this post was submitted on 18 Oct 2023
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Fyi, there's a lot of ~~woo woo~~ (edit: apparently racist term) crap out there that tries to make you believe that somehow the photons can feel that a human is watching them and they choose to behave differently as a result. This is not true. It just means that when you use a detector or some sort of probe that physically interacts with the photons they change their behavior. It's not magic.
The way some of such experiments are done is by creating entangled photons and observing (or not observing) the second photon. No interaction with the first photon, except mysterious instantaneous wave function collapse. Also known as Magic.
Also, their interpretation of what's happening largely falls apart with the quantum eraser variations.
If it's collapse from mechanical measurement side effects, why does it go back to an interference pattern when which path information is erased by a polarizer?
So, it's fine that you don't understand the experiment, it's really confusing and not intuitive. It's not that the photons change their behavior when measured. It's that they pass through two different slits as a probability field, and the field collapses as soon as it is measured in any way. It's not just that the behavior changes, the nature of the photon changes. It doesn't exist as a single point in spacetime until it is measured.
One of the key points that the "it's just mechanical interactions, bro" crowd should be more aware of though are the quantum eraser variations (not the delayed choice quantum eraser).
There is still something rather bizarre about mechanical interactions that measure which path information being sufficient to collapse on their own but suddenly insufficient when something like polarization which erases which path information is added back in later in the chain.
Also, it's worth declaring when giving an answer like this that you are operating under the assumptions of QFT, and that this isn't necessarily for sure what's going on. For example, I'd imagine there's Bohemian mechanics adherents still around somewhere that would take issue with your "it doesn't exist as a single point in spacetime until it's measured."
Can you explain that more simply?
I'm assuming you are asking about the first part?
So the double slit experiment was a starting point, and there's been a bunch of variations testing different aspects.
One of which is that we can 'tag' the photons that go through path A with an indication it went through path A and tag photons passing through path B accordingly.
As would be expected, when tagged this way both result in ballistic patterns as if particles and not waves.
But the neat part is that if you add a polarizer after they are tagged which removes any way of recovering the tagging information about which path they went through, the interference pattern comes back and they behave like waves again.
If the explanation for why it goes from a wave to a particle in the first place is something like "it was disturbed by the act of measurement", adding additional disturbance would seem like the last thing to get it back to behaving like a wave, right?
The variation suggests that the collapse of the wave function relates to the continued existence of recoverable information about the photon, not necessarily the physical mechanics of its measurement at that instant in time.
As for the other comments I made, the TL;DR is that there's easily a dozen different interpretations of why quantum weirdness occurs among physicists, and so very often when you see someone saying "this is how it works" what you are really seeing is "this is how it works in the theory I subscribe to" but a different physicist might have a very different explanation.
The only explanation/representation that everyone can agree on is the mathematical representation, but translating the math into a physical reality is still very much disputed from physicist to physicist.
So for example, the Bohemian mechanics view would have disagreed with the idea that the probabilistic nature of the photon before measurement is a physical reality, instead claiming that it is just a reflection of what we can know about the photon, and that it already physically is a point in spacetime that's being guided by a wave, which is why it has wave-like behavior. But don't worry too much about it - just keep in mind it's worth taking any online explanations of why quanta behave in a certain way with a giant grain of salt as it's not a settled topic.
Despite knowing so much more than we did, the ol' quip holds true,
Anyone who claims to understand quantum physics is either lying or insane.
Thanks. Do you know the many worlds interpretation of the double slit experiment?
Yes, effectively the photon goes through both slits, and the interference pattern or ballistic pattern relates to when decoherence occurs, either at the point a which slit measurement is made or at the point it hits the detector.
Thank you. I had someone sit for about 30 minutes trying to convince me our eyes, without any level of interaction, changed the behavior of photons and quantum particles simply by the fact we were gazing at them. I could not understand how but kept being reassured it was the case.
People take the word "observe" at face value (no pun intended) a bit too often
So you’re telling me that the double slit experiment has reached a sufficient saturation point in modern culture so as to have a conspiracy around it?
It's not a conspiracy.
It's straight up some of the ways in which various accredited physicists were explaining how and why it does the weird things it does.
Von Neuman arguably started it by correctly pointing out that the collapse could be taking place anywhere between the measurement device to the subjective perception of that measurement.
The latter boundary was favored at the time by people like Fritz London, a five times Nobel nominee.
Eugene Wigner further doubled down on the theory, and has the rare distinction of being one of the few people whose gedankenexperiment eventually ended up realizing the very counterintuitive result it was proposed to explore.
These weren't conspiracy theorists.
They were physicists.
Thinking outside the box and from all different angles to try and understand counterintuitive experimental results.
Some of those theories have since been extrapolated from by popsci and new age circles to claim ridiculous things, but the existence of "quantum stickers" to cure your ills doesn't mean Dirac and Schrodinger were crackpots, and so neither does someone claiming "The Secret" like powers based on quantum theory mean that folks like Wigner or Penrose are conspiracy theorists.
It's a legitimate interpretation with a number of very experienced physicists in favor of it over the years, even if not a popular one.
Considering it was one of the basic labs I did in college physics that pretty much every student has to take, and a significant portion of the classes just do the experiments wrong until they get helped, there's probably just enough familiarity to kinda know what's happening but with major misconceptions.
The conspiracy types tend not to enroll in a university to take physics classes.
I was suggesting that it must have gone quite a lot further than what people are taught in classes.
I mean it can happen with any scientific & technological concept that reaches wide enough in the collective consciousness.
Like "collective consciousness"?
from the Wikipedia article on the double-slit experiment
If you read through Wheeler's delayed choice experiments, all the variations he went through to try to pin this down, well... it's hard to avoid the conclusion that the waveform doesn't collapse until the moment that someone looks at the data. In fact, it's hard to avoid the conclusion that the universe is laughing at us every time we try to get a specific answer. This statement from the conclusion is absolutely bonkers if you think about it:
The method of observation determines whether the photon behaved as a wave or a particle, after the measurement is done.
The photon behavior as recorded changes depending on how you examine the record, even "long after" the record is made and the interpretation should be fixed. It quite literally depends on how you look at it.
There's actually no way to prove or disprove consciousness collapse theories, as even if an unmonitored detector causes collapse, you only know about it when a consciousness is reviewing the data. So at best it can be said that direct consciousness collapse theories aren't true, but AFAIK the ones still around are all indirect (i.e. collapse occurs at the point you are reviewing the data).
We could similarly talk about the "woo woo" of multiverse theories and how there's no proof for Everett's interpretation (despite being one of the few popular theories not to need an invalidation of an assumption in the Frauchiger-Renner paradox).
But no proof doesn't equal "not true."
All QM interpretations are up in the air, and an appeal to Copenhagen interpretation is probably one of the most nonsensical given a specific interpretation doesn't even exist for that one and it's effectively just become euphemistic for "shut up and calculate."
What if a computer reviews the data and prints a readout? Is the program a consciousness for this purpose?
Again, the theory would be that collapse (including the state of what is on the paper) occurs upon review of the paper.
Consciousness collapse theories are particularly interesting in the context of the quantum eraser variations of the double slit experiment.
Personally my favorite interpretations ever since reading the Asking photons where they've been paper have been ones incorporating forward and backwards wave functions like the two-state vector formalism or the transactional interpretation.
It's thought provoking to look at experimental results under different interpretation contexts, and is one of the things that frustrating in people thinking there's merit to trying to "pick a team."
Not everything needs to be a team sport, and a variety of interpretations tends to be a good thing as each prompts different types of experiments by their various supporters.
If it isn’t falsifiable then it’s not science, period.
Which is why QM interpretations are considered to be part of Physics philosophy as you can see the link to the weighty writeup on the Copenhagen Interpretation is part of Stanford's Encyclopedia of Philosophy.
But all interpretations are part of philosophy and are currently not falsifiable. Not just the ones someone may not like.
Yeah it tends to be difficult to disprove fantasy when its proponents don't care about evidence.
Right, Roger Penrose and Eugene Wigner and a host of other physicists who subscribe/d to consciousness collapse interpretations aren't people who care about evidence...
It's wild how many people are so quick to be confidently incorrect about something that sounds correct and science-ish but doesn't at all reflect the actual subspecialty nuances.
Literally none of the QM interpretations have evidence supporting their particular interpretation.
At best there's a handful that have been abandoned due to falsification, like interpretations predicated on local hidden variables.
There's no more evidence for Copenhagen or many worlds than there is for consciousness collapse.
There's simply different inherent assumptions that different physicists are willing to entertain, but it's entirely a personal choice and ultimately not evidence driven.
And the picture of assumptions changes over time. For example, post-2018 all popular interpretations other than many worlds have a new "pick at least one of three" assumptions that must be embraced following a new paradox. But currently that's pretty much the only guiding factor, is what assumptions one is willing to entertain.
Even the dictionary says woo-woo refers to the sounds ghosts are supposed to make. Don’t trust randos on lemmy.
What is an eye and the brain if not organic cameras and computers? This is actually an issue in science philosophy.
There is no material difference between observation through tools and through “the bare senses”. Observation is what matters.
Observing quantum phenomena changes it. The tool does not matter.
Yes, but eyes and other sensory organs are passive observers. You can only see photons if they've already been reflected in your direction, and whether you're looking has no impact on if they are reflected or not.
Feels like a kind of "if a tree falls in a forest" scenario. Whether your eyes were in the way or not makes no difference.
It's not even "observing" in that sense. It's just an interaction that forces the waveform to collapse. Basically, if anything requires a result, then it collapses. It doesn't need to record anything or anything like that. It just needs to be effected by (or apply an effect to) the photons.
Actually not correct, words in a lab can mean different things from the popular usage. With Theory being the most popular misconception, as so many people believe that it just means I guess, when in reality it is closer to something we can't test, but if it weren't true so many other things that we can test couldn't possibly be true.
Typically a theory is never proven nor disproven, it is however replaced with a more accurate Theory.
Inside of a laboratory, observation means something less like you saw it, and something more like you measured it. All the observation changing it proves, is that we don't have a method of measuring it that will not interact with it. Which is to be expected given that Quantum phenomenon is legitimately so small that even a microscopic bacterium would say it's tiny.