– is wrong. In the example given, the result would be 3.258c, not 0.994c. In fact, the given formula predicts that the “addition” of two velocities always gives a result greater than their mathematical sum. That’s clearly not the case. If it were true, it would indeed allow faster-than-light travel.
I’m guessing this is a case of poor editing, as I can’t imagine Cecil himself would make such a blatant mistake.
Ugh. I missed the "/"s, and though the quantities were being multiplied instead of divided. How did I make a mistake like that? :smack:
I can be such an idiot sometimes. Worst of all, when I challenge something, I often make these bold declarative statements, without adding qualifiers like “I think”, because I’m so sure I’m right. Then later it turns out I missed something obvious.
Ah well. Better that I should be wrong than a Straight Dope column, anyway.
There’s a neat little trick that relativistic physicists do to make the math a little easier, and that is let c = 1. That is, when you say that something is moving at a speed of 0.6, it’s implicit that it’s 0.6 times the speed of light.
Then the velocity addition formula becomes w = (u + v) / (1 + uv), and the problem reworked is one or two steps shorter:
Um, DrMatrix, did you notice that Some Guy said in the very next post that he misread the equation? He does realize now that he made a mistake. Perhaps you just wanted to know what mistake he made. If not, you’re the third person in this thread to say something stupid as a result of missing something pretty obvious. Perhaps we should start a club!
Yup. I knew from the start that it wasn’t Cecil who actually made the mistake. I just didn’t realize that it was me (duh).
If you read the whole thread, you know that it’s already been established that I made a dumb mistake, so that doesn’t really need pointing out anymore. If you didn’t… well, read my reply to DrMatrix above.