3. TIL That photons do not experience time. They "hit" something the same instant t...

TIL That photons do not experience time. They "hit" something the same instant they are created, regardless of how far they travel, from their own perspective.

In my limited opinion, the coolest thing about Einstein's physics is that light is the same speed in all frames of reference.

What does that mean?

Suppose two guys were standing on top of a moving train, and guy one shoots a bow and arrow at guy 2. The train is moving 30 mph and the arrow is shot at another 20 mph.

From the frame of reference of guy 1 or guy 2 the arrow would seem to be traveling at 20 mph. From the perspective of a stationary guy on the ground the arrow would be traveling at 50 mph (if shot in the direction the train is moving).

So speed is relative to your frame of reference.

Except the speed of light (c). If a space ship were traveling at 0.99 c, and turned on a headlight from the frame of reference of the pilot the light would be leaving the space ship at c. And from the frame of reference of a stationary guy watching the space ship, the light would also be traveling through their frame of reference at c (not 1.99c like you might expect from the arrow analogy).

It turns out the speed of light is some sort of fundamental universally defined constant and for that to work it means a persons perception of time has to change with respect to how close to that person is traveling to the speed of light.

/r/todayilearned Thread Parent Link - phys.org
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