Comments on: Dragging on

By: HDG

HDG — Tue, 24 Apr 2007 21:02:24 +0000

GPB seems to be in the position of modeling their system until they get the result that they expect, and now they’ve asked for yet more time and money to do so. They aren’t doing a blind analysis, I don’t believe. Feel free to correct me if I’m wrong.

If they published a result that disagreed with theory, everyone would think that they didn’t analyse their data (which they’ve had for a year now, and had years to prepare for before that) properly. So how can this be scientifically useful? Their results either agree with theory, in which case they are uninteresting because they’ve essentially massaged their data to get that result, or they’ve wasted a billion dollars getting a result that no one believes. I can launch an experiment which will fail in the same manner for half the price, and take only half the time

And it doesn’t look likely that they’ll get down to the design goal of measuring frame-dragging with 1e-4 precision either. They’re struggling to get 1%.

By: George Musser

George Musser — Tue, 17 Apr 2007 17:10:32 +0000

If we were near a rapidly rotating black hole, frame dragging would jump out at us: a gyroscope would wobble all over the place.

Would frame-dragging have any other obvious effects on intrepid BH-skirting astronauts? Would they feel dizzy, would the precession of particles in their bodies produce radiation, etc.?

George

By: DIS

DIS — Mon, 16 Apr 2007 20:17:16 +0000

High. Modeling the pinned quanta is certainly a herculean task. It’s is not impossible as the gyros were monitored almost continuously and, here the changing polhode might actually help as it causes the orientation of the gyros to change with respect to the measuring squid and thus giving more thorough sampling of the fluxon distribution. Actually there are two approaches to mapping the quanta, one is trying to model allthe single vortex sources and their effect, almost impossible, or modeling the magnetic field measured by the squid, that is modeling the magnetic field multipole distribution and its time evolution. The second is exceedingly difficult but given the amount of data has a shot of succeeding. We’ll see…

By: daniel

daniel — Mon, 16 Apr 2007 18:57:39 +0000

DIS, thanks for the clarification! The electrical patches don’t cause the polhode motion, they just cause it to change with time because of dissipation. What’s perhaps most amazing to me is that the GP-B team is in the process of modeling this effect (we’re talking about describing a complex distribution of pinned quanta of magnetic flux, and their interactions with the various sensors and housings).

By: Neil B.

Neil B. — Mon, 16 Apr 2007 16:39:34 +0000

Part of the precession effect is from “Thomas precession” - a SRT effect. I have never been satisfied with the various accounts of how angular momentum is conserved by the system including the spinning gyro, the AM vector of which shifts around (that goes for the GRT part of it too.) Consider also the curved space problem: transport the AM vector 1/4 circle in perp. direction along a hyperspace, then forward 1/4 circle, then back to starting point and it looks like “free” change of AM direction.

By: Count Iblis

Count Iblis — Mon, 16 Apr 2007 14:14:38 +0000

If this effect could be measured to a very high degree of precision, then one could measure how fast the Earth’s inner core is spinning see here

By: DIS

DIS — Mon, 16 Apr 2007 12:38:08 +0000

Also for people who might prefer a earthly rather than stellar analogy a milliarc second would be the angle subtended by a human hair seen from a mile away. The effect to be measured is equivalent to accurately measuring the angle subtended by 39 human hairs a mile away!

By: DIS

DIS — Mon, 16 Apr 2007 12:27:02 +0000

The patches do not cause the polhode motion. The polhode motion would be there as long as the sphere is not perfect and the spin axis does not lie along one of the principal axii of inertia. This is a purely mechanical effect and has nothing to do with the electrical patches. The patches do play a role in providing a dissipation mechanism and making the polhode period be time dependent as you mentioned.

By: Sunday late night sciency links! « Entertaining Research

Sunday late night sciency links! « Entertaining Research — Mon, 16 Apr 2007 05:04:39 +0000

[...] Daniel at Cosmic Variance explains a very delicate gravity experiment, the results of which will be known by December this year; the experiment to measure the Lense-Thirring precession (apparently, of the order of 40 milli-arcseconds per year), and, according to Daniel, is one of the most technically ambitious projects ever launched into space. Take a look! [...]

By: Mr Odin

Mr Odin — Mon, 16 Apr 2007 03:28:10 +0000

By: JoAnne

JoAnne — Mon, 16 Apr 2007 02:51:02 +0000

Daniel, thanks for posting this!

By: daniel

daniel — Sun, 15 Apr 2007 21:45:13 +0000

I just noticed that Jennifer has a very nice post on exactly the same subject, where she goes into more detail on the problems with the GP-B data analysis. She benefits from actually having been present at Francis Everitt’s plenary talk.