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There's no need for Wave Function collapse or Measurement in Quantum Mechanics

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posted on Mar, 26 2020 @ 06:19 AM
The idea of wave function collapse and measurement has caused so many unnecessary problems when it comes to Quantum Mechanics. Both of these things are nowhere in the theory; they're just postulated because you have a wave function of a quantum system that consists of probable states the particle can be in and once you have knowledge of the state the probabilities go away. Now you’re left with a single state. Scientists assumed there must be collapse of the wave function caused by a measurement.

This leads us to two central problems with Quantum Mechanics. How do you explain wave function collapse and the measurement problem? The problem, no pun intended, is that neither of these things are anywhere in the theory of Quantum Mechanics. Again, they’re just postulated in an ad hoc way to explain features that we see in experiments on quantum systems.

There’s a simple yet elegant answer to this. It’s found in the Relational interpretation of Quantum Mechanics and the recent Wigner’s friend experiment.

Simply, no collapse or measurement occurs. Here’s an explanation from Relational Quantum Mechanics that’s just mind blowing.

All physical interactions are, at bottom, quantum interactions, and must ultimately be governed by the same rules. Thus, an interaction between two particles does not, in RQM, differ fundamentally from an interaction between a particle and some "apparatus". There is no true wave collapse, in the sense in which it occurs in the Copenhagen interpretation.

Because "state" is expressed in RQM as the correlation between two systems, there can be no meaning to "self-measurement". If observer O measures system S, S's "state" is represented as a correlation between O and S. O itself cannot say anything with respect to its own "state", because its own "state" is defined only relative to another observer, O'. If the S+O compound system does not interact with any other systems, then it will possess a clearly defined state relative to O'. However, because O's measurement of S breaks its unitary evolution with respect to O, O will not be able to give a full description of the S+O system (since it can only speak of the correlation between S and itself, not its own behaviour). A complete description of the (S+O)+O' system can only be given by a further, external observer, and so forth.

Taking the model system discussed above, if O' has full information on the S+O system, it will know the Hamiltonians of both S and O, including the interaction Hamiltonian. Thus, the system will evolve entirely unitarily (without any form of collapse) relative to O', if O measures S. The only reason that O will perceive a "collapse" is because O has incomplete information on the system (specifically, O does not know its own Hamiltonian, and the interaction Hamiltonian for the measurement).

What this says is that wave function collapse and what’s called self measurement doesn’t occur. What we call measurement isn’t a problem. It’s just some observer gaining information about a quantum system. The problem occurs because people assume a measurement must cause “collapse” even though this isn’t anywhere to be found in Quantum Mechanics or Quantum Field Theory.

So an observer gains knowledge about the quantum system and it’s wave function just expands to include the observer's obtaining knowledge. So an observer that’s entangled with the wave function of the quantum system can’t measure interference because he or she is a part of the entire system described by the wave function. So Schrodinger’s cat is alive and dead.

Now, an observer O’ that’s external to the S+O system in the lab in the case of Wigner’s friend, is a quantum system and Wigner can do an interference measurement and see his friend, the system and the lab in a superposition of both states.

So the wave function never collapses. Here’s an example.

Wigner’s friend is in the lab carrying out the double slit experiment. The friend sees interference when a photon gun is shooting photons at the two slits.

The friend puts an apparatus next to one of the slits to obtain which path information. The photon behaves like a particle now. This isn’t due to collapse but now the wave function extends to the apparatus next to the slit. The friend gains knowledge about the system and now the wave function extends to the friend and the lab.

No collapse or measurement to cause collapse. The friend sees a classical particle because he’s now a part of the wave function of the quantum system and him, the apparatus and the lab in a superposition of all measurements that can occur.

Wigner outside the lab can confirm this by doing an interference measurement on the results and the system. So Wigner acts as a super observer O’ that can measure and see interference between S+O in the lab.

This has profound implications because it shows, different observers can reach different outcomes of an event. It also shows that a system whether quantum or classical in size is never in a state of collapse. They’re always entangled with some wave function.

What does this show about parallel universes? Say Wigner’s friend is measuring the polarization of a photon. He starts with the wave function that says photon is vertical/photon is horizontal. When he carries out a measurement he only sees a result locally from his frame of reference which is that the photon is vertical or the photon is horizontal. Both of these states exist in superposition but each friend can only measure the state in his or her frame of reference. Wigner outside can measure both states and see interference.

Now, Wigner finds out the results. He’s now part of the system and there’s 2 Wigner’s. One who’s in a universe where his friend measures v and one where his friend measures h. Wigner’s Uncle can act as a super observer and measure interference between all 4 states. These 2 states, Wigner+friend v and Wigner+friend h will eventually decohere and evolve as two separate universes.

So what we call a measurement is observer dependent and is relative to the frame of reference(lab in this case) between S and O.

So this interpretation treats collapse and measurement like Einstein treats the distinction between past, present and future. These things are both relative to the observer’s frame of reference.

posted on Mar, 26 2020 @ 08:17 AM
a reply to: neoholographic

But why so complicated? The wavefunction y(t;v) collapses because you pick a point t when you measure, because you know t you lose the possibility to know v that's just how the uncertainty principle works.
I don't see why that would be a problem? Why I have to invent a system plus observer, plus observer' ....

Think of the little fermion moving around, doing its wave business, if you want to know how fast and which direction it's going you can't nail it to one place because that would mean it loses what you want to know about it. You have to allow for a certain period of t and live with the fact that there's a certain area where it might have been. Now you want to know where it was at the point t: you have to nail it down.
That doesn't do anything to the fermion itself it's just the information you extract.
A wave is some type of movement in time, a function. If you set a point on the t axis as n it "collapses" because you make the description of the movement a simple coordinate. It's no longer a wave function.
And if you invent millions of additional observers it doesn't change that fact.

Also of course the measurement is relative to the one doing the experiment, they could hardly measure what's happening outside of their experiment so... wtf? How is that a statement worth making?

posted on Mar, 26 2020 @ 08:34 AM
Personally I love physics, I love maths, deepest respect for everybody who's smart enough to do it (I'm just a observer) but
If you have to invent 11 dimensions and parallel universes and that at each point a decision is made you split up into infinity... that's maybe good for mental masturbation, but it's not science.

posted on Mar, 26 2020 @ 09:39 AM
a reply to: Peeple

You said:

Also of course the measurement is relative to the one doing the experiment, they could hardly measure what's happening outside of their experiment so... wtf? How is that a statement worth making?

That statement is the key. It's saying whether QM is observer dependent or observer independent.

Wigner's friend is observer dependent. Here's the paper that confirmed Wigner's friend on microscopic scales.

Experimental test of local observer independence

The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the objectivity of observations is not so clear, most markedly exposed in Wigner’s eponymous thought experiment where two observers can experience seemingly different realities. The question whether the observers’ narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. In a state-of-the-art six-photon experiment, we realize this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

What this shows is that what we call wave function collapse and measurement is relative to the observer. So there's only measurement and collapse in the lab because the friend becomes entangled with the wave function of the quantum system. For Wigner outside the lab, it doesn't collapse and he can still measure interference.

This is vs. observer independence which pushes things like a universal wave function. So independent of observation, the universal wave function is the same for all observers,

This is a huge difference between a Relational interpretation of QM and Many Worlds. Many Worlds is observer independent and independent of the observer there's a universal wave function.

The Relational interpretation is observer dependent and says there isn't a universal wave function. Rovelli applies Relativity to QM in this way. He says there's no absolute or universal wave function so a measurement just like time is relative to the observer's frame of reference.

Like I said, that's a huge difference.

posted on Mar, 26 2020 @ 10:15 AM
a reply to: neoholographic

But you still didn't understand that the wave function collapse is an experimental process and not a property of the wave.

Think of a beam of light you got a stream of photons each on their own oscillating in a nice sinus wave through the room and I got that recorded with super (hypothetical) hightech equipment, every three-ish metres every 10^-8 seconds a frame. In between the frames all I know is the photon I'm observing is moving in that direction with its speed. But each frame equals an observer because there is no more wave, there's just a "picture" of a certain light package at a certain place at a certain time.

That doesn't collapse the lightbeam, just my mathmatical prediction turns from a wave with amplitude, frequency etc into "3rd frame; t=10^-6" coordinates.
The observer is just a certain point in time and space.
The collapse more or less a derivative of the wave function for the purpose of extracting information.

posted on Mar, 26 2020 @ 10:21 AM
I'm going to go with the many scientists that disagree...

a reply to: neoholographic

posted on Mar, 27 2020 @ 10:23 AM
Imagine a four person tug-of-war between Einstein, Heisenberg, Schrodinger and Tesla.
Ramanujan is the referee, just for added 'clarity'.
In the end, everybody's got a piece of the rope but nobody "wins".


posted on Mar, 27 2020 @ 02:26 PM

originally posted by: hombero
I'm going to go with the many scientists that disagree...

a reply to: neoholographic
That's a loaded statement...scientists don't even agree with each other on this subject. Not even 50% of the physicists polled believed the Copenhagen interpretation taught in textbooks is correct (which teaches wave function collapse).

A Snapshot of Foundational Attitudes Toward Quantum Mechanics

The sample size was small so the percentages are not a rigorous projection for the scientific community, but the idea that scientists don't agree on this topic is hard to argue with.

See "i. Relational quantum mechanics" in the graph. The 2011 poll shows 6% of the participants favoring the Relational quantum mechanics interpretation which is the topic of this thread.

The wikipedia link neo posted should be close enough for government work, but when neoholographic starts ad-libbing his own perceptions, I would take anything he says with a huge grain of salt.

originally posted by: neoholographic
Simply, no collapse or measurement occurs. Here’s an explanation from Relational Quantum Mechanics that’s just mind blowing.

That's a possibility, that no collapse occurs, but we don't really know. According to the 2011 poll, the highest percentage of responses (42%) believe it does (per the Copenhagen interpretation), but there are plenty who believe in alternate ideas where the wave function doesn't collapse. So far, nobody has been able to prove which interpretation is right, so these are competing ideas without conclusive proof until someone can come up with proof of which interpretation is correct.

edit on 2020327 by Arbitrageur because: clarification

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