1F03_2020C24.pdf - 1 Chapter 24 Black Holes and Curved...

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Chapter 24Black Holes and Curved SpacetimeAstronomy 1F031
Introducing General Relativity2Stellar remnants:White dwarfsNeutron starsBlack holesneed relativityCredit:
Equivalence Principle3Stationary or constant speedNormal weightAccelerating downLighter than normalAccelerating upHeavier than normalCable breaksNo apparent weightCredit: OpenStax figure 24.3Or stationary inspace far from anymassive objectsOr in space far fromany massive objectsand accelerating upat 9.81 m/s2
Gravity or Acceleration?Ball and people fall at samerateBall stays in straight line (unlikenormally)4Credit: OpenStax figures 24.4 and 24.5
Paths of Light and MatterDoes light not obey the equivalence principle?Does light not travel in straight lines?Einstein said the latter; mass bends spacetime5Credit: OpenStax figure 24.6
Spacetime and GravityShortest paths on Earth follow great circles (e.g., lines oflongitude, equator)“Matter tells spacetime how to curve; spacetime tellsmatter how to move” John WheelerRubber sheet analogy for spacetime:6Credit: OpenStax figure 24.8
GR Test 1: Advance of Mercury’s Perihelion7Sun distorts spacetime around itmore than Earth because of itsgreater massSun’s effect on Mercury alreadymeasured but not explainedEach successive perihelionmoves with respect to the lastNewton: 531”/centuryEinstein and observations:574”/centuryCredit:
GR Test 2: Deflection of StarlightDuring total solar eclipse look for stars that youshouldn’t be able to see (because they’re directlybehind the Sun) but youcansee because of thespacetime bending8Credit: OpenStax figure 24.10
Time in General Relativity9Stronger gravity causes time to slow downTest 1: 1959 Harvard physics building clock runs slower at bottom than at topTest 2: 1976 Viking spacecraft; time delays for radio waves sent near SunLots of modern applications (see later slides)Credit: OpenStax figure 24.11
Gravitational Redshift10Time runs slower in higher gFrequency (inverse of time) getssmallerSpeed of light is constant; wavelength

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