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Author Topic:   String! Theory! What is it good for ?!?
Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


Message 46 of 107 (535767)
11-17-2009 8:01 PM
Reply to: Message 32 by cavediver
11-15-2009 4:32 AM


Re: Yes, that's science
And all this, amazingly, before we even got to Woit and Smolin.
Peter Woit has published 8 physics papers over the last 20 years in peer reviewed physics journals and a few more online. Most are available through the SPIRES search engine. His earliest work verified Edward Witten's 1979 quantum chromodynamic formula for the eta-prime mass in terms of the second derivative of the vacuum energy.
Woit argues that there are better approaches than string theory which are not being taken seriously. One line of investigation he has suggested is that "spontaneous gauge symmetry breaking is somehow related to the other mysterious aspect of electroweak gauge symmetry: its chiral nature." In a posting to Not Even Wrong he remarks that
"The SU(2) gauge symmetry is supposed to be a purely internal symmetry, having nothing to do with space-time symmetries, but left and right-handed spinors are distinguished purely by their behavior under a space-time symmetry, Lorentz symmetry. So SU(2) gauge symmetry is not only spontaneously broken, but also somehow knows about the subtle spin geometry of space-time."
Woit believes that a proper investigation of what can be done using the geometry of spinors in just four dimensions (along with many other possibly fruitful ideas) has been prevented by an obsession with theories, such as string theory, that speculate about added dimensions.
Peter Woit - Wikipedia
Woit runs the blog mentioned, which discusses disciplines and ideas he and his supporters class as pseudoscience, using an organizational theme derived from Pauli's comments regarding useless speculation.
Not Even Wrong
... a friend showed him the paper of a young physicist which he suspected was not of great value but on which he wanted Pauli's views. Pauli remarked sadly, 'That's not right. It's not even wrong.'
Not even wrong - Wikipedia
Lee Smolin's story seems a little more complex. He originally wanted the demogorge of String Theory to eat his ideas about Loop Quantum Gravity just as it had eaten Relativity, Quantum Mechanics, Supersymmetry, and the most substantial amount of the LHC schedule. But when the elitist academic aristocracy sniffed at his little preciousss and said "No thanks, Man" he vowed to bring their ivory towers down around their ears.
The 2006 publication of The Trouble with Physics generated much controversy and debate about the merits of string theory. The book was criticised by some physicists, such as Joseph Polchinski[7] and Lubo Motl.[8] In his earlier book Three Roads to Quantum Gravity (2002), Smolin had stated that loop quantum gravity and string theory were essentially the same concept seen from different perspectives. In that book, he also favored the holographic principle. The Trouble with Physics, on the other hand, was strongly critical of string theory and of its prominence in contemporary theoretical physics. Smolin suggests that string theory suffers from serious deficiencies, and has an unhealthy near-monopoly in the particle theory community. He called for a diversity of approaches to quantum gravity, and argued that more attention should be paid to loop quantum gravity, an approach Smolin has devised. Finally, The Trouble with Physics is also broadly concerned with the role of controversy and the value of diverse approaches, in the ethics and process of science.
Smolin's thesis found support in one corner. In the same year as that in which The Trouble with Physics was published, Peter Woit also published a book for nonspecialists, whose conclusion was similar to Smolin's, namely that string theory was a fundamentally flawed research program.
Lee Smolin - Wikipedia

This message is a reply to:
 Message 32 by cavediver, posted 11-15-2009 4:32 AM cavediver has replied

Replies to this message:
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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 47 of 107 (535813)
11-18-2009 5:00 AM
Reply to: Message 46 by Iblis
11-17-2009 8:01 PM


Re: Yes, that's science
Peter Woit has published 8 physics papers over the last 20 years in peer reviewed physics journals
Is that supposed to impress me
That is pathetic. As I said, he is a blogger who has found a niche that has gained him some recognition. And?
Smolin has an axe to grind. LQG is interesting and emerges from some very respectable work of Ashtekar, but has as many problems and issues with experimental verification as M-Theory, and is so far not as successful in giving low energy GR and QG results. But it is still excellent research material. Smolin feels that it is being ignored in favour of M-Theory. Throwing a fit and claiming that M-Theory is a complete waste and full of errors just makes us think he is a twat irrespective of the merits of LQG.

This message is a reply to:
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Son Goku
Inactive Member


(1)
Message 48 of 107 (536605)
11-24-2009 8:23 AM
Reply to: Message 37 by cavediver
11-15-2009 6:06 AM


Re: Yes, that's science
Of course this is incorrect, if we eliminated theories by the fact that they can't yet be tested we would have lost general relativity.
Although on the other hand I find the whole issue ridiculous. Fair enough if there was a big disagreement over QCD or the general framework of QFT, aspects of QM or GR. In that case there really would be a serious issue.
However I find these "battlegrounds" concerning theories which have never been tested (String, Loop Quantum Gravity(LQG), e.t.c.) to be a bit silly. Let's say somebody has strong opinions against LQG, what does it matter? If the theory is correct, they will eventually been shown to be wrong. There were people who thought GR and QFT were a load of arse and to be fair we needed those people, they're part of the scientific method.
I understand that these theories sometimes meet with unfair criticism, but it shouldn't really be a divisive issue like it has become in some people's minds. (Of course I'm not talking about you.)
Also sometimes the criticism can be helpful, I know a few string theorists who were actually surprised to hear that there was no proof that String Theories caculations were finite beyond second order, they'd just assumed Mandelstam's paper demonstrated it. Now there is more interest in the work of D'Hoker and Phong, who recently showed it at second order in this series of four papers:
http://arxiv.org/abs/hep-th/0110247
http://arxiv.org/abs/hep-th/0110283
http://arxiv.org/abs/hep-th/0111016
http://arxiv.org/abs/hep-th/0111040
Introduction here: http://arxiv.org/abs/hep-th/0211111
(I'm way behind, maybe they've now extended it to higher orders, I don't know.)
Of course I understand the frustration that some researches have on this being turned into a public issue by Smolin and Woit bypassing usual academic channels.
Although thankfully this was a mid-2000s issue, (almost) everybody has become more sensible now.

This message is a reply to:
 Message 37 by cavediver, posted 11-15-2009 6:06 AM cavediver has replied

Replies to this message:
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Son Goku
Inactive Member


Message 49 of 107 (536610)
11-24-2009 8:34 AM
Reply to: Message 33 by cavediver
11-15-2009 5:19 AM


Re: Questions
cavediver writes:
This was 1980. But it didn't work... it was so close, but it just wouldn't work as a sensible quantum gravity, despite the low order calculations looking as if there was no way it could fail. Something was missing, but what was a complete mystery. And so Sugra faded into the background.
Hey, I don't know if you've heard but N=8 Supergravity may be renormalizable. Again I know next to nothing about this stuff (which is pretty bad because I consider myself quite well read on renormalization in general, particularly rigorous results.), a link:
http://arxiv.org/abs/hep-th/0611086

This message is a reply to:
 Message 33 by cavediver, posted 11-15-2009 5:19 AM cavediver has not replied

  
Straggler
Member
Posts: 10333
From: London England
Joined: 09-30-2006


Message 50 of 107 (538038)
12-02-2009 5:46 PM
Reply to: Message 34 by Son Goku
11-15-2009 5:42 AM


Re: Questions
I have just seen you logon and it reminded me that I meant to ask:
Fermions and Bosons - I.e. as I understand it those particles that obey the Pauli exclusion principle and those that do not (respectively)
What is the difference in terms of string theory? If all particles are vibrating strings then what makes some fermions and some bosons?
Or have I got the complete wrong end of the stick here?

This message is a reply to:
 Message 34 by Son Goku, posted 11-15-2009 5:42 AM Son Goku has replied

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Straggler
Member
Posts: 10333
From: London England
Joined: 09-30-2006


Message 51 of 107 (538042)
12-02-2009 6:28 PM
Reply to: Message 33 by cavediver
11-15-2009 5:19 AM


Re: Questions
Cavediver writes:
Susy is the attempt to reconcile the two fundemental particle/field types: bosonic and fermionic. In the same way that a neutron and a proton are essentially the same thing (or an up and down quark - same thing really), just differentiated by electric charge. If we could switch off the electric charge, they would be identical. So each boson has a fermionic partner, which it would be identical to if the supersymmetric charge could be switched off and supersymmetry restored.
Looking at your posts it seems that you might have answered my question in Message 50 but that I have not understood properly.
I am not sure.
In terms of the conceptual model of vibrating strings what makes some particles (i.e fermions) obey the exclusion principle but others (i.e bosons) not?

This message is a reply to:
 Message 33 by cavediver, posted 11-15-2009 5:19 AM cavediver has replied

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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 52 of 107 (538372)
12-06-2009 6:11 AM
Reply to: Message 51 by Straggler
12-02-2009 6:28 PM


Answers, part 1
In terms of the conceptual model of vibrating strings what makes some particles (i.e fermions) obey the exclusion principle but others (i.e bosons) not?
Deep question! And perhaps biting off too much - you need to understand what makes particles fermions and bosons in the first place, before we start looking at string theory explanations.
Fermions are particles whose wavefunction changes sign on the swap of any two of the particles; e.g.
,
which immediately gives us the Pauli Exclusion Principle - if two identical fermions are located at the same point, then
and this can only be satisifed if . The lowest atomic orbital is allowed two electrons (1s2) because the electron can be distinguished by its spin - spin up or spin down. But you can only have one spin up electron in the shell, because the addition of a second will again give a zero wavefunction.
Boson wavefunctions are symmetric under exchange, so there is no such restriction -
.
This gives the possibility of
,
which gives rise to, amongst other things, Bose-Einstein condensates and lasers.
These are the only two sensible possibilities. I guess you could try to make a reality where the wavefunction halved on exchange,
,
but follow this through and you'll see it quickly falls apart.
Edited by cavediver, : No reason given.

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Son Goku
Inactive Member


Message 53 of 107 (538402)
12-06-2009 12:18 PM
Reply to: Message 50 by Straggler
12-02-2009 5:46 PM


Re: Questions
Hey Straggler,
I have some idea of how to answer your question, but to be honest I never really learnt much String Theory beyond introductory books. I see cavediver is answering the question, he'd be the person to listen to as he worked professionally in String Theory.

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Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


Message 54 of 107 (538420)
12-06-2009 3:18 PM
Reply to: Message 48 by Son Goku
11-24-2009 8:23 AM


Re: Yes, that's science
Here's a bit more Smolin. Interestingly, for someone who says superstring is unfalsifiable, he sounds like he's proposing two ways to test it
Smolin also points out that the string theory landscape is not Popper falsifiable if other worlds are not observable. This is the subject of the Smolin-Susskind debate. There are then only two ways out: traversable wormholes connecting the different parallel worlds and "signal nonlocality", as described by Antony Valentini, a scientist at the Perimeter Institute.
Lee Smolin - Wikipedia
Is this just nonsense though? The "wormholes as magic breaking causality" sort of problems I'm vaguely familiar with all seem to start with building your wormhole with both ends local and then dragging one end around spacetime to the place or relative date that you want to be able to stargate to. Obviously that won't work in this case. Is there something in string theory that would imply we could get our negative mass or perfect vacuum or whatever configured in such a way as to punch a hole through to another brane?
Here's what Susskind says about Smolin now, having sparred with him
Although the exchanges ended in 2004, the animosity remains. In 2006, Susskind criticized Smolin as a "mid-level theoretical physicist" whose "popular book-writing activities and the related promotional hustling have given him a platform high above that merited by his physics accomplishments."
Leonard Susskind - Wikipedia

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Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


Message 55 of 107 (538739)
12-09-2009 2:02 PM


Bolder-dash ...
... is suffering acute topic splay in a couple of places. I'm culling these remarks from Message 119 of Speed of Light
Bolder-dash writes:
Sorry to say, cavediver and a few others here who have great interest in science appear to be these kinds of people to me-obviously smart guys and have a great grasp of math equations, but perhaps because their minds are so in tune to these numbers, there isn't a lot of room left in there for intellectual imagination.
Just one question which I admit to knowing little about- How does one believe in string theory, while acknowledging that in order to make sense of the numbers we must first create fictitious other dimensions of varying amounts to compensate for the discrepancies, as well as admitting that it is completely untestable? Isn't that much more philosophy than science? Or perhaps not philosophy, but at least fairy tale?
Let's answer this stuff here where it belongs.
Just off the top of my head, the other dimensions in M-theory aren't fictitious, they are theoretical. In physics the word "fictitous" has a specific meaning, as in the case of fictitious forces like centrifugal force. These are effects that we find convenient to describe as if they were forces, but are actually inertia acting in resistance to real forces.
Also, I can't find anyone who is credible who says that string theory is in principle untestable. They just say that it will cost a lot, same as Relativity and the Standard Model have so far. Feel free to post references, though ...

Replies to this message:
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Bolder-dash
Member (Idle past 3631 days)
Posts: 983
From: China
Joined: 11-14-2009


Message 56 of 107 (538740)
12-09-2009 2:13 PM
Reply to: Message 55 by Iblis
12-09-2009 2:02 PM


Re: Bolder-dash ...
Yes, fair enough, this is a better place for this discussion.
The reason I called the other dimensions fictional, is just because the only reason for imaging these dimensions is because they are necessary to make the numbers fit. I think no one can say what these dimensions are, little yet show evidence for them.
To me its a bit like saying 2+2=9 and then when someone replies, no its doesn't it equals 4, and then I said, well in another dimension it equals 9.
And then you said, but that other dimension doesn't exist, I simply said, well its theoretical.
As far as a test for string theory goes, I guess first we have to define these other dimensions, and I don't think that is going to happen.
Edited by Bolder-dash, : No reason given.

This message is a reply to:
 Message 55 by Iblis, posted 12-09-2009 2:02 PM Iblis has replied

Replies to this message:
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Briterican
Member (Idle past 3949 days)
Posts: 340
Joined: 05-29-2008


Message 57 of 107 (538744)
12-09-2009 2:51 PM
Reply to: Message 52 by cavediver
12-06-2009 6:11 AM


/worship cavediver
I cannot pretend to even begin to understand the mathematics behind string theory, but can you answer this simple question for me cavediver?
Using quantum mechanics as an example, I think it is safe to say that there are some outlandish assumptions (or at least outlandish implications of some assumptions) inherent to quantum mechanics, and yet it (QM) is used as a tool to make extremely accurate predictions. This does not prove that it is an entirely complete and accurate model, but it seems fair to say that this demonstrates that it has to be right on some level.
  • Assuming the above statement is an accurate assessment, can the same thing be said of string theory in any sense?
  • If not, what is it that makes string theory so worth pursuing? Is it the potential to marry relativity and QM together?
Thanks in advance!
Edited by Briterican, : Never get it right the first time.

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Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


(1)
Message 58 of 107 (538749)
12-09-2009 3:10 PM
Reply to: Message 56 by Bolder-dash
12-09-2009 2:13 PM


Re: Bolder-dash ...
The reason I called the other dimensions fictional, is just because the only reason for imaging these dimensions is because they are necessary to make the numbers fit. I think no one can say what these dimensions are, little yet show evidence for them.
"Making the numbers fit" is how we discovered several of the planets in our solar system. This is called "predictions." String theory predicts that additional dimensions exist. We simply currently lack the ability to test those predictions and verify or falsify them.
It doesn't mean they're "fictional." It means "if this is correct, then these other things should exist." It's a hypothesis.
To me its a bit like saying 2+2=9 and then when someone replies, no its doesn't it equals 4, and then I said, well in another dimension it equals 9.
"Other dimensions" are not like what you see on Star Trek. When String Theory predicts additional dimensions, it's predicting additional dimensions...like time, length, width, and height. We experience reality in the aforementioned four dimensions, and string theory simply predicts that there may be additional dimensions that we are unaware of.
A dimension is not a reality, or world, or Universe. Much like a mutant is not a half-turtle, half-teenage ninja.
It's difficult for human beings to conceptualize additional dimensions because we only exerience the four. But think of it like the difference between a drawing on paper and the real world. Paper drawings consist only of two dimensions - length and height. The world we experience includes an additional spacial dimension - depth.
Time is also a dimension, but the nature of our existence forces us to only experience time as a linear progression of events in the direction of increasing entropy.
Additional dimensions would be similar, except that we apparently don't experience them directly.
Numbers and computers are far better able to represent additional dimensions than our brains.
As far as a test for string theory goes, I guess first we have to define these other dimensions, and I don't think that is going to happen.
They have been defined. The problem is only that the definition is not what you considered it to be.
String theory's major hurdle, as I understand it, is reaching a point in technological progress where we are able to actually test some of its predictions. Right now, it's like the discovery of a wobble in Neptune's orbit, but lacking the capability to see Pluto. The gravitational tug is forcing us to plug in an additional massive body to make the numbers fit, and so we can theorize that Pluto is out there.

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Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


(2)
Message 59 of 107 (538772)
12-09-2009 10:13 PM
Reply to: Message 56 by Bolder-dash
12-09-2009 2:13 PM


Re: Bolder-dash ...
To me its a bit like saying 2+2=9 and then when someone replies, no its doesn't it equals 4, and then I said, well in another dimension it equals 9.
This isn't totally out of line as an analogy, in that it's similar to the way that dealing with extra dimensions actually affects the math.
My favorite example for explaining cube-square effects is King Kong. If we take a normal 5-foot tall gorilla and make him "ten times bigger" -- ie 50 feet tall, and proportional -- we are actually increasing his total volume a thousand times. He's not just ten times as tall, he's ten times as wide, and ten times as deep, see?
So the first thing that happens is, he falls over. His feet support him based on a ratio of surface to weight, and while the weight has increased at least a thousand times, the surface has only increased one hundred times. In order for his feet to support him at "ten times bigger" (cubed, a thousand times) they themselves are going to have to instead be a smidge less than 32 times bigger (squared, 1024 times) to hold him up. And they won't fit on top of the Empire State Building anymore, will they? (The second thing that will happen is, his bones shatter, because they would need to be 1000 times as dense to support his weight, and changing size won't get you that, he needs a whole different kind of bone structure, but that's enough of this.)
So now let's consider Mr. A Square, of Flatland, who is only aware of two dimensions. The things he thinks of as volume are what we consider surfaces, the things he considers surfaces are what we would call borders. But he has some genuinely 3-dimensional objects penetrating his reality, of which he is only directly aware of a cross-section of. These are alive, for the sake of argument, or some kind of crystal perhaps, that he can effectively "double" the size of by feeding or watering or whatever. Because he is aware of two dimensions, he understands that this is really making them "4 times bigger" from his viewpoint. But in experimentation, by trying to move them around, for example, he determines that they are actually becoming 8 times heavier.
If he thinks about this enough, and extrapolates, he may come to understand that there must be an unexpected third dimension, that he cannot experience in the normal way that he experiences the two he has. If he keeps investigating more and more of these crystals or whatever they are and experimenting, he can become pretty sure of this.
Other phenomena that might alert him to this state of affairs are, if things somehow flip into mirror images of themselves from his point of view. This can happen to 2d objects because of rotation through the 3rd dimension. Another might be, if there are things that seem to appear and disappear, due to the fact that they sometimes penetrate his plane and at other times do not. Stuff falling down onto Flatland and bouncing off, for example. And so on ... He may even figure out a way to move himself in this newly-discovered unsenseable direction!
Now, with quantum mechanics we have long suspected the existence of more dimensions than the 4 we know. We get a lot of effects that seem to indicate this. When we split a photon, we don't get two half-photons, we get two complete photons at half the amplitude. When we break up fermions we get even more astounding results! Fractional spin is another great example, we have to turn a quantum particle around not once but twice to get back to our original state.
Just as a side note, almost everyone tends to use a 6 dimensional view of reality to get through their day: 3 of space, 3 more of time. That is, we believe we can make real decisions about the future, some aspects of which are objectively better or worse (up-down in time) and some of which are just personal preferences (left-right in time.) This has a lot more to do with conceptualizing Wheeler's "Many Worlds" than it does with genuine M-theory, but I think it's relevant to the discussion of whether other dimensions are useful or not, real or not.

This message is a reply to:
 Message 56 by Bolder-dash, posted 12-09-2009 2:13 PM Bolder-dash has replied

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Bolder-dash
Member (Idle past 3631 days)
Posts: 983
From: China
Joined: 11-14-2009


Message 60 of 107 (538824)
12-10-2009 12:06 PM
Reply to: Message 59 by Iblis
12-09-2009 10:13 PM


Re: Bolder-dash ...
Good post...not sure that it makes the needed dimensions for string theory any more believable, but interesting nonetheless.

This message is a reply to:
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Replies to this message:
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