Stanford’s Gravity Probe B confirms two Einstein theories
After 52 years of conceiving, testing and waiting, marked by scientific advances and disappointments, one of Stanford’s and NASA’s longest-running projects comes to a close with a greater understanding of the universe.
Stanford and NASA researchers have confirmed two predictions of Albert Einstein’s general theory of relativity, concluding one of the space agency’s longest-running projects.
Known as Gravity Probe B, the experiment used four ultra-precise gyroscopes housed in a 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.
After 52 years of conceiving, building, testing and waiting, the science satellite has 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, Gravity Probe B’s gyroscopes would point in the same direction forever while in orbit. But in confirmation of Einstein’s general theory of relativity, the gyroscopes experienced measurable, minute changes in the direction of their spin as they were pulled by Earth’s gravity.
The findings appear online in the journal Physical Review Letters.
“Imagine the Earth as if it were immersed in honey. As the planet rotated its axis and orbited the Sun, the honey around it would warp and swirl, and it’s the same with space and time,” said Francis Everitt, a Stanford physicist and principal investigator for Gravity Probe B.
A lasting legacy
“GP-B confirmed two of the most profound predictions of Einstein’s universe, having far-reaching implications across astrophysics research,” Everitt said. “Likewise, the decades of technological innovation behind the mission will have a lasting legacy on Earth and in space.”
Stanford has been NASA’s prime contractor for the mission and was responsible for the design and integration of the science instrument and for mission operations and data analysis.
Much of the technology needed to test Einstein’s theory had not yet been invented in 1959 when Leonard Schiff, head of Stanford’s physics department, and George E. Pugh of the Defense Department independently proposed to observe the precession of a gyroscope in an Earth-orbiting satellite with respect to a distant star. Toward that end, Schiff teamed up with Stanford colleagues William Fairbank and Robert Cannon and subsequently, in 1962, recruited Everitt.
NASA came on board in 1963 with the initial funding to develop a relativity gyroscope experiment. Forty-one years later, the satellite was launched into orbit about 400 miles above Earth.
The project was soon beset by problems and disappointment when an unexpected wobble in the gyroscopes changed their orientation and interfered with the data. It took years for a team of scientists to sift through the muddy data and salvage the information they needed.
Despite the setback, Gravity Probe B’s 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.
Played a role in developing GPS
Innovations enabled by GP-B have been used in the Global Positioning System, such as carrier-phase differential GPS, with its precision positioning that can allow an airplane to land unaided. Additional GP-B technologies were applied to NASA’s Cosmic Background Explorer mission, which determined the universe’s background radiation. That measurement is the underpinning of the “big bang theory” and led to the Nobel Prize for NASA’s John Mather.
“The mission results will have a long-term impact on the work of theoretical physicists for years to come,” 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.”
Over the course of its mission, GP-B 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. Over 350 undergraduates and more than four dozen high school students also worked on the project, alongside leading scientists and aerospace engineers from industry and government.
Sally Ride, the first American female astronaut in space, worked on GP-B while studying at Stanford. Another was Nobel Laureate Eric Cornell, who also studied at Stanford.
NASA’s Marshall Space Flight Center in Huntsville, Ala., managed the Gravity Probe-B program for the agency. Lockheed Martin Corporation of Huntsville designed, integrated and tested the space vehicle and some of its major payload components.
===========================================================
Learn a lot more on testing Einstein’s theories here h/t Dr. Leif Svalgaard via email
In “Light” of the confirmation of General Relativity, what would be the results of the following experiment?
Wrap an Optical Fiber around the equator of Earth. From Point A on the fiber, Send a laser pulse Eastward and Westward simultaneously. What will happen when the two pulses return to point A?
What will be the Time between the Arrival of the Westward pulse (arriving from the east) and the Eastward Pulse (from the west)?
A1. As measured by a clock at Point A.
A2. As measured by a clock a million miles from Earth in Earth’s solar orbit? (no Earth gravitational time dilation at the earth’s surface, but Solar gravitation and orbital speed the same.)
The Earth is a rotating gravitational Field,
and the fiber attached to the earth is in an accelerating frame of reference.
Assume Index of refraction is 1.62 or Speed in fiber is 200,000 km/sec. http://en.wikipedia.org/wiki/Optical_fiber#Index_of_refraction
Circumference of Earth: 40,075.16 kilometers, OK to use 40,000 km even.
Rotational speed of earth at the equator: 465.1 m/s
Let’s assume standard gravity at the equator (without centrifugal Acceleration) is 9.800 m/sec.
B. What happens if the light fiber is replaced by a mirror lined vacuum tube?
C. Is B the same thing as a light fiber (a solid medium attached to the rotating earth) with an index refraction of 1.00?
D. What happens if earth’s gravity acceleration is increased to 98 m/sec (x10)? (and the shape of the earth does not change)
If anyone has a link to pages that describe this experiment, I would greatly appreciate it. Does this experiment have a common name?
The answer to C above is NO. Light would not bend around the circle. You need the wave guide to trap the light into a circular path, and for that you need a core with an index of refraction >1.00.
Stephen Rasey says:
May 5, 2011 at 8:48 am
Wrap an Optical Fiber around the equator of Earth. From Point A on the fiber, Send a laser pulse Eastward and Westward simultaneously. What will happen when the two pulses return to point A?
The simplest way to think about this is to note that because of frame-dragging, the length of the path in the direction of the rotation will look to be about an inch shorter [IIRC]. “Under the Lense–Thirring effect, the frame of reference in which a clock ticks the fastest is one which is rotating around the object as viewed by a distant observer. This also means that light traveling in the direction of rotation of the object will move around the object faster than light moving against the rotation as seen by a distant observer.”
Again wikipedia has a good description: http://en.wikipedia.org/wiki/Frame-dragging
BarryW says:
May 4, 2011 at 4:27 pm
The project was soon beset by problems and disappointment when an unexpected wobble in the gyroscopes changed their orientation and interfered with the data. It took years for a team of scientists to sift through the muddy data and salvage the information they needed.
That bothers me.
You’re not the only one that’s bothered by it. Seems to me they went looking for what they expected, after something unexpected occurred. Confirmation bias, possibly. ARGO data, anyone?
Another point: this is not “proof” or “confirmation” of a theory. The scientific method states that this was only a failure to falsify a prediction. Saying anything else is conjecture.
According to loop quantum gravity space itself has a Planck dimension. This makes one think of ether, however, space has no mass or energy but contains items that do. All makes for some very interesting thoughts.
An analogy might be a projection screen. The screen is real and has qualities but those do not influence the content of the picture being presented on the screen. The screen itself logically exists outside the picture.
Lief, I don’t know the answer to these questions in the fiber loop experiment. But I know there are several things going on.
In the 0.20 seconds it takes for the pulses to travel the fiber, Point A has moved Eastward by about 93 meters. So the Eastward path is 186 meters longer than the Westward path as viewed by Observer A2. So Eastward arrives about 0.93 microsec after Westward?
Or does the velocity of the fiber cancel out the extra distance? The fiber has moved eastward by 93 meters, too. Is the light’s speed added to the fiber’s speed? So that, neglecting frame dragging the points should arrive at the same time? Or at almost the same time (got to be some Lorentz contraction in there somewhere).
If so, then the results for Question B ought to be markedly different from Question A and not just by the difference in the refractive index. But then again, there are mirrored walls are also moving with the earth’s rotation, but I have a hard time adding the rotational speed of the vacuum tube guide to the speed of the wave form inside the guide. That observer A2 away from the earth will object. Yet Simultaneity I don’t think will be an out because all observations will be done at Point A or by a distant observer A2 looking at point A.
On top of all this, we still have to apply the affects of frame dragging where by the Eastward pulse should arrive slightly faster, not slower, than the Westward pulse, all other things being equal.
So, are you saying than in A1
R1: the Eastward pulse arrives (1 in = 0.02 meters = 0.1 nano sec) Earlier than the westward pulse,
R2: the Eastward pulse arrives (0.93 microsec = 930 nanosec) (930-0.1) nanosec LATER than the westward pulse.
Or something else?
Elftone says:
May 5, 2011 at 9:14 am
The scientific method states that this was only a failure to falsify a prediction. Saying anything else is conjecture.
If I predict that a major earthquake [or solar flare or whatever] will occur in three weeks from today at 12 GMT and it does happen, you would call that only a failure to falsify my prediction…
Richard S Courtney:
“I ask, a velocity of the universe relative to what?”
That does seem problematic, doesn’t it? One might say, it is traveling through the same place it expands into. That, however, assumes linear, straight line thinking. I would suggest spinning (velocity) is less problematic. No particle is born void of velocity. Why do we assume, the universe came out of the big bang, without velocity?? GK
Leif Svalgaard:
I think you confused my use of the word “universe” with “galaxy” , but thanks for the reply. GK
Stephen Rasey says:
May 5, 2011 at 10:00 am
I don’t know the answer to these questions in the fiber loop experiment. But I know there are several things going on.
There are special relativity effects that are much larger than the frame dragging. In addition the fiber bending complicates the analysis [which I’ll not attempt here – OT for one]. I don’t think we could measure frame dragging with your experiment. A sharp test of frame dragging will be possible in a few years: The supermassive black hole at the center of the Milky Way causes severe frame dragging of the stars that orbit the hole. Several such stars [at different distance to the center and therefore with different frame dragging] are monitored right now and perturbations of their orbits caused by frame dragging will soon [takes time to collect enough data for a good orbit determination] be apparent.
The universe expands. What is it expanding into?
Last night on “How the Universe Works” it was said that the laws of physics allow the creation of energy from nothing. They never said what law and how does that jive with the conversation of energy law (no matter/energy created or destroyed)?
What is the temperature on the surface of a super massive black hole?
BarryW:
I totally agree. Being in a 50 year project means there must be a lot of pressure to come up with something. People here tend to be much more cautious regarding data manipulation issues, when it comes to other topics.
Comment section should be re-titled Louis Savain’s Rant…
New ways of looking at the box are good, but I must say that after reading several articles on Louis Savain’s blog as well as many of his posts here… he seems to have based much of his rant on dt/dt and inconsistencies between quantum mechanics and relativity… But dt/dt is a non-starter for scientific discussions because time is constant in a reference frame… that’s the beauty of reference frames, time in one frame moves relative to relative to another reference frame… so dt/dt is a mistaken expression…
Louis Savain should instead look at dt (reference frame 1) / dt (reference frame 2) — it is easy to show that this is certainly not a constant… thus time does move…
And — the inconsistency between relativity and quantum mechanics has not stopped either from producing useful, testable, experimental results…
Leif Svalgaard says:
May 5, 2011 at 10:00 am
If I predict that a major earthquake [or solar flare or whatever] will occur in three weeks from today at 12 GMT and it does happen, you would call that only a failure to falsify my prediction…
Nope, I would not… and I would call you brilliant :).
My point, which was badly made by me, is that using the results of one prediction of one aspect of a theory does not confirm that theory. It merely means that, yet again the theory is holding up to some of the most rigorous testing ever, which means – in many respects – it is the best theory we have with which to work. It also means it was an amazing body of work, worthy of respect.
Do understand me: I have no problem or axe to grind with Einstein or his theories of special or general relativity. I do have a problem with inferences made that cannot be supported by the facts as reported. That’s all. Quite simple really.
Re: Rasey May 5, 2011 at 10:00 am
Is the light’s speed added to the fiber’s speed?
No. Otherwise Ring Laser Gyro’s and Fiber Optic Gyros would not work. http://en.wikipedia.org/wiki/Ring_laser_gyroscope
http://en.wikipedia.org/wiki/Fibre_optic_gyroscope
The thought experiment I put forth is equivalent to putting a Fiber Optic Gyro around the earth at the Equator. The Frame Drag is irrelevant in a typical Fiber Optic Gyro, but it matters when the FOG surrounds a rotating planetary mass.
Elftone says:
May 5, 2011 at 11:08 am
I do have a problem with inferences made that cannot be supported by the facts as reported.
The issue at hand is an inference supported by the experiment [‘facts’]. The inference was that yet another one of Einstein’s prediction has been borne out, confirming his theory. ‘Confirmation’ is just a ‘piece of evidence’. Forget about ‘proof’. No scientists use that word.
Leif Svalgaard says:
May 5, 2011 at 11:41 am
Forget about ‘proof’. No scientists use that word.
Completely agree!
Is no one giving me an explanation to my question because no one knows the answer?
Is Louis Savin right, that you don’t know?
http://wattsupwiththat.com/2011/05/04/einstein-proven-right-again/#comment-653506
This isn’t a trick question, it’s genuine, it’s something I’ve wanted to understand for a long time and I thought I would get an explanation here.
Whenever I’ve watched this diagramatic explanation on TV I’ve not been able to understand it. Once, someone said that it was applicable all the way round, 3d, and I thought that must be some very clever physics of time/space that I wasn’t grasping. However, it looks like you don’t have an answer. The 3rd dimension appears to have stumped you.
I have taken an interest in these things on and off, what I’ve managed to gather without having the maths language, but just to make it clear, nothing in the concepts of 20th century science is alien or surprising to me. In fact, I have found it a bit amusing that recently it’s been proposed that matter can go through other matter equally solid and be in two places at once, amused because these concepts have been around for milleniums and I seem to recall that not very long ago scientists were busy poo-pooing this kind of thinking..
Anyway, all I want to know is how this diagram above works in 3D. Because, to me it cancels itself out in 3D.
And after Savin’s reply to me, /#comment-643548, I thought of this: http://www.geom.uiuc.edu/~banchoff/Flatland/
I also thought I should wait to see if there was any answer before concluding, as I have tentatively, that it wasn’t my lack of intelligence, as I’d assumed, that made me think that the diagram and the explanation didn’t describe a three dimensional world and I couldn’t make it make sense in 3D, it was that the concept was nonsense in our physical three dimensional world.
But, before I go the whole hog here, would you Leif and all those who’ve made disparaging remarks about Louis Savin, please give me an explanation that makes sense in 3D reality.
If you can’t explain it, I would appreciate you saying so, I don’t want to keep hanging around in case you reply. If I don’t hear from you, I shall assume that Savin is right, you don’t know what you’re talking about. Because this is a very simple problem, it surely can’t be beyond your abilities to explain it.
“”””” wayne says:
May 4, 2011 at 4:23 pm
Those are some interesting articles Leif. The reference frame dragging was one of hardest concepts to grasp, for me anyway.
It sure seems like NASA could hire an artist that knew the basics of gravity for a story about… gravity. Neat picture but somewhat misleading if you take it too literally! Don’t look at that green-blue mesh and think that is what the real signature of Earth’s gravitational field would actually look like, well, kind of, but not correct.
At the center of the Earth there is no gravity field, zero. “””””
Somebody should quickly inform the sun, that it is having no effect at the centre of the earth’ probably because of all the magnetic shielding around that point. Oh I forgot, that all that iron would be above the curie Temperature.
But amazing that the earth can shiled the sun’s gravity.
I always thought gravity had an infinite range so that shielding is inherently impossible. Just think, if you could actually build an anti-gravity shield, then there would be no gravity on she shielded side, all the way out to infinity, and if you held it up, the entire atmosphere of the earth would rush into the shielded zone, and immediately escape to space; well at the velocity of sound anyway.
Leif Svalgaard says:
May 4, 2011 at 9:23 pm
Leif Svalgaard says:
May 4, 2011 at 9:23 pm
..Yes, I’m a time-cannot-change denier. This experiment was called Gravity Probe B, because there was a Gravity Probe A long ago. In GP-A one atomic clock was sent into space while two clocks remained on Earth. Relativity predicts that the one that was sent aloft would run slower than the two on the ground, and sure enough it did, and by just the amount predicted. http://en.wikipedia.org/wiki/Gravity_Probe_A
End of discussion.
~
Hmm Gravity Probe A
From the wiki
..The probe was launched on June 18, 1976 on top of a Scout rocket and remained in space for 1 hour and 55 minutes, as intended. It then crashed into the Atlantic Ocean.
..The satellite was launched nearly vertically upward to cause a large change in the local gravity seen by the maser, reaching a height of 10,000 km (6200 miles). At this height, general relativity predicted a clock should run 4.5 parts in 1010 faster than one on the Earth.
..The experiment was thus able to test the equivalence principle. Gravity Probe A confirmed the prediction that gravity slows the flow of time, and the observed effects matched the predicted effects to an accuracy of about 70 parts per million
http://en.wikipedia.org/wiki/Gravity_Probe_A
What was up with that wobble on B .. or did I miss something. And what did we do all those years with B?
Vuks..good show..goes to show..behind every great man.. is a great woman..
I love these debates. Love to read all the links everyone throws out and think about it.
One of my favorite quotes is by Einstein
“Now you think that I am looking back at my life’s work with calm satisfaction. But, on closer look, it is quite different. There is not a single concept of which I am convinced that it will stand firm and I am not sure if I was on the right track after all:”
Even with the whole world singing his praises he never quit trying to reconcile why his theories didn’t work to his satisfaction. Never stop trying to find holes in your work and explain them. That alone is his greatest achievement IMHO.
“”””” Louis Savain says:
May 4, 2011 at 10:30 pm
davidmhoffer wrote:
What pleasure or value you get out of announcing that dt/dt disproves him is beyond me.
dt/dt proves via extremely simple logic (which apparently went over your head) that, contrary to the claims of Albert Einstein’s (and many others), there is no such thing as a time dimension. “””””
Well if you want to get down to the ultimate in pedantry; there is no such thing as any of the things we talk about in Physics; or in mathematics. There is absolutely nothing in any branch of mathematics, that actually exists, and can be observed anywhere in the known or unknown universe. it is all a complete fiction, and we made it all up out of whole cloth in our heads.
We also made up all our theoretical models of Physics, and none of those things actually exist anywhere either.
But using our mathematical fictions, and the rules of manipulation we arbitrarily assigned to them, we can predict what our equally fictional models would do if we conducted a particular experiment on them.
We then let other folks know about our results, so they can go and examine the real universe and see, if they can observe any sort of analagous behavior in the real universe, to correspond to what our theories say our models would do.
So if you want to deny the existence of something; be sure to include all of the other things that don’t exist either. (except in our heads).
Myrrh says:
May 5, 2011 at 1:07 pm
Is no one giving me an explanation to my question because no one knows the answer?
The answer is long. Wikipedia has some good pointers: http://en.wikipedia.org/wiki/General_Relativity
Because this is a very simple problem, it surely can’t be beyond your abilities to explain it.
It may be beyond your ability to understand it. By that I mean, that there are fundamental issues about what curvature is and how to express it, and those are not easy to visualize, without resorting to somewhat misleading images [like the bowling ball on a membrane]. Start with the wiki. There are also good books on the subject [referenced in the wiki]
George E. Smith says:
May 5, 2011 at 1:18 pm
I always thought gravity had an infinite range so that shielding is inherently impossible.
The Earth is in free fall around the Sun and thus does not feel any gravity [except its own], just like an astronaut in free fall about the Earth.
Carla says:
May 5, 2011 at 1:22 pm
did I miss something. And what did we do all those years with B?
As usual, yes. We spent all those years developing the technology necessary for B to work.
DirkH says:
May 4, 2011 at 3:32 pm
So, spacetime behaves a litle bit like honey? Why don’t we just call it ether?
Because people would fall asleep.
BarryW says:
May 4, 2011 at 4:27 pm
That bothers me.
Bothers a bunch of people. Data-mining is even more environmentally unfriendly than gold mining with nukes and aerosolised mercury…
Leif Svalgaard says:
May 4, 2011 at 9:38 pm
Leif Svalgaard says:
May 4, 2011 at 9:23 pm
Relativity predicts that the one that was sent aloft would run slower than the two on the ground
Grrr, faster, of course. High gravity slows down time.
So, given this experiment ( http://www.ru.nl/hfml/research/levitation/diamagnetic/) does this mean the frog is operating in a quicker time to the rest of the room because it is weightless, or does it not count because it isn’t gravity? Would a steel ball bearing placed into the apperatus be operating in a slower time to everything else – because it most definitely would be having a force acting upon it.
If it doesn’t count as “anti-grav”, and I’m still subject to local time if I were to use such an apperatus to annul the gravitational field of a black hole, would I have a time gradient from head to toe, given I would no longer turn into silly string? Could I use such a time gradient to time travel?
Luboš Motl says:
May 4, 2011 at 11:43 pm
It’s been an old-fashioned, happy project. But the accuracy of the frame dragging has been an immense disappointment.
With the nearly 20-percent error of the final figure, they would barely prove, at the 5-sigma confidence level, that the effect was nonzero and had the right sign…
Become a climate scientist. Having the right sign isn’t important, and one sigma is enough. (Do I really have to put /sarc there?)
Leif Svalgaard says:
May 5, 2011 at 8:34 am
Nothing can move through space faster than light, but space itself can expand [and does] at any speed. Some of the farthest galaxies found have a red shift in excess of 10 http://cosmiclog.msnbc.msn.com/_news/2011/01/26/5920882-hubble-spots-farthest-galaxy-again which if the galaxy was moving through space would amount to 10 times light-speed.
So does this mean that light emitted past a certain point in the expansion of the distance between us and a star would never reach us because it would need to be faster than light to overcome the expanding? How would this look different from the rest of the universe collapsing behind an event horizon (which of course does not require much speed at all)?
So many questions…so few answers…
Naive question, but is the concept of gravity as a product of the distortion of space-time considered by its proponents to adequately explain the apparent conundrum of gravity acting instantaneously at a distance?
/Mr Lynn
Carla says: May 5, 2011 at 1:22 pm
goes to show..behind every great man.. is a great woman..
The agreement between Einstein and Maric was made at the time when there was no certainty that Einstein would receive Nobel Prize some 3 years later. Eventually whole amount was supposed to be paid into Swiss account, and ex wife was expected to receive annual income.
However Einstein did not ‘honour’ the agreement, he secretly (as archive correspondence confirms) invested large part of the money in the American stock market and lost everything in the subsequent crash.
Two important points here:
1. Why Mileva Maric would insist on the Nobel Prize money if it was awarded, and not on some more immediate and more certain financial settlement.
2. Albert Einstein did not keep his word.
Perhaps, at least a share of the Prize went to a person who deserved a share, but it was not recognised as such.
Einstein said himself: “The secret to creativity is knowing how to hide your sources.”