Time travel has spurred human imagination for decades now and has been a central theme in popular culture through works like Doctor Who, The Time Machine, and Back to the Future. These stories traverse the paradoxes and lures of traveling through time. But how close are these representations to scientific reality? It is possible that while theoretical physics gives some idea about moving to the future, time travel into the past is seen as elusive, possibly impossible.
Einstein’s theory of relativity: A new way of conceptualizing time
Time is understood through the lens of the theories of relativity propounded by Albert Einstein. Time is a variable, neither constant nor accelerating or decelerating in all situations, dependent on the force applied towards it in terms of speed and gravity.
This might open the door for the possibility of at least “time travel” into the future. An approaching object ticking near the speed of light slows down with respect to the observer at rest. In terms of this scenario, we have the twin paradox: If one twin travels in space near the speed of light, while the other remains on Earth, the result is that the twin traveling will appear to age very little.
Though this speed hasn’t been attained, but there is slight time dilation experienced by space travelers such as Scott Kelly, who spends months in orbit. Likewise, time is slowed down as near to a black hole, which is the main reason for intense gravitational fields.
This can be seen in movies like Interstellar, where astronauts “experience” a few hours, while several decades pass on the outside. They are so small that they would hardly be perceptible to people in everyday life but are significant enough to have had to incorporate them into the functioning of GPS satellites to ensure navigational accuracy.
Looking ahead and looking backward: The challenge of time travel
Even though it is possible to move forward in time as even Einstein believes, traveling back is much more complicated. Theoretically, closed time-like curves were proposed, that is, paths through space-time that loop back on themselves.
Theoretically proposing, no proof exists on either counts of their existence and feasibility. Cosmic strings are another speculative theoretical premise which could, in principle, form such loops, but none of the phenomena were ever observed.
Wormholes – the pathways through space-time made famous by fiction – appear to offer yet another theoretical option. Such tunnels could, in principle, connect two distant points in space and might enable a sort of time travel.
The theoretical problems of wormholes are mind-boggling as they would probably collapse under their own weight of gravity, last for only a moment, or require immense amounts of negative energy to be kept stable-an energy form found only in tiny, fleeting pockets in the quantum realm.
Quantum mechanics and its complications as to traveling through time
Quantum mechanics has added another layer in making things complicated, especially in science known for studying the very small. For instance, the observance of non-locality, which states that anything that happens on one particle instantaneously affects another local-as-an-entangled particle, counters are causality.
There are interpretations that suggested retrocausation, where future events influence the past. However, the effects are limited to subatomic particles, not for human time travel or objects into the past. Supposedly, backward time travel would be possible. Still, there are huge barriers to even determining the conditions required to make such a feat possible.
This includes the technology necessary to do so, which is probably beyond our current capabilities. There are also paradoxes, such as the grandfather paradox, which doubts the consistency of such a timeline. This paradox deals with the idea that changing the past might end up erasing your existence.
In theory, it is possible to travel to a future reality based on our present knowledge of physics if one travels at very high speeds or within very strong gravitational fields. The moving back in time, however, is encumbered by theoretical as well as practical problems. While many things about the universe continue to inspire and challenge innovations, time travel into the past might be a fantasy only in the fringes of science fiction.
