1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Anyone want to explain a few things?

  1. Nov 27, 2005 #1
    Hey everyone, i'm brand new to these forums, and have just started getting into the string theory. I was wondering if anyone knew a good elementary site about the string theory, for someone who is just learning about it. If anyone knows a good site, or has the time to explain the basis of it, I would be much obliged :!!)

    Thank you,
  2. jcsd
  3. Nov 27, 2005 #2


    User Avatar
    Gold Member

    What level of physics and math are you currently at?
  4. Nov 27, 2005 #3
    Well, technically speaking I'm at Grade 12 Physics and Grade 12 Math. However, I'm far above the rest of my class, and probably my teacher who doesn't know a thing about what he's trying to teach...

    I've read a few books, including Einstein's Theory of Relativity, but i'm not as far advanced as most of you guys on here :) Our Textbook in class talks about the String Theory briefly, but in no great detail. When I asked my teacher if he knew anything about it, he just said he was never taught anything about sub-atomic particles, or anything to that degree. I've also read a few websites that talk about it, but in such a large amount of detail, I can't really follow it, so I was just wondering if there is a "String Theory for Dummies" out there, or a beginners guide to it.

    Also, if you know the answer to this question, which has been frustrating. Inelastic and Elastic collisions, would atoms colliding be Elastic or Inelastic. Our text and teacher says they are Elastic, but if so, how come matter can lose energy to its surroundings just by sitting there. How else could heat be created if not through the collisions of the atoms?

    Thank you,
  5. Nov 28, 2005 #4
    Andrew, you may find useful information about string theory at superstringtheory.com. Try google.

    I am sure your book has explained that there are two mechanisms of heat transfer. One is conduction, the other is radiation. Mass which is isolated from other matter can lose heat by radiating energy, even into a perfect vacuum, if there were such a thing.

    I am glad for you that you are interested in physics, and I hope you will find the answers to the questions you have posed. Meanwhile, perhaps you will take a small advice. Listen to your teachers, who are trying to give you the basis for understanding. There will be time to go beyond them when you have mastered what they do have to offer you.

    Good luck to you. I hope you find some humility before it comes looking for you.


    Post Script:

    About your last question, having to do with heat and atoms. Atoms are very small, so small that only the very best microscopes, using electrons instead of light, are able to get an image of them. But they are not the smallest thing we know about. Atoms are made of much smaller particles, electrons, neutrons, and protons, mainly. There is rather strong evidence, most or maybe all of it indirect, that the protons and neutrons are also made of still smaller particles, called quarks. Each of these particles has the property we call mass, which will be more familiar to you as weight.

    You will remember that Albert Einstein popularized the idea that mass is the same thing as energy. These smaller particles have mass, and so they have energy. We can extract some of the energy by means of nuclear reactions, which take place at far smaller scales than the atomic processes of chemistry, which you usually associate with heat. Heat is in fact a form of energy. So you should be able to see that heat occurs not only on the stove top, where you can see it, but also at the atomic level, which is where elastic collision processes come in.

    Probably you have been taught that heat energy, such as we see in chemistry, is a matter of elastic collisions between atoms. Now I hope you also see that there is more. Heat is a form of energy. Mass is a form of energy. Since sub-atomic particles have mass, they also have energy, which can be expressed in terms of heat. In fact, we can and do think about heat where there is no atom, no particle, no mass at all.

    Perhaps, since you live in a cold climate, you are familiar with the heat that comes off of hot metallic surfaces, such as hot plates used in cooking, or the iron surface of a wood stove, or perhaps the hot coils of a radiant electric heater. You can feel this heat from some distance. The heat is not carried by particles that collide with your skin, it is carried by electromagnetic radiation, an energy very close in nature to light. This heat does not involve collisions of any kind.

    You may have heard of Cosmic Microwave Background radiation. This is a heat that occurs everywhere at a temperature very close to absolute zero. It is made of the same kind of microwaves you find in a microwave oven. Cosmologists, who study the origins of the universe, think that the CMB is evidence of the original process, often called the big bang, that created the stars and planets and all the dust we are made of. Cosmologists believe that this energy comes from a time BEFORE there were atoms.

    I hope you see now that heat does not only come from elastic collisions between atoms. In fact, this whole discussion has carried you far away from the point your teacher was trying to give you. Perhaps you have already got it and moved on. The idea you need to carry away from this discussion is that atoms are not hard little balls of something, but are made of something smaller. It took humans thousands of years of hard thinking and experimentation to come to this conclusion, which you are being handed as if it were a nickle.

    I recommend that this discussion be moved elsewhere, since it has little to do with the details being considered on this board.

    Again, Andrew Johnson, good luck to you.

    Last edited: Nov 29, 2005
  6. Nov 30, 2005 #5
    Well, I thank you for your reply, and I read it all. ( didn't move on :) )

    Anyways, about my teacher, I don't think you quite comprehend the situation i'm in. He was an English teacher, with a minor in chemistry. Physic's teacher retired, so somehow he got the job. Hes the only physic's teacher in the school, therefore i've had him for Grade 11 and 12. He's been teaching the same course for 3 years now, and yet, he cannot add vectors. Infact, I was the one who showed him how to (properly) add vectors when dealing with Kinematic equations. I don't mean to sound "full of myself" but he really has no clue what physics is about, besides what the text says.

    Also, thank you for clearing up the heat radiation and answering my question. And by the way, I know all about the basis and most the of sub-atomic particles, and know what mass is. Mass and weight are two different things, weight is relative to the force of gravity that your experiencing.

    Thank you for your response,
    Last edited: Nov 30, 2005
  7. Dec 1, 2005 #6
    Hi Andrew

    I think your situation is not unusual. I don't know your teacher and can't comment on his education. I tried to teach science in a middle school and heard plenty from students who didn't listen to lectures, didn't do the reading assignments, refused to participate in class, didn't do the homework, complained there was too much homework, complained they weren't learning anything, complained to anyone who would listen that I did not know how to teach science, told me they were getting "A" marks in all their other classes, threatened my person, assaulted me verbally and physically, destroyed my property when no one was looking, and gave me every reason to give up the idea of trying to make a living based on my rather expensive education.

    Nowadays I eke out a living as an attendant to Downs syndrome children, who behave in a much more reasonable fashion. I have come to entertain the opinion that they are what humans should have become if they had not gone so completely wrong at some genetic turning point sometime in the last million years. But it is only an opinion and I am merely entertaining it for my own amusement, not really holding on to it very tightly.

    You may be suprised to hear that my opinion of my teachers was not much different from your own. I was one of the very students who behaved horribly in class, although I never assaulted anyone bodily or did damage to personal property. I continually asked distracting questions and thought I knew better than my teachers how I should be taught. I now know that I should have shut up and listened. So you see that my downfall as a teacher had a certain poetic justice.

    I am mostly self-taught about the matters on these boards, although I do owe a huge debt of gratitude to the other posters here who have been patient in leading me to the things I wanted to know, especially selfAdjoint and Marcus, although I don't want to slight any of the others who have provided me with hours of interesting conversation and reason to meditate. Nor do I wish to slight you, although I do think you will find your attitude no more successful than mine has been. However you are already a senior in high school and it is probably too late for you to change.

    Consider for example your statement:

    "I know all about the basis and most the of sub-atomic particles, and know what mass is."

    That is incredible.

    I myself have been reading and studying for quite a few years now, but I cannot say as much. What is mass? It happens that quite a few serious workers have spent themselves trying to get a grip on that nut, and I doubt you could get them to admit so much confidence. As for the basis, I suppose you might mean the mathematical basis of spacetime geometry, a subject of much review here on these boards. Wow. String theory, loop quantum gravity, causal dynamical triangulations, category theory, and others. The arguments get quite personal at times. I would hesitate to enter a room where three or more of the combatants were in habitation fully armed, even though it would be vastly entertaining to watch.

    Anyway, Andrew, as an old hack to a young blade, may I say it would behoove you to take a look around. The sharpness of youth wears out quickly on the world's grindstone. You can't just go chopping at the roots without hitting some stones. You may be quick and sharp, and the rocks may be cold and dull, but they will break you quick as anything.

    You do seem to be clever and to have some sense about you. Probably you will survive one way or the other. Even a broken blade can still be of some use. And maybe you do know what mass is and the basis, and maybe you will learn sufficient language to be able to tell the rest of us all about it. Or someone anyway. That would be wonderful.

    Be well,

  8. Dec 1, 2005 #7
    Second the motion for superstringtheory.com
    Last edited: Dec 1, 2005
  9. Dec 2, 2005 #8
  10. Dec 5, 2005 #9
    Well Richard, that is actually quite a good definition of me, give or take a few examples. This is the real me...I don't listen to lectures, rather i sleep during them. I never do reading assignments and rarely hand in Labs. I also never do the homework, but I never complain that there is too much. I never complain I'm not learning anything, nor do I complain about my teacher. At midterm (2 weeks ago) I had an average of 94. Right now im taking Geometry and Advanced Functions, Biology and Physics, my physics mark being a 97, so it's not that i'm blaming my teacher for my bad marks, infact hes a very good teacher, and can teach the course very well, but he doesn't have an understanding outside of what he needs to teach. Hes a great teacher and in no ways is he an idiot.

    The way I meant this is that I know the basic understanding, the introduction to sub-atomic particles. I never said that I have a deep comprehension about it, I just said i have a basic understanding. For example, go up to a random person on the street (hope he isnt a prof.) and start talking about quarks or neutrinos. Do you think he'll have the slightest idea what your talking about? Most likely, no. Now take me, and start talking to me about quarks or neutrinos, will I have a deep, thorough understanding of it? No, but I will have some background in it, therefore I won't be completely lost when your explaining something to me.

    So, without sounding rude or obtuse, let me put this as simple as possible. Lets not have any more low blows at me without you learning a little more about the topic, i.e. me. Basically, get rid of the ignorance. I know you hold yourself to be "wise" and though i fall short of you in years, I'm not a complete moron and hold my own store of wisdom.

    Thank you,
    Last edited: Dec 5, 2005
  11. Dec 5, 2005 #10
    Hi Andrew

    Cool. Lets get on to cases, then. But first, I apologise for my irritability. I didn't really intend any low blows. And as for wisdom and so on, I credit myself with none. Years I do have, and nothing much else.

    I am going to save this frequently and work in edit, since my keyboard has taken on an ugly habit of freezing up. Then I have to reboot and I loose whatever it was I was working on.

    Well, the basics. I was working on a post to greensquall just now and had gotten the string to vibrate in up to eight dimensions when the screen froze. Greensquall wants to name the ten dimensions of superstring theory, so I started with a string under tension, which is kind of a zero state compression wave, you see? You pull on the string, it resists the pull, so you have a one dimensional "wave" that isn't moving but expresses itself as tension in the string.

    Then you can move your end of the string (imagine the other end is fixed somehow) and get the string to go up and down in a single node. If the tension is great, the string just stays pretty much a straight line, but if the tension is rather loose, you get a loop. You have done this in lab I suppose?

    If you move you hand up and down quickly, you can get the string to break into several loops, and you can count the nodes, that is the spots along the string that are not moving up and down, or at least not very much. You can do this with a string under tension on a floor, with one end tied to a doorstop or something. So you see that this is a string moving in two dimensions, where one dimension is in the direction of the length of the string, and the next dimension is in the direction of the amplitude of the waves.

    Then you can tie the string to a doorknob, hold it under slight tension, move your hand up and down, and you get the same two dimensional wave as you did when you had it on the floor, only now it is a two dimensional wave moving vertically. To get a three dimensional wave, move your hand in a circle. Now the wave has a spirol shape as it moves along the string.

    To get four dimensions, you can add another motion to your hand. This time, in addition to the three dimensional spiroling waves, add another element of compression by moving your hand back and forth toward and away from the doorknob end as you move it in circles. You see that you still have the three dimensional spirol wave, but now you have an additional compression wave. To describe this wave you have to describe four directions of movement of your hand.

    I just got froze out and had to reboot again, just as I was trying to extend this to eight dimensions of movement. Huh.

    I'll try again.

    Now notice that your hand, making the four dimensional wave, is moving in a small volume of space. Think of this volume as if it were a unitary point, and begin to add dimensions again, at a slightly larger scale. Up and down, now you have five. Side to side, there is six. In and out is seven. Once again take the slightly larger scale volume as a unitary point. Eight nine ten and I am done.

    Is that how string theorists get ten dimensions? I don't know. Well actually I do know. That is NOT how string theorists get dimensions. They do it with math, solve equations, and come out with the right answer. To get the right answer to come out, they have to put in ten dimensions.

    But anyway I think I have accomplished the forbidden act here, and put a physical image to the idea of ten dimensions. If my image has any merit, it will ignite a firestorm of angry controversy. More likely it is just a naive playing with toys.

    In any case, hope this helps, be well,


    234 at 12.59
    Last edited: Dec 5, 2005
  12. Dec 5, 2005 #11
    A quick interjection, to save myself making a new thread about it. I'm a graduate student about to undertake a first course in string theory (in about two months). Over the Christmas vacation I have an essay to start writing, the topic of which is "Non-perturbative Equivalences of Perturbatively Inequivalent String Theories". I've been down the library today got a copy of Green, Schwarz and Witten, and a copy of Joseph Polchinski's book I, which are going to form some light(!) reading for the next few weeks. My question is this: I fully expect to have difficulties understanding parts of it. Would this forum be an appropriate place to ask any questions that I may have, or would it be better to post it somewhere else, as most discussions here seem to be at the research level?
  13. Dec 5, 2005 #12
    Oh yeah, this is a great place to post your questions. For my part I can't promise any answers, but there are people here who can do the math. Not everyone here is fond of string theory, but probably someone on the boards will have the information and experience you need.

  14. Dec 5, 2005 #13
    Well Richard, thank you for the attempt at trying to allow me to visualize 10 dimensions. Its basically impossible to visualize 10 dimensions in our physical world, so I won't even bother going there yet.

    About my previous post, I'm sorry if I had a tone of offence. Just with you and the insults directed at me, got rather annoying.
    Last edited: Dec 5, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?