Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
But what explains that difference? Based on current understandings, shouldn’t they have arrived at exactly the same time?
Gravitational waves provide dose of reality about extra dimensions
21–30 of 78 posts
Re: Gravitational waves provide dose of reality about extra dimensions
#22Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
The fact that the event was 130 million light years away makes me imagine this chaotic, turbulent network of gravitational waves just ripping through pockets of interstellar space...
I wonder how close you would need to be to "feel" the gravitational wave pass through you. Imagine being in the epicenter of a cluster of them.
Re: Gravitational waves provide dose of reality about extra dimensions
#23Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
But what explains that difference? Based on current understandings, shouldn’t they have arrived at exactly the same time?
I would suspect that the light was affected by a large well on the way. If gravitational waves behave like normal waves then a gravity well shouldn't delay them much but the light would get affected and might change course a bit... enough to delay it for 2 seconds.
Re: Gravitational waves provide dose of reality about extra dimensions
#24> The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't. Do they really mean to say "followed by detections"?…
Yes. Even if the creation events of each part of the spectrum are at the exact same time (which is unlikely) there is going to be matter in between the event and us. That matter will slow the rate of light's propagation.
Ah. Didn't think of that.
Edit: And I didn't see Animats' comment that EM radiation was delayed ~2 seconds. But also that the speed difference was very small.
Re: Gravitational waves provide dose of reality about extra dimensions
#25Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
How do we know that the 2 types of waves came 2 seconds apart? Didn't we have to hunt for the light source after the gravitational wave detection, which must have taken some time? Or were there cameras already trained on this part of the sky?
Edit: Ok, read the linked article, and the explanation is the detection of gamma radiation, which is part of the electromagnetic spectrum 1.7 seconds after the gravitational waves. Not sure which satellite sensor picked them up, but I assume gamma ray observatories are not as directional as light telescopes, since there isn't a huge background of gamma emissions.
Re: Gravitational waves provide dose of reality about extra dimensions
#26> The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't. Do they really mean to say "followed by detections"?…
My understanding is that the detection order follows the underlying phenomena: first the neutron stars fell towards each other, producing gravitational waves, and only then did the stars collide, producing electromagnetic waves.
Re: Gravitational waves provide dose of reality about extra dimensions
#27> The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't. Do they really mean to say "followed by detections"?…
This conjecture also assumes that our understanding of thermodynamics applies in any other hypothetical dimension. It's entirely possible that displacement in these dimensions corresponds to an increase in energy in the system that offsets the "lost" energy.
Anything is possible, but how would you falsify that hypothesis?
Re: Gravitational waves provide dose of reality about extra dimensions
#28Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
How do we know that the 2 types of waves came 2 seconds apart? Didn't we have to hunt for the light source after the gravitational wave detection, which must have taken some time? Or were there cameras already trained on this part of the sky? Edit: Ok, read the linked article, and the explanation is the detection of gamma radiation, which is part of the electromagnetic spectrum 1.7 seconds after the gravitational wav…
The instrument in question is the gamma ray burst monitor (GBM) on the Fermi gammay ray telescope. The GBM does provide some directional data but because it's an all-sky instrument it is fairly crude but not terrifically so, it's able to determine the direction of a signal to within several degrees.
Re: Gravitational waves provide dose of reality about extra dimensions
#29Nice. A related result from the neutron star collision is that the speed of light and the speed of gravity are the same, to within something like 1 part in 10^15. Both light and gravity waves from an event 130 million light years away came in less than 2 seconds apart.
The fact that the event was 130 million light years away makes me imagine this chaotic, turbulent network of gravitational waves just ripping through pockets of interstellar space... I wonder how close you would need to be to "feel" the gravitational wave pass through you. Imagine being in the epicenter of a cluster of them.
I think 0.1G of acceleration difference would be felt as center of inertia shifts from center of mass. Presumably while you're moving. Even more so if weightless.
If the wave is long enough or small amplitude enough you wouldn't feel it.
For something like the neutron star collision, it would be relatively far but not far enough to not get fried by EM radiation.
Re: Gravitational waves provide dose of reality about extra dimensions
#30Earlier quoted context omitted.
This conjecture also assumes that our understanding of thermodynamics applies in any other hypothetical dimension. It's entirely possible that displacement in these dimensions corresponds to an increase in energy in the system that offsets the "lost" energy.
Anything is possible, but how would you falsify that hypothesis?
Indeed. And that's my complaint about the report itself.