L9 general relativity

spacetime

4D combination of space and time

gravity arises from

distortions of spacetime, making time run more slowly

universe may have

no boundaries and no center, but finite volume (kinda like Earth with the boundaries)

object’s number of dimensions is

number of independent directions in which movement is possible

straightest lines on a sphere are

great circles sharing the same center as the sphere, which intersect

geometry on a sphere

angles of a triangle add up to greater than 180 and circumference of a circle is less than 2πr

if you are floating freely, than your worldline is

following the straightest possible path through spacetime

nothing can escape black holes because

spacetime is extremely curved

event horizon

3D surface that is the point of no return for a black hole

equivalence principle

effects of acceleration are exactly equivalent to those of gravity

saddle shaped geometry

straightest distance between two points is a piece of a hyperbola, parallel lines diverge, angles of a triangle add up to less than 180, circumference of a circle is greater than 2πr

free falling objects near the Sun follow

curved paths (rubber sheet)

as an orbiting object moves forward in time, its path

spirals through spacetime

if Sun was compressed, spacetime would become

more curved near its surface

spacetime’s curvature near a black hole

bottomless pit

precession of mercury

disagrees with Newton’s laws but accounted for by general relativity

gravitational lensing

curved spacetime alters the paths of light rays, shifting apparent positions of objects

when object is behind massive object, gravitational lensing makes

it appear to be at multiple points in the sky

gravitational time dilation

time passes more slowly at lower altitudes

indirect detection of waves

observed changes in orbit of a binary system due to gravitational waves carrying energy away

general relativity predicts that movements of a massive object

can produce gravitational waves (just like charged particle produces light waves)

wormhole

shortcut or tunnel through hyperspace (space outside spacetime of our universe)

wormholes are not

prohibited by known laws of physics, but would allow for time travel, which leads to paradoxes that could rule out their possibility