Observation is when a scientist looks at the results of an experiment. That has nothing to do with how the experiments takes place or what the results are. — EnPassant

You will find actually that Schrodinger himself leaned towards Schopenhauer and Vedanta, both of which he wrote about in his later career.

In 1958, Schrödinger, inspired by Schopenhauer from youth, published his lectures Mind and Matter. Here he argued that there is a difference between measuring instruments and human observation: a thermometer’s registration cannot be considered an act of observation, as it contains no meaning in itself. Thus, consciousness is needed to make physical reality meaningful. As Schrödinger concluded, "Some of you, I am sure, will call this mysticism. So with all due acknowledgement to the fact that physical theory is at all times relative, in that it depends on certain basic assumptions, we may, or so I believe, assert that physical theory in its present stage strongly suggests the indestructibility of Mind by Time."

Quantum Mysticism: Gone but not Forgotten

Thus, consciousness is needed to make physical reality meaningful.

Well, that goes without saying. How can meaning exist outside a mind? I think he is talking about something slightly different here.

What if you shrunk people down to the size of an electron and used them in the famous "double slit experiment"? Would you get the same results? What would the experiences of the people be? — RogueAI

Each person would see that they pass through either the left slit or the right slit. As long as you couldn't obtain which-way information from the people or apparatus (e.g., their memory was erased after passing through the slit), then you would observe interference, otherwise not.

It's similar to the Wigner's friend thought experiment.

I just wanted to make an additional comment on the matter of the double slit experiment. It's said that the experimental electron comes off as if self-aware, capable of making observations and decisions based on these observations. If memory serves, some scientists have even gone to the extent of claiming the experimental electron comes to know if an observation has been made/not and makes a decision how to behave. Eerily close to what we mean by "person" - an agency that gathers information about the world and makes decisions based on that information. Basically, electrons behave like conscious people, albeit in a very limited way.

What if you shrunk people down to the size of an electron and used them in the famous "double slit experiment"? Would you get the same results? What would the experiences of the people be? — RogueAI

Either wavey or particley, depending on if you checked on their progress through the slits.

I think what is meant by this question has been misunderstood.

Do you mean having two slits and a stream of people in single file who must pass through one slit?

In this case we might potentially have different results, given that people can think, and can choose which slit to pass through, whereas electrons cannot.

What would the experiences of the people be? — RogueAI

There was a paper recently that was quite interesting, I'll see if I can dig it out (no joy so far). In QM, we're used to thinking of something like an electron being in a superposition of states in a lab setup like the double-slit experiment that is in a well-defined state (i.e. the position of the slits and screen being well-defined, because they're macroscopic). The paper basically asked, as applied to this context, what does the slit-and-screen setup "look like" from the electron's "point of view"? Iirc this gist is that there should be some transformation you can make that takes you from superposed-electron/defined-lab to frame with a well defined electron state, e.g. a well-defined electron position. What does the lab setup look like in this frame?

It would look pretty crazy. The positions of everything in the lab would be put into the converse superposition. So the electron would find that no slit had yet reached us, a slit had already passed us but the screen had not, and the screen had already hit us, all with associated probabilities prior to the lab's wavefunction collapse. The position of the screen that it hit would be smudged out in a banded way, which takes some working through, but is due to the fact that any point on the screen (i.e. relative to one corner) is a) already in a superposition and b) can only be hit with the moderating probability of both slits already having passed behind the electron. All of this will have happened, be happening, and be yet to happen because our well-defined electron position has made a nonsense of momentum. Then something unknown happens and the lab collapses to a single well-defined position with one point on the screen at the origin

Or: blur, blur, blur, hit by a screen.

Ah, here's the preprint: https://arxiv.org/pdf/1712.07207.pdf

Lots of maths, but check out Fig. 3. Unless you like maths, in which case I'm a douche because I basically just said: "You don't need to read it if it's too hard, just look at the pretty pictures". Damned either way, I guess :rofl:

Ah, here's the preprint: https://arxiv.org/pdf/1712.07207.pdf — Kenosha Kid

Nice find. Also here's a brief media summary of that paper, aptly titled How does a quantum particle see the world?

Unfortunately the paper doesn't directly address the double-slit experiment. It seems to me that even if the apparatus is in superposition in the electron's reference frame, the electron still needs to go through one of the slits which is then effectively an interaction with the apparatus. However the which-way information is not available to the observer (since there are no detectors on the slits), so the process remains unitary in the observer's reference frame.

This is similar to the Wigner's friend thought experiment, where Wigner's friend makes a definite measurement while the process remains unitary from Wigner's perspective.

Nice find. Also here's a brief media summary of that paper, aptly titled How does a quantum particle see the world? — Andrew M

Even better find! I was a lazy Googler; I'd read the paper before so new it existed. Thanks for making more of an effort.

It seems to me that even if the apparatus is in superposition in the electron's reference frame, the electron still needs to go through one of the slits which is then effectively an interaction with the apparatus. — Andrew M

But the electron doesn't 'go' in its rest frame, by lieu of a) it's its rest frame and b) its momentum is undefined. (That said, the paper isn't bothered about rest frames as much as un-superposed frames.) At any time, either slits already have a nonzero probability of being behind the electron.

But the electron doesn't 'go' in its rest frame, by lieu of a) it's its rest frame and b) its momentum is undefined. (That said, the paper isn't bothered about rest frames as much as un-superposed frames.) At any time, either slits already have a nonzero probability of being behind the electron. — Kenosha Kid

OK, but the puzzle is to account for what happens when the two apparatus slits go past the electron in the electron's rest frame.

If the apparatus remains in superposition when the slits go past the electron, then the apparatus should similarly remain in superposition when the back screen hits the electron. That is, no definite measurement event would ever occur in the electron's reference frame.

If a definite measurement event does occur at the back screen in the electron's reference frame then a definite measurement event should also have occurred at the slit. It seems to be a similar kind of physical interaction and so should be treated similarly.

As I see it, the electron does go through a specific slit in the electron's reference frame. That is consistent with the relational approach that the paper uses (see quote below), which is that whether a definite measurement occurs or not depends on the frame of reference.

We find that a quantum state and its features — such as superposition and entanglement — are only defined relative to the chosen reference frame, in the spirit of the relational description of physics [16–19, 23, 24]. For example, a quantum system which is in a well-localised state of an observable for a certain observer may, for another observer, be in a superposition of two or more states or even entangled with the first observer. — Quantum mechanics and the covariance of physical laws in quantum reference frames - Giacomini, Castro-Ruiz, Brukner

OK, but the puzzle is to account for what happens when the two apparatus slits go past the electron in the electron's rest frame. — Andrew M

This isn't really in the picture, though. The probability of being beyond the slits grows. That is the closest you can get to "the two apparatus slits go past the electron". You can say, e.g., the probability of the slits being behind the electron is now > 50% for thr first time. That's doable.

That is, no definite measurement event would ever occur in the electron's reference frame. — Andrew M

There's no reason why, if a superposed electron can spontaneously and probabilistically collapse, a superposed laboratory cannot. In fact, I'd suggest the opposite: in the electron's rest frame, the collapse is almost immediate. It seems longer to us due to time dilation.

If a definite measurement event does occur at the back screen in the electron's reference frame then a definite measurement event should also have occurred at the slit. — Andrew M

This is not an argument from quantum theory, I gather, more a philosophical argument as to how quantum mechanics ought to be. The double slit experiment suggests that electron collapse at the slit only occurs if we attempt to observe it at the slit, e.g. if we put something in the way of the slit that causes earlier collapse, such as an electron detector.

This is not an argument from quantum theory, I gather, more a philosophical argument as to how quantum mechanics ought to be. — Kenosha Kid

It's a relational interpretation (which the paper uses, see for example reference [23] in the earlier quote referring to Rovelli's RQM).

The double slit experiment suggests that electron collapse at the slit only occurs if we attempt to observe it at the slit, e.g. if we put something in the way of the slit that causes earlier collapse, such as an electron detector. — Kenosha Kid

Right, the electron detector provides which-way information that collapses the electron superposition in the lab observer's reference frame.

But that doesn't imply anything about what happens in the electron's reference frame when there is no detector. On a relational view, since an interaction occurs at the slit, collapse occurs in both the electron and apparatus reference frames. But collapse doesn't occur for the lab observer since which-way information is not available in the lab-observer's reference frame. So collapse is reference frame-dependent. This is analogous to a Wigner's Friend experiment where a definite measurement event occurs in the friend's reference frame but remains in superposition in Wigner's reference frame.

On a relational view, since an interaction occurs at the slit, collapse occurs in both the electron and apparatus reference frames. — Andrew M

No, the electron is in a fixed state in its frame, that's the point of the paper I linked to. The transformation takes us from a frame in which the lab is in a well-defined position and the electron in superposition to one in which the lab is in superposition and the electron has a well-defined position. It is the lab that undergoes collapse.

However, no reason not to consider an intermediate frame in which both are in superposition. But the wording of the OP, an electron-sized person's point of view, suggested specifically the frame in which the electron's position is defined.

So collapse is reference frame-dependent. — Andrew M

:up:

This is analogous to a Wigner's Friend experiment where a definite measurement event occurs in the friend's reference frame but remains in superposition in Wigner's reference frame. — Andrew M

In the Wigner's friend experiment, collapse is observer-dependent even with a given frame, e.g. the lab frame, and there's some evidence that this is correct (it is experimentally verifiable). However there's a nice symmetry here, you're right, insofar as both Wigner and his friend are well-defined wrt themselves and superposed wrt each other. It might not be a coincidence that the experimental verification of Wigner and the paper on frame transformation roughly coincided... perhaps QM is coming of age. :)

On a relational view, since an interaction occurs at the slit, collapse occurs in both the electron and apparatus reference frames.
— Andrew M

No, the electron is in a fixed state in its frame, that's the point of the paper I linked to — Kenosha Kid

Sorry, yes, just got what you meant. We are more or less on the same page.

We are more or less on the same page. — Kenosha Kid

:up: