Gravity Probe B is a mission that launched a satellite in 2004 to measure space-time curvature near Earth, a direct test of Einstein’s Theory of Relativity.  It follows the Gravity probe A experiment dating to 1976.


The experiment planned to precisely check tiny changes in the direction of spin of four gyroscopes contained in the satellite orbiting at 650 km (400  miles) altitude and crossing directly over the poles. The gyroscopes are essentially free from disturbance so that they provide a near-perfect space-time reference system. They’re intended to measure how space and time are “warped” by the presence of the Earth, and if and how much the Earth’s rotation “drags” space-time around with it; the frame-dragging effect, a field generated by the rotation of Earth.

More detail and specifics of the experiment can be found at See the paragraph heading “Experimental setup” for an interesting recap of the gyroscopes using IM Pegasi HR8703 as a space reference point and the vacuum flask of super-fluid helium the gyroscopes are housed inside of.


NASA submitted a proposal to Science Mission Directorate, Astrophysics Division Senior Review of Operating Missions (Sr. Review), requesting a final 18-month (October 2008 through March 2010), $3.8M extension of GP-B to complete the data analysis and publish the results. Initially the proposal was favorably received and appeared to be in line for the additional funding.

Last week, Sr. Review recommended to NASA that the funding should not be granted. Apparently there is a change at NASA for support for fundamental physics experiments; further information can be found here

I’ve always found gravity to be an interesting subject and hate to see this funding setback. Known as the ‘weak force’, it is nevertheless strong enough to influence objects millions upon millions of miles distant. It is considered weak, because unlike the nuclear force, it does not bind objects tightly together. For example, under gravity, you can throw a ball high up into the air. If gravity was as strong as the nuclear force, you would never be able to pick the ball up off the ground. The only way to separate the ball from the ground would be through some sort of nuclear fission.

The other question is – is gravity even a force? If mass bends space-time and objects fall in this dimple in space towards the large mass, perhaps there is no force at all. This likely is not so.  Scientists believe gravitons may be responsible for the effects of gravity.

I realize funding is not unlimited and projects must be picked and chosen from, still it would be nice to see this project continue.