What is the Universe expanding into..

Do you think there was anything before the big bang?

  • I don't think there was anything before the Big Bang

    Votes: 56 12.5%
  • I think something existed before the Big Bang

    Votes: 200 44.7%
  • I don't think the big bang happened

    Votes: 54 12.1%
  • I think the universe is part of a mutiverse

    Votes: 201 45.0%

  • Total voters
    447
Status
Not open for further replies.
I can't really see a way to make progress (to study General Relativity in some depth) by any other route.

The prerequisites for learning General Relativity are as follows:
  1. Learn vector calculus and calculus-based physics.
  2. Learn electromagnetism (not absolutely necessary, but it’ll help).
  3. Learn the basics of special relativity.
  4. Study some tensor calculus and differential geometry.
  5. Build some intuition for general relativity.
  6. Study from a good general relativity textbook.
More information on these prerequisites, as well as suggested reading sources, can be found on this Profound Physics site:

https://profoundphysics.com/how-to-learn-general-relativity-a-step-by-step-guide/

Me? I'll be renovating some speakers! 😀
 
Last edited:
Nice photo of earth - moon system

A photo taken by NASA's Lucy spacecraft which has been launched to to explore the Trojan asteroids, a population of primitive asteroids orbiting in tandem with Jupiter.

Just don't mention the word fossils! 😉

1667473466368.png


https://solarsystem.nasa.gov/missio...d,Ingalls | Full image and caption About Lucy
 
The Lucy mission is indeed off to visit and photograph Jupiter's Trojan asteroids, which is that 60 degree Lagrange point business:

https://www.nasa.gov/feature/goddar...thousands-of-objects-for-earth-gravity-assist

Already has found an unexpected one with a moonlet 480M miles away if I follow.

https://www.nasa.gov/feature/goddard/2022/nasa-s-lucy-team-discovers-moon-around-asteroid-polymele

I am in luck with General Relativity, since I already have one of the recommended books:

A Lenny Susskind title, Special Relativity and Classical Field Theory. It is better written than the first volume, which was Classical Mechanics and rather lightweight.

IM000251.JPG


It is annoying that I am missing the second volume on Quantum Mechanics, but the library has it. It's these Tensor things that worry me. But we shall get there.

Already I am learning about rotating reference frames, and frame dragging around rotating objects. General Relativity involves non-linear equations, since the gravity field possesses mass and energy in itself.
 
Last edited:
Already I am learning about rotating reference frames, and frame dragging around rotating objects.

"Frame-dragging" is when spacetime itself gets dragged round by a rotating object.

The effect was first predicted in 1918 as a natural consequence of General Relativity (GR).

It was confirmed Earth generates frame dragging in line with GR's predictions when the NASA Gravity Probe B (GP-B) mission managed to measure the effect around our planet.

1667500383346.png


1667500801489.png


https://www.nasa.gov/mission_pages/gpb/

Observations of frame-dragging have been made around distant black holes.

A wobbling of the accretion disc, similar to the wobbling of a spinning top as it slows down, apparently provides evidence of frame-dragging.
 
It eneters for the same reason that eventually a satellite comes crashing into the earth - gravity.

Why do you spend energy of refuting these things. Ponder the rotation of the moon instead. You might crack that one a lucky day.

//
 
Status
Not open for further replies.