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NASA Gravity Probe Launched
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.
It's a pretty fascinating experiment, although 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.
Stanford has a great overview of the mission. It's in pdf format.
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This is an experiment designed to test the correction due to General Relativity of the thomas precession of a tiny spinning sphere.
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.
Wrong theory...E=MC^2 is a proven theory
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]."
However, in 1997 NASA announced that it had successfully tested frame dragging. See also here.
Only Women Bleed (Sex, Sharia remix)
The James Webb Space telescope, when launched, will be temperature controlled by simply putting a shield around it on the sun-side, keeping the telescope side cool and out of sunlight.
A pretty simple idea; as once it cools down to equilibrium temperature, there'll be nothing to heat it up.
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I hear there's rumors on the Slashdots
I believe that was to test the theory that changes in velocity affect time, whereas the current experiment is to test the theory that a rotating object affects time and space.
They put all the gyroscopes in a dewar with 1500 liters of liquid helium to keep it cold. Plus they get to use the helium that evaporates for the stabiliztion thrusters.
what sig?
That's special relativity. General relativity relates to gravity.
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You sure got a purty mouth...
Nope, he was cremated. However, his brain could be spinning in its jar
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.
Say no to software patents.
In all honesty, this probe won't tell us anything we don't already know. At the time the idea was proposed, it was useful. Since then, we've made more precise measurements of gravity and observed relativistic effects.
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.
Down with Saudi Arabia!!!
Alright, disclaimer first:
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.
The video's from PBS's Nova - The Elegant Universe - Newton's Embarassing Secret explains this.
Marx advocated revolutionary overthrow of the existing social order, and abolition of private property and religion. The goal was mandatory egalitarianism, where nobody can ever improve their economic status. Do you really think this can be accomplished without violence and dictatorship? Communism is not some wishy-washy philosophy that says we should all work for the common good and not be greedy; it demands that this system be imposed from above.
I do know, though, that time dilation is measurable and has in fact been measured. I don't remember the exact numbers, only that they were very small, since the Lorenz correction to a (non-relativistic) interval of time is a factor of sqrt(1-v^2/c^2), where v is the velocity of the object in question relative to the observer and c is the speed of light (roughly 3e8 meters/sec). What this means in practical terms is that the wristwatch of, say, an astronaut ends up being a tiny bit slow upon return to earth (that's in addition to, and separate from, timekeeping imperfections in the watch itself). Of course this effect is on the order of nanoseconds, so those guys don't get to file for overtime :)
On the other hand, the atomic clocks aboard GPS satellites most definitely do take this effect into account, and are detuned from their nominal frequency by some small tiny amount to compensate for this.
-H
You seem to misunderstand...time DOES slow down the faster that you're traveling. Einstein's famous twins paradox, for example. Imagine twins born at the same time, one is put on the on a spacecraft travelling through space at near-light speed (since C is unachieveable), and the other child grows up on earth normally. When the earth-twin is 30 years old, his space-twin returns, and is only 3 days old.
-J
Beer, now there's a temporary solution -- Homer Jay S.
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.
9
The Lense-Thirring effect has been observed: http://www.iop.org/EJ/abstract/0264-9381/17/12/30
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 ideas
That statement is plain stupid. Dirac finished school in 1918. 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 more success in Einstein's project in his old age to unify the fundamental forces in nature. Since Einstein grew up with only gravity and electromagnetism as the fundamental forces, Einstein naturally focused on these two. In modern physics, electromagnetism has been unified with the weak interaction and strong nuclear force, but the problem still remains how to make a theory to include gravity with these three other forces. So, one can hardly blame Einstein for failing where modern physic is still searching for answers.
bring it on! --- JFK