NASA Gravity Probe Launched 223
ping pong writes "Forty-five years in the making and 24 hours late, NASA launched the $700 million satellite into orbit today to test Albert Einstein's general theory of relativity. The satellite, which was inserted into a polar orbit, will spend two months getting ready, then 16 months making measurements." NASA's mission news has more.
And if his theory is proved wrong... (Score:5, Funny)
Re:And if his theory is proved wrong... (Score:2)
No, relatively speaking you are a frost pist.
Cheap shot (Score:5, Funny)
Re:Cheap shot (Score:2)
Re:Cheap shot (Score:3, Funny)
That's a lot of money to spend (Score:5, Informative)
Stanford has a great overview of the mission [stanford.edu]. It's in pdf format.
Why has it been in the making for so long? (Score:5, Informative)
The correction to the precession will be on the order of arcseconds (1/3600 of a degree) per year.
There are some very good general relativists who have very severe reservations about this project. If they do detect a signal, I suspect it will be more of a testament to the power of experimental precision rather than a test of GR, which practically every serious physicist believes to be correct.
It's also worth noting that if nothing is seen, it's more likely than not due to the difficulty of detecting such a small signal.
Re:Why has it been in the making for so long? (Score:2)
Re:Why has it been in the making for so long? (Score:2)
Many of the reasons were previously discussed in the previous Slashdot story, "NASA Gravity Probe Set for Launch [slashdot.org]."
Re:Why has it been in the making for so long? (Score:5, Informative)
The correction to the precession will be on the order of arcseconds (1/3600 of a degree) per year.
It's significantly smaller than that -- the precession due to frame dragging is predicted to be only 0.04 arcseconds over one year.
And I agree that the physics community is 99% confident that the Lense-Thirring effect is real. However, I also think this is more because of the aesthetic beauty of the theory, rather than actual measurements. If it were a less fundamental theory being tested I would call it a waste of money, but for something as fundamental as GR I think a confirming direct experiement is justified.
The real question is how many viable alternatives to GR are ruled out by this test, assuming it is successful. For example nearly all viable GR alternatives proposed have weak gravitational wave properties identical to GR, so detecting these waves provides little support for GR. I wonder if the Lense-Thirring frame-dragging effect is more discriminating.
Of course, by far the more interesting case is if the effect is not observed. They seem to have many sigma of signal to noise here, so a null result would be pretty compelling.
Lense-Thirring effect exists (Score:2, Informative)
The Lense-Thirring effect has been observed: http://www.iop.org/EJ/abstract/0264-9381/17/12/30 9
There is no null result. However Gravity Probe B will increase the accuracy of the measurements DRAMATICALLY. Progress in physics has always been made by:
1. new ideas
2. high accuracy measurements allowing to discriminate between those i
Re:Why has it been in the making for so long? (Score:2, Insightful)
Err... I don't think so... every serious physicist strongly believes that relativity laws are an excellent model of the behaviour of the universe in the macroscopic scale.
Science is inherently an asymptotic quest for the truth. Any serious scientist knows that.
Re:Why has it been in the making for so long? (Score:2)
You mean just like every serious physicist believed Newtonian mechanics to be correct till the early 20th century?
Re:Why has it been in the making for so long? (Score:3, Interesting)
Me, I'm hoping we find a divergence with the GR expectation. Some inexplicable data will hopefully inspire a future Nobel Prize winner into making sense of the contradictions and get us a unified theory that can be tested.
Re:Why has it been in the making for so long? (Score:2)
That's the whole point - if they prove the effect, then we no longer have to 'believe' it to be correct
I know, I know - it'll still only be a theory, but it'll have yet more experimental evidence confirming it, which is a good thing(TM).
It's also worth noting that if nothing is seen, it's more likely tha
Re:That's a lot of money to spend (Score:5, Insightful)
Gravity is one of the most important, and least understood forces in the physical world. Mars is just a big rock in orbit around our tiny little sun. Going there is a cooler project that this, but the information garnered from such a mission seems to be less important than what this mission is set to show.
Re:That's a lot of money to spend (Score:2, Insightful)
Re:That's a lot of money to spend (Score:5, Interesting)
Re:That's a lot of money to spend (Score:2, Interesting)
Re:That's a lot of money to spend (Score:5, Insightful)
I think it's really a cheap experiment, considering the importance of the results. If there's something wrong or incomplete in Einstein's theory, we (as in humanity) should know about it, firstly because it's the human nature to try to know more all the time, and secondly because it could be very important in practical terms: you wouldn't want to take a plunge off a cliff with your SUV because your GPS receiver had a slight error, would you?
This is theorical science and experimentation at its best. The price is really cheap to advance mankind's knowledge. Compare this to the weekly cost of certain recent military activities that probably won't bring back much to mankind anytime soon...
Re:That's a lot of money to spend (Score:2)
Re:That's a lot of money to spend (Score:2)
Re:That's a lot of money to spend (Score:2, Interesting)
It turns out that gravity's second-order effects on time are much easier to measure than its second-order effects on motion. Gravitational redshift makes clocks on the Earth's surface run slow compared to clocks far away, to the tune of about 40 microseconds a day. GPS relies on timing differences between signals from
Re:That's a lot of money to spend (Score:3, Funny)
Please explain the downside of SUVs plunging off cliffs...
Re:That's a lot of money to spend (Score:3, Insightful)
Re:That's a lot of money to spend (Score:5, Insightful)
it seems like a lot of money to spend just for testing his theory. I think that recent missions to mars were a bit more interesting.
That boils down to less than $3 per American, spread out over the last 40 years.
To prove conclusively (or not) our most fundamental theory of gravity, space, and time.
Man, you are a cheapskate.
Re:That's a lot of money to spend (Score:2)
Re:That's a lot of money to spend (Score:3, Informative)
Re:That's a lot of money to spend (Score:2, Interesting)
Regards,
Steve
Re:That's a lot of money to spend (Score:2)
Probe componentry (Score:5, Funny)
One of these components can't be had from Sharper Image : can you guess which?
Re:Probe componentry (Score:2)
I believe the third component [sharperimage.com] has been accounted for. NASA engineers will be utilizing Vol. 2 Track 3 in all further netmeeting conferences for their opening exercises.
Re:Probe componentry (Score:2)
A Great Man (Score:5, Insightful)
Re:So did Marx ... (Score:3, Insightful)
Re:So did Marx ... (Score:3, Informative)
Re:So did Marx ... (Score:2, Insightful)
Re:So did Marx ... (Score:2)
They killed that many people attempting to set up communist regimes, and failing. In another 50 years, mass graves will be the only thing left to remind us of communism. I don't think this was quite what Marx had in mind (not that this absolves him from blame).
Re:So did Marx ... (Score:2)
Selected quotes from The Communist Manifesto (feel free to check them against another translation):
the first step in the revolution is. . . to win the battle of democracy
the proletari
Marxism != Stalinism (Score:2, Insightful)
Im not going to go into it now, however, his ideas have almost never used. There has arguabley never been a genuine Marxist/Communist government. Possibley in Chile, for a short while, under Salvador Allende, untill the US killed him (and put Pinchet in charge to rape the country, and kill whomever he pleased).
Sure, many people argue that communism wasn't "true" communism as Marx defined it.
Ami
Perfect Quartz Spheres (Score:5, Interesting)
A quick Google found this link [stanford.edu] with more cool details, including:
* The 1.5-inch diameter rotors are within 40 atomic layers (0.3 millionths of an inch) of a perfect sphere.
* "Electrical sphericity" must be held to parts in ten million.
* Each rotor spins inside a quartz housing with clearances to the rotor of barely one thousandth of an inch.
* To lift the rotor on earth takes 1,000V. In space, only a fraction of a volt is needed.
* In 1,000 years the gyroscope should barely lose 1% of its starting speed.
* To isolate the gyroscope from the Earth's magnetic field, it will be shrouded in four layers of lead balloons, plus an outer shield of iron.
Plus these cool facts (and a ton more), there are steampunk-styled drawings of the manufacturing process.
Seems like NASA could make some money selling the rejects (you know there are plenty) as the ultimate shooters [akronmarbles.com]!
Re:Perfect Quartz Spheres (Score:3, Interesting)
Compare the expected General Relativistic correction to the Newtonian contribution and you'll see why, the GR contribution is about 3-4 orders of magnitude smaller.
Case in point, it took hundreds of years of observations of mercury to determine its orbit precessed by 5599 arcsec
Re:Perfect Quartz Spheres (Score:2)
As with CCD imagers, longer integration times with this instrument translate to higher and higher signal-to-noise ratios in the final data.
Lead balloons (Score:2)
No, this is more interesting (Score:3, Interesting)
I worked as a consultant for the company that was awarded the contract for working on the zerodur glass block that made up the housing for the gyros. They brought us in to try and teach machinists optical fabrication. The tolerances needed for this thing were unbelievable, extremely tough even for a master optician. They manufactured 3 housing blocks, one of them was destroyed during the rough machining process, and an optician trainee who was attempting to polish one of the precision lands
Scientists crossing fingers, pacing (Score:5, Funny)
Re:Scientists crossing fingers, pacing (Score:4, Informative)
Re:Scientists crossing fingers, pacing (Score:2)
is only true in the rest frame of the massive particle
(mc) = (E/c) - p
is the full special relativistic formula
also known as
E = gamma mc
or
(mc) = p_t - p_x - p_y - p_z
in the 4-vector notation
or
(mc) = p_0 - p_1 - p_1 - p_1
or
m = (p*G*p)
where we take the inner product with the metric G
in General relativity we just replace the Special relativity "flat" metric with a curved metric (and we take special care wrt nonorthogonal coordinate systems leading to the dual of vectors being covectors and n
alarm bells (Score:3, Funny)
ding ding ding ding ding!
is this going to be like Event Horizon where the probe travels to Hell and back and then kills most of us?
Re:alarm bells (Score:2, Funny)
The question is who funded it? (Score:2, Interesting)
Re:The question is who funded it? (Score:3, Funny)
Hey, but at least it is the most expensive...
Re:The question is who funded it? (Score:2, Interesting)
Re:The question is who funded it? (Score:2, Funny)
Re:The question is who funded it? (Score:5, Insightful)
Re:The question is who funded it? (Score:2)
Ok, at least the post-secondary education system isn't too shabby. The primary (and even secondary) education systems in the US are designed to turn most people into the mindless drones they were always destined to be anyway. It seems
Einstein... (Score:4, Interesting)
Public Service Announcement (Score:2, Informative)
Click here [google.com]
Re:Einstein... (Score:4, Informative)
Nope, he was cremated. However, his brain could be spinning in its jar [guardian.co.uk]
Remember, this was the man that came up with some of the most complicated theories in modern physics,
He used 'geddonken' experiments,
Gedankenexperimente, i.e. though experiments.
Re:Einstein... (Score:3, Interesting)
Many people had a mathematical understanding of Special Relativity waay before Einstein. You take the rules for Electricity and Magnetism and you immediately see that they don't work right when you add velocities like with Newtonian Mechanics. Newtonian Mechanics has Gallilean relativity. That's right, there was relativity before Einstein.
It is a straight forward exercise to see that Maxwell's Equations (for E&M) have Lorentzian relativity. That's right
Re:Einstein... (Score:2, Informative)
That statement is plain stupid. Dirac finished school in 1918 [st-and.ac.uk]. Einstein published the Special Relativity in 1905 and the General Relativity in 1915. Can you back up your statement?! Beside, it is well known that Dirac was a great admirer of General Relativity, considering the Einstein equations the most beautiful in physics. That is the reason Dirac chose GR as a research topic in 1923 as a young student in Cambridge ...
The Dirac generation might have had
Slow (Score:5, Funny)
Sounds like my girlfriend.
Girlfriend, huh? (Score:3, Funny)
An experiment in inertia? (Score:5, Informative)
That is, inertia in big science funding?
In 1995, the GP-B was described as the "only experiment ever devised to test [the existence of frame-dragging] [sfsu.edu]."
However, in 1997 NASA announced that it had successfully tested frame dragging [nasa.gov]. See also here [scienceweb.org].
Re:An experiment in inertia? (Score:2, Informative)
A black hole is a pretty extreme example of this, too, and such behavior around the singularity is more likely to have alternative explanations than said behavior around earth.
Yay! Hoorah for science, wooo!! (Score:4, Insightful)
Re:Yay! Hoorah for science, wooo!! (Score:3, Interesting)
Newton's Laws of Motion didn't become "bunk" all of a sudden when Einstein (and later QM) discovered holes in it.
The speed of light bit is actually really well tested. It really does take lots more energy to continue speeding things up near light speed, and the trend of that is completely consistent with it taking an infinite amount of energy to get a
about time travel (Score:2)
Re:about time travel (Score:3, Informative)
-J
Re:Yay! Hoorah for science, wooo!! (Score:2)
Sheesh. Let me paraphrase our 100 year old counterparts: "the atomic decay we call 'radiaton' is very well demonstrated. If this so called 'fission' device could be built, it would definitly destroy the entire planet."
Our theories simply do not work if somehow we can move faster than light. A more likely explanation t
Re:Yay! Hoorah for science, wooo!! (Score:2, Interesting)
Re:-1, Troll (Score:2)
Einstain did not say that the speed of light in a vacuum is the fastest attainable speed. He said that it would take an infinite amount of energy to speed up any object/particle that has mass to that speed from below that speed. And that has pretty much been proven.
It somewhat implies that the speed of light is a barrier, but it doesn't exclude the possibility of particles/objects that move faster than the speed of light, and it doesn't say any
Re:-1, Troll (Score:2)
Better understanding of gravity (Score:5, Insightful)
It's a force we can calculate for and predict but we still aren't completely sure HOW it works. So whether this mission proves or disproves Einstein's theories we should at least get data that will help bring us a step closer to understanding a significant force in the universe.
I'm really exicited to see the results in 2 years
We already have a better understanding of gravity. (Score:4, Informative)
The only way this probe will really teach us anything (outside of the engineering that went into its construction) is if it fails, spectacularly. Sadly, those "eureka" moments don't happen very often, and I wouldn't hold out much hope for one here. Then again, the Hipparcos data has caused some debate, while its mission was somewhat routine (although highly precise).
We already know that relativity is wrong (in the same sense that classical mechanics is wrong). This experiment is not designed to figure out exactly how relativity is wrong, rather it is designed to tell us if relativity is wrong at all. Since we already know the answer to that question, it isn't very helpful.
I'm not blaming the guys that worked on this project. There were political/financial/logistical issues that made this launch 20+ years too late to be useful. The PhDs awarded during this project are good, they did some nice work, most notably in materials science and fabrication, but other areas as well. It's just not very meaningful in the areas of physics/cosomology.
Oh well, that's what happens when science is a slave to beauracracy.
Re:We already have a better understanding of gravi (Score:2)
I've never heard anything about relativity being proven wrong, please explain further.
Re:We already have a better understanding of gravi (Score:2, Interesting)
But the purpose of this project is to determine whether all the pred
Re:We already have a better understanding of gravi (Score:2)
However, there is much room for a similar line of research to be done in the future that is very much like this.
Outerspace gravity experiments can do soooo much more than Earth based ones. Things like detecting gravitational waves at different energy ranges, !detecting the Axion!, and probing gravity at small ranges to detect the compactified dimensions of string theory.
Hopefully this can pave the way for the real stuff.
It was actually launched last week (Score:5, Funny)
Its experiments of relativity caused it to move close to the speed of light forcing the effects of time dilation to make it appear as if it was delayed 24 hours, when in reality it was launched long before its scheduled date.
Re:It was actually launched last week (Score:2)
Ah, that explains all these annoying Slashdot dupes [slashdot.org]!
Let's not forget (Score:3, Insightful)
Needless to say, much will need to be discovered even after a successful GP-B mission.
Probes (Score:2, Funny)
this is depressing. (Score:3, Funny)
Wow! (Score:5, Funny)
Sounds like my Girlfrind when we go shopping...
Isn't frame dragging a forgone conclusion? (Score:3, Insightful)
Is the presence of frame dragging a forgone conclusion, given that (a) gravity waves do not travel instantaneously, and (b) the moon is able to maintain a stable orbit around the earth, even though the earth itself is in motion?
My college physics were limited to 2 semesters, but I do recall discussions of a velocity component to gravity. To use more severe example than the earth and moon:
Pretend, for simplicity's sake, that the earth's orbit is circular, and is exactly 8 light-minutes in radius. By the time gravity waves reach the earth from the sun, 8 minutes have transpired, and the sun is certainly no longer in the same spatial position that it was 8 minutes prior. This means that earth is no longer orbitting what it "thought" it was orbitting (if you'll excuse the tongue-in-cheek anthropomorphization.) The only two ways I've ever heard of accounting for this are:
(a) gravity waves are not limited by C, and in fact gravity's effect is felt instantaneously
(b) there is a velocity component to the effect of gravity, that takes into account the speed and direction of travel of the object(s) involved.
I think (a) is pretty much out of favor, right? If so, that leaves (b). Thus, velocity matters... regardless of whether that happens to be linear or angular velocity.
Since rotation is angular velocity... does this not imply that frame dragging exists?
I'm definitely interested in replies from Physics whizzes on this one... it's bugged me for a while now.
Quick attempt at an answer (Score:4, Informative)
Just a grad student, still learning stuff, apologies ahead of time if it's wrong.
Attempt at an answer:
"Frame-dragging", as I understand it, goes all the way back to an old theory of the aether, that the aether is all around us, but is dragged by masses so that some oddball features of special relativity is explained. I'm not sure how this applies to the problem here, so maybe people use frame-dragging to refer to something else.
This part, though, how gravity works, is easier. Einstein's theory relies upon the stress-energy tensor. All forms of energy, including energy due to angular momentum and relative motions, are included in this. Binary pulsars precess and their orbits evolve in time, as do their rotation rates, as energy is radiated away gravitationally. There is definitely a contribution to gravity due to what you call "velocity components". Gravitational signals only propagate at c, so don't worry.
You can look at my first 2 posts on this topic if you like, but basically GR predicts that there will be a precession of this little spinning sphere that's very small and hopefully detectable. If we don't detect it, it's probably due to the difficulty of the experiment, not to the failure of GR.
Re:Isn't frame dragging a forgone conclusion? (Score:3, Informative)
Great spelling at einstein.stanford.edu (Score:2, Funny)
Moon.. naSa.. MOoN..NAsa..moo.... (Score:2, Funny)
Isn't this just NASA spin? (Score:3, Insightful)
The manned spaceflight missions have always had the justification that understanding the effects of zero gravity on humans over extended periods was sufficient to secure funding from the NSF and others but zero-G on humans has been tried and tested over the past 40 odd years and is no longer considered of interest to fundamental science.
The timing seems to indicate that NASA wants to show it can carry out fundamental science experiments even if the results aren't relevant to modern questions in fundamental physics. They even go so far as duplicate well accepted results in a field that has progressed well beyond the best precision of GP-B.
Politics and Funding (Score:2)
If the experiment goes as planned and detects measurable precession, the specific data could be promoted as a valuable piece of military inteligence to make aiming devices, tracking weapons, and positioning systems just a bit more accurate than anyone else on earth (One press release did say that the results weren't being publicly released; just the general findings). Which of course leads to more fu
I thought spin was half the point. (Score:2)
Finest Minds (Score:2)
We read too much sci-fi (Score:2, Interesting)
"Mechanically, the 1.5-inch diameter rotors are within 40 atomic layers (0.3 millionths of an inch) of a perfect sphere, rounder than anything within many light-years distance from us....Only neutron stars are rounder."
Now I know that here on slashdot such things as neutron stars are always only a synapse or two away from our collective consciousness, but I have to say that reading those words sent a shiver up my spine. A sentence th
Not always hard (Score:5, Informative)
A pretty simple idea; as once it cools down to equilibrium temperature, there'll be nothing to heat it up.
Re:Not always hard (Score:2, Interesting)
Re:Absolute Zero? (Score:4, Informative)
Re:hazaah (Score:3, Informative)
Some of us have know this all along (Score:2)
Re:What, no Bush bashing? (Score:4, Funny)