Faster-than-light travel
Relativity forbids ordinary motion faster than light. Warp bubbles and wormholes would instead bend spacetime, but every known design needs negative energy density, which quantum field theory allows only in tiny amounts for very short times. Faster-than-light travel would also allow travel into the past, which most physicists take as a sign that it is impossible. The question is purely theoretical, and there is no experiment.
Open in the interactive tree →In 1994 Miguel Alcubierre found a solution of Einstein's equations in which a bubble of spacetime moves faster than light. It needs negative energy density, and quantum field theory allows negative energy only in tiny amounts for very short times (quantum inequalities). Faster-than-light travel would also allow travel into the past, which most physicists take as a sign that it is impossible.
As of now
No design is known that moves faster than light using only ordinary, positive energy. Warp drives with positive energy proposed in 2021 either stay below light speed or, as Santiago, Schuster and Visser showed in 2022, still violate the energy conditions for some observers. The question is purely theoretical; there is no experiment.
What is missing
- A usable source of negative energy, or a proof that none can exist
- A theory of quantum gravity that says whether spacetime can be shaped this way
- A way around the time-travel paradoxes that faster-than-light travel would allow
Becomes possible once solved
- Reaching other stars within a human lifetime
- Crewed travel between star systems
Open steps
- Energy-condition audit Medium AI leverageCheck every proposed warp and wormhole spacetime against the energy conditions for all observers, not just one family.
- Limits on negative energy Low AI leveragePin down how much negative energy quantum fields can produce, for how long and where (quantum inequalities), and whether any arrangement could hold a warp bubble open.
- Time-travel paradoxes Low AI leverageDecide whether physics forbids closed time loops, which faster-than-light travel would make possible.
Where today's AI could help
Low AI leverage. The open question is whether physics allows it at all. AI can search solutions of Einstein's equations and check energy conditions faster, but it cannot supply exotic matter or settle quantum gravity.
- Search large families of warp and wormhole spacetimes for the designs that need the least exotic energy
- Check the energy conditions for every observer automatically, not just one family (the gap in the 2021 claims)
- Check derivations in general relativity symbolically