How does time exist on earth

theory of relativity: The crooked time

Once you have the feeling that it doesn't go away at all, then again it slips between your fingers and you have no idea where it has got to so quickly - although an hour always has 60 minutes and a day 24 hours. But the Field Marshal Princess Werdenberg already knew about this different sense of time, who, based on a text by Hugo von Hofmannsthal in Act 1 of the opera "Der Rosenkavalier" by Richard Strauss, ponders so aptly: "[] Time is a strange thing. If you live like that, it is absolutely nothing. But then all of a sudden you feel nothing but it: It is around us, it is also inside us. It trickles in our faces, in the mirror it trickles in my temples it flows. And between you and me it flows again. Silently, like an hourglass. O Quin-quin! Sometimes I hear it flowing inexorably. Sometimes I get up in the middle of the night and let the clocks stop. "

Psychology is concerned with what factors it depends on that we perceive time differently, that we have developed a sense of time that does not have to match the information on the clock. From the perspective of philosophy, time is the progression of the present from the past into the future, one asks about the essence of time and so very quickly comes to questions of worldview - and to our self: "The present is the time in which we and the most important thing of all is what we do with our present selves, for what was is carried into the future by the present selves, and what we do now is crucial for tomorrow. If tomorrow is now becomes today Be yesterday. If we don't change the pattern of our emotional behavior, tomorrow will be like yesterday in almost everything, with the exception of the date. The past is history, the future is only a conjecture; the present and the now make both what they are. " This knowledge comes from Moshe Feldenkrais, scientist, martial artist and founder of the Feldenkrais method, a special movement theory; You can read it in the foreword of his book "The strong self. Instructions for Spontaneität" published by Suhrkamp-Verlag in 1992.

A new concept of time
In physics, time was not held up with ideological discussions, since in this scientific discipline it is a fundamental physical quantity that describes the sequence of events and thus has a clear, irreversible direction: from the past that we are researching can, about the present that we are currently experiencing, into the future that is open. It is a central, measurable parameter, it has always run at the same speed since the Big Bang and is therefore a universal benchmark. At least that was what you thought until someone began to think that there was no time for the Big Bang (or before). It was also discovered that the speed of light depends neither on the speed of the light source nor on the state of motion of the receiver used to measure it, which was the basis for Albert Einstein's theory of relativity (the special in 1905, the general in 1915). It says that there is no such thing as absolute time, but that every observer has his own measure of time and that time is just an equal part of our physical model for describing the universe. He linked time with the dimension of space to form "space-time", which spans our universe in four equal dimensions, namely three spatial directions and time. Einstein illustrated this equality with an example: If two people want to meet, it is necessary to identify both a place and a time. If you only have one of the two pieces of information, nothing will come of the rendezvous - you actually need both to really be in the same place at the same time; proof of how suitable this part of the theory of relativity, namely the dependence on space and time, is for everyday use.

However, Einstein made another revolutionary postulate: time does not pass equally quickly in all places. The faster a system, for example a flying satellite, moves, the slower the time runs there. This effect can even be measured in an airplane: When you come back to a stationary watch that is measuring at the same time after a sightseeing flight, you notice that the stationary watch is already showing a slightly later time, i.e. the time in the airplane passes more slowly. The difference is marginal, but today's precision measurements, for example for the satellite navigation system GPS, would not be possible without taking the theory of relativity into account.

The dream of time travel
However, time has a special feature compared to space: You can move forwards and backwards in a space, but you cannot move backwards in time - but you can move forward. Which raises the question of the possibility of time travel: In principle, we fulfill the dream of such a dream by reading historical novels or looking at pictures from the 16th or 18th century and seeing how landscapes, places or people looked (or at least at the time) as the artist saw the time when he did not have to "beautify" the portrait of a ruler). Or we see how a director imagines the near or distant future when we watch a science fiction film. But actually travel to another century by means of a machine? A utopia first described by the English historian, sociologist and author Herbert George Wells (better known as H. G. Wells) in his novel "The Time Machine" in 1895. In it, the protagonist not only travels in two steps far into the future and then back again to the present, he also describes the structure and function of the time machine extremely plausibly. The fact that the novel was actually a violent accusation against the ruling class society in Wells' time was and is gladly swept under the table, especially when it comes to the films.

Marty McFly (Michael J. Fox) and Dr. Emmett "Doc" Brown (Christopher Lloyd) in the film trilogy "Back to the Future" by director Robert Zemeckis did not mess around: They simply traveled effectively and entertainingly using a time machine disguised as a car into the future and into the past, without physics or politics To be considerate. And also Dr. Who is happily cruising through world history - with the help of a telephone booth.

The physicist Stephen Hawking once said that time travel is a politically incorrect topic because you risk public outcry if you waste research money on something absolutely ridiculous. But science does not abandon this topic and only use other terms for it, such as "closed time-like curve". Such a curve returns with a time delay to its four-dimensional beginning, based of course on Einstein's theory of relativity and his already mentioned knowledge that time passes at different speeds, depending on the speed at which a person moves through space. The closer the speed goes towards the speed of light, the slower time goes by for an astronaut on board a spaceship, viewed from Earth. "If the star now travels to a star 500 light-years away and back to Earth at at least 99.9 percent of the speed of light, then the astronaut is ten years older, whereas the Earth is 1000 years", describes the US physicist in the magazine "Geo." "a journey through time into the future. But since, according to the theory of relativity, time runs like a one-way street, the astronaut could not return at all.

Journey of no return
A journey into the past also poses problems: According to Einstein, space-time is curved by gravity, even down to a singularity, that is a place where gravity is so strong that the curvature of space-time becomes virtually infinite and space and time to cease to exist - the physicist John Wheeler named this extremely dense accumulation of matter in 1967 the "black hole". Einstein and his student Nathan Rosen wanted to prove that singularities cannot exist, but they did not succeed. To do this, they found out that two of these space-time funnels can virtually connect in a purely mathematical manner and thus form a bridge, the so-called Einstein-Rosen bridge - the "wormhole" was born. The theoretical structure was given this name in 1957 by John Archibald Wheeler, who compared it to a worm that eats its way through an apple and thus connects two sides of the same space (the surface) through a tunnel. Incidentally, the spaceship "Enterprise" from the "Star Trek" universe uses such a wormhole to travel back in time
But wormholes are not stable because their spherical entrance would be three-dimensional, while the tunnel would be four-dimensional. In order to stabilize and enlarge a wormhole so that a person or even a spaceship can fit through, however, a huge amount of energy is required, which would have to be crammed into the smallest space - and today's technology is not able to do this. But in purely mathematical terms, it could make it possible to travel back in time if a time loop leads through the wormhole. However, no wormhole has yet been found in the cosmos.

But apart from that, there is another problem with time travel to the past: causality, a fundamental principle of physics, could be violated. A good example of this can be found in "Back to the Future": Marty's journey into the past takes him to the time before he was born - and his mother promptly falls in love with him and not his future father. But what would happen if his mother didn't marry his father and he wasn't born as a result? These "what if" paradoxes are denied by some physicists, however, they believe that no matter what a time traveler does, he can only confirm the course of events - which in turn calls into question the free will of human beings. However, an interpretation of quantum physics comes in that assumes the existence of an infinite number of parallel universes in which events develop differently. In this way both the original course of things and the course changed by the intervention in the past would take place. The time traveler would then not return to the original version of the present, but to a parallel world that would be almost identical to the one he had known up to now. This many-worlds theory is originally based on the American physicist Hugh Everett III. back and has many followers to this day.

The Austrian mathematician Kurt Gödel also dealt with the problems of time travel. In 1949, as part of a new solution to Einstein's equations, he discovered an equally new space-time permitted under the theory of relativity - a universe that contains closed timelines. And his universe rotates relatively quickly. It would be mathematically possible that an astronaut could set off into space in a spaceship and return to Earth before he has even left it. In addition, Godel's universe does not expand - his assumptions therefore do not correspond to the world in which we live, but in theory they allow time travel into the past. With this, of course, there is a possibility that someone will meet and interact with the younger version of himself. In the 1990s, physicists solved the fact that this interaction has no influence on the present and the events taking place in it by assuming a coherent universe and symbolizing it with the grandfather paradox: It assumes that one cannot therefore travel into the past , because in this case you could kill your own grandfather and thus prevent your own existence. But in a coherent universe, every act during a time travel into the past has long been part of the grandfather's life story and therefore it is not possible to kill him. Put simply, the question is: How can you change the past when it has already happened?

In any case, the current state of science seems to be that almost anything is possible in theory, but precious little in practice. But head acrobatics is also appealing and thanks to literature, film and your own imagination, time travel in your head fortunately has no limits