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What are strings?

  1. Jun 16, 2004 #1
    how do strings exist in our reality?

    Let's just say, for the purposes of this argument, that a string was broken and stretched until it was perfectly straight (i understand this could never actually happen). That filament, then. Would it exist in one, two, or three dimensions?
  2. jcsd
  3. Jun 17, 2004 #2

    how do strings exist in our reality?

    Let's just say, for the purposes of this argument, that a string was broken and stretched until it was perfectly straight (i understand this could never actually happen). That filament, then. Would it exist in one, two, or three dimensions?

    I am new to the world of Strings... but maybe if I reply someone can reply to my reply.. and through a series of replies we can both learn a little something.

    First it seems that we are dealing with two different aspects of string theory. Firstly if you have a string that is closed looped it is what is known as a Type II string. The first Type of string proposed by Green and Schwarz came about in 1980 and imposed supersymmetry on string theory aka "Superstrings." But this wasn't as good of a theory as the Type II theory which was TRUELY supersymmetric because it accounted for bosons (force particles e.g. photons) AND fermions (elementary particles like electrons)... it also didn't end up having infinities.
    So to move more towards the direction of your question. It is my understanding that the closed loop idea had come about because peeps were asking what would happen if the endpoints of a string could join each other and meet. They hypothesized that strings could break apart and join each other and what not.. but they thought this was only possible because one string could recognize another string due to its endpoints... infact it was said that the end points of the strings were the only part of the string that contained mass.. so if there were no endpoints.. the closed loop picture must be empty space.
    Now if I haven't lost you yet I'll try and clear up where my point is... Superstrings create their own interactions... If it wants to split it can.. if it wants to join up it can... this means that it doesn't have to follow rules from point particle theories which put pressure on the dimensionality of the system in which a string exists. The string itself does that. It seems to me that the important factor isn't so much the dimensionality as it is the topology. There are various versions of strings but what I gain from your question is your interest in Type I and Type II strings and what dimension the strings are themselves. Brian Greene (The Elegant Universe) explained that strings are one-dimensional objects that vibrate to a certain harmonic. Now, what is more amazing (to me) than the actual demensionality of strings is their power. (Here is where topology comes back) If you think about a golf ball and relate that to a string and you say to yourself that this golf ball can bend any way you want.. you'll notice that you can make it into a cube, or a flat sheet... but what else can be done.. well if you make it into a flat sheet and then role the sheet up.. you can go from one topology to another.. you can enter a world with zero holes to one that has one.. from there maybe you could mold it into a doughnut or a drinking glass.

    I would think that the broken string (filament as you say) exists in one dimension.. but there is also the element of time.. which might extend it into the 2nd demension.

    Phew --I hope that helped.

  4. Jun 20, 2004 #3
    What is a string?

    In the early 1900's, much earlier than 1980, there was a major argument between Quantum Theory and Relativity because when distances between points approach 0 distance, QT numbers didn't work. For example, gravity increases as it gets closer to an object. Theoretically, gravity would be infinite when two objects occupy the same place.

    Gravity involves large objects, which can't occupy the same place. If our feet are touching the earth we are a large distance from the center of the earth, so the theory that describes gravity works. The material that generates gravity occupies space, so two pieces of material can't have 0 distance between their centers. The idea of gravity increasing to infinity can't happen.

    At the the much shorter distances of point-particles, certain equations can increase to absurd quantities. Particles CAN approach 0 distance, because of how we define particles. So, two particles can occupy almost the same place. They can get close enough to each other to make the numbers absurd. For example, two particles touching each other would have a nearly infinite gravitational attraction. But they don't, so there is a real problem with theories that work over large distances but don't work over small distances.

    To resolve the issue, someone a long time ago (Kaluza-Klien?) introduced the idea that point particles are really short strings. They were only describing them as strings in their role as points on a line.

    Instead of points they were short lines, or "strings".

    If you use dashes to represent points ------------- you can see how those dashes can only be so close to each other. Making points into short strings solves a lot of mathematical and physical problems.

    But the strange addition is, when points became strings, 6 more spatial dimensions are created in the math.

    But if the points on a line are strings instead of non-dimensional points, there is always enough distance between points so the numbers that are produced by the theories can't become absurd.

    An abundance of mysteries happen because there really is a minimum physical distance between point particles in the real universe. So we get physical data that proves string theory correct, while adding other things that are as odd as 6 extra dimensions. Going by what we observe, we see things that are as strange and outrageous as the 6 extra dimensions the original math told us had to be true if points were strings.

    A string is a two-dimensional thing that exists, and has the tension of the strong force, increasing with the length of the string. It is like a rubber band. We have always believed nothing can exist in the physical world as a two-dimensional object. But a string really exists, and it really occupies space. It really exerts physical force, and it really only has two dimensions.

    To figure out what a string is, then be able to do something with it, we have to find the third dimension of the string, which appears to be two-dimensional.
  5. Jun 20, 2004 #4
    Thanks man

    John... you've cleared up some questions that I've had... Thanks man!

    Is the 2nd dimension that of time when it comes to strings??? I can see why people have resisted the idea of having 2 dimensional objects... it sure would make it tough to eat :)
  6. Jun 22, 2004 #5
    I was of the impression that string theory deals with one-dimensional strings, whereas M-theory try to generalise that into branes, where a brane can be 0 to N dimensional with the total amount of dimensions in the universe being N+1 (time is the last). Am I wrong?

    Strings can break or "make", but there is a length at which the energy of the string is minimal. That length is the planck length. That's because the energy stems from two contributions: vibrational and rotational.

    What I don't know is the number of dimensions are possible. I know that 10 and 11 dimensions are the ones considered the most, but I remember reading 26 as a possibility as well as close to 500. From what I understand it has to do with the consistency of the theory that limits the possible dimensions. Anybody have a definite answer to that?
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