this post was submitted on 04 Jun 2026
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you and two friends, Al and Be, are outside at night time. Al has a flashlight and flashes it at you and Be. Be is 20 feet away from Al, and you're 20 feet behind Be.
The photons from the light Al has hits Be first, so he sees it first. it took .03 seconds(r1) to reach Be.
After that, the photons hit you and you can see it. it took .03 seconds(r2) to reach you from Be.
They were both .03 seconds because you are equally apart and the speed of light is finite.
so, how long did it take the light to reach you from AI?
In this example all 3 observers are in the same reference frame. That is, each of them are moving at the same speed. This is not what the meme is about. In this example the night from Al would reach you 0.06s after he lit it. Which is expected in Newtonian physics.
The problem of the speed of light being the same for all observers is when they move at different speeds.
The scenario is: Alice is inside a train moving at almost the speed of light, and Bob is outside it, looking at the train. Let's set that light moves at 1m/s (for simplicity) and the wagon Alice is in is 1 meter long.
Alice is at one end of the wagon, and turns a flashlight on. Alice will see the other side of the wagon illuminated after 2 seconds (since the light has to reach the other end and bounce back). Since the wagon is 1 meter long and the speed of light is 1m/s.
However, when she turns the flashlight on, Bob is also looking. Let's say that the train moves at 0.99m/s. In that case, after 1 second the light would have traveled 1 meter, but the wagon (and Alice) has traveled 0.99m, therefore the light is only 0.01m away from Alice.
To summarize: after 1 second, in Alice's frame of reference, the light has just touched the other side of the wagon. Meanwhile, in Bob's reference frame, the light has only moved 0.01m away from Alice.
I'm not following how this explanation is supposed to help with their question. Like, what are you trying to get at here?
correct!
this is because the speed of light is finite. meaning it cannot speed up or slow down on its own.
both you and Be are observing the light at the same speed, but at different times and different distances.
...no?