Is Time Travel, Especially Into the Past Possible? | Matt Szydagis | TEDxSchenectady

The speaker begins by highlighting the allure of time travel, referencing popular culture examples like 'Back to the Future' and works by Salvador Dalí and Marcel Duchamp. They emphasize the historical misjudgments about the feasibility of air and space travel, illustrating that even experts can be wrong. The discussion then shifts to Einstein's theory of special relativity, which resolved inconsistencies between mechanics and electromagnetism by asserting the constancy of the speed of light. This theory leads to intriguing phenomena like the twin paradox, which demonstrates time dilation. The speaker mentions Harold Lyons, the inventor of the atomic clock, which has empirically confirmed time dilation effects. They conclude by stating that while time travel might be impossible according to current physics understanding, past misconceptions remind us that our understanding could evolve.

This paragraph delves into the concept of time travel to the future, suggesting that high-speed space travel could technically make it possible, as one could outlive their contemporaries by embarking on a lengthy journey and then returning. The speaker then explores the possibility of time travel to the past, first through mathematical extrapolations based on the theory of relativity, which suggests that surpassing the speed of light could reverse time. However, this idea is dismissed due to the impracticality of achieving such speeds. The speaker introduces the Tipler cylinder, a theoretical construct that proposes time travel to the past through the manipulation of space-time via a dense, rotating cylinder. Yet, this idea also faces practical challenges, such as the need for materials with infinite length or negative energy. The paragraph concludes with a brief mention of the Nobel Prize in Physics awarded for the discovery of gravitational waves, reinforcing the validity of general relativity.

The speaker discusses the impracticalities of time travel, focusing on the need for negative mass or energy and the challenges of creating stable wormholes. They explain that wormholes, as predicted by general relativity, would collapse without exotic matter with negative mass squared. The concept of a tachyon particle, which hypothetically travels faster than light, is also introduced as a potential but unproven solution. The speaker then presents a thought experiment involving a black hole, where an object falling in would appear to freeze at the event horizon from an external perspective, but would continue to fall and be crushed from its own viewpoint. They also touch on the idea of rotating space-time to enable time travel, referencing Professor Ron Mallett's experimental work with laser light and mirrors to create a circulating laser that might rotate space-time sufficiently for time travel. However, questions remain about the feasibility and energy requirements of such an approach.

The speaker transitions to quantum mechanics, exploring its implications for time travel. They ponder the scenario where a particle interacts with itself in the past, potentially creating paradoxes. The lack of a unified theory that combines quantum mechanics and relativity is highlighted as a barrier to fully understanding time travel's possibilities. The ontological paradox is introduced, which involves information or objects without a clear origin, leading to complex problems in quantum mechanics. Several solutions to time travel paradoxes are mentioned, including the creation of parallel universes, predestination, and the universe becoming a Möbius strip with simultaneous timelines. The speaker expresses skepticism about the intellectual satisfaction of these explanations, especially predestination, and acknowledges the challenges of applying quantum effects to macroscopic objects like humans.

In this final paragraph, the speaker addresses the absence of time travelers as evidence against time travel's feasibility, arguing that it simply suggests time travel has not yet been invented. They refute the idea that the lack of tourists from the future disproves time travel, using the example of wormholes to illustrate that one could only travel back to the day the time machine was created. The speaker concludes by outlining the significant challenges to time travel based on current physics, such as the need for faster-than-light speeds, infinite energy, and negative energy materials. They optimistically predict that within 100 years, we might achieve time travel for subatomic particles, despite acknowledging that this view is overly optimistic for their peers. The speaker calls for time travel to be taken more seriously by the scientific community and ends with a humorous note, comparing themselves to the composer Gustav Mahler and a reminder of Einstein's early years, emphasizing the importance of open-mindedness in scientific exploration.