Journey to find time machine (part 1)

For decades since the famous novel "Machine Time" was born in 1895, this problem is still only fictional. But in recent years, time travel has become something like a " craft " in the world of theoretical physicists.

For theorists, this topic still has a lot of recreational meanings. But this time they were " entertained " seriously. Through the causal relationship is a fundamental problem to build a unified theory of physics. If traveling unlimitedly in time is possible, even just in principle, such a unified theory can be seriously affected.

There are two ways to swim

So far, our best understanding of time is based on Einstein's relativistic theories. Special theory predicts an effect called time dilation, which occurs when two observers move relative to each other. This effect is only evident to us when movements are close to the speed of light. Even at jet speeds, time dilation is only a few billionths of a second. However, atomic clocks are accurate enough to detect that expansion and confirm that time actually relaxes due to motion. Thus, traveling into the future is a proven reality, even though the effect that occurs in everyday life is not great.

To see more clearly about this effect, we must look beyond the everyday experience. There are elementary particles in cosmic rays moving very fast but life time is very small. In the " world " (reference system) of these particles, they are only a few minutes before " dying " to cross the galaxy and reach the earth. We stand on the earth reference system and see that they seem to take thousands of years to do so. Without the expansion of time, these cosmic rays would not be present on the earth.

Einstein and Kurt Godel . (Photo: plus.maths.org)

Speeding is a way to " swim " faster than the flow of time. Attractive schools are another way. In general theory of relativity, Einstein predicted that the gravitational field would slow down time, meaning that the rooftop clock would run faster in the ground floor, because the higher the Earth's gravitational field, the smaller. go. Similarly, the clock in space runs faster than an underground clock. This time, the effect is also very small but can still be measured by atomic clocks. In fact, time warping by gravity has been very well applied to the global positioning system. Without this application, some sailors, taxi drivers and cruise missiles would probably be in trouble.

At neutron star surface, gravitational field is so strong, time is about 30% slower than the time on earth. If we stand on such a star and observe, the events on earth will be like a fast-forward movie. We will see that children will only have 7 days off instead of 10 days, and there will be about 2 days of Tet instead of 3. Even if there are people, Neutron will be surprised to ask why on earth, banh chung Damn and peach blossom so quickly?

A black hole can distort time to its fullest, at its " surface ", time will stand against the earth. If you think of the time in each place as a river, here is not " all the rivers flow ". If an astronaut can march to the edge of that " no-flow river ", imagine that he is not doing anything (the gravitational pull of a black hole can tear everything apart) when returning to earth , he will go very far into the future.

Swimming upstream?

In 1948, Kurt Godel of Princeton Institute of Advanced Studies came up with a solution of Einstein's gravitational equation that describes a rotating universe. In this universe, an astronaut can travel through space to return to the past. This is due to the mechanism of the field's impact on light. The rotation of the universe will follow light (and thus the causal relationship of things) involved in its movement. This allows a physical entity to follow a closed loop in space, and it is also a closed loop in time, where there is no need for any process to exceed the speed of light in the intergalactic medium. . Godel's experiment was considered only a mathematical miracle, because observations never showed any sign of a rotating universe. However, that experience nonetheless illustrates that going back in time is not prohibited in the theory of relativity. In fact, Einstein also confessed that he was very concerned about his theory allowing travel into the past in certain situations.

There are other studies that also show the possibility of returning to the past. For example, in 1974, Frank J. Tipler of Tulane University calculated that a cylinder of infinite and large mass density is infinite, when rotating around its axis at a speed close to light, it would be possible. drag light into a closed loop and bring astronauts back to their past. In 1991, J. Richard Gott of Princeton University surmised that cosmic strings - structures that cosmologists believed to be created in the early stages of the Big Bang - could bring about Similar results. But in the mid-1980s, the most realistic context for a major time machine was based on the concept of wormholes.

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