The concept of time travel, journeying through different points in time, has captivated imaginations for centuries. From H.G. Wells’ “The Time Machine” to the “Back to the Future” trilogy and the iconic “Doctor Who,” the allure of altering the past or glimpsing the future is undeniable. But How Can Time Travel Be Possible, and is it grounded in any scientific reality?
Alt text: Illustration depicting a person with a hat seemingly moving through a vortex, representing the concept of time travel.
While “Doctor Who” uses time travel as a narrative device without adhering to strict scientific principles, the question of its possibility remains a subject of serious discussion among physicists. While traveling to the future appears achievable, journeying into the past presents immense challenges and may even be impossible.
Time Dilation: The Key to Future Travel
Albert Einstein’s theories of relativity revolutionize our understanding of space, time, gravity, and mass. One of the core implications of relativity is that time isn’t absolute; its flow is relative to the observer’s motion and the gravitational field they experience.
Emma Osborne, an astrophysicist at the University of York, explains: “This is where time travel can come in and it is scientifically accurate and there are real-world repercussions from that.”
Traveling at High Speeds: The faster you move, the slower time passes for you relative to a stationary observer. This is the basis of the “twin paradox,” where an astronaut traveling at near-light speed would age slower than their twin on Earth. Although not at relativistic speeds, astronaut Scott Kelly experienced this effect firsthand during his extended stay in space.
Strong Gravitational Fields: Similarly, time slows down in intense gravitational fields, such as those near black holes. Osborne illustrates this by stating, “Your head is ageing quicker than your feet, because Earth’s gravity is stronger at your feet.” This phenomenon was central to the plot of the “Doctor Who” episode “World Enough and Time” and the film “Interstellar.”
Alt text: A portrait of Albert Einstein, the father of relativity, whose theories form the basis for understanding time dilation and its potential for future time travel.
Real-World Applications: These effects aren’t merely theoretical. They are crucial for the functioning of the Global Positioning System (GPS). As Osborne notes, “The clocks above click faster than the clocks on Earth”, and must be constantly readjusted. Without accounting for relativistic effects, Google Maps would be inaccurate by about 10 kilometers per day.
Relativity, therefore, demonstrates that time travel into the future is indeed possible. By traveling at high speeds or spending time in a strong gravitational field, one can experience a shorter passage of time relative to the rest of the universe, effectively “jumping” into the future.
The Enigma of Past Time Travel
Traveling backward in time is a far more complex and speculative endeavor. As Barak Shoshany, a theoretical physicist at Brock University, notes: “What we have right now is just insufficient knowledge, possibly insufficient theories.”
Closed Time-like Curves: Relativity offers some theoretical avenues for backward time travel, such as closed time-like curves. These are paths through spacetime that loop back on themselves, allowing someone following the path to return to their starting point in time and space. Kurt Gödel first described such a path mathematically in 1949.
However, the existence of closed time-like curves is purely theoretical, with no observational evidence. Furthermore, even with advanced technology, creating such curves seems highly improbable. As Emily Adlam, a philosopher at Chapman University, says, “Even if we had much greater technological powers than we currently do, it seems unlikely that we would be able to create closed time-like curves on purpose.”
Cosmic Strings: Another theoretical possibility involves cosmic strings – hypothetical objects that may have formed in the early universe. Richard Gott proposed in 1991 that two cosmic strings moving past each other in opposite directions could create closed time-like curves. However, cosmic strings themselves remain hypothetical, and the probability of finding and utilizing them for time travel is exceedingly low.
Wormholes: Wormholes, theoretical tunnels through spacetime connecting distant points, are another concept seemingly allowed by relativity. “Wormholes are theoretically possible in general relativity,” says Vedral. If traversable wormholes existed, they could potentially act as shortcuts through time.
Alt text: A blue British police box, the iconic TARDIS from Doctor Who, symbolizing the fictional possibilities of time travel.
However, the existence of wormholes is unproven. Even if they do exist, they would likely be extremely short-lived and microscopically small, collapsing under their own gravity. Stabilizing a wormhole would require vast amounts of “negative energy,” which is thought to exist only on the subatomic scale.
Quantum Mechanics and Retrocausality
Quantum mechanics, the theory governing the behavior of matter at the subatomic level, introduces even more perplexing possibilities. One such phenomenon is non-locality, where changes in one particle instantaneously affect another entangled particle, regardless of distance.
Some interpretations of non-locality propose retrocausality, where events in the future can influence events in the past. In this view, instead of instantaneous action at a distance, the effect travels into the future and then back to the past.
However, the concept of retrocausality remains controversial. Even if it were real, its application to time travel would be limited. Adlam explains that the retrocausal effects observed involve only tiny numbers of particles, and “The retrocausality is very specifically hidden by the way it’s implemented.” Sending a message to the past through retrocausality would require destroying all records of the transmission, making it impractical.
The Unresolved Question
Currently, our understanding of the universe suggests that future time travel is possible through relativistic effects, but past time travel faces significant, potentially insurmountable, obstacles. However, these conclusions are based on incomplete theories. Relativity and quantum mechanics, while successful in their respective domains, are incompatible.
As Shoshany states, “Until we have that theory, we cannot be sure.” A deeper, unified theory of physics may reveal new possibilities for time travel that are currently beyond our comprehension.
In the meantime, as you have reached the end of this article, you have traveled a few minutes into the future.
