In fact, one of the great mysteries of physics right now is why only quantum objects have that property, and in order to figure that out we have to figure out what interaction “observation” actually is.

This does not stroke with my understanding of quantum physics. As far as we know there is no clear distinction between “quantum objects” vs “non-quantum objects”. The double slit experiment has been reproduced with molecules as large as 114 atoms, and there seems no reason to believe that would be the upper limit: https://www.livescience.com/19268-quantum-double-slit-experiment-largest-molecules.html

This proves that the wave is in fact real, because we can see the effects of it.

The only part that’s proven is the interference pattern. So yes, we know it acts like a wave in that particular sense. But that’s not the same thing as saying it is a wave in the physical sense. A wave in the classic physical sense doesn’t collapse upon observation. I know it’s real in an abstract sense. I’m just questioning the physical nature of that reality.

[–] Sombyr@lemmy.zip 1 points 7 months ago (2 children)

There shouldn't be a distinction between quantum and non-quantum objects. That's the mystery. Why can't large objects exhibit quantum properties? Nobody knows, all we know is they don't. We've attempted to figure it out by creating larger and larger objects that still exhibit quantum properties, but we know, at some point, it just stops exhibiting these properties and we don't know why, but it doesn't require an observer to collapse the wave function.
Also, can you define physical for me? It seems we have a misunderstanding here, because I'm defining physical as having a tangible effect on reality. If it wasn't real, it could not interact with reality. It seems you're using a different definition.

[–] bunchberry@lemmy.world 1 points 4 months ago

There shouldn’t be a distinction between quantum and non-quantum objects. That’s the mystery. Why can’t large objects exhibit quantum properties?

What makes quantum mechanics distinct from classical mechanics is the fact that not only are there interference effects, but statistically correlated systems (i.e. "entangled") can seem to interfere with one another in a way that cannot be explained classically, at least not without superluminal communication, or introducing something else strange like the existence of negative probabilities.

If it wasn't for these kinds of interference effects, then we could just chalk up quantum randomness to classical randomness, i.e. it would just be the same as any old form of statistical mechanics. The randomness itself isn't really that much of a defining feature of quantum mechanics.

The reason I say all this is because we actually do know why there is a distinction between quantum and non-quantum objects and why large objects do not exhibit quantum properties. It is a mixture of two factors. First, larger systems like big molecules have smaller wavelengths, so interference with other molecules becomes harder and harder to detect. Second, there is decoherence. Even small particles, if they interact with a ton of other particles and you average over these interactions, you will find that the interference terms (the "coherences" in the density matrix) converge to zero, i.e. when you inject noise into a system its average behavior converges to a classical probability distribution.

Hence, we already know why there is a seeming "transition" from quantum to classical. This doesn't get rid of the fact that it is still statistical in nature, it doesn't give you a reason as to why a particle that has a 50% chance of being over there and a 50% chance of being over here, that when you measure it and find it is over here, that it wasn't over there. Decoherence doesn't tell you why you actually get the results you do from a measurement, it's still fundamentally random (which bothers people for some reason?).

But it is well-understood how quantum probabilities converge to classical probabilities. There have even been studies that have reversed the process of decoherence.

[–] arendjr@programming.dev 1 points 7 months ago (1 children)

can you define physical for me?

The distinction I tend to make is between physical using the classical definition of physics (where everything is made of particles basically) and the quantum mechanical physics which defies “physical” in the classical sense. So far we’ve only been able to scientifically witness quantum physics in small particles, but as you say, there’s no reason it can’t apply at a macro scale, just… we don’t know how to witness it, if possible.

it doesn’t require an observer to collapse the wave function

Or maybe it does? The explanation I have for us being unable to apply the experiments at a larger scale is that as we scale things up, it becomes harder and harder to avoid accidental observation that would taint the experiment. But that’s really no more than a hunch/gut feeling. I would have no idea how to prove that 😅

[–] Sombyr@lemmy.zip 2 points 7 months ago (1 children)

I see, so your definition of "physical" is "made of particles?" In that case, sorta yeah. Particles behave as waves when unobserved, so you could argue that they no longer qualify as particles, and therefore, by your definition, are not physical. But that kinda misses the point, right? Like, all that means is that the observation may have created the particle, not that the observation created reality, because reality is not all particles. Energy, for instance, is not all particles, but it can be. Quantum fields are not particles, but they can give rise to them. Both those things are clearly real, but they aren't made of particles.
On the second point, that's kinda trespassing out of science territory and into "if a tree falls in the forest" territory. We can't prove that a truly unobserved macroscopic object wouldn't display quantum properties if we just didn't check if it was, but that's kinda a useless thing to think about. It's kinda similar to what our theories are though, in that the best theory we have is that the bigger the object is, the more likely the interaction we call "observation" just happens spontaneously without the need for interaction. Too big, and it's so unlikely in any moment for it not to happen that the chances of the wave function not being collapsed in any given moment is so close to zero there's no meaningful distinction between the actual odds and zero.

[–] arendjr@programming.dev 2 points 7 months ago

Agreed on all counts, except it being useless to think about :) It’s only useless if you dismiss philosophy as interesting altogether.

But that kinda misses the point, right? Like, all that means is that the observation may have created the particle, not that the observation created reality, because reality is not all particles.

I guess that depends on the point being made. You didn’t raise this argument, but I often see people arguing that the universe is deterministic and therefore we cannot have free will. But the quantum mechanical reality is probabilistic, which does leave room for things such as free will.

I can agree with your view to say observation doesn’t create reality, but then it does still affect it by collapsing the wave function. It’s a meaningful distinction to make in a discussion about consciousness, since it leaves open the possibility that our consciousness is not merely an emergent property of complex interaction that has an illusion of free will, but that it may actually be an agent of free will.

And yes, I fully recognise this enters into the philosophical realm and there is no science to support these claims. I’m merely arguing that science leaves open a path that enters that realm, and from there it is up to us to make sense of it.

There is the philosophical adage “I think therefore I am”, which I do adhere to. I know I am, so I’ll consider as flawed any reasoning that says I’m not. Maybe that just makes me a particularly stubborn scientific curiosity, but I like to think I’m more than that :)