Why does time stop when you travel at the speed of light?

Answer 1

Ultimately, it is because time like space is relative. That is to say, how much time you experience relative to someone else depends on how fast you are moving relative to them. The closer and closer you travel at the speed of light relative to them the less and less time you experience relative to them until ultimately you experience none. For more detail go to the related question "When we travel at the speed of light why does time stop." in the Related Questions section below.

Answer 2

As you approach the speed of light, your personal time rate, as measured by an outside observer, will be seen to slow down, and in theory it reaches zero at the speed of light. You can't actually reach the speed of light since that requires an infinite amount of energy, but you can get arbitrarily close to that speed. The alteration in the rate at which time passes happens in accordance with the Lorentz-Fitzgerald Contraction (which see). Given that matter, energy, space, and time all turn out to be inter-related, a sufficiently large change in speed will affect all four of these fundamental factors. That may be a somewhat vague explanation, but the precise explanation requires a lot of mathematics which would not be practical to include in my answer; you would have to go to a serious text on relativity.

Answer 3

I'm going to evade the question by giving you something to think about. If you

think about it long enough and in the right directions, you come to the conclusion

that when things move, they must become shorter and more massive, and their

clocks must run slow:

-- One day, your friend, who is always doing something crazy, comes flying

through your laboratory ... sailing right in the front door and out the back door

without ever slowing down. For some strange reason, he's carrying a ruler and

a clock, and as he swoops through, you decide that you really must know the

length of the ruler, and whether the clock is keeping accurate time. How could

you measure them without making him stop ? Remember that light takes time to

travel from one place to another.

That's your assignment ... to think about this weird situation.

Work on it for a while, but don't be discouraged if you don't get very far. A great many

very smart people worked on it for a very long time, and the first one who actually

worked it out correctly was Albert Einstein, not much more than 100 years ago.