# Tachyon is said to travel faster than light

1. Jan 15, 2005

### DB

The tachyon is said to travel faster than light because it has a negative squared mass.

-How is it possible to have a negative squared mass? Is there alot more too it?

Thanks

2. Jan 15, 2005

### marlon

Yes there is much to it. the reason is coming from symmetry of the formula's used in field theory...

Click on https://www.physicsforums.com/journal.php?s=&journalid=13790&action=view [Broken] and scroll down to the text on tachyons. Let me know if you need additional info...PS :i suggest you also read the text on the Higgs-mass-acquiring system and the breakdown of symmetry, because they are all closely related.

regards
marlon

Last edited by a moderator: May 1, 2017
3. Jan 15, 2005

### dextercioby

1.So far there is no scientifical evidence of a tachyon.

2.Tachyons are theoretical predictions first obtained by Eugene Paul Wigner when he built the theory of the irreductible representations of the full Poincaré group.He rejected them,saying they contradict the theory from which he started,namely Special Relativity.

Daniel.

PS.Yeah,it's a lot more too it.Group theory is the core... Why do i always smile when thinking about "group theory"?? :tongue2:

4. Jan 15, 2005

### marlon

This is a bit over the top, wouldn't you say dexter. As usual this is info that will explain nothing to the original poster. Other then that IT IS WRONG. Tachyons and their "existence" ain't got nothing to do with that, where are you getting all these crack-pot-theories from ??? I suggest you start reading QFT and spontaneous breakdown of symmetry because that is the real and only answer to this question. Don't submerge us in this useless "posh"-sounding vocabularium of yours. Sometimes (and i don't wanna insult here), i really wonder if YOU actually know what you are talking about ??? :grumpy:

Err, maybe because it is your favourite subject...At least you make it seem like that. Let's not get into the knowledge of it though

As always, your best friend

Marlon

5. Jan 15, 2005

### DB

Thanks marlon, interesting stuff. But is the Higgs field considered the vaccum of space? Is it the distortion when a particle travels through a Higgs field that breaks the symmetry?

6. Jan 15, 2005

### marlon

Again i refer to the text i wrote on the Higgs-field, it is all in there. But to be concrete: The Higgsfield is a "trick" used in order to make sure that the groundstate is degenerate. So you need to see it as some copied version of the vaccuum (ie the groundstate). Keep in mind that in QFT the vaccuum is NOT really empty ; it is filled with virtual particles...

The breakdown of symmetry happens when some kind of transition-temperature is reached or when some order-parameter reaches a critical value. You know : like the transition to superconductivity if you will. The distortion of a particle moving through the Higgsfield causes the particle to be surrounded with more and more Higgs-particles. This new bunch of particles is seen as the original particle BUT with mass. This mass is expressed by the surrounding Higgs-particles. Basically you can see the mass as the coupling constant of the interaction between elementary particles and the Higgsfield.

regards
marlon

ps : read the text in my journal on Higgs-fields, here it is : https://www.physicsforums.com/journal.php?s=&action=view&journalid=13790&perpage=10&page=2 [Broken]

you will need to scroll down a bit, but it is the biggest text on this page, so you cannot miss

Last edited by a moderator: May 1, 2017
7. Jan 15, 2005

### dextercioby

Oh,Marlon,you're deadly wrong this time,boy... :tongue2: Than giving me obviuos advice,i think you'd better start reading a book on group theory,Poincaré group theory...Apparently this is not something you know about,which is really awkward and sad at the same time... Tachyonic representations are natural...The eigenvalue of $$\hat{P}^{2}$$ can take negative values as well as positive and zero...It can't take complex (imaginary that is),and i hope you know why...

Read first,Marlon,pull the trigger later...

This is the first thing one learns in QFT:fields,particles and do they come from.Spontaneuos symmetry breaking is among the last...

Daniel.

8. Jan 15, 2005

### marlon

Again wrong, check every book on QFT like Peskin or QFT in a Nutshell or whatever. Stop whinning about the Poincaré-group. What really matters are global and local summetries. U(1) and SU(2) and SU(3) (flavours and colours). You won't have to mention the word Poincaré once. So it is far from essential. Besides, the breakdown of symmetry IS one of the essential parts of QFT. The fact that you don't learn this in the beginning does not alter its importance...

marlon

Please, stop arguing for the sake of arguing and let's keep it on the tachyons.

9. Jan 15, 2005

### dextercioby

Do i feel sudden passing into defense??Let's take it logically:

You this is as possible to me as it is to you:IMPOSSIBLE...

Connecting with "every book",it doesn't make any sense to give examples,right??This is not physics,this is logics...

Bull****,i'm not "whinning"... :tongue2: I'm not an expert in QFT,but two examples will prove my point:
Conformal field theory (CFT) and Supersymmetric Field Theories (SUSY).Where did they come from???U(1),SU(2),SU(3),or SU(N) and its traceless matrices...???Or as natural extensions of the Poincaré group and its fields??

Of course,after making sure you know what you're talking about:fields and particles coming from (irreductible) representations of the (proper) Lorentz group and Poincaré group...

Of course,not once,but A MILLION TIMES UNTIL U DREAM ABOUT IT...

Bull****,it is essential,because it deals with the symmetries of the space-time your whole spontaneously breakable fields are embedded in...It's the fundamental symmetry.Everything is secondary...

I didn't say it was not essential,Marlon...It's essential,once u know what fields are,what they do and why they are important...

I'm arguing everytime u say something wrong...Didn't u get that??Do you think i like it??I hate it,but you give me no choice... :yuck:

Daniel.

10. Jan 15, 2005

### marlon

it is real easy, just take one of the books you have on QFT and look at the content table. There is nothing impossible to it.

Please, try to stay polite. Don't be so insulted everytime you get corrected.

:surprised They have nothing to do with this. Don't dragg in extra posh-sounding-terms just to make a point. Again i say to you : stick to the tachyons and in this context i ask you : HOW DO THEY ARISE IN QFT. Explain in easy language with no difficult terms in it. If somebody is asking about this he won't be helped with your first post. That is my point, and the fact that it is WRONG.

The system is as follows : take a Lagrangian, check its global symmetry and then impose this global symmetry as a LOCAL symmetry. Due to the global symmetry, you will have a conserved quantity (theorem of Noether) that governs (well the corresponding conservation law) interactions between the fields arising from the local symmetry and the matter-fields. The given symmetry-groups therefore arise from local symmetries. That is what it is...That is the clue, that you don't seem to get.

Check out my journal for more info...

What ??? What is the fundamental symmetry ???
depending on what field theory you are working with, the global symmetry differs. So this concept of "fundamental" symmetry is even not possible. Really man ???
What are you saying here ???

Please try to be more specific and be a little bit more mature...You are not perfect dexter, nobody is...

marlon

Last edited: Jan 15, 2005
11. Jan 15, 2005

### dextercioby

I'll be back in about 2 hours...I still think i'm right...Tachyons appear at the very beginning of studying QFT.In the study of particles,seen quanta of the fields...

Daniel.

EDIT:I know i'm not perfect.From time to time I'M JUST RIGHT...This is one of those rare ( :tongue2: ) moments...

12. Jan 15, 2005

### marlon

Ofcourse they do. And particles are always quanta of fields. This is common knowledge. this was not what we were talking about...

marlon

13. Jan 15, 2005

### marlon

you are right about what ??? What is your point ???

marlon

14. Jan 15, 2005

### marlon

The Poicaré-group is the ten-parameter-group that is composed out of Lorentz-transformations (6 parameters to describe them) and the four-parameter space-time-translations. this symmetry needs to be respected at all times in both classical and quantum field theories because is corresponds to the special relativity part of QFT. So they can never be broken because it would yield a result that is not compatible with QFT. This is the part where you are wrong. Tachyons are not-physical but that does not mean they are not inherent to QFT. They are !!!! this is a classical misconception that you made. There are several ways of eliminating non-physical degrees of freedom in QFT like the Gupta Bleuler theory, spontaneous breakdown of symmetry, Fadeev Poppov gohst particles and cutt-off renormalization techniques.

The symmetries at hand here are NOT inherent to the Poincaré-group. They define the field theory at hand. This is where you are wrong. For example : the local SU(2)-symmetry is totally different in nature and it is this symmetry that ,when broken, yields that mass of the intermediate vector bosons that mediate the weak interactions...This is the picture of QFT, nothing else

marlon

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