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Time Travel: What Science Says About Them

In an instant, he was in his lab; The next day, Sam Magruder found himself naked, muddy water to his waist, in a wild swamp, and was running afraid of a dinosaur. This is the essence of the book that paleontologist and evolutionist George Gaylord Simpson called it Demonizing Sam McGruder A world travel through time from 2162 to the Cretaceous period, 80 million years in the past. Simpson, one of the 20th century’s smartest scientific minds, described in his book one of the greatest mysteries physicists faced: time travel.

We live constantly between the present and the past. If light travels at 300,000 kilometers per second, the screen where you read these words is actually from the past. That is why the physicist Albert Einstein (with the help of the German mathematician Hermann Minkowski – Einstein was terrible in mathematics) described time not as static but as a dimension: the space in which we live consists of three dimensions (width, length and depth); Time will be the fourth.

A traveler who travels our world (whether it’s to trash in the corridor, Mars, or the nearest galaxy) will have four coordinates to steer: three from space and one from time – which, traditionally, are moving forward. The first question that arises is: at what speed?

A boundary between the present and the past

According to what Einstein predicted in his theory of special relativity, the faster you advance in the three dimensions of space, the less you progress in the fourth (time). According to the German physicist, there is a limit to how much your acceleration can increase, which is the speed of light. Because, in theory, if you reach for it and pass it over, it will arrive the moment before the light leaves its starting point.

But the closer to the end point, the slower the time – from the point of view of the observer, not for the travelers; This is called “time dilation.”

If you were on a spacecraft thinking of throwing your litter into the orbit of the blue giant Icarus, nine billion light-years from Earth, and still arriving at home in time for the novel, when you return to Earth you will find the sun dead and a planet, like a piece of coal floating Via an unrecognizable solar system.

“The passage of time seems perfectly normal to me. My watch is running at the right speed, I am getting old usually, movies are running at the right speed. I’m not far from my future any more than usual. But I have traveled to my twin brother’s future,” explains physicist Jana Levine of Barnard College About what has come to be known as the “twin paradox”. A journey to the future in this way will be possible; However, the drawback is that only travelers can enjoy their discoveries.

Traveling to the future

Physics has thought of some solutions:

Cilindro De Luc

In 1974, astronomer Frank Tiebler imagined an incredibly dense rotating cylinder-shaped structure, about a hundred kilometers long and ten kilometers wide. Inside, there would be something ten times the mass of the Sun, spinning about billions of times a minute (Tepler suggested that this be done with a rotating black hole, or a neutron star, or even a pulsar; it would be a cylinder, so, it had to be made of strong material. Enough not to be crushed by gravity itself or torn apart by the centrifugal forces that it would be subjected to when rotating).

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The result is that the call is generated Time-locked curve, Or closed time curve – a curvature of space-time that allows you to travel into the future and return to where you left off.

The spacecraft, leaving Earth, will reach that cylinder (known as the Tipler Cylinder) and complete some orbits around it, stay in the area around the structure where space-time is more distorted and then return to Earth, where time passes faster than the ride (the good old dilation of time); How much will depend on how many times you turn the cylinder. The limitations of this project speak for themselves.

Wormholes

Traveling from point A to point B faster than light in a vacuum, according to Einstein, would make anyone possess infinite mass and length. However, assuming that space-time could be doubled, Einstein thought about the possibility of cutting a path using what became known as “wormholes”. The equations make these pathways physically possible; The problem is that in addition to just letting the particles pass through, they will collapse almost instantly.

In the so-called closed-type curve of time, the traveler will always return to the point where his journey began, regardless of how many turns he takes in spacetime.Source: New Scientist / John Papazian / Clone

Astronomer Carl Sagan was the first to think about it, and asked his friend and physicist Cape Thorne to consider whether holes in the fabric of space could be used for a future visit (he used this idea in his book Contact). Thorne, a 2017 Nobel Prize Winner in Physics for his work in the detection of gravitational waves, is one of the founders of the LIGO Gravitational Wave Observatory (LIGO), but is best known for being the film’s best scientific advisor. Interstellar.

black holes

When it comes to director Christopher Nolan’s groundbreaking movie, the movie uses the idea of ​​a spaceship that takes advantage of a black hole’s spinning motion to spin rapidly (the same principle as a Tipler cylinder).

Physicist Stephen Hawking, in an article for the newspaper daily Mail In 2010, he wrote that astronauts “will orbit around the horizon of events, witnessing only half of the time each person spends on Earth. The ship and its crew are said to be traveling in time. Imagine that they have circled the black hole for five years: ten years will pass in place.” Else. But it will be necessary to travel around the speed of light for this to work. “

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Cosmic strings

Astrophysicist Richard Gott has built his career on two of the aspects that most fascinate the average person: time travel and the end of human civilization. Regarding the first element, he argues that it would be possible for humans to use the distortion of space-time caused by cosmic strings (narrow energy tubes, remnants of the beginning of the universe, which extend throughout the universe, that is, they are infinite and intertwined like a cobweb).

These structures will have a mass of ten quadrillion tons per centimeter; According to Gott, two strings parallel to each other and moving one by one would distort enough spacetime (the so-called “gravitational well”) to allow time travel.

Time machines

Since 1895, when British writer HG Wells released the classic movie Time MachineThere is a consensus in science that a person will need a device that not only creates a closed type curve of time but does not harm its occupant.

First, for the machine to reach a passenger speed enough to reach the future, it will take time to work. Physicists thought that a strange form of matter, with a “negative energy density,” still a hypothesis in physics, was important.

In 1984, physicist Miguel Alcoupier launched the idea that it would be possible to contract spacetime in front of a ship, and then shortly thereafter, make it expand behind it, without contradicting the theory of relativity.

In fact, the ship wouldn’t leave, but if it were snugly anchored in a bubble, it would glide through the fabric of the universe. The problem: The motor has to be built with exotic material, to generate passive power – both of which are only in the theoretical field. However, there are already sounds in physics that guarantee that velocities close to the speed of light can be reached without this matter of strange properties.

Among the ideas that have emerged, one may need a structure in the form of a circular cake (where the void is) within a giant gravitational field. Within this group, giant gravitational fields will be able to fold the fabric of space into a closed fabric: To go back in time, the traveler has been running inside the cake, returning to the past with each roll. There is still no technology to precisely manipulate the fields of gravity needed to create a time-like curve.

Another idea, by researchers in applied physics, (an independent group of scientists, engineers, and inventors who advise companies and governments about science and technology for human and commercial applications), proposes a disk-shaped spacecraft (made of ordinary material, in the absence of the strange), from which That would slide driven inertia, after reaching a certain speed.

The designers of the Enterprise NCC-1701-D realized this almost correctly.The designers of the Enterprise NCC-1701-D realized this almost correctly.Source: Alpha memory / playback

Everything looks exciting, but the problem (there is always one) is that this prototype has to be made of materials with a density that is inaccessible to current technology.

Travel to the past

Everyone must have heard of the “grandfather paradox”: the traveler goes back in time and kills his grandfather or even his parents, making his birth impossible, and consequently killing his ancestors in the future.

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Some physicists argue that you will actually be born into a parallel universe – there will be a decision for every decision you make in life (turn left or right, wait for the next elevator or tap what opens in front of you, etc.). Others, that the past cannot be changed, no matter how hard you try.

According to the calculations of researchers German Tobar and Fabio Costa, of the University of Queensland (they have mathematically proven that travel into the past is possible), everything a traveler does (and includes in the work some possibilities that cause the so-called “butterfly effect” – small changes in the initial conditions of large systems, which Can lead to drastic changes in outcomes), events will be modified to avoid temporal paradox.

“If you go back in time to prevent the first person from contracting covid-19, you will become infected and become patient zero. Regardless of what you have done, events around you will be reset and the epidemic will occur, which gives“ me ”the oldest impulse to go back in time to time. Back and stop it.

Back to nowhere

Sam Magruder (the 22nd century chronologist mentioned at the beginning of this article) managed to go back in time, going back to the middle of the Cretaceous, 60 million years ago. To make this possible, George Gaylord Simpson created a process called “disqualification.” Magruder says that the present is, in fact, a “moving point in the temporal moving universe”. He imagines time as a dashed line, as the present “cuts across” infinitesimal periods.

His experiment consists of using the decelerator to extend these periods, starting with “stretching a millionth of a second until you realize it’s five hours.” When the slowdown of time increases to its maximum, it is played in the past, 800 million years since the first human appearance on Earth.

Sam Magruder found he couldn't return to his era because he wasn't there yet.Sam Magruder found he couldn’t return to his era because he wasn’t there yet.Source: Pixabay / Stephan Keeler

Naked, accustomed to the technologies that ensured his survival, Magruder then realized that the journey to the past is a one-way journey: the future has not yet happened, and therefore, there is nowhere to go. We return to the idea of ​​infinite parallel universes,

Although the dilation of time may be (at least hypothetically) the way for humans to visit the future, it appears that we will not be able to return to the past; According to Stephen Hawking who recorded it in his book Black Holes, Small Universes, and Other Essays, “Our best evidence that time travel is [ao passado] This is not possible and it will not be because we have not been invaded by hordes of tourists from the future. “