How far away is travel faster than light?
No object with mass has been shown to travel faster than light, and no faster-than-light signal has been shown. The most discussed route is a warp drive, which changes spacetime around a craft rather than speeding the craft up. Alcubierre's 1994 metric needs exotic matter with negative energy density. Later papers claim positive-energy versions, but these are disputed, and none has been shown to be physically achievable. The 2011 OPERA neutrino result that appeared to exceed light speed was revised in 2012, and the revised measurement is consistent with light speed within its uncertainties.
Very far away. The basic science has not been shown to work.
No faster-than-light travel, and no faster-than-light signalling, has been demonstrated. The warp-drive papers are mathematical solutions of Einstein's equations, and the sources reviewed disagree on whether any of them can be physically realised. Because the core effect has not been shown in any form, the stage is science-unproven. The Horizon scale has no separate theoretical stage, so science-unproven is the closest fit.
The tech tree
Everything recorded on Vrulum that this future needs, oldest foundations at the top and the goal at the bottom. Lines show what each step requires.
- 1994Warp metric shown as a solution of Einstein's equationsDone Unlocked.
- 2012Apparent faster-than-light neutrinos tested and revisedDone Unlocked.
- 2014Faster-than-light signalling with entangled particlesNot started Locked.
- 2016Sub-light interstellar light-sail conceptIn progress Being researched.
- 2021Positive-energy warp solutions proposedDone Unlocked.
- Date not recordedRecord flyby speed of Parker Solar Probe reportedDone Unlocked.
- GoalTravelling faster than lightGoalRequires: Nuclear space propulsion and power, Warp metric shown as a solution of Einstein's equations, Positive-energy warp solutions proposed, Apparent faster-than-light neutrinos tested and revised, Faster-than-light signalling with entangled particles, Sub-light interstellar light-sail concept, Record flyby speed of Parker Solar Probe reported. Locked.
The road so far
4 of 6 steps done, 1 in progress.
- Done · 1994Warp metric shown as a solution of Einstein's equations
Alcubierre's 1994 paper describes a spacetime distortion that would allow motion faster than light as seen by observers outside. The abstract states that exotic matter would be needed to produce this distortion. The metric is a mathematical solution, not a working drive. [1]
- Done · 2021Positive-energy warp solutions proposed
Lentz reports soliton solutions that are sourced by purely positive energy densities, and the 2021 journal version is published in Classical and Quantum Gravity. Bobrick and Martire report that their optimisations cut the negative energy requirement of the Alcubierre metric by two orders of magnitude, and they present a subluminal positive-energy model. Santiago, Schuster and Visser argue that generic warp drives violate the null energy condition. These papers are proposals, and the critiques are unresolved. [2][3][4][5]
- Done · 2012Apparent faster-than-light neutrinos tested and revised
OPERA's 2011 measurement appeared to show neutrinos arriving early. The revised version of the paper, v4 from July 2012, reports an arrival-time offset of 6.5 ns, with statistical uncertainty 7.4 ns and systematic uncertainty +8.3/-8.0 ns. Its relative velocity difference is (2.7 +/- 3.1 stat, +3.4/-3.3 sys) x 10^-6, which is consistent with light speed within its uncertainties. The arXiv comments state that this version replaces all previous ones. [6]
- Not started · 2014Faster-than-light signalling with entangled particles
The no-signalling theorem says that measurements on entangled particles cannot be used by one observer to send a message to another. Walleczek and Groessing describe the theorem as a statement about what observers can do. No faster-than-light signal has been shown. [7]
- In progress · Apr 2016Sub-light interstellar light-sail concept
Breakthrough Starshot was announced in April 2016 and aims for light sails reaching 20% of the speed of light, as reported by Africanews on 13 April 2016. The article says that, using current technology, reaching the nearest star system would take about 30,000 years, and that further research might cut the journey to about 30 years. The article describes an announced concept, not a demonstration. [8]
- DoneRecord flyby speed of Parker Solar Probe reported
NASA's Parker Solar Probe blog, dated 21 March 2025, describes the record-setting flyby speed as 430,000 miles per hour. That is about 0.06% of the speed of light, a figure calculated for this record and not given in the source. It shows how far real spacecraft are from light speed. [9]
Why it matters
If faster-than-light travel or signalling were possible, it would change how spacecraft and communication could be planned, and it would test the basic causal structure of physics. The current evidence points the other way. Clear limits help readers judge claims, and the ways people test them, such as timing checks and energy-condition analysis, show how physics corrects itself.
What stands in the way
- A warp drive needs negative energy density in the Alcubierre metric. Positive-energy versions are proposed but disputed, and the energy-condition critiques have not been resolved.
- The no-signalling theorem blocks faster-than-light communication through entanglement, so an entanglement-based route would need a loophole that the theorem does not allow.
- The 2011 OPERA result was revised after a new analysis of its timing and systematic errors. Any new claim would need the same level of timing and systematic checking before it is taken seriously.
- Breakthrough Starshot's light-sail concept is still at an early stage, and no faster-than-light propulsion has been demonstrated.
Signals to watch
- Independent checks of the positive-energy warp solutions that address the null energy condition critiques.
- A peer-reviewed analysis showing that a warp metric can be produced by known matter at a stated energy scale.
- A faster-than-light signal reported by an independent experiment that has been checked for timing and systematic errors.
- Demonstration of a light-sail propulsion system at a meaningful fraction of light speed, or a test of sail survival at high speed.
Sources
- preprint
The warp drive: hyper-fast travel within general relativity
Miguel Alcubierre. arXiv (journal reference: Classical and Quantum Gravity 11, L73-L77, 1994), 1994. - peer reviewed paper
Breaking the warp barrier: hyper-fast solitons in Einstein-Maxwell-plasma theory
Erik W. Lentz. Classical and Quantum Gravity (IOP Publishing), 38(7), 075015, 9 Mar 2021. - preprint
Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory
Erik W. Lentz. arXiv, 12 Jun 2020. - preprint
Introducing Physical Warp Drives
Alexey Bobrick, Gianni Martire. arXiv (accepted in Classical and Quantum Gravity), 12 Feb 2021. - preprint
Generic warp drives violate the null energy condition
Jessica Santiago, Sebastian Schuster, Matt Visser. arXiv (accepted in Physical Review D), 7 May 2021. - peer reviewed paper
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam
OPERA Collaboration. Journal of High Energy Physics, 2012. - conference paper
The Non-Signalling theorem in generalizations of Bell's theorem
Jan Walleczek, Gerhard Groessing. arXiv (journal reference: Journal of Physics: Conference Series 504, 012001, 2014), 14 Mar 2014. - news
Stephen Hawking helps unveil interstellar travel project
Africanews, 13 Apr 2016. - government report
Parker Solar Probe Primed for Next Close Solar Approach
NASA Science (Parker Solar Probe blog), 21 Mar 2025.
Last reviewed 21 Oct 2026.