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Will future humans use warp drives to explore the cosmos? We\u2019re in no position to eliminate the possibility. But if our distant descendants ever do, it won\u2019t involve dilithium crystals, and Scottish accents will have evaporated into history by then. <\/p>\n
<\/p>\n Warp drives have their roots in one of the most popular science fiction franchises ever, but they do have a scientific basis. A new paper examines the science behind them and asks if a warp drive containment failure would emit detectable gravitational waves. <\/p>\n The paper is titled \u201cWhat no one has seen before: gravitational waveforms from warp drive collapse.\u201d The authors are Katy Clough, Tim Dietrich, and Sebastian Khan, physicists from institutions in the UK and Germany. <\/p>\n There\u2019s room for warp drives in General Relativity, and Mexican physicist Miguel Alcubierre described how they could theoretically work in 1994. He\u2019s well-known in space and physics circles for his Alcubierre Drive. <\/p>\n Everyone knows that no object can travel faster than the speed of light. But warp drives may offer a workaround. By warping spacetime itself, a spacecraft with a warp drive wouldn\u2019t be breaking the faster-than-light (FTL) rule. <\/p>\n \u201cDespite originating in science fiction, warp drives have a concrete description in general relativity, with Alcubierre first proposing a spacetime metric that supported faster-than-light travel,\u201d the authors write. <\/p>\n There are clear scientific barriers to actually making a warp drive. But it\u2019s possible to simulate how one would work and how they may be detectable via gravitational waves in the event of a failure. Warp drives distort spacetime itself, just like binary mergers of compact objects like black holes and neutron stars. It\u2019s theoretically possible that they emit a gravitational wave signal in the same vein as mergers. \u201cTo search for such signals and to correctly identify them in the measured data, it is important to understand their phenomenology and properties,\u201d the authors explain.<\/p>\n It begins with understanding how warp drives might work, and for that, we have to delve deeply into physics. <\/p>\n \u201cThe principle idea behind a warp drive is that instead of exceeding the speed of light directly in a local reference frame, which would violate Lorentz invariance, a \u201cwarp bubble\u201d 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,\u201d the paper states. <\/p>\n The first barrier is that warp drives require a Null Energy Condition (NEC). Physics states that a region of space cannot have a negative energy density. There are theoretical workarounds for that, but for now, none of them are practical. <\/p>\n \u201cOther issues with the warp drive metric include the potential for closed time-like curves and, from a more practical perspective, the difficulties for those in the ship in controlling and deactivating the bubble,\u201d the authors explain. This is because there would be no way for the crew to send signals to the front of the ship. It\u2019s difficult for events inside the bubble to influence events outside the warp bubble, as this paper explains. <\/p>\n \u201cFrom the perspective of simulating the warp drive dynamically, the key challenge is stability,\u201d the authors explain. Equations show that the Alcubierre Drive can initiate a warp bubble using the Einstein Equation, but no known equations can sustain it. \u201cThere is (to our knowledge) no known equation of state that would maintain the warp drive metric in a stable configuration over time. Therefore, whilst one can require that initially, the warp bubble is constant, it will quickly evolve away from that state, and, in most cases, the warp fluid and spacetime deformations will disperse or collapse into a central point.\u201d <\/p>\n Though instability is a prime obstacle to warp drives, it\u2019s also what could make them detectable. If an Alcubierre Drive achieves a constant velocity, it\u2019s not detectable. It generates no gravitational waves and has no ADM mass. ADM stands for Arnowitt\u2013Deser\u2014Misner, named for three physicists. I\u2019ll leave it to curious readers to read more about ADM mass. <\/p>\n But the warp drive is only undetectable if it\u2019s constant and stable. Once it breaks down, accelerates or decelerates, it could be detectable. In their work, the authors allow the warp drive bubble to collapse. \u201cPhysically, this could be related to a breakdown in the containment field that the post-warp civilization (presumably) uses to support the warp bubble against collapse,\u201d they write.<\/p>\n In their formulations, the nature of the ship itself isn\u2019t important. Only the warp bubble and the warp fluid inside are significant. <\/p>\n The researchers simulated the breakdown of the warp bubble. They found that the collapse generated gravitational waves with characteristics different from those generated by mergers. \u201cThe signal comes as a burst, initially having no gravitational wave content, followed by an oscillatory period with a characteristic frequency of order 1\/[R],\u201d they write. \u201cOverall, the signal is very distinct from the typical compact binary coalescences observed by gravitational wave detectors and more similar to events like the collapse of an unstable neutron star or the head-on collision of two black holes.\u201d<\/p>\n \n