From HG Wells onwards, the possibility of time travel is a science fiction classic that fascinates us. One of the last works that explores this possibility, the film Interstellar, directed by Christopher Nolan and whose plot was advised by physicist (and now Nobel laureate) Kip Thorne, became a monumental success.
But if such an illusion ignites our dreams, now it is a rigorous scientific work that proposes that, in principle, this would be possible without violating the laws of physics. Signed by none other than the Argentine Juan Martín Maldacena, from the Institute for Advanced Study at Princeton, with Alexey Milekhin, from the Department of Physics at Princeton University, he postulates that, given certain conditions, it would not only be possible to travel unimaginable distances, but also into the future.
The theoretical exercise bears the suggestive title of Human-traversable wormholes, and refers to a type of cosmic object whose existence had already been considered feasible, although only in quantum physics and in microscopic dimensions. But … “With a catch – the authors clarify -: the time it takes to travel through the wormhole is greater than the time it takes to go from one mouth to the other outside”.
However, in this new work they show that, if there were a series of additional particles (in addition to those that our instruments “see”) and theoretically possible according to some models of matter, these cosmic objects could be formed under conditions such that a being human could go through them. Moreover, in doing so, for relativistic purposes, it would also travel to the distant future.
At first glance, wormholes look like two black holes connected to each other. However, they differ on a key fact: “They do not have a horizon, a border beyond which, if one passes, one cannot get out again,” Maldacena explains from Princeton. “In the case we are studying, one’s tube becomes connects with that of the other, and one can enter through one mouth and exit through the other, and can even exit the other side, jump back and exit through the original entrance. They are like tunnels that would connect two very distant places in our universe, thousands of light years away. “
A long-standing idea
“The idea of these cosmic curiosities dates back to 1935 – says Gastón Giribet, a professor at the UBA and a researcher in theoretical physics, black holes and string theory. Einstein and Rosen, who also worked together in Princeton, realized that there had been a solution of the equations of the theory of general relativity that allowed to build a kind of tunnel in space-time. Both ends of this object look like black holes, and they can be in different universes or even in the same universe, but they share This is something very surprising. Then it was studied a lot. Physicists like Stephen Morris or Kip Thorne considered an important distinction between two types of black holes: non-traversable and traversable. When this idea was first played with, it was speculated that one might now enter one of the second type and exit, for example, in 1947. But the question is: does general relativity allow it? Well, the answer that one hu If it was given a while ago it is ‘no’, because for this to happen, there would have to be exotic energy and matter, which violated some physical conditions; for example, the energy should not be negative, the speed of sound of a wave on them should not exceed the speed of light. Science is a game with rules. “
As Giribet explains, the possibility of microscopic wormholes has been studied for a long time. “Those yes can exist in the simplest theory that we have [el modelo standard de la materia], which describes all the currently known particles – emphasizes Maldacena-. If one assumes that there are no others, they could exist but very small; the distance between the two mouths would be the size of the one you are exploring the Large Hadron Collider (LHC, the gigantic instrument with which the Higgs boson was discovered) “.
The interest of both authors was to explore the possibility that, contrary to what classical physics assures, these objects could be given in larger sizes, even human-sized. “The reason why they are ‘forbidden’ in classical physics is more or less the following – Maldacena illustrates -. Einstein’s equations relate geometry to energy or the density of matter, and in order to have a geometry of this type In the tunnel the energy has to be negative. In classical physics, the energies are positive, but if one considers quantum mechanics, there is a ‘Casimir effect’ that allows there to be a little bit of negative energy. In this case , the object could exist thanks to that negative energy. It is a solution that involves quantum effects. “
For such a geometric distortion of space-time to occur, it would be necessary to assume that there is a type of matter that is theoretically possible, but that it has not yet been detected (massless particles, but that interact weakly with the known one, which would give rise to quantum effects that would make this solution possible). Scientists also failed to elucidate which processes in the universe could give rise to such curiosity.
According to the parameters that Maldacena and Milekhin studied in their work, each mouth of the wormholes would be about 10,000 km wide, comparable to the diameter of the Earth. “If you were to jump through that place, you would come out on the other side after approximately one second and it would be approximately 10,000 light years away,” Maldacena says. “But from the point of view of someone who stayed outside, the time that would have elapsed would be a a little older. That is, it would allow time travel, but only into the future. One could travel 10,000 years in a second. To go and return, it would take 20,000 years. “
Exclusive for intrepid travelers
Of course, it would be a somewhat lonely trip, since very large objects could not enter. “The wormhole is a bit fragile, in the sense that if you want to send too many things, it is destroyed and a black hole is formed; then, you can no longer get out,” he emphasizes. “It is a somewhat unstable configuration. the correct word is ‘metastable’: in principle, it can exist, but if you put too much matter inside it, you destroy it. “
As Francisco Villatoro explains in the magazine Naukas, “a safe trip would require a completely empty space-time at zero temperature, since any type of radiation that entered through both throats could accumulate inside it producing a positive energy that would compensate for the negative energy of Casimir; if that happened during the trip, it would be mortal for the traveler, since it would finish in the interior without possibility of leaving again “.
Although the idea is so disruptive, this solution looks a bit like the one described by the physicist and mathematician Karl Schwarzchild, the first to conceive of black holes and baffled Einstein with his conclusions. “If one studies it properly,” Maldacena says, “it actually describes what we would call two black holes that are connected inside. A kind of wormhole, nothing more than in that case the geometry does not allow one to go from a side to side. The connection opens and closes in such a way that one cannot send a signal from one side to the other, but it cannot be traversed. If one enters, the space collapses before one can leave and one has the vision unusual that it falls into the singularity. It was later seen that by means of certain quantum effects one can delay the collapse and cause it to open and close more slowly, allowing one to pass from one side to the other, if pulled into the right time. The solutions we are discussing now are similar versions, nothing more than this connection remains open for an arbitrarily long time, as long as you want. “
The scientist warns that it is not likely that we will soon find a wormhole that can transport us through our galaxy without the need for a ship. “Surely matter would enter and black holes would form,” says Maldacena and laughs. “I don’t see a very practical way to distinguish them. For me, the interesting thing is that these configurations can exist, that in principle the structure of the body can be changed in this way. space-time. They are a curious solution, but I don’t think they exist in real life. “
However, Einstein felt something similar about black holes almost a century ago and we even have an image of one of those cosmic beasts.
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