Monday, June 03, 2013 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

LARES: a discoball for eurocents that supersedes Gravity Probe B

Fred Singer was intrigued by a new object shot by ESA to outer space, a shiny disco ball that verifies Einstein's general relativity.

See the following preprint and other sources:

LARES succesfully launched in orbit: satellite and mission description by Antonio Paolozzi, Ignazio Ciufolini (arXiv)

The Extraordinary “Disco Ball” Now Orbiting Earth (Physics arXiv Blog)

Wikipedia, A LARES website (ASI, Italy), Lares-mission.COM
It's literally a disco ball, a completely passive object reflecting LASER lights sent from the Earth to its 92 retroreflectors, an 850-pound gorilla wolfram alloy ball that may be exploited to accurately measure the position and orientation of the disco ball and verify the Lense-Thirring effect i.e. rotational frame-dragging predicted by Einstein's theory of gravity.

Recall that Gravity Probe B was very expensive and it was a disappointment, too. If LARES is going to measure these things and perhaps much more accurately, and for a tiny fraction of the price of Gravity Probe B, it will be another piece of evidence that substantial technological improvements are often possible and may allow us to measure things that were once thought to be inaccessible.

Well, the success of LARES will be a bit embarrassing for the people around the design of Gravity Probe B, too, including George Pugh (MIT) and Kip Thorne (Caltech), but their contributions may have been necessary for the progress, too. Things aren't usually invented in the optimal and maximally cheap form at the very beginning.

Because we talk about clever gadgets, let me also mention that the Bell Labs developed a lensless camera (preprint).

Add to Digg this Add to reddit

snail feedback (8) :

reader Dilaton said...

I declare this to be Lumo's disco ball for his Quantum Mechanics gold badge party ;-)

May it gloriously confirm relativity!

Cheers :-)

reader Luboš Motl said...

Thanks, Dilaton, but I can't accept it because I have nothing to do with this sexy experiment!

reader Luke Lea said...

About frame dragging: does a clock run at a different speed if orbiting over the equator in the same direction the earth is spinning than in the opposite direction? And about that Lense effect on the precession of gyroscopes: is it most pronounced when a gyroscope is orbiting over the poles?

More generally, since this is classical physics I thought you might be able to give us curious laymen a qualitative description.

reader Brian G Valentine said...

Good questions Luke, and maybe I can offer an explanation in a completely heuristic and confusing way. : )

In relativity, the natural unit of mass is length (if one wants to convert the equations to dimensionless form, for example). We can convert "mass" units to length by equating the Newtonian "force" Gm***2/r**2 to the rest mass "potential" mc**2/r and solve for our equivalent length r in terms of m, for the mass of the Earth, r= about 1mm, for the Sun about a km.

This length is about the size of the "pucker" of space time round a mass in the direction of its motion. That is to say, the polar coordinates describing the motion of a mass in orbit around the Earth will vary AS A RESULT OF THIS EFFECT (and there are others) will vary from the Keplerian description of the motion by about one mm in the direction of the motion. A satellite in orbit round the Earth will cumulatively track the deviation, and after numbers of satellite orbits the influence might be measurable.

The second influence comes from "frame dragging." An observer on the Earth, spending their life in an enclosure with no means to motion of the Earth in the solar system, could detect the Earth's rotation with a Foucault pendulum. The Coriolis force causing that is fictitious, and vanishes if the frame of reference is not with the rotating Earth. If the observer is a relativist, the observer claims, "everything outside the Earth is revolving around it and producing this Coriolis force."

There is no harm in that description, and is the relativist's standpoint. But that also implies that the frame of reference of the rotating Earth acts reciprocally on everything else. That slight deviation is referred to as "frame dragging." The effect is going to be most apparent in the direction of motion with the most variation of the Coriolis force - that is, circumpolar.

Identifying both effects assumes that all other (standard) corrections have been accounted for - viz. the oblateness of the Earth, the variable density, etc. Accounting for these influences correctly is a matter of contention, and results in debate about the interpretation of these gyroscope and satellite ball experiments.

reader Lorenzo Iorio said...

Look at this story about Ciufolini, Gravity Probe B, and then let me know....

reader Luboš Motl said...

LOL, why don't you link to the paper directly?

Is Iorio another pseudonym of the same person?

reader Lorenzo Iorio said...

Moti, so I would be another pseudonym of....Ciufolini??? Why do not you ring me now? If you had read the screenshots of the entire story, you would have noticed that ArXiv censored itself, but not because they acknowledged an error in identifying Ciufolini after 5 years! Because they would have suddenly changed their policies, which is a lie, also because their policy never did treat cases like this!

reader Lorenzo Iorio said...

A NEW case of scientific misconduct by Mr. Ciufolini as reported by ArXiv. Read the comment by moderators at
It is: " This submission has been made by G. Felici, a pseudonym of Ignazio Ciufolini, who repeatedly submits inappropriate articles under pseudonyms, in violation of arXiv policies " PS. About the OTHER case, the CiuForst one at, now ArXiv has reinstated the original comment explicitly exposing Mr. Ciufolini. Let's wait for the next episode...