Experiments spell doom for physical-collapse explanation of quantum weirdness • Hacker News Board

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

#101

Post by markisus » Fri, Oct 21, 2022, 3:54 PM UTC

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-ray emission. (Weeks after he submitted his paper, he was struck by lightning on a hiking trip in Utah and killed.)

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

#102

Post by yucky » Fri, Oct 21, 2022, 3:59 PM UTC

giraffe_lady wrote: post #68

yucky wrote: post #51

Earlier quoted context omitted.

Isn't it safe to assume that everything on TikTok is make-believe though?

What is the point of this sort of joke? Just to confirm that we all think of ourselves as superior to anyone using tiktok? It's probably overall neither much more or less reliable than other social media like reddit, twitter, instagram and, sorry boys, HN.

It's not a joke. Social media is heavily curated for a specific agenda/angle (at best) and generally full of dis/misinformation. Why on earth would anybody consider what they see on social media to be representative of reality?

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

#103

Post by tsimionescu » Fri, Oct 21, 2022, 3:59 PM UTC

fallingfrog wrote: post #90

lupire wrote: post #9

Earlier quoted context omitted.

Disproving some form of measurable wave function does not provide evidence for MWI, which is unmeasurable and untestable nearly by definition.

Well, the thing is that the MWI is actually simpler than all the other interpretations, because it simply removes the idea of wave function collapse entirely. Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally. Because we live in the macro world, it feels like a single unitary reality is simpler, but actually, the MWI makes fewer assumpti…

It is not simpler, since MWI still needs the Born postulate to actually predict the results of quantum experiments. It replaces this idea of the wave function collapsing with a redefinition of what a measurement apparatus / observer is (in MWI, a measurement apparatus exists in a single "branch" of the wave function).

This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. That is, the Schrodinger equation doesn't actually predict that a particle has some amplitude here and some other amplitude there, as is often presented; instead, it predicts that it is described by some vector which can be decomposed in many different ways. You can say it has some amplitude X here and some amplitude Y there, but with any 2 points in space-time (adjusting the amplitudes). Or, it can have some combination of position and spin with amplitude X, and some other combination of position and spin with amplitude Y. You can choose any basis you like for the measurement, and you will get the corresponding answer.

But, for MWI to actually predict experimental results (and the classical world we live in) you not only have to choose to look at a single element of that basis, but you also have to believe that the classical basis is somehow preferred.

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

#104

Post by addaon » Fri, Oct 21, 2022, 3:59 PM UTC

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…

Reminds me of a golden age (?) science fiction short story -- no idea the author or name -- about a spate of suicides and mysterious deaths among physicists who got too close to "the truth," externally caused by an alien force trying to keep humans in their petri dish.

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

#105

Post by cbruns » Fri, Oct 21, 2022, 4:02 PM UTC

addaon wrote: post #104

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…

Reminds me of a golden age (?) science fiction short story -- no idea the author or name -- about a spate of suicides and mysterious deaths among physicists who got too close to "the truth," externally caused by an alien force trying to keep humans in their petri dish.

Sounds like Three Body Problem. Not golden age though.

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

#106

Post by naasking » Fri, Oct 21, 2022, 4:08 PM UTC

GoblinSlayer wrote: post #100

naasking wrote: post #83

Earlier quoted context omitted.

Is Many-Worlds even falsifiable?

Discovery of non-linearity in the evolution operator would falsify MWI. Like e.g. this germanium experiment gave a positive result.

Yes, because it falsifies every interpretation of quantum mechanics not just MWI itself. I think in context here, "is superdeterminism falsifiable" is as silly a question as "is logic falsifiable" or "is causality falsifiable". Specific mmathematical, causal or superdeterministic models are always falsifiable, but the idea that superdeterminism as a whole is not falsifiable should be no more surprising or interesting than the fact that logic is not falsifiable.

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

#107

Post by tsimionescu » Fri, Oct 21, 2022, 4:09 PM UTC

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…

> it's extremely controversial and taboo because of its implications on free will (e.g., I see no mention of it at all in this article).

"True" free will is ruled out by all existing physical theories, so that's not why it's controversial. The bigger problem with superdeterminism is that it wants to explain physics without assuming statistical independence, even for far away events.

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

#108

Post by naasking » Fri, Oct 21, 2022, 4:10 PM UTC

superposeur wrote: post #84

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…

Agreed — superdeterminism is not so much a theory as a theory-for-a-theory at this stage (a vague guess at the form such a theory might take). It is a sign of the much greater maturity of the physical collapse models that their parameters can be constrained by experiment. The ability to be constrained is a good sign, not a bad one. I love John Preskill’s standard nod to superdeterminism in his writings: without menti…

I think the right way to look at it is that superdeterminism is an umbrella term for a class of theories that have a certain property. Like some interpretations of quantum mechanics are "psi-ontic", meaning the wave function is considered physically real (like many worlds), vs. "psi-epistemic" where the wave function is considered a reflection of our knowledge of reality (Copenhagen).

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

#109

Post by abecedarius » Fri, Oct 21, 2022, 4:14 PM UTC

cbruns wrote: post #105

addaon wrote: post #104

Earlier quoted context omitted.

Reminds me of a golden age (?) science fiction short story -- no idea the author or name -- about a spate of suicides and mysterious deaths among physicists who got too close to "the truth," externally caused by an alien force trying to keep humans in their petri dish.

Sounds like Three Body Problem. Not golden age though.

It's an Asimov story whose title I forget. The truth in question was a defense against nuclear bombs.

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

#110

Post by macrolocal » Fri, Oct 21, 2022, 4:15 PM UTC

lebuffon wrote: post #48

Don't tell anyone, but in the back of my mind I wonder if what we call quantum mechanics has something to do with the rendering engine in this simulation we find ourselves in. Is quantum collapse just us "catching" the engine deciding what to render when we observe something? :-)

Maybe, but it would be a highly non-classical computer. Probably it could cheaply render the most physically plausible paths to specified outcomes, and quickly factor large primes.

Nb. quantum also highlights assumptions made by our brain's rendering engine.