 From the protons which make up the atomic nuclei of everything you see around you, to the Higgs boson which gives mass to other fundamental particles, the history of humanity is also the history of discovering the usual and the unusual in the quantum realm. Now on the science verse, we have talked about trying to find particles that are yet to be found, such as the elusive and hypothetical graviton. However, we recently started discussing tachyons and their weird properties. Now as you are well aware, our current laws of physics found upon the idea of anything other than light moving at light speed, let alone faster than light. Yet there are those that continue to be proponents of the possibility of tachyons being real. So could tachyons actually exist? By now it is well established that in order to reach light speed an object needs to have zero mass like a photon. However if an object like a hypothetical tachyon were to somehow exceed light speed then mathematically it would have imaginary mass. But what exactly does imaginary mass mean and is it something that is feasible with our current understanding of reality? Well to answer that we have to revisit this equation and take a look at it from a mathematical perspective since it's such an abstract concept. Setting the velocity to be greater than light speed gives us an imaginary number for energy. However we could make the tachyon have real energy by making the rest mass imaginary. So what are some of the implications of this? Well as stated in the previous video this means a tachyon's speed and energy would be inversely related. And since the lower limit of a tachyon's speed is light speed this means it would take an infinite amount of energy to slow it down to light speed. Additionally let's say tachyons had an electrical charge. This combined with their speed means they would emit a little something called Sharonkov radiation. This emission of Sharonkov radiation would cause a tachyon to lose energy and thereby accelerate them more and more. At zero energy a tachyon would travel at infinite speed which is just not possible with our current understanding of physics. So essentially the tachyon as mentioned above would be unstable which can make one question the possibility of its existence. When we talk about faster than light speeds and time we start entering areas of physics that are uncertain. One such area is the tachyon standing with the principle of causality. We did discuss this briefly in the previous video. However that was more oriented towards the perception of what a tachyon was appearing to do but not what it was actually doing. It is important we bring this up because a popular notion floated around by proponents of tachyons is that tachyons could be used to transmit signals back in time which opens up the door to some interesting paradoxes. For example let's pretend that we had two individuals floating in the void of space. Individual one sends a signal of light pulses to individual two. At the same time he also sends tachyon one to individual two to alert him of the light signal. However individual two receives the tachyon one signal at a time well before individual one even sent the light signal. After individual two receives tachyon one he sends back tachyon two which would be received by individual one at a point in time before he even sent tachyon one. However individual one receiving tachyon two would only be caused by him sending tachyon one. So what is going on then? This paradox which seems to violate causality has no definite answer. However that hasn't stopped some physicists from trying to propose some potential solutions to reconcile tachyons with causality. One such proposal makes use of the quantum mechanical property of superposition or the ability of a particle or a system to be in many states at once until it is measured. According to the proposal our tachyon would be in superposition up until it was observed meaning it is in a state of being absorbed and emitted at different times all at once. The idea behind this proposal is that it is compatible with quantum theory because it follows the principle of superposition and does not violate relativity because it's not actually traveling through space faster than light thereby not resulting in causality violations. Keep in mind that this is just a proposal that hasn't been experimentally verified yet. There may be more to the idea of tachyons than what was presented there. If they do exist their mechanics would be beyond our understanding for sure. For example it's possible that they do exist but don't interact with matter which travels at sub light speed. Could this be the case then we are centuries or potentially millennia behind trying to unlock the technology and necessary breakthroughs in physics to detect and utilize such a particle. So going back to the question of whether tachyons exist or not the answer is quite uncertain. While our current knowledge of physics frowns at the existence of a particle like the tachyon that doesn't mean that nothing in the future will lead to a breakthrough in our understanding of quantum mechanics which will allow us to reconcile the idea of tachyons with classical mechanics leading to their potential discovery or even creation. However it's impossible to tell if or when such a day will come. In the meantime take a moment to explore other enigmas in quantum mechanics as well as the rest of the universe. 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