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String theory and M-thoery (1 Viewer)
- Thread starter HNCS
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It's not in the syllabus but it's very interesting. I suggest you read "The Elegant Universe" by Brian Greene. You could watch the series made from the book online but it doesn't have anywhere near the same depth.
String theory basically postulates that the particles that exist in the standard model of particle physics (eg. quarks, electrons, neutrinos etc.) are simply (simply... haha) different excitation modes of a fundamental 1 dimensional object called a string (given it's shape ---> that of a string). Strings can be open and closed with different consequences.
However, in order for the theory to work, space needs to have more than the ussual 3+1 dimensions. Bascially we've ruled out extra large dimensions based on experience so string theorists proposed that these extra dimensions could be curled up and small enough that they could have escaped detection by our probing techniques. These dimensions would likely take the shape of mathematical constructs called (calabi-yau manifolds?) or something of the sort.
Anyhow, there are several different string theories that have been created with basic fundamental differences but dualities have been discovered between these theories which actually allows them to be interchangeable (something which is beneficial if you are in a tight spot mathematically where another theory might save you a lot of trouble). In order for these dualities to work you need to increase the number of dimensions to some large number (I forget exactly what) maybe 22 +1 or something. You now have M-theory (M for magic, mystery, mother of all, etc.. take your pick) which is a combination of the 5 central theories.
A very summarised example of one of these dualities is if you imagine a 3 dimensional universe. One dimension is straight and the other is circular and then you have time. It ends up that space is shaped like an infinitely long cylinder. If you then have a string which is wrapped aroudn the cylinder it's energy is determined by vibrational energy (due to translational motion moving along the cylinder) added to its winding energy (from moving around the circular dimension, which depends on howmany times it is wrapped around). The translational energy is proportional to 1/R (R being radius of the circular dimenion) and the winding energy is proportional to R. Since theses energies are added together (and with E=mc^2 etc) it can then be conceived that there are pairs of values for the radius R of the circular dimension where the net energy of the string is equal i.e you get two indistinguishable universes where the string is the same in each but where one universe is very large and one is very small. Duality in a nutshell... good luck making sense of that
.
Hope that satisfies you.
String theory basically postulates that the particles that exist in the standard model of particle physics (eg. quarks, electrons, neutrinos etc.) are simply (simply... haha) different excitation modes of a fundamental 1 dimensional object called a string (given it's shape ---> that of a string). Strings can be open and closed with different consequences.
However, in order for the theory to work, space needs to have more than the ussual 3+1 dimensions. Bascially we've ruled out extra large dimensions based on experience so string theorists proposed that these extra dimensions could be curled up and small enough that they could have escaped detection by our probing techniques. These dimensions would likely take the shape of mathematical constructs called (calabi-yau manifolds?) or something of the sort.
Anyhow, there are several different string theories that have been created with basic fundamental differences but dualities have been discovered between these theories which actually allows them to be interchangeable (something which is beneficial if you are in a tight spot mathematically where another theory might save you a lot of trouble). In order for these dualities to work you need to increase the number of dimensions to some large number (I forget exactly what) maybe 22 +1 or something. You now have M-theory (M for magic, mystery, mother of all, etc.. take your pick) which is a combination of the 5 central theories.
A very summarised example of one of these dualities is if you imagine a 3 dimensional universe. One dimension is straight and the other is circular and then you have time. It ends up that space is shaped like an infinitely long cylinder. If you then have a string which is wrapped aroudn the cylinder it's energy is determined by vibrational energy (due to translational motion moving along the cylinder) added to its winding energy (from moving around the circular dimension, which depends on howmany times it is wrapped around). The translational energy is proportional to 1/R (R being radius of the circular dimenion) and the winding energy is proportional to R. Since theses energies are added together (and with E=mc^2 etc) it can then be conceived that there are pairs of values for the radius R of the circular dimension where the net energy of the string is equal i.e you get two indistinguishable universes where the string is the same in each but where one universe is very large and one is very small. Duality in a nutshell... good luck making sense of that
. Hope that satisfies you.
Last edited:
A good place to start is here -----> http://superstringtheory.com/
Xayma
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Not exactly Kfunk,
The 22+1 demensions (I think) is one of the five central theories. Bosonic String Theory, M Theory showed that Bosonic String theory and the four super symmetry string theory were equivalent as viewed from different limits.
Bosonic String Theory has problems in that Fermions cant be accounted for, and Tachyons exist, particles that travel faster then the speed of light and have an imaginary mass.
One of the main problems with String Theory is it at the moment cant be tested, which means it is more a philosophy then physics. However, if the graviton can be found it supports it.
String theory is prefereed as it is easy to work with 1 Dimensional objects rather then 0 dimensional points, plus the prediction of a graviton, which gives gravity. Essentially two lines can cross and interact, 0D points can't.
The extra dimensions are suspected to be manifolds. As to why we dont see them, we are too big to see, it is like seing an extremly long skinny tube from a very large distance away, it looks 1D. We dont move in those extra dimensions, however, strings may vibrate in them.
An interesting consequence of string theory is that of a minimum length. Nothing in the universe at any time can become smaller then a string which itself has a length of Planck's length.
The 22+1 demensions (I think) is one of the five central theories. Bosonic String Theory, M Theory showed that Bosonic String theory and the four super symmetry string theory were equivalent as viewed from different limits.
Bosonic String Theory has problems in that Fermions cant be accounted for, and Tachyons exist, particles that travel faster then the speed of light and have an imaginary mass.
One of the main problems with String Theory is it at the moment cant be tested, which means it is more a philosophy then physics. However, if the graviton can be found it supports it.
String theory is prefereed as it is easy to work with 1 Dimensional objects rather then 0 dimensional points, plus the prediction of a graviton, which gives gravity. Essentially two lines can cross and interact, 0D points can't.
The extra dimensions are suspected to be manifolds. As to why we dont see them, we are too big to see, it is like seing an extremly long skinny tube from a very large distance away, it looks 1D. We dont move in those extra dimensions, however, strings may vibrate in them.
An interesting consequence of string theory is that of a minimum length. Nothing in the universe at any time can become smaller then a string which itself has a length of Planck's length.
Yeah, my bad. According to wikipedia (the place you would trust for physics... )
"... bosonic string theories are 26-dimensional, while superstring and M-theories turn out to involve 10 or 11 dimensions."
) "... bosonic string theories are 26-dimensional, while superstring and M-theories turn out to involve 10 or 11 dimensions."
Phanatical
Happy Lala
My theories suggest that if time is not linear, then these strings could possibly be measured not just by length, height and width on an incredibly minute level, but also through time. This may even account for things like antimatter and negative mass.
Just a thought.
Just a thought.
Xayma
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I wouldn't take wikipedia as gospel but it is suprisingly accurate, due to the wide number of authors.KFunk said:Yeah, my bad. According to wikipedia (the place you would trust for physics...
"... bosonic string theories are 26-dimensional, while superstring and M-theories turn out to involve 10 or 11 dimensions."
Phanatical, have any mathematical basis for it? As far as I know, antimatter is already accounted for in string theory.
Thanks
Thanks everyone, it's a really big help. I went to the website, it also was a big help.
Also, sorry for my mistake...I posted it in the wrong place, since this is cosmoligy, I thought I shold post here.
THANKS
Thanks everyone, it's a really big help. I went to the website, it also was a big help.
Also, sorry for my mistake...I posted it in the wrong place, since this is cosmoligy, I thought I shold post here.
THANKS
Xayma
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Yeah I know it is correct. I was using 22/23 out of memory cause I couldn't remember the entire thing. My comment was more the wikipedia comment he made, it is accurate but being open source you have to verify it.
M-turkey
Zoom Zoom
If can manage to get a copy of the show "Elegant Universe" hosted by Brian Greene or the book with the same name and author, it explains it very well.
As has been said, String Theory came out with 5 seperate theories. Each one equally valid, ranging from 10 to 20 somthing dimensions.
Steve Weinberg, I think, came out and said that if you looked at the 5 theories the same way, they were saying the same thing.
M-Theory unified the 5 other theories, with a theory that there is a total of 11 dimensions, but also that the universe is made up of 'membranes'
This is compicated stuff.
Brian Greene is supposed to be the leader in the field; some facts about him:
-At the age of five, he could multiply 30-digit numbers.
-by the time he was twelve years old, he was being privately tutored in mathematics by a Columbia University professor because he had surpassed the high-school math level.
These guys are the gifted of the gifted
As has been said, String Theory came out with 5 seperate theories. Each one equally valid, ranging from 10 to 20 somthing dimensions.
Steve Weinberg, I think, came out and said that if you looked at the 5 theories the same way, they were saying the same thing.
M-Theory unified the 5 other theories, with a theory that there is a total of 11 dimensions, but also that the universe is made up of 'membranes'
This is compicated stuff.
Brian Greene is supposed to be the leader in the field; some facts about him:
-At the age of five, he could multiply 30-digit numbers.
-by the time he was twelve years old, he was being privately tutored in mathematics by a Columbia University professor because he had surpassed the high-school math level.
These guys are the gifted of the gifted