H. Dittus et al., TESTING THE WEAK EQUIVALENCE PRINCIPLE AT THE BREMEN DROP TOWER - REPORT ON RECENT DEVELOPMENTS, Classical and quantum gravity, 13(11A), 1996, pp. 43-51
The weak equivalence principle (WEP) has currently been shown to be va
lid to an accuracy of Delta a/a less than or equal to 5 x 10(-12). Fre
e-fall experiments over short distances have attained an accuracy of o
nly 5 x 10(-10). Microgravity facilities such as the 'Bremen drop towe
r' enable long-distance free-fall experiments which may improve the ac
curacy to < 10(-12).