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.
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.
The interference pattern only appears after firing many many photons. They’re still a photon (packet of energy) when creating an interference pattern. It’s the distribution and probability of its location that changes. Not the physical “shape”.
Edit: to clarify further
When not being detected, it’s still just one dot that appears on the sheet. As more and more are fired, the interference pattern shows to show as each photon hits the screen
The meme confuses two things in quantum mechanics. One is the double slit experiment, which confirms that light behaves both as a wave and a particle. That’s what the meme is showing here.
However it’s also throwing in Schrodinger’s, which states that until you look at something it exists in all states - the classic theoretical example being the cat in a box, which is both alive and dead until you open the box. That doesn’t make much sense in the real world, but when looking at quantum particles it is provably true.
Just to complete the set of “principles of quantum mechanics that people know of but don’t fully understand”, there’s the Heisenberg Uncertainty Principle, which states that you can either know the position of something or its momentum (ie where it’s going). The more accurately you measure one of these, the less accurate any measurement is of the other.
Edit: However there’s also what /u/Ada@lemmy.blahaj.zone said below:
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.
So maybe the meme was referring to this variation on the double slit experiment, rather than Schrodinger.
I wouldn't agree with your paraphrased characterization but I think the reason that the experiment results are widely misunderstood is for the same reason any retraction or updated information can't reach the entire same audience as the original information.
The experiment was popularised by Feynman in the 60's and widely discussed as the basis for quantum mechanic. Feynman generally was a fucking rad dude, but he did have a penchant for the poetic, which is probably why he was so popular. Einstein weighed in on the concept too, so big names with big topics in a lunar-landing sci-fi loving era. And quantum mechanics was a fun new mindfuck development in its own right.
So, when a few decades later, the tech catches up to the theory, in experiments by smaller-fame scientists, and the theory further refined; then you've got a legion of adults who grew up with the 60's romantic understanding published in mainstream media, teaching that to the next generation... and you get this.
I can personally blame Brian Greene's 2005 https://www.penguin.co.uk/books/54483/the-fabric-of-the-cosmos-by-brian-greene/9780141011110. His section on the experiment didn't feel right at the time, but feels aren't reals, so I just went with my very limited understanding of an expert's overview. The refined explanation now feels a lot more sensible, for what it's worth.
Okay so what would a more accurate summary be, because what I got from that is that the Dual slit was debunked by us not having the proper tools to actually measure things this small. If that’s not it then I sincerely do not get it.
“The experiment is bullshit, we just can’t measure shit.”
The experiment is limited by our existing tools and evidence, and this will impact both its accuracy and our interpretation of the results, but it's the best we have for now and still worthwhile as a way of producing additional evidence for other researchers.
Also, researchers typically don't condense information into soundbites well, which prevents people from easily understanding and remembering the accurate information. Which allows bad interpretations by other people of the researchers interpretations of rough results to gain traction.
In other words, normal science problems.
An experiment isn't bullshit just because we can't achieve perfection in methodology or human analysis. And we can't refine our theories and tools without multiple inaccurate answers being compared to find congruence.
The bullshit starts with the people whose theories which rely on the inaccurate parts refuse to modify the theory when the evidence disagrees.
Basically my understanding as gathered from the original post, is that the Dual slit experiment does not actually make any meaningful statements because the thing that it intends to measure cannot be accurately measured. However the measurements we got from the imprecise are weird, but that’s to be expected because that’s basically the same as looking at the moon with a magnifying glass and trying to make as accurate astronomical predictions
I want to clarify that the “cannot” here refers not to the inadequacy of our tools (which hypothetically could have been fixed in the future by building better tools), but by a fundamental prohibition of the quantum mechanics theory. Practically, the single-photon lasers and detectors used here are like 90%+ efficient - plenty good enough to distinguish between the two monkey scenarios. But some observables in quantum mechanics are “orthogonal” - you can measure one or the other, but not both at the same time - the math will not allow it. The typical example of that is “position” and “momentum” of a particle.
The math is quite beautiful actually, the analogy I’d use is something like asking “Which way is east at the North Pole?” In your head you can either know “This direction is east.” or “I am standing at the North Pole.” but you cannot hold both pieces of knowledge in your head at the same time.
The orthogonal observables in this experiment are the “which-way top/bottom slit” information and the “which-interference-category Pattern 4/Pattern 5” information. It’s even more beautiful in the delayed choice quantum eraser experiment that I was ranting about here. There, both pieces of information are stored orthogonally in a single photon. You can choose at a later time to either measure it one way, which will tell you the which-way info, or in a different way, which will tell you the interference category info, but there is no hypothetical way to measure it in both. The only way you can get the category info out to allow your computer to draw the interference pattern is if you guarantee that the which-way information has been irrecoverably erased. It is as if the whole universe conspires to censor this information from you! But it’s just the consequence of the math rules in use.
The paper doesn’t use an actual screen, they only have the detector D_S that they move up and down to record the coincidences. I simulated what the monkey would see had there been a screen in place for the purpose of the meme. I copied down the datapoints from the graph and simulated 100,000 photons hitting the screen with the probabilities indicated by those points. My javascript pastie is available here: html.cafe/xcd2a5ed3?k=19f51bff26c65bcf253ee5257a5… Importantly, the monkey can never see images 4 and 5 on the physical screen - those can only be displayed on the computer. The monkey will only ever see image 3, which is the sum of 4 and 5.
Both this paper and the delayed choice quantum eraser experiment paper (arXiv:quant-ph/9903047) only show a single blob, not the double stripe. If anyone has a paper that clearly shows a photo with the double stripes the way it’s shown in the classic monkey meme, I’d like to add it to my collection!
Obviously if the slits are big and wide enough apart you will just get two spotlights, so that doesn’t count. It wouldn’t even demonstrate wave physics, let alone quantum. It has to be a paper where there is some switch you turn on or some filter you slide in place or whatever that makes the image on the physical screen toggle between two stripes and multiple.
If we cover one slit, it will look like figure 3, shifted to the side and at half intensity.
In this experiment, yes. There could be other experiments with electrons instead of light, maybe where you toggle on some kind of magnet to measure which slit an electron goes through, but the measurement itself would still disturb the electrons in a manner where you shouldn’t be surprised when the interference pattern disappears.
I mean, quantum mechanics is still definitely different from classical physics. There are things like the quantum bomb tester, and the Bell inequality violation is still totally real. But the way quantum mechanics has been presented to me in popular science has totally fucked me up. It was not until college quantum physics classes that it all turned out to be actually quite straightforward. And every each time after that when I go back to a research paper underlying some popular science presentation I’ve seen in the past, it turns out there was some giant 3d glasses just off-screen that the presenter somehow “forgot” to mention, and awareness of whose presence totally removes the “fuck”-factor.
Brilliant. Do you call this quantum consciousness, quantum mind or something? At least in German its Quantenbewusstsein. After all these years i remember that photons notice you observe them and behave differently, because it’s ducking interesting.
People will always optimize their methods to maximize resource gain. It’s a fact of life since the dawn of life. Even animals do this.
I’ve seen cancer researchers lie to people with dead loved ones to get funding. I’ve seen physicists do bogus experiments that yield nothing with a nice dark matter story just to get funding… it’s become marketing at this stage.
This is my problem with climate change research. Those who attempt to oppose the “narrative” never get funding. How are we supposed to claim science is unbiased when bias is what’s making the results come out?
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