5 ms·

This seems to come up in every discussion of quantum entanglement. It doesn't travel faster than the speed of light. Information can't travel faster than c. N

This seems to come up in every discussion of quantum entanglement. It doesn't travel faster than the speed of light. Information can't travel faster than c. No need to worry about Trisolarans.

ziofill 2y ago
If "it" = information, then sure. But the collapse of the quantum state is instantaneous.
- Filligree 2y ago
  Only in theories where it collapses, and nobody seriously thinks Copenhagen is correct these days.
seanw444 2y ago
I thought information could only travel as fast as light because that was fastest medium we're currently aware of that can carry information. But that doesn't necessarily preclude other, faster mediums from existing, no?
- krapp 2y ago
  No. It's an absolute, inviolable, universal limit on any and all interactions in the universe. It was recently confirmed that even gravitational waves are limited to the speed of light. This (and the Fermi Paradox) are the strongest evidence that faster than light travel or communication of any kind is impossible. We just call it the "speed of light" because it's the speed that massless particles (like photons) travel at in a vacuum.
  - ThrowAaaaway 2y ago
    Ok, but why?
- cyberax 2y ago
  Not quite. There are two speeds in relativity: the maximum speed and non-maximum speeds (i.e. everything else). It just so happens that light travels at the maximum speed. Supra-luminal signals will almost necessarily imply that it's possible to violate causality by arranging a series of supra-luminal communications. Not every supra-luminal communication violates causality, but it's hard to think of a way to build a consistent theory that would both preclude causality violations and permit at least some supra-luminal signaling.
  - cosignal 2y ago
    I know next to nothing about physics, but isn't the "It just so happens" part of what you said potentially misleading? Isn't it that light is massless, so that directly implies that it would travel at the maximum speed?
    - cyberax 2y ago
      It's a distinction with no difference. Only massless particles can move at the "maximum speed", in our Universe these are photons and gluons. And maybe gravitons, if they exist. Similarly, massless particles can't move below the "maximum speed", as they'll have no energy or momentum and won't be able to interact with anything.
    - MattPalmer1086 2y ago
      Why would the absence of mass force something to travel at the maximum speed? I could understand it being able to travel at that speed; why would it always do so though?
      - cyberax 2y ago
        Theoretically, a massless particle can move slower than light. But then it'll have zero energy and momentum, so it won't be able to interact with anything.
        MattPalmer1086 2y ago
- liquidpele 2y ago
  IIRC It’s not that light is a medium. It is that light goes that particular speed max (photons can go slower in fact) because that is the speed of causality.
- HappMacDonald 2y ago
  Per relativity, any medium that could conceptually facilitate transfer of information or of causality (which are basically the same thing) faster than the speed that light happens to travel at would also be able to reverse direction and arrive at their source in space earlier than the time that they left. That effect is completely unrelated to light itself.
  - bookofjoe 2y ago
    "If time travel is possible, then there is no such thing as time." — Kurt Gödel, Einstein's great friend at Princeton's Institute For Advanced Study. Einstein once remarked that he went to his office "just to have the privilege of walking home with Kurt Gödel." https://imgur.com/a/avUwwHk https://imgur.com/a/avUwwHk https://archive.ph/6doQh#selection-707.279-711.1 https://archive.ph/6doQh#selection-707.279-711.1 https://www.amazon.com/When-Einstein-Walked-G%C3%B6del-Excursions/dp/0374146705 https://www.amazon.com/When-Einstein-Walked-G%C3%B6del-Excur...

This seems to come up in every discussion of quantum entanglement. It doesn't travel faster than the speed of light. Information can't travel faster than c. No need to worry about Trisolarans.

ziofill 2y ago

If "it" = information, then sure. But the collapse of the quantum state is instantaneous.

Filligree 2y ago
Only in theories where it collapses, and nobody seriously thinks Copenhagen is correct these days.

seanw444 2y ago

I thought information could only travel as fast as light because that was fastest medium we're currently aware of that can carry information. But that doesn't necessarily preclude other, faster mediums from existing, no?

krapp 2y ago
No. It's an absolute, inviolable, universal limit on any and all interactions in the universe. It was recently confirmed that even gravitational waves are limited to the speed of light. This (and the Fermi Paradox) are the strongest evidence that faster than light travel or communication of any kind is impossible. We just call it the "speed of light" because it's the speed that massless particles (like photons) travel at in a vacuum.
- ThrowAaaaway 2y ago
  Ok, but why?
cyberax 2y ago
Not quite. There are two speeds in relativity: the maximum speed and non-maximum speeds (i.e. everything else). It just so happens that light travels at the maximum speed. Supra-luminal signals will almost necessarily imply that it's possible to violate causality by arranging a series of supra-luminal communications. Not every supra-luminal communication violates causality, but it's hard to think of a way to build a consistent theory that would both preclude causality violations and permit at least some supra-luminal signaling.
- cosignal 2y ago
  I know next to nothing about physics, but isn't the "It just so happens" part of what you said potentially misleading? Isn't it that light is massless, so that directly implies that it would travel at the maximum speed?
  - cyberax 2y ago
    It's a distinction with no difference. Only massless particles can move at the "maximum speed", in our Universe these are photons and gluons. And maybe gravitons, if they exist. Similarly, massless particles can't move below the "maximum speed", as they'll have no energy or momentum and won't be able to interact with anything.
  - MattPalmer1086 2y ago
    Why would the absence of mass force something to travel at the maximum speed? I could understand it being able to travel at that speed; why would it always do so though?
    - cyberax 2y ago
      Theoretically, a massless particle can move slower than light. But then it'll have zero energy and momentum, so it won't be able to interact with anything.
      - MattPalmer1086 2y ago
liquidpele 2y ago
IIRC It’s not that light is a medium. It is that light goes that particular speed max (photons can go slower in fact) because that is the speed of causality.
HappMacDonald 2y ago
Per relativity, any medium that could conceptually facilitate transfer of information or of causality (which are basically the same thing) faster than the speed that light happens to travel at would also be able to reverse direction and arrive at their source in space earlier than the time that they left. That effect is completely unrelated to light itself.
- bookofjoe 2y ago
  "If time travel is possible, then there is no such thing as time." — Kurt Gödel, Einstein's great friend at Princeton's Institute For Advanced Study. Einstein once remarked that he went to his office "just to have the privilege of walking home with Kurt Gödel." https://imgur.com/a/avUwwHk https://imgur.com/a/avUwwHk https://archive.ph/6doQh#selection-707.279-711.1 https://archive.ph/6doQh#selection-707.279-711.1 https://www.amazon.com/When-Einstein-Walked-G%C3%B6del-Excursions/dp/0374146705 https://www.amazon.com/When-Einstein-Walked-G%C3%B6del-Excur...