Another light question for physicists and astronomers.

Suppose we can travel faster than light. What would the light we were traveling faster than "look" like? Would we be able to see it at all? Would we be able to see anything?

Would the light in our supposed ship be traveling faster than the light outside the ship (light, moving faster than light)? And again, what would that "look" like to us- or would there be any difference at all?

No real reason for this question, other than curiousity.

Are you having a fun afternoon?

You may as well ask, "What is the color of unexposed photographic film?"

Otherwise the photons wouldn't be able to strike your eyes (or whatever equipment you're using) and give you the picture.

Back when "Ask Mr. Science" had a TV show, he did an experiment to show what happens when you ride your bicycle at the speed of light and then turn on your headlight. Funny stuff.

According to how we understand the physics now, the only way we'll end up going faster than light is not actually travelling at a speed faster than light but rather finding a shortcut to arrive at a spot before the light does. (So we skip the space that the light has to traverse.)

Why a black-hole of course, which is what you'd be if you could travel faster than light (your mass increases to infinity as you approach the speed of light). Time would also slow to a stop as you approached the speed of light and you would not experience anything.

We can't conjecture what would happen if we could violate this fundamental law of the universe, although there are several ways around the law, including warping space and wormholes through space, neither of which has been observed and only exist in theory.

...and is no longer infinite. Well that's what the equations say.

does anything happen?

The comedian Steven Wright asks that.

And you can't just suppose can travel faster than light; your mass (M) will approach infinity as your speed approaches that of light. E=MC² still holds.

It doesn't specifically say that you can't travel faster than the speed of light but for all intents and purposes it is the same thing.

Some physicists back in the 70's played around with the idea of Tachyons - particles that always travel faster than the speed of light (taking advantage of that little loophole about accelerating past the speed of light) but the idea was dropped - it would be such a strange beast - always traveling backward in time was just one of its properties - that even Physicists who are pretty comfortable with weird things they let it go.

The speed of light is the time it takes his wife to say "Go" when the light turns green.

This is something of a guess since we don't have any models in which a material object (i.e. one made of matter) can travel even at the speed of light, much less faster. However, if you were traveling faster than the speed of light you would be outrunning any light trying to reach you, so you should see nothing outside your ship.

If we suspend our cosmological model and pretend that you *could* travel faster than light, the light inside your ship would be traveling at the speed of light in your frame of reference, and everything would seem completely normal to the occupants of the ship. A lot of people have a hard time understanding this even for plain old relativity--but in your own rest frame, that is the frame in which *you* are not moving, everything looks to you as it would here on earth, regardless of your speed. Relativity only comes into play when you ask what an external observer would measure. There's a relativistic formula for the addition of velocities. However, that formula becomes imaginary if the speed is greater than that of light. That is, it is imaginary in the mathematical sense, i.e. a multiple of the square root of -1. Imaginary numbers are, in fact, relevant to the "real world" but I don't think anybody's worked out how an imaginary net velocity would be perceived by an observer.

Tachyons are hypothetical particles that *always* travel at faster than the speed of light--in fact they *can't* slow down to or below light speed (c). There's a fairly well developed theory of tachyons although I don't know whether they have a good quantum mechanics for them. But they can't be causally connected to our normal, slower-than-light universe. So you can't see them whether they exist or not :-)

Since it's all speculation anyway, I'd have to speculate that any method of traveling faster than light would entail somehow making a sort of local bubble of space/time that would, to an observer outside the bubble, apparently travel faster than light; but to any occupants of the bubble, nothing would appear out of the ordinary except that the only information they could receive would be from within their bubble. I'm picturing something like what the Alcubierre Metric suggests, wherein the spacecraft itself would not actually be moving at all, but the manipulation of exotic material modifying space/time immediately in front and behind of the bubble's apparent motion would cause the whole region of the metric to, for all intents and purposes, travel at arbitrarily high (FTL) speeds.

If I recall correctly, based on the research of the time, he described something he called the "luxon wall" which was exactly the speed of light. Our universe would be slower than the luxon wall, while there would be another universe that was faster than the luxon wall.

Here's the tricky part, and I confess I don't recall the reasoning behind it, but Asimov concluded that if it were somehow possible to just "leap over" the luxon wall, the hyper-luxon universe you entered would act just like our normal sub-luxon universe. In other words, if you somehow managed to go 1% faster than the speed of light, you would simply perceive yourself as traveling at 1% slower than the speed of light.

I couldn't say what you'd see out your window, though.

Edited for spelling.

As you approach the speed of light, time dilation kicks in and time starts passing slower (for you, as seen by the rest of the universe): If you were driving at the speed of light and switched the lights on, it would take until the end of time just to reach for the switch. Although things would appear 'normal' to you - the light would be moving infinitely slowly, but then so would you (I'm canceling infinities here, which is cheating :))

Moving that quickly, you'd also become infinitely thin and infinitely dense (think of Ann Coulter rushing round the chat-shows).

If you did manage to get that fast, light coming up behind you would red-shift to infinite wavelength and zero energy, so your rear view mirror would be totally black: Light from the front, on the other hand, would have zero wavelength and infinite energy. Take some sunblock. Light from the side would be normal, but since you'd seem to be moving infinitely fast (because of the time dilation) it would be a bit of a blur.

What things would look like moving faster than light would depend largely on what happens to time dilation past lightspeed: I don't think anyone's attempted that yet (in terms of maths), but Asimov's 1% faster = 1% slower that Geoff posted seems reasonable.

Good questions, btw :)

... namely that the effect is that the "blind-spot" in your eye expands
to fill your field of view ... you cannot see light outside your own
frame of reference (your ship) as the relative velocity prevents photons
from "catching up" with you but it is so different from normal darkness
(really just seriously reduced light intensity) as to give a completely
different physiological response - hence the "blind-spot" effect.

"No windows on the Overcee II"!

Although I think that's hyperdrive, isn't it? In normal space (like the Bussard Ramjets he's so fond of) stuff just gets red/blue shifted...

I might be wrong, I'd have to go rumaging though through some boxes to check... :)

> Although I think that's hyperdrive, isn't it? In normal space (like
> the Bussard Ramjets he's so fond of) stuff just gets red/blue
> shifted...

Ah .. that'll be because his hyperdrive takes ships faster than light
(ref OP) while the Bussard drives are fast but sub-lightspeed ...

:-)

(Nice to see another Niven fan :toast: )

...there are people who aren't Niven fans? That's disturbing.
I meant to say hyperspace, not hyperdrive, but I'm glad I didn't - having thought it over, you're perfectly correct. :dunce:

See you down at The Draco Tavern for a sparkler or two...

:D :beer:

"everything is relative" - That's the essence of relativity theory.

Theoretically you can travel the circumference of the universe in far less time than it would take at light speed - as seen from the perspective of the traveler. From the perspective of people staying on earth it would take you millions upon millions of years. Both perspectives are equally valid, equally true.

So FTL travel isn't practical in most cases (even if we'd have powerful enough engines). Also you (the traveler) would experience all kinds of odd relativistic effects.
http://en.wikipedia.org/wiki/Special_relativity

used -t, perhaps you could fit it with a -(lambda) to straighten things out, but I don't think so. (Not that I know, I don't have the math with me, but I should know as I have a physics exam the day after tomorrow). Wait a tick, you might be able to represent it, (in fact it would probably be the best idea) as to treat it as if one wavelength viewed until the speed of light would translate into another when faster.

But taking a quasi-newtonian viewpoint (just for the properties of light, treating it as a 'beam')

You could not 'see'
A) Anything behind you
B) yourself

However, you could 'see' things in front of you. Sort of.


P.S. One last thing: Tachyons were mentioned upthread. One of my teachers, (Who is, btw, an expert at this stuff) Said they were real.... whether he meant mathematically real or physically real, I do not know, but I suspect the former. Trying to check it out, but not much luck thus far.

P.P.S about the tachyons, yes, they do go back in time. If you want them, you destroy them and then they (his words, not mine) "Travel backward in time and create themselves at a later date"

Which is cool.

Cool stuff.