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Author Topic: How do you know which way round a string goes?  (Read 3382 times)

Offline DoctorBeaver

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How do you know which way round a string goes?
« on: 03/07/2007 23:34:24 »
Apparently, in string theory, strings that oscillate to the left behave differently from strings that oscillate to the right. But how can you tell if what appears to be a right-handed string isn't really a left-handed string upside-down? And what about strings that are on their side?


 

Offline Soul Surfer

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How do you know which way round a string goes?
« Reply #1 on: 06/07/2007 10:32:42 »
I think its a bit like right handed and left handed threads  and right handed and left handed gloves you can't turn one into the other without moving it through the fourth dimension (or turning it inside out)
 

Offline DoctorBeaver

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How do you know which way round a string goes?
« Reply #2 on: 06/07/2007 10:43:01 »
I don't think it's as simple as that. Oh, and bear in mind this only refers to closed strings.

Closed strings are 1-dimensional loops. The only permitted oscillations are those that will fit into the circumference an integer number of times (and zero times). In some strings the oscillations go to the right, in others they go to the left. There is no difference in the oscillations apart from them going the opposite way around the loop. That means that an upside-down, left-handed string will look exactly like a right-way-up, right-handed string; except for the fact that they behave differently in some way.

 

Offline Soul Surfer

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How do you know which way round a string goes?
« Reply #3 on: 06/07/2007 11:02:22 »
Osscilation clockwise round a closed loop is different from oscillation anticlockwise its a bit like spin up and spin down in an electron.
 

Offline dentstudent

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How do you know which way round a string goes?
« Reply #4 on: 06/07/2007 11:04:11 »
Apparently, in string theory, strings that oscillate to the left behave differently from strings that oscillate to the right. But how can you tell if what appears to be a right-handed string isn't really a left-handed string upside-down? And what about strings that are on their side?


Is there up-side down in 11 dimensions?
 

Offline Soul Surfer

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How do you know which way round a string goes?
« Reply #5 on: 06/07/2007 11:10:11 »
Remember in quantum theory you gave to measure an object before you know what it is and in measuring "spin" you change it.
 

Offline DoctorBeaver

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How do you know which way round a string goes?
« Reply #6 on: 06/07/2007 11:51:03 »
Osscilation clockwise round a closed loop is different from oscillation anticlockwise its a bit like spin up and spin down in an electron.

I appreciate that. But what I want to know is, what is it about the oscillation that distinguishes a right-way-up loop from an upside-down, opposite oscillation loop? Why is the interaction of a right-string different from that of a left-string?

1 possibility I thought of (I'm either very wrong or I just haven't come across it anywhere yet) is that where part of the string enters higher dimensions, the orientation & direction of the oscillation as it passes into those higher dimensions cause different effects.

For instance, if the oscillation passed from our "normal" 4D universe into D5 then into D6, the effect could be different than had it passed from 4D -> D6 -> D5. If D5 & D6 have an effect on the string (different effects in each dimension) then in 1 case D6 would alter the combined effects of 4D & D5 and in the other case D5 would alter the combined effects of 4D & D6.

As an analogy, (22)+2 is different from (2+2)2

Remember in quantum theory you gave to measure an object before you know what it is and in measuring "spin" you change it.

Strings are too small for us ever to measure them.
« Last Edit: 06/07/2007 12:03:22 by DoctorBeaver »
 

Offline chrisdsn

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How do you know which way round a string goes?
« Reply #7 on: 07/07/2007 07:55:28 »
The same argument could be made regarding non-string (and experimentally
tested) physics. There there is a a difference between left and right-handed
particles. In this case this difference is whether the spin of a particle is
aligned with it's direction of motion or against (it's more complicated than this,
but i'm trying to keep the post short) . The natural assumption
(natural == my guess of what most people would think must be true) is that
physics laws are the same for our world and a mirror image world (parity
invariance). This would allow the "upside down" argument. 

Since around ~1955 this has been known to not respected by reality.
The experimental evidence was found by Wu et al from Columbia, and
the theoretical understanding is due to T.D. Lee and C.N. Yang
(1957 Nobel Prize), who also realized that charge-conjugation
symmetry must be broken (particles are different than
anti-particles).

My (non-expert) understanding is that the left-right difference
in string theory is not necessary theoretically, but just a way
to put together a theory that *might* look like real world.
In other words: they put the difference in by hand, as they know the
real world is like that.   
 

Offline DoctorBeaver

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How do you know which way round a string goes?
« Reply #8 on: 07/07/2007 09:34:38 »
I think I get that. Thanks again Chris.
 

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How do you know which way round a string goes?
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