Exploring the Different String Theories & Their Relationships

In summary: M-Theory was originally a set of 5 string theories which seemed different. Edward Witten united them all to form M-theory. quick summary there.
  • #1
alpha_wolf
163
0
Hi.

Could someone please post a quick summary of which string theories are out there and how they relate to each other? I could only find partial information on this...

Thank you.
 
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  • #2
What I have found are the relationships shown http://physics.about.com/gi/dynamic/offsite.htm?site=http%3A%2F%2Fwww.sukidog.com%2Fjpierre%2Fstrings%2F . M-Theory is 11 dimensions and converges to different 10-dimensional theories depending on how the 11th dimension is compactified. I've also found info about the 12th dimensional F-theory which converges to M-theory or one of the 10-dimensional theories, depending on how its extra dimensions are compactified. What other theories are there, and how are they related? What about that theroy with 26 dimensions - how does it fit in?
 
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  • #3
F-theory?? Where did you find this information? I've been looking and looking everywhere (apparently not everywhere, but a lot of places) for information about F-theory.

26 DEMENTIONS?? Please, tell me [or us] more about this. Please provide a link as well.


Anyway, M-theory was originally a set of 5 string theories which seemed different. Edward Witten united them all to form M-theory. quick summary there.
 
  • #4
Imparcticle said:
F-theory?? Where did you find this information? I've been looking and looking everywhere (apparently not everywhere, but a lot of places) for information about F-theory.

26 DEMENTIONS?? Please, tell me [or us] more about this. Please provide a link as well.


Anyway, M-theory was originally a set of 5 string theories which seemed different. Edward Witten united them all to form M-theory. quick summary there.

Try search for D Marolf ?

Edit:removed one F.
 
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  • #5
Imparcticle said:
F-theory?? Where did you find this information? I've been looking and looking everywhere (apparently not everywhere, but a lot of places) for information about F-theory.

26 DEMENTIONS?? Please, tell me [or us] more about this. Please provide a link as well.
Google search for "F-Theory" (with the quotes) - the 2nd result is what I was taking my info from. As for the 26 dimensions version, I've heard about it a very long time ago (about the same time I first heard of string theory, iirc). I have no idea how it relates to the others. I've heard recently that it's actually one of those five original theories, but I cannot confirm this, especially given that they are all 10 dimensional as far as I know.
 
  • #6
Imparcticle said:
F-theory?? Where did you find this information? I've been looking and looking everywhere (apparently not everywhere, but a lot of places) for information about F-theory.

26 DEMENTIONS?? Please, tell me [or us] more about this. Please provide a link as well.


Anyway, M-theory was originally a set of 5 string theories which seemed different. Edward Witten united them all to form M-theory. quick summary there.
last time i read they don't even know what is this M theory they only think that all the 5 string theories should be united to one theory, M theory.

and about F theory it's been developed by camerun vafa (im not sure about his first name) and it adds another time dimension.
 
  • #7
Thank you

Thank you alpha_wolf, and everyone else. :smile:

Loop Quantum Gravity:
The 5 original superstring theories where unified by Edward Witten in the 90's. M-theory is the product of the unified theories. What M-theory is, is known but it is not fully understood.

Two time demensions? So, IOW, two directions in which entropy can expand? Two directions of disorder expanding...that is an interesting idea.
Say direction A= "future" and direction B= "past".
the past exists and decreases in disorder. At the same time, "A" will continue to increase "forward" (that is opposite to the direction of "B"). Do I understand this correctly?
Does this theory allow for time travel to the past? (maybe not ; time travel to the past defies thermodynamics)
 
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  • #8
loop quantum gravity said:
F theory it's been developed by camerun vafa (im not sure about his first name)

F-Theory was formulated by Cumrun Vafa (from Harvard),
looking for an analog theory to M-Theory for describing non-perturbative compactifications of Type IIB theory.

See for example this

Or

C. Vafa, "Evidence for F-theory." Nucl. Phys. B 469: 403 (1996).
 
  • #9
Can anyone comment on the 26-dimensional version(s) of string theory? Thanks.
 
  • #10
The 26 dimensional version of string theory was the original string theory. It predicted only bosonic matter, and also predicted tachyons which was generally took to be a sign that the theory was unstable. It's still used today as a model for playing around with, and serves as an introduction to string theory in quite a few textbooks.
 
  • #11
Lonewolf said:
The 26 dimensional version of string theory was the original string theory. It predicted only bosonic matter, and also predicted tachyons which was generally took to be a sign that the theory was unstable. It's still used today as a model for playing around with, and serves as an introduction to string theory in quite a few textbooks.
Thanks for your reply. How did it evolve to the 10 dimensional versions?
 
  • #12
Type IIB theory.

What is that?
 
  • #13
Imparcticle said:
Type IIB, what is that?

There are five superstring theories. Type IIB is just one of them.

[type I, type IIA, type IIB, Heterotic E8 X E8, and Heterotic SO(32)]
 
  • #14
alpha_wolf said:
Thanks for your reply. How did it evolve to the 10 dimensional versions?

When you add the fermions to string theory by means of supersymmetry, the quantized theory requires 10 dimensions. It is the same origin of the 26 dimensions in bosonic string theory: you quantize and then you end up with a requirement that is related to the symmetry of the massless states (Í don´t know it very well, so I hope someone can explain better this point.)
 

1. What are the different string theories?

The five main string theories are bosonic string theory, superstring theory, heterotic string theory, type I string theory, and type II string theory. Each theory describes different properties and behaviors of strings, such as the number of dimensions and the types of particles that can exist.

2. How are the different string theories related?

The five string theories are all connected through a process called duality, which allows for the transformation of one theory into another while still preserving its fundamental properties. This means that each theory is a different perspective or representation of the same underlying structure.

3. What is the significance of string theories?

String theories attempt to reconcile the two fundamental theories of physics, general relativity and quantum mechanics, by describing the universe at a fundamental level. They also provide a framework for understanding the behavior of particles and the forces that govern them.

4. How are string theories tested?

Due to the extremely small scale at which strings operate, it is currently impossible to directly test string theories. However, scientists can test the predictions made by the theories through experiments and observations of phenomena that occur at very high energies, such as the behavior of particles in colliders.

5. Are there any challenges or criticisms of string theories?

One of the main challenges of string theories is that they currently lack experimental evidence, making it difficult to confirm their validity. Some critics also argue that the theories are too complex and mathematically abstract, making them difficult to understand and apply. However, many scientists still see string theories as a promising framework for understanding the fundamental nature of the universe.

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