The concept of journeying through time, both forward and backward, has captivated the imaginations of science fiction enthusiasts and physicists alike for generations. From beloved stories like Doctor Who to thought-provoking films like Interstellar, the allure of traversing the temporal dimension is undeniable. But does this fascination translate into reality? Is That Time Travel Possible according to the laws of physics as we understand them?
Doctor Who, with its iconic time-traveling machine, the Tardis, arguably stands as one of the most enduring explorations of this concept. The show, alongside classics like The Time Machine and Back to the Future, delves into the enticing possibilities and mind-bending paradoxes that arise from visiting different points in time. The Tardis itself, famously “bigger on the inside,” operates on principles far removed from our current understanding of physics, a charming element that contributes to Doctor Who’s fantastical nature.
To celebrate six decades of Doctor Who, it’s pertinent to explore the real-world science behind time travel. While the Tardis remains firmly in the realm of fiction, the question of whether time travel is possible in any form remains a compelling area of scientific inquiry. As we delve into the intricacies of time, we’ll uncover that while journeying to the future appears achievable, venturing into the past presents monumental, potentially insurmountable, challenges.
Time travel illustration depicting a person in a hat seemingly stepping through a portal, representing the concept of time manipulation and the question “is that time travel possible?”.
Our exploration begins with Albert Einstein’s groundbreaking theories of relativity, which revolutionized our understanding of space, time, gravity, and mass. A fundamental revelation of relativity is that time is not a fixed, constant entity. Instead, the passage of time is relative and can be altered depending on various conditions. Time can speed up or slow down, a concept known as time dilation, influenced by factors like speed and gravity.
“This is where the genuine scientific basis for time travel emerges, and it’s not just theoretical – it has tangible, real-world effects,” explains Emma Osborne, an astrophysicist at the University of York.
One key aspect of relativity is that time slows down for objects traveling at high speeds. While noticeable time dilation requires speeds approaching the speed of light, the effect is real. This principle gives rise to the famous “twin paradox.” Imagine one twin becoming an astronaut and embarking on a high-speed space journey while the other remains on Earth. Upon the astronaut’s return, they will have aged less than their Earthbound sibling. “If you undertake such a journey and return, you will genuinely be younger than your twin brother,” confirms Vlatko Vedral, a quantum physicist at the University of Oxford. This effect was even observed on a smaller scale in the real-life case of twins Scott and Mark Kelly, where Scott experienced subtle aging differences after spending months in space, albeit at speeds far below light speed.
Similarly, gravity also affects time. Time elapses more slowly in stronger gravitational fields. This means time runs slightly slower at your feet than at your head due to Earth’s gravity being stronger closer to the ground, though this difference is minuscule in everyday life.
Doctor Who cleverly incorporated this concept in the season 10 finale, “World Enough and Time.” The Doctor and his companions find themselves on a spaceship near a black hole, where the extreme gravity causes significant time dilation. Time passes much slower at the front of the ship, closer to the black hole, compared to the rear. This dramatic time difference allows a small group of Cybermen at the rear to evolve into a massive army within what seems like minutes from the Doctor’s perspective. The film Interstellar also prominently features the effects of gravity on time as a key plot element.
Albert Einstein, depicted in a portrait, symbolizing his theories of relativity which underpin our understanding of time dilation and the theoretical possibilities of future time travel.
These relativistic effects, though often imperceptible in our daily routines, are crucial for technologies like the Global Positioning System (GPS). “Clocks on GPS satellites in orbit tick faster than clocks on Earth,” Osborne points out. These minute time differences must be constantly corrected. “Without these adjustments, Google Maps would be inaccurate by about 10 kilometers (six miles) each day,” according to the European Space Agency, highlighting the practical implications of Einstein’s theories.
Relativity, therefore, confirms the possibility of time travel into the future. We don’t necessarily need a complex “time machine” in the science fiction sense. Traveling at near-light speeds or spending time in a strong gravitational field are, in essence, forms of future time travel as they allow us to experience less subjective time while vast stretches of time pass in the external universe. If our goal is to witness the distant future, these are the scientifically plausible pathways.
However, the prospect of traveling backward in time presents a far greater challenge.
“Whether it’s possible or not remains an open question,” says Barak Shoshany, a theoretical physicist at Brock University. “Our current understanding and theories are simply inadequate to definitively answer that.”
Relativity does offer some highly theoretical possibilities for backward time travel, but these are far more speculative. “Scientists have explored various complex theoretical frameworks attempting to manipulate space-time in ways that might enable time travel to the past,” explains Katie Mack, a theoretical cosmologist at the Perimeter Institute for Theoretical Physics.
One such concept involves creating a closed time-like curve – a path through space-time that loops back on itself. Imagine a route where, by following it, you eventually return to the exact same point in space and time where you began. The mathematical framework for such paths was first described by logician Kurt Gödel in a 1949 study, and numerous researchers have since explored similar ideas.
However, this approach faces significant hurdles.
“We have no evidence to suggest that closed time-like curves exist anywhere in the universe,” Vedral states. “It’s purely theoretical, lacking any observational support.”
Furthermore, even if they exist, the feasibility of creating one remains highly questionable. “Even with far more advanced technology than we possess today, it seems improbable that we could intentionally create closed time-like curves,” suggests Emily Adlam, a philosopher of physics at Chapman University.
Even hypothetically, Vedral cautions against the desirability of such a scenario: “You would be trapped in an endless loop, repeating the same events perpetually.”
Doctor Who touched upon a similar concept in the episode “Heaven Sent,” where the Doctor endures the same few hours repeatedly for billions of years. However, this scenario involved repeated teleportation rather than a true closed time-like curve.
Another theoretical construct, proposed by physicist Richard Gott in a 1991 study, involves “cosmic strings.” Gott’s calculations suggested that if two cosmic strings, hypothetical objects potentially formed in the early universe, were to move past each other at high speeds, they could create closed time-like curves around them.
But the existence of cosmic strings themselves is purely hypothetical. “There’s no compelling reason to believe cosmic strings are real,” Mack clarifies. Even if they did exist, the probability of finding two conveniently aligned and moving in parallel is astronomically low. “There’s no basis to expect such a scenario to occur.”
The Tardis’ iconic police box disguise is a result of a malfunction in its chameleon circuit, a camouflage system. This humorous element highlights the fictional nature of Doctor Who’s time travel, contrasting with the serious scientific inquiries into the question “is that time travel possible?”.
Wormholes offer another intriguing, albeit speculative, possibility within the realm of relativity. Wormholes are theoretical tunnels through space-time, acting as shortcuts between vastly distant points. “Wormholes are theoretically permissible in general relativity,” Vedral confirms.
However, the challenges associated with wormholes are substantial. Firstly, their existence remains unproven. “While mathematics allows for wormholes, their physical reality is uncertain,” Osborne notes.
Secondly, even if wormholes exist, they are predicted to be extremely short-lived and unstable. “Wormholes are often conceptualized as connections between two black holes,” Osborne explains. This implies they would possess incredibly intense gravitational fields, causing them to collapse almost instantaneously.
Furthermore, realistic wormholes, if they exist, would likely be microscopically tiny, far too small to even allow a bacterium to pass through.
While theoretical solutions exist to stabilize and enlarge wormholes, they require vast amounts of “negative energy,” a concept that might exist on subatomic scales but is likely impossible to harness or scale up. “Expanding these tiny pockets of negative energy to a usable scale seems unattainable,” Osborne concludes.
Vedral summarizes the situation succinctly: “It doesn’t appear to be a realistic proposition.”
Beyond relativity, quantum mechanics, the other pillar of modern physics, governs the behavior of the universe at the atomic and subatomic level. The quantum realm exhibits phenomena that often defy our everyday intuitions.
One such phenomenon is quantum non-locality. Changes to a quantum particle in one location can instantaneously affect another “entangled” particle, even if separated by vast distances – a concept Einstein famously termed “spooky action at a distance.” This non-locality has been experimentally verified numerous times, as recognized by Nobel Prize-winning research.
“Many physicists find the implications of non-locality unsettling,” Adlam notes. The instantaneous nature of the effect suggests information transfer faster than the speed of light, seemingly contradicting relativity.
Some physicists have proposed alternative interpretations to reconcile these observations with our understanding of time and causality. These interpretations suggest that instead of instantaneous non-local effects, the influence might propagate into the future and then retroactively affect the past.
“Instead of an instantaneous effect, the influence could travel into the future, and then loop back to the past,” Adlam explains. “This would appear instantaneous but would actually involve a journey forward and then backward in time.”
This interpretation introduces “retrocausality,” where future events can influence the past. This challenges our intuitive understanding of time as flowing linearly from past to present to future. In these quantum scenarios, information might be taking a detour into the future and then returning to the past.
However, it’s crucial to note that this retrocausal interpretation is not universally accepted. Many quantum physicists find retrocausality as problematic, if not more so, than non-locality.
Quantum entanglement illustration depicting two interconnected particles, symbolizing the “spooky action at a distance” and the potential implications for retrocausality and the question “is that time travel possible?”.
Even if retrocausality is a genuine feature of quantum mechanics, it’s unlikely to provide a pathway to becoming time travelers in the science fiction sense. “Retrocausality isn’t quite the same as practical time travel,” Adlam clarifies.
Firstly, observed non-locality effects have been limited to microscopic scales involving only a few particles. Scaling this up to macroscopic objects, like humans or even small objects, would be an immense challenge.
Furthermore, even with retrocausality, sending messages to the past seems impossible. “The retrocausal effect is inherently limited in a way that prevents practical exploitation,” Adlam explains.
Consider an experiment where Adam makes a measurement. The outcome of Adam’s measurement is determined by a measurement Beth makes later in time. Beth’s future experiment influences Adam’s past experiment. However, this only works if Beth’s experiment erases all records of Adam’s actions and observations.
“You would be, in a sense, sending a signal to the past, but only by destroying any possibility of reading that signal or benefiting from it,” Adlam concludes. “You can’t practically utilize this to send information or change the past because the act of receiving the ‘signal’ from the future inherently destroys the evidence of it ever being sent.”
So, based on our current understanding of the universe, time travel to the future appears theoretically possible through relativistic effects. However, time travel to the past remains highly improbable and may well be fundamentally impossible.
The crucial caveat is that our current theories, relativity and quantum mechanics, are incomplete and incompatible in certain respects. This suggests the need for a deeper, unified theory that reconciles these frameworks. “Until we have that more complete theory, we cannot be absolutely certain about the ultimate possibilities of time travel,” Shoshany concludes.
Of course, in a very real sense, you are already a time traveler. As you’ve read this article, you’ve journeyed several minutes into the future. You’re welcome to consider that your own, ongoing, time travel adventure.
