Warp drive

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A warp drive ( English to warp, “distort”, “curve”) is understood to be a hypothetical drive mechanism that enables travel at faster than light speed by deliberately bending space-time . Warp drives are known in various designs from science fiction literature, where they are a prerequisite for interstellar space travel .

The compatibility of this drive concept with the general theory of relativity is controversial. This possibility is discussed again and again in the physical literature , whereby the authors arrive at different results.

Warp drive in science fiction

background

Science fiction stories are often set in planetary systems , nebulae, or galaxies that are many light years apart. In order to represent the action conclusively, a type of drive is required that enables travel over astronomical distances in a short time by human standards. For this, a movement at a multiple of the speed of light is necessary, but according to the statements of the theory of relativity - the state of science generally recognized today and often experimentally confirmed - this is impossible. Among other things, it follows from the theory of relativity that an infinite amount of energy would be required for such rapid movement and that the travelers would move backwards through time from the point of view of a third party waiting for them at the place of arrival, for example; they would arrive earlier than they left. Under these circumstances, consistent actions would no longer be possible in the fictional narratives.

The warp drive solves this dilemma, as presented in science fiction literature, by changing spacetime itself instead of moving through space and time so that a spaceship can travel extremely long distances in a relatively short time without moving at high speed to have. In this way he makes the fictitious actions appear plausible.

Concept history

The science fiction author Gene Roddenberry resorted to the concept of the warp drive for his television series Star Trek to describe the management of great distances to other star systems (→ Warp drive in Star Trek ). The term is widely known in science fiction today, but is interpreted differently depending on the author. Even if the concept of a space-time distorting engine is now generally associated with Star Trek, the basic idea is much older. Chester S. Geier described a similar drive in his 1948 novel The Flight of the Starling - referred to there as a "warp generator":

"[The warp generators] ... create a warp in space around the ship ... a moving ripple in the fabric of space."

"[The warp generators] ... create a curvature in space around the ship ... a moving wave in the structure of space."

Even Stephen Baxter's novel The Last Ark describes the use of a warp drive. With several kilograms of antimatter, the protagonists create a tiny “pocket universe”, which, however, from the perspective of the spaceship crew, has a diameter of several hundred meters.

Theories on the feasibility of a warp drive

Spacetime in the theory of relativity

In the general theory of relativity , gravity is traced back to the geometric properties of space-time . These properties are described by the Einstein equations.

Here is the classic gravitational constant , the speed of light and the Ricci tensor . Furthermore is the curvature scalar and the metric tensor . The latter contains the space-time metric and induces a measure of distance. The source of the gravitational field is the energy-momentum tensor .

The theory of the warp drive according to Alcubierre and Van den Broeck

Illustration of the warp metric according to Alcubierre

A functioning warp drive would have to change the space-time area around a spaceship in such a way that the distance between the start and destination point is reduced. The spacetime would have to be compressed in the direction of travel and expanded again after the ship has passed. These changes in spacetime due to gravitational waves would have to happen at faster than light speed, and the spaceship would travel along in this “warp bubble”.

Theoretically, this can be described by defining a certain energy-momentum tensor . Such a description, which is consistent with the formalism of general relativity, was first put forward in 1994 by the Mexican physicist Miguel Alcubierre . However, it is not a strict solution of the Einstein equations , but was constructed directly with the desired properties. In order to satisfy the equations, a fuel with negative energy density would be required, which is also known as exotic matter .

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Since the Alcubierr drive concept would require around ten billion times more exotic matter than the visible universe has in total normal matter, it was improved accordingly by the Dutch physicist Chris van den Broeck. To do this, he closed Alcubierre's warp bubble around two more bubbles. His calculations came to the conclusion that the demand for exotic matter would be reduced to a few solar masses . The outer bubble, i.e. the actual Alcubierre-Warp bubble, is  assumed to be very small (R = 3 · 10 −15 m). The innermost bubble, however, has a surface area that corresponds to a bubble 200 m in diameter. This apparently paradoxical discrepancy should be made possible by a four-dimensional geometry . However, the matter density in both drives is as high as it was in the universe shortly after the Big Bang .

Alcubierre and Broeck assumed a space-time that was previously uncurved. If spacetime is curved, however, according to Sergei Krasnikow, 10 kg of exotic matter should be enough to create such a system of warp bubbles. Krasnikov even claims to have reduced the necessary amount of exotic matter to a few milligrams by further modification of the Van den Broeck metric.

Research by Finazzi, Liberati, and Barceló questioned the stability of the warp bubble.

McMonigal, Lewis and O'Byrne from the University of Sydney came to the conclusion that when the car is slowed down, it emits radiation that is fatal to the environment.

NASA research: Breakthrough Propulsion Physics Project

From 1996 to 2002 NASA funded the Breakthrough Propulsion Physics Project to evaluate exotic propulsion concepts. Within this project, various speculative concepts of the warp drive were described and researched mathematically or using computer models. In 2008 NASA finally stopped this project, but financed further basic university research.

Experiments

In the aftermath of the Breakthrough Propulsion Physics Project, NASA physicist Harold White tried to measure the smallest curvatures of space-time in the laboratory, but it was unsuccessful.

literature

Web links

Wiktionary: Warp drive  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ Alcubierre, 1994.
  2. ↑ Chris van den Broeck: A 'warp drive' with more reasonable total energy requirements. Classical and Quantum Gravity 16 (12), 1999, pp. 3973-3979, doi: 10.1088 / 0264-9381 / 16/12/314 , arxiv : gr-qc / 9905084v5 .
  3. ↑ Serguei Krasnikov: Hyperfast Interstellar Travel in General Relativity. Phys. Rev. D57 (1998) 4760-4766, arxiv : gr-qc / 9511068v6 ; Allen Everett, et al .: Time travel and warp drives - a scientific guide to shortcuts through time and space. Univ. of Chicago Pr., Chicago 2012, ISBN 978-0-226-22498-5 , pp. 122ff.
  4. ^ Sergei Krasnikov: The quantum inequalities do not forbid spacetime shortcuts. Physical Review D, 67, 2003, doi: 10.1103 / PhysRevD.67.104013 , arxiv : gr-qc / 0207057 . (Van Den Broeck's trick pages 18–19)
  5. ↑ Stefano Finazzi, Stefano Liberati, Carlos Barceló: Semiclassical instability of dynamical warp drives. Physical Review D, 79 (12), 2009, doi: 10.1103 / PhysRevD.79.124017 , arxiv : 0904.0141v2 .
  6. ^ Carlos Barceló, Stefano Finazzi, Stefano Liberati: On the impossibility of superluminal travel: the warp drive lesson. , 2010. arxiv : 1001.4960v1 .
  7. ↑ Brendan McMonigal, Geraint F. Lewis, Philip O'Byrne: The Alcubierre Warp Drive: On the Matter of Matter. Physical Review D, in press (June 4, 2012), arxiv : 1202.5708v1 .
  8. ↑ Warp drive: danger to civilization at the travel destination. ( Memento from June 17, 2012 in the Internet Archive ) Wissenschaft aktuell, March 14, 2012 (Summary of the study by McMonigal et al .; accessed June 4, 2012)
  9. ^ Breakthrough Propulsion Physics Project . NASA, November 19, 2008.
  10. ↑ Keith Cowing: Clarifying NASA's Warp Drive Program . SpaceRef, April 12, 2013.
  11. ↑ A Lab Experiment to Test Spacetime Distortion . centauri-dreams.org.
  12. ↑ Jeff Lee, Gerald Cleaver: The Inability of the White-Juday Warp Field Interferometer to Spectrally Resolve Spacetime Distortions . July 29, 2014, arxiv : 1407.7772 .