Tachyons: What to know about the particle that can beat light in a race

Tachyons are theoretical particles that have no or negative mass. Because of these properties, they should be able to travel faster than light, and even time travel.
Christopher McFadden
If tachyons exist, we could communicate at hyperfast speeds, and perhaps even send messages through time.
If tachyons exist, we could communicate at hyperfast speeds, and perhaps even send messages through time.


  • Tachyons are hypothetical particles that can travel faster than light.
  • They were first "invented" in the 1960s and became popular in fiction.
  • If they do exist, it could open the door for faster-than-light communication, among other things.

Imagine a particle with no mass that can travel faster than the speed of light. Can you? Then congratulations, you've mastered the fundamentals of "tachyon."

If it existed and could be utilized, such a particle would completely revolutionize many aspects of our world, including communication.

However, the problem is that just because you imagine something doesn't mean it exists. But that hasn't and shouldn't stop scientists from trying to determine whether these "massless quasiparticles" are out there.

Let's find out some more about these bizarre things.

What are tachyons?

Tachyons are hypothetical particles that always move faster than light. They have never been detected and are believed, by some, to be impossible.

Tachyons: What to know about the particle that can beat light in a race
Tachyons are through to travel faster-than-light.

This is because particles that move faster than light would break our current understanding of the laws of physics.

The term "tachyon" is derived from the Greek word tachy, which means fast.

However, if they are real, such particles might be utilized to transmit signals faster than light. According to the Theory of Relativity, this could defy causality and result in logical dilemmas like the "Grandfather Paradox."

This paradox is exemplified by the impossibility of someone traveling back in time to kill their grandfather. Since that person could no longer go on to create their own parent, it would not, therefore, be possible to go back in time in the first place.

You simply wouldn't exist.

However, there are ways to get around the paradox within the confines of contemporary physics without doing away with time travel entirely.

In any case, it would be strange for tachyons to speed up as their energy goes down, and it would take infinite energy to slow down to the speed of light. There is currently no conclusive experimental proof that such particles exist.

Gerald Feinberg, a physicist and science author, suggested that tachyonic particles may be created from excitations of a quantum field with "imaginary" mass in a 1967 paper entitled "Possibility of faster-than-light particles."

Still, it was quickly shown that Feinberg's model didn't actually account for superluminal (faster-than-light) particles or messages and that tachyonic fields only cause instability, not violations of causality.

Tachyons: What to know about the particle that can beat light in a race
If real, tachyons could open faster-than-light communications.

However, rather than referring to faster-than-light particles, the term "tachyon" is frequently used in current physics to describe fictitious mass fields. These fields are essential in contemporary physics.

Interestingly, some complementary kinds of particles are known to exist and are referred to as luxons (which always move at the speed of light) and bradyons (which always move slower than light).

What is the speed of light, and how do we know?

Most physicists believe that nothing can travel faster than light speed (186,282 miles per second or 299,792.458 km/s). Called the “Universal Speed Limit,” our current laws of physics indicate that this is the fastest that anything will be able to travel, ever.

Tachyons: What to know about the particle that can beat light in a race
Nothing can travel faster than light, so we are told.

But how do we know this?

Before 1600 AD, people thought light moved instantaneously; however, things started to change when the great Galileo became the first person to attempt to measure the speed of light.

To test his theory, he set out to measure the speed of light in 1638. To do this, he and an assistant lit candles on mountaintops, and Galileo's aide would uncover his lantern when he noticed the flash.

Galileo timed the return flash and calculated its speed. However, since he lacked modern timing devices capable of calculating microseconds and relied on his reaction time, the result proved to be way off compared to current estimates.

However, Galileo was astutely aware of this and concluded that light's velocity was not instantaneous but was too fast to be measured using this method.

Tachyons: What to know about the particle that can beat light in a race
Galileo Galilei statue in Pisa, Italy.

In 1676, a young Danish astronomer named Ole Römer attempted to estimate light speed. Römer asked sailors to check their timepieces by observing Jupiter's moon Io in eclipse. It takes 1.769 days to round Jupiter. Minor problem.

At that time, one method used by mariners at sea to verify their clocks was to watch Jupiter's moon Io eclipse the planet. According to measurements, It took 1,769 days to make one complete circle around Jupiter. There was a tiny issue, though.

According to the season, Römer noticed that the interval between eclipses changed slightly. The interval between Io's eclipses gradually grew longer when the Earth moved away from Jupiter; it shrank as it got closer. The combined result meant that the estimated timeframes could be off by more than ten minutes.

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Römer reasoned that the variations in distance between Jupiter, Io, and Earth might account for his observations. The different times taken for Io's orbit reflected the different distances that light had to traverse. In fact,

Rømer interpreted the variation in timing to be related to the amount of time it takes light to travel across the diameter of Earth's orbit. However, he didn't actually calculate the speed of light because the diameter of Earth's orbit was not well known at the time.

Using a similar technique to Gallileo, physicist Armand-Hippolyte-Louis Fizeau showed how the shift in wavelength in the light coming from a star could be used to measure the relative velocities of stars that lie in the same line of sight. He performed the first experimental measurement of the speed of light in 1849. By using a series of cogwheels and light sources, he estimated the speed of light at around 195,732 miles per second (315,000 km/s).

That's within 5% of our most recent laser measurements. All of these experiments showed that light moves at a definite measurable speed.

But why?

Why can't you go faster than light?

To figure out why Albert Einstein considered what would happen if you attached a torch to the front of a moving rocket if light has a finite speed. Since light has a finite speed, he postulated that the light emanating from this torch shouldn't move more quickly than light.

Tachyons: What to know about the particle that can beat light in a race
Einstein was able to explain why we can't go faster than light.

With the help of a number of "Gedankens" (thought experiments), Einstein pondered this problem and came up with an absurd solution: that movement must somehow cause the time to slow down.

The concept of relativity was born. Since then, Einstein's theories have been extensively tested and appear to hold water.

One of the most famous was by Bill Bertozzi at MIT, who accelerated electrons to various speeds in 1964. He then determined their kinetic energy and discovered that the electrons became heavier and heavier as they approached the speed of light.

This got to the point where it was impossible to accelerate them further. The fastest the electrons could go before becoming too heavy to accelerate further?

Why, light speed, of course.

Another significant test had physics professors Joseph Hafele and Richard E. Keating flying synchronized, ultra-precise cesium atomic clocks across the globe on commercial aircraft. After the trips, all the moving clocks disagreed with the reference clock in the lab and one another. For the moving clocks, time passed more slowly, Just as Einstein had anticipated.

It seems, therefore, that as anything moves faster, it masses more and time appears to slow down. This continues until you approach the speed of light, at which point time appears to stop. And if time slows down, then speed does too.

After all, this is a measure of distance traveled over time! Quite simple (well, not really).

Are tachyons a real thing?

The long and short of it is that we don't know. As a concept, they are "real," but scientists have never been able to detect them.

Tachyons: What to know about the particle that can beat light in a race
We never be able to find tachyons.

Another problem is that they have something called "imaginary mass." This term refers to the strange theoretical concept that comes from taking the square root of a negative number.

Regarding tachyons, a particle's mass is only physically meaningful at speeds slower than light (as described above). For this reason, it may prove difficult, if ever possible, for us to "observe" (detect and identify) them.

However, because their mass is "imaginary," they are not technically forbidden under our current understanding of the laws of physics.

But this also doesn't mean they do exist.

Tachyons: What to know about the particle that can beat light in a race
Since tachyons have no mass, we may have trouble finding them.

Most physicists think of tachyons as nonphysical particles because they would need to have imaginary mass, can defy causality, and have never been seen in nature.

There is some discussion as to whether they will eventually be explicitly shown to be impossible or will always be something that is neither explicitly forbidden by the laws of physics nor proven.

However, it would be silly of us not to continue looking for tachyons because they would shed light on an entirely new branch of physics, so naturally, this hasn't stopped anyone from trying.

However, no objects have ever been seen to move at superluminal speeds, except the 2011 neutrino false alarm.

Tachyons are currently accepted as legitimate mathematical creations that don't break specific rules. Still, they are considered: -

  • abhorrent since they contradict our understanding of causation and;
  • impossible to find.

However, others have taken the opposite view, naturally.

They would continue to be theoretical curiosities that no one took seriously if it weren't for their presence in science fiction, either explicitly or through a similar phenomenon.

Think of the near-instant telepathic communication between the "Formics" in "Ender's Game," for example.

Have tachyons ever been observed?

As we've explained above, no, and they may never be.

That being said, experts in the field predict that tachyon-like objects may exist as faster-than-light 'quasiparticles' moving through laser-like media.

Tachyons: What to know about the particle that can beat light in a race
Tachyons are not explicitly forbidden by physics, but that doesn't mean they exist either.

Put another way, like other quasiparticles called phonons and polaritons that are present in materials, they exist as particle-like excitations. Technically, media with inverted atomic populations (like the conditions present inside a laser) are referred to as "laser-like media."

"We are beginning an experiment at Berkeley to detect tachyon-like quasiparticles. There are strong scientific reasons to believe that such quasiparticles really exist because Maxwell's equations, when coupled to inverted atomic media, lead inexorably to tachyon-like solutions," explained Raymond Y. Chiao, professor of physics at the University of California, Berkeley, in an article in Scientific American in October 1999.

To date, scientists have found two different kinds of "faster-than-light" effects in quantum optics experiments. Tachyon-like quasiparticles (in inverted media described above) would, if ever discovered, represent the third kind of faster-than-light effect.

Tachyons: What to know about the particle that can beat light in a race
But, if they exist it could open the door to "instant" communication.

"First, we have discovered that photons which tunnel through a quantum barrier can apparently travel faster than light,"

"Because of the uncertainty principle, the photon has a small but very real chance of appearing suddenly on the far side of the barrier through a quantum effect (the 'tunnel effect') which would seem impossible according to classical physics. The tunnel effect is so fast that it seems to occur faster than light," Chiao explained.

"Secondly, we have discovered a phenomenon that is connected to the well-known Einstein-Podolsky-Rosen phenomenon, in which two distantly separated photons appear to influence one another's behaviors at two distantly separated detectors," he added.

Tachyons: What to know about the particle that can beat light in a race
Since tachyons have an "imaginery mass" we may never find them in particle accelerators.

According to Chiao, Prof. J. D. Franson of Johns Hopkins University made the initial theoretical prediction of this phenomenon. Through experimentation, scientists have shown that twin photons from the same source (a down-conversion crystal) behave in a correlated manner when they reach two separate interferometers.

One way to define this occurrence is as a "faster-than-light influence" of one photon on its twin. However, due to the inherent randomness of quantum events, it is impossible to predict whether a specific photon will tunnel or not, as well as whether it will be transmitted at the final beam splitter.

As a result, sending real messages using faster-than-light communications is, at present, apparently not possible.

Tachyons: What to know about the particle that can beat light in a race
Detecting tachyons could prove difficult.

All very interesting, but could we ever detect them? Incredibly, it might be possible.

Since they travel faster than light, using photons or particles with mass would be entirely out of the question. Any data recovered would likely show an "image" split showing it arriving and departing simultaneously.

However, there may be another way.

Since tachyons have no or negative mass (anti-mass), they would still comprise energy. This should have some effect on gravity (positive or negative) that could be detected if the detector was sensitive enough.

Their ability to travel faster than light may lead to the development of an entirely new detecting technique.

Tachyons: What to know about the particle that can beat light in a race
But, we might be able to with very sensitive detectors.

Particles have been created to travel faster than light in different media, even though the speed of light in a vacuum, c, is an absolute speed limit. The International Atomic Energy Agency states that Cherenkov radiation is produced when electrically charged particles are accelerated up to and beyond the speed of light in some materials, such as water.

If we could develop a means to measure Cherenkov radiation in the near vacuum of space, this would be one method of discovering tachyons if they are electrically charged.

Can tachyons go back in time?

The discovery of the universal speed limit of c, or the speed of light in a vacuum, is one of Einstein's theory of special relativity's most significant and profound findings.

Tachyons: What to know about the particle that can beat light in a race
Is time travel possible with tachyons?

According to Einstein, and as we've explained above, as an object approaches c, both its mass and the energy needed to accelerate it approach infinity. In short, breaching c is inconceivable.

However, in its lowest energy state, a massless particle like a tachyon could travel at this speed or faster. Some believe that such a particle might also be able to travel backward in time.

But how?

The goings on in the universe range from hyperviolent (like a supernova) to completely benign (like you eating an apple). But, all these events occur in the same "space" or fabric called spacetime.

Depending on how close to one another these events occur, they may be what is called "causally linked."

This is a little complex to explain here. But suffice it to say that so long as two events occur within a time period that they can be seen from one another's frame of reference, light travels fast enough to carry the information from one point of spacetime to the other.

If another third event occurred at the same time or in the past, and the distance between the objects is at the same speed as light, observers will never be able to see it.

All is well and good, but one observer may be able to see another event before their counterpart across the galaxy can too. This is all to do with the speed of light having a fixed value.

Tachyons: What to know about the particle that can beat light in a race
Tachyons could give the impression of time travel.

To help you visualize this, consider a cone of light emanating from a point on a flat sheet of paper. Each event (supernova or apple-eating) will produce its own cone of light.

If these cones overlap or touch at any point (they would need an observer in either cone to see the other), the events could be causally linked.

For example, your actions may have (somehow) triggered the supernova, or the supernova somehow made you feel hungry. This connection of events would require some form of information connection that moves fast but slower than the speed of light within the light cone that connects the events.

To this end, the light cone's edges stand in for the speed of light. A signal that travels faster than light is necessary to connect events inside and beyond the light cone. For another third event beyond these cones to ever see or send its information to the others, it would necessarily need to travel faster than light.

Tachyons: What to know about the particle that can beat light in a race
Time travel is widely considered impossible.

This is where tachyons come into play. Such a particle traveling at a speed more significant than the speed of light could violate causality by linking these "non-overlapping light cone" events and giving the illusion of "time travel."

What? Why?

Think about it this way. A signal is sent from event A and received in event B. All observers working in various reference frames agree that A came first if the signal is moving at the speed of light or slower.

But there will be reference frames that claim the signal was received before it was delivered if it was carried by a tachyon and moved faster than light. Thus, the tachyon appeared to have moved backward in time to an observer in this frame.

The idea that the laws of physics should be the same in all non-accelerating reference frames is one of special relativity's core tenets. Therefore, if tachyons can defy causality and advance through time in one reference frame, they can do so in all of them.

Got it? Don't worry, it is a little esoteric and might be an academic problem only if tachyons don't exist.

And that is your lot for today.

While an exciting concept, Tachyons still safely reside in the realm of theoretical physics for now. If they could theoretically exist, it may be "for the birds" if we can never detect them.

Whether or not developments in technologies in the future will enable us to unlock this "secret" aspect of the universe is yet to be seen. Still, it would undoubtedly revolutionize many things if we ever did.

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