The Pioneer Anomaly

[Ivan Seeking]

...In October, a European Space Agency panel recommended a space mission to determine whether Anderson had found something that could rewrite physics textbooks. Some cosmologists even speculate the Pioneer Anomaly might help unravel some of the thorniest problems in theoretical physics, such as the existence of "dark matter" or mysterious extra-dimensional forces predicted by string theory.

For public consumption at least, Anderson and his close-knit group of researchers will not permit themselves the luxury of such grandiose speculation. [continued]

http://story.news.yahoo.com/news?tmpl=story&cid=2026&ncid=2026&e=10&u=/latimests/20041221/ts_latimes/gravitymayloseitspull

Study of the anomalous acceleration of Pioneer 10 and 11
...(Dated: July 9, 2004)
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf

[meteor]

The text mentions that one of the possibilities for the slow down is that the extra dimensions of string theory are tugging at the spacecrafts. I would like how this can be, how can extra dimensions have influence in the dynamics of an object
If this explanation holds true, it would be the so desired experimental confirmation of string theory physics

[Garth]

One question is why is this anomalous acceleration detected on distant spacecraft but not on other orbiting bodies?
It may be explained by a clock drift between atomic clock time and ephemeris clock time, the acceleration being approximately the Hubble acceleration, http://arxiv.org/abs/gr-qc/0403013
ap ~ cH.

Such a clock drift is predicted by SCC.

Garth

[tony873004]

I've heard that it can be explained by a more massive-than-expected Kuiper Belt. Specifically, dust in the Kuiper Belt. If evenly distributed, the gravitational forces of the individual particles would cancel out and be unnoticable to any object that orbits interior to the Kuiper Belt. But once in the Kuiper Belt or outside the Kuiper Belt, their presence would be felt and would add to the mass of the solar system, slowing down any object in or external to the Kuiper Belt. If this were the case, you would also expect a more subtle slowing by any object that left the plane of the solar system. This is the case with the Ulysses spacecraft. It is experiencing slowdown as well, but not as much as the Pioneers.

[meteor]

I've found this article in which is said that the Pioneer anomaly is due to a Berry phase
http://arxiv.org/abs/gr-qc/0401014
According to Wikipedia a Berry phase is "a phase acquired by quantum states when subjected to adiabatic processes, resulting from the geometrical properties of the parameter space of the Hamiltonian."

[Garth]

Well that's cleared that up then!

If so, will the same 'Berry phase' then also explain the MOND anomalous acceleration? It seems we may have a whole new gravitational theory here - with radical consequences.

Garth

[ohwilleke]

MOND makes a rather poor explanation of the Pioneer anomolies because over the distance in which they are observed the effect should vary by a factor of about one third, but in fact the effect is very constant.

I think a better explanation is likely that the satellites are simply moving through a very sparse sea of dust rather than a true vacuum, and that occassional slight reductions in speed due to collisions with these dust particles explains the effect.

[Nereid]

I've seen references to the effect having been detected by analysing Ulysses' orbit ... but haven't ever found a paper on it. This anomaly is particularly maddening ... it's very weak, not reproduced, what's left after lots and lots of other effects are 'subtracted', not easily testable, ...

Let's all hope that LISA gets launched on time!

[TheAntiRelative]

Okay this is really out there but what if they only appear to be slowing when in fact what is happeneing is somewhat similar to the effects seen in all these experiments where they make EM signals seem to travel faster than light.

If they entered a field of some kind that made the timing seem faster we would believe they were closer than they actually are and calculate them as slowing down...

http://archives.cnn.com/2000/TECH/space/07/20/speed.of.light.ap/

We know that light travels different speeds in different mediums. If light seems to be transmitted faster in cesium then it stands to reason that some other particles out there might transmit our communication signal that we use to judge the distance with just a little faster.

IE: Maybe it's an illusion and the effect is very explainable with already known phenomena.

Edit: Then again perhaps I should read more before I shoot my mouth off...
In what way is the distance being measured?

[Garth]

MOND makes a rather poor explanation of the Pioneer anomolies because over the distance in which they are observed the effect should vary by a factor of about one third, but in fact the effect is very constant.

I think a better explanation is likely that the satellites are simply moving through a very sparse sea of dust rather than a true vacuum, and that occassional slight reductions in speed due to collisions with these dust particles explains the effect.
But would not that also cause a varying anomalous acceleration? As the spacecraft slowed down in the outer solar system it would need an increasing density of dust cloud to produce the uniform effect, and it would have to be homogeneous with a density that depended only on the distance to the sun.

Nereid, although the anomalous acceleration is tiny at that range it is a reasonable proportion (10-3) of the Newtonian deceleration.

As the effect has been constant and roughly equal to cH, perhaps it is due to a cosmological rather than dynamical effect, e.g. a drift between ephemeris and atomic clock time.

Garth

[ohwilleke]

But would not that also cause a varying anomalous acceleration? As the spacecraft slowed down in the outer solar system it would need an increasing density of dust cloud to produce the uniform effect, and it would have to be homogeneous with a density that depended only on the distance to the sun.

Suppose the the density of the dust in the area where the change in velocity is observed (the outer solar system) is more or less uniform. As previously noted the change in velocity is a very small percentage of the total velocity (the effect is on the order of 1 x 10^-8 cm/s^2 IIRC). Even with this effect, the change is velocity over the range where the effect is observed is smaller than the uncertainty in the effect (+/- about 12%).

The amount of decelleration caused by travelling a distance X through a cloud of dust a velocity V is basically proportional to the density of the dust cloud. As long as the density of the dust cloud is largely constant and the velocity change is modest, the change in velocity due to dust collisions per unit time should be largely constant. The dust cloud doesn't have to be more dense.

Perhaps I'm not being clear about what I mean by I dust cloud. I am imagining that the vaccum is not really empty and that say, in every cubic meter of "empty space" there is one speck of dust in the entire region of the outer solar system. The number of specks you hit is proportional to the area your forward profile sweeps in a given time period and the accelleration isn't really "towards the sun" so much as it is "in the opposite direction of your velocity vector".

[Nereid]

*SNIP

Perhaps I'm not being clear about what I mean by I dust cloud. I am imagining that the vaccum is not really empty and that say, in every cubic meter of "empty space" there is one speck of dust in the entire region of the outer solar system. The number of specks you hit is proportional to the area your forward profile sweeps in a given time period and the accelleration isn't really "towards the sun" so much as it is "in the opposite direction of your velocity vector".OK, perhaps we can test this idea! :smile:

Since dust is neutral (or, if charged, its path through the solar system not appreciably affected by its charge), the amount of dust striking the Pioneer craft will be the same as the amount of ISM dust hitting the Earth (for the same cross-section) ... well, not really, but as an OOM, perhaps a good place to start.

So, how much dust would be necessary to account for the Pioneer anomaly? How much does this translate to, in terms of tonnes per annum for a random square km of Pacific Ocean (or Antartica)? How does that estimate compare with what's in deep sea cores (or ice cores)?

To re-iterate, we're only interested in OOM for now; if the numbers are vaguely similar (OOM-wise), we might look to refining the estimates. :biggrin:

[ohwilleke]

This, admittedly ill reputed source, calculated quite straightforwardly, that if dust particles are 50 microns, then one particle per 25,000 cubic meters would produce the desired effect. http://www.newtonphysics.on.ca/Anomalous/Acceleration.html

This could not be replicated by Earth measurements because particles that sparse would burn up in the atmosphere and be indistinguishable from pollution and the Earth is much more massive per particle impacted so the orbital effect would be negligable.

[Nereid]

This, admittedly ill reputed source, calculated quite straightforwardly, that if dust particles are 50 microns, then one particle per 25,000 cubic meters would produce the desired effect. http://www.newtonphysics.on.ca/Anomalous/Acceleration.htmlMaybe; maybe not.This could not be replicated by Earth measurements because particles that sparse would burn up in the atmosphere and be indistinguishable from pollution and the Earth is much more massive per particle impacted so the orbital effect would be negligable.A), most ISM dust particles do NOT burn up in the atmosphere; they settle onto the deep ocean floor (actually everywhere, but only there do they comprise a sufficient component to be detected - elsewhere this signal is drowned out)
B), the larger particles which do burn up leave easily detectable meteor trails; analyses of these can give robust estimates of their incidence
C), a number of spacecraft have detected 'micrometeoride' impacts, which can be analysed to calibrate the ISM component
D), and so on ....

Would you care to take another look?

[Chronos]

I've seen references to the effect having been detected by analysing Ulysses' orbit ... but haven't ever found a paper on it. This anomaly is particularly maddening ... it's very weak, not reproduced, what's left after lots and lots of other effects are 'subtracted', not easily testable, ...

Let's all hope that LISA gets launched on time!Agreed. Data from the Galileo probe was also anomalous, yet too weak to be definitive. While no single data set seems compelling, the collective data seems strong enough to merit further research. I believe ESA has a project on this in the works. Can't remember the name off the top of my head, but it may be even more exciting than GPB [gravity probe B]. PF people use too many abbreviations.

[Nereid]

LISA (http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=30467) - Laser Interferometer Space Antenna.

From this site: "However, the more scientists study gravity and its effects on celestial objects, the more mysteries they seem to uncover. One example is the so-called 'Pioneer anomaly', named after the NASA space probes Pioneer 10 and 11, on which the effect was first noticed. The anomaly was revealed when a number of spacecraft were seen to be affected by an unknown force that slowed them down. The same behaviour has now been detected on NASA's Galileo and the joint ESA-NASA Ulysses spacecraft."

[LURCH]

The mechanism I tend to lean toward his radiation pressure from the collision of the solar wind with its own terminus.

[meemoe_uk]

The mechanism I tend to lean toward his radiation pressure from the collision of the solar wind with its own terminus.

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.


I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.
And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this.

[Garth]

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards. True, but the suggestion is that the effect is caused by an imbalance in the radiation input/output due to internal heat and radio transmissions as well as solar radiation. Although there may well be some, and some thrust from gas leakage, these are not enough to explain the anomaly, only part of it.
I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.All good points.
And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this. Why suddenly rubbish "the top scientists"? Evidence is building that the standard model, which has required a series of 'fixes', (Inflation, DM, DE), needs revising but the general approach has been sound, i.e. to conflate tested theory (GR) with precise observations. (Hubble Deep Field, WMAP, S/N Ia etc.)

Garth

[Nereid]

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.


I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.
And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this.Good comments about (solar) radiation pressure and dust.

However, you lost me when you started talking about the 'hubble red shift' - would you mind taking the time to spell this out a bit please? In particular:
- what this 'hubble red shift' is
- how 'the measurement is based on hubble red shift'
- how 'using hubble red shift gives plently of scope for crazy results'

It's OT, but I'm also curious as what relationship you think there is between the 'hubble red shift' and 'that galactic rotation anomaly'.

[LURCH]

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.




Quite true. However, referrign to the solar wind itself, but rather the radiation from the terminus of the solar wind. Nearly all astronomers agree that the solar wind exerts its influence only out to a certain distance from the sun. Beyond that, there is expected to be some sort of prevailing " galactic wind", within which our solar wind forms a sort of bubble. The terminus is the boundary area where the solar wind's influence terminates. This termination is thought to be fairly abrupt (by astronomical standards); a collision, if you will, between the solar wind and the prevailing galactic wind outside.

In most fluids, such a collision would send a shock wave back "upstream" in the form of sound waves. According to the dynamics governing supersonic fluids, the energy of the impact would radiate backwards as EM radiation. So, as pioneer approaches the terminus, it should experience radiation pressure from "in front". This is one of the theorized explanations for the so-called "Pioneer Anomoly" (the one with which I happen to agree).

[ohwilleke]

I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around

It is an obvious solution, but it wasn't considered in the leading paper on the topic. (Dust in the Kuniper belt as a gravitational effect was considered at page 30, here: http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf but not impact with dust). Note that, in contrast, solar radiation and solar wind were considered. Also, while it is obvious that dust could have this effect, it is not obvious that the amount of dust necessary to create this effect is so small. Also, this would explain why we don't see it in planets but do in spaceships.

The mass to sweep area ratio is much higher in spaceships than planets (by a factor of 1 billion to one).

Pioneer 241 kg; Sweep Area 9.4 square meters.
Mars 6.39*10^23 kg; sweep area; 1.45 x 10^14 square meters

Pioneer Mass/square meter= 25.6 kg/sq meter
Mars mass/square meter=4.4*10^9 kg/sq meter


The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.

Why? Also, note that this is not all space, just a particular region at the fringe of the solar system. One should expect that the outer edge of the solar system would have more dust than the inner part of the solar system where the anomolous acceleration was not experienced, because in the inner solar system the planets "swept up" most of the dust, while in the outer solar system, this didn't happen.

The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.

The probes are moving predominantly away from the sun. See page 5 of the paper cited above. Hence the opposite of the largest component of the velocity vector and the direction towards the sun are the same. Moreover, the angle of the movement of the probes relative to straight from the sun is nearly constant, so radial component of the velocity vector would be nearly constant in magnitude.

[Garth]

Actually solar wind and solar radiation pressure are two different things. The solar wind does reach a heliosphere beyond which it integrates with the galactic wind. It is controlled by the prevailing magnetic fields out there. The solar radiation pressure is radial and continues out 'to infinity' (and beyond?) getting weaker (more spread out) as it goes.

Garth

[meemoe_uk]

Hi Ohwilleke, how's it going with the total infinite inverse square force field integral? Still think it's finite?
I'd expect dust to collapse on itself, maybe forming rings like those around saturn. It's just not natural for stuff to spread itself around uniformly.

That link you provide suggests they can measure the position of pioneer very acurately. Pioneer does have a significant tangential to direction of sun velocity component. So it should be possible to distinguish between dust friction force and extra attraction to the sun. The top guys wouldn't miss that.

Dust isn't off the cards, but it's not my fave.

I hadn't considered that shockwave idea. I don't see how it works.
Radiation pressure is like loadsa tiny marbles bouncing off the probe and pushing it away from the sun. OK. But I don't see this shockwave works.
For a start, the galactic wind won't be blowing the probe back towards the sun all the time , with constant force.
Shockwave wise, i don't see the shockwave would bounce back perfectly towards the sun. It would bounce around in an asymetric way.
If it was galactic wind interaction I'd expect the force to vary with respect to the probe position. The idea that the probe has followed a path whereby this shockwave induced force is constant, and always directed towards the sun seems like a million to 1 fluke.

Aside from a crazy distant magnetic field of the sun idea, no I'm all for a revolution.

likelyness scale
1st revolution
2nd dust
3rd radiation shockwave

hi nereid. Yes, I just skimed over how pioneer is tracked. It's doppler shift, not hubble shift, whoops. But still, cosmic scale physics is a mess. So it still follows that one or two anomalys trickle back to solar system scale. hubble red shift, galactic rotation anomaly, they're both in the same bag of mess, that's good enough for me, that's the only connection I need to conclude that hubble's law is probably wrong, the whole thing needs knocking down and rebuilding from scratch, preferably starting with QM at it's foundation.

[ohwilleke]

That link you provide suggests they can measure the position of pioneer very acurately. Pioneer does have a significant tangential to direction of sun velocity component. So it should be possible to distinguish between dust friction force and extra attraction to the sun. The top guys wouldn't miss that.

This would be a concern if the Pioneer anamoly were measured with any great accuracy, but it is not. The error bars are roughly +/- 33% which can hide a multitude of sins.

Another factor that suggests that, e.g., there is not a gravitational effect, is that the Ulysses probate has a significantly different amount of unexplained accelleration.

[Nereid]

Another factor that suggests that, e.g., there is not a gravitational effect, is that the Ulysses probate has a significantly different amount of unexplained accelleration.Do you have a reference reporting the Ulysses acceleration? What about other probes (e.g. Voyagers)?

[errorist]

What about Sedna? Was this kupier belt object around the spacecraft?

[LURCH]

...I hadn't considered that shockwave idea. I don't see how it works.
Radiation pressure is like loadsa tiny marbles bouncing off the probe and pushing it away from the sun. OK. But I don't see this shockwave works.
For a start, the galactic wind won't be blowing the probe back towards the sun all the time , with constant force.
But the proposed mechanism is not the gallactic wind itself, but rather the shockwave caused by the solar wind colliding with it.
Shockwave wise, i don't see the shockwave would bounce back perfectly towards the sun. It would bounce around in an asymetric way.
If it was galactic wind interaction I'd expect the force to vary with respect to the probe position. The idea that the probe has followed a path whereby this shockwave induced force is constant, and always directed towards the sun seems like a million to 1 fluke.
In this case the EM pressure would be expected to be nearly uniform and allways directed toward the sun, because the Terminus of the Soalr Wind is roughly spherical. Since the Solar Wind is nearly simetrical, and moving in the direction away from the Sun, the reflected energy of the impact would also be simetrical, uniform (on the large scale), and in the direction of the Sun (or, more to the point, in the directon away from the Terminus).

[Chronos]

.. But still, cosmic scale physics is a mess.How so? Incomplete is not the same as a mess.So it still follows that one or two anomalys trickle back to solar system scale. hubble red shift, galactic rotation anomaly, they're both in the same bag of mess...What is anomalous about the 'hubble red shift' and how does it relate to galactic rotation anomalies? I don't see the connection....that's good enough for me, that's the only connection I need to conclude that hubble's law is probably wrong, the whole thing needs knocking down and rebuilding from scratch, preferably starting with QM at it's foundation.Dismantle QM and rebuild it from scratch? Even if Hubble's law is wrong, how does that relate to the validity of QM?

[Nereid]

What about Sedna?What about it?Was this kupier belt object around the spacecraft?No.

[errorist]

Could it have been close enough to alter the course of pioneer?

[Nereid]

Would you like to do the math to see if it could've?

What inputs will you need? What equations?

(PS: it's quite simple to do this)

[ohwilleke]

Do you have a reference reporting the Ulysses acceleration? What about other probes (e.g. Voyagers)?

Ulysses is mentioned in passing in the main Pioneer article. I don't have a good reference for Voyagers. I have seen it discussed in footnotes in other papers and the popular press, but believe that the definitive articles on these have not been published (indeed perhaps "suppressed").

[Nereid]

I too have seen references to Voyager, mostly along the lines of 'they're much more active spacecraft, more possible outgassings, radiation modelling much more difficult' etc. IIRC, Pioneer is so much 'cleaner', which is partly why I'm curious about Ulysses ... it's nowhere near as simple a craft as the Pioneers, plus it's still very active ...

Given how faint the Pioneer anomaly signal is (it's what's left after you've accounted for everything else you can model well), I don't think any "suppression" is needed.

[Chronos]

Nobody wants to stick their neck out on a signal that cannot be ruled out as noise. The pioneer data is pretty clean so it is not very controversial to suggest things are not working the way we thought they should. Data from the other probes, as Nereid noted, is not nearly so clear cut. There are hints of possible pioneer-like anomalies, but, not nearly clear cut enough for somebody working on those projects to expose their face to that big an egg. I wouldn't call it suppression, more like self defense. Physicists are both vain and cruel. Jumping the gun is a good way to get hung with a nickname like 'Old Hisser'.

[abycjyvey]

Hi, I'm new and I wonder if this will explain the pioneer anomaly. I think of the universe as an expanding hypersphere. Maybe gravity goes out to the 4th dimension and therefore it takes a 'shortcut' to voyager and slows it down more than calculated. I hope this makes sense to you.

[Garth]

Hi abycjyvey welcome to these Forums!

Although I don't really follow your 'shortcut to the 4th dimension to Voyager' idea, the Pioneer anomaly may have something to do with the Universe's expansion.

Why?
Because the anomalous acceleration is approximately equal to cH the Hubble acceleration, which itself can be explained by a clock drift between atomic and ephemeris clocks.

Such a drift may be linked to the evolution of the universe as a whole by Mach's Principle (through a secular evolution of G).

But there are two other 'cosmic coincidences' here.

The first as I have posted on these Forums before is that Stephenson et al. have studied changes in the length of the day from ancient eclipse records and conclude that, after tidal breaking has been taken into account, there is a residual spinning up of the Earth of 0.6 millisec/day/century. This may be unremarkable and caused by the Earth recovering from the last Ice Age, however I cannot help noticing that this rate of spin up is exactly equal to Hubble's parameter!
(6.10^-4/3600.24/100) yr-1 = 1/(14.4Gyr)

The second is MOND. MOND modifies the normal Newtonian (weak field GR) gravitation so that if the Newtonian acceleration aN is smaller than a0 then the acceleration of an object is given by:
a ≈ (aNa0)1/2,

and Milgrom states MOND--theoretical aspects (http://arxiv.org/abs/astro-ph/0207231)The value that fits the data discussed above is about 10−8cm s−2 the remarkable feature here is MOND's critical acceleration is also approximately equal to the Hubble acceleration.


So may it be that these three anomalies can be explained by applying the expansion of the universe to local gravitationally bound systems as well as to the universe as a whole?

Just a thought.

Garth

[Nereid]

Hi, I'm new and I wonder if this will explain the pioneer anomaly. I think of the universe as an expanding hypersphere. Maybe gravity goes out to the 4th dimension and therefore it takes a 'shortcut' to voyager and slows it down more than calculated. I hope this makes sense to you.An interesting idea ... do you have some math to describe it a little more quantitatively? What other good (astronomical?) observations would your idea account for? How consistent is your idea with GR?

Garth: I think you mean H0, don't you? If so, then the MOND figure would be either a coincidence, or easily testable (what value best fits the rotation curves of very distant spirals?).

Wrt Stephenson et al, would you mind taking some time to read through the Canterbury Ring Laser Project (http://www.phys.canterbury.ac.nz/research/laser/index.shtml)? I'm wondering, first, are they within shooting distance of being able to independently (indirectly) measure the 'Stephenson spin-up'? IIRC, they think they may be able to measure the rotation of the solar system around SagA* ... sometime 'soon'.

The Pioneer paper abstract (http://arxiv.org/abs/gr-qc/?0104064+v4) (may be easier for some folk to get to Anderson et al from here).

[meemoe_uk]

Hi garth,

Why suddenly rubbish "the top scientists"?

I haven't. I've rubbished the current cosmic model.


Evidence is building that the standard model, which has required a series of 'fixes', (Inflation, DM, DE), needs revising


A gross understatment if you ask me!


but the general approach has been sound,


No way. It was sound to start with. Dark matter was the most logical, intuitive way to solve the the galaxy anomalys ( rotation , mass descrepancy ). But when it became aparrent dark matter theory was producing more anomalys than answers, it should have been ruled out.

There you go, I'm rubbishing the top scientists now.

i.e. to conflate tested theory (GR) with precise observations. (Hubble Deep Field, WMAP, S/N Ia etc.)

I really don't like this. All the meticulous science that has to be done. Yet the simple truth is, if the galaxy anomalys can't be solved with the currrent model, all this work of fitting data with current theory is obsolete. It's analogous to fine tuning the motor of a car when it's found it's impossible to fit any wheels.

[Garth]

Garth: I think you mean H0, don't you? a0 = cH0 yes!
If so, then the MOND figure would be either a coincidence, or easily testable (what value best fits the rotation curves of very distant spirals?). That's a very good point. Has anybody already looked at this? One problem with MOND is the value of a0 is only approximate, because of this I am not totally bowled over by its ability to predict galaxy rotation profiles and it would mean that we have to look at high z galaxies to test this hypothesis. Then there would be problems calibrating them.
Wrt Stephenson et al, would you mind taking some time to read through the Canterbury Ring Laser Project (http://www.phys.canterbury.ac.nz/research/laser/index.shtml)? I'm wondering, first, are they within shooting distance of being able to independently (indirectly) measure the 'Stephenson spin-up'? IIRC, they think they may be able to measure the rotation of the solar system around SagA* ... sometime 'soon'.
That's a very interesting link - thank you. The Earth's rotation fluctuates in a short time scale considerably at these levels; witness the effect on its rotation of the recent disastrous Indian Ocean tsunami, so Stephenson smoothes out over many centuries to obtain his result.
meemoe_uk I was referring to your Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not..
I'm actually with you on the need to modify GR - see most of my other posts! But don't be 'shrill' about it, you will be heard more readily!

Garth

[Chronos]

... No way. It was sound to start with. Dark matter was the most logical, intuitive way to solve the the galaxy anomalys ( rotation , mass descrepancy ). But when it became aparrent dark matter theory was producing more anomalys than answers, it should have been ruled out.What dark matter theory has produced more anomalies than answers? What are the anomalies, and who says they rule out dark matter?I really don't like this. All the meticulous science that has to be done. Yet the simple truth is, if the galaxy anomalys can't be solved with the currrent model, all this work of fitting data with current theory is obsolete. It's analogous to fine tuning the motor of a car when it's found it's impossible to fit any wheels.Again, what galaxy anomalies, why can't they be solved and which experts are saying they can't be solved under the current model? Why would scientists conclude current theory is obsolete before comparing the data to current theory? It seems more reasonable to carefully analyze the data and establish what does not and cannot be made to work under current theory before announcing it dead. That simply has not happened. If it did, scientists would be falling all over each other trying to find the new physics. Just because more and better observations result in more questions does not signal a problem with theory - at least not until observation shows things that are forbidden, or absurdly improbable under current theory. No self respecting scientist tosses in or is receptive to 'epicycles', like dark matter, without having ruled out all other reasonable possibilities. We very rarely see things forbidden by theory. We frequently see things not anticipated by theory. That suggests what we already knew - our basic theories are pretty darn good, just incomplete.

[abycjyvey]

An interesting idea ... do you have some math to describe it a little more quantitatively? What other good (astronomical?) observations would your idea account for? How consistent is your idea with GR?
I'm not a mathematician or physicist so please don't ask me difficult questions :rofl: . But I think this: 'An alternative to dark matter is to suppose that gravitational forces become stronger than the Newtonian approximation at great distance' (http://en.wikipedia.org/wiki/Dark_matter) suggests that what I said before might be correct.

[Garth]

I'm not a mathematician or physicist so please don't ask me difficult questions :rofl: . But I think this: 'An alternative to dark matter is to suppose that gravitational forces become stronger than the Newtonian approximation at great distance' (http://en.wikipedia.org/wiki/Dark_matter) suggests that what I said before might be correct.

You are thinking along a 'right' track abycjyvey, though not the only one, and not the standard model one, but this is what MOND postulates:

gravitational acceleration a ~ 1/r2 for a >> a0
and a ~ 1/r for a << a0

where a0 is empirically determined to be about 10-8cm/sec2.

What intrigues me, as I said above, is that first of all a0 is about the same as the anomalous Pioneer anomaly (the subject of this thread!) and secondly that both are approximately equal (within a factor of 2) to the Hubble acceleration cH0.

Is this a coincidence? Beware there are many 'crackpot' theories to be hatched here!

Garth

[meemoe_uk]

What dark matter theory has produced more anomalies than answers?
All of them.
What are the anomalies
Well here's 3 to start with...
1. To get the galaxy to rotate the way it does using standard gravity, the radial distribution of dark matter must be a bell curve. But models show dark matter cannot exist in this distribution, it can only be stable in a 'spike' distribution, which wouldn't cause the rotation that is observed.

2. Originally, dark matter was thought to be just cold baryonic material. But after observations showed that cold baryonic material couldn't fully explian the galaxy kinematics, theorists fell back onto other forms of known energy. One by one, each of these materials been shown to be highly unlikely, so now DM guys say dark matter is composed of stuff never seen before. This is, of course, totally ridiculous. In my opinion, they've only got away with it for 3 lame reasons. (i) They slowly built up to it, moving away from likely candidates ( baryons ), to daft ones. Each step seems only slighty more desparate than the last. (ii) it is the fashion in quantum physics to propose and discover new particles with odd characteristics. Dark matter guys used this fashion to propose a model that worked only with crazy particles.(iii) they are the experts right?what they say MUST be true. not.

3. Dark matter, coupled with standard gravity doesn't explain why omega = 1.

and who says they rule out dark matter?

The MOND guys do.
e.g. Stacy McGaugh
http://www.astro.umd.edu/~ssm/mond/mondvsDM.html

Again, what galaxy anomalies
I've already stated 2 in a previous post. I sense you are disagreeing with my posts without reading them.

why can't they be solved
If you ask me, it's because cosmo guys have been concentrating on the wrong theory.

which experts are saying they can't be solved under the current model?
You've already asked this is the same post.

Why would scientists conclude current theory is obsolete before comparing the data to current theory?
I don't know. Why are you asking?

It seems more reasonable to carefully analyze the data and establish what does not and cannot be made to work under current theory before announcing it dead.
Yep. That's what's been done.

That simply has not happened. If it did, scientists would be falling all over each other trying to find the new physics.

And here we come to your misunderstanding. It has happened, i.e. the 3 anomalys I've discribed. And theorists are inventing new gravity models. But you are looking at the wrong bunch of theorists, the old established dark matter guys. You'll never get any new theory from them. If you'd read some science history, you'd see the old guys rarely come up with new stuff, and rarely like new stuff. e.g. Planck, founder of quantum theory that he is, didn't like quantum theory, and spent his life trying to reconcile his BBR theory with classical theory. There's an old saying, "physics advances, death by death [ of physicists ].". It's the young unknown guys that come up with new stuff.

Just because more and better observations result in more questions does not signal a problem with theory
Correct, but galaxy rotation is an old observation. DM guys have had at least 35 years and $billions to solve it. They've failed.

- at least not until observation shows things that are forbidden, or absurdly improbable under current theory.
I can't think of anything more absurd in the history of physics than the implications of currrent DM and DE models. By your own logic, we should drop DM, because it's absurd.

No self respecting scientist tosses in or is receptive to 'epicycles', like dark matter, without having ruled out all other reasonable possibilities.
I think you'll find no other possibilitys where ruled out before DM. DM was\is the first possibility explored.

We very rarely see things forbidden by theory.
But under current models the galaxy is forbidden to rotate the way it does.

We frequently see things not anticipated by theory.
Frequently? Only in observational cosmology, and if theory, given ample time, cannot explain these observations, then we should chuck it out. Basic science.

That suggests what we already knew - our basic theories are pretty darn good, just incomplete.
Only if the theory can explain the unexpected observations. Since DM hasn't explained galactic rotation, what you say doesn't apply for DM.

Chronos, DM theory is losing support. After 35 years it's produced next to nothing. It's is only a matter of time before it passes into history. When are you going to abandon it?

[meemoe_uk]

Hi Lurch.
But the proposed mechanism is not the gallactic wind itself,
Yes, I know this is incidental, but if we are considering the shockwave, then we should consider the galactic wind, because the direct wind influence could be as substancial as the shockwave. But never mind this. It was just incidental.

In this case the EM pressure would be expected to be nearly uniform and allways directed toward the sun, because the Terminus of the Soalr Wind is roughly spherical.
I really don't seee this. I think the 'solar wind field' will be a pronouced elipsoid, with the contracted part of the elipsoid facing the galactic wind, and extended part on the other side (natch),( sorry can't be bothered with correct geometry terminology!)
Consider the solar wind which is traveling in the same direction as the galactic wind. Logically, it would not meet any boundary abrupt enough to induce a shockwave?, in contrast to solar wind heading against the wind. It may encounter turbulence.

Also, even if I was to accept the shockwave force is into the sun at all point, I don't understand how you deduce the force is constant. You mention and compare 'most fliulds' .In a simple water flow shockwave, the shockwave force is constant. But this is dependant on the water being uniform density. But we are dealing with a non-uniform fluid, i.e. inverse square field. In such a fluid, the shockwave force would disapate to zero as it traveled back to the sun.

Explain

[Chronos]

Meemoe. I agree it would be hard to disagree with your posts without reading them. On the other hand, since I quoted from your posts, odds are good I did read them and merely disagree. That is not a bad thing. PF would not be fun if we agreed on everything. I enjoy the challenge of checking my facts and sources. I'm sure you do too. In that spirit:What dark matter theory has produced more anomalies than answers?All of them.All? How many are there? Any examples?What are the anomalies?Well here's 3 to start with...
1. To get the galaxy to rotate the way it does using standard gravity, the radial distribution of dark matter must be a bell curve. But models show dark matter cannot exist in this distribution, it can only be stable in a 'spike' distribution, which wouldn't cause the rotation that is observed.Assuming the term 'standard gravity' means GR, I ask:
1] Why must the radial distribution of dark matter must be a bell curve? Who said this and what mathematical and empirical evidence do they cite.
2] What models show dark matter cannot exist in this [bell curve] distribution and what mathematical and observational evidence supports this assertion?
3] Who says is dark matter only stable in a 'spike' distribution? What is meant by a 'spike' distribution? What is the theoretical and observational basis for deriving this conclusion?

I only addressed your first point, as you probably noted. The others are pretty much just a rehash.

[meemoe_uk]

All? How many are there? Any examples?
well, Stacy goes on about his own DM theory and how it failed, and then went on about how all DM theory suffer from the same intrinsic illness. You could look at his website. Considering this has been going on for 35 years I'd imagine there been hundreds of failed DM theorys.

The answer to your technical questions - I don't know the specifics of why they some distributions aren't stable. All I know is, current models are run on computer simulations, and modellers watch as the model galaxy collapses\fails. To do this you either need a super computer, to model the 1000000+ particles, or a smart approximation algorithm to run on a slower computer.
Here's a good place to start a gravity modeling interest....

http://dmoz.org/Science/Astronomy/Software/Computational_Astrophysics/

[tony873004]

There's something I don't understand about the theory that says it's caused by collision with dust.

The Pioneer spacecraft are travelling away from the Sun. Most of their velocity is in the radial direction (~12 km/s radial, ~2km/s tangental) with respect to the Sun.

But the dust, in order to maintain a relatively circular orbit around the Sun must be travelling with almost all its velocity in the tangental direction (~0 km/s radial, ~4 km/s tangental). This means that the collisions are not head-on.

So why is the direction of acceleration completely towards the Sun rather than at an angle to the Sun/Pioneer line?

[ohwilleke]

There's something I don't understand about the theory that says it's caused by collision with dust.

The Pioneer spacecraft are travelling away from the Sun. Most of their velocity is in the radial direction (~12 km/s radial, ~2km/s tangental) with respect to the Sun.

But the dust, in order to maintain a relatively circular orbit around the Sun must be travelling with almost all its velocity in the tangental direction (~0 km/s radial, ~4 km/s tangental). This means that the collisions are not head-on.

So why is the direction of acceleration completely towards the Sun rather than at an angle to the Sun/Pioneer line?

If the velocities are as you site then the relative velocity of Pioneer to the dust is about 12 km/s radial and 2 km/s tangential (this is the delta radial velocity and the delta tangential velocity).

Also, the radial surface area is going to be greater than the tangential surface are since the Pioneer probes are not spheres. Imagine a big platter with a relatively compact mass connected to it.

Also, it isn't clear to me that a slight tangential decelleration is ruled out by the data. The tangential effect would be an order of magnitude less than the radial effect.

[matt.o]

this link may interest you guys!

http://arxiv.org/abs/astro-ph/0503368

[ohwilleke]

this link may interest you guys!

http://arxiv.org/abs/astro-ph/0503368

Excellent catch. The paper argues that if the density of outer system dust falls off as 1/r and the mass of that dust is somewhat more the current estimates (less than an order of magnitude) that the Pioneer effect would be produced from the gravitational effect of the dust.

It also notes that Nieto, et al are working on a paper on the collision with dust theory which they compare briefly at the end of the paper noting that the collision theory requires a constant dust density compared to evidence the cite that the dust density is not constant but falls off.

[tony873004]

The dust causing gravity is my favorite theory so far, but it is not without its flaws. This article states that the entire mass of the dust is 1.97 M_{Earth}.

But there is a problem.

A little background first:

The solar system can be treated like a galaxy in this situation. The Sun orbits the galaxy with the exact same period that it would orbit a single large object at the same distance as the Sun / Galactic center distance, and with a combined mass of all the galaxy's mass interior to the Sun. Therefore, any mass exterior to the Sun's position in the galaxy can be safely ignored.

In a sense, this is like the physics question of how much you'd weigh inside a hollow sphere. Your weight would be 0 no matter where in the sphere you were, and no matter how massive the sphere was. If there was a hollow sphere, with 1 Earth mass and 1 Earth radii, 1 cm thick, (very dense material!, but hypothetical, so why not), and you stood on the surface, you'd find that gravity was 9.8, just like the real Earth. But if there were a hole in the surface, and you jumped through the hole, you'd immediately be weightless.

Dust in the Kuiper Belt would behave the same way. Since its assumed to be distributed uniformly, anything orbiting the Sun interior to this dust belt would not feel the gravitational effect of the dust. But anything exterior to the dust would feel it. It would be the same as if you concentrated all the dust together and added it to the Sun.

So far, this seems to work quite nicely for the Pioneer anomoly. There is no anomoly if you are interior to the belt in the same plane as the belt.

But now the problem:

How much dust would it take to cause an additional acceleration of 8.7*10^{-8} cm/s^2

a = \frac{GM}{r^2}

therefore

M=\frac{ar^2}{G}

8.7*10^{-8}cm/s^2 = 8.7*10^{-10} m/s^2

G=6.673*10^{-11}Nm^2/kg^2

r = 1*10^{13}m (roughly the current Pioneer / Sun distance)

M = \frac{8.7*10^{-10}*(10^{13})^2} { 6.673*10^{-11}}

M=1.3*10^{27}kg

\frac{1.3*10^{27}kg}{5.98*10^24 kg/M_{Earth}} = 218.12 M_{Earth}

which is much higher than the article's value of 1.97 M_{Earth}

[Chronos]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.

[ohwilleke]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.

The article argues that there is a modest effect on outer planet orbits, and implies that current predictions are based on the wrong "initial conditions" so to speak.

[tony873004]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.
Not if its all exterior to the outer planets, and evenly distributed. Then the outer planets are like a person in a hollow sphere, unable to feel the effects of the sphere's gravity.

Jupiter orbits exterior to Mars, but tugs Mars eccentricity into and out of round periodically. (Jupiter does this to Earth too but to a much lesser degree). But if Jupiter exploded and formed a belt of dust with 1 jovian mass, evenly distributed over Jupiter's orbit, Mars would no longer know this mass existed.

Observations with IR suggest that 218 Earth masses of dust in the Kuiper belt is unrealistically high.

The article argues that there is a modest effect on outer planet orbits, and implies that current predictions are based on the wrong "initial conditions" so to speak.
The article claims that the dust belt begins just past the orbit of Uranus. It talks about an effect on Neptune, but not the planets interior to the dust belt.

[Billy T]

I did not know of the "Pioneer Anomaly" when I wrote Dark Visitor, but did know that in the early part of the last century that Neptune's orbit was disturbed - Based on his analysis of this disturbance, Percival Lowell founded the observatory near Flagstaff AZ and financed the discovery of Pluto, but Pluto needed to be many times the mass of the Earth to have produced the perturbations. We now know that Pluto is smaller than the moon, so the perturbation, if real, was something else. I used these "Pluto facts" plus the fact that when the universe was about 25 times smaller, the first stars were forming, were larger, aged rapidly and several generations of them left pairs of gravitationally bound black holes behind, long before our sun was born.

If the first member of a BH pair, approaching from the north polar region, passed not too far from our solar system, cutting thru the plain of the ecliptic in 1928, it could have been the cause of Neptune's perturbation and tilted Pluto's orbit plane. The second member of the pair could be approaching about now, but still not detected as black holes do not reflect sunlight.

The hero of my story (Astronomer Jack) has been carefully measuring Pluto and Neptune for several years and from their unexplained residual perturbations computed a rough trajectory for the now approaching second member of the 1928/2008 pair.

In fact there are several reasons why Jack's small (2.2 solar mass) BH now 130 AU from the sun might be more directly noticed. The Pioneer acceleration anomaly would be nearly two orders of magnitude greater, but you might want to think about the other reasons.

Dark Visitor was written as a recruiting tool for the hard sciences. I am a retired professor and very concerned that the western world is now in the process of losing scientific leadership to hard working, studious Asians, as it has already lost technological leadership and many good jobs. I don't want my grandchildren to have only "non-exportable" jobs like cutting some one's hair or selling fast food, etc.

If you share my concern, please visit www.DarkVisitor.com where you will learn how to read entire book for free, get a list of all the science hidden in it, sample text, etc. The target reader is not currently interested in science -that is why it is a scary, but possible real, story of a coming cosmic disaster that change Earth's orbit enough (more elliptic by about 10%) to initiate a new ice age beginning in 2008.

[notknowing]

One question is why is this anomalous acceleration detected on distant spacecraft but not on other orbiting bodies?
It may be explained by a clock drift between atomic clock time and ephemeris clock time, the acceleration being approximately the Hubble acceleration, http://arxiv.org/abs/gr-qc/0403013
ap ~ cH.

Such a clock drift is predicted by SCC.

Garth
Thanks Garth for this interesting reference. The paper is rather convincing and is based on established principles. There is also an interesting analogy with Puthoff's theory (discussed in earlier treads) on the influence of gravity on the electrical permittivity and magnetic permeability of the vacuum (same dependence)- see equation 12.
Now, if this explanation is, even partly, correct, it would probably mean that a number of cosmological "observations" such as redshifts, distances to galaxies, estimates of dark matter (which I think does not exist) and dark energy, etc are erroneous and need to be corrected for this effect. Would you agree on this ?

[Garth]

Thanks Garth for this interesting reference. The paper is rather convincing and is based on established principles. There is also an interesting analogy with Puthoff's theory (discussed in earlier treads) on the influence of gravity on the electrical permittivity and magnetic permeability of the vacuum (same dependence)- see equation 12.
Now, if this explanation is, even partly, correct, it would probably mean that a number of cosmological "observations" such as redshifts, distances to galaxies, estimates of dark matter (which I think does not exist) and dark energy, etc are erroneous and need to be corrected for this effect. Would you agree on this ?

Let me answer cautiously.

Astrophysics is the application of laboratory or 'local' physics to the universe 'out there'. Cosmology is the extension of that discipline to the largest possible scales.

The overall theory that describes the cosmological environment, in which the locally understood and tested theories of atomic processes and nucleosynthesis etc. are set, is General Relativity.

That theory has been well tested in local solar system experiements and on the largest scales produces the standard \LambdaCDM model. That model fits the multitude of observations of Hubble Red Shift, BBN, CMB anisotropies, distant Type Ia supernovae, large scale structure etc. very well.

However it does so by introducing a series of 'entities', Inflation, exotic non-baryonic DM and DE that have not been identified in local physical experiments.

When we discover the Higgs Boson/Inflaton, the DM particle and identify DE in the laboratory (LHC?), measure their properties and show that those observed properties match the cosmological observations then and only then will we know what we are really talking about.

In the meantime questions remain about the development of a Quantum Gravity theory, and pertinent to that, whether GR really does describe local gravitational fields accurately. The Pioneer Anomaly (its Doppler drift is almost equal to the Hubble Constant) may indicate that it does not.

Remember the discovery of Pluto because of a residual anomaly in Uranus' orbit after Neptune had been taken into account? Pluto is too small (by a factor of 2 OOM) to have been the Planet X they were looking for. So unexplained residuals may still exist in the orbits of the outer planets as well!

I think we should have open minds while these questions remain, other theories that are alternatives to, or modifications of, GR have a mountain to climb, however they should not be discarded because of that. Alternative theories to GR (such as SCC (http://en.wikipedia.org/wiki/Self_creation_cosmology)) will have to do even better at describing the universe out there - perhaps Gravity Probe B (http://www.physicsforums.com/showthread.php?t=104694) will shed further light on the issue in April!

Garth

[henryco]

Hi,

Another simple way to understand the pioneer anomaly:

Suppose that at a distance between us and Pioneer the cosmological scale factor in conformal time units switches (a discrete jump) from a(t) to 1/a(t).
As a consequence there will be a 1/a^2(t) deceleration of Pioneer clock (i.e frequency of the radio wave we receive from it) relative to our earth clock (in a theory where the background effects are not suppressed by the local gravitational field as in GR)..
As a straightforward result: (df/dt)/f=-2H0 as you can check and as is observed. This is also, as in SCC, a deceleration of clock explanation of the anomaly but in quite different way: it needs at least to spatial areas with different background evolutions.
The dark gravity theory (gr-qc/0610079) equations admit both a(t) and 1/a(t) solutions and nature has to choose between them at some places in a discrete way in order to restore a better discrete symmetry involved in the fundations of the theory which i cannot devellop here.
As you can see in the paper by ANderson , the effect appeared quite abruptly in 1983 around 12.5 A.U
Within the error bars i couldnt hope a better signature : Pioneer just crossed the background discontinuity in 1983 at 12.5 A.U
The foreseen consequences for the near future are here: www.darksideofgravity.com/armagfr.htm

regards,

F Henry-Couannier

[Chronos]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

[henryco]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

Sure! as far as i know, nothing anomalous was found (and the last article by Turyshev confirms this) in LLR data, but i was also told that this analysis is extremely complicated...

Anyway, exporting their data in the sun reference frame it appears that they can even see with great precision a frame-dragging effect due to the earth motion about the sun in this frame. But the LLR data were taken in the earth rest-frame so, their frame dragging signal is nothing but the effect they themselves injected in their data by lorentz transporting them in the sun rest-frame (see this month article by Turyshev)!

If, and this is what you can read in red in the latest version of my article gr-qc/0610079, if the transformation group is the Gallile one instead of the Lorentz one, you are still OK with all test of PPN alpha parameters which only test boost invariance and not Lorentz invariance as is always claimed.
But under such transformation, g_munu behaves differently. So LLR data analysers may be should not perform a Lorentz transformation.
In GP-B because you test frame-dragging in a frame where the earth is rotating, you can really test what is the correct transformation group under boosts.

F H-C

[henryco]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

Hi,

PLease have a look at gr-qc/0702028 the latest paper by Turyshev, Nordtvedt and co regarding gravitomagnetism.
It says something incredible! It says that the frame-dragging is seen in the frame of the observer (earth frame) where there should be nothing at all since in this frame the speed of the earth vanishes...but they keep using there (badly incorrect) the gravitomagnetic field formula of the sun rest frame. Crazy isn't it?

Best regards

Fred

[Chronos]

Same paper I had in mind, Fred. I didn't notice any problems with their approach, but will read again. Interesting stuff for sure.
http://arxiv.org/abs/gr-qc/0702028
The Gravitomagnetic Influence on Gyroscopes and on the Lunar Orbit
Authors: T. W. Murphy Jr., K. Nordtvedt, S. G. Turyshev

[henryco]

In a previous post i said:

...they keep using there (badly incorrect) the gravitomagnetic field formula of the sun rest frame. Crazy isn't it?

Fred

At least, if they are actually working in the sun rest frame, should they study small acceleration perturbations making the trajectory deviating not from a circle as they did , but from a Lorentz transformed circle (moon trajectory should look like a rugby ball after Lorentz transport from a comoving frame). May be they applied this correction elsewhere but it should be mentionned in the paper formula for these to be correct, not elsewhere, i believe...tell me if i'm wrong.

best regards

Fred H-C

[Garth]

Garth: I think you mean H0, don't you? If so, then the MOND figure would be either a coincidence, or easily testable (what value best fits the rotation curves of very distant spirals?).

A paper by Bekenstein & Sagi in today's physics ArXiv asks the same question as in this old post of Nereid's: Do Newton's G and Milgrom's a0 vary with cosmological epoch ? (http://arxiv.org/abs/0802.1526).

In the scalar tensor gravitational theories Newton's constant GN evolves in the expanding universe. Likewise, it has been speculated that the acceleration scale a0 in Milgrom's modified Newtonian dynamics (MOND) is tied to the scale of the cosmos, and must thus evolve. With the advent of relativistic implementations of the modified dynamics, one can address the issue of variability of the two gravitational ''constants'' with some confidence. Using TeVeS, the Tensor-Vector-Scalar gravitational theory, as an implementation of MOND, we calculate the dependence of GN and a0 on the TeVeS parameters and the coeval cosmological value of its scalar field, \phi_c. We find that GN, when expressed in atomic units, is strictly nonevolving, a result fully consistent with recent empirical limits on the variation of GN. By contrast, we find that a0 depends on \phi_c and may thus vary with cosmological epoch. However, for the brand of TeVeS which seems most promising, a0 variation occurs on a timescale much longer than Hubble's, and should be imperceptible back to redshift unity or even beyond it. This is consistent with emergent data on the rotation curves of disk galaxies at significants redshifts.

Garth

[HenriPoincare]

http://www.space.com/scienceastronomy/080229-spacecraft-anomaly.html