How to make a trip back in time physically possible?

The Idea that we could go back in time to change the past, became one of the favorite techniques in movies, literature and television series. "Harry Potter", "Back to the future", "Groundhog Day" and many other movies promised us the opportunity to make a second choice in his past. For most people this will be an opportunity to remain fantastic, because all the laws of physics indicate that forward movement in time — it is inevitable and necessary. In philosophy arose the paradox, emphasizing the absurdity of such a possibility: if travelling back in time was possible, you could go back in time and kill your grandfather before your parents even met, thereby eliminating the possibility of its own existence. For a long time it was believed that there is no way back. But thanks to the very curious properties of space and time in General theory of relativity, travel back in time may be possible, says physicist Ethan Siegel.

Illustration of the early Universe composed of quantum foam, in which quantum fluctuations occur on the smallest scales. Positive and negative energy fluctuations can create a tiny quantum wormholes

Let's Start with the physical ideas of the wormhole. In the known Universe to the smallest scales on the fabric of space-time manifest as tiny quantum fluctuations. This includes energy fluctuations in positive and negative directions, often occurring very close to each other. Strong, dense, positive fluctuation of energy can create in a certain way curved space, and a strong, dense, negative fluctuation of energy will curve space the opposite way. If you connect two of these in the region of curvature, you get, briefly, a quantum wormhole. If the wormhole you live long enough, you can try to push through it a particle, so that it will instantly disappear in one place of spacetime and appear in another.

a Precise mathematical graph of Lorentzian wormholes. If one end of a wormhole constructed from the positive mass/energy and the other of negative mass/energy, the wormhole becomes passable

To scale all of this, for example, and allowed to pass through the wormhole, the person will need to do something. Although all the known particles in our Universe have positive energy and either positive or zero mass, the possible existence of particles with negative mass and energy in the framework of General relativity. Of course, we have not yet found, but according to theoretical physicists, there is nothing that would preclude the possibility of their existence.

If a substance with negative mass and energy exist, the creation of a supermassive black hole and its counterpart with negative mass and energy, and then subsequent connecting will create a walkable wormhole. No matter how far away you breed two of these combined object if they have enough mass and energy — both positive and negative — instantaneous communication will continue. All great for instantaneous travel through space. But what about time? And here come into play the laws of the special theory of relativity.

According to the law of the special theory of relativity, stationary and moving parts age at different rates

If you are traveling close to the speed of light, you experience a phenomenon known as time dilation. Your movement in space and movement in time are bound by the speed of light: the faster you move through space, the slower through time. Imagine that you have a destination 40 light years away, and you can move with incredible speed: more than 99.9% of the speed of light. If you sit in the ship, go to the star at almost the speed of light, then stop, turn around and return to Earth, you find something strange.

Because time dilation and shortening of length, you can reach your destination in just a year, and then return a year later. But the world will be 82 years old. All the people you knew, much older. So from the point of view of physics of possible time travel: you travel to the future and time travel will depend on your movement in space.

is it Possible to travel in time? Having a large enough wormhole, for example, created two supermassive black holes (positive and negative masses and energies), we could try

If you build a wormhole like the one that we described above, the story will change. Imagine that one end of the wormhole is real, for example, somewhere near the Ground, and the other will travel at speeds close to light. After a year rapid movement of one end of the wormhole, you pass through it. What happens next?

Well, this year will be different for all, especially if all will move in time and space in different ways. If we are talking about the same speeds as before, moving end of the wormhole will age for 40 years, but "calm" the end is just for 1 year. Stand in the relativistic end of the wormhole and get to Earth only a year after the creation of the wormhole, and you will age 40 years.

If 40 years ago someone created a pair of entangled wormholes and sent them on a trip like that, it would be possible to step into one of these today, in 2017, and go to 1978. The only problem is that you too could be in this place in 1978; you had to be with one of the ends of the wormhole, or traveling through space to catch up with her.

Warp-travel to the NASA submission. If you create a wormhole between two points of space to one hole moving relativistically relative to the other, passing through it the observers was aging would be different

And by the way, this form of time travel also prohibits the grandfather paradox! Even if the wormhole was created before you were conceived your parents, you in no way might appear on the other end of the wormhole early enough to go back in time and find your grandfather before this crucial moment. At best you could take their newborns father and mother on the ship to catch up to the other end of the wormhole to allow them to grow up, to age, to conceive you and then go on their own on the wormhole back. Then you meet grandpa in his Prime, but technically, it would happen at a time when your parents were born

The universe gives vent to the most unusual things. Especially if the negative mass and energy really exists in the Universe and they can be controlled. But the journey back in time — this is something completely out of the ordinary. Because of the anomalies as special and General relativity time travel to the past may be possible not only in fiction.