Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Experiments spell doom for physical-collapse explanation of quantum weirdness

quantamagazine.org

Post reply on HN
Print view View original

131–140 of 306 posts

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#131

Post by HALtheWise »

spywaregorilla wrote: post #38
iainmerrick wrote: post #34

Earlier quoted context omitted.

Is that really so weird? That's a very common version of time travel in SF, perhaps the most common. You can travel back in time, and you think you're changing history, but through a series of unlikely coincidences you end up being the person who created the history you were trying to change. Come to think of it, maybe that's more common in short stories, where the "gotcha!" format works. It's probably harder to spin…

It's not weird. It's fun. But it's stupid as a serious time travel proposal. Things like "travel in back in time 5 seconds unless you see your future self is already there" create a hard paradox that this logic cannot solve. Time loops are easily broken by anyone interested in testing them.

If you frame the system as "the universe conspires to create a series of coincidences such that no paradox exists", then it makes perfect sense that nobody chooses to run that experiment, because the simplest coincidence that prevents the paradox is for the characters in question to simply not think to run that particular experiment. This raises the obvious question of how the time machine got invented in the first place, which seems like a great story.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#132

Post by iainmerrick »

naasking wrote: post #86
iainmerrick wrote: post #58

Earlier quoted context omitted.

I have never fully understood that idea, even after reading Hossenfelder's posts about it. The idea that there's a "block universe" and everything is predetermined is comprehensible, sure; but what's the exact mechanism by which Bell's inequality is violated in experiments? Doesn't that require the universe to have been carefully set up to look as if it's acting in a weird non-local way, on an experiment-by-experimen…

We had a recent thread about an article from Tim Palmer who has a good take on this: https://news.ycombinator.com/item?id=33223391 The idea is that the natural laws are fractal, which when mapped out trace many state space configurations. But with a fractal there are always gaps in state space that remain no matter how much you zoom in or out; fractals preserve certain structural invariants at all scales. So the idea…

Superdeterminism gets an unnecessarily bad rap.

If determinism is true, don't you mean "necessarily"? :)

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#133

Post by immmmmm »

Nihilartikel wrote: post #128

I wasn't expecting them to be able to run Doom on a quantum computer for at least another decade!

as a former physicist and quake engine modder, your joke is very nice:)

more seriously, having spent countless nights thinking of QM, it feels a bit like Nature is playing w you and your nerves.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#134

Post by spywaregorilla »

HALtheWise wrote: post #131
spywaregorilla wrote: post #38

Earlier quoted context omitted.

It's not weird. It's fun. But it's stupid as a serious time travel proposal. Things like "travel in back in time 5 seconds unless you see your future self is already there" create a hard paradox that this logic cannot solve. Time loops are easily broken by anyone interested in testing them.

If you frame the system as "the universe conspires to create a series of coincidences such that no paradox exists", then it makes perfect sense that nobody chooses to run that experiment, because the simplest coincidence that prevents the paradox is for the characters in question to simply not think to run that particular experiment. This raises the obvious question of how the time machine got invented in the first p…

Sure sure. And it's fun fiction. But it's obviously not a plausible physics explanation.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#135

Post by tsimionescu »

dchichkov wrote: post #116
jfengel wrote: post #92

Earlier quoted context omitted.

That's right: the "collapse" interpretation is an approximation. You can derive if from the MWI. We already know that the "worlds" separate and almost completely cease interacting. The interactions decrease to the order of "two to the power of Avogadro's number" almost immediately. The collapse interpretation rounds that to zero (at some arbitrary point). To make that more concrete you have to add a term to the equat…

If quantum computers would work, it would be very difficult to explain "where" the computation happens without having some sort of MWI into picture. But if, somehow, quantum computers keep their noise levels up without producing any interesting acceleration I'll expect that a theory would emerge at some point explaining that. And it may disambiguate which interpretation is the one.

Quantum computers are easy to explain in CI as well: they simply exploit certain numerical properties of complex-valued probabilities (unlike the real-valued probabilities of classical probabilistic Turing machines).

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#136

Post by whimsicalism »

pdonis wrote: post #113
jfengel wrote: post #92

Earlier quoted context omitted.

That's right: the "collapse" interpretation is an approximation. You can derive if from the MWI. We already know that the "worlds" separate and almost completely cease interacting. The interactions decrease to the order of "two to the power of Avogadro's number" almost immediately. The collapse interpretation rounds that to zero (at some arbitrary point). To make that more concrete you have to add a term to the equat…

> You can derive if from the MWI. Not as an actual physical process, no. "Collapse" in the MWI just means that, once the "worlds" have decohered, within each "world" the wave function can be collapsed to the one that describes the measurement result observed in that "world", for purposes of predicting future results. But in the MWI this is just a mathematical convenience and doesn't correspond to anything physically…

> doesn't correspond to anything physically happening

It corresponds to the inner product of the two branches of the wavefunction going to 0 due to physical phenomenon.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#137

Post by cb321 »

kgwgk wrote: post #91
cb321 wrote: post #49

Earlier quoted context omitted.

As with any unsettled questions there are pros & cons to the various takes on quantum reality. Part of the appeal of MWI (intrication of observer into observed system as part of the measurement process) to me was always that the instantaneousness you mention here is a very "ordinary" kind of "fastness by synchronization". It's basically just a kind of causal wavefront hitting. There are plenty of "infinitely fast" sy…

> intrication of observer into observed system as part of the measurement process That was already part of von Neumann’s model of measurement over 90 years ago.

Yeah. Perhaps most charmingly treated here: https://arxiv.org/abs/2011.12671 { EDIT: though surely many other places! There are also YouTube videos of this one, though, and Sidney Coleman was really a Feynman-class edutainer, perhaps as under-recognized as von Neumann is relative to say Everett on this topic :-) }.

I should perhaps have used the word "entanglement" rather than "intrication". Oops.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#138

Post by whimsicalism »

herdcall wrote: post #54
dzdt wrote: post #4

There is an often-repeated statement that different quantum mechanical theories are equivalent. This is an over-simplification. Is wave function collapse is a real thing or just an approximation of what happens when a large system is entangled? Some smart people have tried to make theories where wave function collapse is a real thing. These new experiments are working to rule out those ideas. My feeling is that Evere…

Check out "superdeterminism," first proposed by Bell (of Bell's inequality fame) himself and currently being vigorously pursued by Sabina Hossenfelder. There is no "collapse" per se according to this model and everything is really classical with hidden variables, and the entanglement comes because everything shared the same origin (the big bang). A very fascinating and in my opinion the best explanation, though it's…

> though it's extremely controversial and taboo because of its implications on free will

Uhh, no. Essentially all existing physical theories are devastating for any non-compatabilist account of free will.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#139

Post by whimsicalism »

vpfaulkner wrote: post #36

From a layman’s point of view, it seems like we grasping at straws when it comes to these thorny quantum questions. Is fair to say, for example, that we are about as clueless as our ancestors were with the bubonic plague? To a non-expert it can be difficult to separate which theories lay on solid ground and which theories are highly speculative.

It's like we had miasma theory of disease, but miasma theory was actually highly accurate at predicting disease.

So... not really like how our past misunderstanding of disease, which was useless as well as being wrong.

Re: Experiments spell doom for physical-collapse explanation of quantum weirdness

#140

Post by whimsicalism »

markisus wrote: post #101

This tidbit about a prodigious undergraduate struck me. He double majored in math and physics and was about to start his PhD at Harvard. And in a sudden freak accident he was gone from existence. The universe will always remain unfathomable in some ways. > In 1996, Qijia Fu of Hamilton College in New York — then just an undergraduate — proposed using germanium-based neutrino experiments to detect a CSL signature of X…

Seems perfectly fathomable to me.
Post reply on HN