Looks like opspe understands this sort of thing better than I do, but I’ll try to explain with my limited knowledge why things can’t reach light speed. It’s all to do with the Lorentz factor, shown in this equation:

For this equation to work, you must assume that lightspeed is the maximum speed possible, and that it is constant for all observers. This assumption isn’t unjustified, since the experimental work of Michelson and Morley and theoretical work of Maxwell had pretty much proven that assumption to be true over a century ago.
The Lorentz factor is a factor of time dilation. ‘v’ is the velocity of an object you’re observing, ‘c’ is the speed of light, and ‘y’ is the factor of time dilation. You’ll see that as v increases, the bottom of the fraction will tend to zero. This means that y will tend to infinity, so from your point of view, the object will experience a slower flow of time than you. If v were equal to c, the bottom of the fraction would equal zero, and dividing by zero isn’t allowed. v also couldn’t be more than c, because then you’d be taking the square root of a negative number. As a result, no matter what you do to the object, you can never get v to equal c.
I’m fairly certain I’ve missed something crucial in my explanation. Honestly, if somebody sent that explanation to me, I wouldn’t be satisfied with it, but it’s the best I can do. You should trust opspe’s post more than mine.

## Algernon

Dec 02, 2011 at 03:27PM EST