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Comment by alberte | Hacker News Reader

The question should be "If two objects approach at 75 percent the speed of light relative to me then what is their speed relative to each other"

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I agree...I know this is supposed to be about their relativity to each other but the way my mind interpreted the wording was "Why are neither of the two objects traveling at 1.5 times the speed of light?" and I immediately thought "Well because it's relative and you can't say that you driving 60mph and another car going 60 mph in the opposite direction means you're driving at 120mph because you're still driving 60mph

edit: Because the question doesn't specify the speed relative to what exactly, I automatically thought about the speeds of the objects relative to themselves rather than to each other or a 3rd party.

If my car is travelling at 60 mph and there is a car in the opposite direction also travelling at 60 mph (according to a inertial frame of reference) then classical mechanics allows me to say that from my point of view the other car is indeed traveling at 120 mph. But special relativity only allows me to say that the other car is travelling at 119.9999999999990394 mph from my point of view. The higher the speed, the greater the difference in the results from "classical mechanics" and "special relativity" will be.

Or to be even more exact, "... relative to me and I am between them", since speed is scalar; the ships could be meeting each other at a 30 degree angle.

Get out of the way?

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