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Whoa whoa whoa. It's experimentally confirmed that the discrepancy between what GR predicts the cosmological structure of the universe should look like and what

Whoa whoa whoa. It's experimentally confirmed that the discrepancy between what GR predicts the cosmological structure of the universe should look like and what our measurements can glean fits a uniform energy field with a specific density that accelerates expansion. It's never been observed in any other capacity, and dark energy is generally just taken as a way of saying "whatever makes this particular term necessary in GR at certain scales". There's not even a consensus on how to fit it into GR; the simplest and original solution is the cosmological constant, but there's also the approach of treating it as a field that is dynamic (can vary in space and time) in principle but just happens to be too uniform for us to tell. That doesn't even take into account the fact that this could be a sign that GR is simply missing something when it comes to the large scale structure of the cosmos. We've ruled out some proposed alternate theories experimentally but not all, and that's just the proposed ones.

wyager 10y ago
>It's never been observed in any other capacity, The Casimir effect and Lamb shift are strong experimental evidence of vacuum energy, which is mathematically equivalent to Einstein's "cosmological constant".
- johncolanduoni 10y ago
  How are they remotely mathematically equivalent? The Casimir effect/Lamb shift calculations do not need any input from the cosmological constant's magnitude or anything equivalent. You can calculate them with naught but the constants you need to fix the form of QED. If you try to go the reverse direction and claim that vacuum fluctuations are what the cosmological constant is really about, like you said you have to explain a massive (orders of magnitude!) discrepancy. Considering that the cosmological constant is nothing more than a magnitude as far as we can tell, a theory about a link that gives the wrong magnitude is completely useless. You can draw a parallel between them conceptually, but that connection is about as solid as the connection between the cosmological constant and any other isotropic scalar field like the Higgs. This is another speculative explanation, but again there is no theory that actually manages to explain the value.
  - wyager 10y ago
    >like you said you have to explain a massive (orders of magnitude!) discrepancy. Yes, I admitted that earlier. This is the tricky part, not that dark energy exists. There are a number of plausible theories as to why the magnitude of dark energy is much lower than expected, but nothing hard and fast yet.
    - johncolanduoni 10y ago
      No, the tricky part is where you conclusively link the cosmological constant to vacuum energy with no evidence for and a lot against. There are equally plausible theories that connect dark energy to completely different things like the Higgs field, or just leave them unrelated, so appealing to demonstrations of vacuum fluctuations as evidence of dark energy being "experimentally verified" makes about as much sense as calling string theory "experimentally verified" because it agrees with the QFT/GR in the proper domains. What verified, novel predictions do any of the plausible theories make that makes them the defacto solution? I'd be really curious to know because it doesn't appear that many physicists are aware of this defacto solution.

wyager 10y ago

>It's never been observed in any other capacity, The Casimir effect and Lamb shift are strong experimental evidence of vacuum energy, which is mathematically equivalent to Einstein's "cosmological constant".

johncolanduoni 10y ago
How are they remotely mathematically equivalent? The Casimir effect/Lamb shift calculations do not need any input from the cosmological constant's magnitude or anything equivalent. You can calculate them with naught but the constants you need to fix the form of QED. If you try to go the reverse direction and claim that vacuum fluctuations are what the cosmological constant is really about, like you said you have to explain a massive (orders of magnitude!) discrepancy. Considering that the cosmological constant is nothing more than a magnitude as far as we can tell, a theory about a link that gives the wrong magnitude is completely useless. You can draw a parallel between them conceptually, but that connection is about as solid as the connection between the cosmological constant and any other isotropic scalar field like the Higgs. This is another speculative explanation, but again there is no theory that actually manages to explain the value.
- wyager 10y ago
  >like you said you have to explain a massive (orders of magnitude!) discrepancy. Yes, I admitted that earlier. This is the tricky part, not that dark energy exists. There are a number of plausible theories as to why the magnitude of dark energy is much lower than expected, but nothing hard and fast yet.
  - johncolanduoni 10y ago
    No, the tricky part is where you conclusively link the cosmological constant to vacuum energy with no evidence for and a lot against. There are equally plausible theories that connect dark energy to completely different things like the Higgs field, or just leave them unrelated, so appealing to demonstrations of vacuum fluctuations as evidence of dark energy being "experimentally verified" makes about as much sense as calling string theory "experimentally verified" because it agrees with the QFT/GR in the proper domains. What verified, novel predictions do any of the plausible theories make that makes them the defacto solution? I'd be really curious to know because it doesn't appear that many physicists are aware of this defacto solution.