Some open questions in physics

Transcription

1 K.A. Meissner, Unsolved problems p. 1/25 Some open questions in physics Krzysztof A. Meissner Instytut Fizyki Teoretycznej UW Instytut Problemów Ja drowych Kraków,

2 K.A. Meissner, Unsolved problems p. 2/25 Content Quantum Mechanics Standard Model dark matter and dark energy quantum gravity summary

3 K.A. Meissner, Unsolved problems p. 3/25 The most incomprehensible fact about the Universe is that it is comprehensible A. Einstein

4 K.A. Meissner, Unsolved problems p. 4/25 Introduction (part of) reality can be described by numbers there are correlations among these numbers physical laws with proper idealization these laws seem to be universal and rigorous

5 K.A. Meissner, Unsolved problems p. 4/25 Introduction (part of) reality can be described by numbers there are correlations among these numbers physical laws with proper idealization these laws seem to be universal and rigorous we have no idea why these statements hold the answer belongs to meta-physics rather than physics...

6 K.A. Meissner, Unsolved problems p. 5/25 Introduction use of mathematics is the source of tremendous success of physics

7 K.A. Meissner, Unsolved problems p. 5/25 Introduction use of mathematics is the source of tremendous success of physics but mathematics gives us also a rigorous proof that cognition has its limits: Gödel theorem + finite resources Theory of Everything is impossible

8 K.A. Meissner, Unsolved problems p. 6/25 Introduction in any physical phenomenon we distinguish accidental properties (depending on the initial conditions) and inevitable properties (following from the laws of physics)

9 K.A. Meissner, Unsolved problems p. 6/25 Introduction in any physical phenomenon we distinguish accidental properties (depending on the initial conditions) and inevitable properties (following from the laws of physics) the fact that there are 8 (formerly 9) planets seems to be accidental but once we have a planet a 3 T 2 is inevitable

10 K.A. Meissner, Unsolved problems p. 6/25 Introduction in any physical phenomenon we distinguish accidental properties (depending on the initial conditions) and inevitable properties (following from the laws of physics) the fact that there are 8 (formerly 9) planets seems to be accidental but once we have a planet a 3 T 2 is inevitable explanation in physics means converting accidental into inevitable

11 K.A. Meissner, Unsolved problems p. 6/25 Introduction in any physical phenomenon we distinguish accidental properties (depending on the initial conditions) and inevitable properties (following from the laws of physics) the fact that there are 8 (formerly 9) planets seems to be accidental but once we have a planet a 3 T 2 is inevitable explanation in physics means converting accidental into inevitable how far can we go?

12 K.A. Meissner, Unsolved problems p. 7/25 Cube of theories Fundamental dimensionful constants: 1/c,, G

13 K.A. Meissner, Unsolved problems p. 8/25 Quantum Mechanics the most fundamental and extremely successful in our description of the physical world but...

14 K.A. Meissner, Unsolved problems p. 8/25 Quantum Mechanics the most fundamental and extremely successful in our description of the physical world but... conceptual foundations (and limits) of locality, causality, Heisenberg relations unclear

15 K.A. Meissner, Unsolved problems p. 8/25 Quantum Mechanics the most fundamental and extremely successful in our description of the physical world but... conceptual foundations (and limits) of locality, causality, Heisenberg relations unclear problem of measurement (Copenhagen, Everett, Bohm, Penrose,...) totally unclear...

16 K.A. Meissner, Unsolved problems p. 9/25 Particles of the Standard Model Leptons (spin 1/2, qν = 0, q e = 1): ν e e L ν µ µ L ν τ τ L e R, ν er µ R, ν µr τ R, ν τr Quarks (3 colors, spin 1/2, qu = 2/3, q d = 1/3): u d c s t b L L L u R, d R c R, s R t R, b R Spin 1: 8 gluons g (SU(3)), Spin 0: W ± and Z 0, photon γ Higgs H (SU(2) U(1))

17 K.A. Meissner, Unsolved problems p. 10/25 Standard Model extremely successful theory no single experimental deviation verified to unbelievable precision but it cannot be the ultimate theory...

18 K.A. Meissner, Unsolved problems p. 10/25 Standard Model extremely successful theory no single experimental deviation verified to unbelievable precision but it cannot be the ultimate theory... no gauge anomalies # of leptons = # of quarks but why 3 generations???

19 K.A. Meissner, Unsolved problems p. 10/25 Standard Model extremely successful theory no single experimental deviation verified to unbelievable precision but it cannot be the ultimate theory... no gauge anomalies # of leptons = # of quarks but why 3 generations??? why the observed values of masses and coupling constants??? any change we are not here...

20 K.A. Meissner, Unsolved problems p. 10/25 Standard Model extremely successful theory no single experimental deviation verified to unbelievable precision but it cannot be the ultimate theory... no gauge anomalies # of leptons = # of quarks but why 3 generations??? why the observed values of masses and coupling constants??? any change we are not here... why CP violation (and why not enough)???

21 K.A. Meissner, Unsolved problems p. 11/25 Standard Model why spontaneous symmetry breaking H = v 0???

22 K.A. Meissner, Unsolved problems p. 11/25 Standard Model why spontaneous symmetry breaking H = v 0??? why such huge differences in masses??? m t v 1, m ( e v 3 mν ) 10 6, v 10 12

23 K.A. Meissner, Unsolved problems p. 11/25 Standard Model why spontaneous symmetry breaking H = v 0??? why such huge differences in masses??? m t v 1, m ( e v 3 mν ) 10 6, v why proton mass 1 GeV??? (main source of luminous mass)

24 K.A. Meissner, Unsolved problems p. 11/25 Standard Model why spontaneous symmetry breaking H = v 0??? why such huge differences in masses??? m t v 1, m ( e v 3 mν ) 10 6, v why proton mass 1 GeV??? (main source of luminous mass) hierarchy problem v M P (supersymmetry, conformal symmetry)

25 K.A. Meissner, Unsolved problems p. 12/25 Present content of the Universe radiation p ρ 3 negligible luminous matter p 0 4 % (stars 0.5% interstellar gas 0.5% intergalactic gas 3%) dark matter p 0 23 % dark energy p ρ 73 %

26 Nucleosynthesis abundances K.A. Meissner, Unsolved problems p. 13/25

27 WMAP K.A. Meissner, Unsolved problems p. 14/25

28 K.A. Meissner, Unsolved problems p. 15/25 Dark Matter and Dark Energy what is dark matter (supersymmetric neutralino, axion,...)?

29 K.A. Meissner, Unsolved problems p. 15/25 Dark Matter and Dark Energy what is dark matter (supersymmetric neutralino, axion,...)? the answer probably within conventional QFT

30 K.A. Meissner, Unsolved problems p. 15/25 Dark Matter and Dark Energy what is dark matter (supersymmetric neutralino, axion,...)? the answer probably within conventional QFT what is dark energy (cosm. constant?)???

31 K.A. Meissner, Unsolved problems p. 15/25 Dark Matter and Dark Energy what is dark matter (supersymmetric neutralino, axion,...)? the answer probably within conventional QFT what is dark energy (cosm. constant?)??? why ρ DM M 4 P , ρ DM M 4 W 10 54

32 K.A. Meissner, Unsolved problems p. 15/25 Dark Matter and Dark Energy what is dark matter (supersymmetric neutralino, axion,...)? the answer probably within conventional QFT what is dark energy (cosm. constant?)??? why ρ DM M 4 P , ρ DM M 4 W the answer probably requires new (not QFT like) physics quantum gravity?

33 Galaxy collision K.A. Meissner, Unsolved problems p. 16/25

34 K.A. Meissner, Unsolved problems p. 17/25 Gravity gravitational interaction between elementary particles is extremely weak why??? α G = Gm2 p c (for EM interactions α = e 2 /(4πǫ 0 c) 1/137)

35 K.A. Meissner, Unsolved problems p. 17/25 Gravity gravitational interaction between elementary particles is extremely weak why??? α G = Gm2 p c (for EM interactions α = e 2 /(4πǫ 0 c) 1/137) α G is so small stars are so large M C m p α 3/2 G (Chandrasekhar limit) kg

36 K.A. Meissner, Unsolved problems p. 18/25 Quantum Gravity when gravity EM? (G. Stoney, 1881) Gm 2 S r 2 = e2 4πǫ 0 r 2 m S kg

37 K.A. Meissner, Unsolved problems p. 18/25 Quantum Gravity when gravity EM? (G. Stoney, 1881) Gm 2 S r 2 = e2 4πǫ 0 r 2 m S kg Planck (1899) introduced (m P = αm S ) c m P = G kg we expect that QG sets in when E m P c 2

38 K.A. Meissner, Unsolved problems p. 18/25 Quantum Gravity when gravity EM? (G. Stoney, 1881) Gm 2 S r 2 = e2 4πǫ 0 r 2 m S kg Planck (1899) introduced (m P = αm S ) c m P = G kg we expect that QG sets in when E m P c 2 QG fluctuating space-time (???)

39 K.A. Meissner, Unsolved problems p. 18/25 Quantum Gravity when gravity EM? (G. Stoney, 1881) Gm 2 S r 2 = e2 4πǫ 0 r 2 m S kg Planck (1899) introduced (m P = αm S ) c m P = G kg we expect that QG sets in when E m P c 2 QG fluctuating space-time (???) black hole entropy may be the key issue pointing to QG (as black body radiation did)

40 K.A. Meissner, Unsolved problems p. 19/25 Cube of theories Fundamental dimensionful constants: 1/c,,, G

41 K.A. Meissner, Unsolved problems p. 20/25 Quantum gravity proposals very interesting results from the (Lorentzian) path-integral approach (Dynamical Triangulations)

42 K.A. Meissner, Unsolved problems p. 20/25 Quantum gravity proposals very interesting results from the (Lorentzian) path-integral approach (Dynamical Triangulations) String Theory Loop Quantum Gravity

43 K.A. Meissner, Unsolved problems p. 20/25 Quantum gravity proposals very interesting results from the (Lorentzian) path-integral approach (Dynamical Triangulations) String Theory Loop Quantum Gravity both claim solving BH entropy problem neither solved the CC problem nor the initial singularity and initial conditions problems...

44 K.A. Meissner, Unsolved problems p. 21/25 String theory Quantum description of gauge theories and gravity

45 K.A. Meissner, Unsolved problems p. 21/25 String theory Quantum description of gauge theories and gravity UV finite (?) modular symmetry (not proven beyond two loops)

46 K.A. Meissner, Unsolved problems p. 21/25 String theory Quantum description of gauge theories and gravity UV finite (?) modular symmetry (not proven beyond two loops) extremely beautiful mathematically

47 K.A. Meissner, Unsolved problems p. 21/25 String theory Quantum description of gauge theories and gravity UV finite (?) modular symmetry (not proven beyond two loops) extremely beautiful mathematically but...

48 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle

49 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle only first quantized formulation with unknown equations of motion

50 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle only first quantized formulation with unknown equations of motion theory contains higher-dimensional objects (branes) no consistent quantum description

51 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle only first quantized formulation with unknown equations of motion theory contains higher-dimensional objects (branes) no consistent quantum description > admissible (?) vacua (landscape)

52 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle only first quantized formulation with unknown equations of motion theory contains higher-dimensional objects (branes) no consistent quantum description > admissible (?) vacua (landscape) no mechanism to break supersymmetry to leave QFT on almost flat space

53 K.A. Meissner, Unsolved problems p. 22/25 String theory lack of underlying principle only first quantized formulation with unknown equations of motion theory contains higher-dimensional objects (branes) no consistent quantum description > admissible (?) vacua (landscape) no mechanism to break supersymmetry to leave QFT on almost flat space no single new result relevant for low energy particle physics or cosmology

54 K.A. Meissner, Unsolved problems p. 23/25 Loop Quantum Gravity defined quantum mechanically

55 K.A. Meissner, Unsolved problems p. 23/25 Loop Quantum Gravity defined quantum mechanically diffeomorphism invariance (background independence) built in and only diffeomorphism invariant operators allowed (volume, area...)

56 K.A. Meissner, Unsolved problems p. 23/25 Loop Quantum Gravity defined quantum mechanically diffeomorphism invariance (background independence) built in and only diffeomorphism invariant operators allowed (volume, area...) but no connection (yet?) to usual gravity

57 K.A. Meissner, Unsolved problems p. 23/25 Loop Quantum Gravity defined quantum mechanically diffeomorphism invariance (background independence) built in and only diffeomorphism invariant operators allowed (volume, area...) but no connection (yet?) to usual gravity no dynamics mathematically very difficult (inseparable Hilbert spaces, forbiddingly complicated hamiltonian etc.)

58 K.A. Meissner, Unsolved problems p. 23/25 Loop Quantum Gravity defined quantum mechanically diffeomorphism invariance (background independence) built in and only diffeomorphism invariant operators allowed (volume, area...) but no connection (yet?) to usual gravity no dynamics mathematically very difficult (inseparable Hilbert spaces, forbiddingly complicated hamiltonian etc.)

59 K.A. Meissner, Unsolved problems p. 24/25 Quantum Gravity no sign of convergence of different approaches

60 K.A. Meissner, Unsolved problems p. 24/25 Quantum Gravity no sign of convergence of different approaches problems of initial singularity, existence (or emergence) of time and space at distances l P, interpretation of the wave function of the Universe etc. totally unclear

61 K.A. Meissner, Unsolved problems p. 24/25 Quantum Gravity no sign of convergence of different approaches problems of initial singularity, existence (or emergence) of time and space at distances l P, interpretation of the wave function of the Universe etc. totally unclear we are still very far away from understanding quantum gravity

62 K.A. Meissner, Unsolved problems p. 25/25 Summary list of unsolved problems doesn t get shorter...

63 K.A. Meissner, Unsolved problems p. 25/25 Summary list of unsolved problems doesn t get shorter... probably the biggest challenges in physics (that we know of!) measurement problem in QM explanation of values of physical constants cosmological constant and quantum gravity

64 K.A. Meissner, Unsolved problems p. 25/25 Summary list of unsolved problems doesn t get shorter... probably the biggest challenges in physics (that we know of!) measurement problem in QM explanation of values of physical constants cosmological constant and quantum gravity the biggest (meta-physical) mystery: why anything is subject to any law at all?

65 K.A. Meissner, Unsolved problems p. 25/25 Summary list of unsolved problems doesn t get shorter... probably the biggest challenges in physics (that we know of!) measurement problem in QM explanation of values of physical constants cosmological constant and quantum gravity the biggest (meta-physical) mystery: why anything is subject to any law at all? Socrates statement invariably true: I neither know nor think that I know