What are strings made of?

  • #51
Strings would be fundamental if no matter what you did to them the only possible result were strings. Atoms were once considered the same way. It wasn't so much that atoms were pointlike in size. They simply were thought to be indivisible. As soon as it was realized that smaller bodies that were not atoms (electrons) could be removed from atoms, then atoms weren't fundamental any more.
 
  • #52
selfAdjoint
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But it is true that strings remain strings no matter what you do to them. If you cut them apart you have two strings. If you join two together you have one string. Twisting them, knotting them doesn't change their stringyness, and the whole of string theory accepts the unsplittible stringiness of strings. The theory may be wrong about that, but so far there has appeared no reason to think so.
 
  • #53
3,762
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Hold on, I thought M-Theory postulated a minimum size (the Planck's size) for all physical entities...wouldn't this mean that you can't "cut" a string any smaller than it already is?
 
  • #54
According to Pat Schwartz:

""
The string tension in string theory is denoted by the quantity 1/(2 π a'), where a' is pronounced "alpha prime"and is equal to the square of the string length scale.
""
.
link -->
http://superstringtheory.com/basics/basic3a.html

Tstring = 1/2πα' (string tension from length scale)

Lmin ~ 2√α' (minimum length from length scale)

Then Lmin ~ √(2/π)(1/√Tstring)
.

So, is the minimum length bounded below or is the string tension bounded above?

------

bonus: lecture slides on branes.
The Physics of Branes by Sunil Mukhi -->
http://www.ias.ac.in/meetings/annmeet/68am_talks/smukhi/index.html

Branes are more fundamental than strings?
 
  • #55
3,077
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String tension is to mechanical tension as Planck's constant is to angular momentum.
 
  • #56
FilipKunc
isn't there something called "string coupling constant" which defines (correct me if i'm wrong) how easy it is for a string to divide itself into smaller strings??? if strings have a tension, then it is possible to tear them apart, if one pulls hard enough ;).
 
  • #57
Also, open strings can wrap around compact dimensions, even multiple times. So I guess string length is variable.

The wrap count serves as a quantum number?
 
  • #58
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Originally posted by quartodeciman

The wrap count serves as a quantum number?
yup
 
  • #59
Agnst

It has been historically true that one theory of what is the most fundamental conceptual unit of existence had later been challanged by another theory of something even smaller, (and/or larger). I would like to know an elequent 'theory of everything'. Is it possible that there is no fundamental elements/strings/whatever, nor 'theory of everything'? String theory poses one problem for me; when asked, why do strings 'exist'?, the answer, (please correct me if I am wrong), is that strings 'exist' because strings 'exist'. Before (I believe it was Einstein) all 'things' 'existed' in something called the ether (sp?). Einstein had asked, what is ether made from? Isn't saying that strings 'exist' because strings 'exist' like saying strings 'exist' in an 'ether'? That strings 'exist' because strings 'exist' is taking it on faith that strings 'exist' because strings 'exist'. For what reason does this not lead to existentalist angst?

Is there a mathematical proof that there is such a thing as a fundamental?
 
  • #60
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Originally posted by S = k log w
It has been historically true that one theory of what is the most fundamental conceptual unit of existence had later been challanged by another theory of something even smaller, (and/or larger). I would like to know an elequent 'theory of everything'. Is it possible that there is no fundamental elements/strings/whatever, nor 'theory of everything'? String theory poses one problem for me; when asked, why do strings 'exist'?, the answer, (please correct me if I am wrong), is that strings 'exist' because strings 'exist'. Before (I believe it was Einstein) all 'things' 'existed' in something called the ether (sp?). Einstein had asked, what is ether made from? Isn't saying that strings 'exist' because strings 'exist' like saying strings 'exist' in an 'ether'? That strings 'exist' because strings 'exist' is taking it on faith that strings 'exist' because strings 'exist'. For what reason does this not lead to existentalist angst?

Is there a mathematical proof that there is such a thing as a fundamental?
We are looking for physical laws that are logical in every way, and which can be described by mathematics. You've seen Venn diagrams used to show how to construct AND's and OR's of logic. And these AND's and OR's can just as easily be describe in a sample space. These spaces can be parameterized with coordinates. And they look very much like the manifolds talked about in physics. AND's and OR's are included in both.

If we ever expect to find mathematical laws of physics that are logical in every way, then we should realize that they will be a description of how events grow in sample space.

We seem tantilizingly close to justifying the geometry of physics. The Action integral is proportional to the surface area of the world sheet. The Lagrangian is the generalized gradient and is equal to zero so that it describes a geodesic, etc. But they have no reason for this geometry other than to say it works. It might be possible to recognize these world-sheets as growing events in sample space, and the geodesics as the most probable direction of its growth. But this would take a leap of faith on their part to believe that there is a logical explanation for everything even if we don't know it yet. How can we escape the conclusion that physic is a mathematical description of logic when we impose the requirement of logic and mathematics on our physics to begin with?
 
  • #61


Originally posted by Mike2
We are looking for physical laws that are logical in every way, and which can be described by mathematics. You've seen Venn diagrams used to show how to construct AND's and OR's of logic. And these AND's and OR's can just as easily be describe in a sample space. These spaces can be parameterized with coordinates. And they look very much like the manifolds talked about in physics. AND's and OR's are included in both.

If we ever expect to find mathematical laws of physics that are logical in every way, then we should realize that they will be a description of how events grow in sample space.

We seem tantilizingly close to justifying the geometry of physics. The Action integral is proportional to the surface area of the world sheet. The Lagrangian is the generalized gradient and is equal to zero so that it describes a geodesic, etc. But they have no reason for this geometry other than to say it works. It might be possible to recognize these world-sheets as growing events in sample space, and the geodesics as the most probable direction of its growth. But this would take a leap of faith on their part to believe that there is a logical explanation for everything even if we don't know it yet. How can we escape the conclusion that physic is a mathematical description of logic when we impose the requirement of logic and mathematics on our physics to begin with?
We can't "escape the conclusion that physic is a mathematical description of logic when we impose the requirement of logic and mathematics on our physics to begin with". This is my point. How can we avoid agnst? Do all theories lead to questions? It is certainly fun to persue this, but is it possible to find a 'theory of everything'?
 
  • #62
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Originally posted by S = k log w
We can't "escape the conclusion that physic is a mathematical description of logic when we impose the requirement of logic and mathematics on our physics to begin with". This is my point. How can we avoid agnst? Do all theories lead to questions? It is certainly fun to persue this, but is it possible to find a 'theory of everything'?
Please see my Website at:

http://www.sirus.com/users/mjake/StringTh.html [Broken]

where I show how it might be possible to derive physics from logic. If we impose a coordinate system on Venn diagrams and assume a function that tells us whether samples exist or not within a region, then we have the mathematics to describe logic. Then since physical situations are the propositions of logic, and we have a mathematical description of propositions, therefore, we have a mathematical description of physics.

Following the geometry invovled with this scenario, I've come up with something that is beginning to look a lot like string thoery.
 
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  • #63
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Originally posted by Mike2
If we impose a coordinate system on Venn diagrams and assume a function that tells us whether samples exist or not within a region, then we have the mathematics to describe logic. Then since physical situations are the propositions of logic, and we have a mathematical description of propositions, therefore, we have a mathematical description of physics.
The question comes up as to what physical thing are we sampling with time. What is this density function, where did the boundaries of these events come from, etc?

The answer is that it doesn't matter. Whatever it is, the mathematics will be the same.
 
  • #64
3,077
4
For more on LQG, see next month's Scientific American article by Lee Smolin.
 
  • #65
45
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On strings

If Strings are THE fundamental building blocks of everything, and they have a 'tension', then does that mean that they are deformable, and how can anything that is NOT built of other smaller things be deformable ?

It would be nice to have a definitive answer on this preferrably from someone who thought these things up in the first place.

And if they aren't deformable, then how does the 'tension' manifest itself; is it just a 'virtual tension' ?
 
  • #66
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Originally posted by Seafang
If Strings are THE fundamental building blocks of everything, ...
If any kind of integration is done along the length of the string, then they are adding up infinitesimal portions of something that is physical. This also implies a continuous variable that has physical meaning.
 
  • #67
45
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The Logic of angst etc.

I found that discussion to be interesting, particularly the question 'is it possible to have a 'theory of everything' ?

To me the mathematics is all pure fiction; we made it up in our heads, and nothing that we discuss in mathematics exists in nature.

Some won't believe that but it is true. there are no points or lines or circles or any of those things in the universe. But there are approximations to them in our models of the universe. The equation for a sphere does not explain the existence of 8000 meter mountains on the surface.

So it may be possible to create a theory (mathematics) of a 'model of everything'. But I doubt that we can ever construct a model that behaves like the real universe.
 
  • #68
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Originally posted by Seafang
So it may be possible to create a theory (mathematics) of a 'model of everything'. But I doubt that we can ever construct a model that behaves like the real universe.
right. The mathematics comes from imposing an arbitrary coordinate system over the location of the physical objects which are being considered. The set of objects exists independently of the coordinates we impose. And the math we use is an attempt to describe the relationships we see between these objects.

Since the coordinates are arbitrary, we expect the underlying objects to be described by functions that do not change with whatever coordinate system is imposed. These intrinsic characteristics are "invariant" with coordinate transformations. They are "symmetric" with respect to coordinate changes.

It turns out that this requirement of symmetry or invariance is the only thing we need to discern characteristic values that are conserved and do not change with time or position. And because of that we can know when interactions have taken place and what they produced. For we measure these characteristics to have increased or decreased due to interactions with others. We can know that particular events must have taken place because we can see how things have changed.
 
  • #69
I think strings are made out of either taffy or mozerella cheese.

mmmmmm, cheeese.
 
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  • #70
920
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I have the book "Three roads to quantum gravity", and it says that strings are composed of little pieces called string bits. I'm not sure if these pieces are fundamental though
 
  • #71
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Bits and fragments of space-time, as Smolin tends to term them. Together they form space-time.
 
  • #72
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Originally posted by paultrr
Bits and fragments of space-time, as Smolin tends to term them. Together they form space-time.
Hi Paul,

As you remember from superstringtheory.com such concept of Smolin fits into my approach because then the bits (and fragments) are just oscillating spacetime membrane. What appears to us as closed (and open-end) strings may be a mathematical cut of vibrating spacetime peaks (like a circle represents a tube in 2D). You can see what I mean on http://www.mu6.com/stringtheory_peaks.html .

Remember our discussion how only one giant closed string would be identical as a giant spherical membrane? We only needed ONE string to explain all. In the mean time my website developed in graphic presentations such as an image where I point out the similarity of Alan Guth's pocket universes with my holon creation. http://www.mu6.com/spacetime2.html . Guth's false vacuum is then the (non-structural) Prior-Geometry and pocket universes contain then the (structured) duality of holons (Quantum packages/Baskets).

BTW nice seeing your back here ;-)

Dirk
 
  • #73
41
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No, problem. Been mostly buzy on the outside lately and with the holiday and all.
 
  • #74
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Originally posted by pelastration
Hi Paul,

As you remember from superstringtheory.com such concept of Smolin fits into my approach because then the bits (and fragments) are just oscillating spacetime membrane. What appears to us as closed (and open-end) strings may be a mathematical cut of vibrating spacetime peaks (like a circle represents a tube in 2D). You can see what I mean on http://www.mu6.com/stringtheory_peaks.html .
You show a portion of a membrane extruding outwards and strings as a slice of this protrusion. My question is what is this plane that is cutting these protruding portions of the membrane?
 
  • #75
138
0
Originally posted by Mike2
You show a portion of a membrane extruding outwards and strings as a slice of this protrusion. My question is what is this plane that is cutting these protruding portions of the membrane?
Mike2,
I just try to represent 'a string' as a 2D projection of an oscillating 3D membrane peak. A closed string could then represent the avarage vibration of such 'peak'. This a personal vision (different from official ideas). I just try to find out if the actual (official) concept of strings fits with the idea that strings are just part of the brane and - in second stage - can couple to become QM-baskets (second picture). The spacetime is IMO non-breakable and can not be teared or cut. So the 'cutting' is just a graphical 'slide' and 'top-view' projection. Sorry for the confusion.
 

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