3 ms·

Can someone offer some insight as to what gravitational wave physicists hope to find that would be in the realm of "new physics"? So far the most radical thing

Can someone offer some insight as to what gravitational wave physicists hope to find that would be in the realm of "new physics"? So far the most radical thing about this catalogue of BHMs seems to be another orthogonal measurement axis for the universe -- but otherwise seems to be aimed at confirming existing models, right?

NikolaeVarius 6y ago
I mean confirming stellar mass black hole merge events was "new physics" only 5 or so years ago. Finding larger and more massive supermassive black hole mergers is still disputed if they even exist or not. Black holes are still mostly math on a computer and indirect observations of its properties. The actual singularity physics still /shrug not an expert, but try and keep up with space and astronomy science articles
- raattgift 6y ago
  > only 5 years ago You are conflating new physics with new experiments testing the limits of established physics. New physics is the requirement for explanations of observations which cannot accord with or be derived from existing fundamental theory. In the case of merger chirps detected at LIGO, Virgo, and other detectors, that's General Relativity. New physics would be chirps that [a] are traceable to a compact-object merger event through other observations (direct emissions of various types of radiation, and their echoes) but [b] have a chirp waveform that contradicts "balding" (deformations of the event horizons raised by each pair-member on the other should disappear in on the order of horizon light-crossing time) or flavours of equivalence principle (e.g., the universality of free fall shapes the chirp). Nobody working in high energy astrophysics seriously doubts the existence of astrophysical black holes, nor that they are extremely well-modelled by small perturbations of a handful of simple metrics (General Relativity being a metric theory of gravitation). There are plenty of arguments about the details of the perturbations and about whether General Relativity itself can be derived from some more fundamental theory, but those arguments are confronted with quite a bit of observational data that completely support General Relativity and offer no support for practically any proposal which reduces to (or produces) General Relativity in the centres of active galaxies. Furthermore, there is plenty of evidence for the mergers of galaxies, and nothing (in General Relativity) forbidding the merger of such galaxies' central black holes. Nobody should seriously dispute the merger of supermassive black holes, even if the "final parsec" mechanisms that allow for quicker mergers (i.e., billions of years -- less than the age of the universe, in particular -- rather than trillions of years) are not yet strongly understood. > The actual singularity physics are unobserved. Searches for primordial BH evaporation remnants and naked singularities will continue -- you automatically get the latter searches in chirp analysis and multimessenger matching -- and you'd have evidence for new physics if there is any evidence for such things, because they are not allowed by General Relativity. Astrophysically, black holes are characterized by the properties of their event horizons, not the properties of their singularities (even theoretically it's the exterior metric that counts; nobody, especially not Kerr himself, thinks the interior BH metric is generally a good physical description). As long as it stays enshrouded by a horizon (thus protecting the exterior metric tensor and some energy conditions), the matter that has fallen in can be in any sort of arrangement inside the horizon, including but far from limited to a classical singularity. Post Ken Wilson (renormalization and effective field theory), we should be agnostic about such things. > indirect observations of [black hole] properties The chirp mass is a physical property of the black hole pair that is directly measured by gravitational wave detectors, comparable to how the reduced mass is a directly measurable attribute of pairs of non-relativistic celestial objects (and cf. linearized gravity). Chirp masses are verifiable by studying the orbits of stars and molecular clouds around or past the merging pair.
  - raattgift 6y ago
    > and offer no support for practically any proposal which reduces to (or produces) General Relativity in the centres of active galaxies Too late to edit, but this should be "and offers no support ... which fails to reduce to (or produce) General Relativity ...", in case that wasn't clear from context. General Relativity (perhaps frustratingly) continues to survive all confrontations with evidence.
marcosdumay 6y ago
"Confirming existing models" and "searching for new physics" are the same activity. You don't know what will be confirmed beforehand. Trying the existing models predictions with a completely new measurement apparatus is the most promising way to look for new physics.
imglorp 6y ago
Max Tegmark made a nice comment on the Lex Fridman podcast recently. This advancement tells us things about the messenger (gravitational waves) as well as the message (big objects interacting). So it's a twofer, at least.

NikolaeVarius 6y ago

I mean confirming stellar mass black hole merge events was "new physics" only 5 or so years ago. Finding larger and more massive supermassive black hole mergers is still disputed if they even exist or not. Black holes are still mostly math on a computer and indirect observations of its properties. The actual singularity physics still /shrug not an expert, but try and keep up with space and astronomy science articles

raattgift 6y ago
> only 5 years ago You are conflating new physics with new experiments testing the limits of established physics. New physics is the requirement for explanations of observations which cannot accord with or be derived from existing fundamental theory. In the case of merger chirps detected at LIGO, Virgo, and other detectors, that's General Relativity. New physics would be chirps that [a] are traceable to a compact-object merger event through other observations (direct emissions of various types of radiation, and their echoes) but [b] have a chirp waveform that contradicts "balding" (deformations of the event horizons raised by each pair-member on the other should disappear in on the order of horizon light-crossing time) or flavours of equivalence principle (e.g., the universality of free fall shapes the chirp). Nobody working in high energy astrophysics seriously doubts the existence of astrophysical black holes, nor that they are extremely well-modelled by small perturbations of a handful of simple metrics (General Relativity being a metric theory of gravitation). There are plenty of arguments about the details of the perturbations and about whether General Relativity itself can be derived from some more fundamental theory, but those arguments are confronted with quite a bit of observational data that completely support General Relativity and offer no support for practically any proposal which reduces to (or produces) General Relativity in the centres of active galaxies. Furthermore, there is plenty of evidence for the mergers of galaxies, and nothing (in General Relativity) forbidding the merger of such galaxies' central black holes. Nobody should seriously dispute the merger of supermassive black holes, even if the "final parsec" mechanisms that allow for quicker mergers (i.e., billions of years -- less than the age of the universe, in particular -- rather than trillions of years) are not yet strongly understood. > The actual singularity physics are unobserved. Searches for primordial BH evaporation remnants and naked singularities will continue -- you automatically get the latter searches in chirp analysis and multimessenger matching -- and you'd have evidence for new physics if there is any evidence for such things, because they are not allowed by General Relativity. Astrophysically, black holes are characterized by the properties of their event horizons, not the properties of their singularities (even theoretically it's the exterior metric that counts; nobody, especially not Kerr himself, thinks the interior BH metric is generally a good physical description). As long as it stays enshrouded by a horizon (thus protecting the exterior metric tensor and some energy conditions), the matter that has fallen in can be in any sort of arrangement inside the horizon, including but far from limited to a classical singularity. Post Ken Wilson (renormalization and effective field theory), we should be agnostic about such things. > indirect observations of [black hole] properties The chirp mass is a physical property of the black hole pair that is directly measured by gravitational wave detectors, comparable to how the reduced mass is a directly measurable attribute of pairs of non-relativistic celestial objects (and cf. linearized gravity). Chirp masses are verifiable by studying the orbits of stars and molecular clouds around or past the merging pair.
- raattgift 6y ago
  > and offer no support for practically any proposal which reduces to (or produces) General Relativity in the centres of active galaxies Too late to edit, but this should be "and offers no support ... which fails to reduce to (or produce) General Relativity ...", in case that wasn't clear from context. General Relativity (perhaps frustratingly) continues to survive all confrontations with evidence.

marcosdumay 6y ago

"Confirming existing models" and "searching for new physics" are the same activity. You don't know what will be confirmed beforehand. Trying the existing models predictions with a completely new measurement apparatus is the most promising way to look for new physics.

imglorp 6y ago

Max Tegmark made a nice comment on the Lex Fridman podcast recently. This advancement tells us things about the messenger (gravitational waves) as well as the message (big objects interacting). So it's a twofer, at least.