Thank you for the explanation! Almost got into an argument a while back because someone was conflating the layman definition with the QM definition as proof of some kinda metaphysical effect of the human consciousness.
Comment on Don't look now
cynar@lemmy.world 7 months ago
For those confused, it’s worth noting the difference between observed as a layman concept and as a quantum mechanical one.
In QM, to observed is to couple the observer to the “system” being observed. Think of it like “observing” your neighbour, over a fence using a BB gun. When you hit flesh, you know where your neighbour is. Unfortunately, the system has now been fundamentally changed. In a classical system, you could turn down the power, until your neighbour doesn’t notice the hits. Unfortunately, QM imposes fundamental limits on your measurements (heisenburg and his uncertainty principal). In order to observe your neighbour accurately, you need to hit them hard enough that the will also feel it and react differently.
QM behaves in a similar way. Initially, the system is just a single particle, and is not very restrained. This allows it to behave in a very wave like manner. When you observe it, the system now includes the whole observation system, as this coupling propagates, more and more atoms etc get linked. The various restraints cause an effect called decoherence. The system behaves ever more like a classical physical system.
In short, a quantum mechanical “observer” is less sneaky watching, and more hosing down with a machine gun and watching the ricochets.
DumbAceDragon@sh.itjust.works 7 months ago
Zoboomafoo@slrpnk.net 7 months ago
Sure, but that still means the photons derender when nobody is watching them
Rin@lemm.ee 7 months ago
I mean, how else are you going to optimise an open world simulation this big?
where_am_i@sh.itjust.works 7 months ago
That’s a pretty misleading explanation. You’re not applying any force to the system by observing it.
cynar@lemmy.world 7 months ago
Depends on how you are observing it photons impart energy and momentum. The true, detailed explanation is a lot more convoluted, it’s all wave interactions, in the complex plane. However, digesting that into something a layman can follow is difficult.
The main point I was trying to get across is that there is no such thing as an independent, external measurement. Your measurement systems minimum interaction is no longer negligible. How that is done varies, but it always changes the target and becomes part of the equations.
NewNewAccount@lemmy.world 7 months ago
Thanks! I’ve never fully grasped the concept and this really helps.
I’ve always heard it that observing was actually “measuring” and still wasn’t sure why that would impact anything but chalked it up to the quantum world being other-worldly.
Wirlocke@lemmy.blahaj.zone 7 months ago
Honestly physicists don’t actually know what measuring is either. We don’t know when exactly the system is considered “measured” in the chain of entanglement, this is called the Measurement Problem.
Answers range from “shut up don’t think about it” to “there’s an infinite amount of universes split from each other for each quantum event!”.
cynar@lemmy.world 7 months ago
We know how it works, we just don’t yet understand what is going on under the hood.
In short, quantum effects can be very obvious with small systems. The effects generally get averaged out over larger systems. A measurement inherently entangled your small system with a much larger system diluting the effect.
The blind spot is that we don’t know what a quantum state IS. We know the maths behind it, but not the underlying physics model. It’s likely to fall out when we unify quantum mechanics with general relativity, but we’ve been chipping at that for over 70 years now, with limited success.
pcalau12i@lemmygrad.ml 3 weeks ago
Why should we assume “there is something going on under the hood”? This is my problem with most “interpretations” of quantum mechanics. They are complex stories to try and “explain” quantum mechanics, like a whole branching multiverse, of which we have no evidence for.
It’s kind of like if someone wanted to come up with deep explanation to “explain” Einstein’s field equations and what is “going on under the hood”. Why should anything be “underneath” those equations? If we begin to speculate, we’re doing just tha,t speculation, and if we take any of that speculation seriously as in actually genuinely believe it, then we’ve left the realm of being a scientifically-minded rational thinker.
It is much simpler to just accept the equations at face-value, to accept quantum mechanics at face-value. “Measurement” is not in the theory anywhere, there is no rigorous formulation of what qualifies as a measurement. The state vector is reduced whenever a physical interaction occurs from the reference point of the systems participating in the interaction, but not for the systems not participating in it, in which the systems are then described as entangled with one another.
This is not an “interpretation” but me just explaining literally how the terminology and mathematics works. If we just accept this at face value there is no “measurement problem.” The only reason there is a “measurement problem” is because this contradicts with people’s basic intuitions: if we accept quantum mechanics at face value then we have to admit that whether or not properties of systems have well-defined values actually depends upon your reference point and is contingent on a physical interaction taking place.
Our basic intuition tells us that particles are autonomous entities floating around in space on their lonesome like little stones or billiard balls up until they collide with something, and so even if they are not interacting with anything at all they meaningfully can be said to “exist” with well-defined properties which should be the same properties for all reference points (i.e. the properties are absolute rather than relational). Quantum mechanics contradicts with this basic intuition so people think there must be something “wrong” with it, there must be something “under the hood” we don’t yet understand and only if we make the story more complicated or make a new discovery one day we’d “solve” the “problem.”
Einstein once said, God does not place dice, and Bohr rebutted with, stop telling God what to do. This is my response to people who believe in the “measurement problem.” Stop with your preconceptions on how reality should work. Quantum theory is our best theory of nature and there is currently no evidence it is going away any time soon, and it’s withstood the test of time for decades. We should stop waiting for the day it gets overturned and disappears and just accept this is genuinely how reality works, accept it at face-value and drop our preconceptions. We do not need any additional “stories” to explain it.
Theharpyeagle@lemmy.world 7 months ago
To be honest I still chalk it to to that.