Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Massless Strings?

  1. Nov 3, 2004 #1
    how is it that some strings have mass (spin 1/2 particles) while others have no mass at all (spin 2 particles and force carrying particles)? all strings are the same, its just how they move and vibrate that they change from particle to particle, but wouldnt this mean that all strings either have mass or dont?

    also, string theory is supposed to calm the quantum fluctuations at plank scales so that the standard model and GR mix. but wouldnt there not be any quantum fluctutions at that level because there arent any point particles? does this mean that virtual strings hitting each other release less energy than if they where point particles?
  2. jcsd
  3. Nov 3, 2004 #2


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Massive particles are thought to get their mass from the Higgs reaction, which happens at energies just a little higher than we can reach with our biggest current accelerators. The new LHC at CERN is expected to see the Higgs particle.

    String vibrations may underlie all of this, but it's wrong to think of particles as made of little strings. String theory says the particles we see are made of vibrations; vibrations of the strings.
  4. Nov 3, 2004 #3
    that doesnt make sense to me. if particles get their mass at an energy higher than we have reached (which has to be higher than the energy of a particle with mass) then how is it that the particles have mass unless they are constantly at the energy required for the higgs reaction(which we have yet to reach)? seeing as a string has a minimum length, shouldnt it also have a minimum mass (m > 0)?

    and how is it wrong to think of particles made of strings? the vibrations are what make the particle a particle, but the string is where these vibrations come from. therefore particles are made of strings. its like a=b and b=c so a=c where a is the particle, b is the vibration of the string, and c is the string itself.
  5. Nov 3, 2004 #4
    Not just interactions with just Higgs, but also virtual Higgs. A virtual particle can have a much lower mass. Just like the weak happens even in systems with much less energy than the mass of a Z or W boson.

  6. Nov 3, 2004 #5
    You want to check out Brain Greene's work, 2 books he has written
    The Elegant Universe - about 4-5 years old (very good elaboration on String and M-theroies
    The Fabric Of the Cosmos - only about 6 months old and includes the latest Unified theroies aswell the cosmological approch

    Brain Greene isn't in the text book business so everything covered in these books can easly be grasped by the Average person with a interest in the field
  7. Nov 4, 2004 #6
    i'm actually reading the elegant universe, and found the EXACT answer to the question i asked in chapter 10 lol. its when he goes over strings that are wrapped around a circular dimension and says that have mass. then he explains how unwrapped strings also have mass, but it cancels out or something lol. i have to look more into it for it to make more sense.
  8. Nov 4, 2004 #7
    i thought force carrying particles were messenger particles that are used in equasions. I'm therefore not sure that there is proof of them existing as a state of masslike matter. Please clear this up for me.
  9. Nov 4, 2004 #8
    casimir effect
  10. Nov 26, 2004 #9
    To me, string theory is string of assumptions. A solid theory is mainly based on known elements with one or two assumptions. These few assumptions are supposed to provide solution for the original question. Further work then has to be done to verify the dependability of original assumptions.
    Assesing the many assumptions in string theory is next to impossible. Also if we can take the liberty to assume whatever it takes in order to find an answer. finding solutions gets easy but unfortunately it will not be very reliable.
    If mathematics of string theory at times show some coherency, at best we can claim that it shows a part of the picture.
    I may be wrong . Please guide me,
  11. Nov 29, 2004 #10
    Mohsen, your right to wonder if we are on the right track. There is NO data saying its right ... yet. But there is also no data saying its really wrong either.

    What we need is some expermental proof. And its very possible that CERN or another larger atom smasher will find it. The math says they are too small to be seen yet.

    When i first heard the theory of strings i was hooked... It didnt take a second for me to acept it. In my mind it sounded soo true and beautiful it had to be right. Each note of the strings defining its state of existance.

    It has the power to bring cosmology and quantam mechanics together, the science of the very big and the very small. A quest all here know is one of our goals.
  12. Nov 29, 2004 #11
    I know what you mean. It does sound right and true, But we have to question everything even if it means putting aside our feelings for a while
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook