The concept of traversing through time, leaping into the future or revisiting the past, has captivated storytellers and scientists for generations. From H.G. Wells’ “The Time Machine” to the “Back to the Future” trilogy, and the enduring popularity of “Doctor Who,” the allure of time travel is undeniable. But beyond the realm of science fiction, Can Humans Time Travel in reality? Let’s delve into what physics has to say.
This image represents the intriguing concept of time travel, a popular topic in science fiction and a subject of ongoing scientific exploration.
Time Travel to the Future: A Relativistic Reality
Albert Einstein’s theories of relativity revolutionized our understanding of space, time, and gravity. A crucial consequence of these theories is that time is not absolute; its passage is relative and can be affected by speed and gravity. This opens the door to the possibility of future time travel.
“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.
One implication of relativity is time dilation: the faster you move, the slower time passes for you relative to a stationary observer. Imagine one of two twins embarking on a high-speed space journey nearing the speed of light, while the other remains on Earth. Upon the astronaut twin’s return, they would be younger than their Earthbound sibling. This is the “twin paradox” come to life. The Kelly twins, Scott and Mark, experienced this to a small degree when Scott Kelly spent months in space.
Time also slows down in strong gravitational fields, such as those near black holes. The closer you are to the source of gravity, the slower time passes for you. This concept was used in the movie “Interstellar” and the “Doctor Who” episode “World Enough and Time.”
Einstein’s theories laid the groundwork for understanding how speed and gravity can affect the passage of time, making future time travel theoretically possible.
Interestingly, these relativistic effects aren’t just theoretical curiosities; they have practical implications. The satellites used in GPS systems experience time dilation due to their speed and distance from Earth’s gravitational field. Their clocks tick faster than those on Earth, and if not corrected, this would lead to inaccuracies of about 10km (six miles) a day in Google Maps.
Therefore, time travel into the future is theoretically possible, and we don’t even need a “time machine” in the conventional sense. We only need to travel at very high speeds or spend time in a strong gravitational field to experience the effects of time dilation.
Time Travel to the Past: A More Complex Puzzle
While future time travel seems achievable based on current scientific understanding, traveling backward in time poses significant challenges.
“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 are far more speculative. One idea involves creating a “closed time-like curve” – a path through spacetime that loops back on itself. Someone following such a path would eventually return to their starting point in time and space. The logician Kurt Gödel described such a path mathematically in a 1949 study.
However, there are several problems with this approach. First, we have no evidence that such curves exist in the Universe. Second, even if they do, it is unclear how we could create them, even with advanced technology. Third, even if we could create them, entering one would mean repeating the same events over and over again.
Another theoretical possibility involves “cosmic strings,” hypothetical one-dimensional objects that may have formed in the early Universe. In a 1991 study, physicist Richard Gott proposed that two cosmic strings moving past each other in opposite directions could create closed time-like curves. However, there is no evidence that cosmic strings exist, and even if they do, finding two moving in the right way would be extremely unlikely.
Wormholes, theoretical tunnels through spacetime that connect two distant points, are another possibility allowed by relativity. “Wormholes are theoretically possible in general relativity,” says Vedral.
However, wormholes are also problematic. First, we have no evidence that they exist. Second, if they do, they are likely to be extremely short-lived and microscopically tiny. Keeping a wormhole open and traversable would require enormous amounts of “negative energy,” which may not be possible to obtain.
Quantum Mechanics and Retrocausality
Quantum mechanics, the theory that describes the behavior of matter at the atomic and subatomic levels, adds another layer of complexity to the question of time travel.
One of the strange phenomena observed in the quantum realm is non-locality, where a change in the state of one particle can instantly affect another “entangled” particle, even if they are separated by vast distances. Einstein called this “spooky action at a distance”.
Some physicists interpret these experiments as evidence of “retrocausality,” where events in the future can influence events in the past. This goes against our intuitive understanding of time as flowing linearly from past to present to future.
However, the interpretation of non-locality as retrocausality is not universally accepted. Even if retrocausality is real, it is not clear that it could be used to send messages or travel to the past.
Quantum entanglement and non-locality suggest a potential connection between past and future events, hinting at the possibility of retrocausality, although its implications for time travel are still unclear.
The Unification Problem and the Future of Time Travel Research
Relativity and quantum mechanics are both incredibly successful theories, but they are also incompatible. This suggests that we need a deeper, more fundamental theory that unifies them. Until we have such a theory, we cannot be certain about the ultimate possibilities and limitations of time travel.
Conclusion: A Journey Through Time Continues
So, can humans time travel? Based on our current understanding of physics, traveling to the future is possible through relativistic effects, but traveling to the past remains highly speculative and may be impossible. The theoretical possibilities offered by relativity and quantum mechanics are intriguing, but they also face significant challenges. Perhaps future breakthroughs in our understanding of the Universe will reveal new possibilities for time travel that we cannot currently imagine.
