Oct. 11 – 2B03 11/10/2011 9:33:00 AM
Principle of Equivalence:
You can’t tell the difference between the acceleration from a rocket
and acceleration from gravity
Newton vs. GR
Gravitational time dilation
o Before – moving clocks move slower – special relativity
Special vs. general relativity
Big difference is acceleration
Light deflected in (by) a gravitational field
Spacetime and Gravity
Einstein speaks about 3 dimensions of space, and time. 3+1 grid –
curved around massive objects.
Gravity just describes curvature on spacetime about massive
We can measure this deflection on large scales – light rays passing
by sun ex.
Extra kind of redshift from general relativity (beyond the one we
talked about before, Doppler)
Light has to use energy to leave curved space-time
o Energy lowered = red shift. More massive the object, the
more the light is redshifted. In black hole, redshifted so much
that is doesn’t have enough light (energy) to get out .
o In a black hole, light is infitnitely redshifted.
o Black hole – you need something faster than the speed of
light to escape – nothing can escape a black hole.
Time dilation in gravitational fields – in gravity, slower the clocks
move. Stronger the g field – stronger the time dilation.
o Gravity of black holes mad strong – clocks run real slow.
Black holes don’t suck
Spacetime and gravity
Distance bigger – gravitational force gets smaller
Bottom floor – closer to centre of earth – more of a gravitational
pull – clock runs more slowly.
Grid can be stretched, or “warped” – the more massive the objects,
the more warped or distorted the fabric of space time.
Main point – light appears to be bent through the time – but, it
follows most direct route.
o Milions of observations have confirmed this bending.
The stretched ones (arks) are having their light bent.
not completely confirmed – ind