51–60 of 78 posts
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).
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.
I don't get this. Shouldn't the speed of gravity be instant? If it has the same speed as light, the earth would gravitate towards the location of the sun roughly eight minutes ago (like we see the sun basically where it was eight minutes ago) in stead of where it actually is, and thus not hold its orbit.
If the sun were to vanish completely, then an observer above the elliptic of the solar system would see Earth transition from an apparently curved orbit to a straight-line path approximately 8 minutes after the sun's vanishing.
Earlier quoted context omitted.
I don't get this. Shouldn't the speed of gravity be instant? If it has the same speed as light, the earth would gravitate towards the location of the sun roughly eight minutes ago (like we see the sun basically where it was eight minutes ago) in stead of where it actually is, and thus not hold its orbit.
As you're always working with a fixed temporal distance, wouldn't that basically negate any instability? There'd never be a gravitational "correction", as that 8 minute offset would never shift.
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.
I don't get this. Shouldn't the speed of gravity be instant? If it has the same speed as light, the earth would gravitate towards the location of the sun roughly eight minutes ago (like we see the sun basically where it was eight minutes ago) in stead of where it actually is, and thus not hold its orbit.
Earlier quoted context omitted.
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.
Is there nothing that will slow gravity down? Does that mean that gravity is essentially faster than light? I mean not technically, but for all practical cases it would be slightly faster?
For gravitational waves the same effect will happen, as the waves pass through matter with its own stress-energy that will absorb some of the incoming radiation and re-emit it. But gravitation interaction with matter is so much weaker that it would take a significant amount of concentrated stress-energy or order to have the same effect. Sparse matter in interstellar space is too diffuse to experience tidal effects even at the small magnitudes of gravitational waves.
Earlier quoted context omitted.
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.
Is there nothing that will slow gravity down? Does that mean that gravity is essentially faster than light? I mean not technically, but for all practical cases it would be slightly faster?
Gravity cannot travel faster than light in vacuum traveling faster than light in a medium is possible and happens all the time in nuclear reactors for example.
Since interstellar space isn’t empty light can lag slightly behind a gravitational wave but it does not affect the ultimate speed limit of the universe.
Earlier quoted context omitted.
As you're always working with a fixed temporal distance, wouldn't that basically negate any instability? There'd never be a gravitational "correction", as that 8 minute offset would never shift.
Well, real orbits are not perfectly circular (and many stable orbits are far from circular) so the distance (temporal and spatial) certainly changes.
Earlier quoted context omitted.
I don't get this. Shouldn't the speed of gravity be instant? If it has the same speed as light, the earth would gravitate towards the location of the sun roughly eight minutes ago (like we see the sun basically where it was eight minutes ago) in stead of where it actually is, and thus not hold its orbit.
Why would being 8 minutes out of date result in an unstable orbit?
Earlier quoted context omitted.
Well, real orbits are not perfectly circular (and many stable orbits are far from circular) so the distance (temporal and spatial) certainly changes.
That's true - you'd have a possible gravitational blue/red shift at different points.
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.
I don't get this. Shouldn't the speed of gravity be instant? If it has the same speed as light, the earth would gravitate towards the location of the sun roughly eight minutes ago (like we see the sun basically where it was eight minutes ago) in stead of where it actually is, and thus not hold its orbit.