NASA Gravity Probe Set for Launch 250
The Real Dr John writes "NASA announced
yesterday that its longest running program, Gravity Probe B, was ready and
scheduled for launch on April 17th. The project has taken 44 years to complete,
at a cost of approximately $700 million. The reason for the high cost is that
the probe contains the most sensitive gyroscopic equipment ever created, which
will be used to test Einstein's theory of gravity. Einstein predicted that the
gravity created by a large body warped space-time, but he also predicted that if
the large body was rotating it would create a drag effect on space-time
known as frame dragging. Gravity Probe B will be able to test
Einstein's theory using Earth's relatively small gravitational field because the
instruments are so sensitive."
Too sensitive (Score:5, Interesting)
Interesting... (Score:2, Interesting)
More interestingly enough, what can we use this for? No, this isn't sarcasm, but how can we apply these scientific principals to help our daily lives and to understand the universe better?
Comments anyone?
Gravity Probe A (Score:2, Interesting)
(sorry had to ask)
Hopefully the start of another space race (Score:-1, Interesting)
Keep in mind that skilled labour costs in China are a fraction of what they are in the U.S.. The resources of China's space program could easily dwarf those of NASA long before their economy grows larger than that of the U.S.. (This assumes both nations spend a similar proportion of their GDP on their space programs. China may well value it higher and spend even more...) As has been said, they don't exactly have to reinvent every wheel that has led NASA to it's current cutting-edge 1970's shuttle program either. There are plenty of capitalists, many of them in the U.S., who would only be too glad to do a little Cantonese consulting.
This isn't necessarily how things will happen. However, if the Chinese don't do anything stupid their economic and technological superiority is functionally inevitable provided U.S. citizens don't start multiplying like mosquitoes. It's a simple matter of statistics unless you subscribe to some sort of white supremast movment and belive that Chinese minds are inherently inferior.
Personally, I'm thinking it might be a good idea to start early on those Cantonese lessons.
considering string theories (Score:5, Interesting)
Re:Gravity dragging? (Score:5, Interesting)
Of course, this effect also applies to light rays, so the question of what one would actually see is a bit tricky.
Another situation that 'frame dragging' alters from classical theory is orbits around the body. Imagine an observer fixed at a particular set of coordinates in orbit around a rotatng body. If they send photons in orbits around the body opposite directions, they will not be recieved at the same time; that which travels in the direction of rotation will arrive sooner than that travelling in the opposite direction. In extreme cases, it is possible that the photon opposing the direction of motion, although locally moving at the speed of light, won't appear to move at all from the point of view of a distant observer.
An experiment whose time has passed? (Score:5, Interesting)
In addition to the sensitivity problem, I wonder if this could be an experiment whose time has passed.
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 [sfsu.edu]. See also here [scienceweb.org].
Re:Einstein was a (gravitational) drag... (Score:1, Interesting)
I'm afraid I'm of the opinion that Einstein was partially incorrect in this matter. God does, indeed, not gamble with the fate of the universe, but he may well play dice/roulette with it. The universe is a macro object, even if it made up of an, ummmmmm, unGodly number of small "dice."
God is the house, and thus has house odds. The number of dice, and thus the sample size, at every instant, is always equal to that unGodly number of dice.
Thus God himself may lack omniscience in that he never knows what the outcome of any particular roll of a die is going to be, but on the scale that's relevant to anyone who isn't an atom or smaller ( and few of us are) things are perfectly mechanistic nontheless.
The idea that God is perfectly omniscient is a matter of religious dogma, even when applied to a sectarian pursuit such as science. Maybe God ( or whatever) made it that way on purpose because he isn't omnicontent and likes a bit of entertainment now and again. Just as he made that rock that's too heavey for he himself to lift for the challange of it. He'll be the judge of that, not the Pope or scientific theory. Empirical data always trumps dogma.
None of this has anything to do with the Copenhagen "Interpretation" or other such wishy-washy, quasi-mystical philosophies that have grown up around quantum theory. It's simply straight statistical analysis, such as is applied in the kinetic theory of gases.
KFG
Re:Too sensitive (Score:3, Interesting)
Re:Gravity dragging? (Score:3, Interesting)
You may be aware that elctricity and magnetism are intimately connected. In one sense magnetism is an extra force that moving electrical charges exert on other moving electrical charges.
Einstein discovered that gravity can work much the same way. Moving gravitational charges (i.e. masses) generate an extra force on other moving masses. This extra force is sometimes refered to a gravito-magnetism and is usually very weak except when high velocities or enormous masses are involved.
Gravito-magnetism works like ordinary magnetism in that the force is exerted tangetial to the direction of motion of the object. So if you are falling into towards a massive rotating object, then the net effect of all of the moving mass in the rotating body is to give you a little kick sideways, towards the direction of rotation. This makes in look like the straight paths near the rotating body have been twisted around and people refer to this effect as "frame dragging", like the massive body has put a twist into space.
Re:Too sensitive (Score:2, Interesting)
Will it be using a high or low, circular or elliptical, equatorial or inclined orbit?
(i'm sure the info is at the GP-B site, i just missed it)
The electrostatic suspension system also reminds me bit of a Stargate SG-1 episode, Serpent's Venom.
kudos and good luck. You launch on my birthday.
unclear whether it's worth it (Score:3, Interesting)
Very Cool Experiment (Score:3, Interesting)
And probably not much more expensive.
LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics. LATOR also seems to be much more accurate, and less likely to receive interference.
I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.
Cheers,
Justin Wick
Re:unclear whether it's worth it (Score:1, Interesting)
So what? It's usually possible to construct a bunch of theories that all describe one particular phenomena (though they don't agree on all phenomena). Should we stop observing phenomena?
Besides, while many of them have frame dragging, they don't all agree on the amount of frame dragging. GPB is sensitive enough to measure the strength of the dragging.
Well, we should always ask whether a given experiment is worth its cost. But we don't do experiments merely to judge between competing hypotheses. If GPB measured frame-dragging whose magnitude was incontroveribly different from that predicted by GR, then we'd know we'd have to develop a "decent alternative hypothesis" -- even if we don't have any now -- because GR would simply be wrong.
Re:Lets hope it works! (Score:2, Interesting)
Re:Very Cool Experiment (Score:2, Interesting)
Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any of those models are likely to be true, even if string theory itself is true.
It is, but it's also a test of something that we've already measured extensively (albeit much more sensitively). Our existing measurements of frame-dragging are extremely crude.
Why? And, so what? (Unless you're suggesting that GPB will receive so much interference that it won't work.)
The same is true of LATOR or of any other experiment, especially highly sensitive ones.
Re:Gravity dragging? (Score:4, Interesting)
Assume frame dragging exists. If you can find a body that does the gravitationaly lensing and if that body rotates, then the light rays you see coming from the multiple lensed images might produce an interference pattern.
Re:Too sensitive (Score:2, Interesting)
The magnet example was saying this: if you're an observer inside a magnetic substance, you will notice a "preferred direction": the direction the spins in the magnetic are pointing. Thus, there will be a "preferred observer" or "absolute reference frame": one oriented in the same direction as the spins. An observer inside the magnet can absolutely determine whether he is in such a frame: he merely has to measure the magnetization and see whether he's oriented in the same direction as it.
This is despite the fact that the laws of physics, and the laws of electromagnetism, have no preferred direction. Space itself doesn't come with magic arrows pointing in some particular direction. So how did the magnet acquire a spontaneous magnetization in a specific direction? That's spontaneous symmetry breaking. The spins start out aligned randomly, but just by chance, some spins will happen to be pointing more in one random direction then another, and they will pull others into alignment with them, so the entire material becomes magnetized.
Thus, the "total equation" -- the laws of atomic physics and electromagnetism -- do not and cannot predict a specific "absolute direction" in space. They are perfectly rotationally symmetric. Nevertheless, it is possible for a solution of those equations to break the rotational symmetry and acquire a preferred direction, just due to the random dynamics of interacting particles.
In the train example, the symmetry of relativity is not a rotational symmetry but a Lorentz symmetry, saying that there is no preferred state of inertial motion: there is no "absolute reference frame", and so you cannot perform an experiment to determine your "absolute velocity" in space with respect to such a frame. But if Lorentz symmetry is violated (spontaneously broken), then there is such a preferred frame, and an observer inside the train could tell whether or not the train was moving with respect to such a frame.
The is already good evidence of frame draggin... (Score:4, Interesting)
I mean it'll be cool to see if the numbers and the phenomena match, but it's not like there's going to be wild surprise.
Genda
Re:Very Cool Experiment (Score:4, Interesting)
Bold is me, italics is parent.
LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics.
Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any of those models are likely to be true, even if string theory itself is true.
It will test some of the most reasonable/popular models, which is a big step up from having never been tested at all.
LATOR also seems to be much more accurate,
It is, but it's also a test of something that we've already measured extensively (albeit much more sensitively). Our existing measurements of frame-dragging are extremely crude.
Quoting this page:
As you can see, you were mistaken.
and less likely to receive interference.
Why? And, so what? (Unless you're suggesting that GPB will receive so much interference that it won't work.) All it takes is a little bit of interference and the whole thing doesn't work at all, it's so darn sensitive. LATOR is less mechnically intensive.
I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.
The same is true of LATOR or of any other experiment, especially highly sensitive ones.
LATOR's architecture is much different, and I believe by using a long baseline etc, it makes it difficult for interference at one end to screw up the entire experiment. Also remember that it's something that's fairly time invarient, whereas precession is not. The architecture of LATOR seems more likely to deal with sources of interference than something that's based primarily on mechnical components.
But I haven't done the actual math for either, so what do I know?
Cheers,
Justin
Re:Too sensitive (Score:1, Interesting)
Magnets which do that are called "ferromagnets". Iron is one (obviously).
No, that's not true. If there is some external magnetic field that the material is placed in, then that will certainly bias the magnetization in the direction of the external field. But even if you completely isolate the material from all external fields, the spins will still self-align in some direction (picked out by the total magnetization, which is theoretically zero but in practice is always nonzero in some direction) -- provided the temperature is below its Curie temperature. (If the temperature is too high, then random thermal fluctuations will cause the spins to flip too much to remain aligned.)
It is real life. Real magnets experimentally behave the way that this theory predicts.
Again, you're missing the point. There is no "magnetized particle" and "unmagnetized particle". There is a material, made of lots and lots of magnetic particles (spins), and observers sitting inside the material, looking in some particular direction and measuring the magnetization of the material.