The speed of light slows as it traverses through a different medium, but after slowing it finds a way to accelerate back to original speed as it exits that medium. How does it do that?
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Something to keep in mind that any individual photon of light isn’t slowed down. But the medium absorbs and reemits the light causing an overall slowdown.
Think of it like taking a football and passing it through a crowded room. You can’t throw it through people so they have to catch the ball and throw it again. But get it the edge of the crowd and yeet it through open space there’s no more delay from catching and throwing again.
A photon/wave of light doesn’t require an energy source once it’s created. It exists as pure energy and it is its own energy source so it will always go back to its expected speed after it passes through some medium that “slows” its progress.
I have no idea, but what goes through my mind right now is: Photons don’t have mass, therefore they don’t need any energy to accelerate since F = m*a.
The speed of light does not actually change at all, it only appears to. A common misconception is that photons are absorbed and re-emitted, but this is wrong. The real explanation is quite hard to ELI5, but I’ll give it a go.
It starts by understanding that light behaves a bit like ripples in a pool. As these ripples pass through stuff, the stuff jiggles a bit. But the jiggling stuff causes it’s own, slightly delayed ripples. When you add these ripples to the original ripples it looks like one ripple moving slower. So we say “light moves slower” even though the original ripples and the delayed ripples travel at full speed.
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Photons, when traveling through a medium, create secondary waves through the vibrations of atoms of the medium. When taken together the resulting wave is slower than the speed of light.
Light does not accelerate going into or out of a medium.
Fermi Lab does an excellent video debunking some of the misconceptions mentioned in this thread and giving a simplified answer here:
I believe he has other videos that get into the math of it and angle changes as well.
Light always moves at the speed of light. When it travels through a medium, it still goes at the speed of light it just might take a longer path. If light travels through some material at “half the speed of light” it doesn’t actually change speed, it just takes a path twice as long as the straight-line path.
Complicated question, basically impossible to ELI5 but a note on your wording. Light doesn’t accelerate. It can be faster or slower but it’s an instant process there’s not this gradual change in speed. This 9s clearer if you know that photons dont experience time (due to time dilation from travelling at speed of light)
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