Warp Drives: Difference between revisions
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== The Alcubierre warp drive == | == The Alcubierre warp drive == | ||
The first warp drive geometry that satisfied the Einstein field equations of relativity was proposed by Miguel Alcubierre<ref>M. Alcubierre, "The warp drive: hyper-fast travel within general relativity." Classical and Quantum Gravity. 11 (5): L73–L77. [https://arxiv.org/abs/gr-qc/0009013 arXiv:gr-qc/0009013]. Bibcode:[https://ui.adsabs.harvard.edu/abs/1994CQGra..11L..73A 1994CQGra..11L..73A]. doi:[https://doi.org/10.1088%2F0264-9381%2F11%2F5%2F001 10.1088/0264-9381/11/5/001]. S2CID [https://api.semanticscholar.org/CorpusID:4797900 4797900].</ref>. In this geometry, a sphere of space-time moves at an arbitrary speed (potentially but not necessarily a speed much faster than light). Objects at rest within the sphere are moved along with the sphere. Space is expanding at the rear boundary and contracting at the front boundary in order to keep the sphere moving. In order to satisfy the Einstein field equations, the boundary of the sphere must have a negative energy density. The challenges of space-time geometries with negative energy densities are described in our page on [[Wormholes#Exotic_energy_conditions|wormholes]], for our purposes it is enough to note that negative energy densities can pose problems if not handled carefully, there are limits on how much negative energy you can have without nearby positive energy density, and it may not be possible to get enough negative energy to support a warp drive; although none of this is rules out by physics – yet! | The first warp drive geometry that satisfied the Einstein field equations of relativity was proposed by Miguel Alcubierre<ref>M. Alcubierre, "The warp drive: hyper-fast travel within general relativity." Classical and Quantum Gravity. 11 (5): L73–L77 (1994). [https://arxiv.org/abs/gr-qc/0009013 arXiv:gr-qc/0009013]. Bibcode:[https://ui.adsabs.harvard.edu/abs/1994CQGra..11L..73A 1994CQGra..11L..73A]. doi:[https://doi.org/10.1088%2F0264-9381%2F11%2F5%2F001 10.1088/0264-9381/11/5/001]. S2CID [https://api.semanticscholar.org/CorpusID:4797900 4797900].</ref>. In this geometry, a sphere of space-time moves at an arbitrary speed (potentially but not necessarily a speed much faster than light). Objects at rest within the sphere are moved along with the sphere. Space is expanding at the rear boundary and contracting at the front boundary in order to keep the sphere moving. In order to satisfy the Einstein field equations, the boundary of the sphere must have a negative energy density. The challenges of space-time geometries with negative energy densities are described in our page on [[Wormholes#Exotic_energy_conditions|wormholes]], for our purposes it is enough to note that negative energy densities can pose problems if not handled carefully, there are limits on how much negative energy you can have without nearby positive energy density, and it may not be possible to get enough negative energy to support a warp drive; although none of this is rules out by physics – yet! | ||
== Credit == | == Credit == | ||
Revision as of 19:41, 28 February 2026
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Science fiction often features spacecraft that can seemingly move across space and getting between the place of departure and the destination much faster than light could have done. This appears to contradict the theory of relativity, which predicts unequivocally that nothing can move through space faster than light. Because relativity has been incredibly successful at describing nature, with its many other predictions regularly being confirmed to extraordinary accuracy and within the bounds of uncertainty of all the experiments that tested them, it gives confidence that relativity is a correct description of reality. Which seems to rather throw a wet towel on our hopes for rapid travel between stars.
However, while relativity does not allow things to move through space faster than light, it places no such restrictions on how fast space-time itself can expand, contract, or move around. This leads to the idea of a warp drive – the spacecraft remains stationary within a region of highly curved space-time, and that region moves at super-luminal speeds rather than the spacecraft.
The Alcubierre warp drive
The first warp drive geometry that satisfied the Einstein field equations of relativity was proposed by Miguel Alcubierre[1]. In this geometry, a sphere of space-time moves at an arbitrary speed (potentially but not necessarily a speed much faster than light). Objects at rest within the sphere are moved along with the sphere. Space is expanding at the rear boundary and contracting at the front boundary in order to keep the sphere moving. In order to satisfy the Einstein field equations, the boundary of the sphere must have a negative energy density. The challenges of space-time geometries with negative energy densities are described in our page on wormholes, for our purposes it is enough to note that negative energy densities can pose problems if not handled carefully, there are limits on how much negative energy you can have without nearby positive energy density, and it may not be possible to get enough negative energy to support a warp drive; although none of this is rules out by physics – yet!
Credit
Author: Luke Campbell
References
- ↑ M. Alcubierre, "The warp drive: hyper-fast travel within general relativity." Classical and Quantum Gravity. 11 (5): L73–L77 (1994). arXiv:gr-qc/0009013. Bibcode:1994CQGra..11L..73A. doi:10.1088/0264-9381/11/5/001. S2CID 4797900.