Imagine you are riding on a yacht in the ocean and traveling at 20 mph. You then hit a golf ball at 100 mph from the deck of the yacht. You see the ball move away from you at 100mph, while a person standing on a near by beach would observe your golf ball traveling at 120 mph (20 mph + 100 mph). Now imagine you are aboard the Hermes spacecraft traveling at 0.1c (1/10 the speed of light) past Mars and shine a laser from the front of the ship. You would see the light traveling at c (the speed of light) away from your ship. According to Einstein's special relativity, how fast will a person on Mars observe the light to be traveling?

Question

Roger Anthony

Physics

3 October, 09:43

Imagine you are riding on a yacht in the ocean and traveling at 20 mph. You then hit a golf ball at 100 mph from the deck of the yacht. You see the ball move away from you at 100mph, while a person standing on a near by beach would observe your golf ball traveling at 120 mph (20 mph + 100 mph). Now imagine you are aboard the Hermes spacecraft traveling at 0.1c (1/10 the speed of light) past Mars and shine a laser from the front of the ship. You would see the light traveling at c (the speed of light) away from your ship. According to Einstein's special relativity, how fast will a person on Mars observe the light to be traveling?

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Jade Olsen · Answer 1

A naive guess would be 1.1c, according to classical mechanics. But Special relativity posited a new special law of adding velocities; so when one is travelling at 5m/s on a platform moving 5m/s, the result is very very close to 10m/s, but it is not exact. This deviation is more visible in higher speeds. There is a specific formula that gives us the speed of an object when it moves in a frame of reference, but in this case the answer is simple. The speed of light is an absolute barrier to the speed of any object and it is preserved in all frames of reference. Thus, a person will also measure a velocity of c for the light.