Confusion about the speed of light

AI Thread Summary
The speed of light is a universal constant, specifically 299,792 kilometers per second in a vacuum. However, when light travels through different media like glass or water, it appears to slow down due to interactions with the atoms in those materials. This phenomenon does not contradict the universal constant, as the speed of light in a vacuum remains unchanged. The apparent slowing is a result of the light's interactions rather than a change in its fundamental speed. Understanding this distinction clarifies common misconceptions about the speed of light in various contexts.
prane
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So everyone knows the speed of light is a universal constant. However in many phenomena involving light it is useful to think that light is 'slowing down' like light travels slower in glass/ water then it does in a vacuum. How can this be if it is a universal constant?
 
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Speed of light in vacuum is universal constant. Light passing through media interacts with media and slows down.
 
There is a bit about this in the FAQ;

https://www.physicsforums.com/showthread.php?t=511177
 
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