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>The light and the gravitational waves travel along the direct line of sight to us, curling around the gravity wells of intervening galaxies along the way. As a

>The light and the gravitational waves travel along the direct line of sight to us, curling around the gravity wells of intervening galaxies along the way. As a result, the initial burst of light and gravitational waves hid a little gem: the time difference between the arrival of the gravitational waves and the light. All 1.7 seconds of it. I'm not clear on this part. Was the light slower by 1.7 seconds because it interacted with intervening matter?

wiredfool 9y ago
There are two parts to this: * For the theories to be correct, the difference in arrival time between the gravity waves and the light waves would need to be more like 3 years. 1.7 seconds from 130 million LY is a very small difference. * The gravity waves peak as the stars are just approaching each other, the gamma pulse happens when they collide.
- mcguire 9y ago
  "These two seemingly independent metrics [for light and gravity] can explain the structures of galaxies and of collisions between galaxy clusters, but the idea has consequences. For instance, if a something should emit both gravitational waves and light, the two waves will travel by different paths depending on the masses they encounter. So, light and gravitational waves won't arrive at a distant observation point at the same time." However, "The measured delay was so much shorter than the difference predicted by double metric theories that the researchers didn't even bother performing more detailed calculations. There is, in their view, simply no way to include the intervening galaxies and exclude dark matter. This is a dead MOND theory."
0xfaded 9y ago
Disclaimer: not an expert. Photons have an anomalous magnetic moment. Not going to pretend to be qualified to explain it, but if the photons and gravitons are originating from a region with electromagnetic fields, the photons will be slightly retarded compared to the gravitons which as far as we know do not interact. https://en.m.wikipedia.org/wiki/Anomalous_magnetic_dipole_moment https://en.m.wikipedia.org/wiki/Anomalous_magnetic_dipole_mo...
- jpmattia 9y ago
  Disclaimer: Also not an expert. Photons have no magnetic moment. You know this because the propagation of light is unaffected by the presence of the strongest magnetic fields we generate here on earth (which is several tesla.) The article you're linking is not discussing the anomalous magnetic moment of the photon, but the electron. (Also muon and tau, but didactic QED texts usually focus on the electron.) You would expect the electron magnetic moment to be 2 \mu_B, where \mu_B is the Bohr magneton, if you calculated the magnetic moment purely from Dirac's Equation. However, due to coupling with particles winking in and out from vacuum fluctuations, the magnetic moment is slightly different than 2 \mu_B.
acqq 9y ago
At the moment, the researches don't believe that the light was slower, but that it took that much time for the electromagnetic "flash" to be produced, compared to some specific point in the signal observed by the gravitational waves detectors. The later signal is not a point-like but a long signal which gets stronger as the stars get closer and closer to one another and then it disappears once there are no two stars anymore. https://www.forbes.com/sites/startswithabang/2017/10/17/why-neutron-stars-not-black-holes-show-the-future-of-gravitational-wave-astronomy/ https://www.forbes.com/sites/startswithabang/2017/10/17/why-... "It's anticipated that these two speeds are exactly equal, and the delay of the light signal comes from the fact that the light-producing reactions in the neutron star take a second or two to reach the surface." A lot about this event was modeled even before this observation, and there will now be more attempts to make more precise models that better match what was measured. And the best is, these models will be evaluated by the next, planned observations.
- lutorm 9y ago
  The same process, but in a different scenario, was observed in supernova 1987a: "Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to neutrino emission, which occurs simultaneously with core collapse, but preceding the emission of visible light. Transmission of visible light is a slower process that occurs only after the shock wave reaches the stellar surface." This result set a pretty strong upper bound on the neutrino mass because it must be small enough that, across the 168,000 light year distance from the LMC to us, the neutrinos kept their lead on the photons emitted a few hours later. A neutron star is much smaller, the process is much faster, and the event happened much further away, so the constraints on the difference in speed between the gravitational waves and photons should be even more tightly constrained in this event.

wiredfool 9y ago

There are two parts to this: * For the theories to be correct, the difference in arrival time between the gravity waves and the light waves would need to be more like 3 years. 1.7 seconds from 130 million LY is a very small difference. * The gravity waves peak as the stars are just approaching each other, the gamma pulse happens when they collide.

mcguire 9y ago
"These two seemingly independent metrics [for light and gravity] can explain the structures of galaxies and of collisions between galaxy clusters, but the idea has consequences. For instance, if a something should emit both gravitational waves and light, the two waves will travel by different paths depending on the masses they encounter. So, light and gravitational waves won't arrive at a distant observation point at the same time." However, "The measured delay was so much shorter than the difference predicted by double metric theories that the researchers didn't even bother performing more detailed calculations. There is, in their view, simply no way to include the intervening galaxies and exclude dark matter. This is a dead MOND theory."

0xfaded 9y ago

Disclaimer: not an expert. Photons have an anomalous magnetic moment. Not going to pretend to be qualified to explain it, but if the photons and gravitons are originating from a region with electromagnetic fields, the photons will be slightly retarded compared to the gravitons which as far as we know do not interact. https://en.m.wikipedia.org/wiki/Anomalous_magnetic_dipole_moment https://en.m.wikipedia.org/wiki/Anomalous_magnetic_dipole_mo...

jpmattia 9y ago
Disclaimer: Also not an expert. Photons have no magnetic moment. You know this because the propagation of light is unaffected by the presence of the strongest magnetic fields we generate here on earth (which is several tesla.) The article you're linking is not discussing the anomalous magnetic moment of the photon, but the electron. (Also muon and tau, but didactic QED texts usually focus on the electron.) You would expect the electron magnetic moment to be 2 \mu_B, where \mu_B is the Bohr magneton, if you calculated the magnetic moment purely from Dirac's Equation. However, due to coupling with particles winking in and out from vacuum fluctuations, the magnetic moment is slightly different than 2 \mu_B.

acqq 9y ago

At the moment, the researches don't believe that the light was slower, but that it took that much time for the electromagnetic "flash" to be produced, compared to some specific point in the signal observed by the gravitational waves detectors. The later signal is not a point-like but a long signal which gets stronger as the stars get closer and closer to one another and then it disappears once there are no two stars anymore. https://www.forbes.com/sites/startswithabang/2017/10/17/why-neutron-stars-not-black-holes-show-the-future-of-gravitational-wave-astronomy/ https://www.forbes.com/sites/startswithabang/2017/10/17/why-... "It's anticipated that these two speeds are exactly equal, and the delay of the light signal comes from the fact that the light-producing reactions in the neutron star take a second or two to reach the surface." A lot about this event was modeled even before this observation, and there will now be more attempts to make more precise models that better match what was measured. And the best is, these models will be evaluated by the next, planned observations.

lutorm 9y ago
The same process, but in a different scenario, was observed in supernova 1987a: "Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to neutrino emission, which occurs simultaneously with core collapse, but preceding the emission of visible light. Transmission of visible light is a slower process that occurs only after the shock wave reaches the stellar surface." This result set a pretty strong upper bound on the neutrino mass because it must be small enough that, across the 168,000 light year distance from the LMC to us, the neutrinos kept their lead on the photons emitted a few hours later. A neutron star is much smaller, the process is much faster, and the event happened much further away, so the constraints on the difference in speed between the gravitational waves and photons should be even more tightly constrained in this event.