Traveling at the Speed ​​of Light: When Science Fiction Challenges Scientists

“Now, if we add a charge that would make an electrical energy in addition to the gravitational energy, it would make it possible to circumvent this problem and be repelled. [de l’autre côté du trou de ver]. Like a giant magnet, we would be attracted to the North Pole and then repelled by the South Pole. Only once you have done that can you not go back the other way. In the context of narratives that provide for a return journey, this initial shortcut would certainly allow us to move quickly, but would force us to walk around the universe to return to the starting point. “It is as if you took a shortcut to go to church, but to get home again, you had to walk around the village” image Marie-Christine Angonin.

To be able to travel back and forth through the wormhole, as in Interstellar, we would need an energy whose density would be weaker than the vacuum, a mass that can push us back toward a white hole as we approach it. “That’s why we should have a negative mass somewhere,” notes Marie-Christine Angonin. ‘It would be anti-gravity, that is, a place from which we would be rejected instead of being attracted. Anti-gravity is very much present in science fiction, but in everyday life it has never been highlighted, not even in the energies of the vacuum. »

Concepts that are hard to interpret by neophytes, any science fiction fans they may be. This is why the hyperspace narrative reasoning was developed. The vessels guided by the fictional characters pass between two ends of a wormhole at a speed greater than the speed of light, thus justifying a rapid movement that does not delay the plot. Note that the hyperspace of science fiction only borrows certain expressions from science, but that it does not correspond to any scientific theory.


In 1994, the Mexican physicist Miguel Alcubierre developed a theoretical means of superluminal motion that would not violate the physical principle that nothing can travel faster than the speed of light in a vacuum. The Alcubierre metric, in theory compatible with the particular theory of relativity, imagines the possibility of bending space-time. The spacecraft does not move itself faster than light, but is trapped in a “bubble” that allows it to move from point A to point B faster than light would. The said bubble is formed by, on the one hand, the expansion of the space behind the tub and, on the other hand, the contraction of the space in front of the tub.

Only here if this theory respects a priori the laws of physics, so that bending space-time to travel faster than light also requires energy whose density is lower than vacuum. However, the principle of negative mass that Einstein imagines is still today only an unconfirmed hypothesis and difficult to verify.

“The problem is that a particle that goes faster than light will always remain faster than light, to slow it down would require infinite energy,” says Marie-Christine Angonin. “Conversely, it would take an infinity of energy to bring a massive object to the speed of light. And this is not a theoretical infinity, it has been demonstrated by experience. It is for this reason that in particle accelerators it is not cubes of matter that sent, but a single particle, because a colossal amount of energy is already needed for it to be simply relativistic. “

That there are space-time bubbles traveling at the speed of light, or even faster than light, is theoretically possible. But the biggest problem would be putting a ship in one of these bubbles. “We have to stop the bubble, make it go slower than the speed of light, and that is not possible. Technically, there is no physical way to cross this barrier to the speed of light, ”supports Marie-Christine Angonin.

But then, if we think about that “distortion engines” – long theorized by the screenwriters of star trek Can not be developed due to the very need for negative energy, do they ever become a fiction? Not necessarily. Research conducted by an international group of scientists on other classes of “warp engines” was published in 2021 in the journal Classic and quantum gravity.

Researchers in this group, called applied physics, have studied a theoretical “distortion engine” that does not require negative mass. For this to be physically possible, they say, the ship must look like a shield, flat in front and behind. Their demonstration, although incomplete, has the advantage of showing that, from a mathematical point of view, a warp engine could be built.

“Alcubierre’s metrics were an unrealistic idea and completely impossible to implement in everyday physics for several reasons. […] What these scientists have demonstrated is that the Alcubierre metric is a solution among many others that is, so to speak, easier to implement. It is interesting, but it does not mean that it can be done, ”emphasizes Marie-Christine Angonin. “If we take into account the fluctuations of the vacuum, such experiments will only exist in a theory of quantum space time with very small energies and therefore with very small particles. A spaceship with the speed of light is completely unrealistic at the moment. »

Therefore, despite the interest of scientists in these matters for many years, superluminal travel should for a long time remain the privilege of science fiction writers.

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