# Are the stings in string theory, considered to be matter?

1. Feb 3, 2009

### redhedkangaro

Are the stings in string theory, considered to be matter?
Are the fundamental particles of the universe cnsidered to be matter?

2. Feb 3, 2009

### Nick89

Re: Matter

I think anything with mass is considered matter. So I suppose yes, that includes fundamental particles (except massless once such as photons (are they fundamental? no idea)).

No idea about strings, but I think strings are just considered energy.

3. Feb 3, 2009

### malawi_glenn

Re: Matter

matter is excitation modes of the strings.

The elementary particles are indeed considered as matter, even the massless entity called the photon. But matter is not a well defined subject as long as I understand it usage, it is according to me not a fundamental concept.

4. Feb 3, 2009

### redhedkangaro

Re: Matter

So matter and energy are diiferent or are they essentially one?

5. Feb 3, 2009

### malawi_glenn

Re: Matter

I don't think one should use the word "matter" since it is ambiguous - it depends on who you ask what matter is. A particle physicist (like me) would call photons (light) matter, but maybe not a atomic physicist - it is not a fundamental concept, it has no clear definition.

Mass and energy are the same thing, we had long such discussions like a month ago, would be good if you could find those old threads by using the "Search" function. We also had a discussion on what "pure energy" is, if you had the intentions to ask about it too.

6. Feb 3, 2009

### enotstrebor

Re: Matter

Matter has mass (see http://en.wikipedia.org/wiki/Matter), but maybe it is different in your circle of friends.

However, energy and mass are not the same thing!

The photon has energy but no mass. A massed particle has energy but has massed properties which are different than photon properties. Mass can travel at any velocity less than "c" and requires energy to change its velocity, while the photon only wants to travel at "c''.

As massed energy and photon energy behave differently, energy and mass can not be the same thing.

E=mc^2 says that there is a relationship between the two not that they are the same.

7. Feb 3, 2009

### e3bm35

Re: Matter

Greetings! I'm new to this forum and I'm truly impressed with the quality of the discussions.
I especially enjoyed this thread. So the fine folks at Discovery had a contest for the best video explaining string theory in two minutes or less. I thought the winner (String Ducky) was decent. The contenders were pretty good as well.
String Ducky

Last edited: Feb 4, 2009
8. Feb 4, 2009

### malawi_glenn

Re: Matter

There are several definitions of matter in that wiki article. Also think of this, a container with photon gas will have mass and a volume -> will one call the gas matter, and the constituients "non - matter" ? One has probably the same problem with the dark matter, we don't know what it is made up of - why do we call it matter then? Well it has mass and volume one might say, but that has the photon container also..

So, again to answer OP's question if the fundamental particles are considered as matter, it depends on what definition of matter you employ. The definition "everything that an atom is made out of" then only electrons, protons and neutrons are that for sure. But protons and neutrons are not fundamental particles, they are made up by three valence quarks each, and an "energy soup" of virtual quark- anti quark pairs and gluons (but virtual particles don't exists). Hence neutrinos, tau lepton, muon, photon etc, does not made up atoms are and are then not called 'matter' if one employs that definition.

Now energy, work in the units where c = 1, E = m .. got ya! (I work with them all the time..) What the equation tell you is the relation between mass and energy, energy can not be created nor be destroyed, it can only transfer between different KIDS of energy. Mass is one form of energy, angular frequency of electric and magnetic field waves propagating at the speed of light ($$E = \hbar \omega$$ or, working in units of $$\hbar = 1, E = \omega$$). The c and hbar are just conversion factors in the SI system, but such constants are just a choice of gauge - physics is independent of such choices.

So what if 'massed' energy and 'photon' energy behaves differently, all forms of energy behaves differently in some way. What you have shown is just that an electron and a photon have different kinematical properties due to their rest mass. Nothing more.

I could impose that argument in a reverse order. "Now since photon energy behaves different that mass energy, photons can't be energy."

Late edit: Why u think one calls the equation E = mc^2 "mass–energy equivalence formula" ?

Last edited: Feb 4, 2009
9. Feb 4, 2009

### Naty1

Re: Matter

yes, no, in the order asked.

The fundamental entities in string theory are strings, sometime multidimensional: one mode set of vibrations give rise to mass, another basic mode gives rise to energy, another to gravity, yet another is space...space would appear as, say, two dimensional branes and higher....evolving to Penrose spin networks in one formulation.....a more energetic string in the right vibrational mode is heavier (more massive) than another similar mode with lesser energy.

10. Feb 4, 2009

### per.sundqvist

Re: Matter

To make a very simple answer of this: You are confusing the rest mass m0 with the total mass m. The more general version of E=mc^2 reads.

$$mc^2\equiv E=\sqrt{(pc)^2+(m_0c^2)^2}$$

where m is the definition of the total mass in terms of E (the equation you wrote actually). So if m0=0 (for the photon) you get: m=p/c, where p, the momentum is given from the de Broglie relation $$p=h/\lambda$$. Hence, the photon has BOTH mass and energy, by postulate (the equivalence principle $$E=m_{tot}c^2$$).

11. Feb 5, 2009

### lightarrow

Re: Matter

No, the photon has energy but no mass. If you don't believe it, you can have a look at the Particle Data Group informations:
http://pdg.lbl.gov/2008/listings/s000.pdf

12. Feb 5, 2009

### Dmitry67

Re: Matter

no invariant mass - but it has a relativistic mass

13. Feb 6, 2009

### lightarrow

Re: Matter

Yes, I had understood what he intended .
Just a little consideration: if a photon of energy 511 KeV collides head-on with a still electron, since it has the relativistic mass = electron's mass, should it stop moving and give the electron all of its energy? No. Why this doesn't happen? Because relativistic mass concept is useful for nothing. Also, since relativistic mass has already a name: energy (divided by c^2), why do you want to give it another name?

14. Feb 6, 2009

### malawi_glenn

Re: Matter

what we are trying to demonstrate is that mass and energy is the same thing, that there are no such thing as 'pure energy'

15. Feb 6, 2009

### Dmitry67

Re: Matter

Yes, I agree with you, however, it leads toone misconseption we had recently discoered on this forum.

People got used that mass is a gravitational 'charge' and it works as a source of gravity.
Then people read that photons 'do not have mass' and they conclude that, for example, if matter annihilates with anitmatter and it is transformed into light the gravity suddenly dissapears.

16. Feb 6, 2009

### malawi_glenn

Re: Matter

17. Feb 6, 2009

### lightarrow

Re: Matter

I don't know what you intended with "pure energy", however a single photon has energy but not mass.

18. Feb 6, 2009

### lightarrow

Re: Matter

So you are not talking about "mass" in general, but specifically about "relativistic" mass.

19. Feb 6, 2009

### malawi_glenn

Re: Matter

Energy must be bound to something, no thing as "pure energy" circles around in space. "Matter turns into energy" is a misconception.

20. Feb 6, 2009

### Dmitry67

Re: Matter

BTW, does the 'rest'/'invariant' mass have any sense at all ?
- knowing that it is just an illusion, a result or how strongly massless particles (electrons, quarks, ...) interact with the Higgs field? :)