As you know, no object with a positive mass can reach the speed of light. He can always approach it and reach, say, 99.9 (9)% of the speed of light, but he cannot reach the speed of light.
Objects with zero mass can move at the speed of light, such as, for example, elementary particles: photons, gluons and hypothetical, at the moment, gravitons.
What properties should an object possess in order to move faster than light? Very simple — it must have
What is imaginary mass? This mass is a multiple of the so-called
It will not work to see the approach of the tachyon, since we see the reflected light, and the tachyon will reach us faster than the light reflected from it. However, when the tachyon passes the point of its trajectory closest to us, we will be able to see it!
When a tachyon passes through a point closest to the observer, the observer will notice how an object appears out of nothing, which is then divided into two smaller objects moving in opposite directions. Both of these objects are optical illusions caused by
Tachyons have an interesting property — the lower their kinetic energy, the higher their speed. At zero kinetic energy, the tachyon speed would be equal to infinity.
As mentioned above, such a particle should have an imaginary rest mass, but this, in general, is not a big problem, since the particle still cannot be at rest.
A more serious problem is that for such a particle there is such a frame of reference in which it moves in the opposite direction. Thus, if you shoot someone with a tachyon bullet, it turns out that the person was killed before you pulled the trigger. At least there will be a frame of reference in which this would be true.
This scenario does not violate the laws of physics, but violates the principle of free will, because the bullet hits the victim before the shooter pulls the trigger, and thus the shooter cannot «reverse» his decision if he has already seen the hit target.
This paradox violating free will makes me very skeptical about the possible real existence of tachyons.