Q&A: The Speed of Light
The Speed of Light
Question
Hello.
I’m studying physics on my own and don’t have anyone to ask, so I hope this is also an appropriate place for questions like this.
According to special relativity, the closer one moves to the speed of light, the more time dilates for the moving observer (or perhaps one should say that his measurement of time dilates relative to an observer moving more slowly). However, if one looks from the point of view of the light itself and plugs that into the Lorentz transformation, one gets division by zero. My question is what can be inferred from that:
1) Does this mean that the equation itself is not valid in this case, like when people say that Einstein’s field equations break down inside a black hole and we have to wait for the discovery of a new and broader theory.
2) Or does it simply mean that light does not “experience” time. But that is strange—what does that even mean? For example, for an observer on Earth, light created in the sun takes 8 minutes to reach him, but what happens from the “point of view” of the light itself? Does it simply exist all the time and throughout all space (after all, length also contracts for it to zero)? Is it neither created nor destroyed? (How can one even speak about the creation of something that does not “experience” time
and speak about it having come from the sun to us.)
Answer
The formulas are not relevant / not defined for something moving at the speed of light. The mass becomes infinite. A photon's rest mass is 0. Another body cannot reach the speed of light.
Discussion on Answer
Indeed, as I wrote.
Light has no time. In order to measure time you need a clock, and the measurement of time is relative to a clock at rest. Since light can never be at rest—it is always moving at the speed of light—you cannot attach or ascribe a clock to it.
The mass becomes infinite for an object with mass; my question is about light itself, whose mass is 0. So the formulas are still not relevant to it?