Can We Create a Warp Drive for Light? - Josh's Curiousity

[somedudeonline]

TL;DR Summary

Short version: Is creating a warp drive more feasible if we only consider creating it for light itself? This could allow us to send messages (or control rovers on other planets) faster than light and would provide a new avenue to take in the search for intelligent life.

Hello everyone,

Preface: I'm hoping this doesn't violate the speculative or personal theories clause in the forum guidelines. It's really just a curiosity, I'm in no position to argue/develop/push the idea or anything. If this does violate that clause, would you be able to recommend a similar forum that allows for this type of discussion?

I've always been fascinated by all the cool things out in space (SMBH, Magnetars, Exoplanets, etc...). Unfortunately, I didn't realize this was what I should've pursued as a career until after I got my bachelor's in business. Basically, I love the stuff but couldn't begin to understand the actual math/physics behind it so when I have an idea like the one I'm about to describe, the best I can do is think "huh, I wonder if that's possible". Please keep that in mind when responding (dumb it down for me).

So after reading about the new theoretical developments with warp drive technology (supposedly physics allows for a warp drive that doesn't require negative energy). I had the idea of creating a warp drive specifically for light so that we could send data faster (not travel faster but arrive faster, you know what I mean) than light. None of the articles I could find on this new solution (Erik Lentz's) really describe it's limitations so I have no idea how feasible it actually is and my idea probably just applies to the earlier idea that would require a stupendous amount of mass in order to generate enough negative energy to move a ship faster than light.

So my question is a two part-er. 1. Would it be possible to create a warp drive specifically for light or would it have to be created for something more physical like a radio emitter that would have to be loaded with information to distribute once it reaches it's destination? 2. How much mass would be required to generate the necessary negative energy to transport either light itself or an emitter if necessary? My guess would be that something like a radio emitter would probably still require a significant amount of mass while light itself would be in the feasible range. Unfortunately, I think anything that we want to move via warp drive would require some kind of engine that would have to do work to convert the mass to negative energy and regardless of what is being sent, that engine would make the required mass beyond feasible. But as we move closer and closer to the feasible range, I would think that sending information would be our first goal. I also think it should be something we try to figure out how to identify at a distance so that we can improve our search for intelligent life.

Josh

 

[Ibix]

It's helpful if you provide links to what you want to discuss.

Lentz' paper: https://arxiv.org/abs/2006.07125

 

[DennisN]

Summary:: Short version: Is creating a warp drive more feasible if we only consider creating it for light itself? This could allow us to send messages (or control rovers on other planets) faster than light and would provide a new avenue to take in the search for intelligent life.

I had the idea of creating a warp drive specifically for light so that we could send data faster

Sending data faster than light also violates causality and relativity.
Edit: Maybe I misunderstood the premise. Is this about wormholes or not?

 

[somedudeonline]

Sending data faster than light also violates causality and relativity.
Edit: Maybe I misunderstood the premise. Is this about wormholes or not?

Hi Dennis, as I understand it, it's not about wormholes necessarily but warping space around you so that you travel a shorter physical distance in the same amount of time. From an outsider's perspective, you would be traveling the full distance. I'll take Ibix tip and reference the earlier more commonly known (I think) solution to this problem: https://www.researchgate.net/publication/1963139_The_Warp_Drive_Hyper-fast_Travel_Within_General_Relativity

 

[Ibix]

Sending data faster than light also violates causality and relativity.
Edit: Maybe I misunderstood the premise. Is this about wormholes or not?

Warp drive solutions aren't wormholes. I have read that they do allow causal paradoxes, but have not seen a rigorous proof.

OP: I don't think warp bubbles allow you to send light only. The interior of the bubble allows timelike worldlines to "travel" in the bubble, but I think lightlike paths exit the bubble. Certainly they reach the bubble wall where tidal gravity is extremely strong, so I'd tend to suspect messages wouldn't survive long undistorted even if they don't simply exit the bubble.

I'll suggest this be moved to the relativity forum, where it's likely to get more replies.

 

[PeterDonis]

I'll suggest this be moved to the relativity forum, where it's likely to get more replies.

Moved.

 

[somedudeonline]

Warp drive solutions aren't wormholes. I have read that they do allow causal paradoxes, but have not seen a rigorous proof.

OP: I don't think warp bubbles allow you to send light only. The interior of the bubble allows timelike worldlines to "travel" in the bubble, but I think lightlike paths exit the bubble. Certainly they reach the bubble wall where tidal gravity is extremely strong, so I'd tend to suspect messages wouldn't survive long undistorted even if they don't simply exit the bubble.

I'll suggest this be moved to the relativity forum, where it's likely to get more replies.

Thanks!

 

[PeterDonis]

I don't think warp bubbles allow you to send light only.

This is correct. More generally, it's impossible to have a region of spacetime that only contains lightlike (null) worldlines. Any such region must, as a matter of simple geometry, also contain timelike worldlines (and spacelike curves as well).

 

[PeterDonis]

The interior of the bubble allows timelike worldlines to "travel" in the bubble, but I think lightlike paths exit the bubble.

This is correct for a standard Alcubierre warp drive; there are no null worldlines that remain inside the bubble indefinitely.

 

[somedudeonline]

This is correct for a standard Alcubierre warp drive; there are no null worldlines that remain inside the bubble indefinitely.

I see, thank you for the info. So that brings us to the standard Alcubierre warp drive for something just large enough to transfer data (say a few centimeters in diameter and weighing 50 grams). The news article I read ( https://astronomy.com/news/2021/04/warp-drives-physicists-investigate-faster-than-light-space-travel ) states that Chris Van Den Broeck showed that the Alcubierre warp drive allows for a ship with a 100 meter diameter to go ftl using a single solar mass to generate the negative energy rather than the mass of the entire observable universe. So I'm wondering how much mass (roughly) it would take to move something of this data transmitter size rather than an entire ship.

 

[Ibix]

More generally, it's impossible to have a region of spacetime that only contains lightlike (null) worldlines. Any such region must, as a matter of simple geometry, also contain timelike worldlines (and spacelike curves as well).

Indeed, but that wasn't what I meant by "light only" in this context. I was meaning that the Alcubierre warp bubble has a timelike worldline which "hovers" inside the bubble, but I don't know of a solution with a lightlike path that "hovers" in the bubble, which is what would be needed for the OP's "FTL radio" idea. So you couldn't put light (only) inside a bubble and send it off, you'd need machinery.

 

[PeterDonis]

I don't know of a solution with a lightlike path that "hovers" in the bubble

I'm not aware of any such solution either.

 

[Ibix]

I'm not aware of any such solution either.

In fact, isn't the hovering worldline the integral curve of the ADM lapse vector $N^i$ at the bubble center? Wouldn't that suggest you can't have an "FTL radio" solution in the ADM formalism? I think $N^i$ needs to be timelike. That doesn't mean you can't have such a bubble, but would mean you'd need a very different approach to finding one.

 

[PeterDonis]

isn't the hovering worldline the integral curve of the ADM lapse vector $N^i$ at the bubble center?

I believe so, but I'd have to check to be sure. (Also, $N^i$ is the shift 3-vector; the lapse in the ADM formalism is a scalar, $N$.) [Edit: no, this won't work. See below.]

I think $N^i$ needs to be timelike.

I'm not sure this is the case in general in the ADM formalism. But for the particular case of being inside the bubble in Alcubierre spacetime, this might be the case.

Edit: Actually, no, it doesn't make sense to say that $N^i$ is timelike, because the shift $N^i$ is a 3-vector, not a 4-vector. It's a vector "in" the 3-space of the formalism. Which means it doesn't make sense to talk about integral curves of $N^i$ in the 4-d spacetime either.

 

[Ibix]

Edit: Actually, no, it doesn't make sense to say that $N^i$ is timelike, because the shift $N^i$ is a 3-vector, not a 4-vector. It's a vector "in" the 3-space of the formalism. Which means it doesn't make sense to talk about integral curves of $N^i$ in the 4-d spacetime either.

Good point. I was thinking of $N^i$ as like the flagpole in MTW's figure 21.2, connecting two spacelike slices, but as you say, it isn't.

 

[mfb]

I see, thank you for the info. So that brings us to the standard Alcubierre warp drive for something just large enough to transfer data (say a few centimeters in diameter and weighing 50 grams). The news article I read ( https://astronomy.com/news/2021/04/warp-drives-physicists-investigate-faster-than-light-space-travel ) states that Chris Van Den Broeck showed that the Alcubierre warp drive allows for a ship with a 100 meter diameter to go ftl using a single solar mass to generate the negative energy rather than the mass of the entire observable universe. So I'm wondering how much mass (roughly) it would take to move something of this data transmitter size rather than an entire ship.

The paper says "total negative mass [...] of the order of a few solar masses".
This requirement doesn't seem to depend that strongly on the interior volume if I understand the paper correctly. The trick is already to get a larger interior volume with a tiny exterior surface (similar to an atomic nucleus). Give or take an order of magnitude. Even ignoring that negative energy probably doesn't exist, you need to pack all that negative energy into the size of a larger atomic nucleus!