Are blackholes and singularities synonymous?
Are blackholes only one type of singularity or are they the only type? I assume singularities assume a region of infinite density? Would the hypothetical whitehole be the opposite of a singularity?
Comments (11)
It's a common view in physics that a theory of quantum gravity would explain how a singularity is avoided.
Singularity is a cool word mathematicians uncharacteristically coined and people like saying it.
In the case of "the singularity" of AI, the analogy doesn't even make any sense.
In terms of physics, what we can say is that if anything is actually infinite in some characteristic, we cannot measure that as no machine can count to infinity, so there would be no way to verify if a black hole has a point of infinite density even if it was there.
Electrons could have infinite density when measured at a "point" for example; indeed, it's often assumed all the mass of a particle is at a point, so it wouldn't break anything if that were actually true. Whole universe could be infinite in expanse. But no tool can measure infinity so any infinite quantity cannot be verified even if it exists.
Long story short, there are no singularities in "science", as understood as verifiable facts, but they only appear in mathematical models of some situation, generally understood as representing a problem with the theory, not a prediction.
Singularities are categorized in complex analysis. Some are quite tame and easily"fixed", others can be bizarre to the point of reaching beyond one's imagination. Victor Toth addressed this issue on Quorum recently.
:100:
Isn't there a workaround for that?
10 Print "Take that [math]\infty[/math]!"
20 Goto 10
Interesting point. To count to infinity would require an infinity of time. Is time infinite? According to the conventional wisdom, time had a beginning; but we cannot currently be sure that it will have an end. Nothing in science currently excludes the possibility of infinite time.
A singularity is a region where spacetime curvature becomes infinite.
So black holes and singularities are not synonymous. But all black holes contain a singularity according to General relativity.
"Escape" is a tendentious word to use, because it encourages a sort of Newtonian picture of light struggling upwards for some distance and finally succumbing to the force of gravity, as a rifle bullet would on Earth.
But this is a misleading picture. Light naturally travels in a straight line but, because it has mass, it will follow the contours of a gravitational field. In the neighbourhood of a singularity, gravity curves so tightly back on itself that it creates a hard discontinuity in space/time (like the boundary of a blob of oil floating on water) which we call the event horizon. Light which is inside the event horizon continues to travel in a "straight" line, but following the contours of the gravitational field. So the space/time discontinuity prevents us from seeing it.
The natural tendency of a railway locomotive is to travel in a straight line; but, where the tracks are laid, that's where it will go!
Light does not have mass, it has momentum but that doesn't matter either.
It's more correct to say light travels in geodesics in curved space. A geodesic is a straight-line in flat Euclidian space and in (smooth) curved space will appear straight over any sufficiently small distance, but over larger distances may appear curved (such as gravitational lensing).
Quoting alan1000
This is correct and is already built into the theory of black holes.
A collapsing star would, in any case, collapse to a density just enough to become a blackhole on its way to infinite density, and if that actually happens we cannot observe both because it's a blackhole and also we have no devices that count to infinity. That we cannot measure infinity anyways is the more general problem for all conjectures of real infinities in any context (size of the universe, electron density, whether space / fields are continuous in some aspects and so on).
Beyond the event horizon there can easily be a force that stops further collapse.
For example, neutron stars are pretty close to the threshold of becoming a blackhole.
We can easily imagine the universe being such that neutron stars were a bit more dense and became blackholes, and so in this thought experiment, even if we came up with the idea of a neutron star, we could never verify they do actually exist as they'd all be hidden by event horizons.
So if there was some force after a neutron star collapses that kicks in later and prevents further collapse, but was dense enough to be a blackhole, then we'd be in the same situation of having no idea about these forms of matter that prevent further collapse.
And this is not all that counter intuitive, no more strange than why a planet doesn't collapse into a blackhole, the only difference being that we can't see what forces may be at play preventing further collapse in a blackhole.
Also of note, if you want to create a particle accelerator large enough to "really find out", you just end up creating blackholes in your collisions and still can't see what's going on.
This. Also, let's dispel the notion that black holes are "holes," they are clumps of degenerate matter that have overcome degenerate pressures. Once realized this way, it becomes easier to see why there isn't an actual, physical "singularity."