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The principle idea behind a warp drive is that instead of exceeding the speed of light directly in a local reference frame, a ‘warp bubble’ could traverse distances faster than the speed of light — as measured by some distant observer — by contracting spacetime in front of it and expanding spacetime behind it.
Clough et al. proposed a formalism for studying warp drive spacetimes dynamically and produced the first fully consistent numerical-relativity waveforms for the collapse of a warp drive bubble.
Despite originating in science fiction, warp drives have a concrete description in general relativity, with University of Wales astrophysicist Miguel Alcubierre first proposing a spacetime metric that supported faster-than-light travel.
Whilst there are numerous practical barriers to their implementation in real life, such as the requirement for an exotic type of matter with negative energy, computationally, one can simulate their evolution in time given an equation of state describing the matter.
In a new work, theoretical astrophysicists studied the signatures arising from a warp drive ‘containment failure.’
“Even though warp drives are purely theoretical, they have a well-defined description in Einstein’s theory of general relativity, and so numerical simulations allow us to explore the impact they might have on spacetime in the form of gravitational waves,” said Dr. Katy Clough, a researcher at Queen Mary University of London.
“The results are fascinating. The collapsing warp drive generates a distinct burst of gravitational waves, a ripple in spacetime that could be detectable by gravitational wave detectors that normally target black hole and neutron star mergers.”
“Unlike the chirps from merging astrophysical objects, this signal would be a short, high-frequency burst, and so current detectors wouldn’t pick it up.”
“However, future higher-frequency instruments might, and although no such instruments have yet been funded, the technology to build them exists.”
“This raises the possibility of using these signals to search for evidence of warp drive technology, even if we can’t build one ourselves.”
“In our study, the initial shape of the spacetime is the warp bubble described by Alcubierre,” said Dr. Sebastian Khan, a researcher at Cardiff University.
“While we were able to demonstrate that an observable signal could in principle be found by future detectors, given the speculative nature of the work this isn’t sufficient to drive instrument development.”
The authors also delve into the energy dynamics of the collapsing warp drive.
The process emits a wave of negative energy matter, followed by alternating positive and negative waves.
This complex dance results in a net increase in the overall energy of the system, and in principle could provide another signature of the collapse if the outgoing waves interacted with normal matter.
“It’s a reminder that theoretical ideas can push us to explore the Universe in new ways,” Dr. Clough said.
“Even though we are sceptical about the likelihood of seeing anything, I do think it is sufficiently interesting to be worth looking.”
“For me, the most important aspect of the study is the novelty of accurately modeling the dynamics of negative energy spacetimes, and the possibility of extending the techniques to physical situations that can help us better understand the evolution and origin of our Universe, or the processes at the centre of black holes,” said University of Potsdam’s Professor Tim Dietrich.
“Warp speed may be a long way off, but this research already pushes the boundaries of our understanding of exotic spacetimes and gravitational waves.”
“We plan to investigate how the signal changes with different warp drive models.”
The team’s paper was published online in the Open Journal of Astrophysics.
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Katy Clough et al. 2024. What no one has seen before: gravitational waveforms from warp drive collapse. Open Journal of Astrophysics 7; doi: 10.33232/001c.121868
