The concept of time travel, the ability to move backward or forward through time, has captivated writers, filmmakers, and scientists alike for generations. From H.G. Wells’ “The Time Machine” to the “Back to the Future” trilogy and the enduring popularity of “Doctor Who,” the allure of traversing the temporal landscape is undeniable. But is there such a thing as time travel in reality, or is it purely the realm of fiction?
Alt text: A person in a fedora seems to be stepping into a time warp, representing the concept of time travel.
While “Doctor Who” embraces the fantastical aspects of time travel without grounding it in scientific principles, the question of its feasibility sparks genuine scientific inquiry. Could we ever construct a time machine capable of transporting us to bygone eras or future epochs? To answer this, we must delve into our current understanding of time itself, a subject that continues to challenge even the most brilliant minds in physics. Current scientific consensus suggests that traveling to the future is theoretically possible, while journeying into the past faces significant, potentially insurmountable, obstacles.
Time Dilation: A One-Way Trip to the Future
Albert Einstein’s theories of relativity revolutionized our understanding of space, time, gravity, and mass. A core tenet of relativity is that time is not a constant; its flow can vary depending on factors such as speed and gravitational forces.
“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 slows down for objects traveling at high speeds, approaching the speed of light. This gives rise to the classic “twin paradox,” where an astronaut twin traveling at near-light speed ages more slowly than their Earth-bound sibling. Vlatko Vedral, a quantum physicist at the University of Oxford, notes, “If you travel and come back, you are really younger than the twin brother.” The effects have been observed in real life; astronaut Scott Kelly aged slightly less than his twin brother Mark during his extended stay in space.
Similarly, intense gravitational fields, such as those near black holes, also cause time to slow down. “Your head is ageing quicker than your feet, because Earth’s gravity is stronger at your feet,” says Osborne. This effect was dramatized in the “Doctor Who” episode “World Enough and Time” and the film “Interstellar.”
Alt text: Einstein’s theories of relativity explain time compression relative to an observer.
These relativistic effects, while subtle in everyday life, are crucial for technologies like the Global Positioning System (GPS). Osborne explains that GPS satellites experience time at a slightly faster rate than clocks on Earth, requiring constant adjustments. “If we didn’t, Google Maps would be wrong about 10km (six miles) a day.”
Thus, relativity demonstrates that time travel to the future is indeed possible. By traveling at high speeds or spending time in a strong gravitational field, one can effectively fast-forward through time relative to the rest of the universe.
The Thorny Path to the Past
While forward time travel seems plausible, the prospect of journeying into the past presents far greater challenges. “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 avenues for backward time travel, though they remain highly speculative. Katie Mack, a theoretical cosmologist at the Perimeter Institute for Theoretical Physics, notes that physicists have explored ways to “rearrange space-time in order to make time travel to the past possible.”
Closed Time-like Curves: Looping Through Time
One concept is the closed time-like curve: a path through space and time that forms a loop, allowing a traveler to return to their starting point in both space and time. Logician Kurt Gödel published a mathematical description of such a path in 1949. However, this approach faces significant hurdles.
Vedral emphasizes that there is no evidence of closed time-like curves existing in the Universe. Emily Adlam, a philosopher at Chapman University, adds that even with advanced technology, creating such curves on purpose seems unlikely. Moreover, Vedral suggests that even if possible, repeating the same loop endlessly would be undesirable.
Cosmic Strings: A Hypothetical Time Machine?
Another theoretical possibility involves cosmic strings, hypothetical objects that may have formed in the early universe. A 1991 study by physicist Richard Gott proposed that two cosmic strings moving past each other in opposite directions could create closed time-like curves. However, Mack points out that there is no evidence for the existence of cosmic strings, and even if they existed, the likelihood of finding two moving in the required manner is extremely low.
Wormholes: Tunnels Through Space-time
Wormholes, theoretical tunnels through space-time, are another concept entertained by physicists. “Wormholes are theoretically possible in general relativity,” says Vedral.
However, the challenges associated with wormholes are substantial. Osborne notes that there is no evidence of their existence and that, if they did exist, they would likely be incredibly short-lived and unstable, collapsing under their own gravity. Real wormholes would also likely be microscopically tiny.
Alt text: Quantum physics explains entanglement where two connected particles affect each other instantly.
Stabilizing a wormhole would require enormous amounts of “negative energy,” a phenomenon that may only exist on the tiniest scales. Vedral concludes that wormholes do not sound like a realistic proposal for time travel.
Quantum Mechanics and Retrocausality: Messing with the Timeline?
Quantum mechanics, the theory governing the behavior of subatomic particles, introduces further complexities to the question of time travel. One peculiar phenomenon is non-locality, where a change in the state of one particle can instantaneously influence another entangled particle, regardless of distance.
Adlam notes that some physicists are uncomfortable with non-locality because it implies information transfer faster than the speed of light. As an alternative, some have proposed interpretations involving “retrocausality,” where events in the future can influence the past.
However, this interpretation is not universally accepted, with many physicists finding retrocausality as unsettling as non-locality. Even if retrocausality is real, Adlam argues that it is not the same as time travel and would not allow us to send messages to the past. Any attempt to do so would necessarily erase the records of the signal being sent, rendering it useless.
The Verdict: Future Possible, Past Uncertain
Based on our current understanding of physics, traveling to the future appears theoretically possible through relativistic effects such as time dilation. However, traveling to the past faces significant obstacles and relies on speculative concepts with no observational evidence.
The possibility remains that our current theories are incomplete and that a deeper, unifying theory could reveal new possibilities for time travel. Shoshany emphasizes that “Until we have that theory, we cannot be sure.”
In the meantime, as you’ve finished reading this article, you’ve already traveled a few minutes into the future.
