NASA Probe Validates Einstein Within 1%

An anonymous reader writes "Gravity Probe B uses four ultra-precise gyroscopes to measure two effects of Einstein's general relativity theory — the geodetic effect and frame dragging. According to the mission's principal investigator, the data from Gravity Probe B's gyroscopes confirm the Einstein theory's value for the geodetic effect to better than 1%. In a common analogy, the geodetic effect is similar to the shape of the dip created when the ball is placed on to a rubber sheet. If the ball is then rotated, it will start to drag the rubber sheet around with it. In a similar way, the Earth drags local space and time around with it — ever so slightly — as it rotates. Over time, these effects cause the angle of spin of the satellite's gyroscopes to shift by tiny amounts." The investigators will be doing further data analysis over the coming months and expect to release final results late this year.

Re:Finally! That took long enough.

[schwartzg]

True, it did take a while. But I'd like to think it was worth the wait. Also, for those who care, here is a link to the Stanford page http://einstein.stanford.edu/ [stanford.edu] it has the same info as the article along with more stuff about the project.

NOVA did episodes, helps visually

[priestx]

I spent a week watching all the Nova PBS episodes, learning about this and string theory. Even though I'm not a mathematician or physicist, it certainly caught my attention.

http://www.pbs.org/wgbh/nova/elegant/ [pbs.org]

This was a stanford experiment

[scubamage]

This was not a NASA experiment per se, it was a Stanford experiment. The original press release can be found here [stanford.edu]. The official stanford website also lists preliminary findings here [stanford.edu].

links

[SaberTaylor]

sciency details:
http://cosmicvariance.com/2007/04/15/dragging-on/ [cosmicvariance.com] (4:33 p.m.)

Also of interest if you're into this sort of thing, what Beyond Einstein programs will be cut?
http://scienceblogs.com/catdynamics/2007/04/beyond _einstein_iv_showdown_in.php [scienceblogs.com] (April 4)
sad if you compare sticker prices to the $10 billion per month on the Iraq adventure.

wikipedia article and cool picture

[Anonymous Coward]

I assume this is the project: http://en.wikipedia.org/wiki/Gravity_Probe_B [wikipedia.org]

And the probe itself is just astounding: http://en.wikipedia.org/wiki/Image:Einstein_gyro_g ravity_probe_b.jpg [wikipedia.org]

Re:Spinning Weights

[slazar]

Gyroscopes resist changes in angular momentum, not linear momentum. So it only has increased rotational intertia. If you were measuring the box's mass by trying to spin it rather than push it, then yes, it would appear more massive. But if you just pushed it in a straight line, then it would behave the same as if your gyroscopes were still.

On your second question, electrons and subatomic particles don't really spin, they have orbitals. Electron orbitals are the probability distribution of an electron in a atom or molecule. Take a look: http://www.orbitals.com/orb/ [orbitals.com] So it's not really like a gyroscope. But that is an interesting question, i.e. Do electron orbits effect the angular momentum of atoms? How would you measure that experimentally? Does Newtonian Physics operate on that level?

More info

[onx]

For some reason the article and summary only mention that Gravity Probe B was trying to measure was "minuscule" however, I at least find the actual quantity to be FAR more impressive than some journalist calling it small. Anyway want to know the precession?

Frame Dragging Effect (has NEVER before been measured): 1.1x10^-5 degrees per YEAR
Geodetic Effect: 1.8x10^-3 degrees per YEAR

Clearly then, these were not merely "minuscule" shifts...the potential for error is great.

More information can be found at http://www.nasa.gov/mission_pages/gpb/index.html [nasa.gov]

MOND approximates to GR in strong field.

[anandsr]

This means that there are no differences between GR and MOND in the gravitational limit that this test has been conducted. This means that MOND will have the same problem that GR has, if the tests don't come out as predicted. I guess in this case the tests will be considered to be faulty, as there are literally no theories (that are not considered crackpot) that give different results different from GR in the strong field regime. So the tests by Gravity Probe B will not make any difference, though it probably will give GR theorists something more to brag about.

There is a big misconception about MOND, that it is a theory. It is not, it is a law that works very well at the Galactic Level and somewhat at the cluster level. MOND fits all galactic level data to the limit of their expected accuracy. This it does so with a single universal constant. But nobody knows why it works so well.

As such it is very obvious there is something behind MOND. GR cannot explain MOND without fine tuning DM in such a way to give rise to MOND. But since MOND uses only Baryonic matter, it leaves DM with no degrees of freedom, which is not possible, so DM must not exist at the Galactic level.

At Cluster level situation is different MOND does not match up with the missing mass. Which means either there is Dark Matter at the Cluster level or MOND itself is a reasonable approximation of the correct theory of gravity only in the galactic limit. Beyond the galactic level it ceases to be a good approximation.

If there is dark matter at the cluster level then there must be a reason why it does not exhibit itself at galactic levels. This would meant that the dark matter is hot and moving at a high velocity, which allows it to form stable structure only at the cluster scales.

The interesting thing about the universal constant (a0) of MOND, is that if a particle is accelerated by a0 for the whole life of universe then we will get the speed of light. This would seem to provide a hint that a0 is due to the curvature of the universe.

This actually solves a problem in GR. If GR is absolutely correct then the curvature of the universe cannot be determined, which is also called the flatness problem. This problem is currently avoided by assuming that there was an inflationary era when the universe expanded so much that we only see a very small part of the universe which is flat. So that GR equations are correct. But if that is not true and the universe is not really that big then GR will break down because of no fault of itself, but simply because of the curvature of the universe.

So in my opinion GR is correct but the curvature modifies GR in such a way that we observe MOND.

Re:Spinning Weights

[Have Brain Will Rent]

This isn't quite what you are asking but most of the mass of an atom comes from the motion of the constituents of the protons and neutrons. In other words most (80%-90% IIRC) of what we perceive as the rest mass of an atom is actually not rest mass at all but relativistic mass attributable to the motion of quarks.

Late to work.

[pyro_peter_911]

Boss, I was late to work this morning because of frame dragging. I would have been here earlier if spacetime hadn't been warped and then twisted by my car.

Peter

Re:oops

[jpflip]

I was at the announcement at the APS April meeting a couple of days ago. My impression and that of the other physicists I've talked to was that this was darn impressive, but in the end disappointing.

This is a project that has been rolling along for four decades. Over that time, many of the things this experiment was designed to test have been indirectly tested using observations about binary pulsars. Now they're getting hit by incredibly subtle systematics in their apparatus (note that the apparatus was not misconstructed or anything, there are just some surprises that were too subtle to measure until the thing actually reached space). The worry is that the experiment is now not so interesting, even if they managed to beat down their error bars through blood, sweat and tears. If they confirm the predictions of GR everyone will say "gee, great". If they don't, people will be concerned about how well they really understand their error bars. Either way, they don't make the splash one might have hoped all those years ago.

Re:oops - Bingo

[mbone]

Bingo !

I was going to post this myself. The goal was to measure frame dragging. The geodetic effect has been measured before (LLR and binary pulsars),
and is not nearly as interesting (i.e., its hard
to see why you wouldn't have it). It's the frame dragging that motivated the decades of effort and expenditure.

If they can't do frame dragging, the experiment will be deemed a failure.

Re:1%? Consider Newton, Galileo, et al

[JetScootr]

Ptolemy said the planets circled the Earth in epicycles, and mathematically "proved" it to the accuracy of available instruments. This was good enough for about a 1000 years. Together, Newton and Galileo proved heliocentricity, but calculated ellipitical orbits, also wrong, and also within the accuracy of available instruments. Brahe and others eventually measured things so precisely that they were able to find that Newton had an error, but they didn't understand it. Later, someone (I forget who) was able to measure the orbit of Jupiter's (known) moons and show that the speed of light caused an apparent lag in their orbital motions. But planetary orbits still didn't obey Newton precisely.
The world had to wait for Einstein to get an explanation - space/time curvature, etc, predicted the variance from Newton's calculations.
Somewhere in all of this, British scientists predicted the existence of Australia by the wobble it causes in Earth's spin.
Failure of real world measurements to match theoretical predictions can lead to greater discoveries. Sometimes the failure is more significant than success would be.

It's called "Zeno's Paradox"

[JetScootr]

http://en.wikipedia.org/wiki/Zeno's_paradox [wikipedia.org]

Re:Spinning Weights

[wanerious]

One fascinating experiment demonstrates the Einstein-de Haas effect. The electron spins are randomly oriented in a non-magetized cylinder of iron, say, so the total angular momentum is 0. Now turn on an external magnetic field to align all the spins (enclose the cylinder in a solenoid) and, since the iron's total angular momentum now has a preferred direction, the cylinder will *spin* in the opposite sense. An amazing demonstration of "macroscopic" quantum stuff.

Re:I'll hazard three guesses.

[Kozar_The_Malignant]

>Who moded this person a troll, without posting a response?

You can't mod and post. One or the other, but not both.