3 ms·

Slightly tangential but how does the ad hoc nature of things like cosmic inflation seemingly not bother more people? Quite the opposite, it's a rather lauded di

Slightly tangential but how does the ad hoc nature of things like cosmic inflation seemingly not bother more people? Quite the opposite, it's a rather lauded discovery. This is more cosmology than astronomy, but at least reasonably related. That topic alone destroyed my interest in an academic pursuit of astronomy. 'Here's an idea that makes no logical sense, has no physical argument whatsoever (let alone evidence) in support of its existence, and just generally seems completely absurd - but if we ignore all of that, it solves a lot of other pesky problems with reality, as observed, practically falsifying other lauded theories.' Just add more epicycles?

stouset 2y ago
Nobody’s happy with dark energy, it’s just the only framework we have that fits the data. All the other ideas might be brilliant and inspired but are measurably worse at describing the real world. Even the name “dark energy” is a tacit acknowledgment that—along with dark matter—we have no clue what the underlying physics actually is.
- cryptonector 2y ago
  How is timescapes measurably worse? It's not a new theory, so perhaps it's been tested, and if it's failed why is it back in the news? (Sometimes failures get back in the news. It's a fair question.)
  - russdill 2y ago
    It starts with the assumption that our observations of cosmic expansion are false and due to time dilation from a clumpy universe, then works out how clumpy the universe must be to account for our observations. For timescapes to "work" time must run 38% faster in cosmic voids. This works out to a density difference of about 100,000 times what we observe with many existing methods.
    - cryptonector 2y ago
      > It starts with the assumption that our observations of cosmic expansion are false It starts with the assumption that our measurements (observations!) of attenuation and red-shift of standard candles are correct. Your characterization is wildly wrong, unless you meant to use a different word than 'observations'. > and due to time dilation from a clumpy universe, then works out how clumpy the universe must be to account for our observations. Yes, it does work backwards. That's insufficient by itself to say that timescapes is incorrect. It's concerning though because they work out what densities must be in order to explain away all of the attenuation/red-shift disparities. However the reasoning time dilation is not wrong -- in fact, it's blindingly obviously correct if GR is correct, it's just that it might also be wildly insufficient -- it might just be in the noise. > For timescapes to "work" time must run 38% faster in cosmic voids. This works out to a density difference of about 100,000 times what we observe with many existing methods. Thanks. This is responsive to my question, but it's not yet dispositive. We could find that: - some of our observations are incorrect - some of our interpretations of those observations are incorrect - timescapes explains some but not all of the apparent acceleration of the expansion of the universe Also, density differences need to take into account density differences at the time that a ray of starlight we observe today entered each void along the way to us, not current apparent density disparities. It has to be that 8 billion years ago the difference in density between clusters and voids was much starker, though the voids would have been smaller, and perhaps the difference was not enough orders of magnitude.
      - russdill 2y ago
        There's a ton of theoretical work out there that is about building a foundation for future work. This is one of those works. But people tend to overlook the part where the work is just a piece, and many other things most first fall into place and over hype it. This is course isn't the fault of the authors.
lutorm 2y ago
Well, it's not like people pulled it out of thin air. Both inflation and the lambda-CDM models are solutions to the GR equations, so in that sense it's perfectly justifiable to see if general relativity can explain the data. I don't think it's fair to say that it "makes no logical sense".
- misja111 2y ago
  I assume that OP was talking about the cosmic inflation theory that claims there was a rapid expansion immediately after the big bang. I don't see how that's a solution to the GR equation, could you maybe explain/give a link?
  - russdill 2y ago
    There is an addition of a inflation field. Observations show that such an inflation happened, and there's several ideas of inflation fields that are compatible with the standard model and match observations. The equations that make the observed expansion happen in the presence of such a field the friedmann equations, which are GR solutions. The field isn't just something that magically expands things, it just effects energy density. The rapid expansion is then a consequence of GR.
gosub100 2y ago
What do you mean by "bother"? The universe appears to be expanding, so I assume you don't deny that evidence, correct?

stouset 2y ago

Nobody’s happy with dark energy, it’s just the only framework we have that fits the data. All the other ideas might be brilliant and inspired but are measurably worse at describing the real world. Even the name “dark energy” is a tacit acknowledgment that—along with dark matter—we have no clue what the underlying physics actually is.

cryptonector 2y ago
How is timescapes measurably worse? It's not a new theory, so perhaps it's been tested, and if it's failed why is it back in the news? (Sometimes failures get back in the news. It's a fair question.)
- russdill 2y ago
  It starts with the assumption that our observations of cosmic expansion are false and due to time dilation from a clumpy universe, then works out how clumpy the universe must be to account for our observations. For timescapes to "work" time must run 38% faster in cosmic voids. This works out to a density difference of about 100,000 times what we observe with many existing methods.
  - cryptonector 2y ago
    > It starts with the assumption that our observations of cosmic expansion are false It starts with the assumption that our measurements (observations!) of attenuation and red-shift of standard candles are correct. Your characterization is wildly wrong, unless you meant to use a different word than 'observations'. > and due to time dilation from a clumpy universe, then works out how clumpy the universe must be to account for our observations. Yes, it does work backwards. That's insufficient by itself to say that timescapes is incorrect. It's concerning though because they work out what densities must be in order to explain away all of the attenuation/red-shift disparities. However the reasoning time dilation is not wrong -- in fact, it's blindingly obviously correct if GR is correct, it's just that it might also be wildly insufficient -- it might just be in the noise. > For timescapes to "work" time must run 38% faster in cosmic voids. This works out to a density difference of about 100,000 times what we observe with many existing methods. Thanks. This is responsive to my question, but it's not yet dispositive. We could find that: - some of our observations are incorrect - some of our interpretations of those observations are incorrect - timescapes explains some but not all of the apparent acceleration of the expansion of the universe Also, density differences need to take into account density differences at the time that a ray of starlight we observe today entered each void along the way to us, not current apparent density disparities. It has to be that 8 billion years ago the difference in density between clusters and voids was much starker, though the voids would have been smaller, and perhaps the difference was not enough orders of magnitude.
    - russdill 2y ago
      There's a ton of theoretical work out there that is about building a foundation for future work. This is one of those works. But people tend to overlook the part where the work is just a piece, and many other things most first fall into place and over hype it. This is course isn't the fault of the authors.

lutorm 2y ago

Well, it's not like people pulled it out of thin air. Both inflation and the lambda-CDM models are solutions to the GR equations, so in that sense it's perfectly justifiable to see if general relativity can explain the data. I don't think it's fair to say that it "makes no logical sense".

misja111 2y ago
I assume that OP was talking about the cosmic inflation theory that claims there was a rapid expansion immediately after the big bang. I don't see how that's a solution to the GR equation, could you maybe explain/give a link?
- russdill 2y ago
  There is an addition of a inflation field. Observations show that such an inflation happened, and there's several ideas of inflation fields that are compatible with the standard model and match observations. The equations that make the observed expansion happen in the presence of such a field the friedmann equations, which are GR solutions. The field isn't just something that magically expands things, it just effects energy density. The rapid expansion is then a consequence of GR.

gosub100 2y ago

What do you mean by "bother"? The universe appears to be expanding, so I assume you don't deny that evidence, correct?