Reza Ebadi

Precision physics

Precision physics is a tradition of curious people pushing measurement and control to the next frontier. What comes back is both: a better understanding of the universe, and technologies that were not possible — or even imagined — before.

I am drawn to that boundary: the interplay between fundamental physics and technology. I am not convinced there is much distance between the two — at their edges they fade into each other. That is where I see myself as a researcher.

On this page I review foundational topics in the way I think about them.

Before going into any single topic, it is worth standing back and looking at the whole of it: two centuries of people measuring things far better than anyone needed them to, and how much of the life we live today came out of that curiosity.

Every new decimal place is a chance to be surprised Measurement divided by theory, written as 1.000000000000000002, with everything up to the last digit marked old physics, new technology, and the final 2 circled and marked two ways, new physics? or systematics? Either answer is underlined together and leads on to future technology. Below it, a winding timeline of what precision measurement has found: 1798, Cavendish weighs the Earth; 1887, Michelson–Morley; 1889, Eötvös equivalence test; 1913, Millikan's oil drop; 1927, quartz clock; 1936, photomultiplier; 1938, Rabi magnetic resonance; 1946, NMR in bulk matter; 1947, Lamb shift; 1948, electron g−2; 1950, Ramsey interferometry; 1953, Paul trap; 1955, caesium clock; 1956, Hanbury Brown and Twiss; 1957, parity violation; 1958, Mössbauer effect; 1959, Pound–Rebka redshift; 1960, hydrogen maser; 1963, Josephson effect; 1964, SQUID magnetometer; 1967, redefinition of the second (by caesium); 1969, Weber bars; 1972, superfluid helium-3; 1973, single electron in a Penning trap; 1974, Hulse–Taylor pulsar; 1975, gravity in a neutron's phase; 1976, Gravity Probe A; 1977, photon antibunching; 1977, GPS; 1978, laser cooling of trapped ions; 1980, quantum Hall effect; 1983, Pound–Drever–Hall lock; 1983, redefinition of the metre (by c); 1987, magneto-optical trap; 1990, conventional volt and ohm adopted; 1991, atom interferometry; 1992, lambda point in microgravity; 1995, Bose–Einstein condensation; 1995, transition-edge sensor; 1997, superfluid helium Josephson effect; 1997, atomic parity violation in caesium; 2000, optical frequency comb; 2001, superconducting nanowire detector; 2005, optical lattice clock; 2006, muon g−2 at Brookhaven; 2008, Al⁺ quantum logic clock; 2010, proton radius from muonic hydrogen; 2010, a clock sees 33 cm of gravity; 2011, Gravity Probe B; 2015, LIGO; 2015, atom wavepackets half a metre apart; 2016, LISA Pathfinder; 2017, antihydrogen 1S–2S spectroscopy; 2017, antiproton moment to 1.5 ppb; 2019, SI redefined by constants; 2019, squeezed light in LIGO; 2020, fine-structure constant disagrees; 2022, MICROSCOPE; 2022, a clock sees 1 mm of gravity; 2023, electron g−2 to 0.13 ppt; 2023, nanohertz background; 2023, antihydrogen falls down; 2024, thorium nuclear clock. Every new decimal place is a chance to be surprised. measurement theory = 1 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 old physics, new technology new physics? systematics? future technology Cavendish weighsthe Earth1798 Michelson–Morley1887 Eötvös equivalencetest1889 Millikan'soil drop1913 quartz clock1927 photomultiplier1936 Rabi magneticresonance1938 NMR in bulkmatter1946 Lamb shift1947 electron g−21948 Ramseyinterferometry1950 Paul trap1953 caesium clock1955 Hanbury Brownand Twiss1956 parity violation1957 Mössbauer effect1958 Pound–Rebkaredshift1959 hydrogen maser1960 Josephson effect1963 SQUIDmagnetometer1964 redefinition ofthe second(by caesium)1967 Weber bars1969 superfluidhelium-31972 single electronin a Penning trap1973 Hulse–Taylorpulsar1974 gravity in aneutron's phase1975 Gravity Probe A1976 photonantibunching1977 GPS1977 laser cooling oftrapped ions1978 quantum Halleffect1980 Pound–Drever–Halllock1983 redefinition ofthe metre(by c)1983 magneto-opticaltrap1987 conventional voltand ohm adopted1990 atominterferometry1991 lambda pointin microgravity1992 Bose–Einsteincondensation1995 transition-edgesensor1995 superfluid heliumJosephson effect1997 atomic parityviolation in caesium1997 optical frequencycomb2000 superconductingnanowire detector2001 optical latticeclock2005 muon g−2at Brookhaven2006 Al+ quantumlogic clock2008 proton radiusfrom muonic hydrogen2010 a clock sees33 cm of gravity2010 Gravity Probe B2011 LIGO2015 atom wavepacketshalf a metre apart2015 LISA Pathfinder2016 antihydrogen1S–2S spectroscopy2017 antiproton momentto 1.5 ppb2017 SI redefinedby constants2019 squeezed lightin LIGO2019 fine-structureconstant disagrees2020 MICROSCOPE2022 a clock sees1 mm of gravity2022 electron g−2to 0.13 ppt2023 nanohertzbackground2023 antihydrogenfalls down2023 thorium nuclearclock2024

The first notes are under way.