天文宇宙中的黑洞(英文)精品PPT课件

• How to tell difference between accelerating frame and gravity?
– tidal forces
curvature
• Eliminates Newton’s “action at a distance”
• Freely moving bodies follow “shortest path”
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Light ray curved in accelerating frame
Principle of Equivalence (acceleration = gravity)
Gravity attracts light!
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• BUT: to stationary observer light travels on curved paths => Maybe gravity has something to do with… curvature of space ?
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GR: Ei源自文库stein, 1915
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宇宙中的黑洞
• 2007年4月22日下午3：00 • 二教2121教室
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Principle of Equivalence: Einstein 1907
g
Box stationary in gravity field
Paradox: How can gravity attract light if light has no mass?
MASS-ENERGY EQUIVALENCE
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Em2c
Gravity extracts energy from escaping matter
• Equivalence principle: Gravitational field = acceleration
freely falling frames in GR =
uniformly moving frames in SR.
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Aberration of Light
This is a bit hard to vizualize
slow
(spacetime already 4D…)
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Tides
• Problem:
r2
r1
moon
• Gravity decreases with distance => stretch…
Tides
Gravity extracts energy from escaping light
Gravitational redshift, time dilation
Other points of view
same result:
– accelerating frames of reference - apply special relativity
• Einstein: mass/energy squeeze/stretch spacetime away from being “flat”
• Moving objects follow curvature (e.g., satellites, photons)
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Light Rays and Gravity II
• In SR: light rays travel on straight lines => in freely falling frame, light travels on straight lines
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• Tides = gravity changes from place to place
not freely falling ?
freely falling
?? ?
not freely falling
CURVATURE OF
SPACETIME
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Moral: direction of light beam is relative
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Gravitational deflection of Light
Now assume boxes are accelerating
Light path is curved
– spacetime is curved
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Curved Spacetime
• Remember: Gravity warps time
BUT: in spacetime, time and space are not separable
fast
=> Both space and time are curved (warped)
– not necessarily a straight line
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GENERAL RELATIVITY:
EINSTEIN 1915
• Matter + energy determine curvature of spacetime
• Curvature of spacetime determines motion of matter + energy
Box accelerates in empty space
g
Box falling freely
g
Box moves through
space at constant velocity
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Equivalence Principle
• Special relativity: all uniformly moving frames are equivalent, i.e., no acceleration