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Q & A: light speed

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Most recent answer: 10/22/2007
Q:
THE SPEED OF LIGHT IS THOUGHT TO BE THE FASTEST VELOCITY POSSIBLE. SO HOW WOULD YOU DESCRIBE THE SPEED OF LIGHT RELATIVE TO EACH OTHER OF TWO LIGHT BEAMS GOING 180 DEG OPPOSITE DIRECTION? WOULD IT BE 2C? REGARDS I’LL HAVE MORE.
- john t. cartland (age 70)
northbrook, il, usa
A:
John: if by relative speed, you mean the relative speed as described by us in our reference frame, yes, it's 2c.

If you mean "How fast does one beam go from the point of view of the other?" we can't answer it, because we know the rules for switching points of view only for things travelling at LESS THAN c relative to us.

If you were to ask about two protons travelling at 0.99c opposite directions, we can give a real answer. Their relative speed in our frame is 1.98c. But the speed of one as measured by the other is only about 0.99995 c. Strange but true- space and time don't behave the way we feel that they should.

Mike W

(published on 10/22/2007)

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