DJ Strouse

My Goodreads Review
rating: 4 of 5 stars

Review
It is obvious that Lee Smolin cares deeply and sincerely about the future of his field of physics. I read this with the intent to get a balanced view of string theory (having already read Brian Greene’s gushing pro-string theory book ‘The Elegant Universe’) but got so much more. Smolin’s book offers a deeper look at scientific history, culture, and philosophy as well.

I highly recommend this book to anyone who:

• wants an overview of the current state of physics (problems, culture, focuses, experiments, and more)
• is a scientist or physicist
• is considering becoming a scientist or physicist

Note: The notes below were taken as I was reading and help me to synthesize ideas. They are likely quite dull to anyone else, but the following sections may be interesting: 5 Problems of Contemporary Physics, Unifications, Spontaneous Symmetry Breaking,

Book Notes

• Styles of Physics
  • early 20th century: philosophical reflection on difficult fundamental problems (Einstein, Bohr, Heisenberg, Schrodinger)
  • mid 20th century: pragmatic, hard-nosed calculation (Feynman, Dyson)
• Accident of Time: proposals without prospect for experimental proof were punishable by burning at stake! (note to string theorists)
• 5 Problems of Contemporary Physics
  • Quantum Gravity
  • Foundations of Quantum Mechanics (observer-system inconsistency)
  • Unification of Forces and Particles (or disproval)
  • Explanation of How Constants of Standard Model of Particle Physics are Chosen
  • Dark Matter/Energy or Alt. Explanation for Modification of Gravity on Large Scales
• Judging Genius
  • Kelvin (1900): “Physics is over, except for two clouds on the horizon”
  • two clouds = quantum mechanics and relativity
• Elementary Particle Physics
  • 12 particles (6 quarks, 6 leptons) and 4 forces
  • Standard Model has ~20 arbitrary constants (referring to particle properties like mass and strength)
• Dark Matter
  • evidence: mass of galaxy predicted by orbit speeds > combined masses of observed objects
  • either:
    • can’t see most matter (dark matter)
    • underestimation of mass of observed objects
    • overestimation of orbit speed
  • most matter under pressure, dark matter under tension (pulls universe together)
  • yet somehow, so negative a negative pressure that it accelerates cosmic expansion?
  • Universe: 70% dark energy and 26% dark matter (96% unknown matter!)
• Unifications
  • highest goals of physics
    • show commonality (deep)
    • show differentiation (apparent)
  • come in groups: Ptolemy’s cosmology + Aristolian motion vs. Copernican cosmology + Bruno’s stars (based on complementary underlying principles)
  • Historical Unifications:
    • sun and stars (Giordano Bruno burned alive by the Catholic Church for this!)
    • electricity and magnetism
    • motion and rest (Galileo, Ptolemy and Aristotle believed the Earth and heavens had different physics – this was before the train)
    • acceleration and gravity (Einstein’s general relativity)
    • gravitational field and geometry of spacetime (Einstein’s general relativity)
  • False Unifications:
    • heat and matter (phlogiston = the heat particle)
    • light and sound (sound = vibrations in matter, light = vibrations in aether)
    • aether
      • must be very dense (to allow super high speed of propagation)
      • cannot interact with matter (to allow passing)
      • yet matter must be able to interact with waves in it…
      • swing and a miss…
    • atoms as magnetic field line ‘knots’ (lead to fad mathematical ‘knot theory’)
  • Externalities of False Unification Attempts
    • development of ‘knot theory’ (inspired by atoms as magnetic field line ‘knots’)
    • conformal fields – 2D space cut out in time by moving string, used to describe 6D Calabi-Yau (describe 6D in 2D+1)
    • noncommutative geometry (inspired by Penrose’s Twister Theory)
  • Characteristics of Successful Unifications
    • surprising
    • dramastic consequences
    • new predictions
    • may explain contemporary surprises
    • may raise absurd questions that lead to more unifications
    • complementary uni groups create strong predictive frameworks (earth/planets, sun/stars, rest/motion, Earth’s gravity/sun’s force on planets)
  • Unification Strategies
    • show apparent difference is only due to difference in perspective (absolute distinction is only relative)
  • Power of Unifications
    • Maxwell:
      • experimental phenomena relating E and M
      • unification of E and M
      • Maxwell Eqns
      • EM waves
      • speed of light!
      • theory of light
      • radio! infrared! UV!
• Beauty in Science
  • False Leads:
    • 5 planets orbits modeled by Russian doll set of Platonic solids (sphere, dodecahedron, sphere, tetrahedron, sphere) – not your best effort Kepler…
    • atoms as magnetic field line ‘knots’
    • string theory?
• Kepler’s Laws
  • elliptical orbits with sun at focus
  • orbital speed ~ distance from sun
  • first to recognize that sun affected orbits (more than just a big candle!)
• Why Being a Experimental Scientist Trumps Office Work
  • Eddington’s 1919 voyage to observe an eclipse and the bending of light and confirm Einstein’s general relativity
• History of String Theory
  • Kaluza-Klein
    • added dimensions unify gravity and EM (EM = geometry of 5th D)
    • no new successful predictions
    • imposed fixed-radius, curled-up dimensions (static in space and time)
    • violates dynamic Einstein spacetime
    • with dynamic 5th D, Kaluza-Klein theory gives:
      • infinte solutions
      • radius of circle varies over space and time
      • gravitational and electrical effects convert into one another
      • electrical charges vary over time
      • *none observed
  • Yang-Mills: similar case for strong and weak nuclear force
  • Failures of Higher-D Unifications Theories:
    • no new predictions
    • many solutions (the few that describe the world are unstable)
    • not meshed with quantum theory
    • *failure encourages study of particle physics
  • Particle Physics
    • ignores weak gravity and continues
    • ignores dynamic spacetime (GR) and assumes static spacetime (SR)
    • background dependent
    • Quantum Field Theory
      • unify quantum with EM
      • continuous values of field lead to infinite variables
      • photon theory developed easily
      • integrating photons with E charges more difficult
      • QED developed independently by Japanese and Americans (Feynman and Schwinger) during WWII
    • Standard Model of Particle Physics
      • unifying EM with strong/weak
      • required breakdown of proton and neutron into quarks (Gell-Mann and Zweig in early 60s) to allow for breaking proton-neutron interaction down to quark interaction (like breaking molecular interaction down to atomic interaction)
      • experiments at Stanford (proposed by Feynman) confirm 3-quark protons and neutrons
      • 2 Major Principles:
        • Gauge Principles: unify using what is common
          • symmetry – operation that doesn’t change behavior relative to outside world
          • gauge principle – gauge forces can be completely determined by their symmetries
          • strong, weak, EM = gauge forces
          • messenger particles = gauge bosons (gluons, weak bosons, photons)
          • Yang-Mills theories = 50s application of gauge principles to particle physics to predict infinite range forces
        • Spontaneous Symmetry Breaking: differentiate
          • 60s ‘differentiation between unified phenomena’ theory: laws have symmetries not respected by all features of world they apply to
          • ex: children of equal opportunity who develop and differentiate
          • symmetry is spontaneously broken (necessary but highly contingent upon details)
          • symmetry/instability traded for assymmetry/stability
          • consequence: EM/strong/weak unified infite range force > SSB > EM infinite & strong/weak limited
          • phenomenon and particle resulting from SSB named Higgs
          • Weinberg-Salam model of electroweak theory used to unify EM and weak (predicted messenger particles of weak W+, W-, Z all found!)
          • consequence of adding SSB to fundamental theory: properties of universe depend on history & environment (breaking occurs differently depending on temp and pressure)
          • Higgs field = physical quantity signalling when and how symmetry broke
          • Higgs boson = force particle
          • last unconfirmed prediction of Weinberg-Salam model (could be proven by LHC!)
          • unification scale – energy scale at which forces unify
          • weak interaction scale – energy scale at which weak and EM unify (should observe Higgs)
      • QCD: quantum chromodynamics (gauge theory applied to strong – experimentally confirmed)
      • Weinberg-Salam + QCD = Standard Model of Particle Physics
  • GUT Effort using SSB
    • Goal
      • unify forces
      • unify quarks (ruled by strong) with leptons (ruled by electroweak)
    • SU(5): simple solution
      • named for 5 particles it unified: 3 quarks and 2 leptons (electron and its neutrino)
      • turned arbitrary into necessity
      • explained predictions of SM
      • made new prictions: decay of quarks into electrons and neutrions (proton decay)
      • massive tanks built deep underground with ultrapure H2O
      • 25 years later and nothing found…
      • inevitably, physicists toy with constants to make decay more rare but without predictions, theories die
  • Attempts at Unification of Particles and Forces
    • aether theory
    • unified field theory
    • supersymmetry
  • Supersymmetry
    • fermions – matter particles (obey Pauli exclusion)
    • bosons – force particles (reverse Pauli, encouraged sharing > results in fields)
    • SS unified fermions and bosons
      • predicts ‘selectron’ (super electron or boson equivalent)
      • free constant jerry rigg that sucka out of range of current experiments
  • Importance of Background Independence
    • integrates dynamic spacetime
    • QED solved with fixed background…
    • …but gravity cannot be (gravity waves interact, unlike EM waves)
  • History of Quantum Gravity
    • graviton theory developed by Bryce Dewitt in late 40s
    • self-interactin leads to infinities that aren’t solved into 70s
    • apply gravity to QM instead of QM to gravity?
    • important gravity situations: BHs and BB
    • black hole info paradox – QM states conservation of info yet a collapsing BH seems to eat info
    • supergravity fails to explain
    • choice: abandon fixed background OR abandon particles
  • Birth of String Theory
    • Gabriele Veneziano notices ‘rubber band’ formula that fits collision data for particles in an acceleration
    • original details:
      • 25 D
      • tachyon – particle that can exceed c
      • particles that cannot be brought to rest (massless – since mass measures energy at rest)
      • no fermions?
    • Pierre Riamond rehash:
      • fermions in
      • tachyons out
      • 25D > 9D
    • Stringy Details:
      • photons = open or closed strings
      • gravitons = closed strings
      • ends of open string = charged particles (particle and antiparticle)
      • closed loop production: particle-antiparticle collision > ends fuse > photon created
      • string between ends = force between them
      • forces determined by breaking/joining of strings
      • just 2 fundamental constants:
        • string tension – energy per length
        • string coupling constant – probability of splitting
      • law of motion = minimal SA of world sheet
      • field lines = quantized lines of electric flux
      • if true, ST leads to the following conclusions:
        • unify particles and forces as vibrations
        • gauge fields naturally arise as open strings
        • gravitons naturally arise as closed strings
        • supersymmetric ST unifies bosons and fermions
  • ST Revolutions
    • 1st (1984): John Schwarz shows ST anomaly free in 10D and search for meta theory with solutions equal to the many STs begins
    • 2nd (1995): Ed Witten lays out a plan
      • T-duality (topological) – 1/r = r (Planck bouncing)
      • S-duality (strong-weak coupling) – 1/g = g
      • 5 STs unified in 11D
      • 11D supermembrane theory revived
      • 2D branes floating in 11D
      • 1 D wrapped around circular D
      • other D moves in 9D space
      • Witten dubs “M Theory”
      • Brane Theories
        • Polchinski: ST must have more than strings (D-branes)
        • our world = floating 3D brane
        • piling 3D branes can create any symmetries
        • Strominger and Vafa (1996) describe special BHs with BT (biggest accomplishment of 2nd Rev)
      • Malcedena’s New Duality (1997)
        • ST with gravity and 1D = maximally super gauge theory on fixed background with no gravity
        • mental shortcut: electric field lines > each point has a value > value = distance > extra D!
        • only useful if one side of eqn can be defined exactly (gauge theory more likely)
      • Exact vs. Approximate
        • very important distinction
        • approx. between gravitational theory in BH and gauge theory at edge > info can be lost forever
        • exact between > info preserved
      • Cosmological Constant
        • Einstein invented to stabilize spacetime because he was unhappy with dynamic spacetime
        • QT may require CC since Heisenberg states that even with zero temp., energy still present (vaccuum/ground state)
        • Malcedena predicts negative CC
        • 1998 supernova observation shows positive CC
        • problem of moduli stabilization – how to prevent continually evolving geometry in ST
      • Anthropic Principle
        • STs are random
        • one leads to life in our universe
        • dangerous (destroy predictive power of science)
      • Possible Pro-ST Observations:
        • large relic strings (acting as gravitational lenses, duplicating images of stars)
        • extra D (extra forces)
        • supersymmetry (confirmation of WIMPs – weakly interacting massive particles)
        • unified forces (proton decay)
• New Observations in Physics
  • peaks in temperature fluctuations in universe
    • resonant matter in early universe?
    • resonance ~ size
    • wavelength of resonant modes ~ size of universe at point when it became transparent (hot plasma decoupled into energy and matter)
  • preferred direction of universal radiation
    • dubbed “axis of evil”
  • cosmological constant scale R
    • C/R = age of universe
    • C^2/R = acceleration threshhold at which orbits move from not needing dark E to explain them to needing it (Milgrom’s Law)
    • Modified Newtonian Dynamics (MOND) by Milgrom: gravity decreases by d instead of d^2 after magical acceleration
• New Testable Predictions
  • change in physical constants over time
    • measured using simple ratio
    • fine structure constant alpha = [electron charge^2/c]*Planck
  • GZK prediction (Planck scale test of special relativity)
    • cosmic rays – proton beams from far away that collide with atmosphere and create particle showers
    • max speed predicted
      • cosmic rays collide with space photons, create pions (pi-mesons), and slow down
      • effect: speed limit set by pion energy
    • Japanese found protons exceeding energy, so either:
      • originated close enough to Earth to maintain speed
      • wrong data
      • particle larger in mass than proton
      • breakdown in special relativity
    • could also be detected in different times of photons arriving from very distant gamma-ray burst
    • Giovanni Amelino-Camelia leads Planck scale observations
  • Douby Special Relativity (DSR)
    • length contraction + min. length do not mesh
    • currently, c is max speed, planck is min. length (or max E or momentum)
    • DSR proposes that c increases with T and was super-high at BB
    • works in 2D space
    • soccer ball problem Planck max E applies to protons and dogs, yet dogs have many protons…
• Current Quantum Gravity
  • Basics:
    • space is emergent
    • fundamental description is discrete
    • causality is fundamental
  • Penrose’s Twister Theory
  • normally, events primary & relations secondary
  • TT flips, relations primary & events secondary
  • new space composed of light rays in spacetime
  • popular at Oxford in 70s
  • failed to integrate quantum, but lots of valuable math emerged
• Loop Quantum Gravity
  • describe fields in terms of lines
  • lines ‘loop’ in absence of matter
  • precursor to ST (ST = bg indy case of loop QG)
  • decoherence – loss of info through interaction with environment
  • Fotini Markopoulos: particle as emergent excitation
  • particle = waves in quantum gravity
  • loop QG + Marko excitations + preons (new fund. particle) = good QT
• Anthropic View of Science
  • evolved process that works for us in our world
  • paralell to no free lunch search theorem by Wolpert & Macready
• 2 Characteristics of a Scientific Community
  • shared ethic
  • imaginative
    • rel. com. preserves
    • sci. com. progresses
    • relcom professes to know future
    • scicom open to many futures
  • science – “organized skepticism in the reliability of expert opinion” (Feynman)
• Redesigning the SciCom
  • seek risk to maximize return (imitate VCs – 90% of ventures should fail)
  • flatten the hierarchy
  • polarization predicts success
• Rebel Seers
  • Ted Jacobsen (false SR)
  • Joao Magueijo (false SR and variable c)
  • Robert Laughlin
  • Grigori Volovik
  • Xiao-Gang Wen
  • James Bjorken
  • Holger Bech Nielson (random dynamics)
  • ‘t Hooft (holographic principle)
  • Louis Crane (relational quantum theories)
  • Stuart Kauffman
  • Per Bak
  • Lynn Margulis
  • Alexander Grothendieck
  • Julian Barbour

  Questions

• If dark matter is fundamentally under tension, how does it accelerate cosmic expansion?
• How do we distinguish between dark energy and matter?
• Is the notion of a field an oversimplication? (it seems like a stork story for baby physicists)
• Mathematically, how does a background independent theory differ from a background dependent one?
• What is gauge symmetry and what mathematics are needed to understand it? (more in Smolin’s ‘Life of the Cosmos’)
• What is this MOND nonsense?
• Is anyone currently studying the cosmological constant scale and its abundance of apparent coincidences?

  Topics to Explore

• noncommutative geometry
• topos theory – nature of time
• scientific philosophy (Popper, Kuhn, Bacon)

  Conclusion

• String theory has been deformed so many times that its hard to recognize and understand.
• Many interesting and creative ideas have come out of the pursuit of string theory.
• My romantic notion of a period of scientific hermitude has been reinforced.
• Studying the fundamental can be lonely and difficult but is essential.
  
  Related posts
  • Book Review: Three Roads to Quantum Gravity by Lee Smolin
  • Book Review: Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles by Eisberg & Resnick
  • Book Review: The Elegant Universe by Brian Greene
  • Book Review: Solid State Physics by Ashcroft & Mermin
  • Book Review: Spacetime Physics by Edwin Taylor and John Wheeler