[HN Gopher] Newly discovered black hole 'speed limit' hints at n...
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Newly discovered black hole 'speed limit' hints at new laws of
physics
Author : perihelions
Score : 57 points
Date : 2023-08-26 13:28 UTC (9 hours ago)
(HTM) web link (www.livescience.com)
(TXT) w3m dump (www.livescience.com)
| falcrist wrote:
| AFAIK, Gravitational waves are out first method of "seeing" the
| universe that isn't just capturing incoming photons from the
| object under observation. The only exception is neutrino
| detectors, which have hilariously bad resolution.
|
| It seems reasonable to expect new phenomena to be uncovered this
| way.
|
| This seems like a good example of that.
| borissk wrote:
| Also neutrino detectors and gravitational wave detectors allow
| to observe the very early universe. Until something like 300K
| years after the Big Bang the universe was too hot for atoms to
| form and so it was full of particles that block light. But the
| universe became clear for neutrinos a lot earlier and for
| gravitational waves even earlier (think it's milliseconds past
| the Big Bang).
| _Microft wrote:
| These methods also allow to observe the same event in different
| ways. This is known as "multi-messenger astronomy":
|
| https://en.wikipedia.org/wiki/Multi-messenger_astronomy
| lisper wrote:
| This title is seriously misleading. There are no "new laws of
| physics here", just old laws (GR) applied to new regimes (black
| hole collisions).
| borissk wrote:
| Think I read somewhere that the GR prediction on the speed of
| the colliding black holes doesn't match the observations from
| LIGO.
| bowsamic wrote:
| Very interesting. I did not imagine that there would be a
| theoretical maximum on the recoil velocity of such a collision
| below the speed of light, and I definitely didn't expect it to be
| so much smaller than the speed of light
| borissk wrote:
| I guess the maximum comes from the gravity's inability to keep
| them together, when their relative speed gets too high.
| largbae wrote:
| The article seems to claim a speed limit of 0.1c for matter...
| but isn't this already disproven by the speeds reached in our
| particle accelerators?
| gliptic wrote:
| It's not a "speed limit of 0.1c for matter". This limit would
| apply to the scenario they investigated -- colliding black
| holes where the spacetime is massively affected by the mass and
| movement of the black holes.
| borissk wrote:
| And this extreme scenario is where probably any errors in GR
| can be observed, as quantum gravitational effects will become
| visible.
| bowsamic wrote:
| No, GR is expected to work fine in this regime since there
| is no expectation of any quantum effects.
|
| A quantum theory of gravity is only needed when we expect
| there to be significant quantum effects, for example maybe
| in a neutron star and definitely in situations where our
| measurement results depend on a superposition of
| "spacetimes". The reason we don't have a consensus on a
| quantum theory of gravity yet is that gravity is so weak
| that it's usually only detectable in situations that
| involve huge amounts of matter, and it's very rare to have
| huge amounts of matter together and still have the system
| behave in a way that requires quantum mechanics to describe
| it
| changoplatanero wrote:
| It's not talking about the maximum speed of matter under any
| conditions. It's just calculating the maximum speed of a black
| hole when it merges with another one
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(page generated 2023-08-26 23:02 UTC)