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Electrons are easy
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this post was submitted on 11 Jul 2024
1004 points (98.8% liked)
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It's a point but it doesn't actually exist at any point. It exists in a cloud where it could exist anywhere in there.
You can observe it but doing so changes its behavior. Why? Well... Um... Maybe it's just the simulation breaking down?
It's because to observe something you have to interact with it. Dealing with particles is like playing pool in the dark and the only way you can tell where the balls are is by rolling other balls into them and listening for the sound it makes. Thing is, you now only know where the ball was, not what happened next.
In the quantum world, even a single photon can influence what another particle is doing. This is fundamentally why observation changes things.
holy shit the pool explanation is so good, I'm gonna recycle it for sure
Good metaphor
like trying to measure a soft noodle lengthwise with a caliper
So, if we had a machine that could "see" without photons, we could observe an electron directly? (I know nothing about this)
We have such devices, unfortunately they tend to use electrons instead (electron microscopes). We also have devices that just work by measuring the electromagnetic field (atomic force microscopes). Again though, to measure the field you have to interact with it, so you can't do it immaculately.
Electrons are especially hard because they are so incredibly light yet intensely charged compared to everything that can actually interact with them.
When talking about particles, the interaction very rarely involves actual contact, as that tends result in some manner of combination. Two electrons for instance don't really bounce off each other, they just get close, interact and then diverge. If a photon 'hits' an electron it gets absorbed and a new one is emitted. Look up Feynman Diagrams if you want to see some detail to this. I don't think you need any deep knowledge to benefit from looking at them, they are really quite an elegant way to visually show the mathematics.
If you suggest every observation is an interaction then you inherently are getting into the relational interpretation. Which I am not saying you're wrong to do so, I think it is the most intuitive way to think about things, but it is not a very popular viewpoint.
Do expand, please. It has been a while since I have studied this seriously. Do you have any examples of observations that don't involve interacting with the system?
That's not what I'm saying. My point is just that observation = interaction has a lot of implications. Particles are always interacting, so if the wave function represented some absolute state of a system, then the statement would just be incorrect because the wave function would be incapable of ever "spreading out" as it is constantly interacting with a lot of things yet we don't "collapse" it in the mathematics until it interacts very specifically with us.
The only way it can be made consistent is to then say that wave functions are not absolute things but instead describe something relative to a particular system, sort of like how in Galilean relativity you need to specify a coordinate system to describe certain properties like velocity of systems. You pick a referent object as the "center" of the coordinate system which you describe other systems from that reference frame.
You would have to treat the wave function in a similar way, as something more coordinate than an actual entity. That would explain why it can differ between context frames (i.e. Wigner's friend), and would explain why you have to "collapse" it when you interact with something, as the context would've changed so you would need to "zero" it again kinda like tarring a scale.
Often we leave out the referent object and it becomes implicit, such as if we say a car is traveling at 50 km/h, there is an implication here "relative to the earth." That is implied so it doesn't really need to be said, but people can become confused and think 50 km/h is really a property intrinsic to the car because we always leave it out.
That's where a lot of confusion in QM comes from: we usually are concerned with what we will observe ourselves, what will actually show up on our measuring devices, so we implicitly use ourselves and our measuring devices as the referent object and by extension forget that we are describing properties of things relative to a particular coordinate system and not absolute.
AHH, I think I see what you have misunderstood. I am not saying all interactions are observations, rather that observations are a subset of interactions, hence uncertainty.
Furthermore I think it would be more useful to say that the wave function only collapses when it is actually necessary to the interaction rather than when it interacts with 'us'. Unless you can provide a counterexample. Privileging observations made by humans reeks of mysticism in my opinion and is the cause of a lot of the misunderstandings about quantum physics among laypeople.
Saying that observations are a special kind of interaction does seem to be privileging humans, though? What is different from measurements/observations and any other interaction?
I'm neutral on the subject of if there are non-observational interactions. Though I ask again, are you aware of any observations that do not involve interactions?
Edit: I should also point out, that I don't believe an observation necessarily requires a human, mind, or intelligence.
Why do you keep asking that? I already explained I'm not claiming observations = no interactions in extensive detail and you turn around and ask me that gain.
Because you seem to have a problem with me saying that all observations are interactions.
Futher, if it is true that if observations are interactions, then RQM must be true, surely it goes from a fringe interpretation to just simple fact unless you can find a counterexample?
At this point, I'm not even sure I quite see what your point is supposed to be.
I think you are just trying to fight rather than actually have a discussion so I'm not really interested in going on, but I will say one last thing to clarify what I am saying for other people who might be reading.
If you say observation = interaction then this inherently leads you to RQM which is like the definition of the interpretation. As I said at the beginning, I do support this interpretation, I think it's the most reasonable approach, but it should be made clear this is a rather fringe point of view and not supported by most academics. You can see in the paper below only 6% of academics support it. And you clearly don't seem to support it yourself as you seem to be pushing back against that rather than just agreeing with my statement it is the most intuitive way to think about things.
https://arxiv.org/abs/1301.1069
The plurality there support the Copenhagen view where observation really is given a special role.
Without going the route of RQM then you end up with something that is just objectively false as the wave function would be incapable of spreading out since particles are always interacting with things, rendering quantum phenomena impossible.
You can clarify instead by saying observation → interaction, that is to say, an observation implies an interaction, i.e. it inherently always entails an interaction but not interactions are observations, however, if you do this, you end up with the measurement problem. That is to say, you need to actually construct a theory to account for what kinds of interactions actually qualify as a measurement/observation. To quote John Bell...
https://philpapers.org/rec/BELAM
Specifying a theory of measurement is known as an "objective collapse" model and they make different predictions than traditional quantum mechanics because depending on where you set the threshold for what kind of interaction qualifies as an "observation" changes how much the wave function can spread out before being collapsed again by such an "observation."
There are several models of this like the Ghirardi–Rimini–Weber theory and the Diósi–Penrose model but these are ultimately more than just other interpretations of quantum mechanics but ultimately entirely new theories.
It is not so simple just to say "observation is an interaction" and then pretend like the job is done, or else there would be no confusion in interpreting quantum mechanics at all. There is a lot more clarification that has to be made in order for it to make sense.
I think a lot of the confusion people have is around the word “observation” which in everyday language implies the presence of an intelligent observer. It seems totally nonsensical that the outcome of a physics experiment should depend on whether the physicist is in the lab or out for a coffee! That’s because it is!
I have this beef with a lot of words used in physics. Taking an everyday word and reusing it as a technical term whose meaning may be subtly and/or profoundly different from the original. It’s a source of constant confusion.
Physicists seem to love their confusing language. Why do they associate Bell's theorem with "local realism"? I get "local," that maps to Lorentz invariance. But what does "realism" even mean? That's a philosophical term, not a physical one, and I've seen at least 4 different ways it has been defined in the literature. Some papers use the philosophical meaning, belief in an observer-independent reality, some associate it with the outcome of experiments being predictable/predetermined, some associate it with particles having definite values at all times, and others argue that realism has to be broken up into different "kinds" of realism like "strong" realism and "weak" realism with different meanings.
I saw a physicist recently who made a video complaining about how frustrated they are that everyone associates the term "dark matter" with matter that doesn't interact with the electromagnetic field (hence "dark"), when in reality dark matter just refers to a list of observations which particle theories are currently the leading explanation for but technically the term doesn't imply a particular class of theories and thus is not a claim that the observations are explained by matter that is "dark." They were like genuinely upset and had an hour long video about people keep misunderstanding the term "dark matter" is just a list of observation, but like, why call it dark matter then if that's not what it is?
There really needs to be some sort of like organization that sets official names for terminology, kinda like how the French government has an official organization that defines what is considered real French so if there is any confusion in the language you at least have something to refer to. That way there can be some thought put into terminology used.
Yep! Same thing with black holes which are not holes at all!
Even very basic physics terms such as positive and negative electric charges lead to a lot of confusion for ordinary people. There’s nothing positive or negative about them, they’re just names for the fundamental property of protons and electrons that leads them to attract one another.
At least physicists don't call particles "Sonic Hedgehog" like biologists do with proteins
Its that an observation is always an energetic interaction. You can't measure a system without interacting with it and at the particle scale every interaction has enough energy to affect the particle in some way. Like when you light up a room you're slightly heating the molecules in it.
If your room is small enough that the light bulb is bigger than the room, this effect becomes very noticable.