe it isn't, as the models of various curvatures of the universe don't place the universe within something else yet still show it can expand. Don't try to base your view on "common sense" as that will fail you repeatedly when you learn about science.
  16. Oct 5, 2011 #15
    Oh Really? Do tell what this years Nobel prize was all about? I await your explanation of "expansion" and into what said "expansion" is "expanding" into.....

    The prize was awarded with one half to:

    SAUL PERLMUTTER and the other half jointly to BRIAN P. SCHMIDT and ADAM G. RIESS for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.

  17. Oct 5, 2011 #16


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    No, it's not that we don't know.

    Our models of the universe are logical and consistent without there needing to be anything outside it.

    There is no reason to invent anything outside. And "because the idea bothers me" is not a reason.

    The mistake you're making is assuming that the universe (which is as unique as it is possible for a phenomenon to get) should have some precedent in your experience that you can draw on to try to understand it. But seriously, are there other universes that you've encountered that you're comparing this to, such that this one's topology "doesn't make sense"?

    The universe is not obliged to meet anyone's idea of "common sense".
  18. Oct 5, 2011 #17
    But you don't know do you ;)
  19. Oct 5, 2011 #18


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    The nature of the scientific method is that we observe, and we build models that describe what we see.

    Our models describe what we see. And they do it pretty well.

    As for "we don't know" well, we don't know that God doesn't exist either. We also don't know that the late Carl Sagan doesn't have an invisible fire-breathing dragon in his garage, or that a teapot is not orbiting Jupiter.

    But the scientific method has nothing to say about it until and unless our world needs the existence of a God (or an invisible dragon, or a space-faring teapot or an outside-the-universe) to accurately describe its workings.

  20. Oct 5, 2011 #19


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    Yeah, Dave, I tried to point that out in post #4 but he's not going to listen to that point of view cause he knows he's right.
  21. Oct 5, 2011 #20
    Very true and well said however we see that the universe is "expanding". The nobel prize was just awarded for this. What good sir is it expanding into? I ask you in good faith and await your answer.
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