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Anyone smart enough to explain "String Theory" here?
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Do you have any understanding of the Standard Model? Or have you not really studied elementary particle physics yet?
The easiest way to explain the motivations for why string theory came about is to point out a few shortcomings of the Standard Model. An actual explanation of the mathematical framework is beyond the scope of GAF...and probably beyond MY scope as well, but we won't go there.
The easiest way to explain the motivations for why string theory came about is to point out a few shortcomings of the Standard Model. An actual explanation of the mathematical framework is beyond the scope of GAF...and probably beyond MY scope as well, but we won't go there.
I came in here to ask about that. I had it bookmarked on my last computer and lost the link. I think I was actually at the part where they started to explain string theory.Pochacco said:
Does anyone know what the link is? Or at least what the program was called so I could Google it?
And yeah, I got maybe 1/4 through and it was VERY well done and fun to watch.
I bookmarked it, heh.
http://www.pbs.org/wgbh/nova/elegant/program.html
Anyway, so the 5th dimension and beyond works mathamatically but so does the use of imaginary numbers in math. As far as I know, imaginary numbers don't actually exist/can't be observed. So what makes them so sure the 5+ dimensions really exist outside math?
http://www.pbs.org/wgbh/nova/elegant/program.html
Anyway, so the 5th dimension and beyond works mathamatically but so does the use of imaginary numbers in math. As far as I know, imaginary numbers don't actually exist/can't be observed. So what makes them so sure the 5+ dimensions really exist outside math?
WHOAguitarninja
Member
Zero said:
That book is a great place to start.
The 'story' starts actually with relativity and quantum mechanics. These are both fantastically powerful theories that have been both verified to EXTREME accuracy. They both show absolutely no real problems when we use them in the realm that they work best in. ie:quantum mechanics for very small things, and general relativity for very large/massive things. The problem is, in some extreme cases in the universe, they require the use of both theories in order to try and give any accurate predictions. Problem is, the way they are currently formulated, the two theories are mutually exclusive.
General relativity, einstein's theory of gravity, predicts that space is curved (in a fashion that is somewhat hard to visualize....picture a bowling ball on a trampoline, then give it an extra dimension). However, it requires that this curvature be very smooth.
Quantum mechanics makes some predictions that don't really gel well with this. It predicts, to simplify things a bit, that there are particles appearing and disapearing all throught the universe, even in empty space. Any where there is any sort of electric/magnetic field at all(and I can't think of anywhere that doesn't have some sort of field), this should be taking place. It's random, and near instantaneous. And it has a nasty effect of making space-time very rough and bumpy. This only happens, however, at VERY VERY VERY small scales. Scales so small, that in most cases it has no noticeable effect on relativity. However in cases such as blackholes and the big bang, these problems rear their ugly head.
The way particles have been thought in the past has been as 'point' particles. Essentially tiny balls of matter with infinitely small spatial extension. What string theory (and it's big brother M-theory) propose is that these particles are actually small loops of vibrating string. Without getting into things like p-branes and the like, it proposes that all known particles are actually essentially the same type of string, just vibrating at different frequencies.
Here is where it gets weird. These strings are vibrating in not just several directions, but several DIMENSIONS. I can't recall the number for sure, but I beleive it to be 9(it's around there, might be more, don't think it's less than 8).
These 'extra' dimensions are generally thought to be curled up into tiny nuggets that are so small we can't even perceive them.
How small? If you blew up an atom to the size of the known universe, these spaces, and the strings inside, would be about the size of a tree. In other words...pretty damn small.
So what does this do? Well, it's tough to show why without a pencil and peice of paper(although the elegant universe gives a pretty good description/depiction), but these little strings effectively smooth out the roughness and bumps caused by particles appearing and disappearing. They THINK this will solve the problems of the two theories. It should be noted however that, so far as I know, they still have yet to find the full equations that govern this, because the mathematics to do so simply don't exist at this point.
String theory also makes several other very interesting predictions, but I'll leave those for you to discover. Read the elegant universe, it really sums things up in an easy to understand fashion. I read it afer finishing an introductory physics course, not even AP, and it made sense for the most part. I'll probably pick it up again junior year after I finish my quantum classes.
Hopefully this came out clearly enough...it's 3 in the morning here so physics is kindof not trivial for my brain at this point, I'll come back to this thread tommorow.
I have not.-jinx- said:
Yeah, I read that.
So basically it argues that there are "strings" instead of "particles" in the universe. Each string, depending on the tension, can be plucked or strummed to produce a "scale of notes," called the spectrum of the string? The smallest particles of matter that make up the strings are fermions and bosons?
I found a file just now. PM if you want.
EDIT: Thanks, morbidaza.
WHOAguitarninja
Member
Asbel said:
It's interesting you say that, because I just finished up a course on electricity and magnetism that made extensive use of imaginary numbers in regards to electrical impedence.
My professor (who, incidentally, is one of the leading experts on string theory (Jim Gates incase anyone's heard of him....he's actually in that PBS special) had this to say about imaginary numbers. He said, in a nutshell, "Imaginary numbers are no less real than real numbers. When you think of a number, what does it mean? It, in itself, doesn't mean anything. You have to apply some meaning to it. If you say "I have 7", what are you saying. Well, nothing really. A number itself is just a point on a number line. An imaginary number is a point on a number line just the same. A complex number is a point (actually usually a vector, but whatever) on a number PLANE. It's all just different formulations of the same basic idea, just some are more useful in some cases than others."
He was much more concise, but I think that's the gist of what he was trying to say. Weird number stuff doesn't end at imaginary numbers though, there are these things called "grasman numbers"(might have spelling wrong) who's square is zero, but they themselves are not 0. These are actually used in string theory.
About the extra dimenions...as of now, they're not really sure I guess. Too small to REALLY test for. In terms of the theory, it makes mathematical sense. They still don't even know if the theory is correct or not. Although some of it's predictions are starting to be observed (the existance of superpartners is the only I know of...although there may be more). They have also used the theory to mathematically 'build' a black hole. The predictions it gave were in line with what is currently accepted (in regards to the event horizon...which is what they were trying to show. The theory makes some rather odd predictions about singularities that are mentioned in the elegant universe). Until they can test for the extra dimensions though it's all just math.
It's not such a huge jump though to imagine there may be many spatial dimensions, even extended ones like the three we are used to. It may just be that our eyes (or our minds) are sortof "turned" in the direction of the three that we normally see. It's quite easy to make a peice of paper look like a two dimensional object by simply lining it up in such a way that it's spatial extension is hidden from you. It could be that we see in the same way, with the other dimensions "turned' in such a way as to be invisible. This is just me rambling, nothing that one should take even as scientific theory, but it's something kindof interesting to think about if you get that bored.
I saw a very interesting documentary about string theory a year ago. Can't remember much except for that they were talking about quantum theory being used to explain physic in micro terms and newton theory in macro terms. Dunno if this was the basis of string theory or something else entirely different. Also remember that the super genious string theory professor was the one who solved the problem by adding extra dimensions to some model. Interesting, wish I knew what the documentaries name was.
Pudding Tame
Member
Shompla, that was the PBS version of The Elegant Universe you saw.
morbidaza covered a lot of what I was going to say.
The motivations for string theory (more properly, THEORIES) came about because of certain limitations with the Standard Model:
1) Lack of unification with gravity. The Standard Model provided a mechanism for unifying three of the four forces (electromagnetism, weak force, strong force) at high energy, but provided utterly NO way forward to unify with gravitational force. In fact, the Standard Model lacks any kind of quantum theory of gravity. String theory offers one possible mathematical foundation for providing a unified theory of gravity consistent with quantum mechanics.
2) Particle "generations." In the Standard Model, there are three types of particles: hadrons, leptons, and mediators. (Hadrons, which are particles such as protons, neutrons, and mesons, are built out of quarks. Leptons, which are particles such as electrons and neutrinos, are "point" particles. Mediators are the particles which "carry" the four forces mentioned above: photons, gluons, W+, W- and Z0 bosons, and the hypothetical graviton.) As experiments went to higher and higher energies, we discovered that the new particles which were being created were similar to those at lower energies. (For example, a tau particle is a lepton with charge -1, just like an electron...except at a much higher energy.) The same is true with quarks: the stable up and down quarks are "echoed" at higher energy by strange/charmed and top/bottom quarks. Since the number of "elementary" particles kept increasing when the energies increased, it made some people question whether or not any of the particles were TRULY elementary. String theory provides an elegant explanation for this phenomenon by postulating that the higher generations are simply different resonances of the string, much the same as you can play a C note in different octaves of a musical scale.
3) Renormalization. There is some UGLY math in elementary particle physics, and one of the ugliest parts is renormalization. Simply put, it's a technique to "sweep infinities under the rug" which is only justified because of our physical intuition. It's a bit complicated to explain how the infinities result in particle physics, but the same technique has to be done in quantum electrodynamics (QED), and it's probably a better example for this audience. As you probably learned, electric field is proportional to 1/r, where r is the distance from the electric charge. However, what is the electric field at the boundary of a point particle such as an electron? When r -> 0, E -> infinity...but an infinite electric field is nonsensical from a physical point of view. Renormalization is necessary to restore the boundary condition to physical reality. I believe that string theory offers a more elegant mathematical formulation which gets around some of these difficulties, although I doubt I have the mathematical chops to tackle that stuff anymore.
The huge problem with string theories at the moment is that there is NO experimental evidence to confirm or deny ANY of them. For one thing, we have competing formulations of string theory -- is the number of fundamental dimensions 10, 11, or 26? String dimensions are postulated to be unobservable above the Planck length, and we are nowhere NEAR being able to achieve those energies in our current colliders. (Or our future ones -- I seem to remember reading that we'd need a collider the size of our solar system, or something like that.) Science is fundamentally based on evidence, and since there is no foreseeable way to test string theory in the near future, I am personally a little reluctant to embrace it.
The motivations for string theory (more properly, THEORIES) came about because of certain limitations with the Standard Model:
1) Lack of unification with gravity. The Standard Model provided a mechanism for unifying three of the four forces (electromagnetism, weak force, strong force) at high energy, but provided utterly NO way forward to unify with gravitational force. In fact, the Standard Model lacks any kind of quantum theory of gravity. String theory offers one possible mathematical foundation for providing a unified theory of gravity consistent with quantum mechanics.
2) Particle "generations." In the Standard Model, there are three types of particles: hadrons, leptons, and mediators. (Hadrons, which are particles such as protons, neutrons, and mesons, are built out of quarks. Leptons, which are particles such as electrons and neutrinos, are "point" particles. Mediators are the particles which "carry" the four forces mentioned above: photons, gluons, W+, W- and Z0 bosons, and the hypothetical graviton.) As experiments went to higher and higher energies, we discovered that the new particles which were being created were similar to those at lower energies. (For example, a tau particle is a lepton with charge -1, just like an electron...except at a much higher energy.) The same is true with quarks: the stable up and down quarks are "echoed" at higher energy by strange/charmed and top/bottom quarks. Since the number of "elementary" particles kept increasing when the energies increased, it made some people question whether or not any of the particles were TRULY elementary. String theory provides an elegant explanation for this phenomenon by postulating that the higher generations are simply different resonances of the string, much the same as you can play a C note in different octaves of a musical scale.
3) Renormalization. There is some UGLY math in elementary particle physics, and one of the ugliest parts is renormalization. Simply put, it's a technique to "sweep infinities under the rug" which is only justified because of our physical intuition. It's a bit complicated to explain how the infinities result in particle physics, but the same technique has to be done in quantum electrodynamics (QED), and it's probably a better example for this audience. As you probably learned, electric field is proportional to 1/r, where r is the distance from the electric charge. However, what is the electric field at the boundary of a point particle such as an electron? When r -> 0, E -> infinity...but an infinite electric field is nonsensical from a physical point of view. Renormalization is necessary to restore the boundary condition to physical reality. I believe that string theory offers a more elegant mathematical formulation which gets around some of these difficulties, although I doubt I have the mathematical chops to tackle that stuff anymore.
The huge problem with string theories at the moment is that there is NO experimental evidence to confirm or deny ANY of them. For one thing, we have competing formulations of string theory -- is the number of fundamental dimensions 10, 11, or 26? String dimensions are postulated to be unobservable above the Planck length, and we are nowhere NEAR being able to achieve those energies in our current colliders. (Or our future ones -- I seem to remember reading that we'd need a collider the size of our solar system, or something like that.) Science is fundamentally based on evidence, and since there is no foreseeable way to test string theory in the near future, I am personally a little reluctant to embrace it.
WHOAguitarninja
Member
Not to be a boob, but...
it's 1/(r^2) =P. Electric potential is 1/r.
-jinx- said:
it's 1/(r^2) =P. Electric potential is 1/r.
WHOAguitarninja
Member
border said:"The Elegant Universe" is up on a number of torrent sites. Since it's public television I don't think there's really any harm in grabbing it
If I recall correctly, PBS (or maybe it was nova) was offering it on their website after it aired for free. It may still be there.
Thanks for the correction. The point is still true, even though I botched the equation -- you have a function which goes to infinity at r=0.morbidaza said:it's 1/(r^2) =P. Electric potential is 1/r.
Have I mentioned lately that I completely fucking hated EM and apparently have successfully blotted out almost all memories of that crap?
WHOAguitarninja
Member
-jinx- said:Thanks for the correction. The point is still true, even though I botched the equation -- you have a function which goes to infinity at r=0.
Have I mentioned lately that I completely fucking hated EM and apparently have successfully blotted out almost all memories of that crap?
Oh you're not alone. Just finished up my intro EM course (which was apparently taught at a decidedly non-intro level) and several times it made me question my choice of major. Vector based EM concurrently with multi-variable/vector calc is a really confusing combination. Most of last semester was a blur.
:lol I know the feeling. What's your major exactly? I've taken many courses involving EM fields but because I was manly using short term memory to take tests, my understanding of it... well isn't where it should be. Then again, one of my teachers, who was also the department head, said it took him awhile to 'get' EMF too.morbidaza said:
WHOAguitarninja
Member
Double major, physics and math. Apparently I got the hardest(but most indepth) of the intro EM teachers my school offers. The intro EM class(PHYS 272) apparently isn't much different than the intermediate EM class(PHYS 411) when Gates teaches intro. I'm waiting to see my grades from it, we'll see how it turns out...
Let me sum it up for you. Basically so-called science over the years has 'laws' that can't be broken, so a God, or a spirit can't exist. Now suddenly, well look there's more than our dimension here. Whatddya know.
Basically our perception of 'facts' changed every few years in science, which is why its not reliable. We know about 0.000000000001% of everything there is to know about the universe, but that doesn't stop scientific elitists from saying 'this is FACT and can't be proven wrong'. Then suddenly something like the string theory comes along, and things scientists said were wrong for years suddenly aren't. Way to go guys.
Basically our perception of 'facts' changed every few years in science, which is why its not reliable. We know about 0.000000000001% of everything there is to know about the universe, but that doesn't stop scientific elitists from saying 'this is FACT and can't be proven wrong'. Then suddenly something like the string theory comes along, and things scientists said were wrong for years suddenly aren't. Way to go guys.
Ok, let's see if I'm up to this.
Now, you have to apply meaning to every word, not just numbers. When you plot imaginary numbers, you basically create the imaginary (spacial?) dimension, which only exist in math.
We can imagine anything or at least try our hardest. It's just not always practical. There are many things that are invisible to us, like magnetism, radiation and even time. But we know they exist because we can observe their effects on objects. So we don't need to see these extra dimensions to prove their existence, we just need to observe their effects.
Cool, it's like we have an inside source.
Now, you have to apply meaning to every word, not just numbers. When you plot imaginary numbers, you basically create the imaginary (spacial?) dimension, which only exist in math.Glad you brought this up. From what I know, imaginary numbers serve the same purpose by converting ugly equations with polar coordinates into rectangular coordinates, by the addition of the imaginary dimension, so we can use matrices and simplify the math. (Matrix Algebra is mostly just adding, subtracting and multiply) It's seems like the case with string theory as they're adding extra dimensions to simply their math, but I've never heard anyone arguing for the existence of the imaginary dimension.
It's not because men are dreamers and scientists are romantics.
We can imagine anything or at least try our hardest. It's just not always practical. There are many things that are invisible to us, like magnetism, radiation and even time. But we know they exist because we can observe their effects on objects. So we don't need to see these extra dimensions to prove their existence, we just need to observe their effects.- Status