What is time? St. Augustine said: "I know what time is, until I think about it." According to the standard model of physics, time is the fourth dimension, in addition to the three spatial dimensions. So you can go through it. For many years, science fiction writers have relished the possibilities of time travel in a wide variety of details. With each century, we master more and more new technologies, discover new aspects of science. What do we have to learn about time travel before we begin to translate them into reality?
You probably noticed that we are constantlymoving in time. We move through it. At the basic level of the concept, time is the rate of change of the Universe, and regardless of whether we like it or not, we are subject to constant changes. As we age, planets move around the sun, things are destroyed.
We measure the passage of time in seconds, minutes,for hours and years, but this does not mean at all that time flows at a constant speed. Like water in a river, time goes differently in different places. In short, time is relative.
But what causes temporary fluctuations on the way fromcradle to the grave? It all comes down to the relationship between time and space. A person is able to perceive in three dimensions - length, width and depth. Time complements this party as the most important fourth dimension. Time does not exist without space; space does not exist outside of time. And this couple is connected into a space-time continuum. Any event occurring in the Universe must involve space and time.
In this article we will consider the most real andeveryday possibilities of traveling through time in our Universe, as well as less accessible, but no less possible ways through the fourth dimension.
- 1 Temporary Travels to the Future
- 2 Temporary travels in the past
- 3 Black holes and Kerr rings
- 4 Wormholes (wormholes)
- 5 Cosmic Strings
- 6 The Paradoxes of Time Travel
Temporary Travels to the Future
If you want to live a couple of years a little faster,than anyone else, you need to cope with space-time. Global positioning satellites do this every day, overtaking the natural course of time by three billionths of a second. In orbit, time flows faster because the satellites are far from the mass of the Earth. And on the surface, the mass of the planet carries time along with it and slows it down on a relatively small scale.
This effect is called gravitational slowdown.time. According to Einstein's general theory of relativity, gravity bends space-time, and astronomers use this corollary when they study light passing near massive objects.
But what does this have to do with time? Remember - any event occurring in the Universe involves both space and time. Gravity not only pulls together space, but also time.
Being in the flow of time, you hardly noticechange in its course. But quite massive objects - like the supermassive black hole Sagittarius alpha located in the center of our galaxy - will seriously distort the fabric of time. The mass of its singularity point is 4 million suns. Such a mass slows down time by half. Five years in the orbit of a black hole (without falling into it) is ten years on Earth.
Speed also plays an important role inthe speed of our time. The closer you get to the maximum speed - the speed of light - the slower the time. The clock in a fast-moving train will “be late” by one billionth of a second by the end of the journey. If the train reaches a speed of 99.999% light, in one year in a train car, you can travel two hundred twenty-three years into the future.
In fact, hypothetical travels to the future in the future are based on this idea, sorry for the tautology. But what about the past? Is it possible to turn back the clock?
Temporary travels to the past
We found that the journey to the future is taking placeall the time. Scientists have proven this experimentally, and this idea underlies Einstein's theory of relativity, which marks 100 years this year. It is quite possible to move into the future, the question remains only “how fast”? As for travel to the past, to answer this question you need to look into the night sky.
Milky Way galaxy approximately 100,000 widelight years, which means light from distant stars needs to be overcome thousands and thousands of years before it reaches Earth. Catch this light, and, in fact, you just look at the past. When astronomers measure cosmic microwave radiation, they look into the cosmos, which it was 10 billion years ago. But that's not all.
Einstein’s theory of relativity is nothingwhich would exclude the possibility of a journey into the past, but the very possible existence of a button that could bring you back yesterday violates the law of causality, or cause and effect. When something happens in the Universe, an event generates a new endless chain of events. The cause is always born before the investigation. Just imagine a world where the victim would die before the bullet hits her head. This is a violation of reality, but, despite this, many scientists do not exclude the possibility of travel to the past.
For example, it is believed that motion is faster than speed.light can send back to the past. If time slows down as an object approaches the speed of light, can overcoming this barrier turn the clock back? Of course, when approaching the speed of light, the relativistic mass of the object grows, that is, it approaches infinity. Accelerating an infinite mass seems impossible. Theoretically, warp speed, that is, deformation of speed as such, can deceive the universal law, but even this will require enormous energy costs.
But what if time travels into the future and the past depend not so much on our basic knowledge of space, but more on existing cosmic phenomena? Let's take a look at the black hole.
Black holes and Kerr rings
Spin around the black hole long enough, andgravitational time dilation will throw you into the future. But what if you fall right into the jaws of this space monster? We already wrote about what will happen when we dive into a black hole, but did not mention such an exotic variety of black holes as the Kerr ring. Or Kerr’s black hole.
In 1963, New Zealand mathematician Roy Kerrproposed the first realistic theory of a rotating black hole. The concept includes neutron stars - massive collapsing stars the size of St. Petersburg, for example, but with the mass of the Earth's sun. We included neutron holes in the list of the most mysterious objects in the Universe, calling them magnetars. Kerr suggested that if a dying star collapses into a rotating ring of neutron stars, their centrifugal force will prevent them from turning into a singularity. And since the black hole will not have a point of singularity, Kerr considered that it would be possible to get inside without fear of being torn apart by gravity in the center.
If Kerr's black holes exist, we couldgo through them and go out into the white hole. It's like the exhaust pipe of a black hole. Instead of sucking in everything that is possible, a white hole will, on the contrary, throw out everything that is possible. Perhaps even in another time or another universe.
Kerr's black holes remain theory, but if theyreally exist, they are a kind of portals offering a one-way journey into the future or past. And although an extremely developed civilization could develop in this way and move in time, no one knows when Kerr’s “wild” black hole will disappear.
Kerr's theoretical rings are notthe only way possible "shortened" paths to the past or future. In science fiction films, from Star Trek to Donnie Darko, the theoretical Einstein-Rosen bridge is often considered. These bridges are better known to you under the name of wormholes.
Einstein's general theory of relativity admitsthe existence of wormholes, since the theory of the great physicist is based on the curvature of space-time under the influence of mass. To understand this curvature, imagine a space-time fabric in the form of a white sheet and bend it in half. The area of the sheet will remain the same, it itself will not be deformed, but the distance between the two points of contact will obviously be smaller than when the sheet was lying on a flat surface.
In this simplified example, spaceIt is depicted in the form of a two-dimensional plane, and not a four-dimensional one, which it actually is (recall the fourth dimension - time). Hypothetical wormholes work similarly.
Fast forward to space. The concentration of mass in two different parts of the Universe could create a kind of tunnel in space-time. In theory, this tunnel would connect two different segments of the space-time continuum with each other. Of course, it is entirely possible that some physical or quantum properties prevent such wormholes from spawning on their own. Well, or they are born and immediately die, being unstable.
According to Stephen Hawking, wormholes canexist in quantum foam - the smallest medium in the universe. Tiny tunnels are constantly born and torn, linking individual places and time for short moments.
Wormholes may be too small andshort-term for moving a person, but suddenly one day we will be able to find, hold, stabilize and increase them? Provided, as Hawking notes, that you will be ready for feedback. If we want to artificially stabilize the space-time tunnel, radiation from our actions can destroy it, as the reverse sound path can damage the speaker.
We try to squeeze through black holes andwormholes, but maybe there is another way of time travel using a theoretical cosmic phenomenon? With these thoughts we turn to the physicist J. Richard Gott, who outlined the idea of a cosmic string in 1991. As the name implies, these are hypothetical objects that could have formed in the early stages of the development of the universe.
These strings pervade the entire universe, beingthinner than an atom and under strong pressure. Naturally, it follows from this that they give gravitational thrust to everything that passes near them, which means that objects attached to a cosmic string can travel in time with incredible speed. If you pull two cosmic strings closer to each other or place one of them next to a black hole, you can create what is called a closed time-like curve.
Using gravity produced by twowith cosmic strings (or a string and a black hole), a spacecraft could theoretically send itself into the past. For this it would be necessary to make a loop around cosmic strings.
By the way, quantum strings are now veryhotly debated. Gott said that to travel back in time, you need to loop around a string containing half the mass-energy of an entire galaxy. In other words, half the atoms in the galaxy would have to be used as fuel for your time machine. Well, and, as everyone knows, it is impossible to return in time earlier than the machine itself was created.
In addition, there are temporary paradoxes.
Time Travel Paradoxes
As we said, the idea of traveling to the pastslightly clouded by the second part of the law of causality. The reason follows the investigation, at least in our Universe, which means it can spoil even the most elaborate travel plans in time.
First, imagine: if you go back 200 years, you will appear long before you are born. Think about it for a second. For some time, the effect (you) will exist before the cause (your birth).
To better understand what we're dealing with,consider the famous grandfather paradox. You are a time-killer, your goal is your own grandfather. You penetrate the nearest wormhole and approach the lively 18-year-old version of your father’s father. You pick up the gun, but what happens when you pull the trigger?
Think about it. You have not been born yet. Even your father has not yet been born. If you kill your grandfather, he will not have a son. This son will never give birth to you, and you will not be able to go back in time, completing a bloody task. And your absence will not pull the trigger in any way, thereby denying the whole chain of events. We call this a loop of incompatible causes.
Alternatively, you can consider the ideasequential causal loop. It, although it makes you think, theoretically eliminates time paradoxes. According to physicist Paul Davis, such a loop looks like this: a professor of mathematics sets off for the future and steals the most complicated mathematical theorem. After that, she gives it to the most brilliant student. After that, a promising student grows and learns in order to one day become a person whose professor once stole a theorem.
In addition, there is another travel model intime, which includes a distortion of probability when approaching the possibility of a paradoxical event. What does this mean? Let's get back to your grandfather’s killer skin. This time travel model can kill your grandfather virtually. You can pull the trigger, but the gun will not work. The bird will tweet at the right time or something else will happen: quantum fluctuation will not allow a paradoxical situation to take place.
And finally, the most interesting. The future or the past you are heading into can simply exist in a parallel universe. Imagine this as a paradox of separation. You can destroy anything you want, but it will not affect your home world. You will kill your grandfather, but not disappear - perhaps another “you” in the parallel world will disappear, well, or the script will follow the paradox schemes we have already considered. However, it is possible that such a time travel will be one-time and you can never return home.
Totally confused? Welcome to the world of time travel.