Every Way Time Travel Could Work Explained in 9 Minutes

Summary

The video surveys proposed ways time travel might work under relativity and other theoretical physics. Relativistic and gravitational time dilation could let someone travel into the future relative to other people. Proposals for traveling into the past generally involve hypothetical structures or conditions, and none is presented as a demonstrated technology.

Ways to Reach the Future

• Speed-based time dilation: At speeds close to the speed of light, a traveler’s time passes more slowly relative to Earth. The video gives the example of traveling at 99% of light speed, where roughly seven years pass on Earth for every year experienced by the astronaut.
• Gravitational time dilation: Strong gravity slows time relative to regions with weaker gravity. Someone orbiting near a supermassive black hole could experience much less time than a distant twin, while feeling normal themselves.
• Suspended animation: Cooling the body and slowing its biological processes might allow a person to remain unconscious for a long period and avoid experiencing the wait. This does not alter the passage of time: the person remains physically present, and extreme cold and disrupted circulation could damage cells.

Speculative Ways to Reach the Past

• Wormholes: A tunnel connecting distant regions of spacetime might link different times as well as places. Keeping one open could require unusual forms or amounts of energy that may not be available.
• Tipler cylinder: A very long, dense cylinder rotating near light speed could twist spacetime. A spacecraft following a suitable path around it might return to an earlier time.
• Cosmic strings: Hypothetical, extremely thin concentrations of energy from the early universe could alter spacetime’s geometry. Configurations involving moving strings might, in theory, permit paths into the past.
• Warp-drive bubbles: A proposed drive would contract space ahead of a craft and expand it behind, while the craft sits inside a relatively calm region. Carefully arranged bubbles moving in different directions could potentially create a closed route through spacetime.
• Krasnikov pipes: A spacecraft’s outward journey could alter spacetime along its route, leaving a shortcut for a faster return. Two suitably arranged pipes might form a time loop, but the proposal requires controllable negative energy.
• Tachyon antitelephone: If hypothetical particles called tachyons could carry information faster than light, relativity could allow a message to arrive before it was sent in some reference frames. A reply might create a paradox in which the warning prevents the event that caused it.
• Quantum time loops: Theoretical models consider particles interacting with their own past. Proposed consistency rules would prevent an interaction from producing a self-contradictory history. The video notes that this behavior has only been modeled in quantum systems—not achieved by sending anything into the past.
• Ori time machine: A proposed ring-shaped arrangement of matter could warp spacetime so that a circular path leads back to an earlier time. Whether such a structure could be built or remain stable is unknown.
• Gödel universe: A rotating-universe solution to general relativity allows paths that loop into the past. The video says our universe does not appear to have the required global rotation.

Overall, the video distinguishes biological “skipping” of time from genuine time dilation, and separates future-directed effects allowed by established physics from past-directed scenarios that remain highly speculative.

Researchers and Named Sources Mentioned

• Tipler — associated with the Tipler cylinder.
• Krasnikov — associated with the Krasnikov pipe.
• Ori — associated with the Ori time machine.
• Gödel — associated with the rotating-universe model.

No other researchers or specific publications are named in the subtitles.