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Gravitational waves provide dose of reality about extra dimensions

phys.org

11–20 of 78 posts

Re: Gravitational waves provide dose of reality about extra dimensions

#11
post #9

Earlier quoted context omitted.

Makes sense. That’s what I would have thought if not for the area of a sphere in three dimensions remark.

Area = surface area not volume. Physicists tend to drop constant factors when they do calculations, I’ve noticed.

A sphere has surface area and volume. I didn’t claim or imply that I thought area meant volume. It does not have area and the formula for the surface area of a sphere is not pi r^2. I mentioned this in my original post. Then there is the remark that whatshisface made: A = pi r^2, the area of a sphere in three dimensions. That is wrong and most likely a mistake.

When talking about dropping a constant factor are you referring to the 1/r^2 part or dropping a 4 in the statement A=pi r^2. Because if the latter then why keep pi? That’s a constant.

Re: Gravitational waves provide dose of reality about extra dimensions

#13
post #12

the title of the article implies that there is new evidence for the existence of multiple dimensions, while the content of the article is about the opposite being the case

Hard to see how. "Dose of reality" usually means evidence to the contrary. Even if there was some ambiguity, the first line of the article as well as the caption of the opening image make it clear.

Re: Gravitational waves provide dose of reality about extra dimensions

#14

Are there particular theories of quantum mechanics or string theory that are now any less likely? Or is this just confirming what everyone expected all along?

It's yet another limit on the general idea of large extra dimensions:

https://en.wikipedia.org/wiki/Large_extra_dimension

It doesn't say anything about compact extra dimensions (the tiny curled up ones you usually hear about in string theory).

Re: Gravitational waves provide dose of reality about extra dimensions

#15
> 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"? Don't gravitational waves propagate at c? Also, I'm puzzled by "weaker than expected". One issue is calculating expected intensities for gravitational waves vs electromagnetic radiation. The other is calibration of LIGO signals. It's not obvious that resulting uncertainties are small enough for drawing reliable conclusions about gravity leakage.

Re: Gravitational waves provide dose of reality about extra dimensions

#16
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.

Re: Gravitational waves provide dose of reality about extra dimensions

#17
post #16

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?

Re: Gravitational waves provide dose of reality about extra dimensions

#18
post #15

> 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.

Re: Gravitational waves provide dose of reality about extra dimensions

#19
post #16

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?

Lightspeed is that number in a vacuum. Interstellar space is not a perfect vacuum. There will have been some matter to slightly slow the photons.

Re: Gravitational waves provide dose of reality about extra dimensions

#20
post #15

> 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.

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