Why Does Light Slow Down? - Ask a Spaceman!

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If light always travels at the speed of light, how does it slow down when passing through air or water? Does it matter if light is made of particles or waves? What’s the difference between phase velocity and group velocity, and how does that all play into this? I discuss these questions and more in today’s Ask a Spaceman!
Follow all the show updates at www.askaspaceman.com, and help support the show at / pmsutter !
Keep those questions about space, science, astronomy, astrophysics, and cosmology coming to #AskASpaceman for COMPLETE KNOWLEDGE OF TIME AND SPACE! Music by Jason Grady and Nick Bain.

[@extropian314]

Really enjoyed this one. But I find myself still super curious about the _change of direction_ in each model?

[@TaylorShockey]

Fantastic explanation of not just the phenomena but how physics relates to the "truth". Thank you so much for this!

[@advaitrahasya]

The fourth answer will have to wait until Physicists escape the mental prison of Chronocentric Atomism.
It is the simplest - and is inoffensive to intuition, reason and logic … unless one clings to that sub-optimal paradigm.
"matter", being threads of true vacuum spun open by toroidal vortices in the one fundamental substance .… makes the huge stiffness* of "empty space /vacuum" a little spongy, which slows waves in it, just as sound waves slow down when passing from steel into wood.
*Stiffness: Physics currently claims that the Youngs modulus of "space" is 20ish orders of magnitude stiffer than diamond. How Physicists can know that, yet still cling to atomism is a deep mystery indeed.

[@opperhoofdgeilebizon]

If physics is the best science, art is the best pass time 😅

[@sadderwhiskeymann]

I think showing Feynman diagrams would explain things a lot better (without the need to go deep into them)

[@aforementioned7177]

#1

[@alnilam2151]

What did Einstein mean I wonder when he coined the term, "SpookyAction" at a distance: wasit Time or Rotation or how the WorldWorks or even something else oddly? Either Or is another fine mess!?! {\}

[@madderhat5852]

Don't harsh the pie, man.

[@classicalmechanic8914]

Light does not slow down.

[@ChinnuWoW]

Yes it does.

[@jht3fougifh393]

​@@ChinnuWoW Technically it doesn't slow down, in essence. It's more like it's redirected, bent, twisted, or filtered... But "c" is still a constant that's sort of the limit of the universe in terms of causality. That isn't actually changed, not in essence. The specifics of the path (or the photon itself, if you turn on its axis) are just distorted.
It's like saying a string that's 2 feet long is actually 1 foot long, because you folded it in half. The truth is, the string is not actually a foot long, it just seems that way due to how you are looking at the altered state. Allow it to be free again, measure it accurately, and you'll find it remains 2 feet long - as it always actually was. That's what it's like, comparing an uninterrupted beam of light in a vacuum vs various affectations manipulating its path.

[@ChinnuWoW]

@@jht3fougifh393 I know, I was just responding to a baseless statement with another baseless statement to show how worthless of a comment it is.

[@fredjazny]

Why podcast style ? I liked having you on my screen while i was listening to you. English is not my mother tongue and it helped me understand your interesting speech. Subtitles are less handsome ...

[@Alex-kp3hr]

Why the podcast??????? So boring. I enjoy the video versions.