When we talk about tachyons, we talk about many things – journeys at speeds greater than light, free will, quantum death and violent murder. How could a particle spell out so many facets of the world we know?
Tachyons are hypothetical particles that travel with a speed greater than that of light. It was predicted by Indian Physicist E.C.G. Sudarshan (1931 – 2018). The term is also used to refer to excitations in the imaginary mass quantum field, although a tachyon, product of an excitation in that field, would not travel faster than light. For the sake of a wild, intriguing hypothesis, we will use the first definition of the tachyon- a particle that travels faster than light.
If you know anything about relativity, it is that NOTHING can travel faster than light. That would be breaking the most fundamental, widely accepted rules of physics. However thoughts do run wild, and so the birth of the hypothetical tachyon emerges.
For baryonic matter, leptons ( or shall I say, plain, unexotic, boring matter ) it would be impossible to break the universal speed barrier set by the almighty photon. This is because for, say, an proton to travel at light speed, it would require INFINITE energy. For something to travel at the speed of light, it would have to be massless ( like the photon ) and transfer its mass to energy ( since by Einstein’s equation, energy and mass are interchangeable). So, we have set down the first postulate, which is that ordinary particles would need an infinite amount of energy to break the speed barrier of light. Our second inferred postulate for ordinary matter ( not a photon or a tachyon ) is that, as speed increases, mass increases, and so energy too increases.
The opposite of ordinary matter is tachyonic matter. As opposites go, this would mean that as the speed of a tachyon increases, it’s energy decreases. This is counterintuitive, but when you apply the exact same logic to tachyonic particles mean that they would also require a ridiculous amount of energy to even get anywhere near down to the speed of light barrier. Hence, tachyons would require an infinite amount of energy to cross that speed barrier.
Now that we have layed down the fundamentals of tachyon travel, we will get into the interesting part about how tachyons violate causality, and you could say, travel back in time.
- Build two tachyon message transmitters and receivers. You are in the Milky Way.
- Put one in the Milky Way , and station the other in Andromeda.
- Program the tachyon message transmitter in the Milky Way to send out a diplomatic message to Andromeda so that this process takes 6 hours.
- Go to bed at 12am and wake up at 6am the next morning, and plan to send the message at 12pm the next morning.
- Wake up at 6am and realise your Tachyon receiver has received a reply from Andromeda concerning your diplomatic message to them.
- Realise that since tachyons travel faster than light, the reply arrived 6 hours before you intended to send it.
- Cry out in shock that 1) causality is violated, and 2) you have no free will as you cannot change your mind to unsend the message as Andromeda has already gotten your message and sent a reply.
Now, think of this. What happens if someone destroys your tachyon message transmitter after all this out of spite? The message now, can never be sent. So where and how did the tachyon message from Andromeda came to be?
What is the answer?
The answer is the Multiverse.
Since the response message has already been sent, it cannot be unsent. The only possible way to resolve this paradox is to bring in the theory that, in an alternate universe, the transmitter was not broken and the message was sent. Physics is amazing!
Here is another thought experiment by physicist Richard Muller on free will and tachyons, the famed Tachyon Murder Hypothesis.
Say you are holding a tachyon gun. Pull the trigger and Mary, on the opposite side, will die.
You pull the trigger and Mary dies. The authorities arrest you. However, at your trial, it is correct to say that there is a reference frame in which she was killed before you pulled the trigger ( as it is a tachyon gun ) , and in vain effort to try not to violate the laws of physics, you had no other choice other than to pull the trigger. This takes away FREE WILL.
So maybe physicists should drop the research on tachyons. For if they ever found one, they wouldn’t deserve the rightful credit, or the hopeful Nobel prize. Because if they find tachyons, it means they HAD to do it. They have no free will, and so had no other choice other than to find that tachyon.