Is Time Travel Possible?

Moving between different points in time has been a popular topic for science fiction for decades. However, The reality is more complicated than finctions. Not all scientists believe that time travel is possible. Some even say that the travel would be fatal to any human who chooses to undertake it.

Understanding Time
While most people think time is a constant, physicist A. Einstein showed that time is an illusion; it is relative. It can alter for different observers depending on your speed through space. Einstein says time is the "4th dimension." Space is described as three-dimensional place, which provides a traveler with coordinates such as height, length, and width, showing location. Time also provides another coordinate, direction. Although usually, it only moves forward like an arrow.

Einstein's theory of special relativity states that time slows down or speeds up depending on how fast you move relative to something else. Approaching the light speed, a person inside a spaceship would age much slower than his twin at home. Also, according to the same theory, gravity can bend time.

Imagine a 4 dimensional fabric called space-time. When something that has mass sits on that piece of fabric, it causes a curve or a bending of space-time. The bending of space-time causes objects to move on a curved path, and that curvature of space is gravity.

Both the general and special relativity theories have been proven with GPS satellite technology that has very accurate timepieces on board. The effects of gravity, as well as the satellites' increased speed above the Earth relative to observers on the ground, make the unadjusted clocks gain 38 microseconds a day.

This effect is called time dilation, and technically it makes astronauts time travelers. when they return to Earth, they will be very slightly younger than their identical twins that remain on earth if they have one. About 0.02 second younger..

Wormholes
Einstein suggested the theoretical existence of "bridges" through time and space – often referred to as wormholes. His theory has been further developed by numerous physicists including Stephen Hawking and Kip Thorne.

A wormhole would allow an object to travel from one point to another faster than the speed of light, by taking a shortcut through space-time, meaning the object won't break the rule of the so-called universal speed limit — the speed of light — because it will at no point actually travel at a speed faster than light.

"The basic idea if you're very, very optimistic is that if you fiddle with the wormhole openings, you can make it not only a shortcut from a point in space to another point in space, but a shortcut from one moment in time to another moment in time," Professor Brian Greene, a prominent string-theory physicist, told Live Science.

Problem: No wormhole has ever been discovered, and even if it was, it would be far too small for scientists to manipulate for the purposes of time travel – measuring just a billion-trillion-trillionth of a centimetre across. They also pose a significant risk, bringing with them the threat of sudden collapse, high levels of radiation and contact with dangerous exotic matter, Space.com warns.

Cosmic Strings
Described as one-dimensional "cracks in the universe" and some of the strangest structures observed by cosmologists, cosmic strings could help us navigate through time. "Cosmic strings are either infinite or they're in loops, with no ends", explains J Richard Gott, an astrophysicist at Princeton University. "So they are either like spaghetti or Spaghetti Os."

They are thought to have formed billions of years ago, moments after the Big Bang, and because they contain such large amounts of mass, some scientists believe they could potentially "warp" space-time around them. "The approach of two such strings parallel to each other, will bend space-time so vigorously and in such a particular configuration that [it] might make time travel possible – in theory," according to Live Science.

Problem: Again, cosmic strings only exist only in theory. "This is a project a super civilisation might attempt," says Gott. "It's far beyond what we can do. We're a civilisation that's not even controlling the energy resources of our planet."

Furthermore, in order to travel back in time just twelve months, it would require a cosmic loop that contains half the mass of the entire universe, which we are unlikely to see any time soon.

Supermassive Black Hole
Described by Professor Hawking as natural time machines, black holes are so dense that they have a dramatic impact on time, slowing it down more than anything else in the universe. If a spaceship were to orbit a black hole, those on board would only experience eight minutes of time for every 16-minute orbit.

"Around and around they'd go, experiencing just half the time of everyone far away from the black hole. The ship and its crew would be travelling through time," he explains. "Imagine they circled the black hole for five years. Ten years would pass elsewhere. When they got home, everyone on Earth would have aged five years more that they had."

Problem:Black holes are more practical than wormholes because they don't present the same paradoxes and won't be destroyed by feedback. "But it's pretty dangerous," concedes Hawking. "It's a long way away and it doesn't even take us very far into the future.

Travelling at the speed of light
Another possibility would be travelling at the speed of light, a constant, finite speed of 186,000 miles per second. In Einstein's special theory of relativity, “time” as a universal concept. Instead, time passes differently for different observers, depending on the observers' motion and - more importantly, speed.

"If you go fast, your clock runs slow relative to people who are still," explains physicist Professor Brian Cox in the Daily Mail. "As you approach the speed of light, your clock runs so slow you could come back 10,000 years in the future."

Problem: According to the laws of physics, nothing can travel as fast as the speed of light – let alone a spaceship. Even the Large Hadron Collider, the strongest particle accelerator in the word, can't make protons move that fast. "If a proton did achieve that speed, it would need infinite energy to go any faster, and we don't have an infinite supply of energy," explains the BBC's Jennifer Ouellette. Also, the human body would not be able to withstand time travel at all, as travelling at nearly the speed of light would kill you.

So is time travel possible?
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 travelers can at least experience it vicariously through movies, television and books.