Will humans use warp drives to explore the cosmos in the future? We are unable to rule out this possibility. But if our distant descendants ever do, it will have nothing to do with Dilithium crystals and Scottish accents will be a thing of the past by then.
Warp drives have their roots in one of the most popular science fiction franchises of all time, but they have a scientific basis. A new paper examines the science behind it, asking whether a warp drive containment failure would emit detectable gravitational waves.
The title of the paper is “What no one has seen before: Gravitational waveforms from warp drive collapse.” The authors are Katy Clough, Tim Dietrich and Sebastian Khan, physicists from institutes in the UK and Germany.
There is room for warp drives in general relativity, and Mexican physicist Miguel Alcubierre described how they could theoretically work in 1994. He is well known in space and physics circles for his Alcubierre Street.
Everyone knows that no object can move faster than the speed of light. But warp drives could offer a solution. By distorting spacetime itself, a spaceship with warp drive would not violate the faster-than-light speed rule (FTL).
“Although warp drives have their origins in science fiction, there is a concrete description in general relativity: Alcubierre was the first to propose a spacetime metric that supported faster-than-light travel,” the authors write.
There are clear scientific obstacles that make warp drive difficult indeed. But it is possible to simulate how it would work and how it might be detectable by gravitational waves if it went wrong. Warp drives distort spacetime itself, just like binary mergers of compact objects like black holes and neutron stars. Theoretically, it is possible that they could emit a gravitational wave signal similar to that of a merger.
“To search for such signals and correctly identify them in the measurement data, it is important to understand their phenomenology and properties,” the authors explain.
First, we need to understand how warp drives might work, and to do that we need to delve deeply into the physics.
“The basic idea behind a warp drive is that rather than directly exceeding the speed of light in a local frame of reference, which would violate Lorentz invariance, a ‘warp bubble’ could travel distances faster than the speed of light (as measured by a distant observer) by contracting spacetime in front of it and expanding spacetime behind it,” the paper says.
The first obstacle is that warp drives require a zero-energy state (NEC). Physics dictates that an area of space cannot have negative energy density. There are theoretical workarounds for this, but currently none of them are practical.
“Other problems with the warp drive metric include the potential for closed timelike curves and, from a more practical perspective, the difficulties for those inside the ship to control and deactivate the bubble,” the authors explain.
This is because the crew would have no way of sending signals to the front of the ship. It is difficult for events inside the bubble to affect events outside the warp bubble because This document explains it.
“From the perspective of warp drive dynamic simulation, stability is the biggest challenge,” the authors explain. Equations show that the Alcubierre drive can initiate a warp bubble using the Einstein equation, but no known equation can sustain it.
“There is (to our knowledge) no known equation of state that would keep the warp drive metric in a stable configuration over time. So, although one can require the warp bubble to be initially constant, it will quickly move away from that state, and in most cases the warp fluid and spacetime deformations will dissipate or collapse into a central point.”
Although instability is a major obstacle to warp drives, it is also what could make them detectable. If an Alcubierre drive reaches a constant speed, it is undetectable. It does not generate gravitational waves and has no ADM mass. ADM stands for Arnowitt–Deser–Misner, named after three physicists. I leave it to curious readers to read more about it. ADM mass.
However, warp drive is only undetectable when it is constant and stable. As soon as it collapses, accelerates or slows down, it could be detectable. In their work, the authors collapse the warp drive bubble.
“Physically, this could be related to a breakdown of the containment field that the post-warp civilization (presumably) uses to protect the warp bubble from collapse,” they write.
In their formulations, the nature of the ship itself is not important. Only the warp bubble and the warp fluid inside are important.
The researchers simulated the collapse of the warp bubble. They found that the collapse produced gravitational waves with different properties than those produced by fusion.
“The signal comes as a burst that initially has no gravitational wave content, followed by an oscillation period with a characteristic frequency of the order of 1/[R]they write. “Overall, the signal is very different from the typical mergers of compact binary stars observed by gravitational wave detectors and is more similar to events such as the collapse of an unstable neutron star or the head-on collision of two black holes.”
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The authors point out that although the warp drive generates a GW signal, it is outside the frequency range of our current earth-based detectors.
“Proposals have been made for higher frequency detectors, so that in the future one may be able to narrow down the existence of such signals,” they write. The ship itself could also be sending some kind of multimessenger signal, but it’s hard to say how the ship’s matter would interact with normal matter.
“Because we don’t know the type of matter the warp ship was built from, we don’t know whether it would interact with normal matter (apart from gravity) as it travels through the universe,” the researchers explain.
This is a fun thought experiment. It’s possible that someday in the distant future there will be some sort of workaround for faster-than-light travel. If that’s the case, it might be related to a better understanding of dark matter and dark energy. If ETIs exist, they might be able to use fundamental knowledge about the universe that we don’t yet possess.
If they have figured out how to construct and use a warp drive, their activities could, despite all the apparent impossibilities, generate gravitational waves that our future observatories could detect even in other galaxies. But for now, this is all just theory.
“We note that the obtained waveforms are likely very specific to the model used, which has several well-known theoretical issues, as explained in the introduction,” the authors write in their conclusion. “Further work would be needed to understand how general the signatures are and to properly characterize their detectability.”
No doubt some curious physicists will continue to work on it.
This article was originally published by Universe Today. Read the original article.