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Mysterious Force Affects Pioneer 10 & 11 Probes 829

Posted by Hemos
from the launched-into-deepest-space dept.
JabbaTheFart writes "The Guardian is writing that something strange is tugging at America's oldest spacecraft. As the Pioneer 10 and 11 probes head towards distant stars, scientists have discovered that the craft - launched more than 30 years ago - appear to be in the grip of a mysterious force that is holding them back as they sweep out of the solar system. Some researchers say unseen 'dark matter' may permeate the universe and that this is affecting the Pioneers' passage. Others say flaws in our understanding of the laws of gravity best explain the crafts' wayward behaviour."
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Mysterious Force Affects Pioneer 10 & 11 Probes

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  • by prgrmr (568806) on Monday September 13, 2004 @08:37AM (#10234257) Journal
    The question is can we develop the technology to detect tractor beams all the way out there from here?
    • by Lt Cmdr Tuvok (810548) on Monday September 13, 2004 @08:50AM (#10234378) Homepage Journal
      The logic on which you draw your assumption seems to be flawed.

      Contact with the Klingon empire was first made in 2151. Therefore, it is only logical to assume that they were nowhere near human space in 2004. It is most likely that the phenomenon in question was an anomaly caused by temporal vortex flux.

      • by Kethinov (636034) on Monday September 13, 2004 @09:45AM (#10234878) Homepage Journal
        According to the first episode of Enterprise, it takes 4 days to reach Kronos at approximately warp 4. That puts the Klingon homeworld only about 1ly away from Earth, which is 4x closer than the nearest star.

        Logically, we must assume 1. the episode is wrong (correct assumption) or 2. the Klingon Empire is a LOT closer than you thought, Mr. Vulcan.
        • by saudadelinux (574392) on Monday September 13, 2004 @10:13AM (#10235191)
          So, we have to raise the Yamato, outfit her with a Wave Motion Gun, and go out there and whup that ass!
        • by CodeMonkey4Hire (773870) on Monday September 13, 2004 @10:30AM (#10235385)
          (Sorry to be so serious about this, but I was curious.) I'm going to have to agree with you that the episode must be wrong. From this website [], the warp formula for TOS (apparently some of the later shows changed the scale to be asymptotic with 10 being infinite velocity) is given as v = (W^3)*c which seems consistant with some of the numbers I have been seeing.

          From the script of the first episode []:
          TUCKER: I thought the whole point of this was to get away from the Vulcans.

          ARCHER: Four days there, four days back... then she's gone. In the meantime, we're to extend her every courtesy.
          ARCHER : God, she's beautiful

          TUCKER: And fast. Warp four point five next Thursday.
          ARCHER : Neptune and back in six minutes.
          ADMIRAL FORREST: The warp five engine wouldn't be a reality without men like Doctor Cochrane and Henry Archer, who worked so hard to develop it. So it's only fitting that Henry's son, Jonathan Archer, will command the first starship powered by that engine.
          From this it can be deduced that the maximum warp that the new engine was designed for was warp 5, but they were going to be testing out warp 4.5 for the first time.

          If you use warp 4.5 = 91.125*c for 4 days you get 0.998 light-years. This is so close to a light-year (possibly rounding issues) that the writer who came up with 4 days probably forgot to multiply by the number of light-years to Kronos.

          Even if you use warp 5, you get 1.37 light-years. Considering that Alpha Centauri is 4.4 light-years from Earth [], the 4 days at warp 5 idea still sounds absurd.
          • by afidel (530433) on Monday September 13, 2004 @11:08AM (#10235783)
            You say the writer screwed up the calculation, I say he conveniently forgot to do the math and worked in 4 days based on his storyboard timeline. Sure they could imply dead days but that makes the action seem much more spread out which can kill the pacing and energy of a show.
    • by Punto (100573) <puntob@[ ] ['gma' in gap]> on Monday September 13, 2004 @08:51AM (#10234393) Homepage
      Maybe they can reverse the polarity of the probes' guidance system.
    • by Pii (1955) <jedi.lightsaber@org> on Monday September 13, 2004 @08:55AM (#10234429) Journal

      It's a SPACE STATION!!!

  • by jolyonr (560227) on Monday September 13, 2004 @08:37AM (#10234261) Homepage
    What's interesting about this is the craft went in different directions out of the solar system, which rules out something like the mass of an unknown body in the outer solar system affecting their flight.
    • by Lumpy (12016) on Monday September 13, 2004 @08:42AM (#10234303) Homepage
      It could be an example of gravitiontational rippling.

      a very large gravity well may have a ripple that exists some distance from the center of the gravity well. The sun's gravity well is big enough for us to notice this while the sun and other planets we did not notice it. we MIGHT be able to notice something if we look at the data as these probes appriached and passed juipter.

      • by JohnFluxx (413620) on Monday September 13, 2004 @09:12AM (#10234559)
        speaking of gravitational rippling, maybe you can answer a question for me...
        Special relativity says there isn't any particular speed that is at rest, right? Speeds are always relative, right?

        But gravitational rippling leaks energy until the object is at rest, right? So there must be a rest state of zero speed.. so there must be an absolute zero speed?
        • by Yartrebo (690383) on Monday September 13, 2004 @09:22AM (#10234645)
          Gravitation rippling only happens to accelerating objects, so it does not violate relativity. It works the same way as brensstrahlung (ie., breaking radiation). It is believed that accelerating objects emit gravitons (gravity particles) in the same way accelerating charges emit photons (electromagnetic particles). The braking is relative to the object causing the acceleration.
  • for the love of god, (Score:5, Informative)

    by Anonymous Coward on Monday September 13, 2004 @08:38AM (#10234269)
    exactly what was AFFECTED?
  • Or... (Score:5, Funny)

    by deadgoon42 (309575) * on Monday September 13, 2004 @08:38AM (#10234272) Journal
    They could just be hitting up against that big crystal shell that all the stars are painted on.
    • Re:Or... (Score:5, Interesting)

      by M1FCJ (586251) on Monday September 13, 2004 @08:46AM (#10234350)
      I remember reading a quite striking short story about a crystal shell surrounding every solar system and it can only be broken from inside. It works like a semi-permeable interface, preventing aliens coming /communicating inside. A civilization will only manage to get outside of the shell by breaking the "egg". I can't remember the writer of the story nor the name but I think I read it on either Asimov or Analog in the last couple of years. Can anyone recall this story and remind me of its writer please?
  • Matrix (Score:5, Funny)

    by Sir Homer (549339) on Monday September 13, 2004 @08:40AM (#10234286)
    When you think about it, we know so little about deep space. Perhaps the Matrix doesn't go out that far? Clipping problems?
  • The force! (Score:5, Informative)

    by tuxter (809927) on Monday September 13, 2004 @08:40AM (#10234287) Journal
    It is also thought that dark matter is at the centre of galaxies [] Could explain a lot of things, e.g. the expansion/contraction of the universe. Judging by the amount of "tangible" matter in the universe, there is no way to halt the expansion, and it will go on forever. However, if there is dark matter, it could hold enough gravity to halt expansion and force the big crunch. Lots of info on this sort of stuff here []
  • Laws of Physics (Score:5, Insightful)

    by Anonymous Coward on Monday September 13, 2004 @08:40AM (#10234289)
    It is neat to see things like this which challenge our understanding of relatively basic things like gravity. Part of me is still hopeful that we will find some holes in the relativity theory. More than a few scientists have pointed out other inconsistencies between observations and relativity. It would be nice not to be constrained by this whole 186,000 miles per second thing :)

    • Re:Laws of Physics (Score:5, Interesting)

      by colmore (56499) on Monday September 13, 2004 @09:02AM (#10234481) Journal
      As a sci fi reader, I of course hope that light speed is a breakable barrier.

      As someone who studied physics, I'm not too hopeful. The speed limit isn't the result of a few shaky theories, but rather a pretty deeply engrained part of our understanding. If it turns out not to be true, then most of the physics that has been done for the past 150 years is flat out wrong. It would be like discovering that DNA isn't where the genetic code is held, as disasterous, and at this point in our study, as unlikely.
      • Re:Laws of Physics (Score:5, Insightful)

        by thered (256861) on Monday September 13, 2004 @09:30AM (#10234726)
        If it turns out not to be true, then most of the physics that has been done for the past 150 years is flat out wrong

        Using the same logic, you could say that Newton's Laws have been "flat out wrong" for the past 90 years, but for many, many, applications, from automobiles to rocket boosters, they are "perfectly" accurate (from an engineer's point of view).

        • Re:Laws of Physics (Score:4, Insightful)

          by Fortress (763470) on Monday September 13, 2004 @04:46PM (#10239575) Homepage
          > Using the same logic, you could say that Newton's Laws have been "flat
          > out wrong" for the past 90 years, but for many, many, applications,
          > from automobiles to rocket boosters, they are "perfectly" accurate
          > (from an engineer's point of view).

          Newton's Laws have been known to be wrong for 90 years (they were wrong before that, too, we just didn't know it). They are *not* "perfectly" accurate for anything, from an engineer's pov or anyone elses. What you mean to say is that they are SUFFICIENTLY accurate to accomplish the task at hand. The relativistic effects at the speeds you are using are too small to be relevant, but they *do* exist, if measured accurately and precisely enough.

      • Re:Laws of Physics (Score:5, Insightful)

        by finkployd (12902) on Monday September 13, 2004 @10:04AM (#10235071) Homepage
        then most of the physics that has been done for the past 150 years is flat out wrong.

        Frankly I would be suprised if that turned out not to be the case. Are we so vain now as to think that for the first time in human history, we actually have a good grasp on how the universe works? We only know now what our power of reasoning and measuring equipment allows us to understand. It will likely turn out that we have been incorrect about most things physics related as we study further.
    • by interactive_civilian (205158) <`moc.liamg' `ta' `uromam'> on Monday September 13, 2004 @09:10AM (#10234543) Homepage Journal
      Blockquoth the AC:
      It would be nice not to be constrained by this whole 186,000 miles per second thing :)
      Seriously! I agree. Recently I've been playing around with Celestia [], and it really gives you a good idea of how freaking BIG the universe is. (download it and check it out).

      Setting your speed at "c" and it takes a while to get out of the Solar System. Set it at a few AUs per second and you can clear the solar system more quickly, but once you are out, it seems like you are not moving at all. Once you accelerate to a light year per second, things start moving a bit, especially the neighboring stars, but it is still pretty slow going on a galactic scale. If you want to get out beyond the galaxy, I recommend going perpendicular to the galactic plane and accelerating to a few thousand light years per second (ummm...that is rather fast, don't you think).

      Doing this gives you a pretty good perspective on things. Once you are in inter-galactic space, if you aren't moving about a thousand light years per second, it seems like you aren't moving at all. For an even better perspective of mixing size and speed, try manually flying back to Sol. It seems easy, and you even decelerate a bit, but it seems like you are going kind of slow until you suddenly zip past Sol doing about 100 light years per second. Go back and try again.

      Back to the original point, yeah the speed of light is fast, but on a galactic and/or universal scale, it isn't that fast. I too hope they either find some loopholes in relativity, or find some loopholes in the universe (such as Asimov's idea of Hyperspace), or we won't be going anywhere anytime soon.

      Yeah, I know this is deeply in the realm of Science Fiction, but I'm kind of hoping that it becomes Science Fact someday...

    • Re:Laws of Physics (Score:5, Insightful)

      by rdmiller3 (29465) on Monday September 13, 2004 @09:18AM (#10234617) Journal
      This is exactly what those probes were launched for. It's great that they're not behaving as predicted. When everything behaves as we expect we don't learn much, but verifiable errors in our predictions can open entire dimensions of study that we didn't see before.

      To paraphrase Carl Sagan, the real moments of discovery aren't when someone shouts, "Eureka!" but sometime before that when someone mumbles, "Hm, that's weird..."

  • Dissapointment (Score:3, Interesting)

    by Lesrahpem (687242) <{iadnah} {at} {}> on Monday September 13, 2004 @08:41AM (#10234293) Homepage
    It'd just be great if after all this time we actually find out something like it's not possible to leave the solar system without some sort of extreme propulsion system.
  • by Have Blue (616) on Monday September 13, 2004 @08:41AM (#10234301) Homepage
    They're so far away the Matrix is accumulating significant floating point error.
  • by charon69 (458608) on Monday September 13, 2004 @08:42AM (#10234307)
    Obviously, this is merely the result of the space craft leaving the singularity of our solar system, thereby moving outside of Einsteinian laws of gravitation and physics. It can now enter hyperspace... or would be able to if the puppeteers would hurry up and arrange for a hyperdrive shunt to get dropped off.

    Sorry, just finished "Ringworld".
  • *mumbles* (Score:5, Funny)

    by KennethSundby (723521) <{sundby} {at} {}> on Monday September 13, 2004 @08:42AM (#10234308) Homepage Journal
    Ah yes, the good old "If you don't know, blame it on Dark Matter" strikes again.
  • by rooijan (746599) on Monday September 13, 2004 @08:42AM (#10234309) Homepage
    Note to Hemos: The verb is spelled "affect". You know, with an "a". The noun is spelled "effect", but it's the verb needed in the title.

    Sorry, don't mean to sound curmudgeonly and grumpy and so forth, but so few people get this right that I can't stand by and let it slide.

    I'll put the cantankerous old grouch away now...
  • by haggar (72771) on Monday September 13, 2004 @08:45AM (#10234330) Homepage Journal
    From TFA They had been tracking the probes using the giant dishes of Nasa's Deep Space Network.

    This doesn't quite quench my thirst for information: does this mean the probes are still sending radio waves/signals, or just irradiating passively?
    • by applemasker (694059) on Monday September 13, 2004 @08:54AM (#10234422)
      The last signals were recieved from Pioneer 10 in early 2003, but telmetry stopped almost a year before. From the Feb. 25, 2003 press release that "pronounced" Pioneer 10 dead:

      RELEASE: 03-082HQ PIONEER 10 SPACECRAFT SENDS LAST SIGNAL After more than 30 years, it appears the venerable Pioneer 10 spacecraft has sent its last signal to Earth. Pioneer's last, very weak signal was received on Jan. 22, 2003. NASA engineers report Pioneer 10's radioisotope power source has decayed, and it may not have enough power to send additional transmissions to Earth. NASA's Deep Space Network (DSN) did not detect a signal during the last contact attempt Feb. 7, 2003. The previous three contacts, including the Jan. 22 signal, were very faint with no telemetry received. The last time a Pioneer 10 contact returned telemetry data was April 27, 2002. NASA has no additional contact attempts planned for Pioneer 10.

    • by noselasd (594905) on Monday September 13, 2004 @09:51AM (#10234934)
      This doesn't quite quench my thirst for information: does this mean the probes are still sending radio waves/signals, or just irradiating passively?
      Article at physicsweb [] says:

      When the craft were at distances of between 20 and 70 astronomical units, researchers found that the Doppler frequency of microwave signals that were bounced off the craft drifted at a small, constant rate

      So, passive it seems.
  • by sofakingon (610999) * on Monday September 13, 2004 @08:45AM (#10234334)
    I don't know about you guys, but if "something strange" were tugging at my "probe" using "mysterious forces," It would probably be bigger news than the science page of /. !
  • by JeffSh (71237) < minus city> on Monday September 13, 2004 @08:45AM (#10234335)
    im not scientist, and surely these articles are written for the layman, but all of the articles i've read say "something more than the sun's gravity is pulling at the probes"

    wouldn't the planets, especially jupiter, and saturn, and ALL of the misc tiny asteroids in the various belts, exert a pull on the probes as well? some sort of combined solar system gravitational force since the probes are well beyond the last planet?

    doesn't seem that complicated to me, but im definately coming at it from a relatively uneducated perspective then who's saying something's wrong in the first place.
    • by Benm78 (646948) on Monday September 13, 2004 @09:11AM (#10234553) Homepage
      Your idea is basically correct. Any object that has mass excerts a gravitational force on any other object that has mass. As far as we know, this force is not quantized, so there is no lower limit to how small it can become.

      That said, you would have to consider 'how much force?'. The force depends on the masses of both objects involved, and on their distance squared. The acceleration one object experiences is independant of its mass, since this mass cancels out when combining the formulas for gravity and acceleration. You could calculate that the gravitational force of the sun overwhelms that of any planet unless very close to the planet.

      To get any feel of the relative masses: 99.9% of the solar systems mass is in the sun alone. Compared to the earth, the sun is over 330.000 times more massive. Compared to jupiter, the sun is roughly 1000 times more massive.

      However, a more important argument is that we -know- the masses and positions of all major bodies in the solar system, and any deviation due to those is -not- unexpected or unexplained.
  • by Maddog Batty (112434) on Monday September 13, 2004 @08:46AM (#10234351) Homepage
    Bit of an old story [] this.
  • by isa-kuruption (317695) <kuruption&kuruption,net> on Monday September 13, 2004 @08:50AM (#10234377) Homepage
    The Bush Administration is altering the laws of gravity in order to distract us from the situation in Iraq. A bill in Congress right now will nullify the law of gravity as we know it, taking away the rights of individuals to remain firmly planted on the Earth.

  • by jjeffries (17675) on Monday September 13, 2004 @08:51AM (#10234390)
    what can I say... the damn things snagged my sweater during take-off, and I didn't want to say anything...
  • by G Samsonoff (161576) on Monday September 13, 2004 @08:51AM (#10234391) Journal
    Link to the Physics Web article: []
    • by smithwd (210995) on Monday September 13, 2004 @09:40AM (#10234829)
      There was also an article [] on the subject in The Economist a couple of weeks ago. The Economist story refers to a paper [] by Chris Duif that looks at other gravitational anomolies. Specifically there is something called the "Allais effect" which describes a measurable change in the force of gravity during solar eclipses. The effect has been experimentally confirmed by a number of observations with different measurement methods - and is also inconsistent with General Relativity. It will be interesting to see what - if anything - comes from the NASA Gravity Probe [] experiments.
      • by syukton (256348) on Monday September 13, 2004 @10:39AM (#10235488)

        wikipedia link for "Allais effect" []

        Apparently, the motion of a pendelum increases in speed during a solar eclipse; this was discovered by a fellow named Allais and the rest is history.

        I don't know how gravity affects the distortion of spacetime, but given my rudimentary understanding of gravity, somebody between the earth and the moon during a solar eclipse would have the sun's force of gravity plus the moon's force of gravity acting upon them, in addition to the earth's gravity in the opposite direction. I don't know if the cumulative though oppositely-pulling gravitational pulls would cause any gravitational anomalies that would, say, speed up time. But I'd believe it in a sci-fi movie, no doubt.

  • by The Famous Druid (89404) on Monday September 13, 2004 @08:52AM (#10234399)
    Um, I'm way out of my area of expertice here, so forgive me if this is utter drivel.

    The probes are basically big lumps of metal moving at high speed through space.

    How much do we know about the magnetic fields in deep space?

    Could this be some fairly boring electromagnetic effect?
  • by mod_parent_down (692943) on Monday September 13, 2004 @08:52AM (#10234402)
  • Pushing gravity (Score:5, Interesting)

    by RedLaggedTeut (216304) on Monday September 13, 2004 @08:59AM (#10234462) Homepage Journal
    If there was Pushing gravity [] (also discussed before on /. [] ), or just a similar effect, all our calculations and measurements of gravity would be off a little.

    I have no idea whether the effect would be so big though.

    Some (Majorana?) even thought some kinds of matter were radiating "pushing gravity", but I'm really leaning dangerously far out of the window by guessing that this is the way that a black hole a the center of the galaxy causes the anomaly in galactic rotation curve that is observed (that anomaly suggests more (gravitational) pull, too.)

    Please note that the arguments derived from thinking about Pushing gravity might apply even if gravity is not considered pushing by the physics used.

  • by Dexter77 (442723) on Monday September 13, 2004 @09:03AM (#10234490)
    After reading the article I had a flashback about old computer games, where "mysterious force" would tug you back when you reached the end of the area.

    How funny it would be if our world ended after Pluto and the stars would only be 'a painted backcloth'. I wonder what kinda effect it would have on our society. Scientist would propably spend years trying to explaing the phenomena, until one day a human could travel to the edge and verify the obvious.

    Or maybe the aliens that run our world on their supercomputer have not yet coded the rest of the universe. Let's wait for few more years and see if 'the mysterious force' has been removed :)
  • by applemasker (694059) on Monday September 13, 2004 @09:04AM (#10234500)
    Unlike Pioneers 10 and 11, Voyagers 1 and 2 continue to transmit to Earth. In fact, Voyager 1 is further from the sun (93.1 AU) than the furthest Pioneer (86.3 AU).

    Has this effect been observed as to the Voyagers?

    Excellent illustration (updated daily!) of all these probes and their vitals (trajectories, distance, speed, etc.) at Heavens-Above [].

    • by zardor (452852) on Monday September 13, 2004 @09:26AM (#10234698)
      IMHO, the pioneer probes are/were 'spin stabilised', i.e. are constantly rotating in order to keep them stable. This helps to cancel out most forces interfering with them during their journey (i.e. solar wind, light pressure, thermal radation, outgassing etc), and therefore makes it easier to extract the resudial unexplained force.
      However, he Voyager probes are '3-axis-stabilised', i.e. they maintain their orientation in space by means of gyros and thrusters. (This is a very good idea for steadly pointing cameras at planets as you fly past.)
      But, as a result, it is much harder, if not impossible, to compensate for the above mentioned forces.
      The voyagers are probably also affected by the same unexplained force, but this small force is overwhelemed by the uncertantinty of the magmitude of the other forces acting on those spacecraft. Therefore, there is not much point mentioning them!
  • by Anonymous Coward on Monday September 13, 2004 @09:17AM (#10234606)

    As it happens, The Economist recently ran an article addressing some of these issues. The article also provides context and perspective that should be of interest to those participating in this discussion. For convenience, the full text is reproduced below; it is also accessible online [] (may require paid subscription).


    Gravitational anomalies

    An invisible hand?

    Aug 19th 2004
    From The Economist print edition

    [Image] []

    An unexplained effect during solar eclipses casts doubt on General Relativity

    "ASSUME nothing" is a good motto in science. Even the humble pendulum may spring a surprise on you. In 1954 Maurice Allais, a French economist who would go on to win, in 1988, the Nobel prize in his subject, decided to observe and record the movements of a pendulum over a period of 30 days. Coincidentally, one of his observations took place during a solar eclipse. When the moon passed in front of the sun, the pendulum unexpectedly started moving a bit faster than it should have done.

    Since that first observation, the "Allais effect", as it is now called, has confounded physicists. If the effect is real, it could indicate a hitherto unperceived flaw in General Relativity--the current explanation of how gravity works.

    That would be a bombshell--and an ironic one, since it was observations taken during a solar eclipse (of the way that light is bent when it passes close to the sun) which established General Relativity in the first place. So attempts to duplicate Dr Allais's observation are important. However, they have had mixed success, leading sceptics to question whether there was anything to be explained. Now Chris Duif, a researcher at the Delft University of Technology, in the Netherlands, has reviewed the evidence. According to a paper he has just posted on [], an online publication archive, the effect is real, unexplained, and could be linked to another anomaly involving a pair of American spacecraft.

    Three different types of instrument have been used to detect the Allais effect. The first are conventional pendulums, such as the one Dr Allais used originally. The second are torsion pendulums, which work by hanging a bar that has weights at each end from a wire. As the wire twists back and forth, the bar rotates in pendulum-like motion. The third are gravimeters, which are, in essence, very precise scales. All of these instruments measure the acceleration due to gravity at the Earth's surface, a quantity known as g. The Allais effect is a small additional acceleration, so tiny that it would take an apple about a day to fall from a tree branch if it were the only gravitational effect around.

    Allez, Allais

    Dr Duif has examined various conventional explanations for the Allais effect. He finds the most obvious suggestion--that it is a mere measuring error--unlikely, because similar results have been found by many different groups, operating independently and, in at least one case, without knowledge of Dr Allais's results.

    He also discounts several explanations that rely on conventional physical changes that might take place during an eclipse. One of these is that the anomaly is caused by the seismic disturbance induced as crowds of sightseers move into and out of a place where an eclipse is visible. That seems unlikely, given that one of the experiments with a positive result was conducted in a remote area of China while another that had a negative result took place in Belgium, one of the most crowded parts of the planet. Dr Duif also considered the possibility that, because the moon's shadow cools the air during an eclipse, this cooler, and thus denser, air might exert a different gravitational pull on the instruments. This change could, he reckon

  • Obligatory MOND post (Score:5, Interesting)

    by CausticPuppy (82139) on Monday September 13, 2004 @09:22AM (#10234646) Homepage
    Hmm, I've read about this on Slashdot before, and I'm pretty sure I've read about Modified Newtonian Dynamics before.

    The gist is this: MOND is an alternative to the "dark matter" explanation. It makes a modification to newton's laws of motion, whereby gravitational strength.
    The equation F = ma is well known, but with MOND the gravitational inverse square law changes to an inverse linear law when the acceleration due to gravity falls below a critical value, which is very small (i.e. you get pretty far away from the source of gravity).

    This explains most of the observed behavior that is currently explained by dark matter, including the rotation of galaxies which seem to defy newton's laws. Unfortunately, there's still no derived theoretical basis for MOND; as of now it's a rather arbitrary explanation with equations that just seem to work pretty well, and many physicists do not take MOND seriously. Then again, "dark matter" seems just as silly.

    A more in-depth explanation is available here. []

    Interestingly, the MOND critical value for the acceleration (a0) turns out to be the speed of light divided by the age of the universe.

  • by Betelgeuse (35904) on Monday September 13, 2004 @09:22AM (#10234654) Homepage
    MOND []

    Well, it's what some physicists may be thinking, anyway. I suspect that the Guardian article is meaning to hint at this, as well. For those who don't know, MOND is a modification of standard Newtonian Dynamics that has to do with very small accelerations. I'd actually really, really like to see a MONDian calcuation of what the forces should be on those probes and see if it matches their current paths.

    Wow. I think this is the second time I've advocated MOND (a theory which I just barely consider reasonable, and no where near verified) on /.
  • by madsatod (535808) on Monday September 13, 2004 @09:31AM (#10234735)
    I like the following explanation of the anomalous acceleration. No dark matter/20 dimensions/new gravity theory needed here. A small amount of dust in the kuiper-belt that transfers momentum with the probe should be enough to explain the slowdown. Look at: ion.html []
  • dust? (Score:5, Interesting)

    by alexandre (53) on Monday September 13, 2004 @09:55AM (#10234973) Homepage Journal
    Couldn't it be continuously hitting against clouds of dust?
  • Oort cloud (Score:5, Interesting)

    by Nonillion (266505) on Monday September 13, 2004 @10:10AM (#10235157)
    How close are these probes relative to the Oort cloud? I would think that what we are witnessing is that the probes lack the velocity to escape and will eventually become part of the Oort cloud.
  • by nightsweat (604367) on Monday September 13, 2004 @10:17AM (#10235238)
    Yep, Space Barnacles.
  • by gotroot801 (7857) on Monday September 13, 2004 @10:19AM (#10235266) Homepage Journal
    "Space, it seems to go on and on forever. But then you get to the end and a gorilla starts throwing barrels at you."
  • by salec (791463) on Monday September 13, 2004 @10:52AM (#10235625) contains some interesting data that may be a clue:

    "The location of the heliopause, which marks the outermost edge of the solar system, is a subject of scientific speculation. In two papers recently published in the journal Nature, scientists debated whether Voyager 1 has already reached the termination shock, a sign that the heliopause may be near. The termination shock is caused by a reduction in the speed of the solar wind as it slams into cooler plasma at the edge of the solar system and is similar to the sonic boom that occurs on Earth when an airplane crosses the sound barrier."

    So my guess (IANAAP) is they have lost their (solar) wind in the back they had and hence the decceleration. It may not be so simple, though. Perhaps the space on the inside of the heliopause sphere is constantly "sweeped" by solar wind and therefore might have lower density then surroundings (picture: we are in a kind of a solar bubble! :-) ).
    There is a way to put my hypotesis to test: check the temperature readings for signs of friction, or perhaps even cooling.

"Stupidity, like virtue, is its own reward" -- William E. Davidsen