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Sandbox Physics

14 readings · Four interactive models · English and Chinese

Heat, chance and collective behaviour

How do atoms make a liquid, why does climate remember heat, and how can a network recall a picture? Follow the experiments and ideas through fourteen bilingual articles and four interactive models.

Try a change and see what follows

Four ways to make the physics move

  1. Watch magnetic domains compete Change temperature and size, then sample the fluctuations.
  2. Recover a damaged memory Erase part of a picture and let the network update.
  3. Follow heat into the ocean Change the forcing and compare surface and deep-ocean warming.
  4. Pluck a magnetic field Send a wave through a conducting fluid and change its speed.

Reading path · D-R1

What a gas can tell us about atoms

A small discrepancy in a balance, a disappearing liquid surface, and grains suspended in water each opened a different route to matter too small to see.

  1. The extra weight that revealed argon

    How did weighing nitrogen reveal another gas in the air?

  2. How a gas becomes a liquid and loses the boundary

    What must an ideal-gas picture gain before it can explain condensation?

  3. Perrin counted the grains that refused to settle

    How could visible particles reveal the molecular scale of water?

  4. Bridgman opened the way into matter under pressure

    What did a better seal let physicists learn about compressed matter?

Reading path · D-R2

How order survives, changes and gets frustrated

Near a critical point, small patches join larger ones. Long molecules coil, liquid crystals align, and competing magnetic bonds make agreement impossible.

  1. Why very different materials behave alike near a critical point

    How did Wilson make sense of fluctuations at many different sizes?

  2. A liquid can flow and still keep a direction

    What kind of order survives when a liquid crystal flows?

  3. A long molecule behaves like a wandering chain

    Why does the size of a polymer coil depend on more than its total length?

  4. The magnets that cannot satisfy all their neighbours

    What did Parisi discover in the apparently disordered states of a spin glass?

Reading path · D-R3a

Why climate responds slowly to a changing atmosphere

Follow heat through a vertical column of air, then into an ocean that remembers yesterday’s weather. The two stories answer different parts of the climate problem.

  1. Manabe and Wetherald followed heat through the atmosphere

    How could a single column of air reveal the warming caused by more carbon dioxide?

  2. How the ocean remembers changing weather

    How can rapidly changing weather produce slowly changing climate?

Reading path · D-R3b

When a network can remember and learn

A damaged picture can settle back into a stored pattern. Adding random changes lets related networks learn which patterns are common.

  1. How a Hopfield network finds a damaged memory

    How can simple on-or-off units recover a whole pattern from an incomplete cue?

  2. How a Boltzmann machine learns which patterns belong together

    Why would a learning network benefit from making random changes?

Reading path · D-R4

A valve in sunlight, a wave along a magnetic field

A lighthouse valve compares how rods warm in daylight. A magnetic field pulls a conducting fluid back when it bends. In each case, the mechanism tells you what to measure.

  1. The rods that switched a lighthouse off at dawn

    How did Dalén’s sun valve respond to daylight without electricity?

  2. A bent magnetic field can carry a wave

    How can a magnetic field restore the motion of a conducting fluid?

The work came before the prize

Each date below marks a paper or experiment discussed in the reading. Prize dates appear separately; the articles introduce collaborators and the earlier work they built on.

Open the discovery timeline

  1. 1873

  2. 1894

  3. 1907

  4. 1908

  5. 1912

  6. 1942

  7. 1967

  8. 1971

  9. 1972

  10. 1972

  11. 1976

  12. 1979

  13. 1982

  14. 1985

Find the eleven Nobel contributions

1904-1

Lord Rayleigh

1910-1

Johannes Diderik van der Waals

1912-1

Gustaf Dalén

1926-1

Jean Baptiste Perrin

1946-1

Percy W. Bridgman

1970-1

Hannes Alfvén

1982-1

Kenneth G. Wilson

1991-1

Pierre-Gilles de Gennes

2021-1

Syukuro Manabe · Klaus Hasselmann

2021-2

Giorgio Parisi

2024-1

John Hopfield · Geoffrey Hinton

A few words you will meet

Open the glossary
Critical point
The end of the liquid–gas coexistence curve. Above it, liquid and gas can change into one another continuously.
Fluctuation
A quantity’s spontaneous changes around its average, such as the changing magnetization of a warm lattice.
Correlation length
The distance over which a local change tends to be accompanied by changes elsewhere.
Universality
Systems with different microscopic details can share the same critical scaling when dimension, symmetry and interaction range agree.
Nematic order
Elongated molecules tend to point along one common axis even though their centres do not form a crystal lattice.
Frustration
Competing preferences cannot all be satisfied at once. Three spins with pairwise opposite preferences provide a simple example.
Radiative forcing
A change in Earth’s incoming-minus-outgoing energy flow, evaluated with a specified adjustment convention.
Climate feedback
Warming changes radiation, water vapour, clouds or ice, which in turn changes how quickly heat escapes.
Associative memory
A stored pattern can be recovered from an incomplete or corrupted cue.
Energy landscape
A way to picture each network configuration as a height. Updates can descend into different local valleys.
Magnetic tension
A bent magnetic field exerts a restoring force along its curvature in a conducting fluid.
Ideal magnetohydrodynamics
A continuum description of a conducting fluid in the limit where electrical resistivity is negligible on the scales considered.

Continue into neighbouring questions

Magnetism, superconductors and material devicesQuantum physics and the experiments behind itHow light and particles measure matter
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