In a remote corner of theoretical physics, a heretical idea has been around for decades: the existence of particles capable of violating the sacred law of causality, moving faster than light. Are the tachyons, entities never observed but not completely abandoned, which now a new study (I link it here) forcefully brings it back into the limelight.
According to researchers, in fact, a universe dominated by tachyons could surprisingly explain the biggest puzzles of cosmology, from matter to dark energy. A bold hypothesis that remains to be verified, but which could open up radically new perspectives on the nature of the cosmos. Science fiction or physics of the future?
Tachyons, “heretical” particles
Tachyons are hypothetical particles that always move faster than light, challenging one of the pillars of modern physics: Einstein's theory of relativity. You know what he says, right? Nothing can exceed the speed of light in a vacuum, which is approximately 300.000 km per second. To do so would be violative il principle of causality, or the rule according to which every effect must follow its cause.
Yet, tachyons are a mathematically valid solution to the equations of relativity, even if their existence would imply paradoxes. For this reason, most physicists consider tachyons a simple theoretical curiosity, an intellectual exercise with no reality.
A “tachyonic” model of the universe?
The study, in preprint (therefore not yet subjected to peer review) sheds new light on tachyons, placed in a cosmological model in which they constitute approximately 85% of the mass of the universe, and not dark matter.
According to researchers' calculations, an expanding universe filled with tachyons could initially slow down its expansion and then accelerate again. A behavior surprisingly in agreement with observations of our universe, which we know is currently in a phase of accelerated expansion, driven by a phenomenon known as dark energy.
In other words, the “tachyon” model could potentially explain both dark matter and dark energy, the two greatest mysteries of modern cosmology, with a single, bold stroke of the towel. A hypothesis that is revolutionary, or rather, heretical.
Yes, but what about the evidence?
This time I'm anticipating some commentators who really don't like theoretical physics. And I do it to reiterate the obvious: a theory, however fascinating, is only valid if it passes comparison with experimental data. To test their idea, the physicists applied it to observations of type Ia supernovae, stellar explosions that allow them to reconstruct the relationship between distance and expansion of the universe. It was by studying these supernovae, in the 90s, that astronomers discovered the accelerated expansion of the cosmos.
Well, the tachyon model has proven to be just as effective as the standard one (which includes dark matter and dark energy) in explaining supernova data. A surprising result, given the unorthodox nature of the hypothesis.
But this is just the beginning. Today we have access to a multitude of data about the large-scale universe, from the cosmic background radiation (the echo of the Big Bang) to the distribution of galaxies. The next step will be to compare the tachyon model with these increasingly precise and detailed observations. Will it hold up? I doubt it, but that's not the point.
Tachyons, a beautiful and good provocation
The tachyon model is unlikely to pass these more rigorous tests, given the implausibility of the tachyons themselves. But pushing in new directions, even unorthodox ones, is fundamental in cosmology: you never know when a turning point might arrive. Cosmologists have been trying to understand dark matter for 50 years and studying dark energy for 25 years, without conclusive results. The solutions to these puzzles will likely come from unexpected directions.
In this sense, the tachyon model is a fruitful provocation, which forces us to question some of our most deeply rooted certainties, such as the insurmountable limit of the speed of light and the principle of causality. Even if it turns out to be wrong, it will have pushed us into the unexplored territories of theoretical physics, where the answers we seek may lie.
TV, Smiles and Tachyons
The history of science is dotted with "heretical" ideas that have paved the way for conceptual revolutions. Do we want to talk about relativity itself, which in the last century seemed like a bizarre mathematical fantasy and instead redefined our vision of space, time and gravity?
Tachyons, now confined to the fringes of theoretical physics, may one day prove to be the key to a new, deeper understanding of the universe. Or perhaps they will forever remain a fascinating speculation, a thought experiment that reminds us how much stranger and more surprising reality can be than we dare imagine.
In any case, the audacity to challenge dogma and explore the impossible remains the engine of scientific discovery. Because it is only by questioning our certainties that we can hope to open new windows on the cosmos. Behind one of these windows, a faster-than-light universe where the past and the future blur and the laws of physics as we know them no longer apply.
