Freethought & Rationalism Archive

ohwilleke · 04-04-2002, 12:55 PM

Maybe a year or two ago, I saw an brief mention in Science News of experiments
that suggested that the electron,
rather than being a fundamental particle, might, like the proton and neutron,
actually be composed of three subparticles.
Another study suggested particles of 1/5 of an electron charge.
Does anyone know what has happened since?

Links to relevant articles:
<a href="http://www.sciencenews.org/20000930/note3.asp" target="_blank">http://www.sciencenews.org/20000930/note3.asp</a>
<a href="http://www.sciencenews.org/sn_arc99/6_19_99/note7ref.htm" target="_blank">http://www.sciencenews.org/sn_arc99/6_19_99/note7ref.htm</a>
<a href="http://www.sciencenews.org/20000930/note3ref.asp" target="_blank">http://www.sciencenews.org/20000930/note3ref.asp</a>
<a href="http://www.sciencenews.org/sn_arc99/6_19_99/content.htm" target="_blank">http://www.sciencenews.org/sn_arc99/6_19_99/content.htm</a>
<a href="http://www.nature.com/DynaSearch/App/DynaSearch.taf?target=journals&_action=search&firs t_page=true&site_source=nature" target="_blank">http://www.nature.com/DynaSearch/App/DynaSearch.taf?target=journals&_action=s earch&first_page=true&site_source=nature</a>
<a href="http://www.science-frontiers.com/sf115/sf115p15.htm" target="_blank">http://www.science-frontiers.com/sf115/sf115p15.htm</a>
<a href="http://www.sciencemag.org/cgi/search?volume=&firstpage=&author1=&author2=&titlea bstract=Slicing+Electron+Charge&fulltext=&fmonth=O ct&fyear=1996&tmonth=Apr&tyear=1998" target="_blank">A VERY LONG URL</a>

If an electron is composite, does anyone have any idea what this might imply for String theory?

[April 04, 2002: Message edited by: ohwilleke ]
[Edited to fix a very long URL.]

[ April 05, 2002: Message edited by: Bill ]

Bill · 04-05-2002, 02:06 AM

Quote:

Originally posted by ohwilleke:
If an electron is composite, does anyone have any idea what this might imply for String theory?

Based upon what I've read from Brian Greene's book <a href="http://www.secweb.org/bookstore/bookdetail.asp?BookID=186" target="_blank">The Elegant Universe</a>, any discovery of this sort would knock all of particle physics into a cocked hat because the entire standard model (which string theory is an attempt to explain) is predicated upon a table of relationships which, in turn, depends upon the electron being a fundamental particle.

So, if the electron is really composed of three to five "somthings," then the entire table of "fundamental particles" which defines the Standard Model will need to be scrapped, and since string theory is an attempt to explain why that table exists in the relationships stated therein, string theory would lose its "grounding in reality" and could not be reformulated until some sort of replacement for the Standard Model is developed.

Still, the basic idea of string theory (that all "fundamental particles" are really just vibrating loops of space/time "string") would remain intact. But until we settle on exactly what is "fundamental" and what is not "fundamental," string theory can't be developed as a mathmatical "explanation" of that set of relationships.

== Bill

ohwilleke · 04-05-2002, 10:23 AM

This is one of the reasons the whole composite electron idea intrigues me. It an important experimental based parameter for new theories of everything. I am not convinced that it would be a big change in the Standard model itself. Quantum electrodynamics would still hold true for almost all circumstances, and you could just add a few more spin 1/2 particles and another fundamental force with a spin 1 transmitter to the Standard Model chart (? the "uberstrong force" carried by a "U" particle?) that doesn't affect our lives very much. But, it would really confuse string theorists who are already making up all sorts of extra dimensions and supersymmetric particles with no basis in experiment basically in pursuit of a "numerologically correct" theory that predicts nothing different than the existing model.

Bill · 04-06-2002, 05:24 PM

Quote:

Originally posted by ohwilleke:
This is one of the reasons the whole composite electron idea intrigues me. It an important experimental based parameter for new theories of everything. I am not convinced that it would be a big change in the Standard model itself. Quantum electrodynamics would still hold true for almost all circumstances, and you could just add a few more spin 1/2 particles and another fundamental force with a spin 1 transmitter to the Standard Model chart (? the "uberstrong force" carried by a "U" particle?) that doesn't affect our lives very much. But, it would really confuse string theorists who are already making up all sorts of extra dimensions and supersymmetric particles with no basis in experiment basically in pursuit of a "numerologically correct" theory that predicts nothing different than the existing model.

The one thing to remember is that string theory really is grounded in relativity, as the formulaters of its earliest precursor (Kaluza and Klein) felt that relativity itself screamed out for the extra dimension of space in order to be able to properly unify the then-known forces. So, while all of the practical work of string theory might go out the window, certainly the underlying basic concepts would survive the reworking of the Standard Model to incorporate some sort of tri-particle electron.

== Bill

Steven S · 04-07-2002, 08:54 AM

Quote:

Originally posted by Bill:
So, if the electron is really composed of three to five "somthings," then the entire table of "fundamental particles" which defines the Standard Model will need to be scrapped, and since string theory is an attempt to explain why that table exists in the relationships stated therein, string theory would lose its "grounding in reality" and could not be reformulated until some sort of replacement for the Standard Model is developed.

From what I understand of it, I didn't know string theory(ST) is even now "ground[ed] in reality". From what I've read ST predicts every boson has a corresponding fermion of the same mass, or superpartner. This prediction is wrong, or it is better to say, there is still no evidence for it. To explain the lack of superpartners particle theorists say this symmetry is spontaneously broken. But I guess no one knows how this works yet. I think if supersymmetric partners are not discovered in the next round of experiments at CERN and Fermilab this decade ST might be in trouble. Of course if they don't find the Higgs boson either the standard model will be in trouble too.

Bill · 04-07-2002, 11:02 AM

Quote:

Originally posted by Steven S:
From what I understand of it, I didn't know string theory(ST) is even now "ground[ed] in reality". From what I've read ST predicts every boson has a corresponding fermion of the same mass, or superpartner. This prediction is wrong, or it is better to say, there is still no evidence for it. To explain the lack of superpartners particle theorists say this symmetry is spontaneously broken. But I guess no one knows how this works yet. I think if supersymmetric partners are not discovered in the next round of experiments at CERN and Fermilab this decade ST might be in trouble. Of course if they don't find the Higgs boson either the standard model will be in trouble too.

I think that there is broad agreement on the point that the Standard Model (SM) is clearly incomplete. Just how to extend the SM into the next generation of physics is exactly the question being posed by the experiments you refer to, above. I've extracted the following summary from the recent report summarizing the results for Run 1 at Fermilab (the report is <a href="http://d0server1.fnal.gov/projects/results/runi/highlights/highlight_document/Highlights_v18_final.html" target="_blank">HERE</a> for any who are interested):

Quote:

It is an amazing feature of the Standard Model that, despite its extraordinary predictive power, it is almost surely incomplete. There are 26 parameters needed to specify the SM, and these can only be supplied by experiment. The strong and electroweak interactions that jointly make up the SM are seemingly unrelated entities; we would prefer to see a unification of these forces but the SM does not do this. The mechanism that breaks the underlying symmetry of the electroweak interaction, and thereby provides disparate masses to W/Z bosons and the photon, is not understood; in the SM the Higgs boson is inserted to provide the symmetry breaking, but its mass is expected to be 10^14 times larger than that of the W and Z bosons unless some fantastic "fine tuning" is at work. Beyond these defects, the SM offers no clue as to why there are three generations of quark and lepton families with nearly identical properties apart from their mass. It can accommodate, but not explain the existence of CP violation, or why the cosmological constant that should be of order 10^100 GeV is close to zero, or how to get gravity into a unified framework with the other forces.

Twenty years of precision tests of this model have resulted in an enormous number of successful comparisons of data and theory, with no verified departure from the SM. Despite this impressive predictive power, we firmly believe that the SM is nothing more than a low-energy approximation to a more general theory, the one that explains our world in its completeness and puzzling beauty. This is a very interesting situation, comparable to instances in the past that foreshadowed a major shift of paradigm. Are we completely blind in our search for this more complete theory? The answer is "probably not". We have several hypotheses that we consider as strong candidates for extensions beyond the SM. At the same time, it is imperative that we look for any possible deviations from predictions of the SM, and the D� experiment has been a pioneer in such studies.

One set of possible extensions of the SM, usually associated with a postulated new super-strong force involving new massive families similar to the quarks, require the presence of particles called leptoquarks. The leptoquarks would have the properties of both leptons and quarks, and thus would let quarks and leptons interact in a non-SM way. In 1997, the possibility of existence of leptoquarks got a boost from experiments at HERA. By colliding positrons and protons, the HERA experiments could produce single leptoquarks. In February 1997, the experiments H1 and ZEUS announced an excess of events over SM expectations at large q2, with an invariant mass around 200 GeV, which could be interpreted as due to leptoquark production. The evidence was not compelling, but the possible sighting could have had revolutionary implication, and it therefore set the Tevatron experiments in motion to add information.

At D� and CDF, leptoquarks can be produced in pairs via the strong interaction. This mechanism is well understood and is relatively model independent. The high energy of the Tevatron offers the possibility of searching for leptoquarks to masses higher than accessible at HERA. D� physicists immediately teamed up for the search. It took three months of analysis to unambiguously establish that the excess that HERA saw was not due to leptoquarks. D� used advanced data-analysis techniques, such as neural networks and other methods of multivariate analysis, introduced earlier in top-quark studies at D�. These novel techniques allowed D� to establish the world�s best limits on the existence of leptoquarks that could decay into electrons and quarks. The lower limit on mass of the leptoquark from the D� experiment alone was 225 GeV, more than enough to rule out the possibility for the HERA event-excess of being interpreted as evidence for leptoquark production. Combined with the 213 GeV limit obtained by CDF, the two Tevatron experiments were able to rule out the existence of these particles with masses below 242 GeV. More general D� limits on the mass of the first generation leptoquarks (MLQ), as a function of the probability that these particles decay into electron and quark (b), are shown on the left side of Fig. 10.

Supersymmetry (SUSY) has been suggested as a possible cure for many of the shortcomings of the Standard Model. Space-time symmetries such as those of translation or rotations of coordinates lead to momentum and energy conservation. Supersymmetry postulates a further symmetry between bosons (integer-spin particles) and fermions (half-integer-spin particles), thereby generalizing the Poincare group describing space and time. This radical reshaping of our understanding of space-time is also a key ingredient in the theory of strings in multiple dimensions. When used as a phenomenological ingredient of physics at the scale of present-day experiments, it provides a natural solution to the shortcomings of the SM involving the instability of the mass of the Higgs boson, and permits the unification of the strong and electroweak forces. Supersymmetry predicts that each known fermion and boson should have a mirror "superpartner" of the opposite type. Clearly, supersymmetry is broken, since there is no spin-zero superpartner for the electron at 0.511 MeV. But to be self-consistent, supersymmetry predicts that the superpartners should be found with masses below 1000 GeV, and some could be within reach of discovery at the Tevatron.

The D� experiment has searched for traces of supersymmetry in a variety of processes. So far, these searches have not been successful, and have resulted only in limits on the existence of superpartners. Depending on the model parameters, squarks and gluinos (the superpartners of quarks and gluons, respectively) with masses less than about 260 GeV have been excluded. The right side of Fig. 10 shows the region of supersymmetry parameter space over which the D� results have ruled out squarks and gluinos. The parameters M0 and M1/2 refer to the unified masses of the spin zero and spin one-half superpartners at the scale of unification of forces. Limits were also set on masses of charginos and neutralinos, the superpartners of the W, Z, and Higgs bosons. Despite these negative results, hopes are high as capabilities for discovering supersymmetry improve dramatically in the next Tevatron collider run. The mass reach will be about 100 GeV higher than present limits on superpartner masses, bringing D� into a very interesting range of SUSY parameter space.

Among other fundamental symmetries probed by the D� experiment is the "broken" symmetry between the electric and magnetic charges. We know that free carriers of electric charge exist, but there is no trace of a free magnetic charge, or magnetic monopole. If monopoles exist, one would expect pairs of high-energy photons to be produced at the Tevatron at a much higher rate than predicted by the Standard Model. This indirect search, though unsuccessful, yielded the most restrictive limit on the mass of a possible magnetic monopole.

Recently, a novel idea was introduced for physics beyond the SM. It originates from string theory that views all known particles as vibrations of tiny �strings� of energy. The recent success of string theory in explaining entropy flow in black holes has drawn much attention. String theory, or its subsequent elaboration as membrane or M-theory, seeks to explain all physical phenomena using structures in a universe with 10 or 11 spatial dimensions and time. The extra (beyond the usual four) dimensions are believed to be "curled up" at a scale of at most 10�19 cm. However, recent suggestions predict that some of these extra dimensions may be confined to a much larger scale, perhaps of the order of one millimeter. If this is correct, then the highest energy scale we know of, the so-called Planck scale might be much lower than initially realized (~ 1 TeV, and not 10^16 TeV). D� is currently looking for possible manifestations of this predicted signal in several channels.

So, as you say, the next run at Fermilab ought to discover something about the predicted superpartners. Whether or not it goes on and says something significant about string theory itself is another matter entirely. Strings are so small that their study is all but impossible, given the current physical limits on what our instruments can probe. We will probably need to construct an instrument out in space on a huge scale in order to have any real hope of probing string theory directly.

== Bill

Steven S · 04-07-2002, 03:42 PM

Quote:

Originally posted by Bill:
Whether or not it goes on and says something significant about string theory itself is another matter entirely. Strings are so small that their study is all but impossible, given the current physical limits on what our instruments can probe.
== Bill

Well, not detecting superpartners will say something about *super*string theory it seems. See this sci.physics.research newsgroup post from a rather enthusiastic proponent of ST:
<a href="http://www.lns.cornell.edu/spr/2001-08/msg0034596.html" target="_blank">http://www.lns.cornell.edu/spr/2001-08/msg0034596.html</a>
Or if you don't want to wade through much of the text he says supersymmetry is a prediction of superstring theory when one tries to incorporate fermions into ST. Of course, finding superpartners will not say ST is right or wrong but their nonexistence I think makes me doubt ST is on the right track.

Steven S

Bill · 04-07-2002, 04:38 PM

Quote:

Originally posted by Steven S:
Of course, finding superpartners will not say ST is right or wrong but their nonexistence I think makes me doubt ST is on the right track.

Brian Green says that ST is a 21st century scientific discovery that was accidently discovered during the 20th century. It had a major change in "tracks" as recently as 1995, prior to which it was all but "given up for dead." It would not surprise me in the least if at least one more major changes in "tracks" were to be required prior to the penultimate formulation of ST.

So far, nobody has written down ST as anything more than the vaguest sorts of approximations. As the quote I last posted makes clear, it would appear that the entire Standard Model is nothing but a low energy approximation of the penultimate Theory of Everything (ToE). I would not, could not, should not ever say that today's version of ST was "ready for prime time."

Nonetheless, people would not be spending so much time, energy, and money on ST if even the most preliminary sorts of results produced to date weren't so darn intriguing!

== Bill

Steven S · 04-08-2002, 11:25 AM

Quote:

Originally posted by Bill:
Nonetheless, people would not be spending so much time, energy, and money on ST if even the most preliminary sorts of results produced to date weren't so darn intriguing!
== Bill

I'm a physics graduate student working in particle
theory. I'm generally ambivalent towards ST mostly since I don't know enough physics to say whether I like it or not. Although, I'm not as extreme in my views as this guy:
<a href="http://xxx.lanl.gov/abs/physics/0102051" target="_blank">http://xxx.lanl.gov/abs/physics/0102051</a>
I do feel ST may have been somewhat oversold to the public and funding agencies.

Steven S

Bill · 04-08-2002, 07:02 PM

Quote:

Originally posted by Steven S:
I'm a physics graduate student working in particle theory. I'm generally ambivalent towards ST mostly since I don't know enough physics to say whether I like it or not. Although, I'm not as extreme in my views as this guy:
<a href="http://xxx.lanl.gov/abs/physics/0102051" target="_blank">http://xxx.lanl.gov/abs/physics/0102051</a>
I do feel ST may have been somewhat oversold to the public and funding agencies.

I cannot disagree with this point, but even your cited critic notes that many paths seeming lead to common solutions:

Quote:

Another powerful and unifying idea shared by physics and mathematics is that of a group representation. Some of the most beautiful mathematics to emerge from string theory involves the study of (projective) representations of the group of conformal transformations and of one-dimensional gauge groups ("loop groups"). This work is essentially identical with the study of two dimensional quantum field theory. The analogous questions in four dimensions are terra incognita, and one of many potentially promising areas particle theorists could look to for inspiration.

So, even if ST comes to naught, in terms of a "Theory of Everything" (ToE), it does seem clear to me that it is still a fertile field for the development of "new technology" (new mathmatical models, new computational methods, etc.) for resolving whatever finally does emerge as the real ToE.

But I keep reading, over and over again, that this or that aspect of this or that theory appears to be "an approximation" of some aspect of the eventual ToE. I frankly doubt that we are anywhere near a real ToE, and so I am forced to conclude that each useful part of the major theoretical approaches (CI, QED, ST, etc.) brings to the table some small piece of the ultimate ToE.

I can add one thing to this discussion, choosing my point of departure from the critical essay you cite to, above:

Quote:

Sheldon Glashow describes string theory as "the only game in town", but this begs the question. Why is it the only game in town?

From my personal perspective, the answer to this question is found in <a href="http://www.secweb.org/bookstore/bookdetail.asp?BookID=186" target="_blank">Brian Greene's book</a>. Greene notes that ST solves the greatest puzzlement in relativity and quantum mechanics through the simple artifact of eliminating the idea of "point particles" and "point forces." Since the smallest possible thing is a "string" which approximates the Planck size, and thus the "string" is at least two-dimensional (and can NEVER be merely one-dimensional), the perplexing occurrances of infinity in relativity and QM naturally disappear, and they do so in a way that appears to unify gravity, relativity, and quantum mechanics into a single unified whole (the elusive ToE). So far as I know, no purely quantum approach to the unification of gravity has been successful in eliminating the chaos and infinities which lie beneath the Planck level. ST succeeds by demonstrating that something about the Planck size is the natural limit, and that if you press towards a smaller size, the results match those of an increasingly larger size.

With all that said, I will state for the record that I am strongly in favor of diversifying research programs, and so I could certainly support the third and fourth suggestion made by your cited critic:

Quote:

3. Instead of trying to hire post-docs and junior faculty working on the latest string theory fad, theory groups should try and identify young researchers who are working on original ideas and hire them to long nough erm positions that they have a chance of making some progress.

4. Funding agencies should stop supporting heorists who propose to continue working on the same ideas as everyone. They should also question whether it is a good idea to fund a large number of conferences and workshops on the latest string theory fad. Research funds should be targeted at providing incentives for people to try something new and ambitious, even if it may take many years of work with a sizable risk of ending up with nothing.

We seem to have reached a point in human progress where it is no longer possible for a single human brain to encapsulate some key idea and write it down, such as Einstein did for the Theory of Relativity. And as the size, complexity, and costs of the instruments required to verify any given theoretical prediction have grown to astronomical proportions (to the extent that Congress decided to cancel the construction of the supercollider when it was less than 10% finished because of the expense involved), so it seems that we will be forced to either forgo progress or find ways to forum into more efficient teams of theoreticians and experimenters to try to optimize the exploration of what is new in fields such as "high energy physics."

Of course, scientific method requires verification, so some amount of duplication of efforts is required for proper execution of the scientific method. Fermilab and CERN can clearly back each other up, so for the time being, it would appear that things are OK in this regard. But if additional funds can be made available, on either side of "the pond," I would not care to see those funds go into further duplication of efforts, but would rather see them expended on "basic research" into something entirely new.

== Bill

04-04-2002, 12:55 PM	#1
ohwilleke Veteran Member Join Date: Jun 2000 Location: Denver, Colorado, USA Posts: 4,834	Composite electrons. Maybe a year or two ago, I saw an brief mention in Science News of experiments that suggested that the electron, rather than being a fundamental particle, might, like the proton and neutron, actually be composed of three subparticles. Another study suggested particles of 1/5 of an electron charge. Does anyone know what has happened since? Links to relevant articles: <a href="http://www.sciencenews.org/20000930/note3.asp" target="_blank">http://www.sciencenews.org/20000930/note3.asp</a> <a href="http://www.sciencenews.org/sn_arc99/6_19_99/note7ref.htm" target="_blank">http://www.sciencenews.org/sn_arc99/6_19_99/note7ref.htm</a> <a href="http://www.sciencenews.org/20000930/note3ref.asp" target="_blank">http://www.sciencenews.org/20000930/note3ref.asp</a> <a href="http://www.sciencenews.org/sn_arc99/6_19_99/content.htm" target="_blank">http://www.sciencenews.org/sn_arc99/6_19_99/content.htm</a> <a href="http://www.nature.com/DynaSearch/App/DynaSearch.taf?target=journals&_action=search&firs t_page=true&site_source=nature" target="_blank">http://www.nature.com/DynaSearch/App/DynaSearch.taf?target=journals&_action=s earch&first_page=true&site_source=nature</a> <a href="http://www.science-frontiers.com/sf115/sf115p15.htm" target="_blank">http://www.science-frontiers.com/sf115/sf115p15.htm</a> <a href="http://www.sciencemag.org/cgi/search?volume=&firstpage=&author1=&author2=&titlea bstract=Slicing+Electron+Charge&fulltext=&fmonth=O ct&fyear=1996&tmonth=Apr&tyear=1998" target="_blank">A VERY LONG URL</a> If an electron is composite, does anyone have any idea what this might imply for String theory? [April 04, 2002: Message edited by: ohwilleke ] [Edited to fix a very long URL.] [ April 05, 2002: Message edited by: Bill ]</p>

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04-05-2002, 10:23 AM	#3
ohwilleke Veteran Member Join Date: Jun 2000 Location: Denver, Colorado, USA Posts: 4,834	This is one of the reasons the whole composite electron idea intrigues me. It an important experimental based parameter for new theories of everything. I am not convinced that it would be a big change in the Standard model itself. Quantum electrodynamics would still hold true for almost all circumstances, and you could just add a few more spin 1/2 particles and another fundamental force with a spin 1 transmitter to the Standard Model chart (? the "uberstrong force" carried by a "U" particle?) that doesn't affect our lives very much. But, it would really confuse string theorists who are already making up all sorts of extra dimensions and supersymmetric particles with no basis in experiment basically in pursuit of a "numerologically correct" theory that predicts nothing different than the existing model.

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