00:00Exactly what number is this?
00:03She says it's 6
00:04She says it's 9
00:06So, who's right?
00:13Actually, they're both right
00:14They just saw it differently
00:16since they looked at it from different reference frames
00:18Now what exactly are reference frames?
00:21These are just a set of axes
00:22for locating space
00:23and a clock for measuring time
00:25relative to which you make observations
00:28I'll demonstrate
00:30Once this car starts honking
00:32all three observers will record its sound
00:35but sound is a wave
00:37Waves from a moving source, like the car
00:40get bunched up in front
00:41and looser at the back
00:43So, for our case, those behind the car
00:45should hear the loose sound waves
00:47a low pitch
00:48while those in front
00:49should hear a high pitch sound
00:51When I analyzed the recordings
00:53that was exactly what I found
00:56So, what sound was the car really making?
01:01A high pitch sound?
01:03A medium pitch sound?
01:05Or a low pitch sound?
01:07Well, it was really making all three pitches at the same time
01:11each pitch relative to one observer
01:13Then what if we had infinitely many observers?
01:16Then the car would be making infinitely many sounds
01:19each sound relative to one observer
01:22And even if they all disagreed
01:24no one observer is wrong
01:26What each observes is what the sound is
01:29Similarly, if I throw this ball close to the speed of light
01:32its light waves would also get loosened and bunched up
01:36making it appear as different colors
01:38With infinitely many observers
01:40the ball would appear to be all colors at the same time
01:43each color relative to one observer
01:45So sound and light are relative
01:48Ever heard of time being relative?
01:50Consider a light clock with two mirrors
01:52and a photon bouncing between them
01:54Every time the photon hits the bottom mirror
01:56it's one tick of time
01:58So when I start moving
02:00I see it travel in vertical lines
02:02But from your stationary frame
02:04it travels in V's
02:06So since the photon has to travel a longer distance
02:09and the speed of light is constant
02:10each tick takes longer relative to you
02:13So moving clocks run slower
02:16and the faster you run
02:17the slower your clock ticks
02:18So in Olympic races
02:20Usain Bolt is actually the best time traveler
02:22If he ran at 96.8% the speed of light
02:25and took 10 seconds to finish a race according to his clock
02:28A stationary judge would record 40 seconds
02:31to which he would obviously object
02:33But their argument would be pointless
02:35since time is relative
02:37So the really mind-blowing idea here
02:40is that observers in different frames
02:42will perceive different versions of the same reality
02:45And every observer's frame is equally valid
02:48So before you start making any observational arguments with others
02:52First imagine yourself observing through their reference frames
02:57So before you start making any observational arguments
02:58Let's see what happens
02:58Let's see what happens
02:59Let's see what happens
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