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Math Shows Some Black Holes Erase Your Past and Give You Unlimited Futures (vice.com)
dmoberhaus writes: An international team of mathematicians has found that there are theoretical black holes that would allow an observer to survive passage through the event horizon. This would result in the breakdown of determinism, a fundamental feature of the universe that allows physics to have predictive power, and result in the destruction of the observer's past and present them with an infinite number of futures. The findings were detailed in a report published last week in Physical Review Letters.
I'm not in the field either, but I hope someone can explain this a little better since the actual paper is behind a paywall and the oversimplified and popularized Motherboard article doesn't make any sense.
Motherboard says that the laws of the universe, outside of black holes, are supposedly deterministic. That's news to me, I thought quantum mechanics dealt with probabilities and there was no way to predict what part a particle will take. The universe plays dice all the time, it only appears to be deterministic on a large scale when the probabilities of the individual particles average out to a largely predictable macroscopic result.
Then, what does it mean when they say your past is destroyed? Let me get this straight, you fall into one of these special black holes, you survive (which, I assume, includes your memories), yet your past is "destroyed"? I imagine they mean that the laws transfer to a different coordinate system where your past is no longer at negative time coordinates but simply nowhere at all. Which isn't really that unusual. Just use a different coordinate system (one tied to your body) and the past will be there again, still inaccessible at the usual negative coordinates (but formulas for describing your current environment will be very complicated). Pretty sure that's what they meant, right?
OK, what about the unlimited futures? Again, I though quantum mechanics already gave us those. I guess it means that the future will be a lot more undeterministic than usual?
Finally, the big discovery seems to be that you won't be destroyed by all the energy of the universe falling through the event horizon at the same time as you, thanks to the expansion of the universe. But what about spaghettification? Won't you still be killed by the enormous differential gravitation even if you survive the radiation at the horizon? How does the charge of the black hole prevent that from happening?
Thanks in advance to anyone who can clear this up a bit more.
People tend to believe that physics is applied math. It's not. The universe doesn't care about your math. General Relativity is a set of mathematical equations that were picked because they could model the observed experimental data.
The problem here isn't the mathematics or whether it applies to physics - or to reality, for that matter. The real problem is people's lack of insight - including many physicists. Take for example the idea of determinism - naively, this means that everything is pre-determined from some set of equations, which are assumed to have unique, well-defined solutions; but we already know of many cases where seemingly simple sets of equations behave chaotically. Now, I know well enough that mathematically, 'chaos' only means that a dynamic system is extremely sensitive to initial conditions, but since our understanding of quantum mechanics seems to indicate that we can't fix initial conditions of any system with arbitrary precision, there must be a limit to how deterministic any set of deterministic equations are in practise.
The point I'm making here isn't really about whether either GR or QM are 'true' or model reality correctly - we already know they don't - but the fact that we know far too little to make sweeping statements about anything as profound as determinism and causality. Apart from that, I can't see that this new calculation concerning certain types of black holes says anything of the sort; time and causality are strictly local - time experienced being the path integral of something or other in the 4-dimensional space-time manifold - and whether you travel in a closed loop or otherwise pass through events (~ 4-dim points in space-time) that you have passed before, the time you experience is still only your own, individual, highly local time, which does not necessarily have much to do with the rest of the universe.
A final point: mathematics is true - it is the only science that can claim to be absolutely tru, but the price we pay is that it is only true within its set of axioms. What this means is that as long as the axioms of any theory in the empirical sciences, match the reality we're trying to model, the conclusions of the theory MUST be correct - that is in fact the fundamental assumption behind the scientific method: it means we can falsify our assumptions by conducting experiments.
Not quite, e.g.: https://en.wikipedia.org/wiki/Superdeterminism
The point you are making is entirely moot.
Our current understanding of quantum mechanics already dictates that we live in an nondeterministic universe.
Quantum interactions are already expressed as probabilities and uncertainties.
Just look at nuclear decay. There is no way to mathematical model that can calculate when an atom will decay.
Hell, they can't even predict what will happen when you collide two particles.
You get several outcomes with different probabilities of happening.
well, it most certainly can't erase it's own past effects on the universe by entering the black hole.
How can you be so sure? if it did, you wouldn't know.
This is a hacked account, for which the owner can not be held responsible.
Our current understanding of quantum mechanics already dictates that we live in an nondeterministic universe.
Our current understanding on quantum mechanics isn't necessarily correct.
It could be worth to consider that all measurements we have ever done on quantum level are with methods and equipment design with the assumption of determinism being true.
So quantum mechanics appearing to be nondeterministic causes a bit of a paradox.
If determinism is proven to be false then we can not rely on the the measurements that led us to believe that determinism is false.
Quantum mechanics being deterministic but extremely complex would be a much more convenient explanation.
Unfortunately that would make maxwells demon come back and theoretically allow us to disregard thermodynamics. (But again, thermodynamics only really applies to macroscopic systems anyway.)
> Finally, the big discovery seems to be that you won't be destroyed by all the energy of the universe
> falling through the event horizon at the same time as you, thanks to the expansion of the universe.
The catch here is that, "all the energy in the universe," may not be hitting you as you fall through the event horizon, but a lot will, more than likely enough to give you a Bad Day. You're only down from "infinity" to "the horizon observable over the black hole's future," still a pretty big number.
> But what about spaghettification?
Others have answered this, that the gravity gradients are soft enough around a big enough black hole.
There is another fun fact here... For spinning black holes, which I believe means most of them, or at least the big ones we could think of entering in the non-spaghetti state, there are actually two event horizons, and it might be possible to leave from the zone in between them. Gregory Benford, physicist and science fiction author, set several books in that region.
The living have better things to do than to continue hating the dead.
I am a physicist. This is not how quantum mechanics works. Probability and randomness are the result of measurement and not knowing the starting conditions. Should you completely know the quantum state (singular) of all the interacting particles in your system, you could exactly predict the outcome. Our change of "quantum state" to "quantum states" is useful to describe what we observe in the real world, but requires an assumption that the two "states" we're looking at are at some point separated by an infinite distance. This is a fine approximation, but not fundamental to physics.