One doubt about string theory.

In summary, the article argues that the lack of an adjustable dimensionless parameter is a strong point in favor of string theory, as it allows the theory to be more consistent than other theories of QG.
  • #1
arroy_0205
129
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I read somewhere that one power of string theory is that there is no adjustable dimensionless parameter in the theory. Why is this considered a strong point in favour of string theory?

Second, how does the theory help in solving cosmological constant problem? Again there is no adjustable dimensionless parameter which can be put equal to zero. (The article was written long ago, so the author thinks about putting CC=0 but now we know it has a very small positive value.)
 
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  • #2
arroy_0205 said:
I read somewhere that one power of string theory is that there is no adjustable dimensionless parameter in the theory. Why is this considered a strong point in favour of string theory?
String theory should provide a way to "derive" the standard model of elementary particle physics with its different particle species and approx. 20 free parameters as a special solution of string theory where the particles and parameters can be "explained" somehow. It's like looking at quantum mechanics in solid state physics: it can explain in principle a huge number of solid states and their parameters like heat capacity, susceptibility, thermal and electrical conductivity etc.

arroy_0205 said:
Second, how does the theory help in solving cosmological constant problem? Again there is no adjustable dimensionless parameter which can be put equal to zero.
Very interesting question. I always read that string theory has a problem with the sign of the cosmological constant, i.e. that AdS can be understood quite well, but that dS is problematic; I never fully understood why this is the case and why string theory is able to deal with AdS/CFT but fails to explain something like dS/xyz.
 
  • #3
tom.stoer said:
I always read that string theory has a problem with the sign of the cosmological constant, i.e. that AdS can be understood quite well, but that dS is problematic; I never fully understood why this is the case and why string theory is able to deal with AdS/CFT but fails to explain something like dS/xyz.

There are plenty of string models that have a positive CC, for example in the "KKLT scenario". And that dS is more problematic than AdS, is not a property of just strings but, I guess, for any theory of quantum gravity.
 
  • #4
suprised said:
There are plenty of string models that have a positive CC, for example in the "KKLT scenario".
OK, thanks for the hint. KKLT is of course well-known.

suprised said:
And that dS is more problematic than AdS, is not a property of just strings but, I guess, for any theory of quantum gravity.
hm, why? it seems that in LQG and CDT they are rather close to dS; I remember a paper by Witten explaining why dS could be problematic, but it was not very convincing
 
  • #5
tom.stoer said:
I remember a paper by Witten explaining why dS could be problematic, but it was not very convincing

This is what I had in mind, Tom.

At any rate, string theory is as consistent a theory of QG as it can get, at least in the domain where it can be properly defined.
 
  • #6
Thanks for the responses. However I still do not understand why it should matter whether the parameter we are talking about is dimensionless or dimensionful.
 

FAQ: One doubt about string theory.

1. What is string theory?

String theory is a theoretical framework that aims to unify all the fundamental forces of nature, including gravity, into one single theory. It suggests that the fundamental building blocks of the universe are not particles, but tiny, vibrating strings.

2. How does string theory differ from other theories?

String theory differs from other theories, such as the Standard Model, in that it attempts to reconcile the seemingly incompatible theories of general relativity and quantum mechanics. It also proposes that the universe has more than three dimensions, with the extra dimensions being too small to be detected by current technology.

3. What is the evidence for string theory?

Currently, there is no direct evidence for string theory. It is still a theoretical concept and has not been experimentally proven. However, many physicists believe that it has the potential to explain certain phenomena, such as the behavior of black holes, that cannot be fully explained by other theories.

4. What are the challenges facing string theory?

String theory is a very complex and mathematically challenging theory. It also lacks experimental evidence, making it difficult to test and validate. Additionally, there are different versions of string theory, making it hard to determine which, if any, is the correct one.

5. How does string theory impact our understanding of the universe?

If proven to be true, string theory would revolutionize our understanding of the universe. It would provide a unified framework for all of physics and potentially lead to new technologies and discoveries. It also has the potential to answer some of the most fundamental questions about the universe, such as the nature of dark matter and dark energy.

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