B A question about warp bubbles and navigation

[Luis]

Hi everyone,

I've been thinking about the concept of warp drive.

From what I understand, when a ship is inside a warp bubble, it's completely cut off from the external universe. No radiation from the outside can enter the bubble, and nothing inside can interact with the outside while the bubble is active. However, this leads to a serious problem with navigation. If the ship can’t receive any signals from outside, how can the pilot of the ship know where the ship is going while it's in warp?

The most workable solution I can think of right now would be to set a predefined route that goes from one nearby star to the next. For example, you start from Earth and aim for Alpha Centauri. Once you get there, you drop out of warp, recalibrate your navigation systems, then continue on to Barnard's Star. Then you repeat the process again — jump, stop, recalibrate — and gradually work your way toward your final destination by using a series of shorter, manageable segments. It may not be the most elegant method, but to me it seems like the only reliable way to avoid getting completely lost while traveling through space in a warp bubble.

Or maybe the geometry of the bubble itself could slightly react to the gravitational curvature of nearby stars, and a ship could use that to estimate its position.

I'm not a physicist and I've never studied physics formally. I'm just an enthusiast who really enjoys thinking about this stuff, even if I can't do the math behind it. If I've misunderstood anything, I'm totally happy to be corrected.

Has this navigation issue ever been seriously discussed in the literature?

Thanks in advance to anyone who takes the time to respond.

 

[Dale]

I think that is indeed a problem. But I would assume that any civilization that is advanced enough to create a warp bubble would also be advanced enough to have pretty good maps.

 

[Ibix]

Or maybe the geometry of the bubble itself could slightly react to the gravitational curvature of nearby stars, and a ship could use that to estimate its position.

I don't know about navigation research, but with regard to this: if you're causally disconnected from outside, you're causally disconnected. You aren't causally disconnected except the warp bubble might change shape - so this is a no to this one.

 

[PeterDonis]

From what I understand, when a ship is inside a warp bubble, it's completely cut off from the external universe. No radiation from the outside can enter the bubble, and nothing inside can interact with the outside while the bubble is active.

This is not correct for the Alcubierre spacetime. Where are you getting your understanding from?

 

[Luis]

This is not correct for the Alcubierre spacetime. Where are you getting your understanding from?

As I said, I’ve never studied physics in a formal academic setting, and I don’t have the mathematical knowledge required to follow most of the technical literature. If I got something wrong, I'm more than happy to be corrected.

 

[PeterDonis]

As I said, I’ve never studied physics in a formal academic setting, and I don’t have the mathematical knowledge required to follow most of the technical literature. If I got something wrong, I'm more than happy to be corrected.

All this is fine, but it doesn't answer the question I asked you. You said "from what I understand" followed by some fairly specific information. You must have gotten that information from somewhere. Where?

 

[Luis]

All this is fine, but it doesn't answer the question I asked you. You said "from what I understand" followed by some fairly specific information. You must have gotten that information from somewhere. Where?

I don't remember. Over the years, I've read quite a lot of things about Alcubierre’s theories, and it's impossible for me to remember exactly where I read what. But I don't think it's particularly relevant. I believe it would make more sense to just explain where I might've gotten things wrong and how they actually work, rather than focusing on where I might've come across certain ideas.

 

[Ibix]

I must admit I thought Alcubierre's warp bubble was causally disconnected from the exterior too. A bit of reading suggests that the problem is that the interior cannot signal the front of the bubble, which may make it uncontrollable from within but doesn't stop you seeing out. However, there's a region behind the ship that can't signal in, so you can't see things there.

https://arxiv.org/abs/gr-qc/9907019

 

[PeterDonis]

Over the years, I've read quite a lot of things about Alcubierre’s theories, and it's impossible for me to remember exactly where I read what.

Fair enough. But there is a lot of pop science misinformation about the Alcubierre drive, and I suspect that whatever you've read falls into that category.

I believe it would make more sense to just explain where I might've gotten things wrong and how they actually work

The first thing to understand is that there's no such thing as a complete, two-way, causally disconnected region in any spacetime. You can have regions like black holes, where things can go in and not come out, or white holes, where things can go out but not come in. But you can't have a region where things can neither go out nor come in. That's simply not possible.

The second thing to understand is that the common description of the Alcubierre warp bubble as "moving faster than light" can be very misleading. What's actually going on is weirder than that, and defies simple description.

 

[DaveC426913]

From what I understand, when a ship is inside a warp bubble, it's completely cut off from the external universe. No radiation from the outside can enter the bubble, and nothing inside can interact with the outside while the bubble is active. However, this leads to a serious problem with navigation. If the ship can’t receive any signals from outside, how can the pilot of the ship know where the ship is going while it's in warp?

A warp bubble is science fiction. It behaves in whatever fashion makes the story work.

If you want to talk about some less fantastical physics, such as the hypothetical Alcubierre drive, I don't see why one would be cut off from the external universe.

It is stretching space-time, not blocking it.

I don't see why you would not be able to look out any window in your ship and see what navigational objects there are. You would have to compensate in your calcs for delay and distortion, but you could still tell where you are.

Wolf 359 is still dead ahead, Earth still dead behind. They wouldn't even be red/blue-shifted very much. The Alcubierre drive is shrinking space ahead of you, expandng it beind you, not making you go faster. Within the bubble, you may not even be moving at a relativistic speed, so little Doppler Effect.

 

[Jaime Rudas]

I must admit I thought Alcubierre's warp bubble was causally disconnected from the exterior too. A bit of reading suggests that the problem is that the interior cannot signal the front of the bubble, which may make it uncontrollable from within but doesn't stop you seeing out. However, there's a region behind the ship that can't signal in, so you can't see things there.

Signals can be sent from inside the bubble in any direction and will always pass through. Furthermore, any signal emitted in the direction of the bubble from the front exterior will enter the bubble. The only signals that cannot pass through the bubble are those emitted from the rear exterior.

 

[Jaime Rudas]

Within the bubble, you may not even be moving at a relativistic speed, so little Doppler Effect.

In fact, the central idea of the bubble is that everything inside it remains in its center, that is, it doesn't 'move'.

 

[Ibix]

Signals can be sent from inside the bubble in any direction and will always pass through. Furthermore, any signal emitted in the direction of the bubble from the front exterior will enter the bubble. The only signals that cannot pass through the bubble are those emitted from the rear exterior.

That doesn't appear to be what the paper I linked says - it says that there's also a region in front of the ship that the ship cannot signal.

 

[Luis]

A warp bubble is science fiction. It behaves in whatever fashion makes the story work.

In my native language, which is Italian, both the Alcubierre drive and the Star Trek warp drive are referred to as "curvature engine." In this case, I used warp drive because I have seen it used as a more colloquial term to refer to all those models — not just Alcubierre’s — that aim to create a space-time bubble around a spacecraft.

Anyway, thanks for your explanation!

 

[PeroK]

the Star Trek warp drive are referred to as "curvature engine."

Star Trek is fiction and the science within the programme is not real. It's necessary for the purpose of popular entertainment, but has no basis in any physical theories.

 

[Luis]

Star Trek is fiction and the science within the programme is not real. It's necessary for the purpose of popular entertainment, but has no basis in any physical theories.

I never said otherwise. I simply said that, in my native language, both the Alcubierre engine and the science-fictional warp drive from Star Trek are called "curvature engine."

 

[DaveC426913]

I never said otherwise. I simply said that, in my native language, both the Alcubierre engine and the science-fictional warp drive from Star Trek are called "curvature engine."

Right. But for the purposes of this discussion, we really need to pick one of the two and stick with it.

If you want to talk about Star Trek, and its fictional warp drive, we should have this moved to the science fiction forum.

If you want to talk about the theoretical Alcubierre drive, there are real physics surrounding it that we can discuss.

In the former, we can make up stuff, like that it can't pass signals. In the latter, that will have to be supported by real physics.

 

[Jaime Rudas]

That doesn't appear to be what the paper I linked says - it says that there's also a region in front of the ship that the ship cannot signal.

I'll try to correct my argument: the ship is at the center of the bubble, whose radius is R. Signals emitted from the ship in any direction will move away from the ship a distance greater than R, that is, they will pass through the bubble. Signals coming from the rear hemisphere of the bubble cannot pass through, but signals are constantly passing from the exterior to the interior of the front hemisphere of the bubble. What is not correct is to say that "any signal emitted in the direction of the bubble from the front exterior will enter the bubble."

 

[Jaime Rudas]

If you want to talk about Star Trek, and its fictional warp drive, we should have this moved to the science fiction forum.

If you want to talk about the theoretical Alcubierre drive, there are real physics surrounding it that we can discuss.

Yes, that's true, but one could also take into account that Alcubierre himself, in his original paper, specifically mentions the science fiction warp drive.

 

[Dale]

I never said otherwise. I simply said that, in my native language, both the Alcubierre engine and the science-fictional warp drive from Star Trek are called "curvature engine."

Sometimes people don't understand how impactful that can be. I think it is clear from the context that you want to talk about the scientific topics even if you use the words that in English could be confused with the science fiction topics.

 

[DaveC426913]

Sometimes people don't understand how impactful that can be. I think it is clear from the context that you want to talk about the scientific topics even if you use the words that in English could be confused with the science fiction topics.

My concern stems from the opening line, which is:

"I've been thinking about the concept of warp drive. From what I understand, when a ship is inside a warp bubble.."
What warp drive? What warp bubble? My preconceptions? Yours?

For me, this makes it pretty apparent that the thread is going to be about fictional ideas.

"... it's completely cut off from the external universe. No radiation from the outside can enter the bubble ..."

OK, that sounds pretty true-by-author-fiat and science-fiction-write-y to me.


If you want to talk about actual physics, we would have to have an actual theoretical model, such as the Alcubierre drive, which we can discuss objectively.


I simply ask that we define which one we are going to stick with: theoretical, or fictional? Otherwise, there is going to be a lot of "Whoa! Where does that idea come from?"

 

[weirdoguy]

I simply ask that we define which one we are going to stick with: theoretical, or fictional?

And it is perfectly clear from the context and how the thread went on.

 

[Dale]

And it is perfectly clear from the context and how the thread went on.

Yes, e.g. post 7.