D epartment of P hysics Brown APJC – August 2008 Recent Precision Tests of General Relativity Thomas P. Kling Brown Astrophysics Journal Club August 2008

Weak Equivalence Principle D epartment of P hysics Brown APJC – August 2008 Some local frame & Should fall with the same acceleration

Strong or Einstein Equivalence Principle D epartment of P hysics Brown APJC – August 2008 some local frame in free fall & should fall freely along straight lines, or all observations consistent with SR

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 D epartment of P hysics Brown APJC – August 2008

EEP + Ocham’s razor leads directly to...

Schiff’s conjecture (1960): “Any complete, self-consistent theory of gravity that embodies WEP necessarily embodies EEP.” D epartment of P hysics Brown APJC – August 2008

Combine gravity with standard model? Violations of Equivalence Principle Inverse square law D epartment of P hysics Brown APJC – August 2008

Two Projects Lunar ranging at Apache Point Observatory Rotating Torsion Balance of Univ. of Washington D epartment of P hysics Brown APJC – August 2008

Eöt-Wash Group D epartment of P hysics Brown APJC – August 2008 Careful Torsion Balance!

D epartment of P hysics Brown APJC – August 2008

< 100 m – local hill < 10 km – bedrock >  1000 km – Earth Yukawa Potential

Towards galactic center D epartment of P hysics Brown APJC – August 2008

Classical Equivalence Parameter D epartment of P hysics Brown APJC – August 2008

APOLLO Lunar Ranging A pache P oint O bservatory L aser L unar-ranging O peration D epartment of P hysics 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. D epartment of P hysics Brown APJC – August 2008

All about Numbers Previous return rates: 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. D epartment of P hysics 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 D epartment of P hysics 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 D epartment of P hysics Brown APJC – August 2008

Murphy et al v2 D epartment of P hysics Brown APJC – August 2008