The concept of time travel has captivated our imaginations for generations, fueled by iconic stories like Doctor Who, Back to the Future, and The Time Machine. The allure of journeying to different eras, witnessing historical events, or even catching a glimpse of the future is powerfully enticing. But beyond the realm of science fiction, what does real science say? Is time travel merely a fantasy, or could it one day become a reality?
To truly understand the possibility of time travel, we need to delve into the fascinating world of physics and unravel the true nature of time itself. While the Doctor’s fantastical adventures in the Tardis are purely fictional, grounded in imagination rather than scientific accuracy, exploring the real-world physics opens up a conversation about what might actually be achievable, or remain forever beyond our grasp. So, could we ever construct a time machine capable of transporting us to bygone eras or leap forward to future centuries? The answer, according to current physics, is complex and far from definitive. While traveling to the future appears theoretically possible, journeying into the past presents formidable, perhaps insurmountable, challenges.
Let’s begin our exploration with Albert Einstein’s groundbreaking theories of relativity, which revolutionized our comprehension of space, time, gravity, and mass. A core tenet of relativity is that time is not a fixed, universal constant; instead, the passage of time is relative and can speed up or slow down depending on various conditions.
Astrophysicist Emma Osborne from the University of York explains, “This is where time travel can enter the picture, and it’s based on scientifically sound principles with real-world consequences.” One such consequence is time dilation: time elapses more slowly for objects traveling at high speeds. While noticeable effects require velocities approaching the speed of light, the principle is clear. This phenomenon gives rise to the famous “twin paradox.” Imagine one twin becoming an astronaut embarking on a high-speed space journey while the other remains on Earth. Due to time dilation, the traveling twin will age more slowly than their Earth-bound sibling. Quantum physicist Vlatko Vedral from the University of Oxford notes, “If you travel and return, you will genuinely be younger than your twin brother.” The reality of this effect was demonstrated, albeit on a smaller scale, when astronaut Scott Kelly spent months in space, aging slightly less than his twin brother Mark on Earth.
Similarly, gravity also affects time. Time slows down in stronger gravitational fields, such as those near black holes. Osborne illustrates this point by saying, “Your head ages slightly faster than your feet because Earth’s gravity is stronger at your feet.” The science fiction series Doctor Who cleverly incorporated this concept in an episode where the Doctor and companions find themselves on a spaceship near a black hole. The ship’s proximity to the black hole caused extreme time dilation, with time passing much slower at the front of the ship compared to the rear. This dramatic difference allowed a small group of Cybermen at the rear to evolve into a massive army within what seemed like minutes to the Doctor at the front. The film Interstellar also prominently features the effects of gravity on time as part of its plot.
These relativistic effects, though often imperceptible in everyday life, are crucial for technologies like the Global Positioning System (GPS). Osborne points out, “The clocks on satellites tick faster than clocks on Earth,” and these discrepancies must be constantly adjusted. “Without these adjustments, Google Maps would be inaccurate by about 10km (six miles) each day,” according to the European Space Agency, highlighting the practical implications of Einstein’s theories.
Relativity, therefore, confirms the possibility of future time travel. We don’t necessarily need a fantastical “time machine” to journey into the future. Traveling at near-light speeds or spending time in a strong gravitational field are the keys. In essence, these two scenarios are equivalent in relativity. Either way, the traveler experiences a shorter duration of subjective time while decades or even centuries could pass in the rest of the universe. If your goal is to witness the distant future, physics suggests pathways to get there.
However, the prospect of traveling back in time is significantly more challenging. “It may or may not be possible,” states Barak Shoshany, a theoretical physicist at Brock University. “Currently, our knowledge and theories are simply insufficient to provide a definitive answer.”
Relativity offers some theoretical avenues for backward time travel, but these are highly speculative. Katie Mack, a theoretical cosmologist at the Perimeter Institute for Theoretical Physics, explains that researchers are “tying themselves up in knots trying to find ways to rearrange space-time to enable time travel to the past.”
One theoretical concept is the closed time-like curve, a path through spacetime that forms a loop, returning to its starting point in both space and time. Kurt Gödel, a logician, mathematically described such paths in a 1949 study, inspiring further research.
Yet, closed time-like curves face substantial hurdles. Vedral notes, “We don’t know if these exist anywhere in the Universe. It’s purely theoretical with no observational evidence.” Furthermore, creating such a curve seems technologically improbable, even with advanced technology. Emily Adlam, a philosopher at Chapman University, believes, “Even with far greater technological capabilities, it seems unlikely we could intentionally create closed time-like curves.” Even if we could create them, Vedral suggests a less-than-desirable outcome: “You would essentially be trapped repeating the same loop indefinitely.”
Another theoretical possibility arises from the concept of cosmic strings. In a 1991 study, physicist Richard Gott proposed that two cosmic strings, hypothetical objects from the early universe, moving past each other could create closed time-like curves. However, cosmic strings remain purely hypothetical, with no observational evidence confirming their existence. Mack points out, “We have no reason to believe cosmic strings exist.” Even if they did exist, finding two conveniently aligned and moving in parallel would be incredibly improbable.
Wormholes present another intriguing, albeit problematic, possibility for time travel within the framework of relativity. Wormholes are theoretical tunnels through spacetime that could connect vastly distant points, potentially acting as shortcuts. Vedral confirms, “Wormholes are theoretically possible in general relativity.”
However, similar to closed time-like curves and cosmic strings, wormholes face significant obstacles. Osborne reiterates, “It’s been mathematically shown they can exist, but their physical existence is unconfirmed.” Even if wormholes exist, they are predicted to be extremely short-lived and microscopically small due to their intense gravitational fields, collapsing almost instantly. Enlarging and stabilizing a wormhole to allow even a single person to pass through would theoretically require exotic “negative energy,” a concept that may only exist on subatomic scales. Osborne concludes, expanding these tiny pockets of negative energy is likely “not possible in any way.” Vedral succinctly summarizes, “It doesn’t sound like a very realistic proposal.”
Shifting our perspective from relativity to quantum mechanics, the other pillar of modern physics, reveals further complexities. While relativity governs large-scale phenomena, quantum mechanics describes the bizarre behavior of the very small, the subatomic world. Quantum mechanics introduces phenomena that challenge our classical intuitions, such as non-locality. Non-locality describes how changes to one entangled particle can instantaneously affect another, even if separated by vast distances – what Einstein famously termed “spooky action at a distance.” This phenomenon has been experimentally verified numerous times, as recognized by Nobel Prize-winning research, according to Adlam.
The instantaneous nature of non-locality troubles many physicists because it seemingly implies information transfer faster than light, which is considered impossible. Some physicists have proposed alternative interpretations to resolve this, suggesting that instead of instantaneous effects, influences might travel forward in time and then loop back to the past, creating the illusion of instantaneity. This interpretation introduces “retrocausality,” where future events can influence the past, contradicting our usual understanding of time’s linear flow from past to present to future. However, this retrocausal interpretation is far from universally accepted, with many physicists finding it as problematic, or even more so, than non-locality itself.
Even if retrocausality is real, Adlam clarifies that it “is not quite the same thing as time travel” in the way we typically imagine. Observed non-locality effects occur with tiny numbers of particles. Scaling this up to macroscopic objects, like humans, presents insurmountable challenges. Furthermore, even with retrocausality, sending a message to the past appears impossible. Adlam explains that while a future event might influence a past experiment’s outcome, this only works if all records of the past experiment are destroyed. “You would be sending a signal to the past, but only by destroying all records of everything that happened,” making it impractical for intentional time travel or communication.
In conclusion, based on our current scientific understanding, traveling to the future appears theoretically plausible through relativistic effects, while backward time travel remains highly speculative and faces immense, potentially insurmountable, obstacles. The key caveat is that our current theories, relativity and quantum mechanics, are incomplete and incompatible, suggesting the need for a deeper, unifying theory. Shoshany emphasizes, “Until we have that theory, we cannot be certain” about the ultimate possibilities of time travel.
Ultimately, while the dream of time travel persists, for now, it remains firmly rooted in the realm of science fiction. However, as you’ve reached the end of this article, you have, in a very real sense, traveled into the future – by the time it took you to read this, you’ve journeyed several minutes forward in time. You’re welcome to consider that your own personal, albeit very slow, time machine in action.
