Here's the one that has bugged me since I first learned of Hawking radiation as an undergrad: if it is true (it's still unobserved but let's go with it), that means that merely passing through the event horizon allows for violation of the conservation of baryon number.
I generally regard most of the "Star Trek physics" ideas like FTL with the hairy eyeball, but this one really gets me. Being able to violate the conservation of baryon number (and lepton number, for that matter) would point to -- in some scenarios -- mass-energy conversion being a lot more available than the laborious processes of fission, fusion, and particle/antiparticle mutual annihilation.
This PBS SpaceTime video doesn’t talk about the practical uses of Kugelblitzes, but it isn’t a big leap from understanding what they are to how to get energy out of them. Hawking radiation rate increases as schwarzschild radius decreases. If you could make a properly sized black hole you could convert a little bit of mass into a lot of energy. Maybe this could be harnessed to solve all electricity demand issues. Maybe it could be used to make a room sized bomb that blows up Earth. Vote now on your phones.
I didn't say it was unbelievable, it's just ... very interesting, compared to all of the other space opera business. It implies that passing through this empty surface, this topological construct which itself need not have particles nearby (depending on how close you feel the singularity is to "nearby") makes this (and other typically conserved numbers) no longer all that important ... but only from the vantage point of an outside observer.
In other words, relativity is intertwined with this conservation, as it is observer dependent.
I agree. It’s definitely very cool. It really highlights the mass energy equivalence. I’m not at a level of full intuition of relativity, but it’s one of those things that made a lot more sense once I understood mass energy equivalence.
Like where the energy in exothermic fusion comes from: When the strong nuclear force overcomes the electrostatic force, the strong nuclear force increases the kinetic energy (momentum/speed) of the particles. At this point the mass of all particles from their own frames of reference is the same. Once the kinetic energy is lowered (particles are slowed back down to the same speed/temperature of their surroundings) does the mass lower.
Surely the conservation of baryon numbers is just a rule for reactions. I don’t see how crossing the event horizon changes anything. Remember from the POV of the baryon, it never crosses the event horizon. It’s not really ‘destroyed’, it just becomes unobservable to the external universe.
Remember from the POV of the baryon, it never crosses the event horizon. It’s not really ‘destroyed’, it just becomes unobservable to the external universe.
I think this is backwards - for an outside observer nothing ever crosses the event horizon, from the point of view of anything falling towards the event horizon it takes a finite amount of time to cross the event horizon.
How does this interact with the Hawking radiation? ie I throw something into the black hole, how much time do I wait before the Hawking radiation from that matter to manifest itself?
From your point of view - assuming you do not fall into the black hole yourself - nothing you throw into the black hole ever crosses the event horizon so you will have wait forever. You can only see something cross the event horizon if you cross the event horizon yourself and you will see everything cross the event horizon at the moment you cross the event horizon.
My friend is kind of confused. Why wouldn't an observer outside of the event horizon see things falling into it? He says you can glean information from a thing that's outside of the horizon, but a thing falling into it should cease to be observable, at least by his understanding of black holes. My galaxy-sized brain understands this, of course, but my friend's pea-brain doesn't.
An observer outside the event horizon has to accelerate to avoid falling into the black hole itself and in the resulting frame of reference of this observer the horizon of the black hole coincides with future infinity and therefore everything falling into the black hole only reaches the event horizon infinitely far into the future. You can watch Leonard Suskind's lecture on that [1], falling into a black hole starts at about 53 minutes, but depending on your background you may want to start earlier, maybe even several lectures earlier. Looking at those Penrose diagrams is probably the easiest way to see what happens even if it will probably still not make intuitive sense.
True, but from the point of view of an observer at infinity, the baryon falls and comes to a halt, while the event horizon of the black hole expands and encompasses it (or would, if you could measure the diameter of the black hole with sufficient precision).
This is just the essence of the information paradox, expressed in terms of baryon and lepton numbers. Either the Hawking radiation that comes out is ‘correlated’ with the matter that fell in (meaning that black holes have hair) and information is preserved, or they’re not, and information is destroyed. That’s literally the crux of the matter.
That’s a good point, I wasn’t thinking about it in terms of the information paradox, but then the recently proposed solutions look like they have a good chance of panning out.
But anyway I still don’t think this is really an issue regardless. The same could be said of the cosmic event horizon. Vast swathes of the universe are unobservable and causally disconnected from us due to the expansion of the universe separating us at faster than the speed of light. Again, no Baryons are being destroyed in this process, they’re just becoming unobservable _to_us_.
As I see it, there’s a vast cognitive chasm between the cosmic event horizon and the event horizon of a black hole, as the former preserves “continuity of locality” (my term) whereas the latter does not. Basically the the former is only an event horizon for us who are very distant from it, whereas the black hole’s horizon is an abrupt threshold in space. I don’t think it’s healthy to confuse the two.
The locality is all equally continuous in all these cases.
Someone near the black-hole horizon will see nothing unusual, and will not experience a horizon unless they are accelerating like mad to stay there. But someone doing that in flat space will see a horizon too -- see the Rindler coördinatization[1] of Minkowski space. It even has an analogous Rindler horizon, which seems to emit particles from the Unruh Effect[2]. I say seems to because particle number isn't invariant under acceleration. An outside observer will see a particle detector go off, but will interpret the accelerated detector as causing the particles, rather than the horizon.
"Just a rule for reactions" drives quite a lot of physics. Conservation rules are how to describe all of the things that do not happen: why a hammer doesn't vanish, why all of your electrons do not turn into positrons, and so forth.
That's what is so fascinating ... you have this odd topological boundary and it creates a violation in known rules.
You don't need Hawking radiation for mass-energy conversion; simply dropping matter into a Kerr black hole gives up to 42% efficiency, and is far more controllable.
As a true amateur,I don't understand the basic premise of this extremal black hole mystery.
In my simple view, if a charged black whole is extremal and cannot shrink then... the solution simply is that it must grow again. It absorbs particles of the opposite charge until it becomes neutral enough to shrink again and the process repeat until it completely evaporate.
That seems both a simple and straightforward theory.
(Then my other misunderstanding is how a black whole would become so charged when the universe is seemingly so neutral. The law of big number ensures that a black hole would be mostly neutral and the extremal case would only happen for very small ones on the brink of evaporation.)
> In that case, the universe of the far future will be littered with tiny, indestructible black hole remnants — the remains of any black holes that carry even a touch of charge
I don't get that. Wouldn't the charge be neutralized by consuming particles with an opposite charge (which are attracted gravitationally and electrically)? Or even by merging two extremal black holes with opposite charge?
I remember reading somewhere that charged black holes would quickly lose their charge by radiating charged particles rather than, I guess, purely neutral photons. I've been taking that for granted for a while now, but don't remember exactly where I read it. Does anyone know where that hypothesis comes from and how it relates to the work in article?
I think the prevailing notion is another, namely that an electrically charged black hole would quickly neutralise by preferentially attracting particles of opposite charge.
In particular, if a charged black hole creates Hawking pairs, the oppositely-charged particle is more likely to be captured than the same-charge particle.
>"Plumbing black holes for knowledge of quantum gravity originated with Stephen Hawking. In 1974, the British physicist calculated that quantum jitter at the surfaces of black holes cause them to evaporate, slowly shrinking as they radiate heat."
If heat is related to a black hole shrinking, and a black hole shrinking is related to information, then perhaps heat is related to information, and vice-versa.
[...]
>"In that case, the universe of the far future will be littered with tiny, indestructible black hole remnants — the remains of any black holes that carry even a touch of charge..."
You mean like an atom? Perhaps atoms (and other particles, in fact, all other particles) are really just black holes! Perhaps curved space is a better way to look at it... perhaps all black holes (and all particles) are really just curved space... in fact, perhaps all waves are curved space too...
Which would mean that everything in the universe, all of its particles, all of its waves, all of its contents, including the universe itself... is basically curved space... in one form or another...
[...]
>"In a paper published in March in Physical Review Letters, [Garrett] Goon and Riccardo Penco broadened the lessons of the earlier work by proving a simple, universal formula relating energy and entropy. The newfound formula applies to a system such as a gas as well as a black hole."
If gases (particulate matter spread thinly in a thinner medium, i.e., space) can be related to black holes, then black holes can be related to the particles in the gases, which lends additional credence to the idea that all atoms are black holes, although, this being said, it's not a hard proof...
[...]
>"When they combine Einstein’s gravity equations and the equations of electromagnetism, they calculate that a black hole’s charge, Q, can never surpass its mass, M, when both are converted into the same fundamental units. Together, the black hole’s mass and charge determine its size — the radius of the event horizon. Meanwhile, the black hole’s charge also creates a second, “inner” horizon, hidden behind the event horizon."
Super weird idea here... if we thought about a black hole of whatever size holographically, as information, then what would be true if the inner, hidden part of the black hole actually contained a miniature replica, a miniature mirror-image -- of ALL of the information inside this universe, a universe-inside-of-a-universe? That's highly speculative of course, but I think it's an idea worth exploring...
[...]
">When a black hole hits this point, a simple option for further decay would be to split into two smaller black holes."
You mean like + and - on a battery terminal?
Let me go for "full crackpot theorist" <g>...
What if charge, as we know it, in electricity, is implemented by various clusters of small black holes, regions of curved space, that we have (up until this point in time) been calling by such names as "charge", "electron", "electricity", "potential", "potential difference", etc.
When, what you've got might be multiple black holes, split into pairs, where one is a complex conjugate, a mirror image of the other, and they basically want to unify and annihilate, producing various wavelengths (heat/information) in the process?
All physics should be solvable once the correct identities are established between apparently dissimilar phenomena...
> if the inner, hidden part of the black hole actually contained a miniature replica, a miniature mirror-image -- of ALL of the information inside this universe
My line of thought has been similar: If all mass/energy curves space time, then by extension all particles curve space time in proportion to their mass. You can't have only planets and stars curving the fabric of spacetime, it has to be the individual particles that make them up, because duh: if you split a planet in two, each half will keep half the mass and hence half the curvature.[1] You can repeat this all the way down to atoms, nucleons, and electrons. Probably photons, quarks, and neutrinos too.
But that's not how anything works in field theory, QED, etc... they just assume that there's a locally flat background with some "stuff on top" that doesn't distort the background at all. Like a function above the number line.
The key insight is that whatever makes particle curve spacetime must be some inherent, fundamental aspect of their nature. Not an extra "m" attribute that can be anything. That's why rest masses of all particles are consistent, their mass -- their curvature in spacetime -- is the very essence of their nature.
My current best hunch is that particles are like knots or tangles in the fabric of spacetime, inherently curving it. All information is encoded as curvature, and curvature is the only thing that truly exists. In this model, black holes are regions of maximum curvature, vaguely like a ball of yarn. If you want to add one extra "strand" going into the ball of yarn, its cross-section has to be added to the surface area of the black hole, which is why black hole area is proportional to its matter content, not its volume.
1] Not quite though! There is the gravitational binding energy. You have to put energy into a planet to split it up into separate particles, and conversely, planets release energy by the mere act of their forming. Jupiter releases more energy from its interior due to gravitational contraction that it receives from the Sun. In effect, particles are heavier separately than together.
My impression of physics is that space-time is like a field that emanates from energy/matter at the speed of light in a slight curve. When these fields overlap their curves compound - the more energy, the more overlap, the more curvature.
Without energy there is no space-time. Space-time could be thought of simply as information about the energy that it emanates from.
Apologies for the tangent from this amateur. But it seemed similar to your thoughts.
I don't know if anyone had ever bothered to develop it further, or even critique it, but it's interesting how many qualitative phenomena it explains in a straightforward, intuitive way!
Sure, one can speculate that. There is quite a lot of devil in the details, though. One thing that is a bit unclear when it is 'all curved space' is how one would ever get spin 1/2 particles, i.e., non-integer spin particles. E.g., in string theory one has to invent a 'fermionic string' to get them otherwise one only gets integer spin particles. Also it is not clear how 'multiple black holes' are going to be a stable configuration together.
I always thought that the non integer spin was more of an historic artefact, because they measured the photon first. Not my area of expertise, but does the half spin have any meaning?
Well, it acts quite a bit like an angular momentum of that amount, including obeying conservation laws jointly with regular ("orbital") angular momentum.
I don't know of a good way of explaining the half-integral nature without diving into representation theory. The short story is:
1. Conservation laws and continuous symmetries are the same thing. The standard explanation of this is when we move or turn the system, the rules it obeys are the same. Or alternately change our view of the system by picking different origin and axes for our coördinate systems, the form of the rules (how to evolve, how to measure, how to predict) remains the same. This is Noether's theorem.
2. But symmetries don't mean our description of a system is unchanged. It means that our descriptions must change in a compatible way with our new point of view.
3. Cashing this out in math, symmetries are groups acting on states. Having the states transform compatibly means these actions must be "linear representations of groups".
4. A spin-one object has the wave function (normally considered the fundamental state) act like a vector under rotations, and because symmetry under rotation is angular momentum, this must be too.
5. When we do this quantum mechanically, all of our predictions come from the density matrix, where the wave function enters twice (as an outer product). A spin-1/2 object has the density matrix transform like a vector, and the wave-function itself transforms "like a spinor", which is to say, itself.
Apart from in a mathematical sense, how do you actually rotate a spin 1/2 particle say 360 degrees? Does this only apply in derived theorems like the spin-statistics swap of identical particles or is there an actual physical process where say an electron can itself be rotated 360 degrees and then acquire the -1 sign on the quantum amplitude (and then this could be measured by interfering the rotated version of it with itself, sort of like in a double-slit experiment)?
Depends on the spin-1/2 particle. You need something to "grab it with".
Electrons "want to" stay aligned with magnetic fields[1].
Imagine two bar magnets, north to south:
NNNSSS e- NNNSSS, with an electron in the middle.
Spin the magnets around once. Tada! You've spun the electron too. The problem is that slight imperfections in the magnetic fields, as well as everything needed to move them greatly complicate what the actual effect will be on the electron.
To really observe interference patterns, you'll need multiple paths, and many many measurements to tease out statistics. In addition to the fragility, moving stuff around for each measurement is infeasible for this reason. Continuous beams of electrons split and merged by magnet fields, with a continuous parameter on of the paths that can alter how much it is effected is needed. And at this point what's happening to the electrons look a lot more like math than like straightforward rotations.
[1] Actually, they'll precess around the magnetic field axis, but if that axis starts close to the electron's axis, and is moved slowly, it will stay close.
Yes. If you take an electron beam, put it through an [electron] beam splitter, put half through a magnetic field that would spin the electron around once, and recombine the beams you will see interference effects.
Thanks, yeah think I've read about that version before. But "the magnetic field spins the electron around once", doesn't this feel a bit weak? You could conceivably just define "spin around once" as the B-field manipulation that returns the amplitude to +1, not -1. How do you define the B-field interaction in a way that is comparable to "spinning something around once"? I'm not trying to be annoying :) I feel this really is at the core of the spin-1/2 "rotate twice to rotate completely" confusion..
Because it's the "rotation" in comparison to the surroundings that cause the change in amplitude, a global rotation of the electron particle and the rest of the universe doesn't cause the electron to change amplitude, as then it's just a global coordinate transformation.
Yes the difference between integral spin (bosons) and half-integral spin (fermions) particles is one of the most important facts in physics. The two types of particles behave very differently, fermions obey the Pauli exclusion principle and therefore act like matter in the sense of exclusively occupying space. Bosons have no exclusion principle and behave like what we typically think of as energy, light for example. Superconductivity and superfluidity are also manifestations of bosonic behavior in collective systems.
Well, to obtain integer spin one actually does not need any physics knowledge. All of the possible integer spins map one-to-one on the group representations of the rotation group. It is pure mathematics. One thing with half-integer spin is that if an object transforms according to a half-integer representation and one rotates the object by 360 degrees the state function acquires a minus sign. This is difficult to imagine coming from a spatial object, though, because one would be inclined to say that rotating by 360 degrees is the no-op. So, these half-integer spin objects are actually kind of strange and one would probably not have imagined them if one would just take mathematics as the starting point.
A defining feature of a black hole is that because of it's gravity nothing will escape it, not even light. This clearly doesn't hold for atoms. They can be bombarded by photons and electrons and split and fused.
> A defining feature of a black hole is that because of it's gravity nothing will escape it, not even light
One could say that not all events in space time are sufficiently curved to be that of a black hole; the curved space time representing a few atoms may not be as curved as the curved space time representing a black hole.
Wouldn't they if the existence of them is defined by the curvature of spacetime itself (if energy densities in various configurations is composed of spacetime that is curved to various degrees [maybe like how another commentator here, id call this "knottedness"], how the energy densities evolve in a given spacetime configuration is also curved?)?
That is an event as described when spacetime structure is defined as orientable, where as i'm trying to get at what would it be described as if spacetime was non-orientable, and it doesn't seem like its just "Never"[0]
I've seen something that seems similar like what some are talking about here described as[1]:
"If a spacetime is not time-orientable then a closed path exists round which the direction of time reverses. The simplest example of non-orientability is the Mobius strip. On the Mobius strip left-handed and right-handed cannot be consistently defined over the whole surface. A left-handed coordinate basis changes to a night- handed one when going round the circumference of the strip.
The Mobius band can also be thought of as a spacetime diagram for a circular space, S1, and a non-orientable time. The direction of time reverses on a path around the circumference S1 of the band. Note that our usual image of a Mobius strip is as a 2D surface embedded in 3D. However the embedding is not unique and the Mobius can be defined in a number of ways without resorting to any embedding at all.
More importantly, it has topological properties (The non orientability) that can be described independently of the embedding. Of particular interest is a model of a particle as an asymptotically flat spacetime manifold with a region of non trivial topology where time is not orientable."
But its hard for me to come up with a term that can encompass a particle and a black hole (i'm sure there has to be one out there), in different regions in an asymptotically flat spacetime manifold, but exist in the same non trivial topology where time is not orientable.
That means that cinquemb is using the wrong term for what s/he is trying to say. Once you stop thinking of the technical definition of "event", though, there may be the germ of a point there...
Gravity is a strange thing, because as far as I can intuit, it is not constant (even though classical Newtonian Mechanics tells us it is, and even has a constant for it, G) -- but as far as I can intuit, Gravity is relative to both scale and wavelength...
That is, it will bend different electromagnetic wavelengths differently, like a Prism...
To understand this, consider smaller attractive phenomena, for example, magnetism, and electrostatic attraction (you rub a balloon, it "sticks" to surfaces). Those are both attractive phenomena similar to Gravity, just at much smaller scales.
If you have a water wave pool, there are ways to get objects in the water to be attracted or repulsed, via different wave forms.
In fact, maybe this is the problem. We're calling Gravity "Gravity", rather than "attractive/acceleration force at large scale (which again is a law of the squares phenomena, that is, it drops off as the square of the distance, but the distances involved in gravity are very large, planetary sized (or larger) in effect).
So you're right -- it wouldn't hold for light, but perhaps there are smaller analogous, attractive phenomena, that it would hold up for.
And perhaps there are smaller in scale, yet analogous phenomena to light -- like sound or vibration.
See this is the problem in physics... we're calling PRINCIPLES (in this case, the attractive principle) by different names... Gravity, Magnetism, Electrostatic, Strong and Weak Nuclear Forces, etc.).
Every single thing, and every single principle in the Universe -- has analogues of it at different SCALES.
The knowledge of these principles (which can be deduced by simple observation "what is the unifying principle behind these phenomena?") should come before math equations, especially those with constants, BEFORE we make a serious inquiry into physics.
We should ask HOW something would be possible -- rather than trying to figure out WHY (based on current knowledge) it is (or seems) impossible... then we'll start making great strides in physics...
Gravity and electromagnetism are basically the same from a mathematical perspective if you’re just looking at the forces produced: they’re both inverse square, proportional to some intrinsic property of the objects involved. The main differences are the constant in front (gravity is kind of wimpy) and the fact that “electrical mass” can be negative and its force has a minus sign in front. The only reason you see gravity at large scales is that charges mostly cancel out at larger scales, while gravity cannot.
There is a difference though: a test-mass moving freely in a gravitational field does not experience that field (it feels the same as a test-mass in empty space). A test-charge moving freely in an electrical field however will experience an acceleration (it feels something is pulling on it).
I see where you’re coming from (with the naive formulation of the proportional charges/masses and inverse square law) but at relativistic and microscopic level they are very different (including, as another poster observed, the remarkable property that a test-mass accelerated by a gravitational field is unable to observe that field, which is a formulation of the famous Equivalence Principle).
I generally regard most of the "Star Trek physics" ideas like FTL with the hairy eyeball, but this one really gets me. Being able to violate the conservation of baryon number (and lepton number, for that matter) would point to -- in some scenarios -- mass-energy conversion being a lot more available than the laborious processes of fission, fusion, and particle/antiparticle mutual annihilation.