Incoming links: Superconductivity
100 Greatest Discoveries by the Discovery Channel (2004-2005) Updated 2025-04-24 +Created 1970-01-01
Hosted by Bill Nye.
Physics topics:
- Galileo: objects of different masses fall at the same speed, hammer and feather experiment
- Newton: gravity, linking locally observed falls and the movement of celestial bodies
- TODO a few more
- superconductivity, talk only at Fermilab accelerator, no re-enactment even...
- quark, interview with Murray Gell-Mann, mentions it was "an off-beat field, one wasn't encouraged to work on that". High level blablabla obviously.
- fundamental interactions, notably weak interaction and strong interaction, interview with Michio Kaku. When asked "How do we know that the weak force is there?" the answer is: "We observe radioactive decay with a Geiger counter". Oh, come on!
biology topics:
- Leeuwenhoek microscope and the discovery of microorganisms, and how pond water is not dead, but teeming with life. No sample of course.
- 1831 Robert Brown cell nucleus in plants, and later Theodor Schwann in tadpoles. This prepared the path for the idea that "all cells come from other cells", and the there seemed to be an unifying theme to all life: the precursor to DNA discoveries. Re-enactment, yay.
- 1971 Carl Woese and the discovery of archaea
Genetics:
- Mendel. Reenactment.
- 1909 Thomas Hunt Morgan with Drosophila melanogaster. Reenactment. Genes are in Chromosomes. He observed that a trait was linked to sex, and it was already known that sex was related to chromosomes.
- 1935 George Beadle and the one gene one enzyme hypothesis by shooting X-rays at bread mold
- 1942 Barbara McClintock, at Cold Spring Harbor Laboratory
- 1952 Hershey–Chase experiment. Determined that DNA is what transmits genetic information, not protein, by radioactive labelling both protein and DNA in two sets of bacteriophages. They observed that only the DNA radioactive material was passed forward.
- Crick Watson
- messenger RNA, no specific scientist, too many people worked on it, done partially with bacteriophage experiments
- 1968 Nirenberg genetic code
- 1972 Hamilton O. Smith and the discovery of restriction enzymes by observing that they were part of anti bacteriophage immune-system present in bacteria
- alternative splicing
- RNA interference
- Human Genome Project, interview with Craig Venter.
Medicine:
- blood circulation
- anesthesia
- X-ray
- germ theory of disease, with examples from Ignaz Semmelweis and Pasteur
- 1796 Edward Jenner discovery of vaccination by noticing that cowpox cowpox infected subjects were immune
- vitamin by observing scurvy and beriberi in sailors, confirmed by Frederick Gowland Hopkins on mice experiments
- Fleming, Florey and Chain and the discovery of penicillin
- Prontosil
- diabetes and insulin
Condensed matter physics is one of the best examples of emergence. We start with a bunch of small elements which we understand fully at the required level (atoms, electrons, quantum mechanics) but then there are complex properties that show up when we put a bunch of them together.
Includes fun things like:
As of 2020, this is the other "fundamental branch of physics" besides to particle physics/nuclear physics.
Condensed matter is basically chemistry but without reactions: you study a fixed state of matter, not a reaction in which compositions change with time.
Just like in chemistry, you end up getting some very well defined substance properties due to the incredibly large number of atoms.
Just like chemistry, the ultimate goal is to do de-novo computational chemistry to predict those properties.
And just like chemistry, what we can actually is actually very limited in part due to the exponential nature of quantum mechanics.
Also since chemistry involves reactions, chemistry puts a huge focus on liquids and solutions, which is the simplest state of matter to do reactions in.
Condensed matter however can put a lot more emphasis on solids than chemistry, notably because solids are what we generally want in end products, no one likes stuff leaking right?
One thing condensed matter is particularly obsessed with is the fascinating phenomena of phase transition.
What Is Condensed matter physics? by Erica Calman
. Source. Cute. Overview of the main fields of physics research. Quick mention of his field, quantum wells, but not enough details.As of 2020, basically means "liquid nitrogen temperature", which is much cheaper than liquid helium.
The dream of course being room temperature and pressure superconductor.
Timeline of superconductivity from 1900 to 2015
. Source. 
Once again, relies on superconductivity to reach insane magnetic fields. Superconductivity is just so important.
Ciro Santilli saw a good presentation about it once circa 2020, it seems that the main difficulty of the time was turbulence messing things up. They have some nice simulations with cross section pictures e.g. at: www.eurekalert.org/news-releases/937941.
The more familiar transitions we are familiar with like liquid water into solid water happen at constant temperature.
However, other types of phase transitions we are less familiar in our daily lives happen across a continuum of such "state variables", notably:
- superfluidity and its related manifestation, superconductivity
- ferromagnetism
Applications: produce high magnetic fields forAs of the early 2020s, superconducting magnets predominantly use low temperature superconductors Nb-Ti and Nb-Sn, see also most important superconductor materials, but there were efforts underway to create practical high-temperature superconductor-based magnets as well: Section "High temperature superconductor superconducting magnet".
- magnetic resonance imaging, the most important commercial application as of the early 2020s
- more researchy applications as of the early 2020s:
Wikipedia has done well for once:
The current to the coil windings is provided by a high current, very low voltage DC power supply, since in steady state the only voltage across the magnet is due to the resistance of the feeder wires. Any change to the current through the magnet must be done very slowly, first because electrically the magnet is a large inductor and an abrupt current change will result in a large voltage spike across the windings, and more importantly because fast changes in current can cause eddy currents and mechanical stresses in the windings that can precipitate a quench (see below). So the power supply is usually microprocessor-controlled, programmed to accomplish current changes gradually, in gentle ramps. It usually takes several minutes to energize or de-energize a laboratory-sized magnet.
Superconductivity: magnetic separation by University of Cambridge
. Source. Experiments:
- "An introduction to superconductivity" by Alfred Leitner originally published in 1965, source: www.alfredleitner.com/
- Isotope effect on the critical temperature. hyperphysics.phy-astr.gsu.edu/hbase/Solids/coop.html mentions that:
If electrical conduction in mercury were purely electronic, there should be no dependence upon the nuclear masses. This dependence of the critical temperature for superconductivity upon isotopic mass was the first direct evidence for interaction between the electrons and the lattice. This supported the BCS Theory of lattice coupling of electron pairs.
20. Fermi gases, BEC-BCS crossover by Wolfgang Ketterle (2014)
Source. Part of the "Atomic and Optical Physics" series, uploaded by MIT OpenCourseWare.Actually goes into the equations.
Notably, youtu.be/O_zjGYvP4Ps?t=3278 describes extremely briefly an experimental setup that more directly observes pair condensation.
Lecture notes:
Transition into superconductivity can be seen as a phase transition, which happens to be a second-order phase transition.
Can be achieved in two ways it seems:
- macroscopic beam splitter and optical table
- photolithography
Animation of Hong-Ou-Mandel Effect on a silicon like structure by Quantum Light University of Sheffield (2014): www.youtube.com/watch?v=ld2r2IMt4vg No maths, but gives the result clear: the photons are always on the same side.
- quantum dot source. TODO how do you produce identical photons from two separate quantum dots? See also: quantum dot single photon source.
- superconducting nanowire detector. So the device has to be cooled then? Video "Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)" youtube.com/watch?v=7wCBkAQYBZA&t=2497 however says that semiconducting devices can also be used
The most important ones are:
- theory of everything. We are certain that our base equations are wrong, but we don't know how to fix them :-)
- full explanation of high-temperature superconductivity. Superconductivity already has a gazillion applications, and doing it in higher temperatures would add a gazillion more, and maybe this theoretical explanation would help us find new high temperature superconducting materials more effectively
- fractional quantum Hall effect 5/2
Other super important ones:
- neutrino mass measurement and explanation