The structure of strings

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soothsayer
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Quantum mechanics tells us that particles have a wave-like nature: their position, momentum and energy are not absolutely defined, and obey the Uncertainty principle.

One thing that strikes me as peculiar in String Theory is how much internal structure string appear to have at the Planck scale, which seems to invalidate my understanding of quantum uncertainty and wave-particle duality. The idea of some Planck-scale "string" of energy that can be either definitely open or closed seems too determinate and classical for physics at that level. Can someone explain to me why this is not a concern in String Theory?
 

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  • #2
micky_gta
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There are no strings. Scientists just use the word 'string' to describe something that is vibrating. Its easier to understand for most people. Its actually the quantum field that is vibrating.
 
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soothsayer
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Ok, I figured it was something like that. Thanks for explaining it that way to me. So we say that the quantum field is vibrating, and then colloquially describe the quanta of this field as vibrating "strings"? And this is an underlying quantum field which is sort of the building block of all other fields? Also, then, what do string theorists mean when they talk about "open" strings vs. "closed" strings?
 
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Demystifier
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Quantum mechanics tells us that particles have a wave-like nature: their position, momentum and energy are not absolutely defined, and obey the Uncertainty principle.

One thing that strikes me as peculiar in String Theory is how much internal structure string appear to have at the Planck scale, which seems to invalidate my understanding of quantum uncertainty and wave-particle duality. The idea of some Planck-scale "string" of energy that can be either definitely open or closed seems too determinate and classical for physics at that level. Can someone explain to me why this is not a concern in String Theory?
In quantum mechanics of particles, wave function is a function of the (particle) position. One reasonable interpretation of that is that particle is still at one place only, but you simply don't know what that place is.

Likewise, in quantum mechanics of strings, wave function is a function of the (string) position AND shape. Again, one reasonable interpretation of that is that string is still at one place only and has one shape only, but you simply don't know what that place and shape are.

You can say that a string is definitely open if the wave function of a closed shape is zero. Likewise, you can say that a string is definitely closed if ... well, I guess I don't need to finish this obvious sentence.
 
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There are no strings. Scientists just use the word 'string' to describe something that is vibrating. Its easier to understand for most people. Its actually the quantum field that is vibrating.
Either you know a lot about string field theory, or you have no idea what are you talking about.
 
  • #6
FalseVaccum89
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There are no strings. Scientists just use the word 'string' to describe something that is vibrating. Its easier to understand for most people. Its actually the quantum field that is vibrating.

My question would be: what effect--if any--would the finite spatial extent of the 'string' have on the formulation of this particular field theory? To my knowledge, the original QFT formalism came about in the throes of the Standard Model, which presupposes point-like particles. I understand that one of the things that makes a QFT different from classical theories is the concept of discrete excitations composing the field. My question centers around whether the inherent finite spatial extent of the string excitations would change the way the theory plays out in practice.
 

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