A place for majestic STEMLORD peacocking, as well as memes about the realities of working in a lab.
Rules
This is a science community. We use the Dawkins definition of meme.
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.
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 we 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.
Wheeler's delayed-choice experiments demonstrate that extracting "which path" information after a particle passes through the slits can seem to retroactively alter its previous behavior at the slits.
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 fact that it is possible to decide whether a wave or particle feature manifests itself long after—and even space-like separated from—the measurement teaches us that we should not have any naive realistic picture for interpreting quantum phenomena.
The method of observation determines whether the photon behaved as a wave or a particle, after the measurement is done.
Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely.
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 a video about how the delayed choice experiment is compatible with existing quantum physics and doesn't require further weirdness like retrocausality to explain.
I mean, magic is just weird shit that isn't fully understood yet.
That being said, you might as well look at it as branches.
Each state is a possibility, thus both exist.
The "magic" isn't that the probabilities of either state being in effect suddenly collapsed and became reality. The magic is that by observing the result, we collapse our own probability and are suddenly aware of the branch that we exist in. But we also exist in that other branch, suddenly aware that we exist in it. But "both" of us are incapable of viewing that other branch.
Which is all mumbo-jumbo, but I'm a fiction writer, so I don't have to be rigorous :)
"Sufficiently advanced magic is indistinguishable from technology." -Mercedes Lackey or... maybe Larry Dixon. Unclear.
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.
Fucking brilliant! And all of the upvotes assure me that I'm hanging out with the right bunch of nerds on the internet!
That's the best use of that meme I've seen.
You can see all the stripes when you do this. The demonstration is about light's property as a wave.
This is a picture of water so you can see the waves spreading out from the hole. Light does the same thing. And when you have two holes next to each other, the peaks and valleys of the wave will interact with each other.
Now imagine a vertical line where those waves are interacting to the right of the holes. If this were light and the line you imagined was a wall, the parts of the waves that are high are bright and the valleys are dark.
Can someone who understands science explain this to me (what im getting at is its a pregnancy test)
The double slit expiriment demonstrates the duality of the nature of a photon: that it's both a wave and a particle.
When a photon is "observed" (or detected) it has the properties of a particle. However when it's travelling it acts like a wave and can demonstrate interference patterns with other photons.
So when you pass photos through two tiny slits, instead of them just passing right through like a particle, they interfere with each other and when the wave pattern collapses when it is observed on the wall, you see the interference.
That being said, I don't think this cartoon makes sense. I get what they are driving at, as they are saying it acts differently when not observed, but this is not what happens. Also this isn't a ln experiment that deals with observation forcing an outcome, but as I noted it's about the duality. Additionally, the wave pattern on the top is what you would you observe when looking at, so I'm not sure why that is what it would be like if you were looking away.
But maybe I'm missing something.
The double slit experiment is about observation.
When you fire photons through the double slits, one photon at a time, they cause wave interference patterns with themselves as if each photon travelled through both slits.
Yet if you set something up to measure which slit each photon passed through, they no longer interfere with themselves, and give you the two straight lines pattern, rather than the interference pattern.
When you fire photons through the double slits, one photon at a time, they cause wave interference patterns with themselves as if each photon travelled through both slits.
You're right, I forgot about this part of it.
Very clever, made me laugh
So how long until someone comes in here and claims that this it disproves materialism?
"But but the Double Slit!" Is my favorite pseudoscience argument
That's the best use of this meme I've ever seen. Bravo.
Can someone post a search term or some other clue so we can learn?
The double slit experiment demonstrates the wave-particle duality of light.
You shoot photons at a barrier that has two slits in it. The pattern on the backstop appears as in the top right panel: an interference pattern, because light is behaving as a wave.
Next, you set up a detector at the slits, so that you can determine which slit each photon passed through, one photon at a time. Now the pattern on the backstop appears as the lower right panel, not an interference pattern, because each photon is acting as a particle.
Not looking: wave. Looking: particle.
Exactly. The issue is that you can't detect photons without interacting with them. So it isn't observation like so many people think. It's that if you interact with subatomic particles you change their state.
TLDR the goddamn universe makes no fucking sense if you really look at it.
Not looking at it only introduces more uncertainty.
Young's double slit experiment.
When which slit a photon goes through is unobserved, it behaves like a wave and self interferes so many photons create an interference pattern with stripes where self-interactions prevented any photons from appearing.
When the photon is interacted with in a way which leaves permanent information about which slit it went through, it behaves like a particle and the pattern from many photons looks 'ballistic' like you were shooting tiny balls through each slit.
So in the meme when he's not looking at the slits, there's stripes, and when he's looking it's a ballistic pattern.