# Special Theory and String Theory.

## Main Question or Discussion Point

Special Theory predicts that if we could accelerate an object to the speed of light, it would become 2 dimensional in the direction of motion. I'm not sure how many dimensions that String Theory predicts, but my question is this. Does String Theory have a satisfactory way of squeezing all their dimensions into 2?

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Hurkyl
Staff Emeritus
Gold Member
Special Theory predicts that if we could accelerate an object to the speed of light,
Anything could follow this hypothesis, and the conditional statement would be vacuously true -- special relativity says you cannot accelerate an object to the speed of light.

it would become 2 dimensional in the direction of motion.
What special relativity actually says is that if you assign coordinates to space-time in a certain kind of way, then if you increase the coordinate velocity of that object in a sufficiently uniform way, then the coordinate size of that object will appear squashed.

This squashing is not a "real" effect -- it's the same kind of effect you get if you were to look at a book from the side, and then rotate it. Initially, the book is thin, but if you rotate it until you're looking at its front, it becomes wider.

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HallsofIvy
Homework Helper
Special Theory predicts that if we could accelerate an object to the speed of light, it would become 2 dimensional in the direction of motion. I'm not sure how many dimensions that String Theory predicts, but my question is this. Does String Theory have a satisfactory way of squeezing all their dimensions into 2?
No, "Special Theory" does not say anything like that! It says that you cannot accelerate an object to the speed of light. And, therefore, does not say anything about what "would" happen in an impossible situation.

Special Theory predicts that if we could accelerate an object to the speed of light. Emphasis on if.
I'm no expert but surely the Special Theory does predict that. I've always felt that the fact that nothing can reach the speed of light, due to the fact that it would take an infinite amount of energy to achieve was a bit of a cop out for such questions as mine. Its a bit like saying there is no point in talking about time before the big bang because before the big bang there was no time.

Hurkyl
Staff Emeritus
Gold Member
I've always felt that the fact that nothing can reach the speed of light, due to the fact that it would take an infinite amount of energy to achieve was a bit of a cop out for such questions as mine.
Well, too bad. It's your own fault for making statements that special relativity says are vacuous. :tongue:

And besides, you're making implicit physical assumptions that break down at this singularity anyways. For example, the assumption that it makes sense to speak about the acceleration of an extended object.

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Its a bit like saying there is no point in talking about time before the big bang because before the big bang there was no time.
It's funny that you think that answer is a cop out.

What color were your eyes before you were born?

Don't cop out.

Fredrik
Staff Emeritus