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.”
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.
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.
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.
Thank you for raising that caveat. I think it’s a little harsh to say that a Bohmian interpretation is a misunderstanding.
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.
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.
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.
Thank you for raising that caveat. I think it’s a little harsh to say that a Bohmian interpretation is a misunderstanding.