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Space Probes Too Slow - Scientists Ask "Why?"
Posted by
Roblimo
on Wed Sep 29, 1999 04:10 AM
from the inquiring-reseachers-want-to-know dept.
from the inquiring-reseachers-want-to-know dept.
Rudolf writes "Newsweek has an article this week, available here, about NASA calculating that space probes, such as Pioneer 10, 11, and Ulysses, are slowing down more than they should. A team of astronomers and physicists couldn't figure it out, so they published their findings in Physical Review Letters to generate discussion. Several possible causes of the slowing have been discussed, but nothing that completely solves the puzzle. Anyone care to rethink gravity and time?" Update: 09/29 09:00 by H :Thanks to Mark for his link to the original citation.
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More Spacecraft Velocity Anomalies 339 comments
ZonkerWilliam recommends a bulletin from the American Institute of Physics, which discusses a study noting that recent spacecraft, such as NEAR, appear to display velocity anomalies much like those seen in Pioneer 10 (which were observed beginning ten years ago). The anomalies amount to up to 13 mm/sec., with a measurement accuracy of 0.1 mm/sec. Quoting: "A new look at the trajectories for various spacecraft as they fly past the Earth finds in each case a tiny amount of surplus velocity. For craft that pursue a path mostly symmetrical with respect to the equator, the effect is minimal. For craft that pursue a more unsymmetrical path, the effect is larger."
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Is this the Trueman Show ? (Score:1)
Rethink Time and Gravity... (Score:1)
Re:Nah (Score:1)
To be fair, this was my first thought on the subject too, however
Doug
Re:Anti-materia (Score:1)
Er, yes... but the thing is, with EM, both particles repulse one another (with the strength of repulsion diminishing by the inverse square law). However, with gravity, because of the nature of the force involved, the "normal" particle would still be attracted to the "anti" particle (even though the "anti" particle would be repelling it), and as such, they'd chase each other across the universe with a constant force (ie. constant acceleration, which gives infinite energy). Which is a no-go.
Damn. Wish I hadn't jettisoned most of this stuff from my brain.
I'll work on a full treatment of the problem if you like
Simon
Constants in physics could be wrong (Score:1)
Re:Huh? (Score:1)
- Ignore me. Insufficient coffee.
Its not the probes its the measurement thats fault (Score:1)
Wormholes and twists :) (Score:1)
That last bit was serious as far as I'm concerned, but other than a few discussions with a friend of mine who was at CERN (who said that I'm correct in principle... but that some of it was out of his field), I've never had the guts to formally write it down. Not to mention that it'd take me a few years to relearn everything I needed to know, and learn enough about quantum mechanics and space-time theory to be able to determine the wormhole structure
Funnily enough, Kip Thorne never replied to my email... not surprised... I probably sounded like a complete kook
Mind you, a number of professors at my uni (way back when) did buy off on the "gravity as knotted spacetime" part of my theory... and on the whole "time as nonlinear for particles" part of it too...
Maybe at some point I'll join the legions of kooks across the world and put something up on my website. It'll all be geometrical arguments though
Mind you, the theory, as it stands, is in pretty good shape. It has the potential to give another explanation as to why there's more matter than antimatter in the universe (without symmetry breaking, which I've always had a slight dislike for), and also gives a possible method of "faster than light" communication (though that's actually a misnomer). However, that depends on whether or not the half-twist in the wormhole between an electron/positron pair has an impedance high enough that it acts as a reflective barrier to signals squirted into it. The good thing though is that it should be reasonable easily testable, now that molecular cages have been created. Just create one hydrogen molecule, one anti-hydrogen molecule, trap them both in cages, and make sure that the electron around the hydrogen and the positron around the anti-hydrogen were both created in the same particle-pair creation event. Then squirt light into one of them; if the theory holds and there is no reflection at the twist, then the other will "ring" in sympathy, no matter how far away it is physically. Think of the applications
This also explains radiation resistance
[Mind you, if the theory was correct it'd explain why the SETI project hasn't picked up anything]
Si
(Joining a legion of kooks...)
Its not the probes that have slowed (Score:1)
Slashdot Effect (Score:2)
Re:'Extra' gravity, dark matter? (Score:2)
Re: truman show? or just a game (Score:3)
now where is that secret warp factor? I hope the head boss doesn't manifest himself just yet... We haven't even saved our game!
Re: truman show? or just a game (Score:1)
Re:Dust & debris (Score:1)
Re:Not what they think? (Score:1)
There's just something not right with the whole picture as they currently know it. It happened with 3 spacecraft so far, so it's getting more and more unlikely to be something correlated with these long-range craft!
Re:Dust & debris (Score:1)
- All probes use the same instruments (I can see this for the two pioneers, but ulysses? This'd be easy to find out though I guess, and NASA would've checked it first)
- It's always towards the sun... coincidence?
The question is: Do other probes experience a similar "problem"? We've sent so many to space, if it's really a phenomen of gravity or whatnot, it should be universally observed.Another quesition would be, at exactly what distance is Ulysses orbiting the sun? If it's closer to the sun, particle density etc. should be relatively easy to determine.
Somehow I seriously doubt the answer can be easily determined or will even pop up to be some instrument fault etc - NASA would check into these things painstakingly before they released such things. They would also not have said something if it was within the "normal error range".
Unfortunately I am not into astrophysics... so I am mostly clueless... Give me a cisco router any day, but I'll have to surrender before a Pioneer probe. :)
Re:'Extra' gravity, dark matter? (Score:1)
Dark matter isn't what you think it is. When folks talk about dark matter, they're talking about stuff near the center of the universe, black holes, stuff that doesn't show up with traditional methods of detection. Dark matter isn't just 'stuff' floating around Venus.
-- Almost an astrophysicist
Re:Not what they think? (Score:1)
Re:Ether.... (Score:1)
as a planetisimal (sp?), and therefore not a
planet?
--
Re:Ether.... (Score:1)
Re:General Relativity (Score:3)
[This is mostly background to redirect many of the wild posts regarding dark matter attached to this article]
When you measure the velocity at which stars orbit the center of a spiral galaxy (mostly external galaxies like Andromeda, but also in more difficult work on our own galaxy), you see that the stars near the center orbit in a pattern which mimics the pattern of stars we see in that galaxy. That is, if we count the stars in the center and calculate what their mass should be, it matches with the velocity at which the stars orbit (that is, gravity is balanced by centripedal force: called Keplerian rotation). But further out from the center of many galaxies, stars orbit faster than what you would predict by counting all the mass from all the stars you can see. If they are going faster than the gravity must be stronger than what you originally predicted. If all the stars you can see can't make enough gravity, then what? Throw out the theory of gravity which has proved so very successful in the past, or postulate that there must be some matter which you can't see, that is, dark matter.
Most astronomers believe the latter. They think there is not enough eveidence to toss the whole theory. Instead, they assume that galaxies are more complicated that we first thought. What causes this dark matter? Well, it must be something that gives off less light than stars. Some folks have suggested that "ordinary" matter (planets and brown dwarfs) make up the difference. Others suggest "strange" matter (stuff not discovered yet). Finally, the flippant sort of people commonly attribute the extra mass to interstellar Volkswagens (i.e. they don't care what it is just yet; they just want to measure the effect for now).
Why am I saying all of this? I just want people to be a little more informed when the term "dark matter" gets thrown into the discussion.
BTW, the "1/r^2" that the previous poster refers to is the pattern of density of dark matter needed in many galaxies to explain the patter of stellar orbits you see. That is, as you go further out from the center of a galaxy, the density of dark matter decreases by the square of the distance. This is NOT a factor thrown into a gravitational equation. It is a feature added to a density model of a galaxy that helps to explain its rotation curve. It's like needing to account for the mass of the passengers when computing the acceleration of a car. It's NOT a feature of physics.
Article and comments from the web (Score:4)
For those interested, the original articles and articles that cite (and comment) it can be found from the web: gr-qc/9808081 [lanl.gov]
Dust & debris (Score:3)
Sounds like discovery... (Score:2)
Credit to Clarke and Einstien for ideas/quotes, and no credit to a spelling checker cause I didn't use one...
Re:'Extra' gravity, dark matter? (Score:3)
I don't believe the 'ether' concept is totally false. I do agree that 'dark matter' is probably not real at all though. Quantum theory has come across the ZPE (Zero point energy) concept. If you carry the concept out a little more, then wouldn't SPACE HAVE MASS. Which loosely ties into the 'ether' concept. Relativity is not 100% correct or the unified field theory would have been solved by now. So perhaps light's constant nature is only contant while moving though space and time. Meaning, if light can propogate through a void, it could be interacting with space itself which gives it the speed properties of 'C'.
We are visually driven in our research and I believe that limits us somewhat.
Warped space maybe? (Score:4)
Could this be what we're seeing, only on a much larger scale? Perhaps the Sun, with its massive gravity well, has caused time/space to stretch within our solar system, and what we're seeing here is the effect of the probes re-entering "normal" space. From our perspective within the "stretched" area, it would appear that the craft was slowing down.
I would love it if someone could provide more info on this theory, and fill me in on whether or not it could possibly apply here.
There is no void (Score:3)
So while over long times the energy at a given empty volume in space is zero, for short times you are not sure. In fact for very short times it is unsure enough to allow the creation of virtual particles, like an electron positron pair, that "borrow" their energy from the vacuum, and annihilate after a short time, giving back the energy.
Zero Point Energy
Nope, that term describes the fact, that the lowest possible energy state for a harmonic oscillator in quantumn mechanics is non zero.
Re:There is no void (Score:2)
A better way to state this is that, the more accurately you measure one value of a Heisenberg pair, the less accurately you can measure the other. As an analogy, consider a large object like a car. You can exactly determine where the object is by taking a snapshot (assuming you have the ideal camera with the infinitely fast shutter) and measuring the position. However, you have completely lost any information about the speed (and thus the momentum) of the car.
Conversely, if you leave the shutter open for a finite amount of time, you get a blurred image of the car, making it more difficult to figure out the position of the car, but knowing the shutter speed and the absolute length of the blurred image, you begin to get a better idea of the car's momentum.
In the quantum world, things are further blurred in that atomic and subatomic particles are described by quantum wave packets, meaning they don't have an exact position until observed. However, the act of observing an object (bouncing photons off of it) tends to change the momentum of the item. The more accurately you try to collapse the wave function and pin down the item, the more elusive it gets (by increasing its momentum, and thus moving around)!
--
Re:We've known this forever (Score:2)
When we finally send men to Mars, "the diety" is going to have to drug them and hypnotize them into believing they actually travelled to Mars, when in reality, they landed on the dark side of the moon, and went into a secret complex with a big room with walls painted on the inside to resemble Mars, so that the photographic equipment and such broadcasts the expected pictures. Mockups of Pathfinder and Viking will probably also be present.
"The number of suckers born each minute doubles every 18 months."
Re:General Relativity (Score:2)
"The number of suckers born each minute doubles every 18 months."
Re:Warped space maybe? (Score:2)
"The number of suckers born each minute doubles every 18 months."
Hypothesis != Solution (Score:2)
Hypothesis != Solution (Score:2)
I just want to caution Slashdot readers (some of whom seem to be posting) that one scientist's hypothesis does not a solution make. Clearly there is room for debate on this issue, particularly since actually going out to Pioneer and taking measurements is
So, Scientists A&B say, we have something odd here, and nothing we've investigated explains it (first article in physics journal, reported in NS). Scientists C&D say, it looks to us like the probe's excess heat, using these calculations (2nd NS article). That doesn't mean that A&B will automatically agree with C&D (they don't).
It's often said, not entirely tongue-in-cheek, that scientists (who have careers at stake) never admit they're wrong, and that the only way new theories become accepted is for all the old scientists to die off!
In any case, the Pioneer conundrum is a very interesting one. It's not, in itself, evidence of a new force, but it is dramatic example of how complex something as "simple" as a spaceship trajectory can be, and how we don't understand everything yet. (Which to that I say: Thank God, what a boring universe it would be if we understood everything.)
[As for the slashdot kiddies complaining "we heard about this already", maybe Slashdot should stop reporting on, say, Microsoft vs. the DOJ. After all, it was first reported on over a year ago, the fact that they're still arguing is irrelevant. It's old news!]
It would be easier if it went faster (Score:2)
If it is a non-zero term, than it could explain what is being seen, though you would expect the satellites to be experience an anomolous acceleration rather than a deacceleration.
It actually isn't surprising at all that this might occur. There are a number of models that would argue that there are spacetime features in a gravity well (like that of the sun) that would not be present in relatively flat spacetime. The further we get from the sun's well, the more likely we are to begin observing these effects.
Dust & debris, probably not; WIMPS, maybe? (Score:2)
The most interesting prospect that occurs to me is that it could be an example of dark matter in the form of Weakly Interacting Massive Particles (WIMPs). Particles which do not interact via the electromagnetic force would not scatter light nor be affected by inter-atomic forces, and those which do not interact via the strong force would go right through nuclei as well; such particles would be phantoms, only feeling the weak nuclear force and gravity. The planets orbitting in the inner system would tend to eject such particles which ventured in too close, but those in a halo outside the outer planets would be undisturbed. As the probes passed out of the planetary zone and into the halo, they would begin to feel the pull of its mass (there is zero pull inside of a spherical shell). This would manifest itself as an increase in gravity, just as is being observed.
It's been known for many years that galaxies have a lot of mass that isn't visible. Maybe the Pioneers have revealed some of it in our own back yard. Now wouldn't that be cool!
hmmm (Score:2)
I thought this was solved (links) (Score:5)
A month later New Scientist published this story [newscientist.com], suggesting that the slowing was due to the reaction from heat radiated from the probes RTG power plant.
They still appear to be arguing over whether this effect is big enough. Measurements involving heat are notoriously difficult, as the cold fusion debacle showed.
Probably not dust (Score:3)
I initially balked at the idea of 'new physics' to explain this, but when you consider how narrow our field of vision is, there cannot but be more than is dream't of in our philosophy.
These probes have travelled farther than pretty much anything else created by man; anything funky with gravity may only begin to manifest itself over billions of klicks.
My own wild and unsupported theory must go unpublished lest the drooling masses call to my door armed with pitchforks and flaming torches.
'Extra' gravity, dark matter? (Score:4)
Now we've got additional symptoms of the universe being more massive than it ought to be. The probes are slowing down faster than expected, as if there was 'dark matter' collected near the sun.
From these *observations* I propose 2 hypotheses---
1. If dark matter is real, it must be concentrated more densely near the sun and less densely farther away. Otherwise the distribution of dark matter would not slow the probes. This makes sense because dark matter, being massive and subject to normal physical laws, would tend to collect near stars and other massive objects. In any case, why heck can't we see it?
2. Like 'ether', dark matter is not real at all. There is an unkown phenomena manifesting itself here. If so, the unknown force(s) could very well be the same ones that caused the observations that led people to propose dark matter in the first place.
How would _you_ solve the Dirac Equation?
We've known this forever (Score:4)
outside the borders of our solar system.
The probes are slowing down because
they are literally hitting the "wall";
Our solar system system was created
by a diety that didn't want to go
through all the fuss that comes with
creating a complete universe.
Breaking through the borders of our
solar system will let us reach the
realm of the gods.
SEND ME ALL YOUR MONEY AND GET
A SEAT ON MY SPACESHIP TO JESUS!
They made- and apologised for- this mistake before (Score:3)
This BBC article yesterday [bbc.co.uk] about the discovery of yet another Kuiper Belt object [asu.edu] by Pioneer [nasa.gov], mentions at the bottom:
Earlier this year, scientists were puzzled by what was described as a mysterious force acting on the probe. It led to speculation that there was something wrong in our understanding of the force of gravity.
Eventually the effect was tracked down to the probe itself, which was unexpectedly pushing itself in one particular direction.
I expect this new theory will also be dispelled by minor impacts, leaking remainders of fuel, and the fact that space isn't a true vaccuum. I'd be delighted to be proved wrong, of course.
--
Connected story on the BBC (Score:2)
Re:Warped space maybe? (Score:2)
Er, yes, that's known as General Relativity, and is pretty well understood. The test satellite you mention is Gravity Probe B [nasa.gov], scheduled for launch next year.
This sort of thing has certainly been taken into account. Compared to predicting the force due to thermal radiation from the satellites, it's easy. And thermal radiation will always result in a sunward force, because you put the radiators on the dark side of the spacecraft (unless you want it to get really hot while it's still in the inner solar system.)
New physics or something more usual? (Score:2)
There may still be some good explanations so we should not wet our pants, but still it is interesting to speculate a little about possibilities of a new physical theory or phenomenon.
One must remember, that gravity is the only physical fundamental force we have not been able to quantisize. As quantum theory has been a very good explanator and predicter for electric, optic and magnetic phenomenons, I think it could also do something to gravity also.
Gravity has been extremely difficult to quantisize, though. You may have heard of gravitons, but that is still only a name without shape. It seems gravity can not be explained with linear differential equations (like Scrödinger's or Dirac's for electromagnetism) but with nonlinear DE:s. These can not be usually calculated analytically, but only numerically.
So is this a quantum effect of gravity? Maybe we know it someday.
Who is DarkMatter? (Score:2)
Star Trek has done so much to encourage the imagination of scientists, but it also destroys the scientific literacy of non-scientists. Dark matter is definitely one of the casualties.
"Dark Matter" is a loose term referring to mass in the universe that should exist but has not been accounted for yet. The last time I studied astronomy, two of the biggest theories were WIMPs (unknown subatomic particles) and MACHOs (planet-sized junk out in the void). An excellent essay on the subject is available at Berkeley [berkeley.edu].
i wonder if they considered the gravity of the asteroid belt in their calculations.Any astrophysicist who neglected the mass of asteroids, Oort, etc, would be a public laughingstock and unable to show their face in public for a long time. BTW, at reasonably large distances, the gravitation for any collection of objects (such as the asteroid belt, or the entire solar system for that matter) is identical to the sum of their masses located at their center of mass. The calculations are high school AP physics/calc, no big deal.
Not solved...? (Score:2)
General Relativity (Score:3)
doesn't specify a single equation for gravity,
it specifies a set of conditions that an infinite
number of equations fullfill. Einstein just
chose the simplest equation, which may infact
be the wrong choice.
There are a number of known discrepancies in the
current theory such as the speed of the outer
stars in a galaxy and even the outer planets in
our solar system. It has been shown that by
adding a 1/r^2 factor to the gravitational
equation then both of the problems above are
accounted for.
My personal beleif is that astronomers will
eventually give up on the dark matter theories.
Re:Anti-materia (Score:3)
Besides, gravity is caused by knots in spacetime anyway (or to be precise, it's caused by tension between two ends of a wormhole connecting a particle and an anti-particle; whereas the charge is caused by the relative angle of twist of the mouth of the wormhole with respect to the surrounding spacetime... and the reason it's twisted is because that's the minimum stable configuration for a two-mouthed wormhole to exist without collapsing in on itself).
*ahem* sorry.. I was rambling
Simon
Re:'Extra' gravity, dark matter? (Score:4)
I don't think so. If the dark matter were concentrated near the sun, we'd automatically include it in our calculations; most likely in Newton's gravitational constant.
General relativity answered the problems Newton's theory had with Mercury's orbit, and does a damn fine job with all predictions gravitational around the sun. If this is the case, dark matter has to exert a force other than gravity. And if that's the case, the Pioneers' acceleration away from the sun should increase as it moves out of the dark matter's influence.
Of course, I could be talking bollocks.
Murphy (Score:2)
Maybe this is an example of it.
When we look harder at this problem it will go away.