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One of the ones that gets me and may be central to space is the central idea in the Young's double slit experiment, the Michelson-Morley interferometer, the Fab

One of the ones that gets me and may be central to space is the central idea in the Young's double slit experiment, the Michelson-Morley interferometer, the Fabry-Perot interferometer, etc. Indeed, the night I was studying for my final in optics and radiography, I thought of this stuff and never really studied for the exam! So, just shine a light through a beam splitter. So, ballpark half of the light continues on essentially straight and the other half is deflected 90 degrees. Such a beam splitter is in the M-M experiment. For the double slit, it divides the beam. For a Fabry-Perot, it ends up making many such splits. Okay, as we heard from Feynman, we could send just one photon through any of those devices and still get the same interference effects. Feynman also explained that we'd get the same result sending one electron at a time instead of a photon. So, here, to heck with recombining the beams and getting it to interfere with itself. Instead, consider just the beam splitter. So, the photon (or electron, neutron, whatever) is a wave function, and after the beam splitter that wave function is in two parts traveling apart, in the case of the photon, if we add a mirror to have the two halves going in opposite directions, at the speed of light. But such splits of the wave function happen at every window pane, no doubt in every water droplet, etc., that is happen all the time. And such a wave function doesn't split just once but commonly many times. So, the one, poor photon as one simple wave function is soon in dozens of pieces all moving away from each other usually never to come together again. After a billion years, the pieces are still moving away from each other. Then, presto, bingo, one part of that wave function enters our telescope and hits our detector. Then all the dozens of pieces of that wave function, scattered across a billion light years, have to disappear, instantly, since with two telescopes we can never get two detections from the one photon. Well, that's tough to believe. So, maybe the universe is filled with tiny pieces of wave functions condemned to go on forever. Maybe that's the dark matter?

vlasev 9y ago
Or perhaps the wave functions "gains a dimension" in that it spreads evenly (or weighed) in all of space, thus making it that a photon is "almost everywhere" until detection.
lmm 9y ago
> And such a wave function doesn't split just once but commonly many times. So, the one, poor photon as one simple wave function is soon in dozens of pieces all moving away from each other usually never to come together again. After a billion years, the pieces are still moving away from each other. > Then, presto, bingo, one part of that wave function enters our telescope and hits our detector. Then all the dozens of pieces of that wave function, scattered across a billion light years, have to disappear, instantly, since with two telescopes we can never get two detections from the one photon. > Well, that's tough to believe. There are a dozen different possibilities for what the photon has done - a dozen different universes, if you like. As long as the photon never interacts with anything else, this bundle of a dozen universes can act much the same as a single universe. Certainly if you're just looking at a telescope, all dozen versions of that telescope are behaving the same, so they behave like a single unified instance. When the photon hits the telescope in one universe, the perspective shifts: the telescope is now "inside" the 12-way split, either the photon went one way and the telescope recorded it or the photon went another way and the telescope didn't. And when we look into the telescope, we again shift from looking at the superposition from outside to being part of the superposition on the inside. Our language isn't great for talking about this, because it's not a binary is/isn't thing - entanglement is a continuous phenomenon. If you imagine just two photons each in one of two states, then it's easy enough to imagine: photon A is in a superposition of states 0 and 1, photon B is in an independent superposition of states 0 and 1 - each photon has two possible "local universes", but because they're distant and noncommunicating, to each one the other looks like it's in a superposition. And it's easy enough to imagine: photon A is in a superposition of states 0 and 1, photon B is in a superposition of states 0 and 1, but they're entangled such that we know the sum is 1 - here there are two possible "global universes", and we see a superposition between them, but ecah particle knows the other is in the same universe - if A is an 0 then it knows B is a 1 and vice versa. The part that's hardest to imagine is that it's also possible to be somewhere in between these two states: A and B can be partially entangled such that e.g. there's a 75% chance that the sum is 1. > So, maybe the universe is filled with tiny pieces of wave functions condemned to go on forever. Maybe that's the dark matter? No. The evolution of quantum systems is unitary and conserves energy.
- kefka 9y ago

vlasev 9y ago

Or perhaps the wave functions "gains a dimension" in that it spreads evenly (or weighed) in all of space, thus making it that a photon is "almost everywhere" until detection.

lmm 9y ago

> And such a wave function doesn't split just once but commonly many times. So, the one, poor photon as one simple wave function is soon in dozens of pieces all moving away from each other usually never to come together again. After a billion years, the pieces are still moving away from each other. > Then, presto, bingo, one part of that wave function enters our telescope and hits our detector. Then all the dozens of pieces of that wave function, scattered across a billion light years, have to disappear, instantly, since with two telescopes we can never get two detections from the one photon. > Well, that's tough to believe. There are a dozen different possibilities for what the photon has done - a dozen different universes, if you like. As long as the photon never interacts with anything else, this bundle of a dozen universes can act much the same as a single universe. Certainly if you're just looking at a telescope, all dozen versions of that telescope are behaving the same, so they behave like a single unified instance. When the photon hits the telescope in one universe, the perspective shifts: the telescope is now "inside" the 12-way split, either the photon went one way and the telescope recorded it or the photon went another way and the telescope didn't. And when we look into the telescope, we again shift from looking at the superposition from outside to being part of the superposition on the inside. Our language isn't great for talking about this, because it's not a binary is/isn't thing - entanglement is a continuous phenomenon. If you imagine just two photons each in one of two states, then it's easy enough to imagine: photon A is in a superposition of states 0 and 1, photon B is in an independent superposition of states 0 and 1 - each photon has two possible "local universes", but because they're distant and noncommunicating, to each one the other looks like it's in a superposition. And it's easy enough to imagine: photon A is in a superposition of states 0 and 1, photon B is in a superposition of states 0 and 1, but they're entangled such that we know the sum is 1 - here there are two possible "global universes", and we see a superposition between them, but ecah particle knows the other is in the same universe - if A is an 0 then it knows B is a 1 and vice versa. The part that's hardest to imagine is that it's also possible to be somewhere in between these two states: A and B can be partially entangled such that e.g. there's a 75% chance that the sum is 1. > So, maybe the universe is filled with tiny pieces of wave functions condemned to go on forever. Maybe that's the dark matter? No. The evolution of quantum systems is unitary and conserves energy.

kefka 9y ago