No matter what science fiction writers write, modern science does not allow the possibility of travel to the past. But scientists are far from being so united about traveling to the future …
British science popularizer Brian Clegg recently published a book with the spectacular title How to build a time machine: the real science of time travel.
The book discusses ways of practical implementation of man's age-old dream of temporal wanderings. Clegg is a serious educator with an international reputation, so he only talks about projects that can be scientifically substantiated, albeit not 100% proven.
Isolation from time
One such possibility has been repeatedly described by science fiction writers. Take a space walk to interstellar distances, which will require at least two accelerations to near-light speeds, - willows can return to their home planet hundreds or thousands of years after departure, and you yourself will age slightly.
The fundamental possibility of such a temporal voyage is guaranteed by the formulas of the special theory of relativity. True, acceleration to relativistic speeds must also be provided with the help of super-energy-intensive fuel (best of all from antimatter), but these are details.
Promotional video:
However, on the special theory of relativity, the light did not converge like a wedge, after all, you can apply the general one. According to its equations, gravity slows down the speed of time (corrections for this effect are included in the software of satellite navigation systems GPS and GLONASS, and they numerically surpass similar corrections that special theory of relativity prescribes to be introduced in connection with the orbital motion of satellites).
The degree of this deceleration increases with the strength of the gravitational field. Here's another time machine for you: find an area of space with extremely strong gravitation, stay there for a while, and upon your return you will find yourself in the future.
Natural super heavyweights
Gravitational generators are in principle possible, but it is too early to talk about them. However, nature has created in space such natural clumps of gravity as neutron stars. One cubic centimeter of degenerate matter in the center of a neutron star pulls hundreds of millions of tons, while its diameter does not exceed 20-30 km.
Could it be possible to enter orbit near such a space monster and from there catapult into the future? It is not recommended to sit on its surface, it is a hundred times hotter there than in the atmosphere of the Sun.
However, this option is also very unsafe. Any object orbiting a neutron star will be deformed and torn apart by tidal forces. The same would, of course, happen if a ship with chrono-travelers was sent not to a neutron star, but to a black hole.
"Time impenetrable" shell
Clegg is confident there is a way out. Isaac Newton showed that the resultant gravitational force acting on any object inside a massive spherical isotropic shell is strictly zero. This conclusion is fully valid in the general theory of relativity.
Now imagine a neutron star with a cavity in the center. There will be no tidal forces there, and the flow of time in relation to the outside world will still be slowed down.
Thus, already now it is possible to formulate an engineering project for a future supercivilization. It is necessary to break a neutron star into many pieces and build from them a spherical shell around a ship with time travelers.
To protect them from tidal forces, the shell will have to be assembled without breaking isotropy, each time adding two blocks of equal mass from opposite sides, equally distant from the ship. The dismantling will have to be carried out in the same way, otherwise gravity will destroy the chrononauts in the future.
The task of supercivilization
How effective is such a time machine? If you use pure neutron matter as a building material, you can achieve a fivefold slowdown in time - in any case, Brian Clegg gives just such an estimate.
The result is rather modest, so you still have to think about whether the game is worth the candle. However, it can be assumed that supercivilization will have at its disposal technologies that will additionally compress neutron matter to even higher densities.
However, this must be done with caution, otherwise the entire structure will collapse into a black hole with unpleasant consequences for the ship and its crew. So the cost of such an experiment will immeasurably exceed its practical value - at least from our point of view. However, supercivilization may have completely different criteria.
How a neutron star works
After the nuclear fuel in the core of the star burns out, the inevitable gravitational collapse awaits it. If the pressure of a degenerate electron gas is unable to withstand gravity, the electrons are literally "pressed" into the protons of the nuclei, forming neutrons. The end product of this process is a neutron star made of superdense (up to 1015 g / cm3 in the core) matter 10–20 km in diameter.
The structure of a neutron star is quite complex - its atmosphere consists of ordinary nuclei, underneath the cores are suspended in a neutron superfluid, even below it, neutrons combine to form thread-like structures or sheets. The outer core consists of continuous neutron matter, while the inner core can contain even more exotic states of matter such as pion condensate, lambda hyperons, or quark-gluon plasma.