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
I knew it!
I knew that that planet was hovering just metres above a giant solar spiderweb!
And people mocked me….
🙁
I asked:
Leif, are you denying that time cannot change by definition and that, as a result, there can be no motion in spacetime?
Leif Svalgaard replied:
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.
Wow. That’s a complete non-answer. 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. Amazingly, even a few well-known relativists agree with me that time cannot change. Here is what professor Robert Geroch wrote about the possibility of motion/change in spacetime:
Source: Relativity from A to B by Dr. Robert Geroch, U. of Chicago
Of course, Geroch would never publicly extrapolate the consequences of what he wrote in his book about nothing changing in spacetime. Why? Because that would bring a quick end to his career, thanks to people like you. Luckily, I have no such fear. Leif, it’s obvious that you are a truth denier. But why am I not surprised?
End of discussion.
I don’t think so. The discussion has not even begun. Repeat the following 1000 times a day until it sinks in:
Time cannot change by definition.
Nothing can move in spacetime
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. That is all. This is true whether or not you or Svalgaard or anybody else likes it. I must admit that I do get a sense of satisfaction from rubbing the scientific community’s nose in their own excrement. I can’t help it. It’s the rebel in me.
PS. I do note that Svalgaard studiously avoids the argument I posed. Which is to be expected.
The discussion of Monbiot’s essay at Judith Curry’s Climate Etc is also worth reading.
judithcurry.com/2011/05/04/monbiot-on-environmental-fixes/#more-3152
Assuming equal mass in all directions, at the centre of the earth, gravitational force would be equal in every direction, and give the impression of zero gravity. Two masses (the imaginary observer and the earth) must produce a force, even if those forces cancel.
Leif Svalgaard says:
May 4, 2011 at 9:38 pm
Time must run very slowly in a black hole, perhaps barely existing, unless there is some type of a limit to how strong gravity can become.
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…
http://motls.blogspot.com/2011/05/gravity-probe-b-final-results-frame.html
At any rate, one can’t be certain about the power of new experimental gadgets before they’re really tried.
Yes Anthony, I assure you Lief is entirely correct.
The classical view, for which read Einstein, is that at the speed of light mass and gravity become infinite and time ceases to exist in that it does not pass. This creates certain theoretical paradoxes.
Fortunately light does not travel at the speed of light, its group velocity, its actual speed, is always less than its phase velocity, its theoretical speed.
This relationship between mass and speed is elegantly demonstrated in the cathode ray tube where electrons are accelerated at quite low voltages to speeds at which the increased energy of the electrons starts to show up as increased mass instead of increased speed. It is actually very difficult to accelerate an electron beyond about half the speed of light, it just gets massier instead of going faster.
Much the same limitations in a different form presumably occur close to the event horizons of black holes.
Kindest Regards
Louis Savain says:
May 4, 2011 at 10:18 pm
Time cannot change by definition.
Time is what a clock shows. A clock can be oscillations of an atom: “a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”
David said it well:
davidmhoffer says:
May 4, 2011 at 9:26 pm
“Is there some genetic mutation out there that compels people to spew nonsense”
Keith Minto says:
May 4, 2011 at 10:49 pm
Two masses (the imaginary observer and the earth) must produce a force, even if those forces cancel.
Already Newton knew that the mass outside a spherical shell does not produce a gravitational field, only the mass within the sphere. At the center of the Earth, the radius [hence volume and mass] of that sphere is zero, hence no gravity.
rbateman says:
May 4, 2011 at 10:52 pm
Time must run very slowly in a black hole, perhaps barely existing, unless there is some type of a limit to how strong gravity can become.
There is probably a [quantum theoretical] limit, but time inside the event horizon does not run slowly for an observer there. It is the observer outside the horizon that sees the infalling clock slow down [as also shown by the light emitted getting redder and redder and dimmer and dimmer]
When will these physicists learn? They wasted decades of time and money designing. building and then sending a satellite into orbit just for an experiment. Don’t they know that that isn’t how you do science these days? How could you ever believe the results of an experiment like this? All they had to do was build a computer model and that’s all the proof they would have needed.
TerryS says:
May 5, 2011 at 12:06 am
All they had to do was build a computer model and that’s all the proof they would have needed.
You seem to have an over-inflated trust in computer models.
I wrote:
Time cannot change by definition
Leif Svalgaard replied:
Time is what a clock shows. A clock can be oscillations of an atom: “a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”
Complete waste of time. 🙂 See ya around.
Leif Svalgaard writes: At the center of the Earth, the radius [hence volume and mass] of that sphere is zero, hence no gravity.
Any kid who knows his Don Rosa, knows that: http://en.wikipedia.org/wiki/The_Universal_Solvent_(comics)
😉
Re: Leif
*sigh* forgot the /sarc
Louis Savain,
time changes not with dt/dt but with dt/dx.
As with a couple of others here, I still don’t understand what this warping of space time actually is, how does the Earth warp the space time around it as per the diagram since it must be doing so in all directions, unless this is all based on an idea of a flat universe? The honey the Earth is spinning in must be a something, an ether or whatever, which is being pulled around a spinning Earth ‘equally’ in a zero warp field, so there’s no warping only Earth spinning in something. And gravity then what? Does a spinning object attract or repel stuff around it?
In other words, can someone explain this in 3D before invoking a fourth dimension.
>>
Leif Svalgaard says:
May 4, 2011 at 11:58 pm
Already Newton knew that the mass outside a spherical shell does not produce a gravitational field, only the mass within the sphere. At the center of the Earth, the radius [hence volume and mass] of that sphere is zero, hence no gravity.
<<
Your statement is somewhat confusing (mine may be no better). A uniform sphere (constant density throughout) creates a normal gravity field outside (as if the mass was concentrated at its center-of-mass). However, everywhere inside the sphere, the gravitational force would be zero. As you (mathematically) move towards the center of the Earth, the outside mass sphere contributes no gravity force. The inside sphere is smaller and smaller and represents less and less enclosed mass.
This works for any inverse square law. The electric charge also follows the inverse square law and is why Von de Graaff generators work. The electric potential inside a metallic sphere is zero or at ground level. You can discharge a small potential charge to the inside of the metallic sphere, even though the total spherical charge may be several orders of magnitude larger.
It’s also why a Dyson sphere enclosing a star can’t orbit that star –there’s no inside gravity field for the star’s gravity to act on.
It’s harder to show mathematically, but a ring can’t orbit around a star either (as in Ringworld).
Jim
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.
Everything is relative….
A “brick” falls through the air faster than a “brick” sinks in water…
=> Gravity is a conceptual constant.
=> Gravity measurements are not absolute.
A “clock” ticks faster in space than a “clock” ticks on earth…
=> Time is a conceptual constant
=> Time measurements are not absolute.
the gyroscopes experienced measurable, minute changes in the direction of their spin as they were pulled by Earth’s gravity.
Well there is a surprise… opens eyes… rolls eyes.
>>
Louis Savain says:
May 4, 2011 at 10:30 pm
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. That is all. This is true whether or not you or Svalgaard or anybody else likes it. I must admit that I do get a sense of satisfaction from rubbing the scientific community’s nose in their own excrement. I can’t help it. It’s the rebel in me.
PS. I do note that Svalgaard studiously avoids the argument I posed. Which is to be expected.
<<
Since you think that Relativity is incorrect, then you must believe that our physics is only valid for the Earth. If we were to travel to another, distant galaxy, then their physics would be different?
Relativity is an old idea. It dates back to Galileo. It’s the idea that our physics is invariant with respect to reference frame. Newton’s three laws of motion are invariant under Newtonian-Galilean Relativity. Special Relativity makes Maxwell’s equations invariant with respect to inertial frames. General Relativity includes Special Relativity and makes Newton’s gravitation law invariant. General Relativity also includes both accelerating and non-accelerating frames of reference (among other things).
Most people who disagree with Einstein’s Relativity actually agree with the principles of Relativity. They just don’t like how the math works out.
Jim
Young Albert was a very smart guy.
Keith Minto says:
May 4, 2011 at 10:49 pm
Assuming equal mass in all directions, at the centre of the earth, gravitational force would be equal in every direction, and give the impression of zero gravity. Two masses (the imaginary observer and the earth) must produce a force, even if those forces cancel.
There you go, that’s a more proper definition. That has often made me wonder, since all matter resists compression, just where would the highest density inside the Earth occur? The center? Or at some distance toward the surface? Ahhh.. gravity, real strange effects sometimes.
Rabe says:
Louis Savain,
time changes not with dt/dt but with dt/dx.
Wow. I’ve never heard this one before. In physics, the only accepted evolution parameter is t. Sorry. Besides, if moving along the time dimension were possible, it would not require motion in any of the spatial dimensions.
But then again, you knew this. So why even write a comment?
Here’s another strange gravitational effect if curious:
Take a spacecraft approaching the asteroid belt, density evenly spread, and approaching in it’s plane. As you get nearer you would at first think you would be accelerating toward the approaching asteroids in front as they become visible.
Not so, when inside the orbit of the asteroid belt you would not feel it’s gravity at all. But, the minute you cross the belt’s boundary, if you make it across :-), you would immediately undergo a deceleration from the entire asteroid belt’s mass with its center of attraction near the sun. This deceleration would of course decrease at the inverse of the square of the distance, not from the nearby asteroids, but from the center of attraction near the sun.
That’s also a bit anti-intuitive. (and probably no, surely all of the physicists investigating the Pioneer’s anomaly took this strange effect into account (or did they? ☺))
Myrrh wrote:
In other words, can someone explain this in 3D before invoking a fourth dimension.
You’re wasting your time expecting an explanation that makes any sense from the relativist community. There are no people in physics more clueless than relativists. They understand absolutely nothing. They only confuse the hell out of everybody. They certainly have no clue as to why things fall. All that spacetime curvature nonsense is just that, nonsense.
Louis Savin – I’m not the only one here wondering about it. Are you saying we’re not going to get an explanation for this very simple basic question?