This is necessary for most space dramas but has, apparently, become cliche in the eyes of some publications. That being said...

Is it possible for two spaceships flying alongside each other at FTL speed to see each other through their windows?

The only thing that matters is if you can convince me that it is possible.

(The inherent problem in your question is that our current physics says that the speed of light is constant, and independent of the speed of the observer. Thus, if you could somehow go faster than light (which the theory says you can't but anyhow) then, since you're going, er, faster than light, how would you ever see anything? The light bouncing off the thing you're looking at would never catch you up, so you'd, er, never see the thing you're looking at. Even if you're looking at another ship going FTL, makes no difference; the light still travels at the same constant speed, slower than you and therefore invisible. I think you'd see black out the window, not the streaks-for-passing-stars you see out of the Enterprise window when it's going where nobody went before at Warp speed. The idea we often see in movies that in FTL space everything goes bendy and psychdelic colours has no scientific basis, methinks.)

In Melissa Scott's "Dreaming Metal", for example, ship's pilot needed special hardware that was AI-enhanced to navigate space at FTL speed; I believe that in her universe it wasn't possible to see out of a ship at all.

I think that, without entirely contradicting current physics, today's SF can posit wormholes -- connections between 'folds' of space, through which ships travel. Although they move at sub-light speeds, ships get the appearance of FTL by taking short cuts through the wormholes from one region of the galaxy to another.

Then it would depend on your imaginary physics; even if a wormhole were large enough for two ships side by side, it might be necessary for a ship to be exactly in the middle of the wormhole for it to transport the ship accurately and safely; then, the windows would need to be fore and aft so that ships could travel one after another in the wormhole yet see each other.

Another factor would be the length of the wormholes. If they literally just connect folds in space, they might be quite short and a ship might not spend enough time inside to observe anything.

Of course, two ships going faster than light, would have an light reflecting off them, to pass behind them. The other ship would not be seen.

One thing that is used for interplanetary travel, is to also use a quirk in physics that we have not solved, to allow faster than light communications and faster than light vision.

I have heard theories that light does not actually travel at the same speed. They have seen signs of evidence that shows that different wavelengths do move faster than others. That might be something that can be used. At faster than light speed, they might be under the speed of certain wavelengths and not others. The computer could correct the images so things have some normalcy to them when looking at the screens and for navigating.
Exotic particles could move faster. One might be seeing by gravitational waves, or some quantum effect.

For faster than light travel, I prefer digging a hole in the fabric of the universe and then traveling in another dimension to the destination.

Second, we have recently discovered that light is not the speed limit of the universe. We have found that the universe is expanding faster than the speed of light, which has the entire scientific community wringing their hands. So faster than the speed of light is apparently possible, but I couldn't imagine anyone surviving it unless their was something on the other end to reform the energy into matter, such as a transporter from Star Trek.

For example, imagine that you can, in fact, travel through normal time/space above the speed of light, and the light from your pair of ships travels at a fixed velocity. Consider that this light may then describe a cone - a 'light' shockwave inside which your ship can be seen, outside which it cannot - observers behind you can see your ship (with some artifacts of its motion) but observers ahead cannot.

The light cones don't intersect in the present - you can't see the ship next to you now.

Because you're travelling faster than light, the neighbour's light cone cannot catch you and you can't see them in the past either (which is what you can do with stars, let's say).

But, I wonder, can you see the neighbour's light cone in the future? For example, if you are one light-second away, do you in fact see their ship ahead of you, one second in the future? Could you build a technology around this, firing a probe ahead of a ship, and then following the probe in its wake, monitoring the probe's progress to counter events before they've happened?

Yes, it ignores some physics conventions, but isn't that half of the fun of speculation

As an adherent to relativity I would opt for space folding or wormholes rather than FTL. And in that case I would stay away from waving at each other through windows. Warp spaced should be an opportunity to describe something much less mundane.

You guys rock. What a fun conversation!!!

(And special shout-out to Pat for giving the clearest and most amusing parenthetical explanation of relativistic effects of FTL travel that I've seen.)

I don't have anything to add to this conversation but a book recommendation. I'm reading a book right now called Physics of the Impossible by Michio Kaku (by way of a recommendation from @MaryRobinette, who interviewed him for a sf pub recently.) It's a rocking good read so far. I'm on the chapter about force fields. Yet to come are Invisibility, Phasers and Death Stars, Teleportation and a number of other fun bits that are frequent guests in my stories. I would recommend you check it out as it's written by a theoretical physicist as a way to explain what science there is currently for these crazy things we think of as sci-fi, and where he thinks we might be going.

He divides the book into Class I, II and III Impossibilities. Class I Impossibilities are things that are impossible today but don't violate known laws of physics. Class II are technologies that sit at the very edge of our understanding of the physical world. Class III are things that violate the known laws of physics, which he points out is a very small group of things (perpetual motion machines and precognition are in this section.)

If, on the other hand, it is not key to the story.

You could have the character working in the cabin, and a friend comes back from the meeting where it was explained to the passengers.
"How was the meeting."
"They talked about plank theory, quarks, time differencials, phase shifts."
"I thought so." He opens a case.
"Did they use any english?
"No, just a few words here and there, and then not the way we use it."
"I do wish they would speak english when they explain these things rather than scientific. It would make understanding how this works, a lot easier."

The ship, locally, is not moving. It's the local area of space that is moving and taking the ship with it. This bypasses some areas of relativity and solves problems like inertia. You would not feel the acceleration tug as your craft sped up because you are not moving.

I found that answer unacceptable so I postulated my own reason. I am guessing this has been given before, but in this short amount of time I haven't seen it. So all you physics brainiacs out there let me know how this sounds, and let me down gently if this is common thought:

The faster you travel, whether on a planet or in a spaceship, the slower your personal experience of time is (it is relative). When you look out in space, whether up in the sky or out of your spaceship, everything appears to be speeding up due to your personal experience of time slowing (the faster you go, the slower your own time seems) versus the rest of the universe. Therefore the light actually catches you "faster" because you are experiencing slower time (the two negate each other, creating a constant speed of light). Inflation affects neither of these, but creates the red-shift.

I personally find the animated example on wikipedia helpful in understanding this problem.

"A Briefer History of Time", by Hawking and Mlodinow, might help. It's more accessible than Hawking's original book and when I read it some while ago I thought I got it. But I can't explain it now, so if my children ever ask, I'll lend it to them.

quote:

---

...but it's the only way to get some people to some exotic location beyond our solar system and still be able to have some link to the rest of the universe...

---

I have ideas that fulfill this without resorting to FTL travel--not that I am against using FTL--I'm not. It was just your statement that it was 'the only way'.

quote:

---

...but it's the only way to get some people to some exotic location beyond our solar system and still be able to have some link to the rest of the universe. That's what I use it for---the worlds I usually write about are Earthlike-with-a-few-differences...

---

Obviously FTL doesn't and will likely never exist...your comment seemed to suggest that it was the only way (in a story) to get people to some exotic location beyound our solar system.

Apologies if I got the wrong end of the stick.

Another idea: when a jet flies overhead faster than the speed of sound, you don't hear it until after it passes. Perhaps if you fly faster than the speed of light, you'll see some sort of afterimage?

The question of what an audience might willingly believe in an SF story is quite a different one. While I know that FTL cannot be done using known physics, I'm quite happy to go on believing in Star Trek's Warp Drive and its anti-matter crystals, because it's a good yarn.

Interestingly, such stories have been acceptable to SF audiences despite Einstein publishing his theory of relativity at around the same time as SF's Golden Age, if not a little before. (So it's possible to persuade SF audiences to accept science they know is whacky.) I suspect that as more of us grok relativity, and more writers depict FTL in cliches of bright flashes and streaky stars, it becomes less acceptable.

For example, in contrast to Star Trek and Star Wars, we never see Firefly's Serenity entering or exiting FTL. She quickly traverses lightyears, but the writers don't explain how; all we know is that she has an engine, so we can enjoy the drama of the -- single, for heaven's sakes! -- engine failing, without the challenges of getting a modern audience to accept FTL, or some other complicated physics which doesn't move the story along and only risks confusion.

-Fahrion Kryptov