The concept of traversing through time, both forwards and backwards, has been a captivating subject for science fiction authors and physicists alike. The question remains: Is Time Travelling To The Past Possible, and what does science say about it?
Stories like Doctor Who, The Time Machine, and Back to the Future have long explored the allure and complexities of manipulating time, raising intriguing questions about the feasibility of such endeavors. In Doctor Who, the Doctor uses the Tardis, a remarkable vehicle capable of navigating through time and space, famously known for being larger on the inside.
While Doctor Who entertains with its fantastical depiction of time travel, it doesn’t attempt to anchor the Tardis’s capabilities in real-world physics. But what does actual science have to say about the possibility of time travel? Could we potentially construct a time machine and journey into the past, or leap forward to witness the future?
Alt text: Conceptual illustration of a person with a hat seemingly phasing through a swirling portal, representing the idea of time travel.
To address this question, we must understand how time works, a topic that remains a subject of ongoing investigation among physicists. Currently, there’s a consensus that travelling to the future is within the realm of possibility, while travelling to the past faces significant challenges or might be fundamentally impossible.
Time Dilation: The Key to Future Time Travel
Albert Einstein’s theories of relativity provide a framework for understanding space, time, mass, and gravity. A fundamental concept arising from relativity is that time’s passage isn’t constant; it can vary depending on different conditions.
“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.
For example, time elapses more slowly for objects travelling at high speeds, especially as they approach the speed of light. This phenomenon gives rise to the twin paradox, where one twin journeys into space at near-light speed while the other stays on Earth. Upon the astronaut’s return, they will have aged less than their Earthbound twin. This was demonstrated, on a smaller scale, when astronaut Scott Kelly spent months in space.
Similarly, time slows down in regions with strong gravitational fields, such as near a black hole. “Your head is ageing quicker than your feet, because Earth’s gravity is stronger at your feet,” says Osborne.
These relativistic effects are also essential for the functioning of global positioning system (GPS) satellites. “The clocks above click faster than the clocks on Earth” and need continuous readjustment, Osborne notes. Without these adjustments, Google Maps would be significantly inaccurate.
Relativity offers a path to the future. By travelling at speeds close to the speed of light or spending time in an intense gravitational field, a person would experience less time subjectively, while decades or even centuries could pass in the rest of the Universe.
The Challenges of Time Travelling to the Past
Is time travelling to the past possible? Going backwards in time, however, presents significantly greater difficulties.
“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 remain highly speculative. One concept involves creating a closed time-like curve, a path through space and time that loops back on itself. Theoretically, someone following this path would eventually return to their starting point in time and space. Kurt Gödel published a mathematical description of such a path in 1949, and many others have explored the idea since.
Alt text: A portrait of Albert Einstein, a key figure in understanding time travel through his theories of relativity and the compression of time relative to the observer.
However, this approach faces numerous obstacles. As Vlatko Vedral notes, “We don’t know whether this exists anywhere in the Universe… This is really purely theoretical, there’s no evidence.”
Moreover, creating such a closed time-like curve seems incredibly challenging, even with advanced technology. Even if we could, Vedral suggests it may not be desirable, as it could lead to repeating the same events endlessly.
Another theoretical possibility involves cosmic strings, hypothetical objects that may have formed in the early Universe. According to a 1991 study by physicist Richard Gott, the movement of two cosmic strings past each other could create closed time-like curves. However, the existence of cosmic strings remains unproven.
Wormholes and Negative Energy: More Theoretical Hurdles
Wormholes, theoretical tunnels through space-time that could connect distant points, are another concept allowed by relativity. “Wormholes are theoretically possible in general relativity,” says Vedral.
However, the existence of wormholes hasn’t been confirmed, and even if they exist, they’re likely to be incredibly short-lived due to their intense gravitational fields. Real wormholes would also be microscopically tiny.
In theory, these problems could be solved using vast amounts of “negative energy,” but Osborne points out that expanding tiny pockets of negative energy, which might exist on subatomic scales, seems impossible.
Quantum Mechanics and Retrocausality: A Tangled Web
What about quantum mechanics, the theory describing the behavior of matter at the subatomic level? Quantum mechanics introduces the concept of non-locality, where a change in one particle’s state can instantaneously affect another “entangled” particle, regardless of the distance separating them. Einstein famously called this “spooky action at a distance.”
Some physicists propose that this effect might involve information travelling faster than the speed of light, which is generally considered impossible. Alternative interpretations suggest that the effect travels into the future and then back into the past, introducing the concept of “retrocausality.”
While intriguing, retrocausality is far from universally accepted and doesn’t necessarily equate to time travel. Even if retrocausality exists, it might not be scalable to larger objects like humans, and sending messages into the past might be impossible due to the need to destroy records of the signal being sent.
The Verdict: Future Travel Possible, Past Travel Unlikely (But Not Ruled Out)
So, based on our current scientific understanding, travelling to the future is potentially achievable, while travelling to the past faces significant hurdles and may be fundamentally impossible.
The crucial caveat is that our current theories are incomplete. Relativity and quantum mechanics, while successful in their respective domains, are incompatible with each other. A deeper, unifying theory is needed, but it remains elusive. Until such a theory emerges, the possibility of travelling to the past cannot be definitively ruled out.
Of course, as you’ve been reading this article, you’ve already travelled into the future.
