Since H.G. Wells published The Time Machine in 1895, the idea of time travel has fascinated scientists and storytellers alike. While Wells’ novel was purely fictional, it sparked a scientific curiosity that continues today. Theories from Einstein’s relativity to Stephen Hawking’s A Brief History of Time suggest that time is not as rigid as it seems. Now, with the recent discovery of ‘negative time’ in quantum physics, the debate over time travel has been reignited. Recently in a ground-breaking experiment, scientists at the University of Toronto have observed a phenomenon known as ‘negative time’ within the realm of quantum physics.

This discovery challenges our conventional understanding of time and opens new avenues for exploring the fundamental laws of the universe. Movies like Independence Day: Resurgence and Interstellar have popularised the idea of manipulating time, but how close are we to making such concepts a reality? The latest research challenges our understanding of time’s one-way flow and raises intriguing possibilities. What is ‘Negative Time’? Time is traditionally thought to flow in one direction ~ from past to future. This concept, known as the “arrow of time,” is based on thermodynamics which requires that entropy (disorder) always increases with time. However, quantum physics often challenges classical rules.

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In the above experiment, scientists observed photons appearing to exit a material before they entered it. This suggests a ‘negative duration,’ meaning the particles behaved as though time was running in reverse. While this doesn’t mean we can build a time machine yet, it provides evidence that, under special conditions, time might not be strictly linear. Imagine dropping a cup, and instead of shattering, the fragments reassemble in your hand ~ this is what ‘negative time’ would look like on a larger scale. Einstein’s theory of relativity introduced the idea that time is relative ~ it moves differently for different observers depending on their speed and gravitational field. A key concept in relativity is time dilation: the faster you travel; the slower time moves for you.

This has been experimentally verified using atomic clocks on fast moving spacecraft. Astronauts on the International Spa – ce Station experience this on a tiny scale, aging slightly slower than people on Earth. Black holes and wormholes ~ predicted by Einstein’s equations ~ are theorized as possible gateways for time travel. If a wormhole connected different points in space-time, one could, in theory, enter it and emerge in the past or future. Movies like Interstellar depicted time dilation realistically, where a planet close to a black hole experienced time at a much slower rate than distant observers. Independence Day portrayed a more fictionalized but exciting vision of manipulating time to prevent catastrophic events.

The reality, however, is far more complex. While the term ‘negative time’ might evoke images of time travel as depicted in science fiction, the reality is more nuanced. The observed phenomenon does not imply that information or matter is traveling backward in time. Instead, it highlights the probabilistic nature of quantum interactions. The findings suggest that, at the quantum level, particles like photons can exhibit behaviours that challenge our traditional concepts of time. Stephen Hawking was sceptical of practical time travel. He argued that if time travel were possible, we should have met tourists from the future.

He even hosted a “time travellers’ party,” sending out invitations after the event had already taken place ~ no one showed up. Yet, Hawking acknowledged that quantum mechanics and relativity leave room for theoretical possibilities. Understanding such quantum phenomena is crucial for cosmology ~ the study of the universe’s origin and evolution. Insights into quantum mechanics can shed light on the fundamental processes that occurred during the universe’s inception. For instance, phenomena like cosmic inflation, which describes the rapid expansion of the universe in its early moments, are deeply rooted in quantum field theories.

By exploring concepts like ‘negative time,’ scientists can refine models that explain the universe’s evolution from the Big Bang to its current state. How Does ‘Negative Time’ fit in? The discovery of ‘negative time’ could help explain how particles behave in extreme conditions, like near black holes or in the early universe. Some physicists speculate that negative time could play a role in quantum entanglement ~ where two particles influence each other instantaneously across vast distances. If time is not strictly linear, it raises profound questions about causality. Could an effect occur before its cause? Could information travel backward in time?

While current findings don’t provide clear answers, they open exciting new avenues for research. The concept of ‘negative time’ is still in its infancy, but it challenges our understanding of reality. While time travel remains a staple of science fiction, science itself is inching closer to understanding the true nature of time. If researchers continue to uncover quantum behaviours that defy our expectations, the future ~ or even the past ~ might hold surprises beyond our imagination. The discovery of ‘negative time’ in quantum physics experiments is a testament to the complexities and wonders of the quantum world. While it doesn’t offer a pathway to time travel, it deepens our understanding of the fundamental principles that govern the universe.

As research in this field progresses, it may lead to new technologies and insights that could revolutionize our comprehension of time and the cosmos. While Independence Day and Interstellar portray time travel as a thrilling adventure, real science is far from creating a working time machine. However, studying the nature of time in quantum mechanics may lead to new technologies and insights that revolutionise our comprehension of the cosmos. The discovery of ‘negative time’ serves as a reminder that the universe still holds mysteries waiting to be unravelled

(The writer is retired Director, Space Science Office, and Brahma Prakash Professor of ISRO HQ, Bengaluru. The visual accompanying this article is an AI-assisted thematic sketch depicting a surreal landscape where time flows backward, with clocks unwinding and celestial bodies reversing their paths, symbolising the concept of ‘negative time’)