Time travel has remained at the forefront of science-fiction related speculation, with a plethora of books, films, television shows, and other related media having been created in order to explore the possibilities of humanity’s conquest over time.
However, due to the complicated nature of time, no one really knows what would happen if we were to ever hypothetically meddle with it. Many suggestions have been put forward and explored, often with the warning that cataclysmic consequences await anyone who changes the natural order of things.
In this article, I’ll firstly be exploring the facts surrounding what we recognise as ‘time travel’, before we get into the speculative fiction of going back to the past.
So, first thing’s first. It is important to understand that time is not necessarily a constant. Not in the “wibbly-wobbly, timey-wimey” sense that Doctor Who portrays, but rather in the sense that time is relative, and the impact that space has on our bodies can very minutely impact how we age.
The greater amount of time a person spends in space, the slower they age
In a one-of-a-kind study conducted by NASA in 2015, identical twins Mark and Scott Kelly were observed to see how an extended amount of time in space impacted an astronaut’s body. Mark, who retired in 2011, remained on Earth, whilst Scott was sent to the International Space Station for nearly one year. Amongst other genomic abnormalities, it was found that the length of Scott’s telomeres (molecular caps on the ends of our chromosomes, the length of which declines as we age) increased very slightly whilst he was in space, widening the age gap between the twins by 5 milliseconds.
Whilst this difference might seem less than miniscule in the grand scheme of things, the implications for long-term space travel indicate that the greater amount of time a person spends in space, the slower they age.
But why, in that case, is the situation the opposite for atomic clocks (clocks that are regulated by “the vibrations of an atomic or molecular system”, rather than a pendulum)?
Studies to do with ‘Gravitational Time Dilation’ (first described by Albert Einstein in 1907 as part of his Theory of Relativity) have shown that the closer something is to the Earth (or other planetary body) the slower it ages relative to objects around it. By this understanding, the very core of our planet is estimated to be two and a half years younger than its surface.
Two atomic clocks placed at two different heights would eventually read two different times, despite the fact that the time they record should remain absolutely consistent. The clock that is placed higher than the other would tick faster than the one closer to the Earth – which contradicts the findings from the Kelly study.
It is therefore to be believed that external influences, such as radiation or a lack of intense gravity from Earth, were what caused Scott’s telomeres to appear to increase in length, even though he was significantly higher up than his brother. This idea can be supported due to the fact that Scott’s telomeres had returned to their baseline (i.e. pre-space) length within six months of returning to Earth.
Various forms of ‘Time Dilation’ have been explored in films such as Interstellar (2014), where the crew of the Endurance travel to a planet where “one hour [there] is seven years on Earth”, due to the planet’s proximity to an enormous black hole. If we imagine that all of space and time is a piece of fabric, and planets of varying sizes are different objects with different masses, we can see the impact that mass has on the plane of space/time.
The closer we move to the speed of light, the greater distances become compressed
For example: if Earth were the weight of a tennis ball, Jupiter would be the weight of two and a half large bowling balls. The sun, therefore, would be the weight of one and a half double decker busses. If you put these objects onto a (very) large cloth and observed how deeply they sank and stretched the fabric, this is similar to how masses warp the fabric of spacetime.
A common sight in space-travel science-fiction films is the impact on a person’s perception of space when moving close to the speed of light. In such franchises such as Star Trek and Star Wars, a jump to “hyper-speed” results in the scenery outside of a spaceship condensing into hundreds of blurred strips of light. This is known as Lorentz contraction, whereby both time and distance are affected by motion.
The closer we move to the speed of light, the greater distances become compressed. From our reference point, moving at incredibly high speeds, a large distance of several hundred miles is compressed to appear to be only several hundred yards. Such a principal can be observed through particles known as Muons, which are created when cosmic rays strike Earth’s atmosphere.
Travelling to the past remains a mystery
Muons have a very short lifetime – so short that, theoretically, we should not even be able to detect them from Earth’s surface; a muon should have already decayed before it reaches the ground given the time it takes to fall from when it is created. However, due to the concept of ‘Special Relativity’, the distance from the atmosphere to the ground is compressed from a muon’s perspective. So, even though its internal clock continues at the same rate it always has, the distance appears far less and therefore the muons can reach the ground. From our perspective, their internal clocks tick at a slower pace. Hence the ‘relative’ nature of relativity.
Confused yet? I know I am.
What’s important to remember is that we do not experience time in the same way universally. Mayflies, for example, must see us as unageing, unchanging beasts. They experience their whole lifetime in one rotation of the Earth.
Whilst travelling to the past remains a mystery, (as Stephen Hawking wrote, “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future”), the compression of time into the future appears to be right around the corner. Maybe one day, astronauts gone from this planet for hundreds of years will return, only for us to find they have barely aged at all…
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