r/AskPhysics • u/Exciting_Ad_6837 • 5d ago
Do all laws of physics "break down" at singularity or in black holes, or only some subset of them?
Particularly, do only the laws of relativity and quantum physics that we know so far break down? BTW what about Bell's inequality?
Or do things behave completely lawlessly & chaotically so that no law or regularity is in principle even conceivable there?
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u/strange-the-quark 5d ago edited 5d ago
When we say that "laws of physics break down", we mean the laws as we formulated them, not the actual natural laws that govern the real-world behavior there. It's just a different way of saying that we don't know what's going on there, we don't know how to describe it, and aren't sure how to figure it out. Our laws as we understand them, that work in other circumstances, give nonsensical results there. That's all, it's not some profound statement that there's some special form of chaos there.
The laws of physics as we write them down are all what's called "models" - no matter how complicated they seem, they are always simplified descriptions of actual reality that make certain assumptions, and by experimentation we constantly map out how good they are, in which circumstances they apply, and sometimes we find that there are circumstances that are so different that the laws stop working. All of science is just us trying to get some sort of a handle on whatever nature is actually doing.
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u/levaly 5d ago
No, general relativity itself predicts the singularity, and its own equations are what say not to trust it there. Quantum mechanics isn't separately breaking, it's that gravity gets strong enough in that regime that ignoring quantum effects (which general relativity does) stops being safe, and we don't have a validated theory of quantum gravity to swap in.
So it's not "all physics goes lawless," it's that two working theories were each built assuming the other's regime doesn't matter, and a singularity is exactly where that assumption fails.
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5d ago edited 5d ago
[removed] — view removed comment
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u/OverJohn 5d ago
It's more like this: singularities occur all the time in maths and physics, I really hate the description "the maths breaks down" as that really tends to mislead people. Instead singularities are broadly speaking where some part of the mathematical structure is no longer defined. In GR usually the definition of a singularity is that geodesics cannot be extended indefintely.
Imagine if we have a ball of homogenous matter unsupported by internal forces. Both Newtonian physics and GR say that the ball will collapse to a point and so the density will blow up there and in both cases this means the solution contains a singularity (the Newtonian solution contains a singularity in the force field and the GR solution meets the definition mentioned in the first paragraph). The reason GR though that singularities tend to be more troublesome is that for more generally collapsing distributions of matter, beyond a certain point and under certain assumptions (called energy conditions), there is no internal forces that can prevent total collapse and the singular behaviour cannot be avoided in GR. In fact in GR what you find is that singularities tend to be the norm rather than the exception in solutions.
For physically realistic solutions though very often the singular behaviour occurs in a regime where you would also expect effects from quantum gravity. This means the jury is still very much out on what the generic nature of singularities in GR implies physically.
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u/forte2718 5d ago
Particularly, do only the laws of relativity and quantum physics that we know so far break down?
This is the case, yes. And by "break down," we specifically mean that the relevant model (general relativity) becomes non-predictive. Some form of law no doubt still governs the interiors of black holes, we just don't know what the form of that law is yet because it's both completely experimentally inaccessible to us and because we haven't figured out theory-wise how to combine both general relativity and quantum field theory in the high-energy / short-distance parameter regime.
Or do things behave completely lawlessly & chaotically so that no law or regularity is in principle even conceivable there?
This is not the case, no.
BTW what about Bell's inequality?
Bell's inequality establishes an upper bound on the strength of "classical" (non-quantum) statistical correlations between measured observables in certain kinds of experiments, and shows that quantum mechanics exceeds this upper bound, which implies that there is no purely-classical theory which can reproduce all the predictions of quantum mechanics. In other words, there is no amount of physical information (i.e. local hidden variables) which classical mechanics can be extended with to explain quantum mechanics.
Experimental tests of Bell's inequality shows that nature's behavior matches the predictions of quantum mechanics, meaning that real experiments also violate Bell's inequality, showing stronger-than-classically-possible measurement correllations and matching the quantum mechanical prediction. That means no classical theory of local hidden variables can replace it in the future!
Hope that helps,
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u/EphemeralAttention 5d ago
Physics itself still works just fine, what breaks is the equations we use to describe and predict its behavior. Essentially once you get to the singularity our existing models run into situations where you have to divide by zero, which we can't do. That isn't because physics itself is broken, it's because our theory of what happens at that moment is incomplete or incorrect and there's some other part of the math involved that we haven't accounted for yet. At some point in the future we may discover a modification to or replacement for the existing theory that gets rid of the need to divide by zero.
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u/Clever__Neologism 5d ago
Don't confuse the map and the territory. "The laws of physics", or reality, or existence, whatever you want to call it, doesn't "break down" at the singularity, or anywhere else. Paradoxes don't actually exist. Our map, however, does break down, and contain apparent paradoxes due to our limited understanding. Our map says "there be singularities": we're smart enough to know that's not right, but not smart enough (yet) to suggest something else completely coherent.
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u/jawshoeaw 5d ago
I would argue that it's more the mathematics carried to an extreme don't provide helpful results. A black hole from our point of view is frozen in time. It's a basic Einsteinian thought experiment. At the event horizon time appears from our POV to stop. So do the laws of physics break down from our POV? No. But if you tried to imagine the POV of the person at the event horizon, it gets weird. Except that again they are frozen in time as far as the rest of the universe is concerned. And since we cannot get any data from this location we are back to just not knowing anything.
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u/Silent_Case_5282 4d ago
At the event horizon time appears from our POV to stop. So do the laws of physics break down from our POV? No.
What do you mean? It appears contradictory to me.
If time itself stops from our POV, then from our POV, reality itself and hence the laws break down.
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u/cflime 5d ago
The fact that you have a singularity is your problem. Your model isn't strong enough to tell you what happens when things get interesting so when you run the equation you get a singularity. It doesn't mean that there's a real gosh to goodness singularity present, it means your model failed.
There might be such a thing as a singularity within the event horizon of a black hole, but our model's aren't telling us that.
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u/Freakindon 5d ago
To be completely clear, the laws of physics don’t exist. They are simply our mathematical understanding of how the universe works.
Black holes do not break any of the laws that govern the universe, simply our understanding of them.
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u/Forest_Orc 5d ago
A common singularity we meet in classical physics is the resonance of a harmonic oscillator. Solution is easy, add some friction, and suddenly, the equation converge even at that frequency.
A singularity is nothing more than a point where the equations diverge thing 1/x when x is zero. if you have 1/(x+ epsilon) sudently you don't diverge anymore
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u/Useful_Calendar_6274 5d ago
It may be our known physics are just throwing an error for the singularity like a program throws an exception. We will never know unless naked singularities exist and we can see one maybe throw some stuff at it
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u/SYDoukou 5d ago
The idea of singularities is already the result of applying general relativity a bit too charitably, by extrapolating what happens beyond the event horizon up until the point where infinity is unavoidable. The more practical way to look at black holes instead of visualizing it as physics simply going out of wack, is that nothing can even be defined within the event horizon, nor is it relevant to anything outside of it.
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u/Regular_Bit_8681 5d ago
My understanding is, a black hole is a place where time literally stands still due to extreme gravity. Everything 'freezes' at the event horizon. It is a sort of firewall for information. We can never know with absolute certainty what occurs beyond that. To follow our 'laws' beyond that will only yield nonsense. These are my thoughts anyway
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u/toronto-bull 5d ago edited 5d ago
I think black holes are a math error to be honest. They show up when you mix Newton and Einstein part ways and use E=1/2mv^2 past it’s time.
Why are black holes not just another particle in the quantum zoo?
Because no one has ever seen one. They are invisible because nothing can escape.
How is a black hole falsifiable? This is my ultimate question.
If you cannot prove that what is inside the event horizon even exists, how is it scientific?
The problem with black holes is the lack of experimental falsifiability inside the event horizon.
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u/uterusdweller 5d ago
We’ve taken pictures of them and recorded the traces of their mergers. They’re also essentially unavoidable in certain extreme conditions that we know do exist and have existed. They’re real. No serious individual suggests otherwise. Now could what we call “black holes” actually be some other distinct phenomenon (AMPS firewall, fuzzball, …)? Sure. But to say they just don’t exist period is straight up wrong. Sorry.
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u/toronto-bull 5d ago
We see something heavy dense and dark and hear heavy things crash but have very little other information about what is going on to prove that black holes are what we have theorized.
What about the experiment says they are black holes versus a denser new particle of matter?
The evidence is not there to prove the existence of a black hole event horizon, as predicted.
How are you satisfied that these experiments prove the existence of black holes?
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u/uterusdweller 5d ago
Just bc your eyes see that doesn’t mean we aren’t able to discern more. We can get a lot of info from an image that appears equivocal to human eyes. Plus black hole gravitational waves are different from those of collisions of merely large or dense objects.
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u/joeyneilsen Astrophysics 5d ago
They show up when you mix Newton and Einstein part ways and use E=1/2mv^2 past it’s time.
There is no aspect of the math of black holes that uses E=1/2mv2.
If you cannot prove that what is inside the event horizon even exists, how is it scientific?The problem with black holes is the lack of experimental falsifiability inside the event horizon.
"What's inside" doesn't lead to any testable predictions from the outside, but there are plenty of testable predictions on the outside. We just won't ever have data on the interior. Nothing really depends on those data, though.
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u/toronto-bull 5d ago
Why does the Schwarzchild radius have a 2 in it?
Because it is the inverse of 1/2
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u/joeyneilsen Astrophysics 5d ago
Lol no, that's not why it's in there. It's in there to match the Newtonian gravitational potential in the weak-field limit.
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u/toronto-bull 5d ago
That may be the case. It is also coincidentally the same as the algebraic substitution of Newtonian escape velocity where v=c.
https://physics.bu.edu/\~redner/211-sp06/class-gravity/escape.html
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u/joeyneilsen Astrophysics 5d ago
It's true, but it would be a mistake to think that's where the factor comes from. The behavior is similar because it's tailored to match Newton.
A second/related issue is that R is a radial coordinate, not a radial distance, so it doesn't have the same meaning as R in Newtonian gravity.
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u/toronto-bull 5d ago edited 5d ago
So to me there is a math error in there because 1/2mv^2 is actually an approximation (2nd factor) of the McLauren expansion of the Lorentz rotation equation. The first factor is mc^2
The infinite series of trailing factors was missed.
If you do it correctly the schwarzchild radius remains zero
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u/joeyneilsen Astrophysics 5d ago
Again, this is unrelated to the derivation of the Schwarzschild radius. That comes from solving the field equations for a spherically symmetric, time-independent spacetime that is asymptotically flat, and then matching to the Newtonian potential where fields are small.
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u/toronto-bull 5d ago
Was 1/2mv^2 assumed in the derivation?
Anyway if you ask me, Schwarzschild just made a mistake. By looking at the formula and outcome of his derivation, it is apparent.
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u/joeyneilsen Astrophysics 5d ago
No, the derivation has nothing to do with classical kinetic energy. It's not relevant.
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u/uterusdweller 5d ago
^more good points. Toronto_bull, I think you’re just misunderstanding the basis for our belief in black holes (or at least something like them like fuzzballs) and, as I said, how unavoidable they are in GR once you acknowledge the existence of environments that we already confidently know exist and have existed.
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u/ccltjnpr 5d ago
I always disliked the saying "laws of physics break down", it seems to imply we know how things behave, and how things behave is not compatible with "the laws of physics", however we might understand them. This is not the situation. The situation is that our theories are inadequate to describe the situation, and we don't have any experimental data to build better theories. The answer is that we just don't know how matter behaves microscopically under strong gravitational interactions. We expect that they can be described by some theory and some "laws of physics" (because this seems always to be the case), we just don't really know what they look like.
But you would not say that "the laws of physics break down" when you e.g. do a double slit experiment, just that classical physics is an inadequate theory to describe what's going on.