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Why have so many physicists shrugged off the paradoxes of quantum mechanics?

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Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#31

Post by ttctciyf »

btilly wrote: post #15
mjfl wrote: post #12

Earlier quoted context omitted.

Yes there are. Even without invoking any philosophical issues, quantum mechanics admits it's not self-contained. It takes measurement - the act of an outsider interacting with a system, which collapses the wavefunction, as a postulate. Measurement is not described by quantum mechanics.

No, there is not. The Everett aka many-worlds interpretation demonstrates that you can explain the observed effects of measurement without invoking "collapse" of the wave function, and without reference to anything outside of QM.

Many Worlds still owes us an explanation of the apparently huge difference between this, the actual, world and all the other apparently not quite so actual ones, does it not?

The two most promising ideas (IMO) are the idea that the "wave function collapse" is a non-physical event describing a change in our knowledge, the quantum informatics approach as per Philip Ball's recent RI lecture,[1] and the "Relational" interpretation[2] which observes that a measurement always entangles the measuring system with the measured system, and is best treated as such - i.e. as an entanglement relationship; though it seems that this leads to an "entanglements all the way down" view in which these relationships are the ultimate physical reality, rather than the conventional picture of the relationships being secondary to the things which are so related.

The "measurement as entanglement" view is, I know, notably supported by at least one HN poster[3], who I hope will be on hand to correct my no-doubt erroneous rendition :)

1: https://www.youtube.com/watch?v=q7v5NtV8v6I

2: https://en.wikipedia.org/wiki/Relational_quantum_mechanics

3: https://news.ycombinator.com/item?id=12657447

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#32

Post by firethief »

gowld wrote: post #20
btilly wrote: post #15

Earlier quoted context omitted.

No, there is not. The Everett aka many-worlds interpretation demonstrates that you can explain the observed effects of measurement without invoking "collapse" of the wave function, and without reference to anything outside of QM.

Requiring the existence of something that is fundamentally impossible to detect, is a poor resolution to the problem. If there are many worlds, how is it decided which one we are in? MWI is scientifically equivalent to collapse, it's just imagined as a branching instead of a selection among alternatives.

MWI is what happens when you don't require the existence of anything extra (collapse phenomenon). It's like how isn't an unexplained phenomenon--it results from the evolution of the observer's perspective. In MWI there is no event corresponding to collapse for the same reason that Gallileo's model doesn't have any correlate of epicycles.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#33

Post by pmiller2 »

gus_massa wrote: post #2

> Bohr postulated a distinction between the quantum world and the world of everyday objects. A “classical” object is an object of everyday experience. It has, for example, a definite position and momentum, whether observed or not. A “quantum” object, such as an electron, has a different status; it’s an abstraction. Some properties, such as electrical charge, belong to the electron abstraction intrinsically, but other…

> Macroscopic objects are quantum objects. But when the mass is big enough, the position and momentum can be defined simultaneously with an error that is so small that you can just ignore the uncertainty and approximate them as classical objects.

Exactly. And, due to quantum tunnelling, there's a teeny tiny chance I could walk through a wall, but because there are a lot of particles in me that all have to tunnel a relatively large distance, and the probability of even one of my particles tunnelling that far is so tiny, it won't happen.

Intuitively, the difference between quantum and classical objects is a lot like the central limit theorem. Add up a bunch of uncertainties, all of which have similar distributions, and you're going to get something with a very small variance (uncertainty).

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#34

Post by whatshisface »

philipov wrote: post #29
whatshisface wrote: post #21

Earlier quoted context omitted.

A route other than "dividing the world into two categories," has been available since the early days of quantum mechanics, if you believe in many worlds you don't have that problem. It is important to recognize that we are not talking about physics here, we are talking about philosophy. If anything, the greatest shock of quantum mechanics is how it shows that "questions we naturally want to ask about the natural worl…

And that is exactly why it isn't a paradox in quantum mechanics. Quantum mechanics is consistent for the domain of questions it was designed to ask: particle scattering experiments. It's when people push it into philosophy or other unintended domains that they run into problems.

Quantum mechanics is also totally consistent for materials science problems, astrophysical problems (pending gravity), chemical problems (including human beings), and so on. It's really the philosophy that has a quantum mechanics problem. ;)

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#35

Post by Sylos »

gus_massa wrote: post #2

> Bohr postulated a distinction between the quantum world and the world of everyday objects. A “classical” object is an object of everyday experience. It has, for example, a definite position and momentum, whether observed or not. A “quantum” object, such as an electron, has a different status; it’s an abstraction. Some properties, such as electrical charge, belong to the electron abstraction intrinsically, but other…

> This is a common error. Macroscopic "everyday" objects don't have a definite position and momentum. Macroscopic objects are quantum objects. But when the mass is big enough, the position and momentum can be defined simultaneously with an error that is so small that you can just ignore the uncertainty and approximate them as classical objects.

To put this into simpler terms:

Whenever we measure something, we need to throw something at it and then have that something rebound and hit us again. In most experiments, we throw photons and have them rebound into our eyes.

Throwing a photon against a "classical object" - a chair, a ladder, bacteria - is like throwing a tennis ball against a skyscraper. You throwing that does not have no effect at all, but it's very much negligible.

But when trying to measure quanta, you're now throwing your tennis ball at a football, or at another tennis ball. You're gonna be lucky, if it rebounds at all, instead of just pushing the object that you're trying to measure out of the way. (You also don't have any smaller balls to throw.)

That's why when you measure something in quantum physics, you only know that it has this exact value in the moment that you measure it. It's going to be pushed away because you threw something at it, so after your measurement it has a different value.

You also can't observe it over a longer period, so there's no way to know whether it was only in that moment at your measured position or a long time beforehand.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#36

Post by atq2119 »

mjfl wrote: post #26
philipov wrote: post #16

Earlier quoted context omitted.

Yes it is. Measurement is entanglement between the observed system and the observing system. Wave function collapse is an illusion caused by the two systems no longer being separable. They have entered a mixed state. It looks like information is lost in the observed system only because you are ignoring the observer.

You've just replaced the problem of collapse with the problem of which universe we transition to. We are only in one.

To be more precise, we are in all of them, but our consciousness only perceives one of them.

So the real problem isn't in quantum mechanics, it's in what the hell consciousness is and why it works the way it does.

However, note that you can have observations performed by a computer which e.g. counts events, and the counter will exist in all "worlds" (branches of the universal wave function, really), while each incarnation of it only "perceives" one such "world". So the physics works just fine even while we don't fully understand consciousness.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#37

Post by TheOtherHobbes »

philipov wrote: post #29
whatshisface wrote: post #21

Earlier quoted context omitted.

A route other than "dividing the world into two categories," has been available since the early days of quantum mechanics, if you believe in many worlds you don't have that problem. It is important to recognize that we are not talking about physics here, we are talking about philosophy. If anything, the greatest shock of quantum mechanics is how it shows that "questions we naturally want to ask about the natural worl…

And that is exactly why it isn't a paradox in quantum mechanics. Quantum mechanics is consistent for the domain of questions it was designed to ask: particle scattering experiments. It's when people push it into philosophy or other unintended domains that they run into problems.

QM and GR are inconsistent. If you don't see that as a fundamental research problem you're not doing science, you're just treading water.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#38

Post by whatshisface »

mjfl wrote: post #25
whatshisface wrote: post #17

Earlier quoted context omitted.

To further build on what you're saying, by bringing in the concept of a measure-er we have already entered the domain of philosophy, because the special class "measure-er" belongs to the Copenhagen interpretation and the interpretation of quantum mechanics is a philosophical issue by virtue of the fact that it will never be decided experimentally.

Philosophical issues mean that the theory is wrong and new physics will come from their resolution, and thus philosophical issues can be decided experimentally.

We may be using different definitions of the word philosophical. I'm classifying anything that can be decided experimentally as scientific. These interpretations are identical from an experimental standpoint.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#39

Post by nikofeyn »

aik wrote: post #14
nikofeyn wrote: post #10

Earlier quoted context omitted.

you could say that about any paradox. it other words, it isn't a helpful position because it doesn't give any insight. why even have the word paradox? plus, our intuition is just as much a part of reality as your "reality".

Your definition of reality here is unrelated to the OP's point. Quantum mechanics will work the way it does regardless of what your intuition on how it should work thinks. Also the emergence of an apparently paradox is a great heuristic that raises the question of whether our intuition and understanding is wrong or correct.

i didn't define reality, although i implied it to be everything, which was a counterpoint to the commenter's implication that quantum mechanics is reality and our intuition is somehow separate from that.

> Quantum mechanics will work the way it does regardless of what your intuition on how it should work thinks.

i didn't say otherwise, although i think what you've stated is debatable.

Re: Why have so many physicists shrugged off the paradoxes of quantum mechanics?

#40

Post by TheOtherHobbes »

firethief wrote: post #32
gowld wrote: post #20

Earlier quoted context omitted.

Requiring the existence of something that is fundamentally impossible to detect, is a poor resolution to the problem. If there are many worlds, how is it decided which one we are in? MWI is scientifically equivalent to collapse, it's just imagined as a branching instead of a selection among alternatives.

MWI is what happens when you don't require the existence of anything extra (collapse phenomenon). It's like how isn't an unexplained phenomenon--it results from the evolution of the observer's perspective. In MWI there is no event corresponding to collapse for the same reason that Gallileo's model doesn't have any correlate of epicycles.

In MWI the event corresponding to collapse is the supposed appearance of an entire universe, which is - conveniently - impossible to detect. And which "explains" any one timeline of experience as "Actually, that's still just random."

So MWI goes from "That's random and we don't know why" to "That's random, we don't know why, but now we've added a universe too, although we can't prove it exists."

Something about this doesn't seem entirely convincing.

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