View from a ship with an Alcubierre Drive

Question

What would a person on a ship with an Alcubierre Drive see as the drive starts running and once it is running? Once the drive is fully powered, the ship would be going faster than light.

I have found the related question What would an external observer see when passed by an Alcubierre drive ship? It seems from the answers there that the warp bubble does allow light to cross the boundary, but with substantial refraction and wavelength shift effects. Combine this with the fact that the bubble is moving forwards faster than light, so no photons can hit the bubble from behind. I think the result is that you get an extremely distorted and wavelength shifted view of the what is in front of the ship, but I assume there are substantial other factors.

Answer 1

They would see stuff normally, albeit blueshifted and distorted, in a cone in front of them.

Drop the speed-of-light stuff; what can the captain of a supersonic aircraft hear? The exact same logic applies: start going faster than the carrier of information, and you can only receive information from a cone in front of you. The shape is roughly related to the shape that the shockwave going behind the supersonic craft has; imagine drawing the shockwave as the standard cone emanating from behind the craft, then rotate it 180.

A lot of those distortion effects are related to the ultra-high energy density of the spacetime as well as the immense curvature, so if you figure out how to build one without breaking quantum mechanical rules, the image would likely be less distorted as we’d expect. Based on some simulations I did a while back, though, you could expect a fisheye effect from inside the bubble, increasing in strength as you speed up. Once you cross $c$, also expect everything behind you to disappear.

Answer 2

Sometimes genuine worldbuilding questions need explicitly writing advice answers. I guess this is a frame challenge.

What you want is a widget for shortening travel times that fits the tone of a setting where scientists understand the principles that engineers use to make the tools that characters use, not a doctoral thesis on speculative physics with a story glued to it.

To get a plausible FTL technology, you need a black box plus the declaration that inside the black box is a machine that works because modern physics was a little bit incorrect in a complicated way. You can make up a name for the way that modern physics was incorrect if you want, and you can name the black box for something in modern physics (like Alcubierre) if you want.

The blacker the black box, the better your plausibility. So don't put windows on the space ship, or shutter them for FTL for extra radiation protection. They don't have anything close enough to look at, anyway. Characters can look at computer projections of where things effectively are. (The computer projections run on another black box.)

Answer 3

It depends on the construction of your drive

The acceleration of the ship in an Alcubierre bubble is due to the compression of spacetime ahead of it. It is equivalent to that of falling into a gravity well. Consider how that spacetime compression is being achieved and we can speculate as to what the view from inside would look like.

Proposals for such a drive fall into two major categories: Wormholes and Tachyons. While you don't have to be specific with your story, the mechanics would affect the shape of your light cones.

Moreover, according to Serguei Krasnikov,[19] generating a bubble in a previously flat space for a one-way faster-than-light trip requires forcing the exotic matter to move at local faster-than-light speeds, something that would require the existence of tachyons

Additionally, regarding the Alcubierre metric, there are choices to be made as well. Does spacetime unfold behind the ship or in another direction?

An extension of the Alcubierre metric that eliminates the expansion of the volume elements and instead relies on the change in distances along the direction of travel is that of mathematician José Natário. In his metric, spacetime contracts towards the prow of the ship and expands in the direction perpendicular to the motion, meaning that the bubble actually "slides" through space, roughly speaking by "pushing space aside".[9][10]

It follows that we must consider the nature of the compressed spacetime ahead of the ship. Do the geodesic lines diverge out? Only light traveling through the spacetime that is shared with the ship can be seen from the ship.

Wormholes: In this case, a spacetime fold exists (naturally or artificially) in the corridor between your ship and its destination. Light from the far end should be visible normally as you would see looking through a tube. However, you can choose whether the metric allows light to enter the tunnel through the sides or not. If so, it would probably have similar effects as Gravitational Lensing.

Tachyons: In order to fold spacetime ahead of the ship superluminally, something must trave ahead, faster than the speed of light, to deliver the energy required to compress spacetime. Here, all bets are off as tachyons are purely hypothetical and their effects are as well. Is there a Naked singularity ahead of your ship or did your drive produce an event horizon? You could make a case for seeing nothing but black, or bright white as light is distorted by the compressed spacetime ahead.

So to answer your question and give a suggestion: As others have pointed out, writing a dissertation into the story is not ideal. It requires a level of understanding from readers that is really not necessary. As all effects on light seen from an Alcubierre driven ship are hypothetical, pick one, give a short explanation, and your readers will accept it.

Answer 4

An Alcubierre drive bubble is less complex than people think it is. It compresses space in the volume in front of the ship, and de-compresses it behind the ship. This means that, at the same velocity, the ship moves across a greater amount of space.

If you follow that math, another implication is that the volume inside the warp bubble is a medium of higher density than the surrounding space. Fortunately, thanks to Willebrord Snellius, we know exactly how light behaves when passing through a denser medium. Just consider the volume inside of the bubble to be like a bubble of water in air, adjusting for density as a percentage of the speed of light.

The thing I never really got about an Alcubierre drive is what makes them think that the laws of time dilation would be changed. Unless you have some other magic, then you're still going to see normal relativistic blue-shifting of light. If you do have that magic, then you won't.

BUT there will be more of it. A lot more. This is the "running through raindrops" concept. When figuring out how wet you'll get when running through rain, the amount of wet you get doesn't change much if you move faster.

That calculation, however, is based on passing through a fixed volume. Same volume = same wet. This changes if you consider it from the perspective of wet per second. When running, you collect all of the wet in a shorter period of time.

When moving through rain, your exposure to water is a function of your speed compared to the speed of falling raindrops (which, like the speed of light, can be considered a constant). Here's the Wolfram Alpha page on those calculations. You just have to substitute "bright" for "wet".

Answer 5

I am not sure that someone inside the bubble would 'see' anything from the outside at all.

As I understand it, the entire concept of the A-drive is to 'warp' space/time around the bubble, therefore everything including photons would be warped around the bubble as well. For anything from the outside to be 'seen' from the inside, something from the outside would have to be left behind. Not quite sure how that would be handled by physics and that 'conservation of energy and momentum transfer' thing.

Seems to me an A-drive bubble would be the perfect cloaking device, with the Law of Unintended Consequences requiring that not only can the outside not see the cloaked device, but the cloaked device can not by definition detect anything from the outside. To detect anything from the outside, something from the outside would have to be 'left behind' on the inside, thus would result in a 'void' or shadow when 'seen' from the outside.

An even more interesting conjecture would be 'how would entanglement between the inside and the outside' work?

Answer 6

The result can be anything you want for story purposes. An actual Alcubierre drive traveling faster than light would break physics. Relativity, causality and a lot more beside would need to be rewritten to account for the new phenomena.

In such cases there would be little point in asking what the old broken physics predicts because it would clearly be wrong.

It is a bit like asking what does spherical geometry predict about what is north of the North Pole? If someone actually demonstrated such a place, spherical geometry as we know it would be shown to have a flaw and it would have no predictive power concerning such places.

No doubt people will have a range of speculative views one what happens. I would use whichever one fits your purposes best.