Are neutrinos tachyons?

[BlackHole]

Let me start by saying i'm neither a particle physicist nor do i know anything about modern quantum physics but some believe that neutrinos could be tachyons, others are convinced that they can't exist.

 

Tachyons are a putative class of particles which are able to travel faster than the speed of light. Tachyons were first proposed by physicist Arnold Sommerfeld (1961), and named by Gerald Feinberg. The word tachyon derives from the Greek (tachus), meaning "speedy particle"

 

Tachyons have the strange properties that, when they lose energy, they gain speed. Consequently, when tachyons gain energy, they slow down. The slowest speed possible for tachyons is the speed of light.

 

http://physics.gmu.edu/~e-physics/bob/y.htm

 

Another site seems to contradict them by saying that faster than light communication is impossible.

 

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

 

I guess that if these particles really exist, probably we will not be able to see them. Actually this is a complicated topic that I never really unterstood much. The part that I am still a bit confused about is how it is believed that travelling faster than the speed of light will actually result in reversal of time. I believe time and space are not a physical entities so is it because we mark time based on what we are able to see or is it just because how our brain works?

 

Basically, tachyons would violate both: a) theory of special relativity b) causality (also known as cause-and-effect).

 

It seems unavoidable that if tachyons exist, the principle of special relativity must be false, and there exists a unique time order for all observers in the universe independent of their state of motion. In fact plenty experiments show that some things (which are not matter or a physical object) can travel faster than the speed of light. But the universe always manages to ensure that we can never use the effect for anything useful, like building a FTL starship or travelling back in time.

 

Of course there are other theories of time-travel besides tachyons such as: a) wormholes b) cosmic strings c) inflation theory

 

a) A wormhole is a theoretical opening in space-time that one could use to travel to far away places very quickly. The wormhole itself is two copies of the black hole geometry connected by a throat - the throat, or passageway, is called an Einstein-Rosen bridge. It has never been proved that wormholes exist and there is no experimental evidence for them, but it is fun to think about the possibilities their existence might create.

 

b) A cosmic string is basically a disruption in space with a linear form, which has to do with the fact that space can have different phases, and therefore you can disrupt space by making walls, or solid objects, or planar objects, or even straight lines.

 

I believe that the absurtidy of this theory is that it assumes the number of dimensions our universe can have in the first place. Currently we know just of four dimensions in our universe (including spacetime which is fully based on geometry).

 

c) Cosmic inflation is a theory proposed by Alan Guth (1981). According to cosmic inflation the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density (positive vacuum pressure). I think it's also called false vacuum.

 

The contraction is how could vacuum ever contain pressure? Pressure requires force (and force requires energy). Actually density is caused by pressure.

 

Not that i know what all this means but i think it has to do with Einstein's general theory of gravity. Einstein said that space-time has an energy which is always positive (meaning non-zero). According to his theory, bodies create the space around them (differential geometry which is the study of geometry using calculus) and therefore true space or emptiness does not exist.

 

The way i see it, space-time is not a dimension, unless you believe that cosmic strings and wormholes are possible, which would also allow time-travel, which i believe is not possible. I also disagree with him about the concept of singularity which is mathematically impossible (it's like division by zero).

 

Maybe quantum theory and string theory would have to be revised and enhanced in the future (we don't know yet), if they couldn't comply with the experimental method (which we currently don't have).

[swansont]

Let me start by saying i'm neither a particle physicist nor do i know anything about modern quantum physics but some believe that neutrinos could be tachyons' date=' others are convinced that they can't exist.

 

Tachyons are a putative class of particles which are able to travel faster than the speed of light. Tachyons were first proposed by physicist Arnold Sommerfeld (1961), and named by Gerald Feinberg. The word tachyon derives from the Greek (tachus), meaning "speedy particle"

 

Tachyons have the strange properties that, when they lose energy, they gain speed. Consequently, when tachyons gain energy, they slow down. The slowest speed possible for tachyons is the speed of light.

 

http://physics.gmu.edu/~e-physics/bob/y.htm

 

Another site seems to contradict them by saying that faster than light communication is impossible.

 

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

 

[/quote']

 

Neutrinos are not Tachyons because, as you note, Tachyons travel faster than c, and neutrinos do not.

 

The energy of a particle can be written as E = mc²/(1-v²/c²)^1/2

 

If v>c, then either the energy is imaginary (for real mass) or the mass is imaginary (for real energy). (imaginary, mathematically, meaning you have taken the square root of a negative number) So you have to figure out what imaginary mass or energy is. If it doesn't interact with matter comprised of real mass/energy, then we will never detect it.

 

There is no conflict between saying Tachyons travel faster than c and information can't, if you can't use them for communication.

[BlackHole]

Neutrinos are not Tachyons because' date=' as you note, Tachyons travel faster than c, and neutrinos do not.

 

The energy of a particle can be written as E = mc[sup']2[/sup]/(1-v²/c²)^1/2

 

If v>c, then either the energy is imaginary (for real mass) or the mass is imaginary (for real energy). (imaginary, mathematically, meaning you have taken the square root of a negative number) So you have to figure out what imaginary mass or energy is. If it doesn't interact with matter comprised of real mass/energy, then we will never detect it.

 

There is no conflict between saying Tachyons travel faster than c and information can't, if you can't use them for communication.

 

True. Neutrinos have positive mass (slighly above zero) but tachyons do not have a real mass. If they have an imaginary mass, they cannot interact with time-like matter.

 

As to proving theie existence, one basically has to discover a particle interaction which can only be explained by the presence of one or more tachyons. High-enery physicists have searched through some experimental records and so far none of the high-energy accelerator labs have detected an interaction which can only be explained by tachyons. This means that tachyons must be far more weakly interacting than neutrinos. Even if they do exist, tachyons would be extremely difficult to utilize under our current understanding of physics.

 

Basically, the existence of tachyons will violate both special relativity and causality.