arXiv:1012.5417v1 [physics.pop-ph] 24 Dec 2010 ai ibr.Hsdetermination His Hilbert. David 1. FIGURE oyb og(o e nse) fe adsrgl of fanati- struggle and hard superstition cism. often ignorance, finished), against yet people (not his- brave cosmologically long throughout a the accomplished by been to tory has length tiny task explore This extremely to large. the able from been have scales scientists senses brain), “magnified” as and interpreted be and can detection (which analysis for help computers the and With devices Nature. sophisticated of of understanding human the of tus his before! Nature. of day one of expression just first law theorem the any incompleteness announced famous grasp had to Gödel mind fact, ca- too In human unlimited as the the in many of belief by pacity bold viewed a be conveying Sci- German can optimistic, the Physicians, of and Meeting Annual entists 1930 the wissen. at Hilbert werden Wir (“ paper wissen. this entitling statements defiant The possibl find of set to huge way a a no among vacua! become from is solution” might there “true everything” expected apparently the of it- when “theory many, method a for scientific nightmare of the dream of comp The essence facing self. the currently concern is which science issues However, article. this for eti set fpyis yn en a hspresentatio this was means no By physics. of po aspects and ...) certain Stravinsky Dvorak, Mozart, Beethoven, (by music Abstract. fpyisadteectmn ffrse icvre nano a in discoveries foreseen of excitement the rathe and but physics Conference, of the during examined topics different f a combine to dynamic the tried with have connected especially I physics occasion, of questions this On Spectrum. Hadron nayeet n a rl avla h rsn sta- present the at marvel truly can one event, any In h fe-inrtl a ynwbcm rdto fti Co this of tradition a become now by has talk after-dinner The itr ftegetGra mathematician German great the of Picture INTRODUCTION FC etoMxoUiesddd aecaCI,Burjasso Valencia-CSIC, de Universidad Mixto Centro IFIC, )poone yDavid by pronounced ”) oknow to ems nw ewl know. will We know. must We iulAglSanchis-Lozano Miguel-Angel sasrn inspiration strong a is i müssen Wir lex sacl o ute hnigo h ieg fdfeetbr different of sinergy the on thinking further for call a as r e fsrn neato.T hsedsm atricso cla of masterpieces some end this To interaction. strong of s ui b o ya,Ei lpo)wr mlydt illustr to employed were Clapton) Eric Dylan, Bob (by music p nihrti ae)itne sacmrhnierve of review comprehensive a as intended paper) this (neither n o itn future. distant too t n ntedtcino cl)dr matter. dark (cold) of detection the focus- physics), on particle ing and (nuclear “small” mod- the and cosmological els) and (astrophysical “large” be the relationship after-tween the the stress we during Finally mentioned presentation. also dinner were (SM) Model Stan- the dard beyond sectors hidden to spectro- corresponding possible scopies new symmetries, different New physics. between in fields entanglement an conceptual as theories of string example and interaction strong the of come. twining have we where from mind in at keep speaking, us scientifically cannot going, let we are least we If where today. of valuable sure lessons be many us teach can n bu auei nin ree sAitteptit: put Aristotle As Greece. ancient “ in learn- systematic nature of about birth the ing section next the in examine cos- exciting. looks alongside definitely physics, mology, astro-particle future and the 2], elementary perhaps [1, of a (or situation of controversial of such existence spite of) In because the everything”. night- in of believers a “theory buoyant (single?) become some indeed for has vacua mare theory the string anthropic of in question the landscape pending The as invoked. inasmuch is principle controversial, method scientific become the of has behaviour. essence chaotic the even or recently, mechanics More uncertainties quantum of set from a arising by replaced been has century teenth people for background. look wisdom scientific may a conventional without etc) than astrology, appealing creationism, more (e.g. world scientific nat- the ural current of interpretations of false) (but emerge complexity Simpler knowledge. still unavoidable shadows the Nonetheless from society. de- by achievements manded technological the by fueled stoppable, l e yntr eiet know to desire nature by men All e-tl n hpfly msn rsnainwt deep with presentation amusing (hopefully) and ree-style ntesbeun eto,w otmlt h inter- the contemplate we section, subsequent the In olwn h re fteatrdne ak ebriefly we talk, after-dinner the of order the Following nine- the of determinism classical naive the physics, In un- now looks science of advancement the Admittedly, frnesre nQakCnnmn n the and Confinement Quark on series nference ,Spain t, .Hsoyo science of History ”. anches ssical the ate - FIGURE 2. A reconstruction of the entrance of the FIGURE 3. Statue of Alfonso X “the Wise” in Madrid. Parthenon. There is considerable discussion about why Athe- nian culture encouraged philosophy, but a popular theory says that it occurred because Athens had a direct democracy of citi- At the same time, other circumstances hindered the zens, albeit excluding women, metics and slaves. evolution of natural philosophy into modern science, e.g.

• General neglect of experimentation (with few ex- Why (natural) philosophy was born in ceptions like Archimedes or Hero of Alexandria in ancient Greece? the Hellenistic period), as manual labour was gen- erally associated with slavery. The transition from Mythos to Logos, the development • Excessive emphasis by many schools on the moder- of arts and the birth of democracy are likely related phe- ation (of customs) as a route to happiness, thereby nomena in ancient Greek society. Science, the successor preventing society from technological improve- to natural philosophy in modern societies, has inherited ments leading to a better quality of life. many of the moral commitments associated with the be- • Dogmatism of schools and diversion of mathemat- ginning of rational thought, particularly regarding free- ical knowledge towards rather mystic goals, like in thinking and human rights in open societies [3]. the Pythagorean school. Several circumstances led together to the birth of west- Many of the aboveremarksare in ordertoday,since in- ern philosophy in ancient Greece and not elsewhere: [4] tellectual freedom, (self)criticism and dialogue between • Mild weather and plentiful spare time (mainly be- schools of thinking lie at the heart of scientific progress. cause of slave labour), permitting sky observations and outdoors (public) life. • A privileged geographical situation in the Mediter- From Dark Ages to Modern Science ranean sea, favouring the contact with other peoples and cultures, e.g. in Egypt and Babylon. According to traditional history, during the Dark Ages • Commercial relations. Thinkers like Thales were (denoting here the entire period between the fall of Rome also men of action, with curious and enterprising and the Renaissance) scientific knowledge (and culture) spirits. In fact, Athens became a maritime power was almost completely swept away in Western Europe. during the era of Pericles. However, current scholars tend to avoid the term alto- • Self-confidence, freedom of speech, and ultimately gether for its negative connotations, finding it misleading democracy, with intense participation of citizens in and inaccurate for some parts of the Middle Ages. public life. In the Iberian peninsula, the Castilian monarch Al- fonso X, nicknamed “the Wise”, was one of these excep- • Anthropomorphic religion, without holy books and tions. From the beginningof his reign, Alfonso employed a sacerdotal caste. Jewish, Muslim and Christian scholars at his court. The • Absence of a central power, in sharp contrast to the scientific treatises compiled under Alfonso’s patronage Persian empire, contributing to the development of were the work of the celebrated "School of Translators" local schools of thought and (self) criticism. of Toledo. The Alfonsine Tables are particularly well- • A flexible and precise (written) language, allowing known, containing diagrams and figures on planetary the expression of abstract concepts, e.g. atom by movements. Because of this, the lunar crater Alphonsus Democritus. is named after him. FIGURE 4. Picture of the Moon from Galileo’s “Starry Mes- FIGURE 5. Regge trajectories motivating the string descrip- senger”. The small book caused sensation on account of the tion of hadrons. engravings it contained showing the Moon’s uneven surface.

For example, A famous apocryphal quote attributed to Alfonso upon • Fermi effective theory brought on the formulation hearing an explanation of the complicated assumptions of a pre-gauge theory with a V-A structure, which required in the Ptolemy’s view of astronomy was: ± was later interpreted in terms of the Z0 and W If the Lord Almighty had consulted me mediators. before embarking upon creation, I should • The solution to the problem of unitarity violation have recommended something simpler. in the early theory led ultimately to the discovery Indeed, astronomy was called on to play a crucial role in of non-abelian local gauge invariance (Yang-Mills the birth of modern science in the following centuries. theories). Galileo Galilei published Sidereus Nuncius (the • The existence of anti-matter postulated by Dirac is “Starry Messenger”) in 1610, reporting his observa- checked in β + decay. tions of the Moon and, particularly, his discovery of • More recently, neutrino oscillations have been the four satellites around Jupiter. The lunar observations first evidence of physics beyond the SM. showed that the surface of the moon was neither smooth • Neutrino physics is called to play a crucial role in nor perfectly spherical, but was covered with craters astro-particle physics and cosmology. and mountains. Both discoveries were blows to the Aristotelian world-view which was geocentric and main- tained that everything above the Earth was perfect and incorruptible. The door for the return of the old atomistic FROM HADRONIC STATES TO STRING idea of Democritus and Epicurus had been definitely THEORY open. Originally, string theory arose in the late 1960s in an at- tempt to understand various features of the strong inter- Nuclear beta decay: a compendium of action and properties of hadronic states (see Fig.5). The modern physics seed of the idea can be tracedto the dualresonancemodel proposed by Gabriele Veneziano. The picture was that, The correct interpretation of X-rays by Röntgen to- for example, a meson should consist of two quarks tied gether with the discovery of radioactivity by Becquerel together by a piece of ‘string’, acting as a kind of rubber! at the end of the twentieth century was an outstanding In the early 1970s another theory of the strong interac- step forward in modern science. The atom was not to be tion, Quantum Chromodynamics (QCD), was developed, considered as indivisible, in spite of its etymology! and proved very successful indeed. QCD is a gauge non- Below we focus on nuclear beta decay as a good ex- abelian quantum field theory exhibiting some peculiar ample of the conceptual entanglement of many different properties depending on the energy scale: confinement issues in the scientific development. First of all, note that (still to be proved) and asymptotic freedom. the ad hoc hypothesis of the existence of an unseen par- Effective theories, like NRQCD [5] or HQET [6], ticle postulated by Pauli (called neutrino by Fermi), to have become a fruitful approach for different kinematic preserve energy-momentum conservation in beta decay, regimes and mass limits. Let us also mention lattice represents a landmark in the history of physics of the QCD [7] as a well-established non-perturbativeapproach twentieth century. formulatedon a grid or lattice of pointsin space and time. As a result of all this, as well as varioustechnicalprob- lems with the primitive string theory approach, string theory fell out of fashion. In the last few decades, how- ever, string theory [8, 9] has turned out to be well suited for an even more ambitious purpose: to become the “theory of everything”! The basic idea is that elemen- tary particles or force carriers should not be described as point-like, but instead viewed as different oscillation modes of a string - the ultimate constituent of nature. Think of a guitar string. Depending on how the string is plucked and how much tension is in the string, differ- ent musical notes will be created. In a similar manner, the elementary particles could be thought of as the ex- citation modes of elementary strings. Furthermore, the spectrum of string excitations includes a massless parti- cle with two units of spin which can be identified with the graviton, the expected carrier of the quantum gravita- tional field. Therefore, string theory could unify all four known forces of Nature, including gravitation, the unful- FIGURE 6. The epistemological difficulties of the vacua filled dream of many generations of physicists. landscape in string theory has led many physicists to become Moreover, higher dimensional objects (branes) were rather skeptical about it. The title of the book by Peter Woit included in the framework by Joseph Polchinski [10], [13] Not even wrong, corresponds to the Pauli’s term for scien- greatly increasing the number of possible background tifically useless speculative theories (i.e. cannot be falsified). geometries and leading to enormous consequences in later developments of string theory. If string theory is to be a theory of quantum gravity, one with a different vacuum and physical predictions. In then the average size of a string should be somewhere all frankness, this should be somewhat discouraging for 1 near the Planck length (∼ 10−35 m). This means that string theorists . strings would be, in principle, too small to be directly detected by current or expected particle physics experi- ments. Cleverer methods of testing the theory than just Strings strike back: Maldacena’s looking for little strings have to be devised in particle holographic principle experiments. Nonetheless, other possibilities have to be considered, including TeV stringy effects to be poten- Gerard ’t Hooft’s visionary proposal of the holo- tially detected at the Large Hadron Collider (LHC). graphic principle [14] was in part an inspiration for Juan On the other hand, supersymmetry is required in or- Maldacena’s conjecture. Basically, everything that hap- der to include fermions in string theory (stabilizing the pens in a given volume of space can be represented as model too). Supersymmetric partners to currently known taking place (is encoded) on a surface surrounding this particles are supposed to be too massive for detection at volume [15]. accelerators till now. However, the LHC could be on the Maldacena’s conjecture [16, 17, 18] proposes that a verge of finding evidence for supersymmetry. string theory on a certain backgroundspacetime is equiv- An intriguing feature of string theory is that more than alent to a conformal supersymmetric Yang-Mills theory three spacial dimensions exist for self-consistency of the on a lower dimension (AdS/CFT correspondence). Such theory. This is not really a new idea in physics, with a duality implies: Kaluza’s early work showing that general relativity in Strongly coupled dynamics ⇔ Weakly coupled strings five dimensions yields electromagnetism. More gener- ally, string theory provides a theoretical arena in which and vice versa. different compactifications of extra dimensions lead to In particular, one may think of QCD as a scale- many different possibilities for physics beyond the SM. invariant theory (QCD is almost conformal at momenta Note that extra dimensions can be at reach of the LHC much larger than ΛQCD) with a useful correspondence experiments looking for a missing energy signal [11]. with a certain string theory on a anti-de Sitter spacetime Despite all the beautiful and suggestive features (e.g. and a closed manifold (like a five dimensional sphere). dualities) of string theory, there is so far one main prob- lem with it: string theorists end up with a landscape of many possible consistent solutions (10500 or so), each 1 Leaving aside the anthropic principle as an arguable way out [12]. FIGURE 7. Ockham’s razor (entia non sunt multiplicanda praeter necessitatem) is popularly expressed as “the simplest explanation is more likely the correct one”. The exact meaning of “simplest” must be nuanced however.

Can the dual string theory explain confinement, FIGURE 8. Portrait of Dora Maar by Picasso. New symme- hadronization, etc? tries (and their breaking) should furnish a guide useful in the It should be emphasized that the gauge/string dual- search for physics beyond the SM. ity has not yet been proved but many non-trivial tests have been carried out. Some physicists do believe that × × holography is a fundamental property of string theory. For instance, the usual SU(3) SU(2) U(1) group Finally notice that recent data from heavy ion processes of the SM can be extended by a new non-abelian group (like in hidden valley models [27]). Higher dimension at RHIC might be interpreted by invoking a dual string ′ theory [19]. operators at the TeV scale (induced by a Z or by a loop of heavy particles carrying chargesfrom both the SM and the new group) should allow interactionsbetween the SM NEW SYMMETRIES, NEW WORLDS fields and the new particles. Rather exotic phenomenology would show up at the Besides the string description, the SM can obviously be LHC: high multiplicity events, displaced vertices and extended in many different ways. There are reasonable missing energy, long range correlations, etc [28, 29]. and motivated scenarios, most of them including super- symmetry since it provides a solution for the Higgs mass problem [20]. Alternative popular scenarios are, e.g., the FROM THE “SMALL” TO THE “LARGE” little Higgs model [21], warped extra dimensions [22] or AND VICE VERSA technicolor [23]. Minimal extensions of the SM can be seen as a theo- Astronomical observations played a leading role in retical prejudice attached to beauty and elegance of the the early development of natural philosophy in ancient formalism, also supported so far by many successes in Greece (as in previous civilizations) and the scientific all fields of science. Indeed, one should not forget the revolution by Galileo and Newton (alongside many oth- scientific virtues usually attributed to a healthy economy ers). Certainly, “messengers from the sky” (light, cosmic of hypotheses (Ockham’s razor). rays, dark matter ...) will still provide us with essential However, let us point out as a caveat that the third information from/on the Cosmos. generation of quarks and leptons, in the early SM, was Fundamental questions in physics unite the largest in fact not demanded by previous experimental data nor scale (the study of the universe) to the smallest scale (ele- theoretical requirements. In this regard, Einstein warned: mentary particle physics). In particular,the nature of dark matter [30] directly involves both cosmology and cer- Everything should be as simple as possible, tain extensions of the SM (like supersymmetric models) but not simpler. which furnish candidates (e.g. neutralino, gravitino) for the so-called Weak Interacting Massive Particle (WIMP). Among those possible not so much strongly motivated If the Milky Way’s dark matter halo is composed of scenarios beyond our present conventional wisdom, new WIMPs, the WIMP flux on Earth should be about 105 kinds of strong interaction have been considered in parti- cm−2s−1. Therefore direct detection experiments should cle physics [24, 25]. Actually, the existence of additional be able to detect WIMP elastic scattering off nuclei, gauge groups with matter in the fundamental representa- providing a signal if backgrounds are low enough. tions would arise naturally in string theory [26]. The WIMP-nucleon (nucleus) cross section (spin- 4. M.A. Sanchis-Lozano, Filosofía Griega y Ciencia dependent and spin-independent) encodes: Moderna: un viaje en el tiempo desde Aristóteles hasta Einstein, ACDE, Valencia, 2001. 1. Particle physics inputs, including WIMP interaction 5. G. T. Bodwin, E. Braaten and G. P. Lepage, Phys. Rev. properties D 51, 1125 (1995) [Erratum-ibid. D 55, 5853 (1997)] 2. Nuclear properties: hadronic matrix elements de- [arXiv:hep-ph/9407339]. 6. M. Neubert, Phys. Rept. 245 (1994) 259 [arXiv:hep- scribing the quark and gluon content of the nucleon, ph/9306320]. notably concerning strange quarks. 7. C. Gattringer and C. B. Lang, Quantum Chromodynamics 3. Astrophysics: WIMP velocity distribution, Earth on the Lattice, Springer 2010. motion. 8. B. Greene, The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, This is an illustrative example of the multiple fields Vintage Series, Random House Inc, 2000. involved in any claim of observation of dark matter. 9. K. Becker, M.Becker and J.H. Schwarz, String Theory and M-Theory, Cambridge University Press, Cambridge, 2007. 10. J. Polchinski, “Lectures on D-branes,” arXiv:hep- th/9611050. CONCLUDING REMARKS 11. G. Aad et al. [The ATLAS Collaboration], “Expected Performance of the ATLAS Experiment - Detector, Trigger As history teaches us, it is hardly conceivable a steady and Physics,” arXiv:0901.0512 [hep-ex]. development of science which leaves aside any area of 12. L. Susskind, “The anthropic landscape of string theory,” knowledge. In this paper, we have illustrated this point arXiv:hep-th/0302219. of view with several examples from both elementary 13. Peter Woit, Not Even Wrong: The Failure of String Theory & the Continuing Challenge to Unify the Laws of Physics., particle and astro-particle physics, as well as cosmology. Basic Books, 2006. Returning to Hilbert’s quotation, which entitles this 14. C. R. Stephens, G. ’t Hooft and B. F. Whiting, Class. paper, one might complete it by saying: Quant. Grav. 11, 621 (1994) [arXiv:gr-qc/9310006]. 15. L. Susskind, J. Math. Phys. 36, 6377 (1995) [arXiv:hep- We must know ... about everything. th/9409089]. 16. J. M. Maldacena, Adv. Theor. Math. Phys. 2, 231 (1998) In answering these pending big questions about Na- [arXiv:hep-th/9711200]. ture, we should (hopefully) become more “human”, that 17. S. S. Gubser, I. R. Klebanov and A. M. Polyakov, Phys. is, wiser in the broad sense of the word (committed in Lett. B 428, 105 (1998) [arXiv:hep-th/9802109]. world-wide solidarity, respectful towards the environ- 18. E. Witten, Adv. Theor. Math. Phys. 2, 253 (1998) [arXiv:hep-th/9802150]. ment...). After all, we should live up to the name of our 19. W. A. Horowitz, “Probing the Frontiers of QCD,” species: Homo sapiens, “ knowing man”. arXiv:1011.4316 [nucl-th]. 20. M. Drees, “An Introduction to supersymmetry,” arXiv:hep- ph/9611409. ACKNOWLEDGMENTS 21. M. Schmaltz and D. Tucker-Smith, Ann. Rev. Nucl. Part. Sci. 55, 229 (2005) [arXiv:hep-ph/0502182]. 22. L. Randall and R. Sundrum, Phys. Rev. Lett. 83, 3370 I would like to thank the organizers of the IX Con- (1999) [arXiv:hep-ph/9905221]. ference on Quark Confinement and the Hadron Spec- 23. E. Farhi and L. Susskind, Phys. Rept. 74, 277 (1981). trum in Madrid for inviting me to give the after- 24. L. B. Okun, Nucl. Phys. B 173, 1 (1980). dinner talk and write this somehow non-standard pa- 25. J. Kang and M. A. Luty, JHEP 0911, 065 (2009) per for the Proceedings. I acknowledge support from [arXiv:0805.4642 [hep-ph]]. MICINN (FPA2008-02878) and Generalitat Valenciana 26. N. Arkani-Hamed, S. Dimopoulos and S. Kachru, (GVPROMETEO2010-056). I dedicate the after-dinner “Predictive landscapes and new physics at a TeV,” arXiv:hep-th/0501082. talk and this paper to the memory of Francisco Yndurain 27. M. J. Strassler and K. M. Zurek, Phys. Lett. B 651, 374 and Ximo Prades. (2007) [arXiv:hep-ph/0604261]. 28. T. Han, Z. Si, K. M. Zurek and M. J. Strassler, JHEP 0807, 008 (2008) [arXiv:0712.2041 [hep-ph]]. REFERENCES 29. M. A. Sanchis-Lozano, Int. J. Mod. Phys. A 24, 4529 (2009) [arXiv:0812.2397 [hep-ph]]. 30. G. Bertone, D. Hooper and J. Silk, Phys. Rept. 405, 279 1. L. Smolin, The Trouble with physics. The rise of String (2005) [arXiv:hep-ph/0404175]. Theory and the Fall of a Science and what comes next. Houghton Mifflin, New York, 2006. 2. R. Penrose, The Road to Reality: A Complete Guide to the Laws of the Universe, Vintage Books, 2007. 3. Richard Pierre Claude. Science in the Service of Human Rights, University of Pennsilvania Press 2002.