Physicists have just developed a mathematical model of a "time machine". To build it, it's more complicated. "People think that the temporal journey is science fiction, we think it's impossible because we do not, but mathematically it's possible." A sentence signed by Ben Tippet, a mathematician and physicist at the Canadian University of British Columbia, who has just completed a study on "a time machine", published in Classical and Quantum Gravity.

Name Zeus !, will we be able to travel in time as in Back to the future? Not exactly. The time machine that Ben Tippet imagined with David Tsang, an astrophysicist from the University of Maryland, is actually a kind of "box that moves back and forth through space and time" , in a circular motion. Their mathematical model has been dubbed Traversable Acausal Retrograde Domain in Space-time, TARDIS, the same name as Doctor Who's Time Machine.

The four dimensions all connected

"The trick," explain the two scientists, is to use the curvature of space-time in the Universe to "bend time" so as to form in a time circle. A passenger sitting in the time box could then move in the future and go back, reports Science Alert.

Clear? Their mathematical model is based on the idea that we should no longer look at the Universe with one side three spatial dimensions, and on the other a fourth time dimension, but rather that we must imagine these four dimensions working simultaneously . This makes it possible to consider the possibility of a space-time continuum where the different directions in space and in time are all connected to each other.

"Repair eggs and separate milk from coffee"

According to Einstein's theory of relativity, the gravitational effects of the Universe are related to space-time, which would explain the elliptical orbits of planets and stars. If the space-time was "flat", the planets would move in a straight line. But according to relativity, the geometry of space-time bends in the neighborhood of objects of high masses, so that moons revolve around planets, and planets revolve around stars.

What the two researchers say is that it's not just physical space that can be bent and twisted, but also time. "There is moreover evidence that the closer you are to a black hole [objects whose mass is gigantic], the more the time is slowed," says Ben Tippet.

"My time machine model uses space-time curves to bend time in a circle rather than a straight line," he adds. For passengers in this machine, this circle would bring them into the future, worse in the past. "An outside observer who would look at the person inside this time box would see it evolve in the past, repairing broken eggs and separating the milk from their coffee", illustrates the theoretical physicist.

The necessary materials do not exist (yet)

To illustrate their point, the two scientists propose an image with two characters. A is in the "time machine" and B is an observer, the black arrows representing the passage of time. "In his bubble, A would see B advance in time, then go back in. Outside, B would see two versions of A, one advancing in time, and the other receding," explain the researchers.

The problem is that even if the mathematical model of Tippett and Tsang was verified, it would still be necessary to build the famous machine ... What is strictly impossible today, since the necessary materials do not exist. Scientists admit it, moreover, willingly. "It is mathematically feasible, they say, but it is not yet possible to build this machine simply because the materials - what we call exotic matter - that we need to bend space-time have still not discovered. "