3 ms·

But if our eyes regularly emitted photons in this manner, surely evolution would find a way to detect the event?

• lisper 9y ago
  You can detect the emission of the photon (by, for example, measuring the reaction force created by the fact that the emitted photon has momentum). What you cannot do is receive any information about whatever ultimately absorbs that photon.
  • Filligree 9y ago
    The fact that a photon was emitted is, itself, information. It means there's a star out there to absorb it. Of course stars aren't the only things that would absorb photons in this manner, but they'd absorb a lot more than other objects, and you could probably do something with the spectrum as well.
    • lisper 9y ago
      > It means there's a star out there to absorb it. No, it doesn't. If it did, then flashlights would behave differently depending on what you were pointing them at.
      • Filligree 9y ago
        We're talking about hypothetical time-reversed light, not the usual kind.
        • lisper 9y ago
          What does it mean for TR-light to be emitted and absorbed then? Does TR-light carry positive or negative energy? Because if it carries negative energy, and it is absorbed before it is emitted, then TR-light behaves exactly the same as regular light. You've just swapped the meaning of "emitted" and "absorbed".