timhutton / gravityisnotaforce Goto Github PK

I'm experimenting with how to visualise the geodesics in spacetime under general relativity. Please help with suggestions!

Live demo: https://timhutton.github.io/GravityIsNotAForce/

Description: Under general relativity, gravity is not a force - instead it is a distortion of spacetime. Objects in free-fall move along geodesics (straight lines) in spacetime, as seen in the inertial frame of reference on the right. When standing on Earth we experience a frame of reference that is accelerating upwards, causing objects in free-fall to move along parabolas, as seen on the left. More...

Version with more space dimensions:

Version that is accurate in a varying gravitational field:

History:

• 2020-10-19: First version released. Triggered discussions here:
  • Hacker News: https://news.ycombinator.com/item?id=24821141
  • Reddit r/physics: https://www.reddit.com/r/Physics/comments/jdqlzf/gravity_is_not_a_force_freefall_parabolas_are/
  • Twitter: https://twitter.com/_tim_hutton_/status/1317923535105478656
• 2020-11-01: Added more complex view tackling the cases of 2+1 and 3+1 with constant-gravity.
• 2020-11-17: Added version with varying gravity implementing Rickard Jonsson's 2001 paper.

History of the ideas: (please help fill in the gaps!)

• 1985: The book Relativity Visualized by Lewis Carroll Epstein shows how bending spacetime can make straight lines out of parabolas.
• 2001: Rickard Jonsson publishes a paper that tackles the issue in a different way.
• 2013: A YouTube video animates the parabolas idea, citing Epstein's book.
• 2014: A YouTube video by Edward Current showed a physical 'spacetime stretcher'.
• 2019: A paper by Magdalena Kersting references that youtube video and commends the approach to educators. A follow-up paper discusses the limitations of the model.

TO-DO list:

• Can we extend to 2+1 with a point mass? Perhaps by considering a single geodesic (e.g. an elliptic orbit) as a straight line and drawing the rest of the universe as a (possibly very strange) distorted grid around that geodesic?