What is going on with titles? Do physicists really put on boxing gloves hoping that physical violence will resolve a scientific argument? Is this a new widely accepted approach? I find this level of editorializing ridiculous to the point of insulting. I don’t need the imagery of violence to boost my curiosity about a new discovery.
Dark energy from supermassive black holes? Physicists spar over radical idea
81–90 of 116 posts
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#82I'm a layman, but I like this idea intuitively. It's not mentioned in the article, but this theory also necessitates that black holes aren't singularities, which gets rid of what always seemed to me like the biggest hack in physics.
I've always wondered if the "horizon" metaphor in event horizon was more apt than we expected - just like when you approach the earth's horizon, you don't get flattened or fall off, you just reveal more geography - I've always wondered if it were possible that as you approach an event horizon you don't get "squashed into spaghetti" but just reveal more space which is just as "normal" as the space before you approache…
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#83Earlier quoted context omitted.
To an outside observer it would look like you were torn apart by tidal forces, but would it feel that way to you? Or would you feel normal? If it's just space being curved, would you feel nothing just like you feel nothing in freefall? I'm sure this question is wrong...
The "tidal effect" here is due the difference in gravity experienced by parts of you at different distances from the gravity source. Imagine your feet pulled downward hard enough that your bones stretch and/or snap, while you are squished in from the sides. And then more. You'd become a long thin strand of matter, no longer in the shape of a human and no longer feeling anything. It's not "just a ride down" where thin…
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#84>Dark energy is known to make up 70% of the mass-energy of the universe, whereas black holes are a mere fraction of the ordinary matter, which constitutes less than 5% of the universe. Is there some cosmological constraint that says dark energy compressed into a small volume would exhibit gravitational pull and therefore contribute to our measurements of black hole masses? If not then it feels like this is a weak cou…
Well the whole idea is to "make it work" under the constrains of our current understanding (General Relativity). After all , all that Dark Energy is by definition is something that is Contrasting the Gravity as described by general Relativity. If we remove that fact than it doesn't need to be reconciled with anything really. Saying that it is a type of energy that doesn't behave according to general Relativity, you n…
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#85Earlier quoted context omitted.
To an outside observer it would look like you were torn apart by tidal forces, but would it feel that way to you? Or would you feel normal? If it's just space being curved, would you feel nothing just like you feel nothing in freefall? I'm sure this question is wrong...
The "tidal effect" here is due the difference in gravity experienced by parts of you at different distances from the gravity source. Imagine your feet pulled downward hard enough that your bones stretch and/or snap, while you are squished in from the sides. And then more. You'd become a long thin strand of matter, no longer in the shape of a human and no longer feeling anything. It's not "just a ride down" where thin…
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#86Earlier quoted context omitted.
> Outside a black hole there's vacuum, inside a black hole there is… Well, we don't really know but the mass from which it formed has gotta be somewhere, right? Not in the standard black hole model with a singularity at the center, no. In the standard black hole model, the collapsing matter that formed the hole hits the singularity and is destroyed. The interior of the hole is vacuum, just like the exterior. In the a…
> In the standard black hole model, the collapsing matter that formed the hole hits the singularity and is destroyed Sure, but that's a model for which we don't have any observational evidence whatsoever since it's the black hole's interior. That's why I phrased it that way. It doesn't matter, though, even if you say the matter inside the black hole no longer exists (and I'm very happy to entertain that thought): Any…
While this is true, it's not a very strong statement. Physicists extend models all the time into domains where we can't directly test them. The singularity theorems of GR guarantee that the key features of that model, the singularity and the collapsing matter getting destroyed in it, must be true as long as the collapsing matter has the equation of state of ordinary matter. That's why the phase transition I mentioned, to an equation of state corresponding to dark energy, is necessary to avoid forming the singularity and leaving only vacuum in the interior--because the dark energy equation of state violates the energy conditions that are premises of the singularity theorems.
> Any sensible definition of mass of the vacuum black hole (i.e. not necessarily the ADM mass since it's defined at infinity but e.g. some definition of quasi-local mass) will still give a non-zero contribution to the mass density.
Sure, but this "mass" is not due to the continuing presence of matter somewhere inside the hole. It's a property of the spacetime geometry.
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#87Earlier quoted context omitted.
> Outside a black hole there's vacuum, inside a black hole there is… Well, we don't really know but the mass from which it formed has gotta be somewhere, right? Not in the standard black hole model with a singularity at the center, no. In the standard black hole model, the collapsing matter that formed the hole hits the singularity and is destroyed. The interior of the hole is vacuum, just like the exterior. In the a…
> Not in the standard black hole model with a singularity at the center, no. In the standard black hole model, the collapsing matter that formed the hole hits the singularity and is destroyed. The interior of the hole is vacuum, just like the exterior. If the interior of a black hole becomes a vaccume, what continues to assert the intense gravitational pull that the now destroyed matter once created?
The spacetime geometry of the hole. The "pull" you describe is a property of the spacetime geometry. Gravity is not a force in GR, so the "pull" is not being caused by an interaction with matter. Objects moving solely under gravity simply move on geodesics of the spacetime geometry.
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#88Earlier quoted context omitted.
> could it be that supermassive black holes cause a contraction of local spacetime in a way that gives the impression that local space is static while distant space expands? No. That's not how the spacetime geometry around black holes works.
Would you care to elaborate on that statement?
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#89Earlier quoted context omitted.
The "squashed into spaghetti" occurs in "normal space" before you get to the black hole, for most black holes. It is not an effect of anything special about black holes, it's just plain ol' normal tidal effects, turned up to eleven, then turned up until the knob breaks, then turned up some more. Neutron stars will give you a bad day with tidal effects too long before you reach their surface. Very large black holes tu…
To an outside observer it would look like you were torn apart by tidal forces, but would it feel that way to you? Or would you feel normal? If it's just space being curved, would you feel nothing just like you feel nothing in freefall? I'm sure this question is wrong...
Being able to witness varying accelerations would actually be a very strange theory, having instead a twin paradox in which one astronaut takes off and comes back home to a twin (and civilization) crushed to death, whereas the stay-at-home twin sees his twin take off, get crushed to death, and never return home at all. The YouTube videos trying to explain this universe would certainly be epic.
Again, this all happens in normal space too; the black-hole-ness of the black hole is not in play yet. Non-black hole objects can "spaghettify" too.
Re: Dark energy from supermassive black holes? Physicists spar over radical idea
#90I'm a layman, but I like this idea intuitively. It's not mentioned in the article, but this theory also necessitates that black holes aren't singularities, which gets rid of what always seemed to me like the biggest hack in physics.
I've always wondered if the "horizon" metaphor in event horizon was more apt than we expected - just like when you approach the earth's horizon, you don't get flattened or fall off, you just reveal more geography - I've always wondered if it were possible that as you approach an event horizon you don't get "squashed into spaghetti" but just reveal more space which is just as "normal" as the space before you approache…
Why this matters is that when something spaghettifies, the particles at the end can never catch up to the ones at the beginning. The space between the ends of the spaghetti grows. Which also means that the spaghetti can never reach the pit at the center of the black hole, because the pit is farther ahead in its journey.
So our intuition that falling into a black holes means that we'll collide with the center is incorrect. If we could survive the journey, we'd see ourselves falling forever towards something growing infinitely farther away. Like trying to catch up with a falling elevator that's moving faster than we are.
From the outside, we see anything falling in as becoming 2D on the surface, red shifting as it accelerates away from us, becoming time dilated until it appears to freeze, never quite reaching the speed of light from our frame of reference. So even though it's being stretched along the radial axis and perspective should make it look smaller over time as our separation grows, it appears to stay the same size to us as it was when it entered the event horizon.
So a black hole can be thought of as an infinitely long tunnel to.. somewhere.
I prefer to think of it as a bubble which only grows internally. So in a very real sense, a whole universe is being birthed inside.
Unfortunately the math breaks down near the singularity, so maybe the particles do see themselves colliding with a pit. For example, the sun is 8 light minutes from Earth, so even if it was heavy enough to collapse into a black hole, it should still take 8 minutes to reach the center for a particle falling towards it, from its frame of reference.
But I don't think that's how it works. I think that the space flowing in faster than the speed of light overcomes spaghettification, creating a maximum strain inversely proportional to the mass of the black hole. Hawking hinted at this when he thought about what would happen to a human falling into a billion solar mass black hole whose tidal forces are weak enough that they're survivable.
-- edit: this paragraph is wrong, the universe behind also red shifts, which I realized after considering that the object's watch and ours are synchronized during free-fall --
Probably what happens is that the object sees the universe behind it speed up faster and faster as it blue shifts, until it ends in a white-hot flash the number of light-seconds away that the object began falling. Meanwhile the space ahead appears to expand in the same way as inflation, creating a pocket universe containing the mass which has already fallen in. Except that the universe behind appears to also red shift, due to the increasing distance between the object and anything behind. The expansion and contraction probably balance to create a microwave background at a temperature inversely proportional to the age of the universe inside. So the background inside might be hotter than ours since the black hole is smaller than the parent universe.
----
Also if nothing more falls into the black hole and it starts evaporating, matter inside will see previously fallen matter growing away from it. Just like how we see stars and galaxies moving away from us faster than the speed of light when their distance times the Hubble constant exceeds the speed of light, causing our universe to grow lighter and expand faster, which we perceive as dark energy. So matter inside would eventually see the perimeter rushing towards it faster and faster as the black hole loses its mass, with its internal Hubble constant growing larger and larger until the expansion of space rips the matter apart as energy, back into the parent universe as its mass falls beneath a few solar masses.
Which has implications for our universe, where instead of heat death, we re-experience spaghettification as the rate of the expansion of the universe keeps increasing until we explode. Or maybe the expansion only applies outside of our gravitationally-bound galaxy. So eventually the universe would only be our galaxy. But, I tend to think that evaporation still occurs, so even our galaxy would eventually be torn apart. But it would probably have already gone down the drain into the Milky Way's supermassive black hole, Sagittarius A*. In other words, the falling probably never ends. Which implies that maybe the universe is infinite, although we can never reach the parts moving away from us faster than the speed of light.
Until we invent warp drive or meet aliens or something. Just so everyone knows, I completely made all of this up, starting from first principles after watching a lot of PBS Space Time and How the Universe Works. But that's ok since astrophysicists don't have a reference to point to that disputes my unfounded claims yet:
https://jila.colorado.edu/~ajsh/insidebh/schw.html
Also, my description doesn't consider the quantum aspect of spaghettification, or how particles might behave inside gravitational barriers:
https://en.wikipedia.org/wiki/Particle_in_a_box
https://en.wikipedia.org/wiki/Quantum_tunnelling
I haven't found a clear summary yet for how the wave function behaves in a gravity gradient or under extreme time dilation, or when space is moving near or faster than the speed of light.
Shoot, I just realized something after writing this out. Two particles in free-fall without external forces should have synchronized watches. The object falling into the black hole may not actually lose synchronization with us. Does anyone know if that's correct?
https://en.wikipedia.org/wiki/Synchronous_frame
https://www.physicsforums.com/threads/question-regarding-tim...
If the clocks stay synchronized until the lead object reaches the pit, what happens if the pit is never reached?