The concept of journeying through time, leaping into the future or revisiting the past, has been a captivating theme in science fiction and a topic of serious inquiry for physicists. Shows like Doctor Who, movies like Back to the Future, and novels like The Time Machine have fueled our imaginations with the possibilities – and paradoxes – of temporal displacement. But is time travel merely a fantasy, or does it have a basis in scientific reality? This article delves into the current understanding of physics to explore if Can People Time Travel.
The allure of time travel has captivated audiences for generations, sparking countless stories and scientific inquiries. Alternative text: Person with a hat stepping through a portal representing time travel.
While Doctor Who embraces time travel without adhering to strict scientific principles, the question remains: can we, in the real world, construct a time machine to visit bygone eras or glimpse future events? The answer, according to our current understanding, is complex. While traveling to the future appears achievable based on established physics, journeying into the past presents formidable challenges, bordering on impossibility.
Time Dilation: Your Ticket to the Future?
Albert Einstein’s theories of relativity revolutionized our understanding of space, time, mass, and gravity. A central tenet of relativity is that time is not absolute; its passage is relative to the observer’s motion and gravitational environment. Time can speed up or slow down depending on these factors.
“This is where time travel can come in and it is scientifically accurate and there are real-world repercussions from that,” explains Emma Osborne, an astrophysicist at the University of York.
One consequence of relativity is time dilation: time passes more slowly for objects traveling at high speeds. As an object approaches the speed of light, time slows down significantly relative to a stationary observer. This leads to the “twin paradox,” where an astronaut traveling at near-light speed would age more slowly than their Earth-bound twin. Upon returning to Earth, the astronaut would be younger, effectively having traveled into the future. Scott and Mark Kelly exemplified this on a smaller scale when Scott spent months in space.
Similarly, time is affected by gravity. The stronger the gravitational field, the slower time passes. Thus, time passes slightly slower at your feet than at your head due to Earth’s gravity. The movie Interstellar and Doctor Who episode “World Enough and Time” use this concept, where characters near a black hole experience drastically different rates of time passage compared to those further away.
Einstein’s theories suggest that manipulating time through velocity or gravity is theoretically possible. Alternative text: A portrait of Albert Einstein, who developed the theory of relativity, which has implications for time travel.
These relativistic effects, while subtle in everyday life, have practical implications. The satellites used in Global Positioning Systems (GPS) experience time dilation due to their speed and distance from Earth’s gravitational field. Osborne notes, “The clocks above click faster than the clocks on Earth” and require constant readjustment. Without these corrections, Google Maps would be significantly inaccurate.
Therefore, relativity allows for a form of time travel: moving into the future. By traveling at relativistic speeds or spending time in a strong gravitational field, one can experience less time subjectively, effectively “jumping” ahead relative to the rest of the universe.
The Thorny Path to the Past
Traveling backward in time is far more problematic. “It may or may not be possible,” says Barak Shoshany, a theoretical physicist at Brock University. “What we have right now is just insufficient knowledge, possibly insufficient theories.”
Relativity offers some theoretical possibilities, but they are fraught with challenges. One idea involves creating closed time-like curves (CTCs), paths through spacetime that loop back on themselves. Someone traveling along such a path would eventually return to their starting point in time. Logician Kurt Gödel proposed a mathematical description of CTCs in 1949.
However, there’s no evidence that CTCs exist in the universe. Furthermore, creating them would likely require technological capabilities far beyond our current reach. Even if we could, Emily Adlam, a philosopher at Chapman University, suggests that traversing a CTC might trap you in an endless loop, repeating the same events indefinitely.
Another theoretical concept involves cosmic strings, hypothetical one-dimensional objects that may have formed in the early universe. In a 1991 study, physicist Richard Gott calculated that two cosmic strings moving past each other could create CTCs. However, cosmic strings remain purely hypothetical, and even if they exist, finding two aligned in the necessary configuration would be extraordinarily unlikely.
Wormholes: Tunnels Through Time?
Relativity also allows for the theoretical existence of wormholes, tunnels through spacetime that could connect distant points. “Wormholes are theoretically possible in general relativity,” confirms Vlatko Vedral.
The TARDIS from Doctor Who embodies the paradoxes and possibilities that make time travel so compelling. Alternative text: Doctor Who’s TARDIS, a blue police box, sits on a street.
However, several obstacles plague the wormhole concept. First, there’s no evidence of their existence. Second, even if they do exist, they would likely be extremely short-lived, collapsing under their own gravity. Third, real wormholes would likely be microscopically small.
Overcoming these challenges would require vast amounts of “negative energy,” a concept that exists only on the subatomic scale. Expanding these tiny pockets of negative energy to create a traversable wormhole seems implausible.
Quantum Mechanics: Spooky Action and Retrocausality
While relativity deals with large objects and gravity, quantum mechanics governs the behavior of subatomic particles. Quantum mechanics introduces peculiar phenomena, such as non-locality, where entangled particles can instantaneously influence each other regardless of distance. Einstein famously called this “spooky action at a distance.”
Some physicists interpret non-locality as evidence of retrocausality, where future events can influence past events. This interpretation eliminates the need for instantaneous communication, suggesting that the effect travels into the future and then back to the past.
However, retrocausality remains a controversial interpretation. Moreover, even if it’s real, it may not lead to practical time travel. Observations of non-locality have only involved tiny numbers of particles. Scaling this up to macroscopic objects would be immensely challenging.
Furthermore, even in these scenarios, sending messages to the past might be impossible. As Emily Adlam explains, the retrocausal effect might be hidden by the need to destroy all records of the signal being sent.
The Verdict: Future is Possible, Past is Problematic
Based on our current scientific understanding, traveling to the future appears feasible through relativistic effects like time dilation. However, traveling to the past remains highly speculative and faces significant theoretical and practical obstacles.
The limitations of our current theories leave room for possibility. Relativity and quantum mechanics are incompatible, suggesting the need for a deeper, unified theory. Shoshany concludes, “Until we have that theory, we cannot be sure.”
In the meantime, as you’ve reached the end of this article, you have already traveled several minutes into the future.
