Thread: Speed of light = ?

OK, so light speed in a vaccum is 299,792,458 m/s. And according to the special theory of relativity, that is a constant and as you apporach it time slows down, right? So, then when you reach it time stops completely. When you reach light speed, then you would travel a distance over 0 time, and we all know that only chuck norris can divide by zero, otherwise the result is undefined. So my question is, why is the speed of light 299,792,458 m/s when it would be undefined if time stopped, traveling an infinite distance in no time at all.

The first thing is: Time never 'slows down' like that. Suppose Brad is on a spacecraft that is gradually approaching speed of light (with respect to earth), and Angelina is watching him from earth. Angelina will see that movements of Brad is slowing down over time, or, in other words, she will observe that a clock on the spacecraft is moving slower and slower with respect to a clock in Angelina's room, i.e, on earth. But Brad would never agree with Angelina if she says he's gettin slower. In fact, he is not getting slower, it's time that is getting dilated in his spacecraft as observed from Angelina's frame. Same is the case when Brad looks at Angelina, he will see everything on earth getting slower, since earth can also be said to be moving away from him at the same speed.

Now let us take this assumption to the critical limit- the speed of light. Angelina will see Brad getting 'freezed', and vice versa.

But this case is impossible-an object can never reach this speed limit, because the energy required to accelerate it to this speed will require infinite amount of energy to be expended, which is impossible.

Originally Posted by diparnak

The first thing is: Time never 'slows down' like that. Suppose Brad is on a spacecraft that is gradually approaching speed of light (with respect to earth), and Angelina is watching him from earth. Angelina will see that movements of Brad is slowing down over time, or, in other words, she will observe that a clock on the spacecraft is moving slower and slower with respect to a clock in Angelina's room, i.e, on earth. But Brad would never agree with Angelina if she says he's gettin slower. In fact, he is not getting slower, it's time that is getting dilated in his spacecraft as observed from Angelina's frame. Same is the case when Brad looks at Angelina, he will see everything on earth getting slower, since earth can also be said to be moving away from him at the same speed.

Now let us take this assumption to the critical limit- the speed of light. Angelina will see Brad getting 'freezed', and vice versa.

But this case is impossible-an object can never reach this speed limit, because the energy required to accelerate it to this speed will require infinite amount of energy to be expended, which is impossible.

but i'm sure brad and angelina will make a movie to the contrary... actors

Originally Posted by diparnak

The first thing is: Time never 'slows down' like that. Suppose Brad is on a spacecraft that is gradually approaching speed of light (with respect to earth), and Angelina is watching him from earth. Angelina will see that movements of Brad is slowing down over time, or, in other words, she will observe that a clock on the spacecraft is moving slower and slower with respect to a clock in Angelina's room, i.e, on earth. But Brad would never agree with Angelina if she says he's gettin slower. In fact, he is not getting slower, it's time that is getting dilated in his spacecraft as observed from Angelina's frame. Same is the case when Brad looks at Angelina, he will see everything on earth getting slower, since earth can also be said to be moving away from him at the same speed.

Now let us take this assumption to the critical limit- the speed of light. Angelina will see Brad getting 'freezed', and vice versa.

But this case is impossible-an object can never reach this speed limit, because the energy required to accelerate it to this speed will require infinite amount of energy to be expended, which is impossible.

That wasn't the question.
The question was why is the speed of light 300,000,000 m/s for an independant observer when light in its own frame travels any distance in 0 time.

if you would to reach light speed in normal spsace universe would implode becuase of the infinite mass

Maybe it is not 0 time. Maybe it is 'approaching' 0 the closer it gets to light speed. So in fact, light speed might be 299,792,458 m/0.0000000000001 second.

Otherwise, you are right, it wouldn't make sense. It's similar to the mpg indicator in a vehicle. Some people believe their engine suddenly consumes zero gas when at a red traffic light, because the indicator goes up to 0mpg. But you ain't gettin 0mpg, fool, it's just that you re not moving, so that means you get zero mile, but you still consume energy.

Originally Posted by paindealer

OK, so light speed in a vaccum is 299,792,458 m/s. And according to the special theory of relativity, that is a constant and as you apporach it time slows down, right? So, then when you reach it time stops completely.

It is not possible to reach the speed of light (in the context that you are using it, unlike in the context that Einstein used it, as described below). Therefore, it is always necessary to go slower than the speed of light. As you say, the speed of light is a constant, and so your speed is irrelevant to your perception of the speed of light.

When you reach light speed, then you would travel a distance over 0 time,

This is not possible.

So my question is, why is the speed of light 299,792,458 m/s when it would be undefined if time stopped, traveling an infinite distance in no time at all.

The speed of light is 299,792,458 with respect to all observers (non-light) because it is a constant, as you accepted above. The fact that it would be zero if time stopped is not relevant to observers, as it does not apply to them.

It does apply to light, however. Einstein said that everything in the universe moves at the same speed, the speed of light. This speed is divided into 4 dimensions of motion, 3 of space and 1 of time. 100% of all of the motion of light is in the dimensions of space, and therefore there is 0% of its motion available for motion through time. As all non-light must have some of its motion through space-time as motion through time, it cannot devote 100% of its motion to motion through space, and therefore cannot be like light.

Originally Posted by Imaplanck.

That wasn't the question.
The question was why is the speed of light 300,000,000 m/s for an independant observer when light in its own frame travels any distance in 0 time.

If you look at a clock traveling past you at the speed of light, the clock would appear to be stuck on a moment in time - but it would still be moving away from you at the speed of light.

This is getting confusing. Could we go back to talking about Brad and Angeline?

JA Cambece
JA Cambece Law Office

Originally Posted by Scifor Refugee

Originally Posted by Imaplanck.

That wasn't the question.
The question was why is the speed of light 300,000,000 m/s for an independant observer when light in its own frame travels any distance in 0 time.

If you look at a clock traveling past you at the speed of light, the clock would appear to be stuck on a moment in time - but it would still be moving away from you at the speed of light.

Yes thats what I said!
For any independent observer(an observer not moving a c) no matter what the relative velocity light will be observed at 300,000,000m/s(minus a very small amount, obviously). For light itself - that very same ray of light can travel 50LYs, 50000000LYs or any distance you care to mention in 0 time.
His question 'why is light speed 289,900,000m/s?' however can only be greeted with: I don't know it just does(certainly the impertinent replies here have borne that out anyway(the guy obviously already understands SR to make the question in the first place)).