>The speed of light is constant. >But actually it gets reduced by 30% when traveling through water

>The speed of light is constant
>But actually it gets reduced by 30% when traveling through water
Uuuuh..?

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  1. 2 months ago
    Anonymous

    so yeah its more like the speed of light is constant in a vacuum a perfect vacuum at that.

    • 2 months ago
      DoctorGreen

      If it can be reduced, It can be increased

      and this is the baseline. no increase, no decrease
      It is quite obvious

      • 2 months ago
        Anonymous

        > if it can be reduced, it can be increased

        Why would you think that? There's plenty of cases where you can move something in one direction, but not in the other. Take boiling water. You can cool down boiling water by removing it from the heat source, but you can't significantly increase its temperature. Any increase in temperature beyond 100C that occurs in a boiling water will just increase the speed at which the phase change to water vapor happens and you're stuck with a pot of water that is on average 100C.

        • 2 months ago
          Anonymous

          You think that but have you ever poured lava into a pot?

        • 2 months ago
          Anonymous

          >Pressure cooker

          • 2 months ago
            Anonymous

            There’s still always a limit, or phase shift, at every pressure, until you reach more exotic zones of temp/pressure

  2. 2 months ago
    Anonymous

    >DA SPPPPEEEEEEEEDDEE UV LYYYTTTEEEE!!!!
    >omg its so fast!!!!
    >and i'm soooo smart cause i know about it!!!

  3. 2 months ago
    Anonymous

    >he doesn't know about fast light

  4. 2 months ago
    Anonymous

    It gets confusing because there is the speed of light, and the "speed of light"
    "Speed of light" as a phrase is a metaphor for the constant c, which is the delay in time over distance for all electromagnetic interactions.
    Light is just made up from a whole series of constant, waving, high frequency electromagnetic interactions coming together to form a whole system: a traveling waveform.
    The interactions that make up the wave are constant, but, unless traveling in a vacuum, the overall waveform can be deformed and slowed by any charged matter in its path.

    People say "speed of light" instead of "c" because light is a real, tangible thing. You can see a beam of light, and imagine it having a speed. But its not a perfect metaphor, because light can slow down.
    When people say "the speed of light is the same for all observers", they are talking about the "speed of light". When people say "the speed of light slows down in water", they are talking about the speed of a given instance of light.

    • 2 months ago
      Anonymous

      Schizophasia

  5. 2 months ago
    Anonymous

    The instantaneous speed of light never changes regardless of what medium it is travelling through. As the light passes through a medium like water it gets absorbed by water atoms it comes into contact with and then re-emitted again at the speed of light. This absorbtion and re-emission of each photon takes a non zero amount of time, so over some distance the overall time is slower than the speed of light. But when the photons are actually moving between atoms through the water and aren't absorbed into the atoms they're travelling at the speed of light

    • 2 months ago
      Anonymous

      Not op but why would they conveniently get re-emitted directly opposite of the absorption point?

      • 2 months ago
        Anonymous

        They don't all the time. I'm pretty sure that's why the deeper you go underwater the darker it becomes, because the photons are going all over the place, some of them back out the way they came, so there's less and less light the further you go

        • 2 months ago
          Anonymous

          They would have to all the time, otherwise some of the photons would charge through with their speed unchanged. This would destroy coherence and make lenses useless.

      • 2 months ago
        Anonymous

        They do. That’s why the equations of electromagnetism change in a medium.

    • 2 months ago
      Anonymous

      That is not true, it's a common misconception about refraction. As said it would scatter the light (

      Schizophasia

      ).
      What actually happens is the medium interacts and electrons oscillate in a way that emits other EM waves, these interfere with the incident wave. The combined interference pattern propagates at a slower speed.

      • 2 months ago
        Anonymous

        Photons do not slow down in any medium. They travel at constant speed. It's the interactions with other particles in the medium that cause it to progress over a distance slower than it would in a vacuum
        >in exotic materials like Bose–Einstein condensates near absolute zero, the effective speed of light may be only a few metres per second. However, this represents absorption and re-radiation delay between atoms, as do all slower-than-c speeds in material substances
        https://en.wikipedia.org/wiki/Speed_of_light#In_a_medium

        • 2 months ago
          Anonymous

          vacuums don't exist in this universe
          >referencing wikipedia
          its like announcing that you're low iq and have education and no idea what you're talking about

        • 2 months ago
          Anonymous

          Nope. They're describing this expotic case not refraction in general.
          https://en.wikipedia.org/wiki/Refraction
          >Common explanations for this slowing, based upon the idea of light scattering from, or being absorbed and re-emitted by atoms, are both incorrect. Explanations like these would cause a "blurring" effect in the resulting light, as it would no longer be travelling in just one direction. But this effect is not seen in nature.

          >A correct explanation rests on light's nature as an electromagnetic wave.[5] Because light is an oscillating electrical/magnetic wave, light traveling in a medium causes the electrically charged electrons of the material to also oscillate. (The material's protons also oscillate but as they are around 2000 times more massive, their movement and therefore their effect, is far smaller). A moving electrical charge emits electromagnetic waves of its own. The electromagnetic waves emitted by the oscillating electrons interact with the electromagnetic waves that make up the original light, similar to water waves on a pond, a process known as constructive interference. When two waves interfere in this way, the resulting "combined" wave may have wave packets that pass an observer at a slower rate. The light has effectively been slowed.

          • 2 months ago
            Anonymous

            This.
            Please don't make the classic midwit error of trying to understand light as a spray of photons, or try and explain the properties of light with photon absorbtion and emission. Light has always been understood as oscillating, omnidirectional waves of force radiating outwards. The idea of the photon only came later as an explaination for what these waves are made of. Don't even think about photons when trying to understand the behavior of light.

          • 2 months ago
            Anonymous

            I love how this massive description of what light is and why it doesnt get absorbed/emitted can barely afford a sentence for what actually happens. What are wave packets? Why do these wave packets arrive slower? The author couldnt be fricked, he was too busy fuming about the aborption of light

          • 2 months ago
            Anonymous

            The second section tells you that. Reading is hard. Wavepackets are photons.

        • 2 months ago
          Anonymous

          Nope. They're describing this expotic case not refraction in general.
          https://en.wikipedia.org/wiki/Refraction
          >Common explanations for this slowing, based upon the idea of light scattering from, or being absorbed and re-emitted by atoms, are both incorrect. Explanations like these would cause a "blurring" effect in the resulting light, as it would no longer be travelling in just one direction. But this effect is not seen in nature.

          >A correct explanation rests on light's nature as an electromagnetic wave.[5] Because light is an oscillating electrical/magnetic wave, light traveling in a medium causes the electrically charged electrons of the material to also oscillate. (The material's protons also oscillate but as they are around 2000 times more massive, their movement and therefore their effect, is far smaller). A moving electrical charge emits electromagnetic waves of its own. The electromagnetic waves emitted by the oscillating electrons interact with the electromagnetic waves that make up the original light, similar to water waves on a pond, a process known as constructive interference. When two waves interfere in this way, the resulting "combined" wave may have wave packets that pass an observer at a slower rate. The light has effectively been slowed.

          What about gain assisted superluminal propagation? Why does a plasmonic excitation have a vacuum transit time 320x faster than actual photons traversing the same distance?

          • 2 months ago
            Anonymous

            Where are you reading that from? Quote the source.

          • 2 months ago
            Anonymous

            Because phase velocity of waves can exceed the speed of light. But group velocity can’t — hence the limit on information transfer.

          • 2 months ago
            Anonymous

            But what if it isn't a phase versus group velocity hand wave and it really is traveling superluminal?

            Where are you reading that from? Quote the source.

            https://www.scribd.com/document/208319/NEC-Time-Travel-Experiment-in-2000
            The attached PDF is tangentially related

          • 2 months ago
            Anonymous

            >what if it isn’t
            But it is, moron. You asked a question and got an answer. Frick off

          • 2 months ago
            Anonymous

            >But what if it isn't a phase versus group velocity hand wave and it really is traveling superluminal?
            Well if you produce a source you can find out instead of guessing.
            >The attached PDF is tangentially related
            Not a source then.

          • 2 months ago
            Anonymous

            Read the link titled "Gain Assisted Superluminal Propagation" moron. That is the title of the paper. It's the scribd link.

          • 2 months ago
            Anonymous

            Because phase velocity of waves can exceed the speed of light. But group velocity can’t — hence the limit on information transfer.

            This guy answered that question, precisely with the same explanation that the paper’s author gives (albeit in short hand - phase velocity vs. rephasing, which are both the same thing fundamentally). And as your paper states, information cannot travel faster than light speed, since group velocity can’t.
            I’m impressed he pulled the answer out that quickly and accurately. You got owned bro

          • 2 months ago
            Anonymous

            Wang specifically states in his Nature followup that it is not a phase versus group velocity thing and that it indeed appears to be moving faster than light. He wrote the follow-up after everyone came out to say it's just "muh phase versus group velocity". Could the discrepancy be due time reversal of the group velocity ala' phase conjugation? Genuine question

          • 2 months ago
            Anonymous

            https://www.nature.com/articles/35018520

            >The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.
            i.e. not actually FTL.

          • 2 months ago
            Anonymous

            Dunno about follow-ups but this paper states plainly that’s it’s “rephasing”, aka it’s the phase that’s “anomalous”, and not any group. This effect cannot cause group velocity to exceed the speed of light, since it is related to the change in phase velocity, not the phase velocity itself

          • 2 months ago
            Anonymous

            https://www.nature.com/articles/35018520

  6. 2 months ago
    Anonymous

    its not constant

  7. 2 months ago
    Anonymous

    In a vacuum, stupid 🙂

  8. 2 months ago
    Anonymous

    Water is a vacuum?

  9. 2 months ago
    Anonymous

    Photons spend 30% of their time hanging out with water molecules. When moving between water molecules they move at exactly c. It's the difference between an evening walk and a pub crawl.

  10. 2 months ago
    Anonymous

    >The speed of light is constant
    >in a vacuum

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