# String Theory, M-Theory, whatever

• Compaq

#### Compaq

Does these strings have mass?

So, everything's made of these strings. Obviously, dark matter would also be made of strings, vibrating to give them certain properties? What makes them vibrate?

Are photons made of strings? If strings have mass, then the mass can't just vanish, if photons are strings..

Could strings vibrate a certain way to be energy? I kow there's a connection between energy and mass, but does energy have mass?

I know, lousy questions. It's just that I'm wondering.

## Answers and Replies

Yes, strings have mass, but the amount depends on the way the string is vibrating. This also answers you second question: the type of vibrations determines what type of particle the string corresponds to. In turn, there is a vibriational mode which corresponds to the photon. This vibrational mode does not carry any mass - just like the photon.

Yes, strings have mass, but the amount depends on the way the string is vibrating. This also answers you second question: the type of vibrations determines what type of particle the string corresponds to. In turn, there is a vibriational mode which corresponds to the photon. This vibrational mode does not carry any mass - just like the photon.

This is interesting, can you maybe elaborate a little on the way in which the vibrational mode determines mass?

Also (if this question makes sense) in these cases does the string actually "have mass"? Or would it be more correct to say that the vibrational energy of the vibrating string is equivalent to a certain amount of mass?

So, everything's made of these strings. Obviously, dark matter would also be made of strings, vibrating to give them certain properties? What makes them vibrate?

It's possible, but NOT obvious. Not likely in my layman's opiion. Dark matter appears unique in that it's the only matter that does not reflect light...and nobody knows what it is. Dark energy consitutes about 70% of the universe, dark mass about 26% and all common matter (neutrons,protons,electons,etc) only 4%...we know little about 96% of the universe! A guess is that when we figure out dark matter and dark energy we'll have new insights into what constitutes "common" matter.

Quantum jitters (energy) are reflected in overall of string vibration energy...yet quantum jitters of strings alone reflect negative energy!...for the graviton, the energy cancellation between quantum jitters and string vibration energy is perfect...hence a zero mass gravitational like particle emerges.

Are photons made of strings? If strings have mass, then the mass can't just vanish, if photons are strings..

Some strings appear as gravitons, other as photons. Some are bosons (matter particles) some fermions (force particles)...but string theory is incomplete and largely unproven experimentally while it has offered significant insights...in a sense mass CAN vanish becauseit's a reflection of energy and quantum energy can offset string vibrational energy. In field theories, photons are waves (fields); in quantum theory photons are quanta (particles);in string theory, they are vibrating strings...one dimensional bits of energy. Take your pick!

Could strings vibrate a certain way to be energy? I kow there's a connection between energy and mass, but does energy have mass?

yes, energy is equivalent to mass...as formulated by Einstein...His stress energy tensor reflects gravity resulting from mass,energy,stress...in string theory, gravitons and photons, for example, have energy but no mass in accordance with the standard model of particle physics. Higher modes of energy vibrations resuls in higher mass particles.

You can try Brian Greene's books (Fabric of the Cosmos, The Elegant Universe) or Lee Smolin's The Trouble with Physics for good discussions of all this...available in paperback...

Or would it be more correct to say that the vibrational energy of the vibrating string is equivalent to a certain amount of mass?

I like that better.

Those interested can find a discussion of string theory in Wikipedia at...
http://en.wikipedia.org/wiki/String_theory

It jumps right into rather advanced concepts at points, typical of Wikipedia, but you can get a basic idea of some of the ideas used...Greene and Smolin have clearer explanations in my opinion along with interesting insights...

Also I posted a brief discussion thread about how space time might emerge from string theory here in physics forums: