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Are there any potential competing theories this detection could also support? I'm wondering how much room there is here for confirmation bias, but I suppose tha

Are there any potential competing theories this detection could also support? I'm wondering how much room there is here for confirmation bias, but I suppose that's a pretty hard thing to measure without the benefit of hindsight.

Steuard 11y ago
Even before this discovery, it's been pretty solidly established that any alternative theory to General Relativity would need to behave essentially identically to GR in the limits where we've been able to test it. So, for example, the "low energy limit" of string theory is general relativity (plus other content, in most cases). I'm not sure whether the loop quantum gravity folks have a working low-curvature limit yet (I'm out of touch), but that would be a requirement for them, too. At first glance, I'd guess that this discovery only strengthens that conclusion: even a small deviation from GR might well change the detailed behavior of an immensely high curvature situation like a black hole merger, and what we saw seems to have been a spot on match for the GR-based models.
- davrosthedalek 11y ago
  Well, they extracted a lot from the waveform: Distance, the two masses, the resulting mass. I could imagine that a competing theory gives the same waveform maybe with different values for these parameters.
  - pdonis 11y ago
    A "competing theory" would first have to match the GR predictions in all the other regimes where it's already been tested. But doing that is an extremely strong constraint on a theory, to the point where the only theory that can meet it is GR itself. Physicists know this because alternative theories to GR have been constructed and tested, and they have all failed. See, for example, here: https://en.wikipedia.org/wiki/Alternatives_to_general_relativity#Results_of_testing_theories https://en.wikipedia.org/wiki/Alternatives_to_general_relati...
    - effie 11y ago
      That's a very common sentiment, but a mistaken one. Theories do not get accepted only if they match the predictions of the previous theories. People value other features besides accuracy of predictions, like simplicity and explanatory power. Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced; Ptolemy's scheme was way better in accuracy, but utterly complex and explained little.
      - pdonis 11y ago
        You're missing the point. I agree that matching the predictions of experiments (not previous theories--I'm talking about experimental results that match the predictions of GR, not just those predictions themselves) is not a sufficient condition for a theory to be accepted (which is what you are saying); but it is certainly a necessary condition (which is what I was saying). > Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced Yes, and it wasn't accepted at the time it was introduced. Actually, Copernicus' theory in its original form was never really "accepted"; what was accepted was Kepler's reformulation using elliptical orbits, based on Brahe's more accurate observations. Kepler's model was more accurate than Ptolemy's, and that was a key factor in its acceptance.
        effie 11y ago
        I agree with you that if a new theory was to replace the old one for making specific set of predictions, it should give predictions of similar or better accuracy. But I do not think that replacement is necessary for the new theory to compete or be accepted; it is the new benefit it brings, whatever its nature may be, that is crucial. The two can temporarily both be accepted to coexist, if both have their strengths. For example, quantum theory does not make the same predictions as classical theory when it comes to classical experiments (mechanics, basic EM phenomena) and is largely useless in that domain. It only gives probabilities of results of specified experiments of certain kinds; it does not reproduce the old predictions (like definite trajectories, Moon phases or solar eclipses), but provides new results (like resonance frequencies of atoms and molecules and their bond energies). Similar thing can happen with a new theory of gravity; it may not give the same prediction for Mercury perihelion precession, but it may be able to explain other things, like why the inverse square law, why no repulsive gravity or why the mutual gravity force between electrons is so much lower than the mutual EM force. Explanation for oddities in Mercury motion could then wait for further data and repetition of calculations. It is natural to expect of any new theory to bring new results, but demanding that it reproduces all the old ones along is too much. That happens rarely and such expectation only prevents any new ideas from being considered.
nanofortnight 11y ago
Einstein–Cartan theory is the only viable classical alternative. I am unfamiliar with modern alternatives to comment.

Steuard 11y ago

Even before this discovery, it's been pretty solidly established that any alternative theory to General Relativity would need to behave essentially identically to GR in the limits where we've been able to test it. So, for example, the "low energy limit" of string theory is general relativity (plus other content, in most cases). I'm not sure whether the loop quantum gravity folks have a working low-curvature limit yet (I'm out of touch), but that would be a requirement for them, too. At first glance, I'd guess that this discovery only strengthens that conclusion: even a small deviation from GR might well change the detailed behavior of an immensely high curvature situation like a black hole merger, and what we saw seems to have been a spot on match for the GR-based models.

davrosthedalek 11y ago
Well, they extracted a lot from the waveform: Distance, the two masses, the resulting mass. I could imagine that a competing theory gives the same waveform maybe with different values for these parameters.
- pdonis 11y ago
  A "competing theory" would first have to match the GR predictions in all the other regimes where it's already been tested. But doing that is an extremely strong constraint on a theory, to the point where the only theory that can meet it is GR itself. Physicists know this because alternative theories to GR have been constructed and tested, and they have all failed. See, for example, here: https://en.wikipedia.org/wiki/Alternatives_to_general_relativity#Results_of_testing_theories https://en.wikipedia.org/wiki/Alternatives_to_general_relati...
  - effie 11y ago
    That's a very common sentiment, but a mistaken one. Theories do not get accepted only if they match the predictions of the previous theories. People value other features besides accuracy of predictions, like simplicity and explanatory power. Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced; Ptolemy's scheme was way better in accuracy, but utterly complex and explained little.
    - pdonis 11y ago
      You're missing the point. I agree that matching the predictions of experiments (not previous theories--I'm talking about experimental results that match the predictions of GR, not just those predictions themselves) is not a sufficient condition for a theory to be accepted (which is what you are saying); but it is certainly a necessary condition (which is what I was saying). > Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced Yes, and it wasn't accepted at the time it was introduced. Actually, Copernicus' theory in its original form was never really "accepted"; what was accepted was Kepler's reformulation using elliptical orbits, based on Brahe's more accurate observations. Kepler's model was more accurate than Ptolemy's, and that was a key factor in its acceptance.
      - effie 11y ago
        I agree with you that if a new theory was to replace the old one for making specific set of predictions, it should give predictions of similar or better accuracy. But I do not think that replacement is necessary for the new theory to compete or be accepted; it is the new benefit it brings, whatever its nature may be, that is crucial. The two can temporarily both be accepted to coexist, if both have their strengths. For example, quantum theory does not make the same predictions as classical theory when it comes to classical experiments (mechanics, basic EM phenomena) and is largely useless in that domain. It only gives probabilities of results of specified experiments of certain kinds; it does not reproduce the old predictions (like definite trajectories, Moon phases or solar eclipses), but provides new results (like resonance frequencies of atoms and molecules and their bond energies). Similar thing can happen with a new theory of gravity; it may not give the same prediction for Mercury perihelion precession, but it may be able to explain other things, like why the inverse square law, why no repulsive gravity or why the mutual gravity force between electrons is so much lower than the mutual EM force. Explanation for oddities in Mercury motion could then wait for further data and repetition of calculations. It is natural to expect of any new theory to bring new results, but demanding that it reproduces all the old ones along is too much. That happens rarely and such expectation only prevents any new ideas from being considered.

nanofortnight 11y ago

Einstein–Cartan theory is the only viable classical alternative. I am unfamiliar with modern alternatives to comment.