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.
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Learn a lot more on testing Einstein’s theories here h/t Dr. Leif Svalgaard via email
wayne says:
May 4, 2011 at 4:23 pm
“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.”
It’s only the net acceleration due to gravity that is cancelled out. You are confusing that with the field density, which should be at a maximum at the centre of the Earth. (i.e. There should be no need to show an inverted dimple in the grid as proposed earlier.)
George E. Smith says:
May 5, 2011 at 1:18 pm
“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.”
Ah, I love sarcasm, but it seems to have got the better of you. The gridmap takes no account of the effect of the sun’s gravity. 😉
And the Curie temp affects magnetic properties (permeability, susceptibility, etc.) as I’m sure you are well aware, so if you’ve solved the problems of electromagnetogravitation then, please, don’t hold back.
“I always thought gravity had an infinite range …”
Yes. Looking carefully at the diagram I notice a “heliopause” in the drag frame, yet I doubt there should be any reason to expect any such dragpause, or spinpause.
Smokey, lacking a PhD is a problem for some of us.
Perhaps one could dress in a cape and give the ol “ant on the surface of a balloon= expanding universe” lecture?
http://wattsupwiththat.com/2011/05/04/einstein-proven-right-again/#comment-654069
Slacko says:
May 6, 2011 at 7:41 pm
wayne says:
May 4, 2011 at 4:23 pm
“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.”
It’s only the net acceleration due to gravity that is cancelled out. You are confusing that with the field density, which should be at a maximum at the centre of the Earth. (i.e. There should be no need to show an inverted dimple in the grid as proposed earlier.)
No, I wasn’t speaking of field density but acceleration. You think it would be at maximum but I know there is none at the center, in fact, no such field exists at all. It is just that if you could hollow out a room at the center of the Earth to perform an experiment you would find no acceleration from gravity at all, no curvature of geodesics, flat space and you would be weightless. Gravity in Einstein’s general relativity is not a field, I did mention that didn’t I, well, I shouldn’t have, my mistake, that is a conceptional effect of the curvature itself.
The dimple needs to be there for the lines shown seem to be representing the acceleration caused by the curvature and there isn’t any at the center and it does decrease linearly (if the density is constant) all of the way from the surface downward to the center. The general idea of that graphic is fine but for that tiny detail.
If you don’t believe it write a small program to integrate it numerically, maybe you have not been surprised by that very fact yet. Before I did that very thing a few years ago I didn’t realize that. Now I do so though others might learn a bit from my effort.
Bart said on Einstein proven right, again
May 6, 2011 at 5:05 pm
I should have pointed out that relative velocity of 98.36% of the speed of light would give a Doppler redshift of 10.
Doppler or cosmological red shift, it makes no difference. At a red shift of 10 the expansion speed is the equivalent of 10 x light speed, but since the galaxy is not moving at all we can easily see it. What happens is just that the wave length of the radiation is getting larger and larger, 10x in fact.
I think that I beginning to understand this a bit better,the equations of Newton and Einstein don’t deal with actual space and time just our measurement of space and time,Einstein though sees Gravity as a field rather than as an attraction between two objects.
Moderators, please do not let people who do not even know mathematics crowd the place with nonsense. This gentleman Louis Savain does not know simple differential equations, when he claims that dt/dt is constant means that time does not change.
He cannot understand the simple concept that variables are checked against each other and produce functional shapes in either space or time, not against themselves.
Has he not been given enough exposure? He has his own site anyway.
Bart, May 6:
I am pleased to be included in your discussion.
However, you are missing my point, and that is probably my fault, that the succession of events outside and inside of our bodies ARE what we percieve as time flowing. Just like the cogs on the gears in a clock, where one particular cog must meet another particular cog for the next pair to be able to meet, we have the sensation of time as events pass in succession in our field of view.
These successions will probably be at the same rate everywhere, happening at a discrete fraction of c, which appears to be a universal figure.
The Lorentz transformations make objects appear not to travel faster than light, but in their own frame they do. How would the rocket know when to stop accellerating and instead gain mass? And in reference to what?
I found that this view of time helped a lot when reading Einsteins book. You may say it led to my misunderstanding of the subject, but I am not so sure of that.
Leif Svalgaard says:
May 6, 2011 at 10:07 pm
“Doppler or cosmological red shift, it makes no difference.”
It makes a huge difference.
“At a red shift of 10 the expansion speed is the equivalent of 10 x light speed.”
The relationship you are using only holds in the low redshift regime.
Headbomb and Blackburne
Wot de Hell is going on?
Wicked Pediants.
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Bart says:
May 7, 2011 at 2:27 am
“Doppler or cosmological red shift, it makes no difference.”
It makes a huge difference.
“At a red shift of 10 the expansion speed is the equivalent of 10 x light speed.”
The relationship you are using only holds in the low redshift regime.
My point is that the expansion speed can exceed light speed as your graph shows.
I suspect that everything in G.R. could be explained by viewing space as a collection of processors (one per Planck unit of space) and matter as information.
For example, the more matter in the vicinity of any space unit would require more “processing time”. Hence, external to that unit, “time” would slow down. It would be interesting if someone (smarter than me) would try and determine a processing algorithm that would encompass what we see in physics. Or, maybe someone or team is already working on it.
It wouldn’t mean the analogy is correct, but it might lead to further insights.
Louis Savain;
The truth is that reasoning has nothing to do with credentials. It has to do with simple logic that everybody can understand. >>>>
Unfortunately sir, some reasoning is rather complex and cannot be reduced to simple logic that everybody can understand. Credentials or no credentials, some problems require genius to understand and solve. It may not require genius to understand their work, but it may require high intelligence and considerable education. What was a difficult (but solvable) problem for Einstein is a work of wonder for some who study for years to understand it and add to it through experimentation or other means, a matter of interest for some who understand it in general and can see the real world results of application of the better understood portions, and some people lack either the education (formal or otherwise) and/or intelligence to understand at all.
Einstein supposedly said everything should be made as simple as possible, but not simpler. Your arguments through out this thread are a classic example of over simplifying by an order of magnitude.
By analogy, almost anyone can be taught how to drive a car. Quite a few people can taught how to fix one. Some people, with the assistance of computers, can design working components for a car. Very very few people actually understand in detail exactly how the explosion of the fuel/air mixture in the combustion chamber works to the point that they can improve upon it.
By your thought process, cars don’t work because you demand a simple explanation for what happens in the combustion chamber, and there just isn’t one. Unfortunately, millions of people who also don’t understand, and couldn’t if they wanted to, get into their cars every day and drive around.
Leif Svalgaard says:
May 7, 2011 at 5:26 am
“My point is that the expansion speed can exceed light speed as your graph shows.”
Yes, according to current theory, it can. But, that is old news to me. What I am perplexed by is that, I was taught that nothing could be observed beyond the Hubble radius. That’s no problem, as this object falls within the Hubble radius (13.2 Mly versus 13.8 Mly). But, with a Hubble constant of ~71 km/sec/Mpc, that translates to a recession velocity of 0.96 times the speed of light. Yet, the Wikipedia chart I linked to says it should be about 1.3 to 2.3 times the speed of light if the redshift is 10.3.
I’m not sure how this redshift number is being calculated or what it means. Have to go back and brush up on the subject…
davidmhoffer says:
May 7, 2011 at 9:33 am
blah, blah, blah
Time cannot change by definition and nothing can move in spacetime for a very simple logical reason that even school kids can understand. If you don’t get it, don’t blame me. Blame yourself. You are either mentally challenged or you are one of the deceivers. See you around.
anna v says:
May 7, 2011 at 1:34 am
Moderators, please do not let people who do not even know mathematics crowd the place with nonsense. This gentleman Louis Savain does not know simple differential equations, when he claims that dt/dt is constant means that time does not change.
Don’t blame me for your own stupidity. And trying to shut me up is not going to work. I’m planting seeds all over the place and there is nothing you can do about it.
REPLY: Actually yes there is, your behavior is getting out of bounds – so since you said in the previous comment “see you around”, I plan to enforce that stated position of yours, even if you write another whiny blog post about it like you did last time you were snipped by a moderator. – Anthony
Dan says:
May 7, 2011 at 2:05 am
“These successions will probably be at the same rate everywhere…”
This is very tricky topic. It plays all sorts of havoc with our intuition. Indeed, the first place to start is in defining time. What is time? We tend to think of time as fundamental, as some underlying absolute bedrock of reality. But, it is actually nothing of the sort. It is completely relative. How many clock ticks take place before we perceive we have digested a big meal, for instance? The time we take to digest the meal is relative to the time it takes for the clock to tick N times.
The number of clock ticks needed for us to digest is more or less set, at least locally. If we are near the clock, it will generally require N ticks for us to begin feeling alert and hungry again. But, that does not necessarily mean that a clock somewhere else will tick N times before the clock and our digestive system agree that it is time once again to eat.
It is unfortunate that students are introduced to Special Relativity as depending on relative velocity. It really does not. If, at the moment of creation, two spaceships were brought into being traveling at a constant speed toward one another, then their clocks would run at the same rate, and they would agree on the time since creation when they passed each other. But, in the real world, this relative velocity can only be achieved by one or the other or both objects accelerating away from and then toward one another. Accelerating your spaceship causes your clock to tick slower relative to an identical unaccelerated one. This is how the fabled “Twin Paradox” is resolved. In some sense, you see, accelerating through space builds up a resistance to change in time, relative to how it would have been had we not accelerated. We do not perceive the change locally, in a region which has accelerated with us. But, things have changed, relative to the region we accelerated away from.
And, therein lies the answer to your question:”How would the rocket know when to stop accellerating and instead gain mass?” It gains mass continuously as it accelerates. Its mass is still the same relative to anything which accelerated with it, but it has increased with respect to objects and observers which it left behind. And, all that means is that its trajectory relative to those observers will evolve as though its mass were the greater value.
This reply is getting pretty long-winded. Hopefully, it is of some use to you.
Bart says:
May 7, 2011 at 11:31 am
– 13.2 Mly versus 13.8 Mly should have been 13.2 Bly versus 13.8 Bly.
Bart says:
May 7, 2011 at 11:31 am
What I am perplexed by is that, I was taught that nothing could be observed beyond the Hubble radius. That’s no problem, as this object falls within the Hubble radius (13.2 Mly versus 13.8 Mly).
Because of the expansion of space we can actually see out to a distance of more than 40 Gly, because what we now see at 13 Gly was emitted 13 Gyr ago, but is now actually some 40 Gly away.
Bart,
thank you for taking the time to reply to my comments, as well as many others.
You say that both space and time are warped.
Analogies are often made of warped 2 dimensional space. These can be convex or concave, and result in geometry where the angles of a triangle do not add to 180 degrees, or the ratio of the circumference of a circle to the diameter is not pi. However, when you examine these warped planes, the result occurs because the plane is warped into the third dimension. Therefore, if 3d space is warped, it must be warped into a fourth dimension of space. The problem is, in the GR model there are only 3 dimensions of space and 1 of time.
The definitions of space being warped include the fact that the internal angle of a triangle does not add up to 180 degrees. How do you construct such a triangle? By projecting a laser beam. If it was the case that the angles did not add up to 180 degrees, it would be because gravity is bending the light beams. Is it not the case that the bending of light by gravity is being used as a proxy for bending of space? In classical Newtonian physics, the bending of light by gravity would be explained as just that – bending of light by gravity – not as warping of space. Therefore, this warping of space is just a mathematical contrivance to base geometry on the path of a light beam.
In the physical sense, space is not warped because there is no other dimension to warp it into.
Louis Savain says:
May 7, 2011 at 11:41 am
“Time cannot change by definition.”
I know… don’t feed the troll. But, I just had to chuckle at this. It reminded me of Gavin Schmidt opining on the appropriateness of global average temperature as a metric for climate change, saying ‘“Climate sensitivity” is *defined* as being the equilibrium response of the global mean surface temperature to a change in radiative forcing while holding a number of things constant…’
Science is so much easier if you can just force Nature to obey your dictates via definitional fiat.
Leif Svalgaard says:
May 7, 2011 at 12:51 pm
“Because of the expansion of space we can actually see out to a distance of more than 40 Gly, because what we now see at 13 Gly was emitted 13 Gyr ago, but is now actually some 40 Gly away.”
We cannot “see” something until the light gets here. But, I see your point. So. 0.96c*40/13 = 2.9c, which is consistent with the chart and a redshift of 10.3. But, that is an anticipatory redshift. Weird, but perhaps that is what is meant.
Bart says:
May 7, 2011 at 1:23 pm
We cannot “see” something until the light gets here.
One more time: what is now at 40 Gly we see because its light was emitted 13 Gyr ago and thus has ‘just’ got here.
Vince Causey says:
May 7, 2011 at 1:02 pm
“In the physical sense, space is not warped because there is no other dimension to warp it into.”
This was the genius of Riemann, who freed differential geometry from the confines of embedded manifolds and allowed them to be generalized into the abstract. You do not have to have another dimension to warp it into.
Here’s an analogous situation that might resonate. Consider a two dimensional surface embedded in 3-d space. Suppose you are a two dimensional being living in a seemingly infinite plane. The plane is spinning about its center of mass in 3-d space, but you don’t know that, because all you can perceive lies in the plane. All you know is that, when you are at a particular spot, you feel no force against you. But, when you move away from it, you are pushed farther away from it, and pushed harder the farther you go. To you, your space is warped, and wants to channel you in a particular direction (away from the spot).
I can’t visualise empty space being warped or bent because I don’t think it has that property ,force will pass through empty space without affecting anything.Empty space is just empty space,I can’t visualise empty space bending and causing light and matter to follow a bent path even if that is true.
Leif Svalgaard says:
May 7, 2011 at 1:51 pm
“One more time: what is now at 40 Gly we see because its light was emitted 13 Gyr ago and thus has ‘just’ got here.”
One more time: We cannot “see” something until the light gets here. The light traveled 13.2 Bly, not 40 Bly. It left the object 13.2 Byr ago.