Call me crazy but, I think there might a speed faster than C

[suckstobeyou]

if you have one train inside another train both traveling close to C in the same direction what would be the speed of the second train inside of the first one for an observer standing on the ground?

lets extend this to a billion embedded trains what's the speed of the inner-most train to an obserevr on the ground?

 

[Danger]

I don't know the math, but you're not going to get that inside train to light speed. You'll still run into the 'infinite energy required' problem, regardless of whether it's strictly under its own power or is in part parasitical upon the outer train.

 

[Doc Al]

relativistic addition of velocities

if you have one train inside another train both traveling close to C in the same direction what would be the speed of the second train inside of the first one for an observer standing on the ground?

The speed would be close to but less than C.

The speed would be given by the relativistic addition of velocities formula:
$$U' = \frac{U + V}{1 + \frac{U V}{c^2}}$$

V is the speed of the first train with respect to the ground, U is the speed of the second train with respect to the first, U' is the speed of the second train with respect to the ground. You can see that the relative speed of the second train will never exceed the speed of light.

 

[Danger]

Thanks for the formula, Doc. I never figured there'd be one simple enough for me to work out by myself.

 

[suckstobeyou]

that sux:grumpy:

 

[Pengwuino]

Thanks for the formula, Doc. I never figured there'd be one simple enough for me to work out by myself.

*slaps danger*

What kinda physisist are you :tongue2:

 

[Danger]

I'm not a physicist (although I know how to spell it :tongue: ), or an engineer, or anything else of the sort. As I've stated in other areas, I never finished high-school and have a grade 9 math education.

 

[dicerandom]

that sux:grumpy:

Actually I think it's quite wonderful, although I think I understand how you feel about it. The ideas behind Special Relativity are extremely disconcerting at first, you have to adjust your entire perspective of space and time in order to come to terms with the ideas. However, once you have done so the theory is extremely simple and beautiful, it's really quite amazing.

 

[suckstobeyou]

you're very positive... that's really wonderful.

can anybody help me out with my other problem here?

https://www.physicsforums.com/showthread.php?t=103987

 

[Danger]

Not me... for the above-mentioned reason.

 

[x2468]

hey guys. new here.

I remember reading that a group of scientists managed to slow down light? also, if at the point a start becomes a black whole, the light it was giving off should now begin to be pulled into the black hole by gravity correct? thus the light must slow down and change direction. or in any case, a black hole must be slowing light down at some point? thus, if light can be slowed down then it is not constant and there is little reason to believe it can't be sped up as well? that ideas been on my mind for a while. been lookin for some answers.

 

[Morbid Steve]

hey guys. new here.
I remember reading that a group of scientists managed to slow down light? also, if at the point a start becomes a black whole, the light it was giving off should now begin to be pulled into the black hole by gravity correct? thus the light must slow down and change direction. or in any case, a black hole must be slowing light down at some point? thus, if light can be slowed down then it is not constant and there is little reason to believe it can't be sped up as well? that ideas been on my mind for a while. been lookin for some answers.

But you've got that incorrect. This black whole has mass, and therefore something to 'stop' the light. When you shine light at a brick wall does it keep going? Nope. It's merely stopping and being refracted into -blackness- (black is simply the absence of color).

 

[aalmighty]

umm, I don't think mass is something which 'stops' light, a sheet of glass had mass the last time I checked.