# Faux faster than light travel?

I know that FTL travel is thought to be impossible since the amount of energy required to propel an object of any mass become infinite the closer you get to the speed of light.

HOWEVER, since speed is relative to an observer, isn't all that is required to reach FTL speed as follows:

(1) Ship "A" heads North at slightly greater than half the speed of light.

(2) Ship "B" heads South at slightly greater than half the speed of light.

That way for people on Ship "A", they feel like they're standing still, but looking at Ship "B", Ship "B" is indeed traveling at FTL speed.

Comments?

### 6 Answers

- 1 decade agoFavourite answer
Nope, it doesn't work like that. Because of the time dilation effect, each observer will measure that other moving at less than the speed clocked by a "stationary" observer between them. Their relative velocity as measured from the moving ships will still be less than c.

If their speeds are v1 and v2, the formula that gives their relative velocity in their own frames of reference is:

u = (v1 + v2)/(1 + v1v2/c^2)

If they are each moving at, say, 60% of the speed of light, then they will each see the other moving at a velocity

u = (.6 + .6)/(1 + .36) = 1.2/1.36 = 0.882

i.e., each will see the other moving at 88% of the speed of light.

- 1 decade ago
Their red shift would equal 1, true. However...

The people on ship "A" would be able to detect the red shift of light coming from ship "B", but would have to 'adjust' it in order to actually 'see' it. Once adjusted for their known speed, they would be able to tell that the other ship is only moving at 1/2 the speed of light.

(The mass of the object accellerating to the speed of light does not actually become infinite UNTIL the speed of light is reached. Until then, it's still finite, even at .99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999...(infinite number of 9s here)...9 c.

- zee_primeLv 61 decade ago
When you're dealing with relativistic speeds, that is, speeds comparable to that of light, one plus one doesn't equal two; it equals less than two. If you add up any two speeds you'll still get, at most, the speed of light. If I'm moving towards you at half the speed of light and shine a torch at you, the light leaves me at the same speed as it reaches you; 300 000 km. a second.

- 1 decade ago
You're overlooking 2 things:

1) light appears to be going at c no matter what speed you're going at beside it. If I'm going at .5c and I measure the speed of light, it will still be c and not .5c

2) There is a formula that takes this fact into account to add relativistic speeds. Redo your little experiment with this formula and see how the result differs from c

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- 1 decade ago
Although this would have the appearance of faster than light speed when observing the other ship, still light speed has not been reached, so in my opinion your theory would be correct, faux light speed, at least in appearence.

Source(s): makes sence - 1 decade ago
Can a space craft accelerate and reach the speed of light and multiples of C?

Today's science says no.

What does tomorrow's science say?

maybe....just maybe. Remember, one time they believed the earth was flat. today we know it's not.

Take todays science with a pinch of salt, tomorrow may change it forever