Life is like riding a bicycle. To keep your balance, you must keep moving
- Einsteins. I feel now a bit confused, since the man himself told us that everything is relative.
So if I stay still everything else in this world run past me so based on relative theory, I'm actually moving and fast.
Einstein's theory of relativity doesn't say "everything is relative"
You can distill it down to two main things:
1. Speed of light is constant regardless of your speed of travel. Speed of light is normally denoted as lower case c.
2. If you are in a frame of reference that is not under acceleration, all the physical laws you measured will remain the same as another frame of reference not under acceleration.
His special theory of relativity came first. It explores physics traveling at c or at closed to c. He later generalized it to low speed and that is his general theory of relativity.
That "the speed of light is constant regardless of your speed of travel" implies a lot of things crazy to our common sense. Most of all, everything we measure is then relative to the speed of light including how we experience the passage of time.
For example, if I am moving away from you at 1000 meters per second away from you, and I fire a bullet traveling at 3000 meters per second toward you. Normal (not near c) common sense would be the bullet moves in my frame of reference at 3000 meters per second. But since I am moving 1000 meters per second away from you, the bullet will be moving at you at 3000-1000=2000 meters per second. That would be what you would measure.
But for light, it always travel at c. If I am travaling 0.9c away from you and I fire a laser towards you. In my frame of reference moving 0.9 c away from you, my laser ray is moving 1.0c within my frame of reference. In your frame of reference, that laser ray is
not moving at 1.0c-0.9c=0.1c towards you. Instead, it is moving at 1.0c toward you just the same. Speed of light is always c!
So, that means that the way your clock is running is not the same as mine which is moving 0.9c away from you. Everything else we measured will be affected by how our clocks are running different.
It also follows that if you can continue to speed up closer and closer to c, your clock runs slower and slower as compare to mine. In theory, it will take infinite energy to increase your speed to c, but say you can keep increasing your speed, at c, your clock stops. For a photon, the moment it dies is the exact same moment when it was born. We may see in our frame of reference that the photon is created at 0:00:01 and at 0:00:02 it hits the wall and was absorbed. For the photon in its frame of reference moving at c, time didn't move as compare to my clock being not-traveling. It was created and then immediately hit the wall and was immediately absorbed. Photon is eternal, time doesn't move.