Quantum field theory lecture by Tobias Osborne (2017) Lecture 4 by 
Ciro Santilli 37 Updated 2025-07-16
Ciro Santilli 37 Updated 2025-07-16- quantization. Uses a more or less standard way to guess the quantized system from the classical one using Hamiltonian mechanics.
- youtu.be/fnMcaq6QqTY?t=1179 remembers how to solve the non-field quantum harmonic oscillator
- youtu.be/fnMcaq6QqTY?t=2008 puts hats on everything to make the field version of things. With the Klein-Gordon equation Hamiltonian, everything is analogous to the harmonic oscilator
Quantum field theory lecture by Tobias Osborne (2017) Lecture 14 by Ciro Santilli 37 Updated 2025-07-16
Ciro Santilli 37 Updated 2025-07-16On Ubuntu 20.10 PostgreSQL 12.6, login with
psql on my default username without sudo fails with: stackoverflow.com/questions/11919391/postgresql-error-fatal-role-username-does-not-existThis is the one that worked on Ubuntu 21.04: stackoverflow.com/questions/11919391/postgresql-error-fatal-role-username-does-not-exist/38444152#38444152Explanation:
sudo -u postgres createuser -s $(whoami)
createdb $(whoami)You can now run shows that peer authentication is available to all users apparently:
psql without any password. This works without password due to peer authentication:sudo cat /etc/postgresql/12/main/pg_hba.conflocal all postgres peer
# TYPE DATABASE USER ADDRESS METHOD
# "local" is for Unix domain socket connections only
local all all peerList users:output:
psql -c '\du' List of roles
Role name | Attributes | Member of
-------------+------------------------------------------------------------+-----------
ciro | Superuser, Create role, Create DB | {}
owning_user | | {}
postgres | Superuser, Create role, Create DB, Replication, Bypass RLS | {}Delete user later on:
psql -c 'DROP USER username;'Help toplevel:
helpList supported SQL commands:
\hShow syntax for one type of command:
\h SELECTList all databases:which shows:
psql -c '\l' Name | Owner | Encoding | Collate | Ctype | Access privileges
-------------+----------+----------+-------------+-------------+-----------------------
ciro | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 |
postgres | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 |
template0 | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
testdb0 | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 |
(6 rows)If you didn't give a database from the command line e.g.:you can do that afterwards with:
psql\c testdb0Let's create a table and test that it is working:
psql testdb0 -c 'CREATE TABLE table0 (int0 INT, char0 CHAR(16));'List tables, no special tables:gives:
psql testdb0 -c '\dt' List of relations
Schema | Name | Type | Owner
--------+--------+-------+-------
public | table0 | table | ciro
(1 row)View table schema: stackoverflow.com/questions/109325/postgresql-describe-tableoutput:
psql testdb0 -c '\d+ table0' Table "public.table0"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
--------+---------------+-----------+----------+---------+----------+--------------+-------------
int0 | integer | | | | plain | |
char0 | character(16) | | | | extended | |Insert some data into it and get the data out:output:
psql testdb0 -c "INSERT INTO table0 (int0, char0) VALUES (2, 'two'), (3, 'three'), (5, 'five'), (7, 'seven');"
psql testdb0 -c 'SELECT * FROM table0;' int0 | char0
------+------------------
2 | two
3 | three
5 | five
7 | seven
(4 rows)Delete the table:
psql testdb0 -c 'DROP TABLE table0;'An optical multiplexer!
This section discusses the pre-photon understanding of the polarization of light. For the photon one see: photon polarization.
People were a bit confused when experiments started to show that light might be polarized. How could a wave that propages through a 3D homgenous material like luminiferous aether have polarization?? Light would presumably be understood to be analogous to a sound wave in 3D medium, which cannot have polarization. This was before Maxwell's equations, in the early 19th century, so there was no way to know.
Got it working as mentioned at: github.com/cirosantilli/feathers-chat/tree/sequelize-pg
Bibliography:
There's also a
heroku branch at: github.com/feathersjs/feathers-chat/tree/heroku, but it also seems to use NeDB? So you can have a filesystem in Heroku? Doesn't seem so: stackoverflow.com/questions/42775418/heroku-local-persistent-storagegothinkster/realworld implementations based on Express.js.
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