Slashdot Mirror
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.
could this post be considered a relatively first post?
We fail to understand the gravity of this situation.
Yeah, I guess I'm funny like that.
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.
Wireless News www.DailyWireless
The experiment uses three key components: a spinning sphere, a telescope and a star.
One of these components can't be had from Sharper Image : can you guess which?
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
The greatest men are those who keep shaking up the world even after they are long gone. Albert Einstein wasn't a businessman, or a soldier, but look how much research and spending has been affected by his findings. Kudos!
The most facinating tidbit from the NASA article is the absoutely beyond perfect Niobium-coated Quartz spheres at the heart of the ultra-precise gyroscopes.
A quick Google found this link 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!
Stressed? Me? Of course not. Stress is what a rubber band feels before it breaks, silly.
"E had just better equal MC squared...E had just better equal MC squared..."
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.
I think that Einstein would turn over in his grave if he knew that we were spending 700 million dollars to test one of his theories. Remember, this was the man that came up with some of the most complicated theories in modern physics, and he did it in his head. He used 'geddonken' experiments, and however useful it may be to 'prove' his theories, one has to wonder what he would think...
> will spend two months getting ready
Sounds like my girlfriend.
Norman Cook's Ode to Sl
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)
All quoting aside, I wonder what will or would happen if the theory of relativity turns out to be nothing but bunk. It wouldn't be the first time our scientists knew something, even if it were based partly on observation. I'm no physicist, but I know Einstein's made assumptions that haven't been proven wrong or right, for example the speed of light in a vaccum is the fastest attainable speed in the universe. Just because we haven't doesn't it doesn't. And what about the unexplainable increase in velocity of the voyager probe as it neared the edge of the solar system? When I read that article, I remember thinking "wouldn't it be great if I was alive to see such a monumental discovery, along the lines of 'the earth ain't flat no more'?" I think it'd be so cool (ok, interesting) if this experiment means we need to rewrite our laws of gravity.
Gravity is a force that effects everything in our universe (and in theory some other universes :P )
:)
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
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.
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?
What most people don't know is that it was actually launched last week.
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.
I really don't think the financial analysis is the correct one. I'm fairly sure the US will derive enough benefit to justify the cost, although the benefit is admitedly difficult to quantify and is amortized over the rest of our specie's existence. Does it matter if the rest of the world gets a free ride? They do pure science too, and we benefit. Science is a collaborative effort. This isn't some billion dollar defense department project seeking a military advantage over a perceived adversary. This is about scientific discovery and learning things that have never been known. In my cynicism concerning politics, I sometimes forget to be optimistic about the science.
>> My ultraviolent Linux switch video.
That the hope of theoretical physicists is to unite gravity with the other forces, understanding the why and how of divergance, and hopefully uniting quantum dynamics with general relativity (properly fund NASA!, GWB) creating one theory to explain them all.
Needless to say, much will need to be discovered even after a successful GP-B mission.
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!!!
Sounds like my Girlfrind when we go shopping...
I am become Troll, destroyer of threads
well it *is* 4/20 after all...
-
There's a question I wanted to ask the last time this probe was discussed on slashdot, but alas I discovered the discussion too late to be assured a viable discussion.
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.
HSJ$$*&#^!#+++ATH0
NO CARRIER
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.
Are you sure you're posting on the right site?
Not that I think the science isn't valid enough for NASA to afford this (they've obviously got money to burn) but isn't NASA trying this on as a means to validate their science budget from which they feed?
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.