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Oct.11 - 2B03.docx

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McMaster University
Laura Parker

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  Rocket-ship ex. 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 objects.  We can measure this deflection on large scales – light rays passing by sun ex. Gravitational redshift  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. Black Holes  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. Space-time  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. Gravitational Lensing  The stretched ones (arks) are having their light bent. Gravity Waves  not completely confirmed – ind
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