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The universe has been expanding since the Big Bang. This expansion of the spacetime fabric can be estimated by the Hubble’s constant, and is usually compared (analogously) to a ballon being blown up, where its surface represents the 4 dimensions. One of the flaws in this analogy is that in our classical world a balloon, when blown up, has its surface become thinner and thinner (a direct consequence of the conservation of energy). The fabric of the spacetime however, is not becoming thinner as the universe expands (as far as we know). Spacetime is elastic (a direct consequence of Special and General Relativity), but, as it expands, its 4-dimensional “surface” is not becoming thinner, or weaker, or harder etc., it simply continues to be the same for ever and ever (right?). Supposing that the spacetime is fundamentally composed of discrete pieces of energy/matter (strings, or any other fundamental particle), this expansion will eventually reveal that this apparent continuous fabric is actually made of these quantized substances. This phenomenon could be understood as the creation of “little holes” — represented by the dashed lines in the third circle of the drawing — in the spacetime structure.

If these holes were to exist, most likely they would be quickly regenerated by other pieces of the fabric of spacetime — red spots in the drawing — once we do not observe these holes. Question: Doesn’t this regenerated process violate conservation of energy? I mean, where do these “pieces” of spacetime come from (assuming that each of these pieces stores energy)?

Qmechanic
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DiBeos
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    Energy conservation does not hold in GR. https://physics.stackexchange.com/q/306838/ – BowlOfRed Aug 20 '20 at 19:33
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    "Spacetime fabric" is a poetic phrase used in popular descriptions of physics for laypeople, but note that general relativity does not model spacetime as a physical material. – J. Murray Aug 20 '20 at 19:38

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All analogies are imprecise, but the balloon analogy is a particularly bad one, in my opinion, because it creates the impression that space is a substance that persists through time. In reality, all of the space at a given time is "new" inasmuch as it's just a different part of the spacetime manifold.

Spacetime may be made of something more fundamental, but if so it will presumably still have the basic properties that spacetime has, including not being "substance-like". Anything that did behave like an ordinary substance would break Lorentz invariance, which would be... very surprising, at least.

benrg
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