Frequently Asked Questions
Common questions about tachyons answered
The Basics
What exactly is a tachyon?
A tachyon is a hypothetical particle that always travels faster than the speed of light. Unlike ordinary matter which can never reach light speed, tachyons can never slow down to light speed - they exist permanently in the faster-than-light realm. The word comes from the Greek "tachys" meaning swift.
Do tachyons really exist?
No experimental evidence for tachyons has ever been found despite decades of searching. They remain purely theoretical particles that are mathematically possible within special relativity but face significant challenges when combined with other physics theories. Most physicists believe they probably don't exist as actual particles.
Who discovered tachyons?
Tachyons weren't discovered - they were proposed. Physicist Gerald Feinberg coined the term and developed tachyon theory in his 1967 paper "Possibility of Faster-Than-Light Particles." E.C.G. Sudarshan independently developed similar ideas around the same time. Earlier physicists including Richard Tolman had considered faster-than-light particles as early as 1917.
How fast do tachyons travel?
Tachyons travel at speeds greater than light speed (c), but there's no single tachyon speed - different tachyons could travel at different velocities, all faster than c. Theoretically, a tachyon's speed increases as it loses energy. At infinite speed, a tachyon would have zero energy, while at the speed of light (which it can never reach), it would have infinite energy.
Physics & Properties
Why do tachyons have imaginary mass?
In Einstein's special relativity, the relationship between energy, momentum, and mass requires that faster-than-light particles have imaginary rest mass (a multiple of the square root of -1). This isn't because they're "imaginary" in the sense of not being real, but rather it's a mathematical property needed to make the equations work. The imaginary mass allows tachyons to have real energy and momentum while traveling faster than light.
Does faster-than-light travel violate Einstein's theory of relativity?
No, tachyons don't violate special relativity - they're actually consistent with its mathematics. Einstein's theory states that nothing can accelerate from below light speed to above light speed, not that nothing can exist traveling faster than light. Tachyons would always have been faster than light since their creation. However, they do raise serious questions about causality that challenge our understanding of the physical world.
What's the difference between tachyons and photons?
Photons (light particles) travel at exactly the speed of light and have zero mass. Tachyons would travel faster than light and have imaginary mass. Photons are real particles we observe constantly. Tachyons are hypothetical and have never been detected. Also, while adding energy to a photon increases its frequency, adding energy to a tachyon would slow it down.
Can tachyons interact with normal matter?
This is unknown. If tachyons exist, they might interact through gravitational or electromagnetic forces, or they might have their own unique interactions. However, any strong interaction with normal matter would make them easier to detect. The fact that we haven't detected tachyons suggests either they don't exist or they interact very weakly with ordinary matter.
Time Travel & Causality
Can tachyons be used for time travel?
In theory, tachyons appear to travel backward in time in certain reference frames according to special relativity. However, this doesn't mean they could be used for practical time travel. Most physicists believe that even if tachyons exist, there must be some principle that prevents them from being used to send information to the past, which would create paradoxes. The "chronology protection conjecture" suggests nature prevents time paradoxes.
What are tachyonic antitelephones?
A tachyonic antitelephone is a thought experiment showing how tachyons could theoretically be used to send messages to the past. By carefully choosing reference frames and sending tachyon signals back and forth, it might be possible to create a closed timelike curve allowing communication with the past. This is one of the main theoretical problems with tachyons - no one has found a satisfying resolution to this paradox.
What is the "reinterpretation principle"?
Proposed by Gerald Feinberg, this principle suggests that a tachyon traveling backward in time in one reference frame can be reinterpreted as an anti-tachyon traveling forward in time in another frame. This helps maintain some consistency, but doesn't fully resolve all causality issues.
Could tachyons cause time paradoxes?
Potentially yes, which is one reason most physicists are skeptical of their existence. If tachyons could carry information and be controlled, they might allow creating situations where you receive a message before it was sent, or even prevent yourself from sending it. The laws of physics as we understand them should prevent such paradoxes, but exactly how remains unclear if tachyons exist.
Detection & Observation
How do scientists look for tachyons?
Researchers search for tachyons in multiple ways: measuring particle velocities in accelerators, analyzing cosmic ray timing, looking for particles with negative mass-squared, searching for vacuum Cherenkov radiation, and observing astronomical events for faster-than-light precursors. Despite extensive searches over decades, no tachyons have been found.
Has anyone ever detected a tachyon?
No confirmed tachyon detection has ever been made. There have been experimental anomalies that briefly suggested faster-than-light particles (like the OPERA neutrino result in 2011), but all have been traced to experimental errors or mundane explanations. Current experiments place very stringent limits on tachyon properties.
Are neutrinos tachyons?
No. While some early neutrino experiments hinted at negative mass-squared values, modern precision measurements have confirmed that neutrinos have small but positive mass. The KATRIN experiment and others have definitively ruled out tachyonic neutrinos. Neutrinos travel very close to the speed of light, but still slower than light.
What would happen if we detected a tachyon?
A confirmed tachyon detection would be revolutionary for physics. It would force us to reconsider our understanding of causality, time, and the structure of spacetime. It would likely lead to new theories connecting quantum mechanics, relativity, and potentially quantum gravity. However, such a discovery is considered extremely unlikely by most physicists.
Theory & Applications
What are "tachyonic fields" in quantum field theory?
In quantum field theory, a tachyonic field is one with negative squared mass. Rather than representing actual faster-than-light particles, these fields indicate vacuum instability. The field will "roll down" to a stable minimum through a process called tachyon condensation. This mechanism is important for understanding spontaneous symmetry breaking and the Higgs mechanism.
How do tachyons relate to string theory?
In string theory, tachyons appear as ground states in certain configurations, particularly in bosonic string theory. However, they indicate unstable states rather than physical faster-than-light particles. Tachyon condensation in string theory describes how unstable D-branes decay to stable configurations. Superstring theory, which includes fermions, is tachyon-free in its stable ground state.
Could tachyons explain dark energy or dark matter?
Some cosmologists have proposed tachyonic fields as models for dark energy, the mysterious force accelerating cosmic expansion. These models use the mathematical properties of tachyonic fields but don't involve actual faster-than-light particles. There's no evidence suggesting tachyons are related to dark matter, which behaves like slow-moving massive particles.
Why study tachyons if they probably don't exist?
Tachyons serve as important theoretical tools for understanding the limits of our physical theories, exploring causality and time, testing consistency of mathematical frameworks, and studying phenomena like symmetry breaking. Even if physical tachyons don't exist, the concept helps physicists probe deep questions about the nature of spacetime and quantum mechanics.
Common Misconceptions
Can we use tachyons for faster-than-light communication or travel?
No. Even if tachyons exist, there's no known way to produce, control, or detect them on demand. More importantly, using them for communication would likely violate causality and create time paradoxes. Most physicists believe that if tachyons exist, there must be fundamental principles preventing their use for signaling.
Is quantum entanglement related to tachyons?
No. While quantum entanglement produces correlations faster than light, it cannot transmit information faster than light, so it doesn't involve tachyons. Entanglement is a purely quantum mechanical phenomenon fully consistent with special relativity and the impossibility of faster-than-light signaling.
Are tachyons the same as warp drive?
No. Tachyons are hypothetical particles that travel through space faster than light. Warp drive concepts (like the Alcubierre drive) involve distorting spacetime itself to allow effective faster-than-light travel without violating relativity. Both are speculative, but they're completely different ideas based on different physics.
Do tachyons have infinite energy?
No. This is a common misconception. While tachyons at the speed of light would have infinite energy (which is why they can't slow down to light speed), tachyons traveling faster than light have finite energy. In fact, as a tachyon speeds up, its energy decreases, approaching zero at infinite velocity.