Incoming links: Gravity
100 Greatest Discoveries by the Discovery Channel (2004-2005) Updated 2024-12-15 +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
Unifies both special relativity and gravity.
Not compatible with the Standard Model, and the 2020 unification attempts are called theory of everything.
One of the main motivations for it was likely having forces not be instantaneous, but rather mediated by field to maintain the principle of locality, just like electromagnetism did earlier.
The Kibble balance is so precise and reproducible that it was responsible for the 2019 redefinition of the Kilogram.
It relies rely on not one, but three macroscopic quantum mechanical effects:How cool is that! As usual, the advantage of those effects is that they are discrete, and have very fixed values that don't depend either:One downside of using some quantum mechanical effects is that you have to cool everything down to 5K. But that's OK, we've got liquid helium!
- atomic spectra: basis for the caesium standard which produces precise time and frequency
- Josephson effect: basis for the Josephson voltage standard, which produces precise voltage
- quantum Hall effect: basis for the quantum Hall effect, which produces precise electrical resistance
- on the physical dimensions of any apparatus (otherwise fabrication precision would be an issue)
- small variations of temperature, magnetic field and so on
The operating principle is something along:Then, based on all this, you can determine how much the object weights.
- generate a precise frequency with a signal generator, ultimately calibrated by the Caesium standard
- use that precise frequency to generate a precise voltage with a Josephson voltage standard
- convert that precise voltage into a precise electric current by using the quantum Hall effect, which produces a very precise electrical resistance
- use that precise current to generate a precise force on the object your weighing, pushing it against gravity
- then you precisely measure both:
- local gravity with a gravimeter
- the displacement acceleration of the object with a laser setup
How We're Redefining the kg by Veritasium
. Source. The Kibble Balance, realizing the Kilogram from fundamental constants of nature by Richard Green
. Source. Presented in 2022 for a CENAM seminar, the Mexican metrology institute. The speaker is from the Canadian metrology institute- youtu.be/ZfNygYuuVAE?t=854: they don't actually use the Quantum Hall effect device during operation, they only use it to calibrate other non-quantum resistors
The Watt balance and redefining the kilogram by National Physical Laboratory
. Source. Nothing much, but fun to hear Kibble talking about his balance in beautiful English before he passed.Subtle is the Lord by Abraham Pais (1982) chapter III "Relativity, the special theory" mentions that this fact and its importance (we want the laws of physics to look the same on all inertial frames, AKA Lorentz covariance) was first fully relized by poincaré in 1905.
And at that same time poincaré also immediately started to think about the other fundamental force then known: gravity, and off the bat realized that gravitational waves must exist. general relativities is probably just "the simplest way to make gravity Lorentz covariant".
Explains beta decay. TODO why/how.
Maybe a good view of why this force was needed given beta decay experiments is: in beta decay, a neutron is getting split up into an electron and a proton. Therefore, those charges must be contained inside the neutron somehow to start with. But then what could possibly make a positive and a negative particle separate?
- the electromagnetic force should hold them together
- the strong force seems to hold positive charges together. Could it then be pushing opposite-charges apart? Why not?
- gravity is too weak
www.thestargarden.co.uk/Weak-nuclear-force.html gives a quick and dirty:Also interesting:
Beta decay could not be explained by the strong nuclear force, the force that's responsible for holding the atomic nucleus together, because this force doesn't affect electrons. It couldn't be explained by the electromagnetic force, because this does not affect neutrons, and the force of gravity is far too weak to be responsible. Since this new atomic force was not as strong as the strong nuclear force, it was dubbed the weak nuclear force.
While the photon 'carries' charge, and therefore mediates the electromagnetic force, the Z and W bosons are said to carry a property known as 'weak isospin'. W bosons mediate the weak force when particles with charge are involved, and Z bosons mediate the weak force when neutral particles are involved.
Weak Nuclear Force and Standard Model of particle physics by Physics Videos by Eugene Khutoryansky (2018)
Source. Some decent visualizations of the field lines. What does it mean that photons are force carriers for electromagnetism? Updated 2024-12-15 +Created 1970-01-01
TODO find/create decent answer.
I think the best answer is something along:
- local symmetries of the Lagrangian imply conserved currents. gives conserved charges.
- OK now. We want a local symmetry. And we also want:Given all of that, the most obvious and direct thing we reach a guess at the quantum electrodynamics Lagrangian is Video "Deriving the qED Lagrangian by Dietterich Labs (2018)"
- Dirac equation: quantum relativistic Newton's laws that specify what forces do to the fields
- electromagnetism: specifies what causes forces based on currents. But not what it does to masses.
A basic non-precise intuition is that a good model of reality is that electrons do not "interact with one another directly via the electromagnetic field".
A better model happens to be the quantum field theory view that the electromagnetic field interacts with the photon field but not directly with itself, and then the photon field interacts with parts of the electromagnetic field further away.
The more precise statement is that the photon field is a gauge field of the electromagnetic force under local U(1) symmetry, which is described by a Lie group. TODO understand.
This idea was first applied in general relativity, where Einstein understood that the "force of gravity" can be understood just in terms of symmetry and curvature of space. This was later applied o quantum electrodynamics and the entire Standard Model.
From Video "Lorenzo Sadun on the "Yang-Mills and Mass Gap" Millennium problem":
- www.youtube.com/watch?v=pCQ9GIqpGBI&t=1663s mentions this idea first came about from Hermann Weyl.
- youtu.be/pCQ9GIqpGBI?t=2827 mentions that in that case the curvature is given by the electromagnetic tensor.
Bibliography:
- www.youtube.com/watch?v=qtf6U3FfDNQ Symmetry and Quantum Electrodynamics (The Standard Model Part 1) by ZAP Physics (2021)
- www.youtube.com/watch?v=OQF7kkWjVWM The Symmetry and Simplicity of the Laws of Nature and the Higgs Boson by Juan Maldacena (2012). Meh, also too basic.