Can you travel back to the past? Films say yes, science isn't so sure
Time travel has been part of the popular imagination for long. From science fiction classics like The Time Machine and Back to the Future to contemporary films like Interstellar played on the notion of slipping through time — whether to witness the past, and even be a part of it, or to glimpse the future.
But the very idea raises profound questions about physics, causality, and the nature of reality itself. Is time travel possible? And if so, under what conditions?
Time travel as a concept predates modern physics. H.G. Wells' The Time Machine (1895) introduced it as a literary device, but it wasn't until the 20th century that science began to grapple with the possibility in earnest. Albert Einstein's theory of relativity showed that time is not absolute or constant — it can stretch and compress depending on the speed at which you travel and gravity.
In 1949, the logician Kurt Gödel, a close associate of Einstein, proposed that under certain exotic conditions — such as a rotating universe — it might be possible to trace a path through spacetime that loops back into the past.
Einstein was reportedly disturbed by the implications. Although his equations didn't explicitly forbid time travel, they suggested a universe far stranger than he was comfortable with.
In fact, we're all time travelers, constantly moving forward at the steady rate of one second per second. But general relativity allows for more dramatic effects. Clocks on high-speed spacecraft or near massive objects like black holes tick more slowly relative to those on Earth, a phenomenon confirmed by experiments using atomic clocks on airplanes and satellites. This is why astronauts on the International Space Station age a tiny bit more slowly than the rest of us.
Traveling backward in time, however, poses far greater challenges. Theoretical constructs such as wormholes — shortcuts through spacetime — or closed timelike curves might permit backward travel, at least on paper. Physicists like Kip Thorne have explored these ideas, but all rely on speculative ingredients like 'negative energy,' which has never been observed in the required form or quantity.
Even if time machines could be built, they raise troubling logical paradoxes. The most famous is the grandfather paradox: what happens if you travel back and prevent your grandparents from meeting? If you were never born, how did you travel back in the first place?
One proposed resolution is the Novikov self-consistency principle, which asserts that any events in the past caused by a time traveler must be consistent with the history that gave rise to the traveler. Alternatively, some theories in quantum mechanics suggest the existence of branching universes — where each change spawns a new, parallel timeline, thus avoiding contradictions.
Still, the paradoxes remain a sticking point. Stephen Hawking, a noted skeptic, once hosted a 'party for time travelers' but sent out the invitations only after the event. No one came.
Science fiction has explored these dilemmas with enthusiasm and creativity. In Back to the Future, small changes to the past ripple through to the present. In Interstellar, time dilation near a black hole causes years to pass on Earth in what feels like minutes to the protagonist — a scenario rooted in real physics. And in Avengers: Endgame, quantum time travel is introduced, though it serves more as narrative convenience than scientific plausibility.
These portrayals, while imaginative, underscore the central challenge: even if time travel is mathematically permitted, making it physically possible is another matter altogether.
At present, there is no experimental evidence that time travel to the past is possible. Most physicists believe that quantum effects, energy constraints, or deep features of spacetime geometry would ultimately prevent it. Some even argue that time travel could violate the second law of thermodynamics, which dictates that entropy — disorder — always increases, thereby giving time its 'arrow.'
Nevertheless, time travel remains a topic of legitimate scientific exploration. It tests the boundaries of our understanding of spacetime and causality. It also tests the interplay between general relativity and quantum mechanics — two theories that, to this day, remain fundamentally incompatible.
Why are we so fascinated by time travel? Perhaps because it represents the ultimate form of agency — the power to revisit lost moments, correct mistakes, or witness beginnings. But time, for now, seems to move only forward.
Still, as our theories of the universe deepen, and our technology improves, the question remains open — even if only slightly. Until then, time travel may continue to thrive best not in laboratories, but in the pages of books and on cinema screens, where imagination travels faster than any particle known to physics.
Shravan Hanasoge is an astrophysicist at the Tata Institute of Fundamental Research.
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Time of India
21 hours ago
- Time of India
Ax-4 Pushed Back Again, No New Date Yet
Representative image BENGALURU: The launch of Axiom-4 mission (Ax-4), which will take India's Group Captain Shubhanshu Shukla and three others to space, will not happen this Sunday or Monday. There's no fresh date announced as of Friday. Nasa, Axiom Space and SpaceX standing down from the launch as the space agency needs additional time to continue evaluating International Space Station (ISS) operations after recent repair work in the aft (back) most segment of the orbital laboratory's Zvezda service module. 'Because of the space station's interconnected and interdependent systems, Nasa wants to ensure the station is ready for additional crew members, and the agency is taking the time necessary to review data,' a statement read. Stating that they appreciate the historic nature of this mission for India, Poland, and Hungary, the statement added that the crew remains in quarantine in Florida, and the astronauts stand ready to launch when the station is ready to receive them. The launch, originally targeted for May 29, was deferred to June 8 following the detection of an issue in the electrical harness of the Crew Dragon module, Isro had said earlier. by Taboola by Taboola Sponsored Links Sponsored Links Promoted Links Promoted Links You May Like Buy Brass Idols - Handmade Brass Statues for Home & Gifting Luxeartisanship Buy Now Undo It was then postponed by a day to June 9 — which was not publicly announced — and then rescheduled to June 10. The June 10 launch was rescheduled once again. During preparations for a hot fire test on June 8, SpaceX engineers detected a liquid oxygen (LOX) leak in Falcon-9. An anomaly was also found in one of the engine actuators, which was subsequently replaced along with its controller. Expecting a quick resolution of the LOX leak, the mission was initially rescheduled for June 11. Isro said it had stressed on crew safety in review meetings. Mission partners on late on June 10 decided to postpone the launch further to conduct a test to validate the corrections carried out. After postponements owing to liquid oxygen (LOX) leak in the Falcon-9 rocket, the wait for Axiom-4 mission launch and India's Shubhanshu Shukla going to space got extended further because of an issue at the International Space Station (ISS). The mission partners then announced June 19 as a probable date. And Nasa, earlier this week said it was continuing to work with Roscosmos (Russian space agency) 'to understand the most recent repair efforts to seal small leaks'. The leaks located in the aft segment of the space station's Zvezda service module, have been monitored by flight controllers for several years, Nasa said. 'Recent repair efforts by Roscosmos appear to have stabilised pressure in the transfer tunnel, though teams are still evaluating whether the leaks have been fully sealed or if air is flowing into the area from the main station,' it added. On June 18, another announcement said that the launch could happen on June 22 with a back-up date available on June 23. At present, Nasa, Axiom or SpaceX have not yet committed to a new launch date.
Deccan Herald
a day ago
- Deccan Herald
NASA puts off Sunday's launch of Axiom-4 mission to International Space Station
The space agency needs additional time to continue evaluating International Space Station operations after recent repair work in the aft (back) most segment of the orbital laboratory's Zvezda service module, it said.
Indian Express
a day ago
- Indian Express
Shubhanshu Shukla's Axiom-4 mission delayed again, NASA to announce new date soon
National Aeronautics and Space Administration (NASA) on Friday announced that the Axiom-4 mission, set to carry Indian astronaut Shubhanshu Shukla to space, has been delayed once again. This is the sixth time the Axiom-4 mission is being delayed. The mission was rescheduled for June 22 after technical snags, and NASA will announce the new date for the launch shortly. The International Space Station (ISS) said in a statement, 'NASA, Axiom Space and SpaceX continue reviewing launch opportunities for Axiom Mission 4. NASA is standing down from a launch on Sunday, June 22, and will target a new launch date in the coming days.'
