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Everything You Wanted to Know about Tachyons

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The universe is made of different types of particles interacting with each other and giving off energies of different types and spectrums. The universe, when analysed, is a very minute fashion revealing a plethora of particles that make up the atoms, called subatomic particles like neutrinos, bosons, quarks, leptons, etc. 

Tachyon is one such hypothetical subatomic particle that always travels faster than the speed of light. Tachyons are still not physically detected in any experiment, but their existence is mathematically hypothesized.

What is Tachyon? 

The word “Tachyon” is derived from the Greek word “tachy”, meaning swift. A tachyon is a quasiparticle that travels at speed faster than light. Tachyons exhibit unusual property wherewith the increase of speed of the particle, the energy decreases. In the case of other subatomic particles, the energy increases with an increase in speed. Thus, it would require an infinite amount of energy to slow down a tachyon to the speed of light. 

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Discovery of Tachyons : ECG Sudarshan Tachyon 

The first hypothesis pertaining to these faster-than-light-particles was given by German physicist Arnold Sommerfeld, in 1904, who called them meta-particles. Gerald Feinberg first coined the term tachyon in 1967 in a paper related to faster-than-light particles and their kinetics with respect to special relativity. 

Now, when we talk about tachyon Sudarshan’s name deserves an obvious mention. Indian-American physicist, E.C.G Sudarshan proposed the quantum theory for Tachyons, which challenged Einstein’s theory that nothing can move faster than light. 

Properties of Tachyons

In special relativity, tachyon-like particles have space-like four-momentum, as opposed to time-like four-momentum in normal particles. Currently, the mass of tachyons is considered imaginary. As per the Lorentz Invariant theory, if we implement the same formula for Braydon’s (slower than light particles), it shows that the total energy of the particle is dependent on its resting mass and its kinetic energy. When the velocity of the particle is greater than the speed of light, the denominator becomes an imaginary number, as the value under the square root becomes negative. As the energy of the tachyon has to be real, then the numerator, mc2 must be imaginary, thus indicating that the mass of the tachyon must be imaginary. 

We have already established that the speed of tachyon increases with a decrease in energy. Energy starts approaching zero as the velocity of tachyon approaches infinity. Thus, as Braydon’s can’t break the light speed barrier, tachyons are unable to slow down to speed slower than light speed. 

Observation of Tachyons

As tachyons move at speeds greater than the speed of light, it is not possible to observe them in real-time. After tachyons have passed through a point in space, the observes would see two images of it. The observer would observe an appearing and a departing image in the opposite direction. This is called the double image effect, which is normally observed in the light field of a superluminal object. 

Cherenkov’s Radiation

It is theorized that a tachyon with an electrical charge would lose energy in the form of Cherenkov’s radiation, like every other subatomic particle. When they exceed the speed of light in that medium (speed of light varies in different optical mediums, the commonly referred speed of light is measured in hard vacuum). As in Tachyons, the speed increases with energy decreases; loss of energy causes it to accelerate and form a hyperbola in space-time. But, the single hyperbola is formed of 2 oppositely charged tachyons with opposite momentum, which annihilate when they reach an infinite speed at the same place in space. 

Even neutral tachyons lose energy through gravitational Cherenkov’s radiation due to their gravitational mass. Interaction of tachyons with other particles causes irradiation of Cherenkov’s radiation into those particles.  

Causality of Tachyons

If tachyons were able to move faster than light, then they would violate causality according to relativity and can give rise to situations like the Grandfather’s paradox. The situation can be understood by applying the relativity of simultaneity in special relativity, which states that there would be disagreement on the simultaneity of two events in two points in space, which cannot take place in different inertial frames of reference. 

If we send a signal from one location to another, if the signal is moving at speeds below the speed of light, the transmission event is before the reception event (linear causality of events). However, signals faster than the speed of light, supposedly transmitted using a tachyon beam, would always have some points in time where the signal would be received before it is sent, almost like the signal has travelled back in time. 

Did You Know?

  • The idea for faster-than-light-particles by Gerald Feinberg was inspired by a science fiction story called the “Beep”.  

  • Tachyons have been used to explain technologies in science fiction movies like Star Trek, which has concepts like tachyon beam, anti-tachyon, etc. Who doesn’t remember deep space tachyons from the 3rd season of Star Trek: Deep Space Nine (Explorer episode)! 

  • MMORPG Eve Online also featured six different types of "Tachyon Lasers" or tachyon light.

FAQ (Frequently Asked Questions)

Q1. Can Tachyons be used for Time Travel? 

Ans. It has been theorized that tachyons may be the key to time travel to the past. Theoretical physicists Albert Einstein and Arnold Sommerfeld formulated a thought experiment called a Tachyonic antitelephone. The tachyonic anti telephone allows the user to send a message to their past self, as the signal can travel backwards in time. As per general relativity, as a particle approaches the speed of light, time slows down, so crossing the light speed barrier may cause a reversal of the flow of time. This is all still purely theoretical, and still, it contradicts the causality principle of relativity. 

Q2. What is the Reinterpretation Model?

Ans. The reinterpretation model states that a tachyon travelling back in time can also be interpreted as a tachyon travelling forward in time, as the observer is unable to distinguish between the appearing and departing tachyon. Any attempt to detect a tachyon from the future would simultaneously create a tachyon in the present and send it forward in time due to causality.