The notion of traversing through time, both forward and backward, has captivated the imaginations of storytellers and scientists alike. From H.G. Wells’ “The Time Machine” to the adventures of Doctor Who and the escapades in “Back to the Future,” the allure of manipulating time is undeniable. But Can U Time Travel in reality? Let’s delve into what physics has to say.
While Doctor Who’s TARDIS, a vehicle capable of navigating time and space, is a beloved symbol of time travel, it’s firmly rooted in science fiction. The show doesn’t attempt to ground its temporal mechanics in real-world physics. But what about the actual possibilities? Could we ever construct a time machine to visit past eras or leap into the future?
According to our current understanding, traveling to the future is plausible, while journeying into the past presents formidable, potentially insurmountable challenges.
The foundation for understanding time travel lies in Albert Einstein’s theories of relativity, which revolutionized our understanding of space, time, mass, and gravity. A core concept is that the flow of time isn’t constant; it can accelerate or decelerate based on specific 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.
Time Dilation: A Journey to the Future
One consequence of relativity is time dilation: time elapses more slowly for objects moving at high speeds. While the effect is negligible at everyday speeds, it becomes significant as one approaches the speed of light. This leads to the famous twin paradox: if one twin travels through space at near-light speed while the other remains on Earth, the traveling twin will age more slowly. “If you travel and come back, you are really younger than the twin brother,” says Vlatko Vedral, a quantum physicist at the University of Oxford. The effects have been seen with astronauts such as Scott and Mark Kelly when Scott spent extended periods in space.
Similarly, time slows down in strong gravitational fields, such as those near black holes. “Your head is ageing quicker than your feet, because Earth’s gravity is stronger at your feet,” says Osborne.
These relativistic effects, though minuscule in our daily lives, are crucial for technologies like the Global Positioning System (GPS). The clocks on GPS satellites experience time at a slightly faster rate than clocks on Earth and must be constantly adjusted. “If we didn’t, Google Maps would be wrong about 10km (six miles) a day.”
Relativity implies that future time travel is possible. No need for a time machine, per se. Simply travel at speeds close to the speed of light or spend time in an intense gravitational field. Doing so allows you to experience a relatively shorter period of time while decades or centuries pass in the rest of the universe.
Backwards Time Travel: A Thorny Path
While traveling to the future appears feasible, reversing course presents immense hurdles. “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 a few theoretical possibilities for backward time travel, but these remain highly speculative.
Closed Time-like Curves and Cosmic Strings
One concept involves creating a closed time-like curve: a path through spacetime that loops back on itself. Someone traversing such a path would eventually return to their starting point in time and space. While mathematically possible, as demonstrated by Kurt Gödel in 1949, there’s no evidence that these exist in the universe. Furthermore, even with advanced technology, creating them seems improbable. Even if we could, “You would literally be repeating exactly the same thing over and over again,” says Vedral.
Another theoretical idea involves cosmic strings: hypothetical, incredibly dense objects that may have formed in the early universe. In 1991, physicist Richard Gott proposed that two cosmic strings moving past each other could create closed time-like curves. However, cosmic strings remain purely theoretical, and even if they exist, the chances of finding two aligned in the right way are astronomically low. “We don’t have any reason to believe cosmic strings exist,” says Mack.
Wormholes: Tunnels Through Spacetime
Wormholes, theoretical tunnels through spacetime, offer another potential route for time travel. In theory, spacetime could be folded, creating a shortcut between distant points. “Wormholes are theoretically possible in general relativity,” says Vedral.
However, we lack any evidence that wormholes actually exist. Even if they do, they are likely to be extremely short-lived and microscopically small. A wormhole, by definition, has an extremely intense gravitational field. “It would collapse under its own gravity,” says Osborne.
Stabilizing a wormhole and making it traversable would require an enormous amount of “negative energy,” something that may only exist on the subatomic scale.
Quantum Mechanics: A Spooky Interpretation?
Quantum mechanics, the theory governing the behavior of matter at the atomic and subatomic levels, introduces even stranger possibilities. One such phenomenon is non-locality, where a change in one particle’s state can instantaneously influence another entangled particle, regardless of distance.
Some physicists interpret these experiments as evidence of “retrocausality,” where events in the future can influence the past. Instead of having an instantaneous non-local effect, you would just send your effect into the future, and then at some point it would turn around and go back into the past,” says Adlam. “It would look instantaneous.” But in reality, the effect would have gone on a journey into the future and back again.
However, this interpretation remains controversial, with many physicists finding retrocausality as unsettling as non-locality. Even if retrocausality is real, it likely wouldn’t enable practical time travel. The observed effects involve only tiny numbers of particles, and scaling them up to macroscopic objects would be incredibly difficult.
Furthermore, even if information could be sent to the past, it might be impossible to retrieve it. As Adlam explains, such a signal could only be sent by destroying all records of the events that allowed it to be sent.
The Unknown Theory
So, while future time travel seems plausible based on our current understanding of relativity, backward time travel remains firmly in the realm of speculation. The loophole, however, is that our current theories are incomplete. Relativity and quantum mechanics, while successful in their respective domains, are incompatible. A deeper, unifying theory is needed, but it remains elusive. “Until we have that theory, we cannot be sure,” says Shoshany.
In the meantime, remember that as you’ve read this article, you’ve already traveled a few minutes into the future!
