Einstein’s Happiest Thought

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Einstein’s Happiest Thought. Micro-world Macro-World Lecture 7. Equivalence between gravity & acceleration. a. Man in a closed box on Earth. m I a. m G g. g. Since m G =m I , if a=-g , the conditions are equivalent. Man in a closed box on an accelerating rocket in deep outer space. - PowerPoint PPT Presentation

Text of Einstein’s Happiest Thought

  • Einsteins Happiest ThoughtMicro-world Macro-World Lecture 7

  • Equivalence between gravity & accelerationaMan in a closed box on EarthMan in a closed box on anaccelerating rocket in deep outer space.Since mG=mI, if a=-g, theconditions are equivalentgmGgmIa

  • The happiest thoughtI cannot tell the difference between being on earth orin a deep-space rocket accelerating with a=-g

  • ImaginationThis cannot be due to coincidence. There must be some basic truth involved.

  • Einstein didnt accept mG=mI as a coincidenceThese two environments must be exactly equivalent.

  • Einstein Equivalence Principlein his wordswe [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration o the reference system [Einstein, 1907]

  • So what?What would happen if I were to shine a light beam through a window on the rocket?sraight linesraight line

  • If the rocket is accelerating, the light beam bendsat2

  • Since the accelerating rocket and gravity are equivalent, gravity must cause light to bendgt2for our room L6m:very, very tiny effect Lon Earths surface

  • Does gravity cause light to bend?Very tiny effect: need very stronggravity and a long lever arm. Lookat the bending of light from a star bythe Sun. (Only possible at an eclipse.)Sir Arthur Eddington1882-1944gsun 27xgearth

  • Eddingtons 1919 Expeditions

  • Africa1919 eclipseMeasurement: q =0.0005500.000030in agreement with Einsteins prediction1919 Eclipse

  • New York Times:

  • Gravitational lensing

  • Dark Matter astronomy

  • Mass induces curvature in space-time

  • The curvature is what we feel as gravity

  • Seoul Rio120

  • 170Seoul RioCartesian vs non-Cartesian coords

  • The Earth is round

    170??This is how KAL goes

  • GeodesicsThe shortest distance between 2 points isAlong a geodesic. It is a straight line In Cartesian systems

  • Great Circlesspherical geometryThe shortest distancebetween two points onthe Earths surface correspond to GreatCircles: the intersectionsof planes passing throughthe center of the Earthwith the Earths surface.

  • In this figure, the shortest distances are indicated bythe blue lines.