Time Travel — Commuting to the Past and Future

H.G. Wells’ groundbreaking book, The Time Machine, was published in 1895. Since then, physicists and theorists have been writing serious papers about time travel for nearly a century. However, the idea of time travel has posed many legal and moral dilemmas. While humans have yet to enter a time machine and travel back in time, we do know that clocks on planes and satellites travel at a different rate than clocks on Earth. When we think of “time travel,” however, we normally think of traveling at a rate faster than 1 second per second. That kind of time travel sounds like it belongs in a movie or a science fiction novel. Is it possible in real life? Research says yes.

Is There Proof that Time Travel is Possible?

Albert Einstein first came up with an idea about how time behaves over a century ago. He called it the theory of relativity. This theory states that time and space are connected to each other. However, Einstein has stated that our universe has a speed limit. No entity can travel faster than the speed of light. So how does this relate to time travel? According to Einstein’s theory, the faster we travel, the slower we undergo time. A few experiments have been performed to test this theory.

An Experiment with Two Clocks

One experiment made use of two clocks set to the exact same time. One clock remained on Earth, while the other was put in an airplane that was travelling in the same direction as the Earth’s rotation. Once the airplane made its trip around the world, scientists made a comparison of the two clocks. The clock that was on the fast-moving airplane had a slight delay from the clock on the ground. This experiment revealed that the clock on the flight showed a time that was slightly slower in time than 1 second per second.

Time Travel in Everyday Life

Although it is currently not possible to travel back and forth in time, the math of time travel has an effect on the stuff we use every day. GPS satellites assist us in determining how to get to new locations. NASA scientists also use a high-precision variant of GPS to map the location of satellites in space. To get around town, GPS relies on time-travel calculations. At a speed of around 14,000 kilometers per hour, GPS satellites orbit the Earth very rapidly. GPS satellite clocks are slowed by a fraction of a second as a result of this (similar to the airplane example above).

Gravity Affects Time

The satellites orbit Earth at a height of around 20,200 kilometers above the surface. This potentially increases the speed of GPS satellite clocks by a fraction of a second. Here’s why it happens: According to Einstein’s theory, gravity bends space and time, slowing the passing of time. The gravity of the Earth is much weaker higher up in the atmosphere, where the satellites orbit. The clocks on GPS satellites operate faster than clocks on the ground as a result of this. These combined effects make the clocks on GPS satellites experience time at a slightly faster than 1 second per second pace. Math is generally used by scientists to correct these time gaps.

Inspiration from Fiction

In the movie Interstellar, the protagonist and his crew land on a planet with an intense gravitational field created by a nearby black hole, which causes time dilation. Time slows dramatically for the crew on the planet due to the black hole’s strong gravitational effect, making one hour on the surface equivalent to seven years on Earth. While Interstellar is a work of fiction, we can see science rapidly catching up. So, why hasn’t mankind been able to make such significant strides forward in time? This question has a simple answer: velocity.

Gravitational Acceleration

To send a traveller years into the future, mankind will have to either use the extreme gravitational acceleration induced by black holes or send the traveller rocketing into space on par with the speed of light (about 1 billion km/h). With our present technologies, humans can only leap a few microseconds into the future. The trio of astronauts who flew Nasa’s Apollo 10 mission holds the world record for the highest speed. The astronauts’ capsule reached a top speed of 39,897km/h on their way back from a lap around the Moon in 1969.

Can Dark Matter Make Time Travel Possible?

It is believed that dark matter is necessary for the construction of Time Machines. Theoretically, it is not possible to obtain so much dark matter. However, research reveals that time machines can be created without dark matter. A doughnut-shaped hole is encased inside a sphere of normal matter at the start of the journey. Space-time could be bent on itself within this doughnut-shaped vacuum, forming a closed time-like curve, using centered gravitational fields. To travel back in time, a traveler will race around inside the doughnut, each lap taking them further back in time. However, there are a few problems with this theory. To create such a closed time-like curve, the gravitational fields needed would have to be extremely powerful, and controlling them would require extreme precision.

Time is an Illusion

Just because we perceive time as flowing in one way, it doesn’t mean that we can precisely define the past and future. When it comes to time travel, many argue that changing the past may lead to life-threatening repercussions back in the present. However, researchers prove paradox-free time travel is possible mathematically, demonstrating that the universe can self-correct to prevent contradictions. If this is true, we will never be able to change events in the past to build a new future, even if we could travel back in time. If this is the case, then there may be no need for a time machine in the first place.

The Paradoxes of Time Travel

The Grandfather Paradox

Aside from the physics issues, time travel can present some unusual situations. The grandfather paradox, in which a time traveler eliminates his parents or grandparents, is a classic example. Some scientists believe that if this were to happen, you would not be born in one alternate universe but in another. Others argue that the photons that makeup light prefer self-consistency in timelines will sabotage your plans.

The Twin Paradox

Gravity is seen in a different light thanks to Einstein’s General Relativity. Gravity, rather than being thought of as a force, is defined by general relativity as bending or warping of space-time. However, special relativity is sufficient to get us started in terms of time travel. Special relativity does not allow us to travel back in time, but it does allow us to travel forward at a pace that we can regulate. Due to special relativity, two identical twins may have different ages, resulting in a “twin paradox.” Assume you take your spacecraft to the Alpha Centauri star system at a very high speed (near the speed of light), while your twin stays on Earth. When you arrive home, you’ll see that you are younger than your twin.

Present Time Travel Experiments

Turning Back Time

Russian physicists conducted a time-reversal experiment and were able to turn time back by a fraction of a second. While the complex conjugation needed for time reversal is exponentially unlikely in nature, the experiment demonstrated that one can design a quantum algorithm that requires complex conjugation and thus reverses a given quantum state. They were able to show backward time dynamics for an individual particle and a fraction of a second using this algorithm on an IBM quantum computer.

Simulating Time Travel

On a quantum computer, researchers can easily simulate opposite-in-time evolution, or simulate running a process back into the past. They conducted an experiment to actually see what happens with a complex quantum world if an entity travels back in time, creates small damage, and comes back. It was found that not much is affected in the present. This means there would likely be no butterfly effect if we were to alter the events of the past.

Understanding How the Universe Works

The Muon g-2 experiment’s first finding suggests the presence of unknown particles or forces. These results may have far-reaching consequences for future particle physics research, as well as a better understanding of how the universe functions. Discoveries about how the world functions at the atomic level often lead to significant advancements in technology, including the advancements needed to make time travel a possibility.

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