Free will and the Many-Worlds interpretation of QM

[accelafine]

I did watch an MIT lecture on Youtube on that experiment. I don't recall him mentioning its name though. I do recall noticing that there seemed to be NO females in the lecture hall. How can anyone not be interested in this? I just wish my maths/physics knowledge was better (and my brain in general)

Yeah it's definitely super interesting, though maybe not that easy to talk about in a way that interests most people.

So I consider this to be almost a simplified version of the double slit experiment, because really the same things happen in both experiments: when the experimenter adjusts the experiment so that they know which path it took, it acts as if it took one path - when the particle can take both paths unperturbed, however, somehow the availability of both paths allows interference to occur.

So what does this all have to do with free will? Well, depending on how you view free will (which is a philosophical issue rather than a physical one), potentially nothing at all.

The two large schools of thought wherein people argue we have free will are libertarian free will and compatibilist free will. For compatibilists, how exactly physics functions doesn't have much bearing on the question of free will at all - a compatibilist free will is compatible with any physics that might underpin our world. For at least some, maybe most, libertarians, however, "randomness" is required for freedom.

https://www.informationphilosopher.com/ ... of%20atoms.

Whether or not randomness exists in the world at the quantum level is apparently a matter of interpretation. The particle goes through the slit, but what decides where the particle actually lands? Why did it land in this band instead of that band? There are deterministic ideas of quantum physics, like bohmian mechanics, where they say there's a specific bit unmeasurable or unpredictable reason why it landed here instead of there; there are interpretations that involve randomness, like Copenhagen, which say that the wave function decides the probability distribution but the actual result is kind of randomly selected by the universe among the available options; and then there's Many Worlds, which I would argue is kind of a hybrid view. It's meta-deterministic, but from inside the universe it feels random, it feels indistinguishable from Copenhagen.

Do you think randomness is required for free will?

I"m not sure if you are genuinely interested in what I think, or if you are just trying to show off your 'superior knowledge'. Judging by your past behaviour I suspect it's the latter. I'm not easily fooled

[Flannel Jesus]

I"m not sure if you are genuinely interested in what I think, or if you are just trying to show off your 'superior knowledge'. Judging by your past behaviour I suspect it's the latter. I'm not easily fooled

Have I been anything other than polite here? Yes, I'm interested - out of everybody in the forum, I'm probably in the top 2 or 3 interested in this conversation with you, maybe top 1.

What do you think?

[accelafine]

I"m not sure if you are genuinely interested in what I think, or if you are just trying to show off your 'superior knowledge'. Judging by your past behaviour I suspect it's the latter. I'm not easily fooled

Have I been anything other than polite here? Yes, I'm interested - out of everybody in the forum, I'm probably in the top 2 or 3 interested in this conversation with you, maybe top 1.

What do you think?

Is that why you were such a pr1ck on the other thread about this? And I know enough to know that you don't know any more than I do.

[Flannel Jesus]

Is that why you were such a pr1ck on the other thread about this? And I know enough to know that you don't know any more than I do.

You made this thread obviously because you wanted to talk about it. I also want to talk about it.

If you don't want to talk about it with me, you can go back to conversing with Henry Quirk and IC.

I also don't know what other thread you're talking about. You seem to have a grudge about something I've long forgotten.

[accelafine]

There aren't a lot of QM threads on here. You must have the memory of a goldfish to not remember.

Physics and philosophy are not mutually exclusive. What would physics be without philosophy? It wouldn't exist.

[Flannel Jesus]

There aren't a lot of QM threads on here. You must have the memory of a goldfish to not remember.

Physics and philosophy are not mutually exclusive. What would physics be without philosophy? It wouldn't exist.

You can sit on your grudges, despite the fact that we've had a perfectly fine conversation up until you decided to bring up your grudges again, and not continue literally the only conservation where another person was seriously talking about the things you want to talk about...

or you can at least temporarily forget all the times I was a jerk to you, just like I've been temporarily forgetting all the times you were a jerk to me - there's plenty of that too, I haven't brought it up until now because it's simply not relevant - and we can maybe talk about a thing which mutually interests us both, and which hasn't seemed to interest much of the rest of the forum, like we have been.

[accelafine]

There aren't a lot of QM threads on here. You must have the memory of a goldfish to not remember.

Physics and philosophy are not mutually exclusive. What would physics be without philosophy? It wouldn't exist.

You can sit on your grudges, despite the fact that we've had a perfectly fine conversation up until you decided to bring up your grudges again, and not continue literally the only conservation where another person was seriously talking about the things you want to talk about...

or you can at least temporarily forget all the times I was a jerk to you, just like I've been temporarily forgetting all the times you were a jerk to me - there's plenty of that too, I haven't brought it up until now because it's simply not relevant - and we can maybe talk about a thing which mutually interests us both, and which hasn't seemed to interest much of the rest of the forum, like we have been.

I just don't buy that you are interested in anything I have to say. Prove me wrong.

[Flannel Jesus]

I just don't buy that you are interested in anything I have to say. Prove me wrong.

There's no way to prove my mental state to you outside of telling you it. I can tell you I'm sad, there's no way for you to know I'm sad other than me saying it. Maybe I'm happy and I'm lying, or maybe I'm telling the truth and I'm sad.

I've had an honest conversation with you in this thread up to this point, I don't see why I would start lying now. I'm interested in what you have to say about the relationship between free will and randomness. There's no proof beyond me saying it.

Worst case scenario, you take me seriously, you share your thoughts, and... what? I say "sike! I was only faking. I can't believe you'd think I was interested". That's not that bad haha, you're on a philosophy forum, talk a bit about your philosophy. I won't say sike, I pinky swear

[Harbal]

And if you instead keep the bottom path intact and remove the top path, you get a really similar result: the 50% that go up top get sent out into space, and of the ones remaining, they hit the mirror at the bottom, then the beam splitter, and 50% of the ones remaining are seen by Output1 and 50% by Output2

bottom-only.jpg

Again, straight forward, doing exactly the things we would expect these mirrors to do.

So naturally, when you allow the photons to take both paths, what should happen? Well surely just the combined results of the ones that take the top path and the ones that take the bottom path. So 50% at Output1 and 50% at Output2, right? That would be the intuitive expectation.

But that's not what happens. What happens is:

weird.jpg

ALL of the photons go to one detector, and NONE of them go to the other detector.

And, crucially, this doesn't just happen when you're sending a stream of photons, it happens even when you send one at a time.

So what's so weird about that? Well, because most peoples intuition would tell them, either the photon took the top path or the bottom path - if it took the top path, we know 50% of them end up at Output1 and 50% at Output2. If it took the bottom path, we know 50% of them end up at Output1 and 50% at Output2. Every photon MUST have taken one of the two paths, so... why are they all ending up at Output1?

And the bizarre answer that seems to explain our observations is, the photon did not in fact either take the top path or the bottom path. There is some sense in which the photon kind of took both paths.

You can't really explain these results in any sensible way if you view photons as little balls that take one path or the other. Our only working models of quantum physics require modelling it as if the universe is calculating both paths simultaneously, and the "wave functions" of these paths can intefere with each other.

Do the photons travel in a single stream, or are they part of a sort of beam? If that's a stupid question, could you pretend it isn't?

All the photons go to one output, but is it always the same output, ie. output 1?

Do the photons from both paths hit the final splitter at exactly the same point, so that the streams are merged when they leave the splitter? If so, do we know what would happen if they hit the splitter at different points and then were deflected so that they only came together at the point of hitting the detectors/outputs?

On the top path, there is a symbol labelled relative phase difference. What's happening there?

[Flannel Jesus]

And if you instead keep the bottom path intact and remove the top path, you get a really similar result: the 50% that go up top get sent out into space, and of the ones remaining, they hit the mirror at the bottom, then the beam splitter, and 50% of the ones remaining are seen by Output1 and 50% by Output2

bottom-only.jpg

Again, straight forward, doing exactly the things we would expect these mirrors to do.

So naturally, when you allow the photons to take both paths, what should happen? Well surely just the combined results of the ones that take the top path and the ones that take the bottom path. So 50% at Output1 and 50% at Output2, right? That would be the intuitive expectation.

But that's not what happens. What happens is:

weird.jpg

ALL of the photons go to one detector, and NONE of them go to the other detector.

And, crucially, this doesn't just happen when you're sending a stream of photons, it happens even when you send one at a time.

So what's so weird about that? Well, because most peoples intuition would tell them, either the photon took the top path or the bottom path - if it took the top path, we know 50% of them end up at Output1 and 50% at Output2. If it took the bottom path, we know 50% of them end up at Output1 and 50% at Output2. Every photon MUST have taken one of the two paths, so... why are they all ending up at Output1?

And the bizarre answer that seems to explain our observations is, the photon did not in fact either take the top path or the bottom path. There is some sense in which the photon kind of took both paths.

You can't really explain these results in any sensible way if you view photons as little balls that take one path or the other. Our only working models of quantum physics require modelling it as if the universe is calculating both paths simultaneously, and the "wave functions" of these paths can intefere with each other.

Do the photons travel in a single stream, or are they part of a sort of beam? If that's a stupid question, could you pretend it isn't?

Not a stupid question, it happens either way. It happens when you send a beam, it happens when you send 1 photon per second.

All the photons go to one output, but is it always the same output, ie. output 1?

Yes

Do the photons from both paths hit the final splitter at exactly the same point, so that the streams are merged when they leave the splitter?

They don't come in at exactly the same point, but they leave the splitter in a way that makes it indistinguishable where they came from, yeah

On the top path, there is a symbol labelled relative phase difference. What's happening there?

If you change the phase shift of the beam splitter, you can get different interference patterns. I've described what happens if you set it up for complete interference, but the interference is actually adjustable.

[Flannel Jesus]

If it only happened when there was a stream, it might not be that quantumly-weird - because you could always explain interference by different photons interfering with each other. But because it also happens with 1 photon at a time, you know it has some quantum weirdness - how can 1 photon be interfering with itself, just because you opened up another path for it to take?

[Harbal]

On the top path, there is a symbol labelled relative phase difference. What's happening there?

If you change the phase shift of the beam splitter, you can get different interference patterns. I've described what happens if you set it up for complete interference, but the interference is actually adjustable.

I don't understand that at all. I'm out of my depth, but thanks.

[Flannel Jesus]

On the top path, there is a symbol labelled relative phase difference. What's happening there?

If you change the phase shift of the beam splitter, you can get different interference patterns. I've described what happens if you set it up for complete interference, but the interference is actually adjustable.

I don't understand that at all. I'm out of my depth, but thanks.

It's okay to just pretend like that doesn't exist, unless you're actually doing quantum experiments or want to do real calculations

[Harbal]

If you change the phase shift of the beam splitter, you can get different interference patterns. I've described what happens if you set it up for complete interference, but the interference is actually adjustable.

I don't understand that at all. I'm out of my depth, but thanks.

It's okay to just pretend like that doesn't exist, unless you're actually doing quantum experiments or want to do real calculations

I want to be mystified and amazed by all this quantum stuff, but it's hard when you don't understand how the experiments work.

[Flannel Jesus]

I don't understand that at all. I'm out of my depth, but thanks.

It's okay to just pretend like that doesn't exist, unless you're actually doing quantum experiments or want to do real calculations

I want to be mystified and amazed by all this quantum stuff, but it's hard when you don't understand how the experiments work.

The most important thing to be amazed by here is just that there is such a mirror (or beam splitter), which can be set up in such a way, that having both paths available for a single photon is enough to prevent it from one output and make all of them go to the other output, but when you block the top path or the bottom path, the photons get split 50/50 between output1 and output2. This is enough to strongly imply that an individual photon doesn't just simply take an individual path when both paths are open.

The naive view would be, "this photon went from point a to point b, it obviously either took the bottom path or the top, I just don't know which path it took". It seems experimentally as though the naive view cannot be the case.