7 ms·

Place a detector in front of the slits. Only a single particle in a single slit is detected. There is no "splitting" of the particle that we can see. Edit: If

Place a detector in front of the slits. Only a single particle in a single slit is detected. There is no "splitting" of the particle that we can see. Edit: If you try to actually define "wave function collapse" and "observer" you are back into the same mumbo-jumbo as "wave-particle duality". They are just placeholders that obscure the mystery.

richardw 7y ago
We know it arrives as a particle. We don’t know it travels as a particle. What we know is that it acts very wave-like when it travels. If I were forced to bet, I’d say it travels like a wave and arrives like a particle. That doesn’t mean “duality”. It means the condition required to arrive somewhere require a set of values that are packet-like. But we insist that it’s a packet all the way through, so the discussion remains confusing to lay people for 100 years. If you measure before/at the slit you affect the experiment. You affect how it travels through the slits, removing the interference pattern. So yes it’s not split but that has no bearing on when the detector is not at the slit. They’re different situations and have different outcomes.
- imtringued 7y ago
  So you are saying that light is always a wave but when it is being absorbed by an atom it somehow consumes the "entire" wave, no matter how spread out?
  - animal531 7y ago
    I was reading now that photons when created are already at light speed, they don't accelerate. That's because they are in this instance a wave, and a wave is a distortion of its medium; the whole wave can instantly be created at a certain speed (for example throw a rock into a pond, the waves will immediately radiate at speed). So in reverse then, when absorbed the wave could be cancelled out and it is forced into particle behaviour?
jayd16 7y ago
Why can't a particle induce a wavelike field that interacts with slots and itself?
- ridewinter 7y ago
  Because there's only one particle that we can observe going through one slit. Cover up the other slit that nothing is going through and there's no interference. Edit: I think I understand what you're saying. The field isn't separate from the particle - the particle is the quantized field itself.
  - brian-armstrong 7y ago
    I believe "everything is fields" is indeed a common interpretation. Particles are an unnecessary component we invent because of our familiarity with "stuff" This lecture is long but goes into the everything is fields idea https://youtu.be/gEKSpZPByD0 https://youtu.be/gEKSpZPByD0
    - jabl 7y ago
      In this interpretation what we colloquially call a particle is essentially a (localised) quantisized interaction between two fields (or self interaction in a single field). As strange as it sounds, it does make some sense. Think of elementary particles; we never observe them as such, we only observe them when they're interacting with something.
      - Erlich_Bachman 7y ago
        And also "we only observe them when they're interacting" - that process itself, the observing is also just made up of such interactions so at every step of the way there are these interactions, and those are basically the only ones we have direct access to, not the particles themselves. So it makes a lot of sense actually.
  - Quekid5 7y ago
    > The field isn't separate from the particle - the particle is the quantized field itself. Yes. A particle is nothing but a very localized wave. Aka. "everything is fields." (At least that's may layman's understanding having read quite a bit about this in recent years.)
mbell 7y ago
If you place a detector in front of (or behind!) the slits the wave function collapses and there is no interference pattern. This is all part of the mystery of it, as soon as you 'observe' a particle, in any way, it stops acting like a wave. See the Delayed Choice Quantum Eraser experiment for even more weirdness, a good video on it: https://www.youtube.com/watch?v=8ORLN_KwAgs https://www.youtube.com/watch?v=8ORLN_KwAgs
- aeternum 7y ago
  Only the Copenhagen interpretation suffers from the mysterious collapse and time travel issues. Interpretations like Many Worlds make it significantly less 'mysterious': https://www.preposterousuniverse.com/blog/2019/09/21/the-notorious-delayed-choice-quantum-eraser/ https://www.preposterousuniverse.com/blog/2019/09/21/the-not...
  - TheOtherHobbes 7y ago
    Many Worlds is just Copenhagen trying to pitch a science fiction TV series. The issues don't disappear at all, they just get obscured by story telling about other universes. The more you try to nail down MWI on specifics - like exactly when and how universes appear, and how many there are, and how this process is supposed to map back to a probability distribution in one of the universes - the less and less plausible it becomes.
    - Erlich_Bachman 7y ago
      Thank you, I thought it was just me. Like in what possible state of mind is reasoning about endless universes apparently being born out of thin air all the time (and also dependent on observation and interaction of partciles, but not if there is no interaction, there is also no way to hop between them) easier than somewhat tricky but still quite logical wavefunction collapse? It only requires to stop thinking about these particles as physical balls of matter and instead of a bit different entities which can behave like a particle and like a wave, and like something in between, dependent on what they are forced to interact with each moment...
magicalhippo 7y ago
That was my idle thought btw (mentioned in another comment), that this "either it's here or it's there" sounds a lot like the way two entangled particles behave in a Bell test. If Alice measures up, Bob measures down... if the particle does through the left slit, it's not going through the right slit. So my thought was maybe the particle in the two-slit experiment was entangled with itself? Like I said, idle thoughts of a layman so not sure how right, wrong or not-even-wrong this is but hey, always fun to think about QM :)
RangerScience 7y ago
IANAP. My (bad) understanding is based on trying to grok Scott Aaron's book on quantumn computing, which AFAIK does a really excellent job educating on, among other things, WTF quantumn physics. I am open to being horribly wrong, as I don't even know how to properly tell if I know what I'm talking about. That out of the way - The "thing" is neither a particle or a wave, it's a propagating probability amplitude. With one slit, you get a simple probability distribution. With two slits, you get a complex probability distribution, where the amplitudes are summed (and since they can be negative, sometimes sum to zero) The detector adds constraints to the probability amplitudes, zeroing part of the complex probability of the double slit, thus reducing it to a non-complex distribution.
- platz 7y ago
  Now do you think that propagating probability amplitude is a real physical thing?
  - RangerScience 7y ago
    Yes, actually! I just went looking and can't find it, but there was a science paper years ago about dropping.... hydrogen ions into liquid helium? The expectation was that the electrostatic forces would create "bubbles" of empty around the ions, which (the bubbles, not the ions) would then be detected when they reached the bottom. They found those bubbles. They also found many differently sized bubbles, all smaller, in a size distribution correlating to the probability that the ion would pierce the surface tension of the liquid. The interpretation was that the smaller bubbles were the "pieces" of the waveform that traversed the surface tension. This was taken as evidence the waveform is an actual thing that actually exists. I really wish I could find it...
    - notanote 7y ago
      “Can the wave function of an electron be divided and trapped?” https://news.brown.edu/articles/2014/10/electron https://news.brown.edu/articles/2014/10/electron
  - 7y ago
Erlich_Bachman 7y ago
>There is no "splitting" of the particle that we can see. "that we can see". That's exactly the difference. The observation (measurement) affects the state of the system. That's like quantum mechanics 101.
- bookofjoe 7y ago
  "Nobody really understands quantum mechanics."—Richard Feynman
mcv 7y ago
This just increases the mystery. The particle only goes through one of the slits only when you're able to detect through which one it's going. When you can't detect that, it goes through both slits. So observation influences whether or not the particle is going through both slits or only through one. This is to me the most baffling aspect of QM.
Balgair 7y ago
TIRF is going to be very hard to explain away here without modern QM. With a TIRF microscope you use the 'Evanescent Wave' to image fluorescent molecules in macro objects like neurons or diamonds. Like, you can see, even more clearly, the yeast that makes your beer. https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope https://en.wikipedia.org/wiki/Total_internal_reflection_fluo... https://lightmicroscopy.ucdenver.edu/img/seminars/June17.png https://lightmicroscopy.ucdenver.edu/img/seminars/June17.png

richardw 7y ago

We know it arrives as a particle. We don’t know it travels as a particle. What we know is that it acts very wave-like when it travels. If I were forced to bet, I’d say it travels like a wave and arrives like a particle. That doesn’t mean “duality”. It means the condition required to arrive somewhere require a set of values that are packet-like. But we insist that it’s a packet all the way through, so the discussion remains confusing to lay people for 100 years. If you measure before/at the slit you affect the experiment. You affect how it travels through the slits, removing the interference pattern. So yes it’s not split but that has no bearing on when the detector is not at the slit. They’re different situations and have different outcomes.

imtringued 7y ago
So you are saying that light is always a wave but when it is being absorbed by an atom it somehow consumes the "entire" wave, no matter how spread out?
- animal531 7y ago
  I was reading now that photons when created are already at light speed, they don't accelerate. That's because they are in this instance a wave, and a wave is a distortion of its medium; the whole wave can instantly be created at a certain speed (for example throw a rock into a pond, the waves will immediately radiate at speed). So in reverse then, when absorbed the wave could be cancelled out and it is forced into particle behaviour?

jayd16 7y ago

Why can't a particle induce a wavelike field that interacts with slots and itself?

ridewinter 7y ago
Because there's only one particle that we can observe going through one slit. Cover up the other slit that nothing is going through and there's no interference. Edit: I think I understand what you're saying. The field isn't separate from the particle - the particle is the quantized field itself.
- brian-armstrong 7y ago
  I believe "everything is fields" is indeed a common interpretation. Particles are an unnecessary component we invent because of our familiarity with "stuff" This lecture is long but goes into the everything is fields idea https://youtu.be/gEKSpZPByD0 https://youtu.be/gEKSpZPByD0
  - jabl 7y ago
    In this interpretation what we colloquially call a particle is essentially a (localised) quantisized interaction between two fields (or self interaction in a single field). As strange as it sounds, it does make some sense. Think of elementary particles; we never observe them as such, we only observe them when they're interacting with something.
    - Erlich_Bachman 7y ago
      And also "we only observe them when they're interacting" - that process itself, the observing is also just made up of such interactions so at every step of the way there are these interactions, and those are basically the only ones we have direct access to, not the particles themselves. So it makes a lot of sense actually.
- Quekid5 7y ago
  > The field isn't separate from the particle - the particle is the quantized field itself. Yes. A particle is nothing but a very localized wave. Aka. "everything is fields." (At least that's may layman's understanding having read quite a bit about this in recent years.)

mbell 7y ago

If you place a detector in front of (or behind!) the slits the wave function collapses and there is no interference pattern. This is all part of the mystery of it, as soon as you 'observe' a particle, in any way, it stops acting like a wave. See the Delayed Choice Quantum Eraser experiment for even more weirdness, a good video on it: https://www.youtube.com/watch?v=8ORLN_KwAgs https://www.youtube.com/watch?v=8ORLN_KwAgs

aeternum 7y ago
Only the Copenhagen interpretation suffers from the mysterious collapse and time travel issues. Interpretations like Many Worlds make it significantly less 'mysterious': https://www.preposterousuniverse.com/blog/2019/09/21/the-notorious-delayed-choice-quantum-eraser/ https://www.preposterousuniverse.com/blog/2019/09/21/the-not...
- TheOtherHobbes 7y ago
  Many Worlds is just Copenhagen trying to pitch a science fiction TV series. The issues don't disappear at all, they just get obscured by story telling about other universes. The more you try to nail down MWI on specifics - like exactly when and how universes appear, and how many there are, and how this process is supposed to map back to a probability distribution in one of the universes - the less and less plausible it becomes.
  - Erlich_Bachman 7y ago
    Thank you, I thought it was just me. Like in what possible state of mind is reasoning about endless universes apparently being born out of thin air all the time (and also dependent on observation and interaction of partciles, but not if there is no interaction, there is also no way to hop between them) easier than somewhat tricky but still quite logical wavefunction collapse? It only requires to stop thinking about these particles as physical balls of matter and instead of a bit different entities which can behave like a particle and like a wave, and like something in between, dependent on what they are forced to interact with each moment...

magicalhippo 7y ago

That was my idle thought btw (mentioned in another comment), that this "either it's here or it's there" sounds a lot like the way two entangled particles behave in a Bell test. If Alice measures up, Bob measures down... if the particle does through the left slit, it's not going through the right slit. So my thought was maybe the particle in the two-slit experiment was entangled with itself? Like I said, idle thoughts of a layman so not sure how right, wrong or not-even-wrong this is but hey, always fun to think about QM :)

RangerScience 7y ago

IANAP. My (bad) understanding is based on trying to grok Scott Aaron's book on quantumn computing, which AFAIK does a really excellent job educating on, among other things, WTF quantumn physics. I am open to being horribly wrong, as I don't even know how to properly tell if I know what I'm talking about. That out of the way - The "thing" is neither a particle or a wave, it's a propagating probability amplitude. With one slit, you get a simple probability distribution. With two slits, you get a complex probability distribution, where the amplitudes are summed (and since they can be negative, sometimes sum to zero) The detector adds constraints to the probability amplitudes, zeroing part of the complex probability of the double slit, thus reducing it to a non-complex distribution.

platz 7y ago
Now do you think that propagating probability amplitude is a real physical thing?
- RangerScience 7y ago
  Yes, actually! I just went looking and can't find it, but there was a science paper years ago about dropping.... hydrogen ions into liquid helium? The expectation was that the electrostatic forces would create "bubbles" of empty around the ions, which (the bubbles, not the ions) would then be detected when they reached the bottom. They found those bubbles. They also found many differently sized bubbles, all smaller, in a size distribution correlating to the probability that the ion would pierce the surface tension of the liquid. The interpretation was that the smaller bubbles were the "pieces" of the waveform that traversed the surface tension. This was taken as evidence the waveform is an actual thing that actually exists. I really wish I could find it...
  - notanote 7y ago
    “Can the wave function of an electron be divided and trapped?” https://news.brown.edu/articles/2014/10/electron https://news.brown.edu/articles/2014/10/electron
- 7y ago

Erlich_Bachman 7y ago

>There is no "splitting" of the particle that we can see. "that we can see". That's exactly the difference. The observation (measurement) affects the state of the system. That's like quantum mechanics 101.

bookofjoe 7y ago
"Nobody really understands quantum mechanics."—Richard Feynman

mcv 7y ago

This just increases the mystery. The particle only goes through one of the slits only when you're able to detect through which one it's going. When you can't detect that, it goes through both slits. So observation influences whether or not the particle is going through both slits or only through one. This is to me the most baffling aspect of QM.

Balgair 7y ago

TIRF is going to be very hard to explain away here without modern QM. With a TIRF microscope you use the 'Evanescent Wave' to image fluorescent molecules in macro objects like neurons or diamonds. Like, you can see, even more clearly, the yeast that makes your beer. https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope https://en.wikipedia.org/wiki/Total_internal_reflection_fluo... https://lightmicroscopy.ucdenver.edu/img/seminars/June17.png https://lightmicroscopy.ucdenver.edu/img/seminars/June17.png