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I’ve always wondered, has there ever been a definitive experiment where one photon hits a slit and on the other side two photons come out, but then when you add

I’ve always wondered, has there ever been a definitive experiment where one photon hits a slit and on the other side two photons come out, but then when you add a photon observer, it immediately only comes out on one side? Or has the proof always been mathematical rather than a live experiment? Edit: Thank you all for the responses, it has been very educational. It appears I was misunderstanding the most important aspect of the double slit experiment. A photon is a wave function when unobserved, it literally goes through both slits and creates an interference pattern like how waves in water would. However, when observed at the slit, or at the detector screen, the wave function collapses and only one photon(billiard like particle) will be detected.

judofyr 2y ago
Are you referring to the double-slit experiment? If so, yes: It has always been an experiment. The experiment came before any theory explaining the behavior AFAIK. https://en.m.wikipedia.org/wiki/Double-slit_experiment https://en.m.wikipedia.org/wiki/Double-slit_experiment
ryoshu 2y ago
Live experiments have been done and they get really weird: https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
marcosdumay 2y ago
What does "one photon hits a slit and on the other side two photons come out" mean? There is no photon multiplication happening on the double slit.
- galaxyLogic 2y ago
  One photon hits the slit and one photon comes out. It is only if you repeat the experiment many times that you start to see a strange wawe-like pattern in where the photons hit. It is as if every photon that went through the slit is somehow aware of all other photons that did so too so each photon can choose the (random) position where it hits on the wall behind the slit such that together they look like as if a WAWE went through the slit. That is (one reason) why they call it "Quantum Weirdness". God is playing dice with us
  - chowells 2y ago
    > It is as if every photon that went through the slit is somehow aware of all other photons that did so too Why isn't it just that there's a probability density function that describes the aggregate outcomes of a large number of samples from a random process? Why is "memory" involved?
    - apt-apt-apt-apt 2y ago
      I think because instead of two clusters like you'd expect from random BBs being shot, you get multiple bands like you'd see with interfered waves. Even when shot one at a time.
  - marcosdumay 2y ago
    No. The same photon is aware of all alternative paths it can take, without creating or interacting with any other photon. There's no photon multiplication, and no "all other photons" changing their path. There is some inter-photon interaction because they are bosons. But it's not significant enough to impact the multi-slit experiment. And the experiment works exactly the same way if you send only one photon at a time.
Etheryte 2y ago
The experiment came first, all the rest of it came after to try and figure out why the results are as weird as they are.
out_of_protocol 2y ago
Double slit experiment did happen and totally reproducible even then photons/electrons are sent by one at a time. "two photons come out" part makes no sense though. On a target side, there's always single hit after single photon/electron, but distribution of theses hits as if said electron got through both slits and interfered with itself P.S. the funny thing is - this works on any small thingy, measured up to 2000 atoms-big, as if it's the property of the universe itself
- bad_haircut72 2y ago
  I would love to try this experiment with something basketball sized out in space. Like we build an enormous basketball detector behind a double slit inside an unobservable black box. If thr basketball started acting like a wave I would be sooo freaked out
  - whatshisface 2y ago
    The largest double-slit projectile I know of is C-60, a soccer-ball shaped molecule of sixty atoms. https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4 https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4
    - randunel 2y ago
      That website's captcha is horrible!
      - heylook 2y ago
        Or amazing.
      - nextts 2y ago
        I got cats with sunglasses
        qingcharles 2y ago
shagie 2y ago
The double slit experiment has been replicated even with fairly hefty molecules. https://www.nature.com/articles/s41567-019-0663-9 https://www.nature.com/articles/s41567-019-0663-9 > Here, we report interference of a molecular library of functionalized oligoporphyrins with masses beyond 25,000 Da and consisting of up to 2,000 atoms, by far the heaviest objects shown to exhibit matter-wave interference to date. It would be awkward to say that the 2000 atom molecule comes out of both sides... but it does, until you look. The double slit experiment is not a duplication cheat of reality... it's weirder than that.
- mock-possum 2y ago
  Am I misunderstanding the significant of the double slit experiment? I thought the takeaway wasn’t that the particle comes out both sides, the implication is that the behavior of a single particle is the same as the behavior of multiple particles - that is to say, it appears to be an interference pattern, even when there should be no other particles to interferes with the single one.
  - l33tman 2y ago
    No you're understanding correctly (I think), the behaviour of a single detected particle depends on all possible paths it could take to get to the detection. This is fundamental to 100 years of quantum mechanics and underlies most of physics including all semiconductors, materials science, chemistry, lasers, etc. The double slit experiment is just a very good illustration of the principle boiled down to its essentials, which is why it's everywhere in pop-sci. It makes for more accessible story than describing how a hydrogen atom works.
somat 2y ago
I think the problem is in insisting on referring to the photon as a particle. In fact the photon may not actually exist. and I have questions as to what "single photon experiments" are actually measuring. let me explain. The EM field is not quantized, or at least not quantized at the level of a photon, what we call a photon is the interaction of the EM field with matter, or more precisely with the electron shell of matter. it is the sound of the wave breaking on the shore, not the wave. Now none of this actually matters as the only method we have of interacting with the EM field is through matter(electrons really) so we can only measure it in photon sized increments.
- deleted 2y ago
  [deleted]
- jayd16 2y ago
  Just for sake of argument, when looking at it from this angle, EM particles could exist and we lack the ability to emit a single one? But then why would these "single photon" double slit problems not split the particle bunch further?
  - somat 2y ago
    I honestly don't know, that is my question as well. However note that we can only perturb the em field in photon sized energy levels, and we can only pick up disturbances of the em field in photon sized bunches as well. Not sure what this implies for how em field energy is accumulated on electrons in order for us to detect it.
- jabl 2y ago
  Well, the EM field CAN be quantified. Just look up any textbook on quantum field theory. And the quanta of the EM field is called the photon. But, to "solve" the wave /particle conundrum, I like to think of it as fields all the way down. A "particle" is then a localized and quantisized interaction of said field with another field. If you think of particles as small billiard balls flying through space on some ballistic trajectory, you'll soon run into all kinds of trouble and the mental model breaks down.
- 2y ago
financetechbro 2y ago
If you want to learn more of about current theory and experiments I suggest you pick up “Waves in an impossible sea” by Matt Strassler
analog31 2y ago
Perhaps the closest thing would be some nuclear decays that spit out two gamma rays of equal energy in opposite directions. I'm struggling to remember which isotope does this.
- muhdeeb 2y ago
  It’s a cadmium isotope. Super cool technique, I think perturbed angular correlation. https://en.m.wikipedia.org/wiki/Perturbed_angular_correlation https://en.m.wikipedia.org/wiki/Perturbed_angular_correlatio... I haven’t used it for my research, but it’s an incredible local probe of electric and magnetic fields in materials. There’s no other technique that I’m aware of that smuggles information about the chemical structure of a single coordination sphere into such clean, distinct emissions. The brief excited state of the isotope after the first emission event and before the second is sensitive to practically everything. It all shows up in the deconvoluted spectra. Shame nearly all the isotopes that work for this are not ones that are super interesting for modern quantum materials. Perhaps that will change out of necessity.
GeoAtreides 2y ago
RE: your edit You still do not understand what is happening, please READ the article, it shows that the wave function doesn't go through anything and the it certainly doesn't create the interference pattern.
DanielVZ 2y ago
I really don’t understand the topic much but this veritasium video is quite eye opening and goes into further depth than any layman explanation I’ve ever seen in the topic: https://youtu.be/qJZ1Ez28C-A?si=6gSQYcJPpaSIt1x1 https://youtu.be/qJZ1Ez28C-A?si=6gSQYcJPpaSIt1x1
lmm 2y ago
> I’ve always wondered, has there ever been a definitive experiment where one photon hits a slit and on the other side two photons come out, but then when you add a photon observer, it immediately only comes out on one side? Or has the proof always been mathematical rather than a live experiment? Only one photon comes out, but it can interfere with itself if it had the possibility of going through either slit. That nuance aside, the Quantum Eraser Experiment is a real physical experiment that covers what I think you're asking about. If you send photons through double slits in a setup where you can tell which slit the photon went through, you don't get an interference pattern. If you can't tell, you do get the interference pattern.

judofyr 2y ago

Are you referring to the double-slit experiment? If so, yes: It has always been an experiment. The experiment came before any theory explaining the behavior AFAIK. https://en.m.wikipedia.org/wiki/Double-slit_experiment https://en.m.wikipedia.org/wiki/Double-slit_experiment

ryoshu 2y ago

Live experiments have been done and they get really weird: https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

marcosdumay 2y ago

What does "one photon hits a slit and on the other side two photons come out" mean? There is no photon multiplication happening on the double slit.

galaxyLogic 2y ago
One photon hits the slit and one photon comes out. It is only if you repeat the experiment many times that you start to see a strange wawe-like pattern in where the photons hit. It is as if every photon that went through the slit is somehow aware of all other photons that did so too so each photon can choose the (random) position where it hits on the wall behind the slit such that together they look like as if a WAWE went through the slit. That is (one reason) why they call it "Quantum Weirdness". God is playing dice with us
- chowells 2y ago
  > It is as if every photon that went through the slit is somehow aware of all other photons that did so too Why isn't it just that there's a probability density function that describes the aggregate outcomes of a large number of samples from a random process? Why is "memory" involved?
  - apt-apt-apt-apt 2y ago
    I think because instead of two clusters like you'd expect from random BBs being shot, you get multiple bands like you'd see with interfered waves. Even when shot one at a time.
- marcosdumay 2y ago
  No. The same photon is aware of all alternative paths it can take, without creating or interacting with any other photon. There's no photon multiplication, and no "all other photons" changing their path. There is some inter-photon interaction because they are bosons. But it's not significant enough to impact the multi-slit experiment. And the experiment works exactly the same way if you send only one photon at a time.

Etheryte 2y ago

The experiment came first, all the rest of it came after to try and figure out why the results are as weird as they are.

out_of_protocol 2y ago

Double slit experiment did happen and totally reproducible even then photons/electrons are sent by one at a time. "two photons come out" part makes no sense though. On a target side, there's always single hit after single photon/electron, but distribution of theses hits as if said electron got through both slits and interfered with itself P.S. the funny thing is - this works on any small thingy, measured up to 2000 atoms-big, as if it's the property of the universe itself

bad_haircut72 2y ago
I would love to try this experiment with something basketball sized out in space. Like we build an enormous basketball detector behind a double slit inside an unobservable black box. If thr basketball started acting like a wave I would be sooo freaked out
- whatshisface 2y ago
  The largest double-slit projectile I know of is C-60, a soccer-ball shaped molecule of sixty atoms. https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4 https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4
  - randunel 2y ago
    That website's captcha is horrible!
    - heylook 2y ago
      Or amazing.
    - nextts 2y ago
      I got cats with sunglasses
      - qingcharles 2y ago

shagie 2y ago

The double slit experiment has been replicated even with fairly hefty molecules. https://www.nature.com/articles/s41567-019-0663-9 https://www.nature.com/articles/s41567-019-0663-9 > Here, we report interference of a molecular library of functionalized oligoporphyrins with masses beyond 25,000 Da and consisting of up to 2,000 atoms, by far the heaviest objects shown to exhibit matter-wave interference to date. It would be awkward to say that the 2000 atom molecule comes out of both sides... but it does, until you look. The double slit experiment is not a duplication cheat of reality... it's weirder than that.

mock-possum 2y ago
Am I misunderstanding the significant of the double slit experiment? I thought the takeaway wasn’t that the particle comes out both sides, the implication is that the behavior of a single particle is the same as the behavior of multiple particles - that is to say, it appears to be an interference pattern, even when there should be no other particles to interferes with the single one.
- l33tman 2y ago
  No you're understanding correctly (I think), the behaviour of a single detected particle depends on all possible paths it could take to get to the detection. This is fundamental to 100 years of quantum mechanics and underlies most of physics including all semiconductors, materials science, chemistry, lasers, etc. The double slit experiment is just a very good illustration of the principle boiled down to its essentials, which is why it's everywhere in pop-sci. It makes for more accessible story than describing how a hydrogen atom works.

somat 2y ago

I think the problem is in insisting on referring to the photon as a particle. In fact the photon may not actually exist. and I have questions as to what "single photon experiments" are actually measuring. let me explain. The EM field is not quantized, or at least not quantized at the level of a photon, what we call a photon is the interaction of the EM field with matter, or more precisely with the electron shell of matter. it is the sound of the wave breaking on the shore, not the wave. Now none of this actually matters as the only method we have of interacting with the EM field is through matter(electrons really) so we can only measure it in photon sized increments.

deleted 2y ago
[deleted]
jayd16 2y ago
Just for sake of argument, when looking at it from this angle, EM particles could exist and we lack the ability to emit a single one? But then why would these "single photon" double slit problems not split the particle bunch further?
- somat 2y ago
  I honestly don't know, that is my question as well. However note that we can only perturb the em field in photon sized energy levels, and we can only pick up disturbances of the em field in photon sized bunches as well. Not sure what this implies for how em field energy is accumulated on electrons in order for us to detect it.
jabl 2y ago
Well, the EM field CAN be quantified. Just look up any textbook on quantum field theory. And the quanta of the EM field is called the photon. But, to "solve" the wave /particle conundrum, I like to think of it as fields all the way down. A "particle" is then a localized and quantisized interaction of said field with another field. If you think of particles as small billiard balls flying through space on some ballistic trajectory, you'll soon run into all kinds of trouble and the mental model breaks down.
2y ago

financetechbro 2y ago

If you want to learn more of about current theory and experiments I suggest you pick up “Waves in an impossible sea” by Matt Strassler

analog31 2y ago

Perhaps the closest thing would be some nuclear decays that spit out two gamma rays of equal energy in opposite directions. I'm struggling to remember which isotope does this.

muhdeeb 2y ago
It’s a cadmium isotope. Super cool technique, I think perturbed angular correlation. https://en.m.wikipedia.org/wiki/Perturbed_angular_correlation https://en.m.wikipedia.org/wiki/Perturbed_angular_correlatio... I haven’t used it for my research, but it’s an incredible local probe of electric and magnetic fields in materials. There’s no other technique that I’m aware of that smuggles information about the chemical structure of a single coordination sphere into such clean, distinct emissions. The brief excited state of the isotope after the first emission event and before the second is sensitive to practically everything. It all shows up in the deconvoluted spectra. Shame nearly all the isotopes that work for this are not ones that are super interesting for modern quantum materials. Perhaps that will change out of necessity.

GeoAtreides 2y ago

RE: your edit You still do not understand what is happening, please READ the article, it shows that the wave function doesn't go through anything and the it certainly doesn't create the interference pattern.

DanielVZ 2y ago

I really don’t understand the topic much but this veritasium video is quite eye opening and goes into further depth than any layman explanation I’ve ever seen in the topic: https://youtu.be/qJZ1Ez28C-A?si=6gSQYcJPpaSIt1x1 https://youtu.be/qJZ1Ez28C-A?si=6gSQYcJPpaSIt1x1

lmm 2y ago

> I’ve always wondered, has there ever been a definitive experiment where one photon hits a slit and on the other side two photons come out, but then when you add a photon observer, it immediately only comes out on one side? Or has the proof always been mathematical rather than a live experiment? Only one photon comes out, but it can interfere with itself if it had the possibility of going through either slit. That nuance aside, the Quantum Eraser Experiment is a real physical experiment that covers what I think you're asking about. If you send photons through double slits in a setup where you can tell which slit the photon went through, you don't get an interference pattern. If you can't tell, you do get the interference pattern.