In the novel by Kurt Vonnegut’s “Slaughterhouse number 5 or The Children’s Crusade,” the main character named Billy Pilgrim was abducted by aliens. Aliens from the planet Tralfamadore reveal to Billy the secret of time travel and allow him to feel like one of them, giving him the opportunity to move to different time periods of his own life. It is also noteworthy that for the Tralfamadors there is no death, since death is only a period in time that you can look at at any time.
A similar idea can be seen in the 2016 film “Arrival”. But if we distract from science fiction works and think about the Universe surrounding us , then how do we know if it is possible to actually travel in time?
In 1915, Albert Einstein was able to more or less explain our world. So far, the general theory of relativity (GR) remains the best description of gravity in modern physics. The predictions of the theory were confirmed by numerous observations and experiments carried out both in the last century and in the present.
GR predicted the discovery of supermassive black holes and gravitational waves. Thus, we say again and again: “Einstein was right.” However, today researchers are in search of a new theory that can explain the reasons why the universe expands with acceleration. But according to GTR, our Universe should not expand faster and faster. Scientists believe that the mysterious dark energy – the invisible substance and the driving force of the Universe – is responsible for accelerating the expansion of the Universe.
But there are other inconsistencies: recently, researchers discovered a black hole in our galaxy, which, according to GTR and our knowledge of the evolution of stars, should not exist. It turns out that we need a new fundamental theory of everything, which will be consistent with both general relativity and quantum theory.
The genius of Albert Einstein
Isaac Newton reflected on the fundamental forces of the universe long before the birth of Albert Einstein. Shakespeare describes his thoughts about our place in the Universe in the best possible way:
“The whole world is a theater, and the people in it are actors.”
Newton believed that all objects in the Universe are actors on the stage: the Sun, comets, a dog, and even an apple. And the scene itself was space and time, two things that are absolute, and nothing can affect them. The clock moves at a constant speed, regardless of where they are, Newton believed.
These thoughts laid the foundation for classical mechanics, which could explain almost everything. However, the word “almost” is unacceptable if we try to explain how the whole Universe works , and not just its part.
After about two hundred years, Albert Einstein suggested that space and time can be combined with all objects in the universe. What Newton considered absolute, Einstein made part of the play. According to GTR, three dimensions of space and one dimension of time are combined into one four-dimensional space-time. And space is not inviolable: there are massive objects that can affect the shape of the space itself, as well as the passage of time. But that’s not all: Einstein argued that time is individual. Theoretically, this allows for the possibility of special “paths” in space-time that can deviate into the past – these are kind of closed curves along which you can go back to an earlier point in time.
One of the most talented philosophers and mathematicians of the 20th century, Kurt Gödel believed that a particle can get to a point in its own past through closed time-like curves . However, for Gödel’s assumption to work, our Universe must rotate, and its size must remain unchanged. But you and I are well aware that the Universe is expanding with acceleration. After Godel, other scientists created theories that were consistent with Einstein’s concept. But even if closed time-like curves exist in order to pass them, it is necessary to achieve a speed exceeding 220 thousand kilometers per second. However, the inconsistency of GR with the fact of the accelerating expansion of the Universe and the existence of closed time-like curves is only the tip of the iceberg when it comes to time travel, because we are faced with a much more serious problem:
Einstein’s theory in no way correlates with quantum physics. And this is the biggest problem in modern physics. We really need a different theory to describe the universe. A theory that will take into account the quantum nature of matter.
One of the attempts to explain the Universe by placing all the points over, is string theory . Sheldon Cooper from The Big Bang Theory, as you know, worked precisely on it. However, string theory is also not without problems: for it to be correct, the existence of six additional dimensions of space is necessary.
Along with string theory, there is a theory of loop quantum gravity , a theory of causal sets, and many others. Nevertheless, despite the fact that, none of them today is not able to fully explain everything that happens in the universe, scientists are in no hurry to write them off. At least when thinking about time travel.
So, the study , which scientists from Oxford University who worked on it, suggests that the creation of a time machine is actually possible. The paper considers the logical, metaphysical and physical possibility of time travel, based on the existence of closed time-like curves.
Scientists believe that these curves can be detected with the help of new technologies and argue that none of the proposed paradoxes excludes time travel. Also in the work, researchers write that time travel is possible in accordance with the theory of quantum gravity, the theory of strings and the theory of loop quantum gravity. Be that as it may, there are more questions today than answers.
Is it possible to stop time?
Albert Einstein demonstrated that time is relative: it moves slower if an object moves fast. Events do not occur in the prescribed manner. There is no single universal “now,” in the sense in which Newtonian physics would describe it . It is true that many events in the universe can be streamlined, but time is not always clearly divided into past, present, and future.
Some physical equations work in any direction. One of the aspects of time perception that many of us share is how we think about our past: we present it as a gigantic video library, an archive in which you can familiarize yourself with the recordings of our own life events. Some theoretical physicists, for example Carlo Rovelli, go in their thoughts even further, believing that time is not linear or does not exist at all. However, although some physicists suggest that time does not exist, our perception of time exists. That is why the evidence of physics is at odds with how we perceive the course of life. Our understanding of such meanings as “future” or “past” does not necessarily apply to everything in the Universe, but reflects the reality of our life here on Earth. However, as in the Newtonian idea of absolute time, faith over time can lead us astray.
Some researchers believe that the passage of time can be stopped, although this may not be practical. To understand how to stop time, one must again turn to the theory of relativity by Albert Einstein: the speed of light is 299 792 458 meters per second and is constant in the entire Universe. This speed remains unchanged even if the observer moves relative to it. However, according to data obtained by researchers from the University of South Maine, our perception of light can be changed. Theoretically, this means that our perception of time can also be changed using a phenomenon known as “time dilation”. Time dilation is the time difference when measured at two hours. Imagine that one of these clocks is mounted on a spaceship that moves at or near the speed of light, while the other clocks remain on Earth.
When the spacecraft reaches the speed of light, time at two o’clock starts to go differently. Since the speed of light is constant, it may seem that the time on the ship will move much slower.
The results of the study showed that the greater the speed of the ship, the greater the effect of time dilation. Only when the ship’s speed approaches the speed of light, the effect of time dilation becomes significant. Thus, if the spacecraft reached the speed of light, then time on board would simply stop.
You can try to imagine that the ship will continue to move at the speed of light until 2214. In that case, two hundred years would have passed for us, and nothing would have changed on the ship. This is extremely strange, but theoretically correct. However, do not forget that from the point of view of the fundamental laws of physics, it is impossible to achieve the speed of light.
Professor Stephen Hawking believed that Einstein’s research in the field of gravity, space and time, since 1915, may have solved the problem of time travel . The answer, as you probably already understood, lies in wormholes.
A wormhole is a passage through the fabric of spacetime that connects two remote points of space. Thus, a wormhole can connect not only two different places in the Universe, but also two different Universes. Recall that the British theoretical physicist did not exclude the possibility that black holes and wormholes could be a portal to other universes. Moreover, one of Hawking’s latest works was devoted to parallel Universes. If representatives’ developed civilizations exist and possess the technologies necessary for space travel, it is possible that they can travel from one part of the galaxy to another and in a week or two they can return home before they set off. That is a paradox.
And yet, when it comes to time travel, do not forget about the most important thing – every night, when we look at the starry sky, we see the past. The light of distant stars reaches our planet millions of years later, and the objects that emit it have long been extinguished. Despite the fact that you and I are not the Tralfamadorians and our perception of time is very limited, we still have devices with which we can look back in time and see the signs of the Big Bang. It turns out that we are all time travelers.