If you have ever reminisced about any past event of your life, like your school days, your first date, or any random event, you might have pondered a fascinating question: our minds can go back in time, but our bodies can’t? This is the paradox of time: Is it possible to physically travel back in time?
Historically, time was considered absolute, meaning that time flows uniformly for all observers within the universe, as described by Isaac Newton. However, our understanding of time has undergone a significant shift since Einstein’s theories of relativity. This theory argues that time is relative, meaning that time passes at a different rate based on an observer’s speed. For instance, if you measure time using an atomic clock on a high-speed airplane, you will observe that time passes slightly slower on the airplane than on the ground due to time dilation. Likewise, time spent by astronauts in space is slower than time on earth due to speed and gravitation strength (an idea of general relativity). Einstein resolved time malleability by arguing that time and space can bend.
However, we move in space in any direction, but we only move in one direction in time. Our universe has a certain rule in which bodies can flow through time. This is often defined with the second law of thermodynamics, which argue that bodies move from order to disorder, or entropy. Systems in our reality move from order to disorder, and this is the property that informs us of the direction of time. A dropped glass shatters, but shards don’t reassemble, and ice melts in warm water but doesn’t refreeze on its own. This irreversibility explains why we cannot move back in time.
Eisenstein’s theory of relativity also informs us about theoretical time travel, but with limitations. A body cannot travel faster than the speed of light, as it would violate causality. Special relativity works at the quantum level while general relativity focuses on macro and cosmos, like wormholes (hypothetical tunnels that allow time travel through spacetime like shortcuts). Imagine travelling from Ceylone to Australia by narrowing through the earth rather than flying around earth’s surface. Theoretically, a wormhole connects distant points in space and time, possibly opening doors for faster travel and even taking you back in time.
Stephen Hawking, proposed an idea called the “chronology protection conjecture”. This concept argues that the laws of physics prevent time travel to the past to prevent paradoxes, like the grandfather paradox (killing your grandfather before your birth). So there is a conjecture that the laws of nature will always be such that time travel into the past is not possible. Hawking’s idea of conjecture is certainly true in Einstein’s special theory of relativity, but not in his general relativity due to the existence of wormholes. Most theoretical physicists, including Hawking, argue about the conjecture that nature “protects” the timeline, making travelling in the past forbidden.
Interestingly, we cannot travel back in time as our minds do, but we see a glimpse of the past with our eyes. When you gaze at a sparkling body in the sky at night, you actually see stars. You are not seeing it as it is now, but as it was possibly millions of years ago. Light has a finite speed (about 300,000 kilometers per second), so it takes sufficient time to reach us. The star we see today might have exploded long ago, yet its light reaches us now, allowing us to see into the past. The James Webb Telescope is able to capture infrared light that provides a window to look at the universe in its early stages. When light travels a particular distance, it turns into infrared light. The James Webb Telescope has the ability to capture that infrared light.
So next time, if you yearn to see the past, then look at the photos, think about memories, or engage in stargazing. Travelling back in time is elusive, so these activities can satisfy you. Regardless of the future discoveries, the arrow of time will always firm.
