The concept of traversing through time, leaping into the future or delving into the past, has captivated storytellers and scientists alike for generations. From classic novels to blockbuster movies, the allure of time travel is undeniable. But beyond fiction, How Do You Travel Through Time according to the laws of physics?
Science fiction masterpieces like Doctor Who, H.G. Wells’ “The Time Machine,” and “Back to the Future” have brilliantly explored the tantalizing possibilities and perplexing paradoxes inherent in time travel. In Doctor Who, the iconic Tardis allows for journeys across both space and time, famously defying spatial dimensions by being “bigger on the inside.” While these narratives ignite our imaginations, they often sidestep real-world physics for the sake of storytelling.
But what does science say? Could we ever engineer a time machine to witness historical events or glimpse future civilizations? To answer this, we must first understand the nature of time itself – a concept that continues to puzzle physicists. Current scientific understanding suggests that traveling to the future is not only plausible but already happening, while journeying into the past presents formidable, potentially insurmountable, challenges.
Let’s begin with Albert Einstein’s groundbreaking theories of relativity, which revolutionized our understanding of space, time, gravity, and mass. A core tenet of relativity is that time is not absolute; its passage is relative and can be altered. Time can speed up or slow down depending on various conditions, a phenomenon known as time dilation.
“This is where the real science of time travel begins, and it’s not just theoretical – it has tangible, real-world consequences,” explains Dr. Emma Osborne, an astrophysicist at the University of York.
One key aspect of relativity is that time slows down for objects moving at high speeds. The closer you approach the speed of light, the more significant this effect becomes. This principle underlies the famous “twin paradox.” Imagine one twin becoming an astronaut and embarking on a high-speed space voyage while the other remains on Earth. Due to time dilation, the traveling twin will age more slowly than their Earth-bound sibling. “Upon returning from a space journey, the traveling twin would genuinely be younger,” confirms Dr. Vlatko Vedral, a quantum physicist at the University of Oxford. Astronauts like Scott and Mark Kelly have experienced this effect firsthand, with Scott’s time in space resulting in subtle but measurable differences in aging compared to Mark on Earth.
Similarly, gravity also affects time. Time runs slower in stronger gravitational fields. “Your head actually ages slightly faster than your feet because Earth’s gravity is stronger at your feet,” Osborne points out, though this difference is minuscule on Earth.
The science fiction show Doctor Who cleverly incorporated this concept in the episode “World Enough and Time.” The Doctor and his companions find themselves on a spaceship near a black hole. Time passes at different rates on the ship, with time slowing down dramatically closer to the black hole. This temporal distortion allows a small group of Cybermen at the rear of the ship to evolve into a massive army in what appears to be mere minutes from the Doctor’s perspective. The movie Interstellar also prominently features the effect of gravity on time as a crucial plot element.
While these relativistic effects are imperceptible in our daily lives, they are crucial for technologies like the Global Positioning System (GPS). “Clocks on GPS satellites in orbit tick faster than clocks on Earth,” Osborne explains. These time differences must be constantly corrected. “Without relativistic adjustments, GPS systems like Google Maps would quickly become inaccurate by about 10 kilometers (six miles) each day,” according to the European Space Agency.
Relativity, therefore, unequivocally demonstrates the possibility of future time travel. No elaborate time machine is needed; simply traveling at near-light speeds or spending time in a strong gravitational field will do. In essence, these are equivalent in relativistic terms. For the traveler, time will pass more slowly, while decades or even centuries could elapse in the rest of the universe. If your goal is to witness the distant future, these are the scientifically validated methods.
However, venturing into the past is a far more complex and speculative endeavor.
“Whether backward time travel is possible remains an open question,” states Dr. Barak Shoshany, a theoretical physicist at Brock University. “Our current understanding and theories are possibly insufficient to definitively answer this.”
While relativity opens doors for future travel, it also hints at theoretical possibilities for time travel to the past, albeit much more convoluted ones. “Physicists have wrestled extensively with the fabric of space-time, attempting to bend and twist it in ways that might permit travel to the past,” notes Dr. Katie Mack, a theoretical cosmologist at the Perimeter Institute for Theoretical Physics.
One theoretical concept is the closed time-like curve – a path through space-time that forms a loop. Following such a path could, in theory, bring you back to your starting point in both space and time. The mathematical groundwork for this concept was laid out by logician Kurt Gödel in a 1949 study, and numerous physicists have explored this idea since.
However, closed time-like curves face significant hurdles.
“We have no evidence that closed time-like curves exist anywhere in the universe,” emphasizes Vedral. “It remains purely theoretical with no observational backing.”
Furthermore, even if they exist, creating them is another challenge entirely. “Even with far more advanced technology than we possess today, deliberately creating closed time-like curves seems exceptionally improbable,” suggests Dr. Emily Adlam, a philosopher of physics at Chapman University.
Even if we could create them, Vedral cautions about their nature. “You would essentially be trapped in an endless loop, repeating the same segment of time perpetually,” he explains.
Doctor Who touched upon a similar theme in the episode “Heaven Sent,” where the Doctor is trapped in a time loop, reliving the same hours for billions of years. However, this scenario in the show was achieved through repeated teleportation, not a closed time-like curve.
Another theoretical avenue for backward time travel involves cosmic strings. In a 1991 study, physicist Richard Gott proposed a scenario where two cosmic strings, hypothetical objects possibly formed in the early universe, moving past each other in opposite directions could create closed time-like curves.
While mathematically intriguing, cosmic strings are purely hypothetical. No cosmic strings have ever been detected. “There’s no compelling reason to believe cosmic strings actually exist,” Mack points out. Even if they did, the probability of finding two conveniently aligned and moving in parallel is astronomically low. “It’s highly improbable such a scenario would naturally occur.”
Why is the Tardis a police box?
The Tardis, Doctor Who’s time machine, is famously disguised as a British police box due to a malfunction in its chameleon circuit, a camouflage system. Ironically, chameleons primarily change color for communication, not camouflage.
Wormholes present another intriguing, albeit highly speculative, possibility. Relativity theoretically allows for the existence of wormholes, tunnels through space-time that could act as shortcuts between distant points. Imagine folding space-time like a piece of paper and punching a hole through it – that’s the basic idea of a wormhole. “Wormholes are theoretically permissible within the framework of general relativity,” Vedral confirms.
However, like cosmic strings and closed time-like curves, wormholes remain purely theoretical. “While mathematics suggests their possibility, their physical existence is unconfirmed,” Osborne clarifies.
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 immense gravitational forces that would likely cause a wormhole to collapse almost instantly under its own gravity.
Furthermore, theoretical wormholes are predicted to be microscopic in size. Traversing even a bacterium through a wormhole, let alone a human, would be impossible.
Theoretically, these limitations might be overcome by invoking “negative energy,” a concept from quantum physics. While the overall energy density of space must be positive, quantum theory allows for minuscule pockets of negative energy. “Expanding these tiny regions of negative energy might, hypothetically, stabilize a wormhole,” Osborne suggests. “However, achieving this seems practically impossible with our current understanding and technology.”
Vedral succinctly summarizes the wormhole scenario: “It doesn’t sound like a realistic prospect for time travel.”
What about quantum mechanics, the other pillar of modern physics? While relativity governs large-scale phenomena, quantum mechanics describes the realm of the very small – atoms and subatomic particles. In this quantum world, phenomena often defy classical intuition.
One such phenomenon is quantum non-locality. Changes to a quantum particle in one location can instantaneously affect another “entangled” particle, regardless of distance – what Einstein famously termed “spooky action at a distance.” This has been experimentally verified numerous times, as recognized by the Nobel Prize in Physics.
“Many physicists are uncomfortable with the implications of non-locality,” Adlam notes. Instantaneous influence seemingly violates the cosmic speed limit – the speed of light.
To resolve this apparent paradox, some physicists have proposed alternative interpretations that challenge our conventional understanding of time. These interpretations suggest that what appears as instantaneous non-local effects might actually involve influences traveling forward and then backward in time.
“Instead of instantaneous action at a distance, the effect could travel into the future and then loop back to the past,” Adlam explains. “This would mimic instantaneousness, but the effect would have actually taken a detour through time.”
This introduces the concept of retrocausality – future events influencing the past. This contradicts our usual perception of time flowing linearly from past to present to future. In these quantum interpretations, information might be taking temporal detours, traveling to the future and back to affect the past.
However, it’s crucial to note that retrocausality is a highly debated interpretation and not universally accepted within quantum physics. Many physicists find retrocausality as unsettling, or even more so, than non-locality.
Even if retrocausality is real, it’s unlikely to provide a practical pathway for human time travel. “Retrocausality is not equivalent to time travel in the way we imagine it,” Adlam clarifies.
Firstly, observations of non-locality have been limited to microscopic scales with very few particles. Scaling this up to macroscopic objects like humans or even a sheet of paper would be an immense, potentially impossible, leap.
Furthermore, even at the quantum level, sending messages to the past via retrocausality appears impossible. “The retrocausal effect is inherently concealed by its implementation,” Adlam explains.
Consider an experiment where Adam makes a measurement in a lab. The outcome of Adam’s measurement depends on a measurement Beth makes later in the future. Beth’s future action influences Adam’s past result. However, this only works if Beth’s experiment completely erases all records of Adam’s initial measurement.
“You could, in a sense, send a signal to the past, but only by destroying all evidence of sending that signal and the events that preceded it,” Adlam says. “This makes it practically unusable for sending meaningful information or creating paradoxes.”
So, based on our current understanding of physics, future time travel seems achievable through relativistic effects, while past time travel remains firmly in the realm of speculation and faces immense theoretical and practical obstacles.
The key caveat is that our current theories, relativity and quantum mechanics, are incomplete and incompatible with each other. A deeper, unified theory is needed to reconcile them, but this “theory of everything” remains elusive. “Until we have that more complete theory, we cannot be entirely certain about the ultimate possibilities and limitations of time travel,” Shoshany concludes.
Of course, in a very real sense, you are time traveling right now. As you’ve read this article, you’ve journeyed several minutes into the future. Enjoy the ride!
