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

171–180 of 306 posts

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

#171

Post by krohling »

pred_ wrote: post #151
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…

> Is wave function collapse is a real thing or just an approximation of what happens when a large system is entangled? I've listened to enough Carroll to convince myself that I think MWI makes sense, but what I never got is that it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: We see a particular result of an experiment with many possible a priori outcomes, bu…

> it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is:

According to MWI, all possible results of an experiment are manifest and real. You're asking "which particular entangled state we end up in?". You end up in all of them. For a 2-state superposition system, there are 2 versions of "you" that exist after the experiment, both of which are equally real. Subsequent measurements of the quantum system will appear to be "collapsed" for both versions of you but each will see different and opposing values.

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

#172

Post by d_tr »

ryeights wrote: post #158
pdonis wrote: post #119

Earlier quoted context omitted.

The MWI does not postulate extra universes, although that pop science description is unfortunately common even though it is wrong. The MWI just says that the one universe that exists is actually very, very different from what we perceive. (To be clear, I'm not saying this correct description makes the MWI any more palatable. I am just clarifying exactly what kind of unpalatableness the MWI requires.)

Can you elaborate on this? The Wikipedia page for MWI says >The many-worlds interpretation implies that there are most likely an uncountably infinite number of universes. https://en.wikipedia.org/wiki/Many-worlds_interpretation

Not the parent, but I 'd say this amounts to how you define a "universe". There is a single wavefunction which says that one "copy" of you observes result A and another "copy" observes result B. Using the phrase "many universes" implies that these two scenarios are considered as "different universes". I personally do not like this phrase and find it misleading.

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

#173

Post by criddell »

im3w1l wrote: post #123
naasking wrote: post #87

Earlier quoted context omitted.

Circular. You have to already accept many worlds to take this as evidence of worlds. You can argue for Many-Worlds on grounds of parsimony and clarity, but that's it.

No I don't think so. Many worlds is basically the hypothesis that we can put arbitrarily large systems in superposition. Like schroedingers cat that is both dead and alive, but instead it could be the whole lab, the whole planet, the whole galaxy that is simultaneously in two different states. We could test this by trying to actually do it, by putting really large and complex systems in superposition. If they both ev…

> We could test this by trying to actually do it, by putting really large and complex systems in superposition.

Is there any hope that one could actually do this? The article mentions that large systems may be self-observing (via gravity).

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

#174

Post by Filligree »

pred_ wrote: post #151
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…

> Is wave function collapse is a real thing or just an approximation of what happens when a large system is entangled? I've listened to enough Carroll to convince myself that I think MWI makes sense, but what I never got is that it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: We see a particular result of an experiment with many possible a priori outcomes, bu…

That’s just hidden variable theory. The answer for MWI is “all of them”.

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

#175

Post by krohling »

TheOtherHobbes wrote: post #94
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…

I don't see how relabelling "collapse" to "separation" and adding more or less infinitely proliferating universes solves the problem. MWI also contradicts itself. Supposedly the universes are independent, but if their influence doesn't define the wave equation they do nothing to help explain it. It's a very strong and exceptional claim with absolutely no evidence to support it. "Feeling" isn't enough.

I don't believe "feeling" has anything to do with the MWI interpretation. At least I've never heard it described that way.

Given the equations that describe quantum mechanics (ie Schrodinger equation) MWI is essentially the "null hypothesis". No equations that describe collapse have ever passed the rigor of experiment and all collapse theories require modifications to the mathematics of QM. The burden of proof here is on theorists that support collapse theories not proponents of MWI.

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

#176

Post by jameshart »

simonh wrote: post #164
plutonorm wrote: post #157

Earlier quoted context omitted.

Broad statements, do you have the time to elaborate?

Dark matter affects some galaxies, but the rotation of others is completely explained by the observable matter. Why would one galaxy be influenced by its many worlds twins, but not another?

Sci-fi plot concept answer: because one galaxy is populated by sentient life, and the other isn’t.

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

#177

Post by lamontcg »

krohling wrote: post #171
pred_ wrote: post #151

Earlier quoted context omitted.

> Is wave function collapse is a real thing or just an approximation of what happens when a large system is entangled? I've listened to enough Carroll to convince myself that I think MWI makes sense, but what I never got is that it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: We see a particular result of an experiment with many possible a priori outcomes, bu…

> it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: According to MWI, all possible results of an experiment are manifest and real. You're asking "which particular entangled state we end up in?". You end up in all of them. For a 2-state superposition system, there are 2 versions of "you" that exist after the experiment, both of which are equally real. Subsequent…

> You end up in all of them.

Except that I've only ever experienced ending up in one of them, so exactly how did the "I" that is typing this right now wind up here, and not in some other branch?

There's an unexplained bifurcation of consciousness implied by MWI which it cannot explain (although I think it suggests the appeal of MWI since it gives enough wiggle room that people think that their free will could control which universe they wind up in, which appeals to everyone's inner Malcolm Gladwell).

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

#178

Post by kgwgk »

pdonis wrote: post #119
TheOtherHobbes wrote: post #96

Earlier quoted context omitted.

You don't think postulating an unknown number of extra universes with a very poorly defined relationship with each other qualifies as an extra assumption?

The MWI does not postulate extra universes, although that pop science description is unfortunately common even though it is wrong. The MWI just says that the one universe that exists is actually very, very different from what we perceive. (To be clear, I'm not saying this correct description makes the MWI any more palatable. I am just clarifying exactly what kind of unpalatableness the MWI requires.)

"The MWI" is not one thing. There are many-people saying many-things about those many-worls.

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

#179

Post by lamontcg »

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…

> Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally.

Title article is literally about trying to test those theories experimentally.

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

#180

Post by olddustytrail »

ryeights wrote: post #158
pdonis wrote: post #119

Earlier quoted context omitted.

The MWI does not postulate extra universes, although that pop science description is unfortunately common even though it is wrong. The MWI just says that the one universe that exists is actually very, very different from what we perceive. (To be clear, I'm not saying this correct description makes the MWI any more palatable. I am just clarifying exactly what kind of unpalatableness the MWI requires.)

Can you elaborate on this? The Wikipedia page for MWI says >The many-worlds interpretation implies that there are most likely an uncountably infinite number of universes. https://en.wikipedia.org/wiki/Many-worlds_interpretation

Let's say we generally subscribed to the flat earth theory. But that causes many problems with our actual measurements. So someone proposes the "many earths" theory, where there are many flat earths connected at different angles.

If you could travel between these many earths, you could even end up in one - let's call this mythical land "Australia" - where South was up!

Sounds a bit crazy but some people believe it could really exist.

Post reply on HN