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Mystery Force Affecting Probes
imipak writes: "The BBC reports that after exchaustive investigations, NASA scientists have run out of possible explanations for the mysterious tiny course deflections experienced by the Pioneer and Voyager spacecraft as they head out of the solar system towards the heliopause. Could it be that there's something wrong with our theory of gravity? (Well, yes, we already know that...) or could it be Oort Cloud objects? The tenth planet? Informed comment, please!"
Slashdot Readers
Hurrah! Please explain it for me, guys. I have a friend at NASA who would really like to know.
If they're slowing as they get very far from the Sun, that seems to imply that the force of gravity is not dropping of quite as fast as 1/r^2.
The problem is, as the article points out, we would have seen the effects of this on the orbits of the planets if this was the case.
I'm personally wondering about drift in the probes' radio sources throwing off the doppler measurements, but if this was happening they should have caught it already (you can directly measure the probes' positions by measuring the round-trip signal times to them at a few different imes during the year).
I am extremely offended at your attitude. My father spent the last years of his life _skeptically_ examining all the evidence gathered throughout the THIRTY years the pioneer probes were operational.
The fact that you can sit in your armchair and question his objectivity, wonder, and *passion* for the mysteries of life makes me physically ill.
Any failing of science is OUR fault. OUR faliere to educate. OUR faliure to recognize our biases. OUR faliures to drag concieted shits like you out of the dark ages.
My (recently deceased) dad is on that paper.. he believed that it was most probably (b) (outgassing of some sort, possibly a malfunction/weakness common to both pioneer probes). No real evidence of that of course, and a "mysterious" force is more publishable ;) Still it is very spooky.
(g) and (h) were (in his opinion) the least likely.
Note that the paper was actually first released in April, and just revised today.
Could it be that there's just more mass in the solar system than we think? Wait, hear me out. I'm not talking about Planet X or a bloated G, I'm talking about ambient stellar gas.
Here's the deal: On the Earth, the gravitatinal forces acting on you at the surface all sum out to equal to the forces that would be exerted by a point source with the Earth's mass and a distance r, the diameter of the Earth. Though that ocean to your left and that continent to your right pull you in opposite directions, and the ground under your feet is pulling harder than the ground in China (um, unless you're in China, in which case, 'hi'), but it all sums out exactly right to a point mass at radius r.
Now, take that example and pose it to the solar system. Forget about the forc of solar wind blowing, and realize that all that wind has mass, and exists everywhere. It's pretty thin, but it's a lot thicker than the four hydrogen atoms per cubic meter in deep interstellar space. All that stuff, wispy as it is, has mass, and even though most of it is so godawful far away, the net gravitational effect of all of it is as if there were an additional point source inside the sun, with the mass of all the stray gasses and particles inside the huge sphere that has the sun as the center and the space probe on the outer surface.
What makes the math even more wonky is that, assuming a roughly even distribution of gas as inversely proportional (or inverse square, or even constant, doesn't matter in this case as long as it's uniform by uniform radius) to the distance form the sun, then the farther out the probe goes, the more mass there is behind it, and the farther back the point source goes.
If the density were uniform (it's not) then the effect of this force would actually increase as the probe got further away. As it is, it may be a constant force. For conceptualization's sake, if you had a well to the center of the earth and went to the bottom (forget magma, use the moon if it makes you feel better) you'd be weightless. Go halfway up, and you'd have a force of one-half g. Go to the surface and you are being pulled with a stronger force than you were when you were closer to the center.
Anyhow, HTML's bad for math, but I just wanted to get the idea out there. I don't have enough info on particulate density over the scope of the solar system and beyond to make any educated numbers anyhow. Hopefully someone out there does.
Kevin Fox
--
Kevin Fox
The interstellar medium (interstellar gas & dust) is much less dense than normal around our solar system due to the Scorpius-Centaurus Association superbubble and the Geminga supernova bubble. Perhaps we're seeing a slight increase in the ISM density -- of course these researchers should know all about this, so it's still a puzzle...
If they're slowing as they get very far from the Sun, that seems to imply that the force of gravity is not dropping of quite as fast as 1/r^2. If the strength of gravity is higher than inverse square and great distances, perhaps that effect would explain the "missing mass" problem? There isn't really any missing mass. This effect makes it look like the galaxies are more massive than they really are.
--Fermat
The only problem with this analogy is that the precession of Mercury's perihelion occured in the area of the highest graviational field within 4 light years. This is where you would expect to find simplier theories to break down.
:-) The shape of galaxies - and interactions of galaxies in clusters and super-clusters, shows that the universe is "flat" on the scale of many millions of light years. If you equate that to the size of the earth, then 1 meter represents about 1 LY, and the helipause will easily fit within a postage stamp. Or maybe the period at the end of this line. Something definitely "flat" by any reasonable definition.
In contrast, the probes are in areas with a relatively small gravitational field. While the field is smaller than anything this side of Pluto's orbit, it's not that much smaller. (The contribution from the sun is lower, but the contribution from the entire Milky Way, and our gravitationally bound galactic cluster, is just as large.) A breakdown in the existing theory just doesn't make sense here - and even if it does break down, where does the energy come from?
As for the issue of the space of the universe... get a grip.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
An early theory of gravity said it pushed in all directions at the same time but things with mass blocked it slightly. The attraction force is simply the delta of pushes from two sides not being equal. This was thrown out because things in space would slow down over time. However...
it appears that things do slow down over time. The deep space probes are not the only ones showing this. The gps sats are doing it and this is one of the problmes that gravity probe B is suppoed to help solve. I guess it means we have a wrong view of what keeps up stuck on this world.
It's Protector Brennan, making slight alternations to make certain that the probes don't eventually travel to planets with possibly-hostile alien species, thereby alerting them to the existence of humans.
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
New Physics Theory Highlights:
Due to the fact that the size of the anomalous acceleration is of order cH, whereH is the Hubble
constant (see Eq. (56)), the Pioneer results have stimulated a number of new physics suggestions.
For example, Rosales and S anchez-Gomez [136] propose that aP is due to a local curvature in
light geodesics in the expanding spacetime universe. They argue that the Pioneer eect represents
a new cosmological Foucault experiment, since the solar system coordinates are not true inertial
coordinates with respect to the expansion of the universe. Therefore, the Pioneers are mimicking
the role that the rotating Earth plays in Foucault's experiment. Therefore, in this picture the
eect is not a \true physical eect" and a coordinate transformation to the co-moving cosmological
coordinate frame would entirely remove the Pioneer eect.
From a similar viewpoint, Guruprasad [137] nds accommodation for the constant term while
trying to explain the annual term as a tidal eect on the physical structure of the spacecraft
itself. In particular, he suggests that the deformations of the physical structure of the spacecraft
(due to external factors such as the eective solar and galactic tidal forces) combined with the
spin of the spacecraft are directly responsible for the detected annual anomaly. Moreover, he
proposes a hypothesis of the planetary Hubble's ow and suggests that Pioneer's anomaly does
not contradict the existing planetary data, but supports his new theory of relativistically elastic
space-time.
stvang [138] further exploits the fact that the gravitational eld of the solar system is
not static with respect to the cosmic expansion. He does note, however, that in order to be
acceptable, any non-standard explanation of the eect should follow from a general theoretical
framework. Even so, stvang still presents quite a radical model. This model advocates the use
of an expanded PPN-framework that includes a direct eect on local scales due to the cosmic
space-time expansion.
Belayev [139] considers a Kaluza-Klein model in 5 dimensions with a time-varying scale factor
for the compactied fth dimension. His comprehensive analysis led to the conclusion that a
variation of the physical constants on a cosmic time scale is responsible for the appearance of the
anomalous acceleration observed in the Pioneer 10/11 tracking data.
Modanese [140] considers the eect of a scale-dependent cosmological term in the gravitational
action. It turns out that, even in the case of a static spherically-symmetric source, the external
solution of his modied gravitational eld equations contains a non-Schwartzschild-like component
that depends on the size of the test particles. He argues that this additional term may be relevant
to the observed anomaly.
A proposal to modify the theory of gravity in order to provide an explanation of the Pioneer
anomaly has also appeared. Capozzielo et al. [141] discuss the possibility of determining the
stability and characteristic geometrical and kinematical properties of galaxies strictly based on a
minimal action whose value is on the order of the Plank constant.
Due to the fact that the size of the anomalous acceleration is of order cH, whereH is the Hubble
constant (see Eq. (56)), the Pioneer results have stimulated a number of new physics suggestions.
For example, Rosales and S anchez-Gomez [136] propose that aP is due to a local curvature in
light geodesics in the expanding spacetime universe. They argue that the Pioneer eect represents
a new cosmological Foucault experiment, since the solar system coordinates are not true inertial
coordinates with respect to the expansion of the universe. Therefore, the Pioneers are mimicking
the role that the rotating Earth plays in Foucault's experiment. Therefore, in this picture the
eect is not a \true physical eect" and a coordinate transformation to the co-moving cosmological
coordinate frame would entirely remove the Pioneer eect.
From a similar viewpoint, Guruprasad [137] nds accommodation for the constant term while
trying to explain the annual term as a tidal eect on the physical structure of the spacecraft
itself. In particular, he suggests that the deformations of the physical structure of the spacecraft
(due to external factors such as the eective solar and galactic tidal forces) combined with the
spin of the spacecraft are directly responsible for the detected annual anomaly. Moreover, he
proposes a hypothesis of the planetary Hubble's ow and suggests that Pioneer's anomaly does
not contradict the existing planetary data, but supports his new theory of relativistically elastic
space-time.
stvang [138] further exploits the fact that the gravitational eld of the solar system is
not static with respect to the cosmic expansion. He does note, however, that in order to be
acceptable, any non-standard explanation of the eect should follow from a general theoretical
framework. Even so, stvang still presents quite a radical model. This model advocates the use
of an expanded PPN-framework that includes a direct eect on local scales due to the cosmic
space-time expansion.
Belayev [139] considers a Kaluza-Klein model in 5 dimensions with a time-varying scale factor
for the compactied fth dimension. His comprehensive analysis led to the conclusion that a
variation of the physical constants on a cosmic time scale is responsible for the appearance of the
anomalous acceleration observed in the Pioneer 10/11 tracking data.
Modanese [140] considers the eect of a scale-dependent cosmological term in the gravitational
action. It turns out that, even in the case of a static spherically-symmetric source, the external
solution of his modied gravitational eld equations contains a non-Schwartzschild-like component
that depends on the size of the test particles. He argues that this additional term may be relevant
to the observed anomaly.
A proposal to modify the theory of gravity in order to provide an explanation of the Pioneer
anomaly has also appeared. Capozzielo et al. [141] discuss the possibility of determining the
stability and characteristic geometrical and kinematical properties of galaxies strictly based on a
minimal action whose value is on the order of the Plank constant.
Someone you trust is one of us.
All these craft are still within the heliopause and will be so for a long time. They're moving outward faster than the solar wind, which means they're flying into it. The vacuum of space is only mostly a vacuum, remember, so the combined impacts of many little atoms will add up over time. The Pioneer craft, in particular, have been out there 20+ years, so the culmulative effects have had time to add up, and these would tend to slow the crafts over time. This effect is not negligible, or solar sails wouldn't work.
Also, as probably a lesser effect, there's all the virtual particles that are springing up in front of the craft and getting run into before they can meet their natural antipartners. These also will register as mass impacts and tend to slow the vehicles.
The first cause in particular will only get worse when the first craft hits the heliopause. At that point, it will no longer be plowing along with, but faster, than our Sun's wind, but head on into new solar winds. I wonder how much more difficult this makes it to come up with enough energy for eventual real interstellar travel.
Just a late night thought or two... but it doesn't seem unreasonable.
--
--
I don't want to rule the world... I just want to be in charge of mayonnaise.
I'm not sure what planet you're on because you seem to be trying to write an anti-science diatribe and yet much of what you say is no different from the view of a scientist.
---- SIGFPE
There is no reason to suppose gravity gradients are even across large distances (>20 A.U.) If you pour over your references, you'll see that at no point, from the General Theory on up, does any theorist take into account the possibility that between strong influences (astral bodies), spacetime must be smooth. in fact, it is perfectly reasonable to suppose that there are variations large enough to account for these variances in trajectory. The universe is not beholden to your 'rubber sheets and marbles' analogy for gravity.
(1) What you described is called "vacuum energy", and is actually one of the suspects. However, current physics has a problem : the predicted vacuum energy is 10^(120) (that's 1 followed by 120 zeroes) larger than the actual measured vacuum energy (called the cosmological constant by some people). With respect to the Pioneer 10 acceleration, the predicted VE will be too big, the measured VE will be too small.
(2) Not likely. Small things can theoretical deflect the probe. However you run into two showstoppers (i) things are too small to make any difference (ii) the things will deflect the probe, averaged out, in an "isotropic" way (what this means is that, on average, there will be no net deflection).
(3) Possible. But this uneven distribution will be detected long before. It's discussed in the paper that I listed in another post here. The punchline is that such things will also cost deflection of the planets, and we don't see that.
Hope this helps.
Mode (3) smart-aleck mode. Press * to return to main menu.
Check out the JPL final paper on this.
:
Possibles are
(a) Heat Ejection (b) Gas Leak (c) Clock Drift (d) Anomalous objects (pretty dead, despite BBC giving prominence) (e) modifications to gravity (f) solar radiation pressure (g) systematics of observations (h) antenna radiation pressure
Let the armchair speculation begin. (But remember to read the paper to check your answers!) Have Fun!
Mode (3) smart-aleck mode. Press * to return to main menu.
While this news report is very likely just a measurement error, we must be reminded that the last time we discovered an error in a celestial body's trajectory we reinvented the notion of the universe.
One of the big open questions of the day is: What is the shape of the universe? Euclidean, hyperbolic, a torus--we aren't sure. It is thought that each of these geometries would profoundly affect an object moving across the universe in a different way. These NASA probes could in a sense be the moving laboratory that we need to understand what exactly our universe looks like.
Robert
http://wso.williams.edu/~rmcgehee
And that was one of the most important creative leaps that led to quantum mechanics that gave us electronics, computing, and hence Slashdot. Almost as if my miracle, the equations worked! After some eighty years, we still don't admit that particles are waves, but it is one heck of a model. In principle, physics is not about what is real, it is about models of the nature. (Insert your favourite definition of reality from the Matrix here.) Physics does a lot of things purely systematically, but new theories like wave mechanics require those what-if ideas that may seem stupid at the first glance. The validity of a model can usually be tested by experiment, and if it fails then we can be certain that the idea was 'stupid' indeed. We can only let Nature judge which models are better.
I agree that ultimately physics should be about particles - or rather whatever the fundamental objects turn out to be (strings? a very elegant _model_ but maybe nothing more). The problem is, before we get there, we want to be able to model the larger scales as well. We can quite safely model the largest scale of the universe without worrying about the underlying forces between individual particles. Maybe that model (i.e. General Relativity for now) isn't absolutely accurate, but it's better than having to wait for a theory of everything - which BTW may never come up.
--
Escher was the first MC and Giger invented the HR department.
For each of the other 3 forces (weak, strong, electromagnetic), we have discovered a "carrier" particle for that force.
The strong force is carried by particles called "gluons" while the weak force is carried by "weak bosons". The electromagnetic force is carried by "photons". These have been detected in particle accelerators. Scientists have a name for the carrier particle of gravity - "graviton", but it has never been detected - yet.
The strong and weak force have a relatively (no pun intended) limited range. The strong force has a range of only about 1x10^-15 meters. On the other hand, gravity and the electromagnetic force have infinite ranges. Perhaps we're wrong about the gravity force, considering we don't even have a carrier particle. Maybe its strength isn't an inverse squared relationship for infinitely long distances - or it's simply an approximation.
Too bad I don't know nearly enough about experiments testing the gravitational constant and how well we've applied it to extrasolar objects.
"The universe seems neither benign nor hostile, merely indifferent." --Carl Sagan
You'll see lots of speculation by people who have no idea what they're talking about, but at least that won't get modded up. You'll also see lots of speculation by people who have a very slight idea of what they're talking about, and even though that speculation is little better, it will get modded up by other people who have a slight idea of what they're talking about, because it sounds plausible.
Maybe a legitimate space scientist or two will post with something that might actually be useful. Maybe--possibly--that will get modded up. More likely it won't, because it will be over most people's heads, or because he came too late to the conversation (say, two days from now) when no one's going to use mod points on the story.
Assuming your characterization of the BBC story is accurate (/.ed, can't get to it right now), and assuming that the BBC story itself is accurate--both of which are nontrivial assumptions--why wouldn't the quoted "NASA scientists" be the informed comment you're looking for? Is anyone here going to give you a better answer than the "we don't know" you got from the NASA scientists?
(Don't mind my ranting, I'm just in an anti-/. mood today.)
Never take moderation advice from sigs, including this one.
Or they could put the recording on Napster and wait until the RIAA tries to sue them.
Jedi:"You will alter your course."
Probe:[ continues course ]
Jedi:(under breath) "Oops."
[ Jedi waves hand in front of probe ]
Jedi:"You will alter your course."
[ back on earth... ]
BBC News:"Mystery force tugs distant probes"
Ewige Blumenkraft!
Ewige Blumenkraft!