GR confirmed again!
Researchers have confirmed, in the journal Nature, one of General Relativity’s last unproven predictions - that of frame dragging, which says that a spinning object (like Earth) bends and warps space-time around it. To understand this, imagine twirling a spoon in a cup of coffee, or better yet, putting a spinning top in honey. The water or honey would twist a little bit, following the spinner, and anything floating on the surface would be dragged with it. In the same way, two satellites in orbit around Earth were found to be dragged off course by about 2 metres a year. (Just for the record, this probably has nothing to do with the Pioneer anomaly mentioned a couple of days ago.)
You might recall (if you are a devoted reader!) that I posted a couple of months ago on gravity probe B which is a satellite that’s testing the same theory, but with gyroscopes. Despite being scooped by a low cost, ground based observation team (d’oh!) the Gravity Probe will still have an important role to play - some scientists are still skeptical of the accuracy of today’s findings. Gravity Probe B will give highly accurate and irrefutable results (hopefully positive results!) which will settle the debate once and for all. Only one prediction then remains to be proven - the existence of gravity waves. But that’s another post…
[…] The European Space Agency announced today a new test of the final not-quite-verified predictions of general relativity - gravitomagnetism, or as its more commonly known frame dragging (which is actually a subset of gravitomagnetism). It’s based on the idea in general relativity that mass deforms space, and that’s what produces gravity. The old analogy is placing a bowling ball on a trampoline - it warps the space around it, and so a golf ball placed nearby will roll towards it. Of course, that’s just an analogy, but the theory is much the same idea, at least mathematically. Frame dragging builds on this and says that as body moves and particularly rotates, it can “drag” space with it, affecting other objects in a way we wouldn’t expect from our traditional picture of gravity. It’s something akin to rotating a spoon in a jar of honey - honey far away from the spoon will be dragged around by that motion, albeit slowly (but again, this is just ana analogy!) Experimental evidence from satellites suggests strong agreement between general relativity and experiment, although the big test will be the results from Gravity Probe B which will hopefully be not too long away. In both these cases, because the frame dragging effect is so minisculy small, long term experiments in orbit were needed to observe the effects. […]