Is time travel possible?

Is time travel possible? The short answer is "yes you can," and you're in the process of doing it now, speeding towards the future at a staggering speed of one second every second. You're basically traveling through your time at the exact same pace regardless of whether you're watching the paint dry or wishing you had more time to spend with a pal who is from out of town.

 This isn't exactly the kind of time travel that has captured numerous science fiction writers or inspired a genre so vast that Wikipedia lists more than 400 titles within this category, "Movies about Time Travel." In the popular franchises "Doctor Who," "Star Trek," and "Back to the Future," characters get into an exotic vehicle to blast back into the past or spin to the future. 

Once they have been through the past, they have to consider the consequences of changing the present or past in light of facts from the future (which is the point where time travel stories meet the concept of parallel timelines or alternative timelines).

While many are enthralled with the notion of changing our past or even seeing into the future prior to its arrival, no one has ever performed the kind of back-and-forth time travel found in science fiction or even thought of taking a person through a long time period that doesn't cause harm to them along the way. 

In fact, like the physicist, Stephen Hawking pointed out in his work "Black Holes and Baby Universes" (Bantam 1994), "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."

Science supports a certain amount of time-bending, however. For instance, Albert Einstein's concept of special relativity claims that time is an illusion that is able to move relative to the observer. Anyone who travels at the speed of light experiences time, along with its consequences (boredom and aging), far more slowly than an observer sitting still.

This is why the astronaut Scott Kelly aged not much more in the course of one year on the moon than his identical twin, who was on Earth.

There are also other theories of science concerning time travel, which include the bizarre physics that develops from wormholes, black holes, and string theory. In the majority of cases, however, time travel is still the subject of a growing number of science fiction novels, films, TV shows, comics, video games, and much more.

Special Relativity and Time travel to the future

Einstein came up with his theory of special relativity around 1905. Alongside his expansion, his theory of general relativity was able to become one of the most fundamental principles of contemporary science. Special relativity is the study of the relationship between time and space for objects that move with constant speed in straight lines.

The simplest explanation of this theory can be deceivingly simple. The first is that everything is assessed in relation to something different—which is to claim that there isn't an "absolute" frame of reference. The second is that the speed of light remains constant. It's the same, regardless of the circumstances, and regardless of the location where it is measured from. Thirdly, nothing can move faster than light.

The real-world experience of time travel is derived from these simple tenets. A person who is traveling at a high speed experiences time slower than an observer who is not moving through space.

While we don't push humans to speeds that are near light speed, however, we do send them soaring around the earth at 17,500 miles per hour (28,160 km/h) on the International Space Station. NASA astronaut Scott Kelly was born the day after his twin brother and fellow astronaut Mark Kelly. 

Scott Kelly spent 520 days in orbit, whereas Mark spent 53 days in space. The differences in the rates at which they lived their lives throughout their lives have actually increased the age gap between two men.

Space.com earlier published: "So, where [as] I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older," Mark Kelly spoke during a panel discussion on July 12, 2020."Now I've got that over his head."

General Relativity and GPS

The difference that low earth orbit makes in an astronaut's life span may be negligible--better suited for jokes among siblings than actual life extension or visiting the distant future--but the dilation in time between people on Earth and GPS satellites flying through space does make a difference.

The Global Positioning System, or GPS, helps us know exactly where we are by communicating with a network of a few dozen satellites positioned in high Earth orbit. The satellites circle the planet from 12,500 miles (20,100 kilometers) away, moving at 8,700 mph (14,000 km/h).

According to special relativity, the faster an object moves relative to another object, the slower that first object experiences time. According to the American Physical Society publication Physics Central, this effect cuts 7 microseconds, or 7 millionths of a second, off each day for GPS satellites with atomic clocks.

Then, according to general relativity, clocks closer to the centre of a large gravitational mass like Earth tick more slowly than those farther away. So, because the GPS satellites are much farther from the centre of the Earth compared to clocks on the surface, Physics Central added, that adds another 45 microseconds to the GPS satellite clocks each day. 

Combined with the negative 7 microseconds from the special relativity calculation, the net result is an added 38 microseconds. This means that in order to maintain the accuracy needed to pinpoint your car or phone--or since the system is run by the U.S. Department of Defense, a military drone-- engineers must account for an extra 38 microseconds in each satellite's day. 

The atomic clocks on board don't tick over to the next day until they have run 38 microseconds longer than comparable clocks on Earth. Given those numbers, it would take more than seven years for the atomic clock in a GPS satellite to unsynchronize itself from an Earth clock by more than the blink of an eye. 

(We did the math: if you estimate a blink to last at least 100,000 microseconds, as the Harvard Database of Useful Biological Numbers does, it would take thousands of days for those 38-microsecond shifts to add up.)

This kind of time travel may seem as negligible as the Kelly brothers' age gap, but given the hyper-accuracy of modern GPS technology, it actually does matter. If it can communicate with the satellites whizzing overhead, your phone can nail down your location in space and time with incredible accuracy.

Can we go back in time with Wormholes?

According to NASA, general relativity may also offer possibilities that allow people to travel back in time. But the reality of such a method is that it is not a piece of cake.

Wormholes are thought of as "tunnels" through the fabric of space-time, which could link diverse moments or locations in real life to other locations or moments. They are also called Einstein-Rosen bridges, or white holes as opposed to black holes. Theories about wormholes exist. Although they take up a lot of space (or space-time) on the screen in sci-fi and science fiction, no wormholes whatsoever in any form have ever been found in actual life.

Stephen Hsu, a professor of theoretical physics at the University of Oregon, explained the situation to Space.com and its sister website, Live Science, as "very hypothetical at this point.""No one thinks we're going to find a wormhole anytime soon."

Various time travel theories

Although Einstein's theories seem to create a problem for time travel. Some researchers have suggested alternative solutions that allow leaps between the past and present. The theories that are proposed have one flaw: as the scientists have figured out there's no way that an individual could withstand the type of gravitational pulling and pushing that each one needs.

Infinite Cylinder Theory

The astronomer Frank Tipler proposed a mechanism (sometimes called the Tipler Cylinder) that could take the matter with a mass of 10 times as large as the sun's mass and roll it into a huge and very dense cylindrical. It was the Anderson Institute, an organization for research on time travel described the Cylinder to be "a black hole that has passed through a spaghetti factory."

After spinning the black hole's spaghetti for with a few billion rotations per minute, a spacecraft nearby and following an exact spiral of the cylinder could be able to travel backward in time along a "closed, time-like curve," according to the Anderson Institute.

The main issue is that for this Tipler Cylinder to become a reality the cylinder will need to be infinity long or comprise something unknown to us. At the least for the near future, infinite interstellar pasta is not within our reach.

Time donuts

A theoretical physicist Amos Ori at the Technion-Israel Institute of Technology in Haifa, Israel, proposed an idea for the creation of a time machine from curved space-time elongated donut-shaped vacuum, enclosed by a sphere that is composed of regular matter.

"The machine is space-time itself," Ori explained to Live Science. "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."

There are a few limitations to the time machine of Ori. First, those who travel to the past would not be capable to travel to a time before the creation and development of the donut in time. Furthermore, and perhaps more important the design and creation of this machine will depend on our capability to alter the gravitational field at will -- an ability that is theoretically feasible but is not within our reach right now.

Time travel theories in tv shows and movies

Time travel has always featured prominently in science fiction. As early as the "Mahabharata," an ancient Sanskrit epic poem was written about 400 B.C., humans have imagined the possibility of altering times, Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science.

 Every time-travel-related story is a unique interpretation of space-time. It glosses over a few scientific difficulties and paradoxes to fulfil its plot goals. There are films that pay homage to science and physics, for example, such as "Interstellar," which was a 2014 movie directed by Christopher Nolan. 

In the film, Matthew McConaughey is able to spend a few hours on a spacecraft orbiting the supermassive black hole. However, due to time dilation, observers on Earth are able to experience these hours in the form of years.

Some choose a more whimsical approach, such as, for instance, the "Doctor Who" television series. The show features Doctor Who, who is the extraterrestrial "Time Lord" who travels in a spaceship that resembles the blue British security box. 

"People assume, as the Doctor explained in the show, "that time is a strict progression from cause to effect, but actually, from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff."

 A long-running series like "Star Trek" and the "Star Trek" movies and TV series, along with comic book universes like DC and Marvel Comics, revisit the idea of time travel. This is a non-complete (and extremely subjective) list of the most significant or noteworthy stories of fiction about time traveling: