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
Z says:
May 5, 2011 at 2:49 pm
Bothers a bunch of people. Data-mining is even more environmentally unfriendly than gold mining with nukes and aerosolised mercury…
It shouldn’t, because all that means is that they learned to understand their instrument, lending more credence to their result.
does it not count because it isn’t gravity
It doesn’t count. You could have the same effect just standing on the floor. In both cases there is a force balancing gravity.
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
You certainly could [e.g. a rocket motor] to prevent getting close to the hole, but once you are inside the event horizon, no force can saved you.
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?
Yes, but there is an even more fundamental limit. We can not see anything further away than the age of the Universe allows us. Light from a galaxy 1 billion light-years away we’ll never see.
So many questions…so few answers…
We actually have answers to most of this. There is a dearth of good questions.
Leif – I’m not asking about general relativity, and a page of stuff that doesn’t address my specific problem with this is of no use to me.
My post is here: http://wattsupwiththat.com/2011/05/04/einstein-proven-right-again/#comment-653506
If the mass of the Earth is warping space around it which is what is then pulling in stuff which is gravity, it can only be doing this exactly as in the diagram, on a plane. It cannot be extrapolated to three dimensions. Because gravity is happening on every part of our Sphere. The warping then is equally so in all directions from the Earth. These cancel each other out. Therefore, there is no warping.
Since there is zero warping, what are these measuring? A honey surrounding the Earth is not a description of a two dimensional warp field. It’s a something that is being moved about by the spinning Earth in a zero warp field.
Unless you can explain directly and specifically how space is warped in three dimensions in our real three dimensional world, then the concept of there being a warp in space around our Earth into which things are pulled which is gravity is wrong.
While I was posting my previous post, I was thinking that this reminded me of some of the problems I have with AGW explanations and some examples I’ve come across while exploring this. One of which is that NASA had to junk the Stefan-Boltzmann stuff 40 years ago because it wasn’t accurate enough for its moon projects, it related to a flat Earth and they needed to work in three dimensions. Another example is, can’t recall the ‘laws’ offhand, anyway, it’s in measuring the amount of oxygen in the blood by shining a red and a near infrared light through the finger in an oximeter, they each are obsorbed differently and the final measurement has to be adjusted to compensate for the fact that the two ‘laws’ used don’t actually relate to real world conditions.
But, it seems to me. That there is something much more intrinsically wrong with the space warp concept. It is simply unrealistic in a three dimensional world because such a reaction of a body warping space all around it would cancel out the warp, so leaving a zero warp. So that can’t be an explanation for gravity.
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?
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Good question. I consider it a terrible analogy.
SamG says:
May 4, 2011 at 4:47 pm
I don’t get why the warping of space time is depicted as occurring on a single plane. Is this for illustration purposes only? I would have thought a large body bends space time in every direction.
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It’s difficult to visualize 4d spacetime and a 2d surface. It’s suppose to convey that matter tells spacetime how to bend, and spacetime tells matter how to move.
To Leif Svalgaard:
You may have set yourself up as the in-house physics expert on this blog but the inconvenient truth remains (in spite of your uneducated denial above) that nothing can move in spacetime and time cannot change by definition. Therefore, there is no time dimension as you, Einstein and the rest of the relativist crowd insist and have insisted on for a hundred years. This is rather sad (and almost inexcusable) because many generations of students have been brainwashed into chasing after a red herring. What a waste of intellect. And what a calamity for the world in terms of inhibiting scientific progress and prolonging human misery.
How to Falsify Einstein’s Physics, For Dummies. Read it and weep.
[Second try. It seems that my comments are no longer accepted by Anthony]
To Leif Svalgaard:
You may have set yourself up as the in-house physics expert on this blog but the inconvenient truth remains (in spite of your uneducated denial above) that nothing can move in spacetime and time cannot change by definition. Therefore, there is no time dimension as you, Einstein and the rest of the relativist crowd insist and have insisted on for a hundred years. This is rather sad (and almost inexcusable) because many generations of students have been brainwashed into chasing after a red herring. What a waste of intellect. And what a calamity for the world in terms of inhibiting scientific progress and prolonging human misery.
How to Falsify Einstein’s Physics, For Dummies. Read it and weep.
Anthony,
Why are you no longer accepting my comments? A simple explanation would be the honorable thing to do. You are doing the same thing regarding relativity that the global warming alarmist are doing regarding climate change science. Shame.
Myrrh says:
May 5, 2011 at 3:37 pm
It is simply unrealistic in a three dimensional world because such a reaction of a body warping space all around it would cancel out the warp, so leaving a zero warp. So that can’t be an explanation for gravity.
Your problem is with the 2D analog of space warping. As I’ve said that is a somewhat misleading image. From the page you wouldn’t bother with: “At its core are Einstein’s equations, which describe the relation between the geometry of a four-dimensional, pseudo-Riemannian manifold representing spacetime, and the energy-momentum contained in that spacetime.[32] Phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories), correspond to inertial motion within a curved geometry of spacetime in general relativity; there is no gravitational force deflecting objects from their natural, straight paths. Instead, gravity corresponds to changes in the properties of space and time, which in turn changes the straightest-possible paths that objects will naturally follow.[33] The curvature is, in turn, caused by the energy-momentum of matter.”
Curvature [warp] can be defined in any number of dimensions. I’ll try one more time: http://en.wikipedia.org/wiki/Theoretical_motivation_for_general_relativity gives a backgrounder that you should read and try to understand. You can ask specific questions about specific points of that exposition and I’ll try to explain. It is not good enough that you simply say “I don’t get it”. It takes an effort ‘to get it’. Make that effort.
Juice says:
May 4, 2011 at 4:51 pm
I still don’t see how you can drag space. I can see gravity warping space (can I?) but I don’t get why spinning drags it. It’s as if we have the luminous aether again.
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It’s not dragging space – it’s dragging spacetime. Newtonian gravity, i.e., space + time, don’t predict the effect.
Hey Anthony,
Why are my comments being rejected? Why are you censoring me while giving the resident relativist deceiver, Leif Svalgaard, a free rain on your blog? Do you have one standard for climate change and another for relativity?
[Reply: I am doing most of the moderating today, not Anthony, but other duties have been a priority and I haven’t approved comments as quickly I normally do. You are not being censored, your comments have been posted. But you should be cautioned against referring to Dr. Svalgaard, an esteemed solar physicist, in derogatory terms. If you continue, your comments will be deleted. ~dbs, mod.]
Louis Savain says:
May 4, 2011 at 10:18 pm
Do you realize that you are confusing the observed motion of a ticking clock with changing time? Clocks do not measure changing time. They only measure static and abstract temporal intervals.
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I think you’re confusing time intervals. The clock in your rest frame should tic at a constant rate (within acceptable precision limits) – otherwise it’s not a clock by definition.
If a second identical clock is moving relative to you at speeds approaching the speed of light, and you use the clock in your rest frame to estimate it’s tick rate, the tick rate of the second clock will change.
Can you guess how it will change? If not, then you need to review the special relativity portion of the book.
Robert Geroch’s book is a great little book on both special and general relativity is highly recommended for anyone curious about relativity.
Leif – again with the free fall in your explanation*, as you’ve given me in a previous discussion and as above, is not what free fall means. So I still don’t understand what you’re saying and it will continue to not make sense to me because it is apparently based on a two dimensional understanding of mass. I can’t follow your explanations on four dimensions because the base is not logical in three dimensions.
Can’t you just answer my three dimensional problem? If there is something called space (or space/time) in which a body impinges warping it, then it must be impinging on it equally with all its mass in every direction, which cancels all the impinging out.
[*You said re free fall: “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.”
This is not the definition/explanation of free fall, which is, that it is only gravity acting on it. So, the Earth feels the Sun’s gravity.
]
Watts up?
Sorry – that free fall info from: http://www.physicsclassroom.com/1dkin/u1l5a.cfm
aggh. http://www.physicsclassroom.com/class/1dkin/u1l5a.cfm
missed the class..
The Physics Classroom – Physics Tutorial – One Dimensional Kinematics Lesson 5
Free Fall and the Acceleration of Gravity
Myrrh says:
May 5, 2011 at 4:32 pm
not make sense to me because it is apparently based on a two dimensional understanding of mass.
That statement does not make sense to me
I can’t follow your explanations on four dimensions because the base is not logical in three dimensions.
Again, does not make sense to me. Spacetime is warped in four dimensions.
Can’t you just answer my three dimensional problem? If there is something called space (or space/time) in which a body impinges warping it, then it must be impinging on it equally with all its mass in every direction, which cancels all the impinging out.
And why would that be? And spacetime does not have three dimensions, so why are you hung up on a ‘three-dimensional problem’?
This is not the definition/explanation of free fall, which is, that it is only gravity acting on it. So, the Earth feels the Sun’s gravity.
gravity acting on it is not the same as feeling gravity. In classical terms we can say that the gravitational force of the Sun is precisely balanced by the centrifugal force of the Earth in its orbit, so that the Earth does not feel any residual force. Same thing with an astronaut in space. If he drops his hammer it will just float there right next to him. They are both weightless and ‘weight’ is just the force with which gravity presses you against the weight-scale. Now, in General Relativity there is no gravity at all, just the distortion of spacetime and a body simply moves in a straight line.
Myrrh says:
May 5, 2011 at 5:01 pm
Free Fall and the Acceleration of Gravity
more on free fall:
“In Newton’s view, astronauts in Earth orbit are in free fall, since they are in effect falling around the Earth [which is free-falling around the Sun]. They are accelerated by gravity toward the Earth, but their inertia in the direction tangential with their path results in a curved path around the planet. In essence, they are always missing the planet in their fall toward it.
One way to view this situation, is to note that gravity by itself does not produce a weight-like force (a g-force) that people can directly sense, since gravity acts upon all parts of the body and the body only senses mechanical stresses (which to a good approximation, gravity does not produce, by itself). Thus, even a person standing on the Earth does not actually feel the pull of “gravity,” but actually feels only the push of the ground, acting upward. If this push of the ground is suddenly removed (for example, in a free fall in an elevator), the person experiences weightlessness, because all the forces which have caused the sensation of “weight” have been removed, even though gravitational interactions continue.
Often, the terms zero gravity or reduced gravity are used to mean weightlessness as it is experienced by orbiting spacecraft. The idea of gravitation itself being greatly reduced in this situation is not technically accurate in the physics of Newton, although it is accurate in the physics of Einstein (general relativity).
Spacecrafts are held in orbit by the gravity of the planet which they are orbiting. In Newtonian physics, the sensation of weightlessness experienced by astronauts is not the result of there being zero gravitational acceleration (as seen from the Earth), but of there being no g-force that an astronaut can feel because of the free-fall condition, and also there being zero difference between the acceleration of the spacecraft and the acceleration of the astronaut.”
Leif – the problem perhaps is that I’m not making myself clear enough?
Your link to the Theoretical motivation for general relativity says:
“General relativity addresses two questions:
1. How does the curvature of spacetime affect the motion of matter?
2. How does the presence of matter affect the curvature of spacetime?”
Doesn’t address my specific point because it begins with an assumption that spacetime curvature exists.
I’m asking specifically about the diagram which may well call itself ‘space/time’ curvature, but is a description of how gravity works in space. It says, that gravity works by a mass impinging on something surrounding it that it can warp, bending it, so an object heading towards that mass will roll into the warped space, (however it does this while travelling in a straight line is irrelevant to me). The space is warped, that’s the claim.
I’m saying that can only be two dimensional, (exactly as in the diagram), because a mass will impinge itself in all directions equally, (if such a thing was happening), cancelling out all the individual impinging on all the points touching the surrounding space, in a three dimensional space.
So, there is no warp.
Louis Savain says:
May 5, 2011 at 3:51 pm
and time cannot change by definition.
So, what is the definition of time? And whose definition?
Stupid question,
in this thread i’ve read nothing can move faster than light (slow as it is),
due to problems with mass.
Yet, the “big bang” theory postulates ??, an expansion much faster than the speed of light. So, is there a speed limit or not?
u.k.(us) says:
May 5, 2011 at 6:00 pm
Yet, the “big bang” theory postulates ??
Actually: measures an expansion much faster than the speed of light. So, is there a speed limit or not?
There is a speed for moving through space[time], but not for the expansion of space. The farthest galaxy we know of sits motionless in space that currently expands at more than 10x the speed of light [we infer this from its measured redshift].
u.k.(us),
An excellent book that answers your question is Prof Brian Greene’s The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Highly recommended.
The expansion of the universe during inflation following the Big Bang was not bound by the speed of light, which is a universal constant – but only within the universe. Greene explains it much better, with very little math involved, except in the appendix. He has a talent for explaining the physics clearly, no matter what the reader’s education level. IMHO, only Asimov was better at explaining things. [Amazon has used copies cheap, and hundreds of good reviews. You can also read a random sample of the book.]
One thing that Prof Greene explains made me do a lot of thinking: he said that by using conservative numbers, physicists determined that if the current size of the visible universe was much smaller than a grain of sand, inflation would have made the total size comparable to the size of the earth.
Our visible universe has a radius of less than 14 billion light years. Even though we cannot have any effect beyond that limit [and vice-versa], that doesn’t mean the universe ends there. That’s just our grain of sand. As every year passes, the radius of our visible universe gets one light year bigger. And the universe is different for each of us, because each of us is in the center of our own 28 billion light year-diameter sphere. There is no ‘edge’ to the universe.
[Snip. Arguing with a moderator’s decision is pointless. ~dbs]
Myrrh says:
May 5, 2011 at 5:17 pm
I’m saying that can only be two dimensional, (exactly as in the diagram), because a mass will impinge itself in all directions equally, (if such a thing was happening), cancelling out all the individual impinging on all the points touching the surrounding space, in a three dimensional space. So, there is no warp.
A massless photon coming towards a massive body from a given direction will deviate from the usual Newtonian straight line and seem to follow a curved [warped] trajectory. This is observed everywhere around the mass and shows that the space is warped everywhere. The warping only depending on the distance from the mass. We see this at every solar eclipse [e.g. at the one in 1919 that made Einstein famous] or when receiving radio signals from spacecraft passing near the Sun. Thus space[time] is observed to be warped. This is an experimental fact. Einstein’s GR theory is the explanation of this [and many other effects that depend on warping]. That you don’t get it, is not a problem of understanding but of fixation with something you can’t even articulate to make sense. You see, in physics, the criteria is not if something makes sense [quantum mechanics does not], but if it has predictive power. GR predicts a frame dragging of a certain size. The experiment that is the topic of this thread has measured just such an effect in accordance with the prediction. This gives us confidence that the equations are a ‘correct’ description of how Nature works to the accuracy we can currently observe.
George E. Smith, no shielding from other masses. I keep thinking people here at least know enough to properly limit such simple examples themselves, my bad.