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Space Probes Too Slow - Scientists Ask "Why?"
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.
Clearly, the probes are slowing down because of the load on their systems caused by the Slashdot Effect.
-- Ed Avis ed@membled.com
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.
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!
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.
For those interested, the original articles and articles that cite (and comment) it can be found from the web: gr-qc/9808081
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)
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...
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>>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.
--Scott 8-}
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.
There is nothing so pathetic as seeing a beautiful young theory roughed up by a tough gang of facts.
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.
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."
These are my friends, See how they glisten. See this one shine, how he smiles in the light.
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."
These are my friends, See how they glisten. See this one shine, how he smiles in the light.
(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!]
lake effect weblog
{Network engineer in Chicago--looking for work!}
(not a personal slam at teraflop, you obviously understand the issues)
... somewhat impractical.
I just want to caution Slashdot readers (some of whom seem to be posting) that one scientist's hypothesis does not a solution make. Clearly there is room for debate on this issue, particularly since actually going out to Pioneer and taking measurements is
So, Scientists A&B say, we have something odd here, and nothing we've investigated explains it (first article in physics journal, reported in NS). Scientists C&D say, it looks to us like the probe's excess heat, using these calculations (2nd NS article). That doesn't mean that A&B will automatically agree with C&D (they don't).
It's often said, not entirely tongue-in-cheek, that scientists (who have careers at stake) never admit they're wrong, and that the only way new theories become accepted is for all the old scientists to die off!
In any case, the Pioneer conundrum is a very interesting one. It's not, in itself, evidence of a new force, but it is dramatic example of how complex something as "simple" as a spaceship trajectory can be, and how we don't understand everything yet. (Which to that I say: Thank God, what a boring universe it would be if we understood everything.)
[As for the slashdot kiddies complaining "we heard about this already", maybe Slashdot should stop reporting on, say, Microsoft vs. the DOJ. After all, it was first reported on over a year ago, the fact that they're still arguing is irrelevant. It's old news!]
lake effect weblog
{Network engineer in Chicago--looking for work!}
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.
In illa quae ultra sunt
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!
Time is Nature's way of keeping everything from happening at once... the bitch.
They should have used Energizers
A month later New Scientist published this story, 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.
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.
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?
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 about the discovery of yet another Kuiper Belt object by Pioneer, 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.
--
Andrew Oakley - www.aoakley.com
Aparently P10 has discovered a new planetoid http://news.bbc.co.uk/hi/english/sci/tech/newsid_4 60000/460095.stm
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.
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.
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.
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
Coming soon - pyrogyra
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.