Highlights in physics Highlights in physics today: today: 100 - PowerPoint PPT Presentation

Highlights in physics Highlights in physics today: today: 100 years after the 100 years after the birth of birth of Beppo Occhialini Beppo Occhialini (Milano, 16 February 2007) String Theory: a unified description of a unified description of String Theory: elementary particles & interactions ? ? elementary particles & interactions (Gabriele Veneziano, CERN & CdF) 16.02.2007 Beppo 1

Introduction Introduction 100 years ago, when G.O. was born, two revolutions had already shaken two sacred XIX th century beliefs: 1. The belief in absolute determinism absolute determinism when Max Planck, in 1900, introduced the constant h h and started the quantum quantum 1900 revolution. revolution 2. The belief in absolute absolute time time when Albert Einstein, in 1905, 1905, starting from the invariance of the speed of light in the vacuum, c c, arrived at his theory of Special Relativity Special Relativity. 16.02.2007 Beppo 2

In that same year AE also gave an important contribution to quantum theory by explaning the photoelectric effect as due to light quanta (photons) of energy E = h f E = h f In 1915 1915 Einstein made yet another ground-shaking proposal: Starting from the universality of free-fall, he arrived at a geometric theory of gravity, General Relativity General Relativity, whereby Newton’s constant, G G , determines the amount by which matter (energy) bends spacetime. 16.02.2007 Beppo 3

In the second half of his scientific life Einstein tried to combine in a single conceptual framework all these beautiful developments (embodied in h h, c c and G G) Meanwhile, thanks to the effort of many physicists, including G.O., the panorama of elementary particles and fundamental interactions had drastically changed It had grown more and more complicated with the discovery of the nuclear nuclear and weak weak forces, and of a host of new particles endowed with one and/or the other interaction, besides electromagnetism Einstein’s search for unification unification looked more and more like a remote, impossible dream dream 16.02.2007 Beppo 4

When I started entering elementary particle physics, in the late sixties, G.O. and the physicists of his generation had already collected an incredible amount of exciting data, but a theoretical synthesis looked as remote as ever. Yet, some kind of revolution was boiling…. It came to completion within a « golden decade » (1965- 1974) that culminated in the construction of the Standard Standard Model of elementary particles. I have been very lucky to Model enter PP just at that time… 16.02.2007 Beppo 5

Such diverse phenomena as atomic levels, nuclear reactions, radioactity, were understood, in the standard model, as different realizations of a single theoretical structure, known as a gauge theory. Its three possible realizations: A Coulomb Coulomb phase with a massless gauge boson  A Higgs Higgs phase with massive gauge bosons  A confining confining phase with a dynamically generated mass-gap  represented, respectively, the electromagnetic electromagnetic, , weak weak and strong force, 3 of 3 of the the 4 4 known basic interactions strong 16.02.2007 Beppo 6

It is hard to overestimate the importance of such an achievement. I am sure it will remain in the books of physics like Maxwell’s or Einstein’s equations did (do). But, once more, Einstein’s dream was as far as ever from being realized. There was no way to bring his General Relativity (GR) to terms with QM. GR GR remained, obstinately, a completely classical classical, deterministic deterministic theory. "I must seem like an ostrich who forever buries its head in the relativistic sand in order not to face the evil quanta" (Einstein, 1954) 16.02.2007 Beppo 7

Outline Outline • A huge hierarchy of scales • Travel on a «meta-theoretical» cube • Cosmology needs unification • Classical and quantum patologies of Einstein’s gravity • A lesson from the Electro-Weak theory • String Theory: a 3-ingredient cocktail • Quantum magic and Einstein’s dream • String’s cube and problems ahead • Conclusion 16.02.2007 Beppo 8

Einstein’s dream was to unify our understanding of the « infinitely infinitely » » small small « & the the & « « infinitely infinitely » large » large More quantitatively: 16.02.2007 Beppo 9

Minimal (quantum) length/time scale Maximal (classical) length/time scale

Travel on a on a meta-theoretical meta-theoretical cube cube Travel 1/c 6 3 5 8 h 1 4 2 7 G 16.02.2007 Beppo 11

The cube cube redrawn redrawn The 8 Relativity 5 (1/c) 6 Gravity(G) Quantum (h) 3 4 2 1 16.02.2007 Beppo 12

The trivial vertex trivial vertex The 8 Relativity 5 6 Gravity 7 Quantum 3 4 2 1 16.02.2007 Beppo 13

The simplest edges: I : I The simplest edges 8 Relativity 5 6 Gravity Quantum 3 4 2 1 Newtonian Gravity: : the solar the solar system system Newtonian Gravity 16.02.2007 Beppo 14

The simplest edges: II : II The simplest edges 8 Relativity 5 6 Gravity Quantum 3 4 2 1 Special relativity Special relativity 16.02.2007 Beppo 15

The simplest edges: III : III The simplest edges 8 Relativity 5 6 Gravity Quantum 3 4 2 1 Non-relativistic Quantum Quantum Mechanics Mechanics: : H-atom H-atom Non-relativistic 16.02.2007 Beppo 16

The most relevant faces: I most relevant faces: I The 8 Relativity 5 6 Gravity Quantum 3 4 2 1 General Relativity General Relativity 16.02.2007 Beppo 17

NG + SR = GR NG + SR = GR General Relativity (GR) Our «Standard Model» of «Standard Model» of classical gravity classical gravity Our Corrections to NG better and better tested better and better tested Corrections to NG New predictions 1. Black Black holes holes (direct (direct evidence evidence) ) 2. Gravitational waves Gravitational waves (indirect (indirect evidence evidence) )

Sagittarius A* Sagittarius A* M>10 6 solar solar masses? masses? M>10 6 16.02.2007 Beppo 19

Binary 1913+16 1913+16 Binary 16.02.2007 Beppo 20

VIRGO(Cascina) LIGO (USA) LISA Explorer(CERN) 16.02.2007 Beppo 21

The most relevant faces: II most relevant faces: II The 8 Relativity 5 6 Gravity Quantum 3 4 2 1 Quantum field Theory Theory Quantum field 16.02.2007 Beppo 22

SR + QM = QFT SR + QM = QFT «Standard Model» of elementary particles elementary particles «Standard Model» of (verified to high precision, LEP..) The quantum-relativistic nature of the SM manifests itself through real and virtual particle production Radiative corrections are essential for agreement with the data: The SM SM is is not not a a semiclassical semiclassical theory theory! ! The

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ATLAS detector detector, LHC, CERN: , LHC, CERN: ATLAS Hunting the Higgs boson + ?? boson + ?? Hunting the Higgs 16.02.2007 Beppo 25

What about face III? about face III? What 8 Relativity 5 6 Gravity 7 Quantum 3 4 2 1 Newtonian quantum gravity? Yes, it’s possible! 16.02.2007 Beppo 26

Gravitationally bound quantum states of Gravitationally bound quantum states of neutrons: applications and perspectives neutrons: applications and perspectives H.Abele, S.Bassler, H.G. Bor ner, A.M.Gagarski, V.V.Nesvizhevsky, A.K.Petoukhov, K.V.Protasov, A.Yu.Voronin and A.Westphal Gravitationally bound quantum states of matter were observed recently due to unique properties of ultracold neutrons. We discuss here the actual status and possible improvements in this experiment. This phenomenon could be useful for various domains ranging from the physics of elementary particles and fields, to surface studies, or to foundations of quantum mechanics . http://www.panic05.lanl.gov/abstracts/250/proc_Nesvizhevsky_250.pdf 16.02.2007 Beppo 27

Summarizing so far: NG + SR = GR = SMCG NG + SR = GR = SMCG SR + QM = SMEP SR + QM = SMEP Both work wonders…but

L.H.S. : Classical Geometry R.H.S. : Quantum Matter Sounds inconsistent. E.g.: Classical cosmological constant or quantum-corrected potential energy of a scalar field? And what about the supposed quantum origin of LSS in the Universe? An impossible marriage marriage? ? An impossible The issue is not just a conceptual one: it becomes physically relevant in a cosmological context 16.02.2007 Beppo 29

Cosmology occupies all the interior of our cube! 8 Relativity 5 6 Gravity Quantum 3 4 2 1 16.02.2007 Beppo 30

Expansion of the Universe the Universe Expansion of Very hot and dense Universe Far past Very hot Universe Very high energies (R) Very dense Univers Very high curvature (G) Very high curvature Quantum processes (Q) Far in space space Back in time Back in time (c finite) Far in Deep connection between L L H H and T T P P 16.02.2007 Beppo 31

The more we go towards the past the more we approach vertex no. 8! 8 Relativity 5 6 Gravity Quantum 3 NG + SR + QM NG + SR + QM 4 2 = GR + SM = = GR + SM = 1 ?? ?? 16.02.2007 Beppo 32