We are currently working on the following projects:

  1. testing the Equivalence Principle with high sensitivity and the greatest practical generality. We are currently sensitive to equivalence-principle violating interactions with Yukawa ranges between infinity and 1cm. Our existing sensitivity for long-ranged interactions is at the 10-13 level.
  2. searching for short range inverse-square law violating interactions with ranges of less than 1mm. One notable prediction suggests that gravity penetrates extra, compact dimensions so that the gravitational inverse square law must be modified at short ranges. Arkani-Hamed, Dimopoulos, and Dvali have offered this as an explanation of the hierarchy problem. Our current experiment will be sensitive to this effect if gravity exists in six dimensions. Check out our first paper on the short range experiment and a recent update
  3. searching for CPT-violating fields and for new spin-dependent forces that could arise from torsion fields or from exchange of axion-like particles. These projects are done using electron-spin-polarized test bodies and/or sources that have virtually no external magnetic fields.
  4. measuring the Newtonian Constant G using a novel technique. This is the most poorly determined fundamental constant; the CODATA value has an uncertainty of 0.0128%. Recently the German PTB (their Institute of Standards) obtained a value differing from the CODATA value by 0.5%! The leading sources of systematic error in the existing CODATA value are uncertainties in the mass distribution of the torsion pendulum and effects of anelesticity in the torsion fiber. We have invented a new technique that virtually eliminates both of these sources of error.

We currently operate four torsion pendulum instruments (Eöt-Wash II, Eöt-Wash III, Big G, and Short-Range). The Eöt-Wash and Big G instruments are continuously rotating torsion balances. The Short-Range inverse-square experiment is being done with a stationary balance that sits just above a rotating attractor.


Torsion Pendulum used in the Rot-Wash Instrument

8-Body Torsion Pendulum used in the Eöt-Wash III Instrument

Torsion pendulum and attractor used in the short-range experiments

Pendulum, containing about a mole of polarized electrons, used to search for spin-coupled forces

(click figures for enlarged images)

Eöt-Wash Group Contact

For more information, contact:
Eric Adelberger at (206) 543-4294 or eric@npl.washington.edu
Blayne Heckel   at (206) 685-2401 or heckel@phys.washington.edu
Jens Gundlach  at (206) 616-2960 or gundlach@npl.washington.edu