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Science

Space Probes Too Slow - Scientists Ask "Why?" 197

Posted by Roblimo 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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Space Probes Too Slow - Scientists Ask "Why?" More

Space Probes Too Slow - Scientists Ask "Why?"

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  • Maybe the stars we see are just painted on the walls around the solar system ;)
  • Yeah yeah, working on it... timescape theory page will be up once my Unlogic theory page is re-formatted...

  • Re:Nah (Score:1)

    by drudd ( 43032 )
    Impossible, the force they measured was towards the sun, not opposite the probe's line of motion (which would be the case if it were losing velocity to collisions).

    To be fair, this was my first thought on the subject too, however :)

    Doug
  • Errrr, hate to break it to you, but their does exist a force that repels matter. It is called E&M. You know, same potential as gravity, but it can repel as well as attract. Last I checked it isn't playing hell with our concepts of energy conservation. By the way, it does take an infinite amount of energy to create a point charge (classically speaking). Just make it a footnote and forget about it since ervery thing else works.

    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
  • It has been suggested that physical constants indicate our lack of understanding of physics. What if the speed of light isn't constant? If you accept the emerging scalar physics, a new school that uses Maxwell's original euqations, than the speed of light should not be constant.
  • Perhaps the orbit is polar so that the orbital plane of the satellite is at 90 degrees to the spin of the earth? (assuming it's spin poles and not magnetic poles).

    - Ignore me. Insufficient coffee.
  • I have heard about this in the past and I remember someone brought up the point that it may not be that the probes have slowed, but the distance being measured from the probe to eath is being measured by radio waves. Anyway, the theory was that radio waves can travel faster when not acted on by the gravity of a near by solar system thus giving a readin of a shorter distance. May not be right but it is a distinct possiblity.
  • Was that last bit serious? (I'm not a physics student if you couldn't tell) Sounds like something I read in NS some time ago about a guy who had resolved the universe down to information theory and reakoned that everything was to do with wormholes (explained entanglement and quantum randomness and everything else to boot).

    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 ;) (time I got down to the patent office).

    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...)
  • I have heard about this in the past and I remember someone brought up the point that it may not be that the probes have slowed, but the distance being measured from the probe to earth is being measured by radio waves. Anyway, the theory was that radio waves can travel faster when not acted on by the gravity of a near by solar system thus giving a reading of a shorter distance. May not be right but it is a distinct possiblity.
  • Clearly, the probes are slowing down because of the load on their systems caused by the Slashdot Effect.
  • Your first theory cannot be correct. "it must be concentrated more densely near the sun and less densely farther away" violates one of the leading views on space and time-- that the universe looks and acts the same no matter where you are. The second theory-- If dark matter did exist, I seriously doubt it would have any effect on the space probe because A) It is too sparse B) If it weren't, we'd have found more by now And back in the day, people used the "Ether" theory to explain why light always travels the same speed and similar effects. It is my opinion that the apparent error in this probe's speed and acceleration are due to it's moving through space/time at 27,000 mph. This probably has a small effect locally, but over time it builds up and in effect, moves through time slower than you or I. Of course, that is all Einstein's general theory, and the NASA guys have already looked at that.. I would be really interested in seeing them post all of their equations and work so we can check for errors.

  • Re: truman show? or just a game (Score:3)

    by Anonymous Coward on Wednesday September 29, 1999 @01:20AM (#1650981)
    Haha, maybe when the probes get that far they'll find a package, whose written contents say, "very good, you humans. Now go on to level 2", and suddenly we're back as cavemen on a different planet, perhaps to a gas giant, to make things more difficult.

    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!

  • Reminds me of how often I wish I could "save the game" IRL before attempting something risky ("hum, I wonder if brute force will fix the problem" ;)
  • Not all dust is in orbit, wise-guy.
  • But why is it that these scientists get a number, and beleive it to be correct under conditions they beleive are correct, and then complain about it when either one of the numbers can be very wrong? Because that's their job as scientists! If their theories and observations don't agree, then one or the other is fundamentally flawed. This particular example is rather disturbing, because Newton's Laws(and yes, the scientists at JPL have accounted for General Relativity as well) are remarkably precise for moving bodies, and this constant deceleration is much larger than any uncertainties in their measurements. The scientists are very willing to accept that perhaps it's a measurement error, but then their previously well-understood measurement theories and practices will have to be amended.

    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!

  • But they said:
    Things really got weird when they looked at Pioneer 11, a sister ship headed in the opposite direction, and then at the Ulysses probe, currently circling the sun. They, too, seemed to be experiencing unexplained tug in the direction of the sun.
    So this would mean that:
    • 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)

    by Anonymous Coward
    One of the discrepancies that drives the dark matter theories is that the universe appears to contain much more mass than we can see. Dark matter is just a theoretical substance that has not been proven to exist[...]

    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

  • Oops, typo. That final sentence should be "so it's getting more and more LIKELY to be something correlated with these long-range craft!" Sorry about that.
  • If I recall correctly, wasn't Pluto reclassified
    as a planetisimal (sp?), and therefore not a
    planet?

    --
  • Which of the current nine planets doesn't actually count as a planet?
  • At this URL [bbc.co.uk] the article mentions that Pioneer 10 will reach the stars of the constellation Taurus in about three million years.


    At this URL [zetatalk.com] is presented a star chart showing what is supposed to be the course of an unknown tenth planet in the solar system, which according to this page will pass by the earth in 2003.


    What is interesting is that the current location of this "Planet X" is given to be just above Orion, in the leftmost portion of Taurus. Does anybody have more detailed information on exactly where in Taurus Pioneer 10 is, so this correlation could be checked closer?

    Marv

  • Re:General Relativity (Score:3)

    by ChrisDolan ( 24101 ) <chris+slashdot.chrisdolan@net> on Wednesday September 29, 1999 @06:46AM (#1650991) Homepage
    Contrary to mettw's post, the speed of outer stars in a galaxy does not in any way constitute a discrepency in any theory of gravity.

    [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.

  • Milky Way (Score:1)

    by Anonymous Coward
    Its the milk doing it!!
  • Probably lack of sleep, but would that be the 'cosmic constant' that Einstein later removed from the theories because he'd only put it in to keep his theories in line with his own (personal. as opposed ot scientific) views on the universe?

    If not, oops :-)

    - Wondering where all that caffenie went.

  • Article and comments from the web (Score:4)

    by kaip ( 92449 ) on Tuesday September 28, 1999 @11:28PM (#1650994) Homepage

    For those interested, the original articles and articles that cite (and comment) it can be found from the web: gr-qc/9808081 [lanl.gov]

  • Like maybe there's still infalling dust from the Kuiper belt, or the Oort cloud, and since it's not being swept up by planets or moons, it's fairly constant...and would surely affect a *very* unstreamlined vehicle.

    For that matter, if the vehicle was decelerating before, and there was more infalling dust, there might be some backwash (no, I didn't say "something to push against, duhhhh"), radiative or otherwise.

    mark "would really prefer something more interesting, Mr. L. Green Man...."
  • I just hope they don't find a 2100 century equivalent to the old theory claming that space was filled with ether. Perhaps we have a 9'th planet. (not very likely explanation)

  • Nah (Score:1)

    by Anonymous Coward
    These probes have bad aerodinamics, and space isn't a pure vacuum. The poor thing bumps into an area with more hydrogen and slows a bit down. You cant't meassure everything.
  • (Score 0; Meant to be amusing)

    Nah. Dark Matter's just the lost socks and things that have fallen behind the fridge of every civilization that's ever existed. Unwanted and unneeded, they create their own wormholes out into the void to be alone with their sorrow.

    "Life. Don't talk to me about life."

    --

  • Dust & debris (Score:3)

    by Jerom ( 96338 ) on Tuesday September 28, 1999 @11:35PM (#1651000)
    We don't have precise estimates yet on how many dust and small debris is floating out there. Maybe the impacts of big amounts of small objects slows probes down. (The debris in itself would be moving towards the sun, due to it's gravitation)
  • It is true that cosmologists are discussing the possibility of a non-zero cosmological constant (Einstein's lambda), but the subtlety of the effect is way to small to be evident on the scale of the solar system and masses like the Sun's. The realm where lambda may be relevent is in very high densities, like just after the the Big Bang, or over very large distances (like the diameter of the observable universe).

    Anyway, if lambda (or any odd theory of gravity) could affect Pioneer, then we would likely see it in the orbit of the outer planets, I would think... It seems MUCH more likely to me that something peculiar to the spacecraft (like directional heat dissipation) could cause the effect.
  • Believe it was 2010, (Arthur C. Clarke) where discovery was droping into Io (I believe) due to a LARGE em tube/field between Jupiter/Io... yes, basing on fiction (that I don't understand completlely) but brings up the point that "The Universe is not only stranger then we imagine, but stranger that we can imagine." Goes to show we have a lot to learn...

    Credit to Clarke and Einstien for ideas/quotes, and no credit to a spelling checker cause I didn't use one...
  • Supposing that there is a nearly constant layer of dark matter throughout the universe (thus gravitational effects would not be present), the slowdown could be caused by the frictional effects of dark matter. This might be a hypothesis. I don't know enough about dark matter and stuff, however.

  • Re:Ether.... (Score:1)

    by Anonymous Coward
    It depends what you understand by "ether", but it's undoubtfuly proven that the space void is _not_ empty. This is not matter but energy (I think the correct name is Zero Point Energy). I read some very interesting papers about this, and I'm sure you can find many detailed explanations on the web ...
  • what do you mean, I hope? the idea of an ether was really nice in teh first place, which is why people clinged to it so much, now if this turns out to be a new michelson and morley experiment that is a good opportunity for th eeinstein of the next century
    ---

  • Re:'Extra' gravity, dark matter? (Score:3)

    by MrCynical ( 63634 ) on Wednesday September 29, 1999 @01:44AM (#1651009)
    >>Like 'ether', dark matter is not real at all.

    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)

    by BrianH ( 13460 ) on Wednesday September 29, 1999 @01:45AM (#1651010)
    Physics majors are welcome to correct me here (I'm a bit outside of my field), but I seem to remember reading an article a while back discussing the possibility that gravity warps time/space (Scientific American or Popular Science...I don't remember which). The theory held that large gravitational wells, and especially large rotating gravitational wells, literally pull at the fabric of time/space and stretch it out near the center of the affected area. To prove/disprove the theory, the scientists involved were going to put a satellite into orbit and set a high mass object into a rapid spin. If the theory was correct, spacetime distortion would be detectable around the outer edges of the rotating test object.

    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.
  • Any two objects held apart from each other posses potential energy governed by the strength of the field and the distance. If the force was repulsive the effective distance the objects could travel would be infinite rather than finite (as it is with normal gravity) thus the potential energy in the bodies would be infinite. Since the force between two objects never reaches zero they would constantly repel each other, with increasing amounts of the infinite potential energy being converted to kinetic. The result, everything traveling at speeds infinitly close to light speed.

    Er, has the person who came up with this argument heard the news that an infinite series can have a finite sum? It's not like this is a new mathematical discovery mentioned on /. last week, after all....

    If there is such a thing as gravitational repulsion, and it follows the same inverse square law as gravitational attraction, then the potential energy of two gravitationally repulsive masses equals the escape energy of two corresponding gravitationally attractive masses. Let a block of upsidasium fly off into space, and it will (ignoring air resistance, etc) fly off into space at escape velocity, not "infinitely close to light speed".
    /.

  • I wasn't thinking straight. If there was enough matter to affect the probes we'd be able to detect its effects on the planets. Crazy theory.



    Come to think of it, 27000 miles per hour is not all that fast. That's only a few kfps more than the top speed that the Apollo astronauts travelled at during their lunar transfer.



    In order to get all the way out to Jupier, Saturn, etc, the probes must have started out MUCH faster. A tiny relativistic error could throw off NASA's calcuations by a whole lot.



    It depends on how they're calculating distance to the probes. Suppose the probes are sending beeps that are known to be 1 second apart. Compare the measured time between beeps and you can find the probe's _speed_. To get the actual distance, you'd probably have to ping it and wait for it to respond while measuring the time it took.



    Another possible way that you might determine speed and distance could be for the probe to send precise time from an onboard atomic clock. The clock would measure different time than on earth due to relativisitic speeds; the total difference

    between earth time and space probe time would be a history of the probe's entire journey. It's pretty complicated. You'd have to know how far away the probe was in order to figure out how much of the time difference was due to distance and how much was due to time dilation.
  • And before anybody gets pedantic with me, I know that objects like black holes cause massive warping of time and space, so the theory that gravity affects it isn't new. I seem to remember that this theory was somehow...different. I just don't remember what the difference was :)

  • There is no void (Score:3)

    by mvw ( 2916 ) on Wednesday September 29, 1999 @01:51AM (#1651014) Journal
    What you mean is a consequence of Heisenberg's uncertainty principle [aip.org] that holds too for the pair energy and time and Einsteins' equivalence of energy and matter [aip.org].

    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.

  • Reboot the probe, and it will speed back up (they should be damn glad it didn't just crash!)

  • Re:We've known this forever (Score:1)

    by Anonymous Coward
    From US Patent 4,462,954:
    I like to mention that in general nuclear power is recognized as the ultimate energy supply for man. But I questioned that because matter is already the product of a secondary energy source created when nothing, meaning absolute space in a high degree of symmetry as existing between the stars decays into a lower form of energy, therefore, the ultimate of energy are universal forces in space in a stage of harmony. But when universal forces which one can describe as gods or goddesses come out of balance perhaps because of territorial disputes then infinity is converted into antimatter and space into matter, the ultimate in fuel, meaning if man ever can leave the solar system and travel in intersteller space there is no more need for fuel because one travels inside the ultimate of energy meaning being among gods or godesses. I hardly can believe that a specimen like the human can physically enter the terrain of gods or godesses, but I know, we can travel into any distance, any dimension, or any domain mentally, therefore it is most important to keep a precise trace on Pioneer 10, in my opinion the announcement of Pioneer 10 leaving the solar system on June 18, 1983 was a hoax in bad taste. If Pioneer 10 can travel in interstellar space than man can travel in between the stars far simpler, far more efficient than ever imagined before in a space without limitations of speed meaning it takes millions of light years for a space vehicle to reach the nearest star, but it would take only a fraction of a second to reach any start througout the universe by a single thought . . . a thought is energy superior to matter and without a nucleus structure, therefore not bounded to electro magnetism or gravitational forces which do not exist in interstellar space. Therefore, measurements conducted throughout the universe by light speed are false because the photon of light behaves quite different in interstellar space as in comparison to planetary space.on to planetary space.
  • Man, does that ever take me back....
    ---
  • No, one simple statement of the HUP is that you can't simultaneously know exactly where you are AND where you are going (dx * dp >~ h). With regards to the dE * dt formulism, it simply means that lower mass particle/antiparticle pairs are allowed to live for longer times that their heavier counterparts.

    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)!

    --

  • If you read the original article, it mentions that the Pioneers are "spin stabilized"; i.e. the spacecraft is spinning around its axis in order to remain stable as it moves forward. Considering the speed at which it is going, it is probably encountering both gas drag and dust particles at a high rate of speed. While a direct impact with a dust particle would not appreciably slow it down, the impacts of many particles could cause the spacecraft to vibrate infinitestimally, and at that velocity, could amplify the drag effect of hydrogen gas in that non-empty "empty" space, leading to the observed slowdown with no apparent cause.

  • Any two objects held apart from each other posses potential energy governed by the strength of the field and the distance. If the force was repulsive the efective distance the objects could travel would be infinite rather than finite (as it is with normal gravity) thus the potential energy in the bodies would be infinite. Since the force between two objects never reaches zero they would constantly repel each other, with increasing amounts of the infinite potential energy being converted to kinetic. The result, everything traveling at speeds infinitly close to light speed.

    not true. As a poster after you on the original parent thread noted, repulsive forces do exist, as you'll study in any E&M class. You basically forgot a negative sign in your account. You're correct in observing that these two particles (if repulsive) will travel to infinite distance from each other (in a closed system). However, it is this infinite distance which has relative zero potential energy. You INCREASE your potential energy as you bring the two particles together (for this hypothetical repulsive case). Just like with two attractive bodies, potential energy increases as you separate them, here potential energy decreases as you separate them.

    As a final note, if everything was repulsive, you wouldn't eventually have everything travelling at speeds of light, but instead equally and infinitely spread out from each other. Everything would be at rest relatively to everything else.

  • It's the gerbils, stupid! (Score:1)

    by Anonymous Coward
    Those gerbils on those treadmills powering the probes can't run forever, you know.
  • Just proving that on the web, folks can grab an Old News story and run with it. /. should hang their head for not researching the story.

  • Don't sweat it. You get what you pay for.

    People gripe when the same article is posted twice a week apart. A year apart can be forgiven, and, after all, it's not the same URL

  • It's Because the universe is expanding. And seeing as Earth is at it's centre anything travelling away from Earth will be subject to this effect, the more distance between Earth and the moving object - the more dramatic the effect.....
  • I would be really interested in seeing them post all of their equations and work so we can check for errors

    Cool. Open Physics. So long as ESR doesn't get involved. He's even been deleting entries from the jargon file, y'know...

    axolotl
  • No it's the world's best caramel...

  • Do you actually understand anything more about dark matter than "it's got mass and we can't see it"? Your dark matter hypothesis (where the dark matter effect permeates space) would be essentially the same as conventional Hot Dark Matter theories, an example of which would be massive (but still very light!) neutrinos. Unfortunately HDM theories alone can explain observations no better than Cold Dark Matter theories on their own. It's a lot more complicated than just "we can't see all the mass that's out there".

    Relativity is not 100% correct or the unified field theory would have been solved by now

    Er. Calculus is not 100% correct or we would be able to symbolically integrate sinc(x). (cough)bullshit(/cough).
    You can't necessarily solve any given equation. Of course, I'm not saying relativity is necessarily right, just that your logic is flawed.

    We are visually driven in our research and I believe that limits us somewhat

    Oh, I suppose we should just listen to the stars instead?
    Yes, it would be nice to be able to sense gravitational fields directly in the brain or the like. But we can't and never will be able to. It's not an important consideration since we can't change it. What is far more limiting is that we are also economically driven in our research, so the important things often don't get funded because they are not of short-term commercial importance.

    axolotl
    PS. Sorry if this comes across as flamage, but it irritates me a little when people try to convince others of their ideas when those ideas are half-formed, have no supporting evidence or theory and don't even fit with existing data, let alone predict anything. It's nothing more than cargo cult science and achieves only the spread of people with little clue about real science.
  • Did you ever wonder why a candle's flame is hotter at the top where hardly any light is put out than at the base? That answers why the corona of the sun is hotter than the surface.

    -----
  • Actually, the universe ends just outside the orbit of the moon. "the diety" to which you refer has gathered-up the space probes, and positioned holy radio transmitting sources at the locations where the probes should be and they are broadcasting data, spoofing what NASA expects to be hearing from the probes.

    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."
  • Now, who was it who was arguing with me a few weeks ago about how flawless newtonian physics was, and how we (mankind) had complete understanding and mastery of the laws of nature?

    "The number of suckers born each minute doubles every 18 months."
  • I think that's the effect that causes "frame dragging", and I assume they're compensating for that, or at least have eliminated that as a potential cause for the discrepency in their data.

    "The number of suckers born each minute doubles every 18 months."
  • I think the math here would be simple.
    Space (the stuff between matter) is more densely packed the more mass there is.
    Space is very dense inside the sun.
    Space is less dense outside the sun.
    Space is even less dense 1M miles from the sun.
    Space is made up of regions of densely packed space and not so densely packed space.

    If you are traveling through a less dense subject, you travel slower (relatively)...the further away from the local source you go, the greater your acceleration in the opposite direction would appear to be from a distant reference.

    Here's a kitchen reference: sound travels about 700 mph in air at sea level and 680mph about 10,000 feet up where the air is less dense.

    From alt.sci.physics.acoustics [deja.com] Speed of sound in water is

    " Fresh water at 20 degrees C is 1481 m/sec.
    Seawater at 13 degrees C is 1500 m/sec.
    "

    Seawater is ....yes, that's right...MORE dense then fresh water.

    Now there are some variables here such as heat from the sun creating a less dense "atmosphere" at the surface of the sun and into regions close by, but i think that matter ejected would have much greater effects on the satellite and therefor would be a more noticeable acceleration.

    not that I'm an expert or anything though :)

  • It seems that one effect of an expanding universe is that we underestimate the effect of gravity. For example, if one viewed the orbit of the earth from 'outside' of the universe it would appear as an elliptical spiral instead of an ellipse and that elliptical spiral would appear to expand over time. [As a simplified example, if we consider the center of the Sun as a stationary point and view a trace of the center of the Earth over the course of an arbit (i.e., a year) then the ellipse would not close. This is because the point in space corresponding to the (assumed stationary) center of the Sun and that of the center of the Earth at the beginning of the orbit will have moved away from each other slightly over the course of the year.] Because we consider the orbit to be an ellipse, our measurement of the gravitional force between the Sun and the Earth, in this case, is slightly too low. This would apply to any gravitionally coupled objects like the Sun (and other bodies in the Solar System) and a spacecraft.

    As a question to the more physics and cosmology oriented slashdotters: This makes sense to me in a Newtonian view of gravity - is this effect already accounted for in an Einsteinian view of space and gravity? Is this a plausible explanation for the observed effect?

    Note: There was an earlier, more tongue-in-cheek, post about the expansion of the universe which includes a reply stating that this would result in an increase in the observed effect. [The vague wording is intentional.] It is true that the expansion would lead to an increase in the measured velocity of the spacecraft, but it would not effect the measured deceleration. [Although a decrease in the rate of the expansion of the universe would.]

  • It occurred to me that perhaps the probes were slowing because their trajectories were too linear, trying to escape the solar system, while natural objects travel in orbits and join the dance of the system. Perhaps this acceleration discrimination is related to the organizational force which clearly exists, but which isn't fully explained by the traditional gravity theory. In other words, if you try to leave the dancefloor, someone pulls you back into the fray. This would explain phenomena on both a quantum and super-galactic scale.

  • (not a personal slam at teraflop, you obviously understand the issues) I just want to caution Slashdot readers (some of whom seem to be posting a lot) 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 ... somewhat impractical. 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. We heard it all last year, we know what we think. It's old news!]
  • (not a personal slam at teraflop, you obviously understand the issues)

    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 ... somewhat impractical.

    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!]
  • Apparently they now think there is another planetoid beyond pluto causing this.

    http://news.bbc.co.uk/hi/english/sci/tech/newsid _460000/460095.stm
  • They (international astronomy community) had a vote; Pluto stayed a planet.
  • I once read a book I got out of the library at UConn (Univ. Connecticut). Found it totally by accident one day.

    The author(s) purported that if you take the geologic age of Earth and map out the "disasters" that they form a definite period, something like roughly every 30,000 years or so.

    The supposition was that we actually live in a BINARY solar system, with the sun's twin being a black dwarf, and that it and the sun were drifting apart.

    The answer as to why it hadn't been seen yet was simple: we've only had astronomy for (at most) 10,000 years, and only recently (300 years) had telescopes at all. If at this time this body was at the furthest point out of the orbit, we'd not have seen it.

    The book was published in the 70s, I think. I wonder if the Hubble has dismissed such a theory, or if it's even been up long enough (13 years?) to have mapped enough of the "local galaxy" to have done so? Hmm...

  • The distance of the probes is measured from earth, so I don't think miscalibrated onboard instruments could have much effect.
  • I don't know about there being a lot more than was originally expected, but I do recall reading that most matter in the universe is dark matter. Something along the lines of 99%. Basically if the only matter that existed in the universe were "light" matter then the universe would be too "light"(weight-wise) and would be expanding at such a rate that single atoms would never have had the oppurtunity to form into anything.

    This is an interesting idea though. The only thing I'm thinking is that if the problem is dark matter, shouldn't it effect planets too?
  • If yer a member of the church of the sub-genius, yer diety is "Bob". I think you can see him by executing "xscreensaver -mode bob" or something like that (my xscreensaver is borken, so I cannot check :^( )
  • As I noted in my other post, if it was gravity effects it would show up not as *constant* acceleration but acceleration that drops. Remember newtons law of universal gravitation? The acceleration due to gravity changes with square of the distance.

    Simon.
  • Zecharia Sitchen [sitchin.com] has written a series of books that cover the existance of Nibiru [crystalinks.com], a planet with an elliptical orbit that comes close to the earth every 3,600 years. The return of this planet closely parallels jumps in the human experience(beginnings of agriculture, metalworking, etc).
  • Just how well have they calc'd friction effects?

    Friction in a vaccuum is notoriously difficult to predict correctly, even if you get the density correct. What if the mean-free-path velocity distribution is _NOT_ anisotropic? (the same in all directions)

    -- Robert
  • The clock would measure different time than on earth due to relativisitic speeds; the total difference between earth time and space probe time would be a history of the probe's entire journey. It's pretty complicated. You'd have to know how far away the probe was in order to figure out how much of the time difference was due to distance and how much was due to time dilation.

    but at the velocities the probe is travelling at, relativity has a negligible effect.
    Time dilation is proportional to 1/sqrt(1-beta^2) where beta = v/c. In this case, 27 000 mph ~ 12 km/s, so beta = 12/300000 ~ 0.00004. this means that for us as observers, we would see the probe's clock running slower by a factor of about 1.00000000324.

    imabug
  • I wonder if there is a strange spacetime drag going on here
    It's funny how explanations like this pop up readily; my own first thoughts were along similar lines. I blame Star Trek.
    The problem with any sort of drag is that it doesn't seem to affect everything. In order to get to Saturn Cassini has to fly around a whole bunch of planets (Venus twice), and that sort of calculation wouldn't be possible. The V'gers would also have missed out on the outer planets.
    If this drag is a feature of spacetime, however, and acts only on accelerating bodies, it may be negated by gravity. Which is why we can't detect it near the sun.
    Usual warning:IANAA and I'm making it all up.
  • IIRC dark matter refers to matter that must exist for our current theories to work but cannot be detected for whatever reason. So it could very well be floating around Venus, or there could be a huge chunk of it on my monitor. The point is we can't detect it (yet) so we really don't know where it hangs out, why it hangs out there, or if it hangs out anywhere at all.
  • FWIW: The principle of Occam's Razor states that the simplest explaination is usually the correct one, lacking other data. Granted, in this case, we lack an awful lot of data, but I think the principle still holds. Assuming that there must be an undiscovered branch of physics at work is a bit extreme, I think. You might as well say there are giants pushing on the probes, or dragons blowing them off course. (Read Issac Asimov's Nightfall for the reference.)

    I'm not saying you are right or wrong. I am just doing my part as a /.'er: Adding fuel to the fire. :-)
  • FYI: 3 hydrogen atoms/m^3 is the critical density of the universe as a whole, IIRC; galaxies are lots denser.
    BUt it could be something new, like the heliopause ending closer to the sun than thought...
    Unlikely. The Solar wind is moving faster than waves can travel through it (supersonic). When a supersonic flow encounters an obstacle (and the heliopause is going to be one), it creates shock waves, turbulence and all kinds of fun. In a magnetized plasma like the solar wind this means lots of energized electrons spiralling around lines of magnetic force, creating synchrotron radiation and whatnot. The heliopause will be detectable from some distance away by its radio emissions; it won't sneak up as a curious change in the spacecraft drag.
  • Not a physics majour, but I didn't think the ether theory existed to explain why light always travels at the same speed. IIRC, the ether theory was discarded for the precise reason that light always travels at the same speed.

    This was the famous Michelson-Morey intraferometer experiment. The ether theory suggested that the ether was an absolute reference frame, and they were trying to measure the speed of the Earth's movement through the ether by comparing the time it took two light beams to travel the same distance in different directions. Of course, no matter which way they did it, those two light beams always traveled the same distance in the same time. So, either Earth moves immeasurably slowly through the ether (kinda strange since we're spinning round the sun rather quickly), or light goes the same speed no matter which way you look at it.

    I thought the ether theory existed because physicists felt that all waves required a medium to travel in. The ether was the medium that EM wave traveled in. But, ether would have been an absolute reference frame, which contradicted Newton (no absolute reference frames). Anyway, no need for ether anymore...
    ---
  • Sorry about that. I had a proxy time-out.
  • then wouldn't SPACE HAVE MASS
    It could, if it wasn't just a convenient abstraction.

    Relativity is not 100% correct or the unified field theory would have been solved by now
    You presume that there is a unified field theory to be discovered. It may be that the very small and the very large operate in different universes.
    Yeah, I'm a Mac programmer. You got a problem with that?
  • It seems obvious to me.
    The probes are slowing down as they penetrate the membrane more commonly referred to as the Cell Wall.
  • Gallileo (at least), as well as perhaps another of the probes listed, are not in interstellar space. IIRC, Gallileo was sent to Jupiter to study Jupiter, and has not left Jupiter because it's studying Jupiter. I must emphasize, that Jupiter is not in interstellar space. Jupiter is the 5th planet from the sun, just outside of the asteroid belt.


    :-) (Keywords bolded for effect)
  • What I meant is why dont they think that they are wrong? They should be quicker to accept that they could have messed up some calculations.

    ---------------------------
    "I'm not gonna say anything inspirational, I'm just gonna fucking swear a lot"
  • Einstein's first set of solutions to the General Relativity problem included a constant (lambda) which allowed for Gravity, at a very great distance to be a repulsive rather than attractive force. The term was included for mathematical completeness, but most people have always set it to zero.

    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.
  • The debris in itself would be moving towards the sun, due to it's gravitation
    Much like our Earth is.
    Actually, really small debris particles get blown right out of the Solar System by light pressure. Slightly larger dust particles "see" the same light pressure coming from just a bit ahead of the Sun (due to their orbital velocity), which gives them a continuous braking force; they spiral into the Sun if they don't hit a planet first. And all of this stuff can be seen, because it scatters light.

    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)

    by Anonymous Coward
    They should have used Energizers

  • I thought this was solved (links) (Score:5)

    by teraflop user ( 58792 ) on Tuesday September 28, 1999 @11:44PM (#1651098)
    I first saw this story in New Scientist a year ago [newscientist.com]. I think it was reported in Slashdot at the time.

    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)

    by rde ( 17364 ) on Tuesday September 28, 1999 @11:49PM (#1651101)
    I don't think it's dust, or hydrogen, or heat radiation. If you read the original paper, it refers to an "anomalous, constant acceleration (my boldies).
    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)

    by Kartoffel ( 30238 ) on Tuesday September 28, 1999 @11:53PM (#1651102)
    One of the discrepancies that drives the dark matter theories is that the universe appears to contain much more mass than we can see. Dark matter is just a theoretical substance that has not been proven to exist; many people would say that it's a fake thing made up to explain weird phenomena (like the ether theory 100 years ago).

    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)

    by Anonymous Coward on Tuesday September 28, 1999 @11:55PM (#1651105)
    The universe simply doesn't exist
    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!

  • 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.

    --

  • Aparently P10 has discovered a new planetoid http://news.bbc.co.uk/hi/english/sci/tech/newsid_4 60000/460095.stm
  • I seem to remember reading an article a while back discussing the possibility that gravity warps time/space

    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.)

  • I don't think the deceleration could come from directional thermal radiation. The power absorbed or produced by the probe is not constant: the power from the battery drops exponentially in time and the power absorbed from the sun drops as inverse square of distance from the sun. The probes are on different distances from the sun, are of different types and the time spent in space is different also.

    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.

  • 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.

  • gr-qc/9906113 [lanl.gov] says:
    We conclude that Murphy's proposal (radiation of the power of the main-bus electrical systems from the rear of the craft) can not explain the anomalous Pioneer acceleration.
    Someone who has more time and knowledge of the matter should look into these....

  • General Relativity (Score:3)

    by mettw ( 10328 ) <matthewNO@SPAMmparry.com.au> on Wednesday September 29, 1999 @12:20AM (#1651143) Homepage
    It should be noted that general relativity
    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)

    by spectecjr ( 31235 ) on Wednesday September 29, 1999 @12:27AM (#1651145) Homepage
    Problem: Anti-Matter doesn't repulse matter. In fact, there's a very good reason for this (namely being that by Feynman and Wheeler, you can look at anti-matter as just being matter going backwards through time; so it's the same stuff, just going in a different direction). Also, imagine if something that had a repulsive effect on matter actually existed? I can't remember the exact details of the argument, but me and my physics tutor worked out that if such a substance were to exist, you'd end up with it chasing across the universe, eventually gaining near-infinite energy. FROM NOWHERE. Which violates the principle of conservation of energy (and equally, by reversing the argument, would require infinite energy to create such a particle in the first place). [this is much worse than quantum physics, which violates the conservation of energy law and allows particles to "borrow" energy, as long as they give it back before anyone looks hard enough and notices that its gone...]

    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)

    by rde ( 17364 ) on Wednesday September 29, 1999 @12:28AM (#1651156)
    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.
    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.
  • Dosn't this Murphy guy have a law ?
    Maybe this is an example of it.
    When we look harder at this problem it will go away.

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