What are tachyons?

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Offline RobotGymnast

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What are tachyons?
« on: 06/04/2009 03:22:19 »
Can somebody explain tachyons to me? Wikipedia isn't exactly the best resource for things like this. I just don't understand how something can travel superluminally; isn't the speed of light supposed to be the maximum possible speed? I realize that tachyons are theoretical, I was just wondering if someone could explain it a bit to me.

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« Last Edit: 13/04/2009 22:38:45 by chris »
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Offline lightarrow

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Re: What are tachyons?
« Reply #1 on: 06/04/2009 17:52:14 »
Can somebody explain tachyons to me? Wikipedia isn't exactly the best resource for things like this. I just don't understand how something can travel superluminally; isn't the speed of light supposed to be the maximum possible speed? I realize that tachyons are theoretical, I was just wondering if someone could explain it a bit to me.
Special relativity forbids a massive body to reach or to overtake light speed, starting from lower speeds, but don't forbids, in theory, the existence of bodies which have always had greater speeds and that will never slow down to light speed or less. I don't know much more than this.

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Offline RobotGymnast

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Re: What are tachyons?
« Reply #2 on: 06/04/2009 21:42:36 »
oh that makes sense, I suppose. Does anybody know why they are theorized to exist and what they are supposed to explain?
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Ethos

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Re: What are tachyons?
« Reply #3 on: 06/04/2009 21:51:35 »
I was thinking that somewhere I read where scientists had preformed experiments that suggested that information was transferred from one location to another above light speed. For such an event to occur, a carrier of information surpassing c would have to exist. I seem to remember that this experiment involved quantum interactions. Not sure now where or when I read about this.................Ethos

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Offline RobotGymnast

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Re: What are tachyons?
« Reply #4 on: 06/04/2009 21:58:25 »
makes sense, but what about the idea that it's occurring at subluminal speeds through some sort of fold in space-time? I've heard that theory bandied about as well.
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Offline Vern

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Re: What are tachyons?
« Reply #5 on: 06/04/2009 22:07:30 »
It is entangled photons that seem to pass information at faster than light speeds. When the polarization of one of a pair of photons is changed, the other of the pair seems to instantly take on that polarization. I suspect that there's another mechanism at work, but don't have a clue about what it might be.

I don't think there's a theory that suggests that tachyons actually exist. There is a body of work that fits them into the Quantum Mechanical realm, but it only suggests that if they existed, they would have certain properties.

I think the closest we can come to observing them is in media such as water when an electron can exceed light speed in that medium. 

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Offline DoctorBeaver

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Re: What are tachyons?
« Reply #6 on: 06/04/2009 22:27:02 »
All theories that contain tachyons have been shown to be flawed. So, sorry Star Trek, you've been led up the wrong wormhole.

I believe tachyons first reared their ugly little heads in baryonic string theory and that theory was condemned to the shredder quite a while ago.
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Offline RobotGymnast

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Re: What are tachyons?
« Reply #7 on: 06/04/2009 22:40:39 »
Ah.. it just interested me because it came up in Watchmen, and I love arguing with their science; it's usually flawed or just plain wrong.
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Offline Mr. Scientist

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Re: What are tachyons?
« Reply #8 on: 09/04/2009 21:55:33 »
Can somebody explain tachyons to me? Wikipedia isn't exactly the best resource for things like this. I just don't understand how something can travel superluminally; isn't the speed of light supposed to be the maximum possible speed? I realize that tachyons are theoretical, I was just wondering if someone could explain it a bit to me.

Here, i will explain it. This is the best way i have been able to explain tachyons to friends and alike: (I apologize the math has tex tags on the sides of the equations)

Bradyonic Matter, Luxons and Tachyons

A Bradyon, also been known to be called as a Tardyon are particles with mass and a rest energy which concurrently never reach the speed of light. Because
they have what is called inertia and a gravitational mass (as shown by the Weak Equivalance Principle of General Relativity), it would reqire an infinite
amount of energy to accelerate, (let's say an electron) to accelerate to the speed of light. Since it would require more energy than what is visible in the
observable universe, this seems to be a ''barrier'' or a ''limit'' if you like in nature that can never be violated. The root word ''Brady'' means slow.

A Luxon is by classification, all particles of energy which have no inertial or gravitational mass, so they always move at light speed. This speed is roughly
186,350 miles per hour... which means this speed must remain constant in all inertial frames. The Bradyonic Matter can have speeds that vary however when
the speed of light is used to measure this. In this sense, we often think of the speed of light as a universal measuring stick.

A Tachyon is a hypothetical particle with a negative energy density. This negative energy allows them to move through spacetime with as little effort
or energy as possible.
 
The root word ''Tachy'' as in Tachcardia from fast heartbeat means -- obviously ''fast.'' Problems with the existence of tachyons do exist which makes their
existences questionable. A long time ago, there was a research group who proposed trying to generate & detect tachyons, which are not neutrinos.

It is alleged that particles traveling faster than light will generate Chernkov radiation, which is shifted as a color of blue.

Martin Gardiner wrote a Mathematical Games each month in Scientific American and is generally believed to be very knowledgable in physics. 

Doctor Gardiner showed that the equations relating to Tacyons predicted the following (among other properties).
As mentioned above tacyons would generate Cherenkov radiation in a vacuum. Adding energy to tacyons slowed them down with the velocity of light as
the lower bound. In fact, a tachyon would find an infinite amount of energy at this lower bound limit, much like a Bradyon would find an infinite amount of
energy at the limit of lightspeed. Another strange prediction was that tachyons lost energy if they could be sped up. Hence, the existence of tachyonic matter
and their supposed fields seems... unlikely, but they are not completely ruled out (1).

The facts of photon energy

What is the energy of the photon?

The energy of the photon is best said to be purely kinetic. Kinetic energy is derived from classical physics, where: [tex]E_k=\frac{1}{2}Mv^2[/tex].The key
equation to prove this is [tex]m^2c^4 = E^2 - p^2c^2[/tex], the contribution of [tex]mc^2[/tex] is called the rest energy, the stuff of rest matter, and all
other contributions to the energy are called kinetic energy. Since the photon has no rest energy, then the energy it can have must be a purely kinetical
energy.

A photon does not have any mass. It does contain however a non-zero momentum or as we often call it, a 4-momentum [tex]p^{\mu}[/tex] where [tex]p[/tex] is
for momentum, and for a photon it must be inforced to [tex]p=\frac{1}{2}\gamma Mv^2[/tex], as we shall soon see. The photon is said to move along what is
called a Null trajectory, [tex]p^{\mu}p_{\mu}=0[/tex], where in terms of its energy we have [tex]-E^2+|p|^2=0[/tex].For the given unit vector [tex]\hat{v}[/tex]
in the directionality of the motion of a photon (which is a unit of kinetic energy), we state that [tex]\rightarrow{p}=\hat{v}E[/tex], so the modulus of the
photon is given as [tex]|p|=E[/tex].

There has been some sensitive tests to experimentally-see whether the photon has a mass or not, and the lowest limit given is an absurd number of
[tex]10^{51}kg[/tex], but that should not be interpreted that the theory of photons work better with having a mass.

When calculating the energy of systems, we have an equation in relativity that provides a way to measure energy given as the famous [tex]E=Mc^2[/tex]. However
since in relativity we have the concept of an invariant mass, or a rest energy, we need to invoke the equation [tex]E=\gamma Mc^2[/tex], where the key
Greek symbol ''gamma'' [tex]\gamma[/tex] reduces the factor of [tex]M[/tex] to zero. So the mass is said to be zero in consequence. Gamma has a value of
[tex]\gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]. Another way to derive the idea that photons have no mass but do have a momentum is by concluding mathematically
the following.

the equation [tex]E=(Mc^2)^2+p^2c^2[/tex] should be taken into consideration. Deriving that formula, you remove the [tex](Mc^2)^2[/tex] part and you get:

[tex]E=\sqrt{(Mc^2)^2(1+\frac{p^2}{(Mc)^2})}=Mc^2 \sqrt{1+\frac{p^2}{(Mc)^2}[/tex]

thus taking the tailor expansion of the sqaure root gives us:

[tex]E=Mc^2(1+\frac{p^2}{2(Mc)^2}+...)[/tex]

so that [tex]E=Mc^2+\frac{p^2}{2M}+...[/tex]

which derives the relation (which is an approximation)

[tex]p \approx \frac{1}{2}Mv^2[/tex] where it must be approximated for low velocities. If we are talking in terms of relativitic speeds, then
[tex]p=\frac{1}{2} \gamma Mv^2[/tex].

The energy of photon and its momentum are related to its frequency and its wavelength. The usual expression is given as:

[tex]E=\hbar \omega=h \nu=\frac{hc}{\lambda}[/tex]


Notes



(1) - They have a rest mass M that also has an imaginary value [tex](M^2<0)[/tex]. It turns out that [tex](E=M_g)[/tex], the observable mass-energy of
these light weight particles, becomes ''real'' and ''positive''. If a particle was able to defy the light-speed barrier so that v was greater than
[tex]c[/tex], then both [tex]g[/tex] and [tex]E[/tex] would become imaginary quantities, because [tex]\beta[/tex] would be larger than [tex]1[/tex] and
[tex](1 - \beta^2)[/tex] would be negative.We can create neurtino's from the decay of tritium. The basic underlining rule is through the relativistic
relation between energy and momentum [tex]E^2 = P^2 + M^2[/tex]... and we work out that it is mass squared that works out the neutrino mass from tritium
decay... but this mass squared can be seen in light of either a positive reult or a negative result, and if it is a tachyon, containing a very light weight
 amount of imaginary matter of about [tex](i)(12 eV)[/tex], there is the big problem that nothing fuitful will arise out of this... because the theorists
do not believe. or cannot be sure if its qualities would be observable or known.
http://www.youtube.com/watch?v=SZGcNx8nV8U

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Offline RobotGymnast

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Re: What are tachyons?
« Reply #9 on: 10/04/2009 16:28:44 »
that was... complex and long, and I sort of got confused around the mathematical part, but I think I understood the gist of it.

It's starting to look like tachyons represent "negative" or "inverse" particles? Energy goes up, speed goes down, and vice-versa? I don't mean antimatter, I just mean they sort of appear... flipped from where I stand.

Thanks, that clarified a lot of it (including why they were ever conceived)
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Offline Democritus

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Re: What are tachyons?
« Reply #10 on: 13/04/2009 17:11:13 »
RobotGymnast
Congrats for exploring where many fear to tread.
Take nothing as gospel there.
Not me, not Mr Scientist (in error by a factor of 3,600 re luminals, surely a typo  [:)]), not anyone.
Tachyons...a notion before its time. If you wish, explore further... times might suit you. 
Best wishes
Democritus

   




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Offline RobotGymnast

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Re: What are tachyons?
« Reply #11 on: 13/04/2009 21:48:30 »
I think my head would start hurting too quickly if I research that; I'm sort if the process of learning quite a few other things, and most of my time is spent in a classroom (guess what we're learning in science? Cumulus means "heaped".. amazing, no?)
I'm 15. I live in Ontario, Canada.