Notes (October 2019)


Japan’s gravitational wave observatory KAGRA will start its operations in December 2019. KAGRA will be the fourth gravitational observatory. KAGRA will share data and coordinate activities with the US-based LIGO observatories and the Italy-based Virgo observatory. There is a gravitational wave detector called GEO600 in Germany but it is not sensitive enough to detect gravitational waves. GEO600 is used for technological development. India is planning to build a gravitational wave observatory as well. KAGRA is the first gravitational wave detector built underground. Seismic noise will be much reduced. Also, the mirrors of KAGRA are cooled to 20 Kelvin. This will improve the detection sensitivity greatly.

I learned from Tommaso Dorigo’s blog post that the decay of the Higgs particle to an electron-positron pair has not been confirmed yet. The expectation is that this happens 2% of the time but unfortunately there is not enough statistics to confirm this decay mode (background is very noisy). Confirming H–>ee and measuring the probability of this particular mode is important scientifically as well as psychologically. Otherwise, how can we confidently claim that all elementary particles including electrons get their masses from the universal Higgs field? I saw a similar question in Chriss Quigg’s Ljubljana talk. He expressed it as: “Is the Higgs field the only source of fermion masses?”

KATRIN experiment in Germany announced a new upper limit for a neutrino: 1.1 eV.

European particle physics community has a formal process to determine the priorities. They call it the “strategy update” which is updated every 5 years. The most recent “strategy update” was launched in 2018. As part of this process a summary called the “briefing book” (250-pages) was published. It is a free book available to the public. You can get it from this link.

Winners of the 2020 Breakthrough Prize In Life Sciences, Fundamental Physics And Mathematics Announced. The physics prize was awarded to the Event Horizon Telescope Collaboration. The $3 million prize will be shared equally with 347 scientists co-authoring any of the six papers published by the EHT on April 10, 2019, which can be found here.

The 2019 Nobel Prize in Physics were awarded to James Peebles, Michel Mayor and Didier Queloz. You can learn more about the physicists and their work in these documents:

Scientific background document prepared by the Nobel committee for physics

Quanta Magazine’s coverage of the 2019 Nobel Prize in Physics

NYT’s coverage of the 2019 Nobel Prize in Physics

Quantum Computing

I highly recommend John Preskill’s Quanta article titled “Why I called it ‘Quantum Supremacy'”. This is regarding the recent rumors that Google’s 53-qubit quantum computer achieved quantum supremacy in a specific computational task. John Preskill reminds us that he proposed the term “quantum supremacy” in 2012 to describe the point where quantum computers can do things that classical computers can’t, regardless of whether those tasks are useful. He also reminds us that the term “quantum supremacy” became controversial. Scott Aaronson has been discussing quantum supremacy forever in his blog. He reacted to the latest rumors with 2 new blog posts here and here.

Natalie Wolchover’s Quanta article titled “To Invent a Quantum Internet” is very good. This article brought my attention to the quantum repeaters (devices that relay quantum entanglement). It is amazing that crystals doped with erbium atoms can do this. These can store and re-emit a photon with exact same properties (polarization, shape, direction, and entanglement). THIS IS MAGICAL.


I started reading articles in Scholarpedia. In the past I consulted SEP (Stanford Encyclopedia of Philosophy) and Wikipedia first but Scholarpedia is a good resource as well. The “main” page of Scholarpedia is not well designed. I recommend the this page as the “landing page” of Scholarpedia.

Models of the Self

I am reading the book “Models of the Self” (eds: S. Gallagher and J. Shear).

I also recommend Thomas Metzinger’s Scholarpedia article titled “Self models“.


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