# Couple of Speed of Light Qs

I have a feeling I already know the answer to these questions, but given that physics gets a little squirrelly when you get around light speed, I figure I’d better ask.

If I was riding in a nuclear powered rocket at 99% the speed of light, could I lift my arm? (I’m figuring I probably could, provided it wouldn’t exceed the SoL, but there’s that whole “infinite mass” thing.)

Next, what would the mass of the rocket exhaust be at near the SoL?

Third, what the hell would an “inverse tachyon pulse” be (ala ST:TNG)?

If you turn on your headlights while driving at the speed of light, what happens?
and
If I fire a gun while near light speed, will the bullet EXCEED light speed?
As for #2, umm, well, that’s a very good question.
And for #3, of course, that’s just the opposite of a NORMAL tachyon pulse.

1. Your arm would only feel the acceleration, if any, of the rocket. Relativistic effects are perceived only by those in a different reference frame. You would not know that anything had changed. Time, mass, length, all would appear to you exactly as under earth conditions.

2. The mass of the exhaust is dependent on the equation m[sub]e[/sub] = gamma times m[sub]o[/sub], where gamma is called the Lorentz factor: 1 divided by the square root of (1 - v[sup]2[/sup]/c[sup]2[/sup]). Note that this is highly dependent on v, so that even slight variations in one’s speed close to c makes for huge differences in the final result. Again, however, this is only noticeable to someone looking at you from another reference frame. You would not notice any change in your rocket or its exhaust.

3. Gobbledygook. Pure gobbledygook.

(1 + 2) [Rhubarb’s link to Cecil’s column is perfect] Maybe I could add/re-iterate one or two things: Special Relativity works frame-wise like a Galilean Relativity in that every inertial frame sees itself as being still (hence “relativity” - every other frame is relative to one’s own frame). The laws of physics according to you (in your own frame), lifting your arm, shining a flashlight, etc. are no different than what one would expect being still. It’s the observance of such things from other frames that produces the odd results predicted by Special Relativity.

Because of the SR modeled, “warped”, perception of other frames, velocities do not add straight in those other frames. v3 = (v1 + v2)/(1+v1v2/c^2) is the SR solution, instead of v3 = v1 + v2. Mass and gravity are also “normal” from and to other objects that are all in your frame. Also, others attempting to stop you from other frames may find that the impulse provided by an impact does not follow a straight momentum calulation, p = mv – more like p=mv/sqrt(1-v^2/c^2). Energy also follows a similar pattern in SR. Your “responses over time”, observed from other frames, will also be scewed and your length in the direction of motion.

The fun Einstein Limit question is that if you were to be moving at c and you shined a flashlight forward, would you blow up?
One - the question produces an undefined, divide by 0, in SR. But if one were to speculate - the time one experiences when observed from any other frame would be 0, thus your finger flipping the switch would take an eternity. As well, your length would be contracted to a point where you are 2-D in every other frame.

As far as “inverse Tachyon Pulses”… “All good things” was a sweet finale for Star Trek the Next Generation! One would have to discover the generalized properties of tachyons before one might be able to project what an “inverse tachyon” would entail. Since we haven’t discovered any verified tachyons in accelertor tests yet, it would be difficult to say what any of the final properties and limitations of tachyons might be. :dubious: