Was Einstein right?

This is the title of chapter #19 from the course “Dark Matter, Dark Energy: The Dark Side of the Universe”, already commented in previous posts. This time some of today’s notes have to do with to great physicists. Apart from equations or theories that try to explain our Universe, it is also important to know a little bit of History of Science and be aware of these names:

  • Urbain Le Verrier: Le Verrier is mentioned in this chapter as he was the guy that made a prediction about the existence of a planet, not known in the first half of the 19th century. That planet was Neptune. He was also the first to report that the slow precession of Mercury’s orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets. You know, the same precession that was explained later by Einstein`s General Theory of Relativity.
  • Mordehai Milgrom: Israelei physicist that proposed the MOND or Modified Newtonian Dynamics as an alternative explanation to Dark Matter. MOND is a hypothesis that proposes a modification of Newton’s law of gravity to explain the galaxy rotation problem.
  • Vera Rubinshe was the astronomer that pointed out the phenomenon known as the galaxy rotation problem (already mentioned): discrepancy between the predicted angular motion of galaxies and their observed motion.
  • Jacob Bekenstein: another Israeli physicist famous because he contributed to the foundation of black hole termodynamics. He was the first one to suggest that black holes should have an entropy.
  • The bullet cluster: two colliding clusters of galaxies into one, whose Gravitational lensing studies are supposed to provide the best evidence of Dark Matter.
  • The Friedmann Equation: it is a well-known relationship between the energy density of the Universe, the expansion rate (Hubble constant) and the curvature of space. It governs the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity. That is:

(8πG/3 ) ρ = H2 + K

  • The Cassinni probe: spacecraft mission launched in 1997 to study Saturn and its moons.

Although I would recommend purchasing the original videos from The Teaching Company, this chapter can be seen on YouTube here (part 1) and here (part 2).

An additional comment/confession that I’m not sure if I’ve already done before: you may realize that some of these notes or definitions are in some parts copy-pasted directly from Wikipedia. This is because I’m just trying to have short notes to illustrate (mainly for myself) what I’ve been reading/watching/working on… And what a better definition (of course, not always) that the one that appears on the Wiki, validated many times before…