Striving for Simplicity

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Striving for Simplicity

• Christopher Pethick
• Nordita

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The people we celebrate
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• thoreau2.jpg

Life is frittered away by details. Simplify,
simplify. H. D. Thoreau, Walden
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• In the midst of this chopping sea of civilized
  life, such are the clouds and storms and
  quicksands and thousand-and-one items to be
  allowed for, that a man has to live by dead
  reckoning, and he must be a great calculator
  indeed who succeeds.

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The importance of experiment and observation
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• My greatest concern was to replace the ordinary
  calculations of uncertain accuracy with better
  ones having error bounds, in order to raise the
  crude manners of theoretical physics to the more
  cultivated level of experimental physics.
• Walter Thirring, Quantum mechanics of atoms and
  molecules, 1979.

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• Simplicity how to throw out the bathwater but
  keep the baby
• Simple but not simplistic

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• Touchstone is the confrontation with phenomena
• Review of Goldberger and Watson, Scattering
  Theory, ca. 1965
• physicists methods of vigor rather than
  rigor.

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The devil is in the detail

• Per ardua ad astra
• (Through struggles to the stars)

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The need for diversity

• Monocultures are boring and susceptible to
  disease
• Evolution is an inefficient process, with many
  failed attempts
• (Funding agencies do not always appreciate this.
  Challenge is to create ecological niches.)

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The contradictions of Thoreau

• Lived in cabin in woods, but
• Dinner with the Emersons
• Collect gossip in town every day or two
• Confusion between simplicity as a guiding
  principle and its implementation in practice
• Details unavoidable
• In search for simplicity we are dependent on
  others

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Nuclear physics a rich field

• Strong interactions.
• Range particle spacing
• Non-central forces
• Multicomponent systems
• Finite systems
• Lots of data. Numerous probes. Spectroscopic
• Non-zero temperature
• Extreme conditions
• Connections to other fields and applications

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Stimuli in the quest for simplicity

• Vary energy
• Vary density
• Change neutron excess
• Increase precision of measurements
• New probes
• Other unusual conditions (fast rotation, high
  temperature)
• Related systems (electron gas, neutron stars,
  quantum liquids, ultracold gases)
• Serendipity

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Neutron stars and dense matter

• Early work (Baade, Zwicky, Oppenheimer, Volkoff,
  Wheeler, Salpeter, Zeldovich, Novikov,
  Ambartsumian, Cameron, )
• Detection proposed. Cooling of neutron stars.
  Accretion.
• Discovery of rotation-powered pulsars (1967).
  Hewishs telescope. Cheap, low tech,
  unfashionable frequency, designed for other
  purposes, but good time resolution. Good graduate
  student
• Discovery of accretion-powered pulsars.
• UHURU X-ray satellite (1971).

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• Neutron stars became a legitimate field of study
  for physicists. Reality check.
• (Bethe, Negele, Siemens in Copenhagen )
• Nuclear matter theory dominated by
  Brueckner-Bethe theory. (Bethe review, 1970)
  (No hope for liquid helium)
• The challenge of supernuclear densities.
• Eye-opening (Pandharipande, LOCV)
• Neutron-rich matter. (Simplicity of neutron
  matter)

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Ladders and bubbles

• Physics around 1960.
• Summing a geometrical progression.
• Nuclear physics ladders
• Solid state physics -- bubbles
• Gerry appreciated the need to sum bubbles and
  ladders. Induced interactions, Babu and Brown.
  Led to renormalization group approach. Schwenk,
  Friman, Brown, Kuo, Bogner,

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Many developments since 1970

• Many-body methods. Cluster expansions
• Computing
• Monte-Carlo techniques
• Liquid helium
• Clusters
• Many experimental observables (single-particle
  properties)
• Neutron stars
• Ultracold atomic gases

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Bottom line

• The road to simplicity is not simple
• Gerry, Peter and Wolfram are superb practitioners
  of the art of throwing out the bathwater, but
  keeping the baby.
• HURRAH !!!!