The dumb questions thread

[DBT]

Retrocausality as a solution to nonlocality/entanglement?

The appeal of retrocausality

''First, to clarify what retrocausality is and isn't: It does not mean that signals can be communicated from the future to the past—such signaling would be forbidden even in a retrocausal theory due to thermodynamic reasons. Instead, retrocausality means that, when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past.

In the original Bell tests, physicists assumed that retrocausal influences could not happen. Consequently, in order to explain their observations that distant particles seem to immediately know what measurement is being made on the other, the only viable explanation was action-at-a-distance. That is, the particles are somehow influencing each other even when separated by large distances, in ways that cannot be explained by any known mechanism. But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence.''

 

[Kharakov]

Yes, EM transmits at all speeds. QED makes wrong predictions if you don't add in all the superposed possible paths at non-c speeds.

I meant vacuum c, and basically, when traversing materials, it's still traveling at c, but it's going through complex deformations of space (ziggy zaggy patterns) rather than straight paths, which is why the difference in apparent velocity. Unless, of course, the demon is tricking you.

 

[Kharakov]

Retrocausality as a solution to nonlocality/entanglement?

The appeal of retrocausality

''First, to clarify what retrocausality is and isn't: It does not mean that signals can be communicated from the future to the past—such signaling would be forbidden even in a retrocausal theory due to thermodynamic reasons. Instead, retrocausality means that, when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past.

In the original Bell tests, physicists assumed that retrocausal influences could not happen. Consequently, in order to explain their observations that distant particles seem to immediately know what measurement is being made on the other, the only viable explanation was action-at-a-distance. That is, the particles are somehow influencing each other even when separated by large distances, in ways that cannot be explained by any known mechanism. But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence.''

Smart block universe. It's like a smart phone, but less phony, unless you get an 80s era briefcase phone. In which case, it's blocky, in a retro way.

 

[fast]

C is exact. It's not a rounded number. It's set as exact, so even if light by scientific standards in the past could go a teensy weensy past c, it cannot do so today as the maximum is not just limited by reality but now by definition. That transition has implications and that's what puzzles me. I'm not sure what the implications are.

 

[Bomb#20]

Retrocausality as a solution to nonlocality/entanglement?

It's an old idea; Penrose was advocating it in one of his books.

 

[Bomb#20]

Yes, EM transmits at all speeds. QED makes wrong predictions if you don't add in all the superposed possible paths at non-c speeds.

I meant vacuum c, and basically, when traversing materials, it's still traveling at c,

I'm not talking about index of refraction. I meant vacuum c too; and "non-c" includes faster than c as well as slower. A photon from Alpha Centauri has a nonzero amplitude for arriving in four minutes instead of four years. (A very, very small amplitude, due to destructive interference.) Feynman discusses this in his book "QED". And I recall seeing an article several years ago about an experiment where somebody clocked photons at 1.7 c over a sub-micron path.

but it's going through complex deformations of space (ziggy zaggy patterns) rather than straight paths, which is why the difference in apparent velocity. Unless, of course, the demon is tricking you.

The ziggy zaggy patterns aren't really deformations of space; they're the photon being repeatedly absorbed and re-emitted by electrons in the material. If you fire a proton through the material it will go in a straight line and win a race with the photon; if the slow-down were caused by space deformations then presumably they'd affect protons as well.

 

[Kharakov]

I'm not talking about index of refraction. I meant vacuum c too; and "non-c" includes faster than c as well as slower. A photon from Alpha Centauri has a nonzero amplitude for arriving in four minutes instead of four years. (A very, very small amplitude, due to destructive interference.) Feynman discusses this in his book "QED". And I recall seeing an article several years ago about an experiment where somebody clocked photons at 1.7 c over a sub-micron path.

You sure it wasn't woo? I'm poking around, and I can't find anything other than phase velocities in excess of c, with all photons traveling at c (with some longer paths through certain mediums, which a proton would not travel). Maybe you're talking about renormalization, which Feynman didn't find mathematically rigorous anyway?

but it's going through complex deformations of space (ziggy zaggy patterns) rather than straight paths, which is why the difference in apparent velocity. Unless, of course, the demon is tricking you.

The ziggy zaggy patterns aren't really deformations of space;they're the photon being repeatedly absorbed and re-emitted by electrons in the material. If you fire a proton through the material it will go in a straight line and win a race with the photon; if the slow-down were caused by space deformations then presumably they'd affect protons as well.

Cannon ball vs. ball of lint. Who will travel a straighter path through a wind tunnel with multiple baffles? We'll never know!

 

[DBT]

Retrocausality as a solution to nonlocality/entanglement?

It's an old idea; Penrose was advocating it in one of his books.

Yes, an old idea that appears to be showing signs of resurrection, some saying that as absurd as it seems, it's no more unlikely than entanglement...''spooky action at a distance'' which appears to violate relativity, the speed of light, etc.
,

 

[Jokodo]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

What's the hypothetical maximal acceleration you can give the asteroid-target object system without losing the target? I know you can't go beyond the asteroid's gravitational acceleration at whatever altitude you have your target in orbit, but is there a precisely calculable even lower limit above which the orbit deteriorates into a highly eccentric one so you still lose your satellite at its periapsis? Or is *any* amount of continued acceleration eventually going to lead to this? (Preliminary calculations using the higher theoretical maximum suggest that it would take at least 3.5 years to accelerate Ceres to 0.1c without pushing hard enough for loose rocks on its surface to be left behind, more if you want to keep something in orbit.)

What would be the energy requirements for accelerating an asteroid (let's not be skimpy, take Ceres, anything smaller than that and we're probably too slow to be of much use) at such a rate?

If tried to do some of the calculations with Wolfram Alpha, but I seem to get the wrong kinds of units in the result: I was expecting watts and got newtons for Ceres gravity * Ceres mass.



I'm considering the logistics of moving a wormhole entrance to an interstellar destination. I'm assuming macroscopic wormholes can be created and stabilised for all practical purposes indefinitely, but in their creation the laws and speed limits of causality in 3d-space still have to be obeyed: Or in other words, the shortcut through a higher dimension the wormhole represents cannot be used for its own creation. I'm also assuming that it is, partly for this reason, impractical to create the entrances more than a few light-seconds, light-minutes at most, apart, and the only way to get a useful interstellar wormhole is to move it conventionally. And since the wormhole doesn't know the difference between a ship, a container hull, and a planet surface, and will transport them all across indiscriminately, the only safe place for it is in orbit and the only safe way to transport is is to pull it gravitationally.

 

[fast]

Edited out

 

[Bomb#20]

You sure it wasn't woo? I'm poking around, and I can't find anything other than phase velocities in excess of c, with all photons traveling at c (with some longer paths through certain mediums, which a proton would not travel). Maybe you're talking about renormalization, which Feynman didn't find mathematically rigorous anyway?

It's not woo or phase velocity; it's group velocity during quantum tunneling. I'm poking around too, and I gather physicists have been arguing about the speed of tunneling since the 1930s. This paper explains the effect:

A simple heuristic argument to estimate the tunnelling time goes as follows. To surmount a square barrier of height V, a particle with energy E must ‘borrow’ an amount of energy V − E. According to the uncertainty principle, this must be ‘repaid’ after a time T = 1/(V − E) in units with ħ = 1. This provides a crude upper bound for the tunneling time. If the width of the barrier is a, then the effective speed of the particle during the tunneling process must exceed a(V − E). As a can be made as large as we please, there is no upper bound on this effective velocity. In particular, it may exceed the speed of light, in apparent violation of relativistic causality.​

This is from a paper by some of the experimenters:

The fourth of these experiments shows that, even at the one-particle level, there exist nonlocal effects in quantum mechanics: in tunneling there exist superluminal time delays of the tunneling particle. None of these nonlocal effects violates Einstein causality, due to the uncontrollable randomness of quantum events. In the fourth experiment, there is another way to understand that Einstein causality is not violated; the front velocity, at which discontinuities propagate, never exceeds c​

 

[Bomb#20]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

...

I'm considering the logistics of moving a wormhole entrance to an interstellar destination.

Shoot some mass into the wormhole entrance. I'm no expert on GR; but the wormhole will surely do something to the motion of the object you shoot in. So by all the normal rules of physics, the object should in turn do something to the motion of the wormhole entrance. Action ==> equal and opposite reaction. Use the recoil to move the wormhole entrance in your preferred direction.

 

[Kharakov]

You sure it wasn't woo? I'm poking around, and I can't find anything other than phase velocities in excess of c, with all photons traveling at c (with some longer paths through certain mediums, which a proton would not travel). Maybe you're talking about renormalization, which Feynman didn't find mathematically rigorous anyway?

It's not woo or phase velocity; it's group velocity during quantum tunneling. I'm poking around too, and I gather physicists have been arguing about the speed of tunneling since the 1930s. This paper explains the effect:

A simple heuristic argument to estimate the tunnelling time goes as follows. To surmount a square barrier of height V, a particle with energy E must ‘borrow’ an amount of energy V − E. According to the uncertainty principle, this must be ‘repaid’ after a time T = 1/(V − E) in units with ħ = 1. This provides a crude upper bound for the tunneling time. If the width of the barrier is a, then the effective speed of the particle during the tunneling process must exceed a(V − E). As a can be made as large as we please, there is no upper bound on this effective velocity. In particular, it may exceed the speed of light, in apparent violation of relativistic causality.​

This is from a paper by some of the experimenters:

The fourth of these experiments shows that, even at the one-particle level, there exist nonlocal effects in quantum mechanics: in tunneling there exist superluminal time delays of the tunneling particle. None of these nonlocal effects violates Einstein causality, due to the uncontrollable randomness of quantum events. In the fourth experiment, there is another way to understand that Einstein causality is not violated; the front velocity, at which discontinuities propagate, never exceeds c​

I have to get ready for something, but at first glance, it looks wooish... and it probably basically means what I'm about to say I think...


I do have a (to me) non-woo idea about "FTL" causality (as in objects can be a single whole, with the appearance of being spread out over space or time, which is what I suppose entanglement is), which allows for FTL information transfer (but it isn't FTL transfer, it's rather the whole thing evolves at once, there is no "information transmission distance").

Show

 

[Jokodo]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

...

I'm considering the logistics of moving a wormhole entrance to an interstellar destination.

Shoot some mass into the wormhole entrance. I'm no expert on GR; but the wormhole will surely do something to the motion of the object you shoot in. So by all the normal rules of physics, the object should in turn do something to the motion of the wormhole entrance. Action ==> equal and opposite reaction. Use the recoil to move the wormhole entrance in your preferred direction.

If I were an expert on GR, I probably wouldn't have asked. But shouldn't the "equal and opposite reaction" be, if anything, to move the far entrance closer to you rather than farther away? And if it works, is this method actually more efficient than accelerating Ceres?

 

[bilby]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

...

I'm considering the logistics of moving a wormhole entrance to an interstellar destination.

Shoot some mass into the wormhole entrance. I'm no expert on GR; but the wormhole will surely do something to the motion of the object you shoot in. So by all the normal rules of physics, the object should in turn do something to the motion of the wormhole entrance. Action ==> equal and opposite reaction. Use the recoil to move the wormhole entrance in your preferred direction.

If I were an expert on GR, I probably wouldn't have asked. But shouldn't the "equal and opposite reaction" be, if anything, to move the far entrance closer to you rather than farther away? And if it works, is this method actually more efficient than accelerating Ceres?

That depends on which way the 'exit' is pointing - if it has to point directly away from the 'entrance', then it would presumably have to accelerate towards that 'entrance'. That's not a problem though, if the two don't interact when they pass each other; You point the whole thing in the opposite direction from your destination, and pour matter into the 'entrance' until the exit reaches you with significant momentum, passes you without interacting (You might want to dodge), and then carries on towards the target. If the two ends do interact, then what would happen is up to you - they are your imaginary wormhole entrances, so you are God and can give them whatever properties your narrative requires.

 

[humbleman]

Great postings full of fantasies with wormholes, time tunnels and similar crap. Congratulations, but still I don't know where the hell all of you have learned such a nonsense.

Dumb question:

Why some animals change the color of their skin in Winter season?

 

[James Brown]

(Suspects I'm being set up for a trap.)

It provides an evolutionary advantage. Changing seasons changes the background against which animals must hide. Animals that can blend in have a greater advantage in the game of hunter vs. prey. But a color that works well in a summer forest environment would stand out against a white wintry background.

 

[humbleman]

(Suspects I'm being set up for a trap.)

It provides an evolutionary advantage. Changing seasons changes the background against which animals must hide. Animals that can blend in have a greater advantage in the game of hunter vs. prey. But a color that works well in a summer forest environment would stand out against a white wintry background.

No, not a trap or similar.

When I asked why, you just gave an answer of what a theory says about it.

However, the wolf have no idea that its skin changes, then, such is not camouflage because the animal has no control of it, same with other animals.

What that theory mentions is simply wrong.

It must be a real reason why some species have their skin color changes in Winter. Somebody knows it?

 

[Jokodo]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

...

I'm considering the logistics of moving a wormhole entrance to an interstellar destination.

Shoot some mass into the wormhole entrance. I'm no expert on GR; but the wormhole will surely do something to the motion of the object you shoot in. So by all the normal rules of physics, the object should in turn do something to the motion of the wormhole entrance. Action ==> equal and opposite reaction. Use the recoil to move the wormhole entrance in your preferred direction.

On second thought, I'm unsure this would do the job: it's the wormhole as a whole that does something to the mass you shoot in, not just the far exit. So I guess this would shift both exits. So this might be useful for creating a shortcut from Sirius to Alpha Cen but less so for linking the Solar System to either.

 

[bilby]

Imagine you have an object with mass you want to move over astronomical distances, and which you can not encase or otherwise directly push, and which is also electrically neutral so magnets won't help either. I can think of one and only one way to move such an object: have it orbit another body (say an asteroid) and push *that* body so it's pulled along by its gravity. Am I missing an obvious alternative?

...

I'm considering the logistics of moving a wormhole entrance to an interstellar destination.

Shoot some mass into the wormhole entrance. I'm no expert on GR; but the wormhole will surely do something to the motion of the object you shoot in. So by all the normal rules of physics, the object should in turn do something to the motion of the wormhole entrance. Action ==> equal and opposite reaction. Use the recoil to move the wormhole entrance in your preferred direction.

On second thought, I'm unsure this would do the job: it's the wormhole as a whole that does something to the mass you shoot in, not just the far exit. So I guess this would shift both exits. So this might be useful for creating a shortcut from Sirius to Alpha Cen but less so for linking the Solar System to either.

Not so. If you had a water tank up nice and high, and used a hosepipe to siphon water from the tank down to the ground, the water coming out will push the hose outlet/nozzle backwards; But the water going in won't exert a significant force on the inlet end of the pipe.

If your reaction mass approaches the inlet from a wide range of directions, but all leaves the outlet moving in the same direction, the outlet will accelerate, but the inlet need not.

Of course, I don't know whether the wormhole has properties similar to a hosepipe. A rigid pipe would accelerate as a whole; but presumably there's nothing that fixes the distance between the two ends of your wormhole, and they are free to move independently - in which case the hosepipe might be a fair analog.