# Is Time Travel Possible? Physics Behind Time Travel

We all travel in time, don’t we? From the last year, we’ve moved up one year. Another way to say this is that we all are travelling forward at the same speed. But our topic at hand is, can we travel faster or slower? Or can we travel backwards or forward in time? It is indeed kind of mind-boggling to wrap our whole head around that concept. And there are countless imaginative theories. What if time-travel was possible? Would we be able to prevent something bad from happening? But if so, then what’s the guarantee that something more ominous might not happen? Let us dive deep into the depth of it all. Is all of this science fiction or is it truly possible?

## Physics behind time travel

To understand the concepts of time travel you need to understand a few theories and about a few hypothetical things.

The first name we get to our mind while talking about Time Travel is Albert Einstein and his Theory of Relativity. Understanding these theories completely is very difficult and there are very less people in the world who understand it completely. But this theory proves two special things with which we can travel in time. They are

1. If we travel with speeds closer to the speed of light, time will move slower for us (by the Special Theory of Relativity). But achieving such speed is very difficult and the reason again comes from Einstein. Einstein gave a mass velocity relation which tells that our inertial mass increases with velocity. The equation is

Einstein’s Mass Velocity Equation

Where,

• is the magnitude of the velocity
• is the speed of light
• m0 is the rest mass of the body
• m is the relativistic mass

2. Gravity distorts space and time and time moves slower in places with high gravitation (by the General Theory of Relativity). Know more about Gravity time dilation.

The Theory of General Relativity predicts the existence of something called Wormholes. A wormhole is a special solution to Einstein’s Field Equation. Wormholes are like passages or shortcuts between two points in space. Physicists say that we can travel in time through Wormholes but there are serious problems. We will discuss the problems in the next section.

One more hypothetical thing one needs to know is Exotic Matter. Exotic Matter is such a matter which have negative mass and repels the mass we see. At first, scientists believed that exotic matter cannot exist as it contradicts Einstein’s theories but some of the researchers have claimed that they have found a solution to Einsteins General theory of relativity which allows the existence of negative mass.

## Is time travel possible?

The BBC’s long-running science-fiction series Doctor Who, celebrating its fiftieth day of remembrance on twenty-three Nov, centres on its name character’s adventures through time and house. However, he may extremely skip between totally different periods of history at will?

Travelling forwards in time is amazingly simple. Einstein’s special theory of relativity, developed in 1905, made it clear that if we can travel at speeds close to the speed of light, we can travel into the future. Thanks to Einstein

If one were to go away from Earth inside a spacecraft moving at a considerable fraction of light speed, and is available back, solely a number of years may need to be passed on board however many years may have gone along on Earth. This leads to the “twins paradox“. What is twins paradox? Suppose one of a twin goes on the above-mentioned spacecraft and comes back, he would find himself much younger than his twin.

There’s just one drawback, once after you travel into future, coming back to the time where you started is difficult. There is a possibility of travelling back in time if traversable wormholes exist in reality. Wormholes are known to exist at microscopic levels and even if traversable wormholes exist they would collapse in seconds because of gravity. To keep Wormholes open we would need Exotic matter which is still hypothetical.

Assuming exotic matter exists and wormholes also do, even then we can’t go to any point in past. First of all, we need to have a machine to travel through a wormhole and with that machine we can travel back only to the time when the machine was created. Even if we create machines which have no effect with time and if could travel back to any point in time, we still have problems like the Grandfather paradox.

More restrictively still, theoretical work by Kip Thorne of Caltech employing a partial unification of general theory of relativity with natural philosophy recommended that any hole that enables time travel would collapse as before long because it fashioned.
Thorne did, however, resolve a noticeable issue that might arise because of my time travel (within the orbit of general relativity). The “grandfather paradox” involves going back in time and accidentally killing one’s grandfather before one’s father is planned – preventing one’s own birth.

Not only that, if time travel becomes possible anyone could go into the past and change the future randomly which is very dangerous.

Time Travel (Credi: Pixabay)

A man travels back into the past and marries a woman. After that, he returns to the present. The woman whom he married gets pregnant and has a son. After a few years, that son becomes the time traveller who goes to the past and marries the woman.

So who is the son and who is the father?

1. Stephen Hawking once believed that time travel is impossible

Stephen Hawking used to think that time travel is impossible. He claimed there would be some physical law which would prevent time travel and he even named it as “chronology protection conjecture”. But in the following years, unable to find any such physical law, he changed his statement and he stated as below

3. Many of us are time travellers

Many researches have proved that time flows quickly on higher altitudes on earth. Scientists have compared time from two atomic clocks, one was on a mountain and one was at sea level. The clock on the mountain was faster by 90 Billionths of a second.

So if you want to add a few billionths of a second to your life, stay in basements.

If someone travels back in time and kills the first human, there should be no life and the human who went there should disappear. What? These paradoxes really sound terrific.

There are many other paradoxes and theories, people say that

• All great scientists could probably be time travels and didn’t know how  to go back
• All the amazing structures like the Pyramids, Kailashnath Temple etc might be built by the time travellers and the list goes on

Space and time are two sides of the same coin

Space And Time are simultaneous phenomena (like mass and energy), and together form the fabric of the universe known as space-time. A demonstration of four-dimensional space-time’s inseparability is the fact that, as astronomers often remind us, we cannot look into space without looking back into time. We see the Moon as it was 1.2 seconds ago and the Sun as it was 8 minutes ago.

Also, in accordance with Einstein’s general theory of relativity, a massive object in space stretches the fabric of both the space and time around it. For example, our Sun’s mass bends its surrounding space so that the Earth moves in a straight line but also circles within the Sun’s curvature in space. The Sun’s effect on time is to slow it down, so time runs slower for those objects close to the massive object. Interestingly, gravity is the result of mass stretching the fabric of the space-time around it. Gravity also has an infinite range such that no matter how far apart two masses are in space they will always experience some gravitational pull towards each other. Theoretical physicists have tried to explain this phenomenon in terms of gravitons, S-Theory, and M-Theory, but even today a successful quantum theory of gravity is yet to be found.

## Wrapping up!

While time travel does not appear possible — at least, possible in the sense that the humans would survive it — with the physics that we use today, the field is constantly changing. Advances in quantum theories could perhaps provide some understanding of how to overcome time travel paradoxes.

One possibility, although it would not necessarily lead to time travel, is solving the mystery of how certain particles can communicate instantaneously with each other faster than the speed of light.

In the meantime, however, interested time travellers can at least experience it vicariously through movies, television and books.