Gravity Probe B Confirms Two of Einstein’s Space-Time Theories

by Nancy Atkinson on May 4, 2011

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Einstein's predicted geodetic and frame-dragging effects, and the Schiff Equation for calculating them. Credit: Stanford University

Researchers have confirmed two predictions of Albert Einstein’s general theory of relativity, concluding one of NASA’s longest-running projects. The Gravity Probe B experiment used four ultra-precise gyroscopes housed in an Earth-orbiting satellite to measure two aspects of Einstein’s theory about gravity. The first is the geodetic effect, or the warping of space and time around a gravitational body. The second is frame-dragging, which is the amount a spinning object pulls space and time with it as it rotates.

Gravity Probe-B determined both effects with unprecedented precision by pointing at a single star, IM Pegasi, while in a polar orbit around Earth. If gravity did not affect space and time, GP-B’s gyroscopes would point in the same direction forever while in orbit. But in confirmation of Einstein’s theories, the gyroscopes experienced measurable, minute changes in the direction of their spin, while Earth’s gravity pulled at them.

The project as been in the works for 52 years.

The findings are online in the journal Physical Review Letters.

Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time. Image credit: NASA

“Imagine the Earth as if it were immersed in honey,”.said Francis Everitt, Gravity Probe-B principal investigator at Stanford University. “As the planet rotates, the honey around it would swirl, and it’s the same with space and time,” “GP-B confirmed two of the most profound predictions of Einstein’s universe, having far-reaching implications across astrophysics research. Likewise, the decades of technological innovation behind the mission will have a lasting legacy on Earth and in space.”

NASA began development of this project starting in the fall of 1963 with initial funding to develop a relativity gyroscope experiment. Subsequent decades of development led to groundbreaking technologies to control environmental disturbances on spacecraft, such as aerodynamic drag, magnetic fields and thermal variations. The mission’s star tracker and gyroscopes were the most precise ever designed and produced.

GP-B completed its data collection operations and was decommissioned in December 2010.

“The mission results will have a long-term impact on the work of theoretical physicists,” said Bill Danchi, senior astrophysicist and program scientist at NASA Headquarters in Washington. “Every future challenge to Einstein’s theories of general relativity will have to seek more precise measurements than the remarkable work GP-B accomplished.”

Innovations enabled by GP-B have been used in GPS technologies that allow airplanes to land unaided. Additional GP-B technologies were applied to NASA’s Cosmic Background Explorer mission, which accurately determined the universe’s background radiation. That measurement is the underpinning of the big-bang theory, and led to the Nobel Prize for NASA physicist John Mather.

The drag-free satellite concept pioneered by GP-B made a number of Earth-observing satellites possible, including NASA’s Gravity Recovery and Climate Experiment and the European Space Agency’s Gravity field and steady-state Ocean Circulation Explorer. These satellites provide the most precise measurements of the shape of the Earth, critical for precise navigation on land and sea, and understanding the relationship between ocean circulation and climate patterns.

GP-B also advanced the frontiers of knowledge and provided a practical training ground for 100 doctoral students and 15 master’s degree candidates at universities across the United States. More than 350 undergraduates and more than four dozen high school students also worked on the project with leading scientists and aerospace engineers from industry and government. One undergraduate student who worked on GP-B became the first female astronaut in space, Sally Ride. Another was Eric Cornell who won the Nobel Prize in Physics in 2001.

“GP-B adds to the knowledge base on relativity in important ways and its positive impact will be felt in the careers of students whose educations were enriched by the project,” said Ed Weiler, associate administrator for the Science Mission Directorate at NASA Headquarters.

Sources: NASA, Stanford University


Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Lawrence B. Crowell May 6, 2011 at 4:11 PM

Gravity waves come about when arrangements of gravitating bodies, which are as you say warping space, are in motion. The causality principle states that an influence traverses an interval at the speed of light or less. So if these gravitating bodies are in a certain dynamical configuration the information about how that “warping” evolves reaches the distant hinterlands away from this system in a causal manner. These are gravitational waves. It is similar to the change in a configuration of charged particles, where the electric field lines adjust themselves away from this system in an electromagnetic wave.

Now do not go running off thinking you actually understand what gravitational radiation is. There is a lot more here, and a deep understanding requires an understanding of the Petrov-Penrose-Pirani solutions based on eigen-Killing vectors of the Weyl curvature. A gravity wave is a situation where without any source in vacuum there is a change in the Weyl curvature as measured by observers on various geodesics.


forrest noble May 6, 2011 at 4:37 PM

@ Andrew James,

Thanks for the civil demeanor of your last postings.

That matter creates “gravity waves” may be a very valid idea but what impact would gravity waves have in cosmology if they were not the cause of gravity but just an effect? even though a Nobel Prize was given for the “discovery” of gravity waves.

This thread is about gravity Probe B and its impressive achievements so I don’t wish to discuss my own ideas but the reason why I say in my book that the Pan Theory is a simpler and more logical model is because dark matter, dark energy, Inflation, the expansion of the universe, no extra dimensions, etc. etc. are not needed for this model — whereby I provide observational data in some cases showing that this model (my own mathematical formulations) better match observed reality than mainstream formulations: GR and the Hubble Formula.

As to the clarity of my postings, I have a book editor for the wording of my book/ theories but none for these postings :)

Andrew James May 7, 2011 at 10:46 AM

Sorry, gravity waves are not being discussed here. It is about General Relativity and the proof by the Gravity B probe of frame-dragging precession.

Also very nice way of avoiding scrutiny by saying “This thread is about gravity Probe B and its impressive achievements so I don’t wish to discuss my own ideas.” ; but this particular discussion just happens to be what Gravity B is investigating and your assertion that what it found does not support General Relativity. We are not talking of your wrong Pan Theory, we are talking of aspects of it relating to General Relativity.
Your assertions in your on-line personal theory “book” clearly shows you lack the necessary understanding of relativity. If you cannot substantiate your earlier claims that General Relativity is somehow wrong, the you should retract your incorrect statements. The only reality here is your views are mostly wrong and misguided.

Olaf May 7, 2011 at 10:58 AM

That Pan Theory sounds more logical, does not automatically mean that it is based in reality it could still be fiction.

Torbjorn Larsson OM May 8, 2011 at 8:31 PM

“dark matter, dark energy, Inflation, the expansion of the universe,” The three first _are_ needed in standard cosmology, the later is a simple observation (that is predicted from standard cosmology).

It is simply wrong to say that parsimony can overrule theory (i.e. the use of prediction from observation).

Torbjorn Larsson OM May 8, 2011 at 8:54 PM

By the way in this context, dark energy doesn’t need the direct expansion of the universe to be tested anymore. It is observed by its effect on CMB alone:

“For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra.

Our CMB-only measurement of the dark energy density Omega_Lambda confirms other measurements from supernovae, galaxy clusters and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.”

I.e. CMB spectra + gravity lensing of CMB provides evidence for DE. Also note that the CMB first dipole is a much better fit with DE, fig 1!

interI0per May 6, 2011 at 7:59 PM

Let’s just call it idle speculation eh?

Would the incoming photons from the guide star be deflected in the ‘gravity well’ too?
I would say so.. it is after all the very effect they are looking for.

Lawrence B. Crowell May 6, 2011 at 8:07 PM

The gravity Probe B integrates the deviation over a long time. Each photon has a tiny deviation over a very short period. This ends up being a very small error.


Andrew James May 7, 2011 at 1:35 PM

I’ve just read an excellent Sky and Telescope on-line article of this “Gravity Probe B: Relatively Important?” by Shweta Krishnan. This gives another different slant on this UT story. See

(This is one of the best general astronomical related articles about astronomy and astrophysics I’ve read for some time. It is detailed and place the story in its historical context. Bravo!)

forrest noble May 7, 2011 at 8:15 PM


“That Pan Theory sounds more logical, does not automatically mean that it is based in reality it could still be fiction.”

Your quote above is certainly true, but I think this theory is arguably equally or better supported by observation than the BB model which also may be just fiction. The determining factor for any model should be predictions that match observations with few unpredicted surprises such as those observations that led to changes of theory that necessitated Inflation, dark matter, and dark energy.

This model needs none of these add-on hypothesis to explain what is being observed.

Andrew James May 7, 2011 at 10:12 PM

Observation. Flexing ego (or pretending in your own fictions) does not improve hypothesis or theories either. If what you say is true, then the non-existent followers of your own personal theory do not accept your assertions. No ground base of support means something equally as important; your’s is a bigger fiction than the one you wish to supplant.
Predictions here is you are just wasting your’s and everyone else time; and when you realise it, you will not be able to bear the disappointment. I just hope you wake up to your folly before it is all too late.

forrest noble May 7, 2011 at 9:24 PM

“…….but this particular discussion just happens to be what Gravity B is investigating and your assertion that what it found does not support General Relativity”

I made no assertion concerning Gravity Probe B or General Relativity, only that the accuracy findings of frame dragging were within an accuracy of 19% (I posted a link) and not the 1% accuracy that they hoped for. I too think the error was probably related to the equipment or the design of the experiment rather than the theory. The mathematical variations of the Pan Theory to GR do not become readily apparent until after maybe 2 light years distance so I cannot presently (or maybe never) dispute GR at distances less than this distance such as the Earth’s “frame dragging” effect and the experimental results of Gravity Probe B.

This variation between these gravitational models is best observed, measured, and compared at galactic scales which is unrelated to Gravity Probe B.

Andrew James May 7, 2011 at 9:59 PM

Sorry. Much of what you say here is very silly, and what is said, is really meant to confuse or just avoid scrutiny. If you cannot or will not answer basic questions and are unwilling to be confronted in what you have already said, there is no point saying anything more.
One thing we can truly assert. Your own fantasy placed in your so-called Pan Theory is not fooling me or anyone.
A cosmologist you clearly are not. :(

Lawrence B. Crowell May 7, 2011 at 10:12 PM

The evidence for the big bang is pretty conclusive. First there is the Hubble expansion result that the velocity of a galaxy is related to its distance d a constant H = 75km/sec/Mpc, v = Hd. This applies locally,and for much greater distances there is a deviation from this. The other is the abundance of deuterium and helium in the universe, which is predicted by the thermodynamic conditions of the early universe. The other is the CMB due to the end of the radiation dominated period, and the flatness of the universe is evidence for inflationary big bang. The big bang has emerged as a very substantial part of the scientific canon of knowledge.


forrest noble May 7, 2011 at 10:25 PM

@Andrew James,

Since this thread should focus on Gravity Probe B, if you or anyone else wishes to discuss anything else in cosmology whereby I could answer all questions concerning all observations or otherwise, and provide alternative equations relating to the Pan Theory, contact me at

Andrew James May 7, 2011 at 10:48 PM

You said; “Although there is strong evidence that a vortex model of gravity seems valid, and there are a number of such competing models, the predictions of General Relativity can only be considered to still be in the running since no other model seemed to predict things any better. There was no clear advantage of General Relativity over a few other competing models that also predict the same frame dragging effects.”

This is wrong. Your own document, with quotes from it, shows this is statement is wrong. General Relativity has passed every test to date with flying colours. You state this to validate you own view, and not to examine the implications of the support for general relativity by science, physics and cosmology. Your own bias ignores the fact of the possibility that Gravity B’s instrumentation might be faulty or some unknown error has occurred.

To quote the independent S&T link earlier; “The truth is, we did. The LAGEOS satellites, lunar ranging, the Cassini mission’s radio experiment, and binary pulsars, to name just a few, have all verified general relativity — including these two particular predictions — sometimes to much higher accuracy than Gravity Probe B.”

Your statement (above) simply says your assertion is wrong and false; also verifying your Pan Theory rejection of General Relativity is unsubstantiated.

End of line.

forrest noble May 7, 2011 at 11:07 PM

Your quote: “Your own bias ignores the fact of the possibility that Gravity B’s instrumentation might be faulty or some unknown error has occurred.”

I think you did not read this statement of mine above.

‘I too think the error was probably related to the equipment or the design of the experiment rather than the theory” (General Relativity), at least within the scope of this experiment,

Andrew James May 7, 2011 at 11:35 PM

Nice try, but I read it perfectly well, and I expected such a response..

The problem you now have is that you cannot ignore use that excuse to deny your even earlier statement (which is also false, and now openly shows you have just contradicted yourself); I.e. “The original purpose of the gravity B probe was to generally “prove” Einstein’s theory of General Relativity, After a great effort which involved high-cost funding and many years preparation which included many scientists and computations, the observations did not find that the calculations of General Relativity fit within the acceptable tolerances predetermined beforehand as necessary for proof of theory.”
This again does not mean General Relativity is wrong nor that “…the observations did not find that the calculations of General Relativity fit within the acceptable tolerances predetermined beforehand as necessary for proof of theory.” (Your words.)

Either way you look at it, you cannot conclude (like your Pan Theory or your own statements here) that; “There was no clear advantage of General Relativity over a few other competing models that also predict the same frame dragging effects.”

Again your clearly bias opinion is not substantiated that General Relativity is unproven and is logically reaffirmed. I.e. You don’t really believe the instrumentation was at fault, otherwise you would not be stating; “There was no clear advantage of General Relativity over a few other competing models that also predict the same frame dragging effects.” Why is that?

forrest noble May 8, 2011 at 12:01 AM

My quote: “There was no clear advantage of General Relativity over a few other competing models that also predict the same frame dragging effects.”

Your question: “Why is that?”

My quote above was my opinion concerning the Gravity B Probe experiment relating to the frame dragging measurement results within a 19% error factor, concerning the predictions of GR.. And as I said the error I believe was probably with the experiment or equipment since accordingly such a wide variance has not showed up in other related experiments.

Andrew James May 8, 2011 at 8:35 PM

…and, of course, general relativity was proven to be perfectly correct, yet again.

So why believe in another theory? All other models are both unnecessary and unsubstantiated (including you own.)

Why doubt, when there is no need to doubt!

Torbjorn Larsson OM May 8, 2011 at 8:37 PM

So you do accept the experiments at large, and that the GB Probe was correct after successfully having some large systematic effects taken into consideration. Then why argue that it didn’t test GR, when it is obvious to everyone that it did?

forrest noble May 9, 2011 at 1:49 AM

As I said before, I think the divergence of Gravity Probe B measurements from GR predictions was likely due to errors of the experiment or the equipment. The primary reason for my conclusion is that observations were not consistent with themselves and diverged greatly from the expected quantities before they narrowed down the error divergence range to “within 19%” of the predicted value.

This being said, I would not be surprised if the fault was instead or also with GR or the interpretation of it concerning the frame dragging effect.

This has also been discussed by others concerning Gravity Probe B before it was launched or made any measurements.

Quote from link above

Testing history

Gravity Probe B is intended to measure the frame-dragging effect to an accuracy of 0.3 percent, and will be the first direct measurement of the effect and of its magnitude. While many scientists feel confident that the results from Gravity Probe B will simply confirm Einstein’s predictions, there are those who expect that the answer will be something quite different. As Nobel laureate Chen Ning Yang put it: “Einstein’s General Relativity theory, though profoundly beautiful, is likely to be amended . . . The Stanford experiment is especially interesting in that it focuses on the spin. I would not be surprised at all if it gives a result in disagreement with Einstein’s theory.”

Andrew James May 9, 2011 at 4:24 AM

Self-validation for the sake of ego or being heard is so ridiculous.
Saying “amended”, doesn’t mean your saying; “There was no clear advantage of General Relativity over a few other competing models that also predict the same frame dragging effects.”

Yang was talking about the geodetic effect, and as far as anyone knows, it precessional movement is also predicted by General Relativity. It’s effect on the Earth and Moon’s motion. It is NOT the measure of the frame dragging effect. Gravity Probe B found the geodetic effect was verified to a precision of better than 0.5% percent , as announced on 14th April 2007.
In this case Yang was talking about the geodetic effect. Possible variations are thought to be from Thomas Precession, which is a kinematic effect as seen in gyroscopes spinning velocity. This effect is actually occurs in the flat spacetime under Special Relativity. The calculation of the effect is notoriously difficult in multiple inertial frames.
The problem is knowing all the effects within the solar system bodies that have effects on the correct frame dragging effect of the Earth.

You will find (again) the error is not that of General Relativity but of other similar effects that effect the final result. Yang is talking about this not you rather doltish ideas that General Relativity is wrong or incorrect.

So as per usual you use half-truths and distortions to validate your wrong cosmological conclusion. No one is fooled by what you say. (Yet again). Again it puts you at odds with the physics community who know far more and much better than you; leaving you clearly beyond your depth.
Nice try though, but sadly, no cigar…

Andrew James May 9, 2011 at 4:26 AM

Note: You’re going to have to do much better than this to win this argument.

Anonymous May 15, 2011 at 3:41 PM

Is frame-dragging created by a form of friction? The explanations online do not really seem to address the underlying physics understandable to the lay-person.

Torbjörn Larsson May 15, 2011 at 7:32 PM

It _is_ general relativity, so I’m not too certain of the physics which I haven’t studied at that level of theory. However:

No, it isn’t the phenomena of friction, since that acts between bodies in contact. It is a phenomena of general relativity, which acts between bodies and the spacetime they are in.

For reasons that are too long to start the description with, relativity predicts that clocks ticks with relative differential rates.* Clocks that are moving free in space ticks the fastest. So we want to keep track of “free space”, which is the reference to go to.

Around a rotating mass, the spacetime volume that best approaches free space in character is dragged around the mass in the direction of rotation. Free space is called “an inertial frame” in relativity, so this is “frame dragging”.

The way it comes out in practice with the effect of frame dragging and its effect on other masses close to the rotating mass is an added precession of gyroscopes.

Does that help?

* This has to happen to keep physical laws the same everywhere in free space, which is what is expected and observed. But the way it happens becomes a bit … involved.

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