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It's not supposed to make sense... (lemmy.blahaj.zone)

submitted 4 days ago by FundMECFSResearch to c/science_memes@mander.xyz

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[-] AppleTea@lemmy.zip 79 points 4 days ago

When researchers say "observe" they actually mean "measure". And when you're working with sub-atomic particles, "measure" isn't some passive activity. It's an active thing. When you measure small particles you are applying some force upon them, changing them in some way from how they would otherwise act.

Imagine if you were tasked with measuring traffic on the other side of the planet, but you had no cameras. The only tool you had was a gigantic 30 ton, satellite-networked pendulum swinging across the highway. The only way you know if there are cars on the highway is if the pendulum thwacks into one of them. That's quantum particle physics.... I think.

[-] kayzeekayzee 32 points 4 days ago

Not exactly. Quantum physics applies no matter how you measure it. The double-slit experiment is an example of this: Photons moving through two slits will form a wave interference pattern on a detector plate, even though the detector doesn't affect the position of the photons beforehand.

It's more like: when you become aware of the results of a quantum measurement, you yourself become a part of the quantum system, and being a part of the system requires measurements to have real values. Whether you should interpret this as a wave-function collapse or branching into multiple parallel universes is up for debate though.

[-] Brainsploosh@lemmy.world 6 points 4 days ago

Honest question: what happens afterwards? When we've stopped observing, does it reassemble into it's superpositive form? Are we depleting quantum states somehow?

[-] kayzeekayzee 2 points 3 days ago* (last edited 3 days ago)

Sorta! According to the Heisenberg Uncertainty Principle, there's an upper limit to how much we can "know" about the given state of a quantum system. This isn't an issue with our measurements, but a fundamental property of the universe itself. By measuring one aspect of a quantum system (for example, the momentum of a particle), we become less certain about other aspects of the system, even if we had already measured them before (such as the position of the same particle).

Though (as far as we know), we aren't going to run out of quantum states or anything like that.

[-] Brainsploosh@lemmy.world 2 points 3 days ago

Thank you for your answer!

Maybe I'm too dense, but what happens with other quantum states that aren't position/velocity based? I'm thinking things like when we collapse spin, e.g. in entangled particles.

I've heard that entangled particles are "one use", I'd assume they can be restored and possibly re-entangled, but how?

[-] kayzeekayzee 3 points 3 days ago* (last edited 3 days ago)

Good question! You are certainly not dense!

The position-momentum uncertainty relationship is just a specific case of a more general relationship. There are other uncertainty relationships, such as between time and energy or between two (separate/orthogonal) components of angular velocity. The relationships basically state that whenever you measure one of the two values, you are required to add uncertainty to the other.

Unfortunately, this is kinda where my knowledge on the subject starts to hit its limits. As for spin, it has a lot of effects on the energy of the system it's involved with, so I believe the energy-time or angular momentum exclusion principles would apply there.

You might also be thinking "why not have two entagled cloned particles, and measure the momentum of one and the position on the other?". While you can duplicate particles, there are reasons why that doesn't work that I don't really remember tbh. I'm sure PBS Spacetime on Youtube has an episode on it somewhere though if you're interested