Wilson Ting
The Gravity of Spacetime
Traditional View of Gravity from Newton
Gravity:
an attractive force
strength determined by distance (r) between 2 masses
Fg = (Gm1m2)/r²
Inversely proportional to the distance
Einstein’s Theory of General Relativity (GR)
Properties not covered in Newton’s Theory of Universal Gravitation
Acceleration & gravitation can’t be distinguished (equivalence principle)
A: elevator accelerates upwards in 0 gravity
B: room isn’t accelerating, but is subject to gravity
Light ‘falls downwards’ in both situations
Takeaway: gravity affects light’s path even though photons are massless & we think of gravity as acting between masses
1st Verification of General Relativity
Verified that bending of light by mass == bending of space
Light just follows this curve
Any particle w/ mass or energy is affected by gravity
I.e massless photons w/ energy
Application of Einstein’s General Relativity
NASA’s probe B
Verified 2 predictions of General Relativity
Geodetic Effect: spacetime warping via gravitational field of massive object (Earth)
Frame Dragging Effect: the amount a rotating object pulls on spacetime
Analogy: “[imagine] Earth spinning in honey. As Earth rotates it drags space and time with it as it would a surrounding sea of honey.”
Summary
Newton: described gravity’s effects
pull directly between masses along line connecting them
Einstein: proposed mechanism behind gravity
Bending of spacetime by mass and objects follow their own ‘straight-line’ path through this curvature
General Relativity as a ‘Theory of Everything’?
No :(
Incompatible with quantum mechanics (QM): a study of interactions at the subatomic level
Example: uranium atom decaying, photons hitting a solar cell...
QM describes interactions resulting in ‘quantum jumps’ -> probabilistic outcomes
GR describes continuous events -> deterministic outcomes
Scaling GR down to the quantum level or scaling QM up to galactic dimensions
-> nonsensical answers
Here's a Quick Video on the Concept of Spacetime!
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