The theory that dark matter could be composed of tachyons is aspeculative idea in physics. Tachyons are hypothetical particles that, unlike normal matter, always travel faster than light. According to current understanding of physics, they violate the laws of causality and have yet to be observed.
As for Dark matter, that’s a mysterious substance that makes 85% of the universe’s mass. It’s effects are obderved through gravitational lensing and its affect on stellar orbits in a galaxy. It interacts with gravity but not light, making it difficult to detect directly. Tachyons, with their unique properties, are proposed as a candidate for dark matter because they could explain some aspects of dark matter’s behavior. Some theories suggest tachyon interactions could mimic the gravitational effects we observe with dark matter.
The downside of the theory
Tachyons are still purely theoretical. If they were observed, their existence would force us to rethink our current understanding of physics. In some models describing them, tachyon interactions could lead to instabilities in the universe, which thankfully we don’t observe. Finally, some theories suggest tachyons would have played a larger role in the early universe and wouldn’t be a significant component of dark matter today. There’s a lose-lose for you.