Tachyon?????

[webboffin]

Could someone please explain to me what exactly is a tachyon?

All I know that it can travel faster than light and thus possibly go backwards in time - if such a thing exists.

 

[Joe_Sixpack]

A tachyon is a theoretical particle that has the speed of light as its minimum speed. This, of course, causes some interesting mathematical conclusions about it - its mass would be imaginary (i.e. the square root of a negative number) and it would be constantly traveling backwards through time.

Don't sweat too much about it - even if they did exist they would like be inherently undetectable. Further there is no evidence that they do actually exist - just a neat way of showing how the math of Special Relativity would react to a faster than light particle.

 

[webboffin]

Thanks Joe Sixpack I couldn't find much on the web about it.

I would doubt there existance in a common sense world because if they are travelling backwards in time then they must of began when the universe was at an end (which has not happened yet) if they do exist then maybe the big crunch or whatever means of universal death created them first. Either way it is interesting.

 

[Joe_Sixpack]

"I would doubt there existance in a common sense world because if they are travelling backwards in time then they must of began when the universe was at an end (which has not happened yet) if they do exist then maybe the big crunch or whatever means of universal death created them first. Either way it is interesting."

Actually under Hawking style Boundraryless Universe model, this wouldn't be a problem at all. Backwards or forwards through time would be just symmetrical.

 

[Late_Cretaceous]

The tachyon was the result of early attempts to find a "grand unified thoery". It was really a mathematical byproduct that demonstrated that there were serious flaws in the model. Currently, h supersting theory (and M-theories) adds different spatial dimentions to the universe thus elimiating the tachyon.

 

[lucaspa]

Today at 02:25 PM Late_Cretaceous said this in Post #5

The tachyon was the result of early attempts to find a "grand unified thoery". It was really a mathematical byproduct that demonstrated that there were serious flaws in the model. Currently, h supersting theory (and M-theories) adds different spatial dimentions to the universe thus elimiating the tachyon.

The tachyon is a theoretical particle allowed by Special Relativity.  Light speed in a vacuum is a barrier.  While particles are forbidden to travel faster than the speed of light, the math also allows for particles that can only travel faster than lightspeed and can never travel slower than lightspeed.  It has nothing to do with grand unified theory.

Since Special Relativity seems unassailable, M-theories must incorporate Special Relativity and be consistent with it. Therefore I'd like more information and specifics that these have "eliminated" the tachyon.

 

[lucaspa]

Yesterday at 08:48 PM webboffin said this in Post #1

Could someone please explain to me what exactly is a tachyon?

All I know that it can travel faster than light and thus possibly go backwards in time - if such a thing exists.

http://scienceworld.wolfram.com/physics/Tachyon.html

Notice the last paragraph.

"1.  Tachyons:  can we rule them out.

The special theory of relativity has been tested to unprecedented accuracy, and appears unassailable.  Yet tachyons are a problem.  Though they are allowed by the theory, they bring with them all sorts of unpalatable properties.  Physicists would like to rule them out once and for all, but lack a convincing nonexistence proof.  Until they construct one, we cannot be sure that a tachyon won't sudently be discovered."  Paul Davies, About Time, 1994.

 

[Late_Cretaceous]

An exerpt from "The Illustrated Enclopedia of the Universe" 2001 on Superstring Theory:

"It turns out that with ths change [particles being strings instead of point-like objects], the force of gravity can be unified with the other three forces. In other words, string theory shows a way of resolving the incompatibility problem between quantum mechanics and general relativity.

The original version of string theory was discovered in 1968 by Gabriele Veneziano (b.1942). However, his theory suffered from a number of problems, such as its prediction of faster-then-light particles (called tachyons), something physicists could not accept. Then, with the discovery of supersymmertry, a new version of string theroy emerged in the mid-1980s, which did not suffer from the problems of Veneziano's theory."

You are right to say that tachyons themselves have not been eliminated (afterall, how can one prove that something does not exist). However, it seems that the case for the existance of tachyons is still hypothetical. Contrast this to the case of the Higgs particle which have been observed at CERN.

 

[lucaspa]

Today at 03:52 PM Late_Cretaceous said this in Post #8

An exerpt from "The Illustrated Enclopedia of the Universe" 2001 on Superstring Theory:

"It turns out that with ths change [particles being strings instead of point-like objects], the force of gravity can be unified with the other three forces. In other words, string theory shows a way of resolving the incompatibility problem between quantum mechanics and general relativity.

The original version of string theory was discovered in 1968 by Gabriele Veneziano (b.1942). However, his theory suffered from a number of problems, such as its prediction of faster-then-light particles (called tachyons), something physicists could not accept. Then, with the discovery of supersymmertry, a new version of string theroy emerged in the mid-1980s, which did not suffer from the problems of Veneziano's theory."

You are right to say that tachyons themselves have not been eliminated (afterall, how can one prove that something does not exist). However, it seems that the case for the existance of tachyons is still hypothetical. Contrast this to the case of the Higgs particle which have been observed at CERN.

You can prove that entities don't exist. It's called falsification.  After all, it is proved that a worldwide Flood doesn't exist.

Now, the quote shows bad science, not refutation of tachyons.  Scientists will accept what the data shows, whether they want to or not.  Tachyons cause all kinds of problems, and physicists would prefer that they don't exist.  But what we would prefer has no bearing on what actually exists.

So, what the quote says is that newer versions of string theory don't have tachyons (although I need to check that out more; this is the first I've seen that).  The problem here is that string theory itself has never been tested; so we don't know if it is correct.

The only "test" of string theory so far has been that it is consistent with the knowledge we already have. But since the two theories of Relativity and QM also account for everything we see, that doesn't say much.  What string theory does is provide unity. But unity is a basic assumption about the universe, not a proven quantity.

Yes, we haven't detected tachyons, altho one experiment says they may have.  However, that is not the same as refutation. See the Davies quote in post #7.

 

[Quath]

Today at 12:52 PM Late_Cretaceous said this in Post #8 
Contrast this to the case of the Higgs particle which have been observed at CERN.

I don't think that the Higgs particle has been found.  I would be glad to find out that it has been.  If it has, can you give me a reference?

Scott (Quath)

 

[Quath]

I remember I talked to a physicist about tachyons. He said if you were to go faster than the speed of light your distance and time axis switch. So tachyons could go forward or backward in time. We go forward or backward in their time by chosing left or right. Of course, it is just playing with equations without knowing something more fundamental to explain if they should exist.

Scott (Quath)

 

[webboffin]

Wow, this shows the complexity of the situation.
I was thinking when something is travelling at near speed of light and eccelerating to light speed and it also has a mass then that means the mass of whatever it is will also be increasing to point infinty [yeah I know about needing infinate energy too]. What is infinate mass, would it's gravity also be infinate?

 

[Jutsuka]

Today at 06:45 AM webboffin said this in Post #12

Wow, this shows the complexity of the situation.
I was thinking when something is travelling at near speed of light and eccelerating to light speed and it also has a mass then that means the mass of whatever it is will also be increasing to point infinty [yeah I know about needing infinate energy too]. What is infinate mass, would it's gravity also be infinate?

Any normal matter cannot accelerate to c (speed of light) because the mass of that matter would become infinite wich would then need an infinite amount energy to reach c.

Any mass that becomes infinite will usually collapse and form a singularity with infinite gravity also called a "black hole".

 

[fragmentsofdreams]

Tachyon's are an example of times when mathematical phenomena are difficult to interpret. Until we observe something or develop a new theory that survives falsification, we have little ability to figure out whether tachyons are ruled out by Nature as well as their exact properties.

 

[Late_Cretaceous]

Scott, it is actually on the same page as the reference i cited for Lucaspa. Accordingly, the Higgs particle was detected at CERN in 2000.

As far as tachyons go, it seems even they are still very hypothetical (but possible).  I remeber reading something about tachyons ponentially having "negative mass" - has anyone else come across that?.

 

[MartinM]

Today at 03:36 PM Late_Cretaceous said this in Post #15 As far as tachyons go, it seems even they are still very hypothetical (but possible).  I remeber reading something about tachyons ponentially having "negative mass" - has anyone else come across that?.

Not negative, imaginary. Recall that the relativistic equation for the energy of a free particle is

E = gamma*m

where gamma = sqrt(1 - v^2), and m is the rest mass of the particle.

For tachyons, v^2 > 1 and so gamma is imaginary. Since E is an observable quantity and must be real, this requires that the rest mass must also be imaginary. This is not a huge problem, since tachyons can never slow down to sublight speeds, let alone be found at rest.

 

[lucaspa]

Today at 09:21 AM fragmentsofdreams said this in Post #14

Tachyon's are an example of times when mathematical phenomena are difficult to interpret. Until we observe something or develop a new theory that survives falsification, we have little ability to figure out whether tachyons are ruled out by Nature as well as their exact properties.

Pretty much. Tachyons are allowed by Special Relativity.  That doesn't mean they exist or don't exist.  Only that, if Special Relativity is correct (and it seems to be), then tachyons are possible.  We can't say they are impossible unless and until we can falsify them. Or, as Davies says, construct " a convincing nonexistence proof".

Notice that tachyons asnd deity are a lot alike in science: unobservable with current methods, a pain in the rear end, but possible and allowed.

 

[Quath]

Today at 07:36 AM Late_Cretaceous said this in Post #15

Scott, it is actually on the same page as the reference i cited for Lucaspa. Accordingly, the Higgs particle was detected at CERN in 2000.

One of my co-workers worked at CERN in 1995 looking for the Higgs.  I asked him about it.  He showed me this webpage: http://jupiterscientific.org/sciinfo/higgsupdate.html.  Basically, they have some 2 standard deviation events.  However, they need 5 standard deviations for it to fit the criteria to be a discovery.  He said it is quite easy to discover anything in all the data that was generated.  Sometimes electronic noise would interfere or some cosmic rays would mess up some samples.  Also data at the extreme ranges they were looking at were still in highly uncertain areas of knowledge.  So basically, the Higgs is still undiscovered, but it looks promising.

Scott (Quath)

 

[webboffin]

what is imaginary mass? How can a mass be imaginary isn't that like pretend mass? Doesn't make sense to me.

 

[Quath]

Imaginary mass only has "real" meaning if it is multiplied by another imaginary number. You can treat time as if it were a regular dimension like height, length or depth but with imaginary units instead of real units. But to see the "real" value of time, you need to square it (which gives a negative number).

Imaginary numbers in physics are more of a mathematical tool. However, so are negative numbers, fractions, and irrational numbers. So imaginary mass is just a tool to let us know that gravity and inertia would be extremely odd to deal with with tachyons.

Scott (Quath)