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D epartment of P hysics Brown APJC – August 2008. Recent Precision Tests of General Relativity. Thomas P. Kling Brown Astrophysics Journal Club August 2008. &. Should fall with the same acceleration. D epartment of P hysics Brown APJC – August 2008. Weak Equivalence Principle.
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Department of Physics Brown APJC – August 2008 Recent Precision Tests of General Relativity Thomas P. Kling Brown Astrophysics Journal Club August 2008
& Should fall with the same acceleration Department of Physics Brown APJC – August 2008 Weak Equivalence Principle Some local frame
& should fall freely along straight lines, or all observations consistent with SR Department of Physics Brown APJC – August 2008 Strong or EinsteinEquivalence Principle some local frame in free fall
Department of Physics Brown APJC – August 2008 Implications for gravity • Gravity is “curved space-time” • Gravity is a metric theory • Freely falling observers = locally flat region • Freely falling test bodies fall along geodesics
Department of Physics Brown APJC – August 2008 EEP + Ocham’s razor leads directly to . . .
Department of Physics Brown APJC – August 2008 Schiff’s conjecture (1960): “Any complete, self-consistenttheory of gravity that embodies WEP necessarily embodies EEP.”
Department of Physics Brown APJC – August 2008 Combine gravity with standard model? Violations of Equivalence Principle Inverse square law
Lunar ranging at Apache Point Observatory Rotating Torsion Balance of Univ. of Washington Department of Physics Brown APJC – August 2008 Two Projects
Department of Physics Brown APJC – August 2008 Eöt-Wash Group Careful Torsion Balance!
Department of Physics Brown APJC – August 2008 Yukawa Potential • < 100 m – local hill • < 10 km – bedrock • >1000 km – Earth
Department of Physics Brown APJC – August 2008 Towards galactic center
Department of Physics Brown APJC – August 2008 Classical Equivalence Parameter
Department of Physics Brown APJC – August 2008 APOLLO Lunar Ranging A pache P oint O bservatory L aser L unar-ranging O peration
Department of Physics Brown APJC – August 2008 Basics of LLR • Apollo missions & others left Moon reflectors. • Measure time of flight. • Past 15 years: about 1-3 cm precision.
Department of Physics Brown APJC – August 2008 All about Numbers • Previous return rates: 0.002 to 0.01 photons return per pulse . . . Typically get 15 to 40 photons return per pointing. • To get mm precision, need about 225 to 1300 photons returning.
Department of Physics Brown APJC – August 2008 APOLLO Contributions • Larger aperture (3.5 m), better seeing (1.1 arcsecond) means higher return rate. • Higher energy laser: • 90 ps FWHM Nd:YAG • 20 Hz & 115 mJ/pulse • Best return rate: Apollo 15 at 1.33 photons per shot
Department of Physics Brown APJC – August 2008 Stuff making you worry • Tides change surface height ~ 350 mm • Crustal loading from atmosphere, ground water, etc. ~ 2-5 mm • Atmospheric propagation delay must be modeled
Department of Physics Brown APJC – August 2008 Murphy et al. 0710.0890v2
