# Alternative theories being tested by Gravity probe B

by Garth
Tags: alternative, gravity, probe, tested, theories
 P: 27 If the solar system changes "orientation" we are not just talking parallax. VLBI does not account for changes in the solar system’s orientation to reference points outside the moving frame. Quote from NASA VLBI website: “Changes in the Earth’s orientation in inertial space have two causes: the gravitational forces of the Sun and Moon and the redistribution of the total angular momentum among the solid Earth, ocean and atmosphere. VLBI makes a direct measurement of the Earth’s orientation in space from which geoscientists then model such phenomena as atmospheric angular momentum, ocean tides and currents, and the elastic response of the solid Earth.” Please note the present methodology is only concerned with local changes - within the frame of the solar system – thereby effectively employing a static solar system model. Yet measurements are made to points far outside the moving frame – without accounting for any motion of the frame relative to the reference points. If the solar system curves through space we would never know it under current methodology because all changes in earth orientation are attributed to local causes. If the total precession observable includes some component of solar system motion then even though GP-B is be far above the precessing earth it would still pick up some component of precession (due to SS motion) but think it was noise. A careful reading of the press releases suggests this is exactly the type of “noise” that GP-B has been bothered with since inception. http://www.space.com/businesstechnol..._b_031231.html
PF Gold
P: 3,273
Polestar, as the measurement is that of the change of angle between the axis of a gyro and the distant quasar, are you claiming the changes in the solar system orientation also changes to orientation of the gyro?

The changes in the Earth's orientation you mention, its change of axis, would not affect the satellite.

The early Space.com site you linked to does accurately predict
 Several members of the review at the time voiced a minority skepticism about the large extrapolations required from ground testing to GP-B's performance in space. Furthermore, this same minority thought it likely that some "as yet unknown disturbance" may prevent the spacecraft from performing as required.
Why does the build up of electrostatic patches not seem to you to be "exactly the type of “noise” that GP-B has been bothered with since inception."?

Garth
 P: 27 As the SS curves through space the spacecraft, in orbit around the earth, must move with it. Just as GP-B will detect a change in orientation due to the spacecrafts orbit around the earth (seen as a 97 minute wave), and due to the earth’s orbit around the sun (a longer waveform), so too will it detect a change due to the solar system’s change in angular velocity relative to the guide star. I don’t see how it could be any other way. Of course, the later signal probably looks like noise (thought to be polhode or something else) because the short period of the experiment relative to the long wave makes that form difficult to see. All I’m saying is don’t throw out the baby with the bathwater until we know what is hiding in that bathwater. Re: electrostatic patches. I don't know enough about this to offer an opinion. But I would start with the assumption that those \$800 million gyros have done their job and probably picked up real signals far more subtle than we can imagine. EOP is still a science in progress.
PF Gold
P: 3,273
 Quote by Polestar101 As the SS curves through space the spacecraft, in orbit around the earth, must move with it. Just as GP-B will detect a change in orientation due to the spacecrafts orbit around the earth (seen as a 97 minute wave), and due to the earth’s orbit around the sun (a longer waveform), so too will it detect a change due to the solar system’s change in angular velocity relative to the guide star.
The "solar system’s change in angular velocity relative to the guide star" will be caused by its motion around the galaxy, I have dealt with the motion of the galaxy itself above (it is negligible).

Orbiting the galaxy would cause a geodetic precession of

$$(\frac{M_G}{M_E})^\frac{3}{2}(\frac{R_E}{R_G})^\frac{5}{2} \times 8 \text{arcsecs/yr }$$

(See MTW 'Gravitation' page 1119 eq 40.35)

i.e. about 10-8 arcsecs per year.

I think this can also be safely ignored!

Garth
 Sci Advisor PF Gold P: 3,273 The is a general point here that is being overwhelmed by the discussion of a hypothetical solar companion star. To save further confusion and time wasting I will re-iterate it. It is this. If other effects such as poholde and perturbing forces are eliminated then gyros 'point in a constant direction' in space. The curvature of the space-time around the Earth cause two effects on that 'constant direction' that was measured by GP-B, the geodetic and frame-dragging precessions. The direction of the GP-B gyros axes was referenced to a distant quasar. All motions of the Earth around the Sun, the Sun around a possible companion, the Sun around the galaxy and the galaxy through space would add up to around 10-3c, as that guide quasar is approximately 1010 light years away then all motions create a parallax of no more than OOM 10-13 rad i.e. ~ 10 -5 milliarcsecs, far smaller than those caused by the curvature of the Earth and Sun's gravitational field that were measured by the experiment. They can be safely ignored as negligible. Garth
P: 23
 Quote by Garth It is this. If other effects such as poholde and perturbing forces are eliminated then gyros 'point in a constant direction' in space. The curvature of the space-time around the Earth cause two effects on that 'constant direction' that was measured by GP-B, the geodetic and frame-dragging precessions.
So, the direction at which the gyroscopes point is not constant, but subjected to, at least, two effects: geodetic and frame-dragging precessions.

Now, imagine for a moment that the movement of the solar system towards the solar apex has an actually unknown characteristic that causes precession in the same way as either geodetic or frame-dragging. I'm not saying that these are geodetic/frame-dragging effects, just that they behave similarly, affecting the orientation of the gyroscopes, that of the earth, and that of the rest of the solar system.
Suppose that this precession is a small component of what we consider to be the known axial precession due to lunisolar causes, as Polestar101 suggested.
Now, when you send a probe to the space to measure small precession effects predicted by GR, your gyroscopes start behaving in an unexpected way.
That's what Polestar101 is saying, if I understood correctly. And I think that that's a possibility that clearly deserves a closer scrutiny.

 All motions of the Earth around the Sun, the Sun around a possible companion, the Sun around the galaxy and the galaxy through space would add up to around 10-3c, as that guide quasar is approximately 1010 light years away then all motions create a parallax of no more than OOM 10-13 rad i.e. ~ 10 -5 milliarcsecs, far smaller than those caused by the curvature of the Earth and Sun's gravitational field that were measured by the experiment.
Those are the known, small effects, predicted by GR. Imagine for a moment that there actually are unknown effects, whose causes are being mistaken in the GP-B experiment.

Mauro
P: 1,750
 Quote by Polestar101 You can't simply eliminate polhode and other perturbing forces to save the experiment without first being able to exactly quantify these effects. And to try and measure them by eliminating anything that does not get to the GR goal is circular reasoning and bad science.
This doesn't make any sense at all. They DO quantify the podhole effect. It was quantified and understood and taken into account from the start. There is an additional effect which was stronger than anticipated; from a tiny residual change on the gyroscopes, which gives an additional effect on the motions. There is no doubt at all that this effect exists. Most of the work of the extended data analysis phase HAS been to quantify this effect -- and not by assumption. When quantified, it can be extracted to reveal any underlying signal.

This is an extra factor influencing the gyroscopes which was larger than anticipated, and has been at the root of the limited accuracy to which results could be given.

The description by Polestar101 is very misleading. It's not bad science at all -- it is precisely what science should do to test GR as well as they can without making assumptions. They quantify all influences and obtain the residual signal, which stands then as a test of the predictions from the frame-dragging effect. There is no assumption of GR involved in that process. Without the proper quantification of the electromagnetic forces, the accuracy of the test is very weak. With proper quantification, the test will improve, though it is unlikely to get to the level of 1% which had originally been hoped.

There's a nice summary of the issues in The Gravity Probe B Bailout, IEEE Spectrum, Oct 2008. This report is describing how the team was able to secure additional funding; and their own project page gives more on the existing funding. (Gravity Probe B -- current status -- updated November 12, 2009. The work is ongoing, and primarily this is focused upon quantifying the effects of the electromagnetic influences, so that they can be properly take into account -- without just making assumption -- and so improving the accuracy of the true independent test of GR.
PF Gold
P: 3,273
Quote by maurol2
 Quote by Garth It is this. If other effects such as poholde and perturbing forces are eliminated then gyros 'point in a constant direction' in space. The curvature of the space-time around the Earth cause two effects on that 'constant direction' that was measured by GP-B, the geodetic and frame-dragging precessions.
So, the direction at which the gyroscopes point is not constant, but subjected to, at least, two effects: geodetic and frame-dragging precessions.
You have not understood the experiment. If other effects are eliminated then the gyro's do 'point in a constant direction' in space. It is space itself that is curved by the presence of the Earth's, and to a lesser degree, the Sun's gravitational fields. There is a further effect caused by the dilation (or 'curvature') of time.

It is this curvature of space-time that cause the geodetic precession and frame-dragging effects that GP-B measured.

Please start another thread about whether the Sun has a companion or not, it is irrelevant to this experiment.

Garth
 Mentor P: 8,287 Offtopic posts have been removed, mostly to here. Please keep this thread on the topic of comparing published theories that have made proper predictions for the Gravity Probe B experiment.
P: 23
 Quote by cristo Offtopic posts have been removed, mostly to here. Please keep this thread on the topic of comparing published theories that have made proper predictions for the Gravity Probe B experiment.
I've noticed that you've deleted my last reply to Garth, in the name of "topicness". Do as you please. I couldn't care less, except to mention that I don't see why you didn't removed Garth's last comment too. He was the one which initiated that avenue towards "offtopicness", so to speak, presuming about the geometrical migth of GR.
 P: 29 Hello Garth and all, I just want to point out that strictly because of the very nature of this thread Garth you're not in a position to say "It is this curvature of space-time that cause the geodetic precession and frame-dragging effects that GP-B measured." There may be other theories apart from mine, on the list of theories that are still viable in the light of the results, that give conceptual interpretations other than curvature for the measured effects. But whether or not others do it, PSG certainly does. Equation 3 of the second paper on PSG published in a peer reviewed journal, here http://journalgp.awardspace.com/journal/0202/020203.pdf generates the curvature component of the geodetic effect from flat space, simply from assuming that an effect like a refractive medium slows matter in the same way as it slows light. That's 2/3 of the effect potentially explained, and because the other 1/3 doesn't require curvature, the equation works as a proof that curvature doesn't necessarily have to be the cause. (Wikipedia, nevertheless, still defines the geodetic effect as a direct result of curvature.) You checked the equation, found it gives the right numbers, and then put PSG back on the list of viable theories, after more than a year off it. The reason it deserved to go back on the list was that the only premiss that went into the equation was the original starting premiss of PSG, ie that light and matter are slowed by sqrt(1 - [2GM/rc^2]) in a gravity field. (So the equation vindicated the theory, and showed that in the earlier prediction I was wrong, but PSG wasn't.) Sorry to restate this, but it seems directly relevant to what you've said about the interpretation of the results. (BTW, have been hoping to get back in touch anyway.) Best wishes, Jonathan Kerr
P: 23
 Quote by JonathanK But whether or not others do it, PSG certainly does. Equation 3 of the second paper on PSG published in a peer reviewed journal, here http://journalgp.awardspace.com/journal/0202/020203.pdf generates the curvature component of the geodetic effect from flat space, simply from assuming that an effect like a refractive medium slows matter in the same way as it slows light. That's 2/3 of the effect potentially explained, and because the other 1/3 doesn't require curvature, the equation works as a proof that curvature doesn't necessarily have to be the cause. (Wikipedia, nevertheless, still defines the geodetic effect as a direct result of curvature.)
Very interesting. Are you suggesting that this is related also to the origin of the rotation of the planets, or I misunderstood/read too much?

Talking about the likely effect of refractive mediums, you might be interested in this 2003 paper by Consoli & Constanzo:
The motion of the Solar System and the Michelson-Morley experiment

They re-analize the Michelson-Morley, Miller and other interferometry experiments, and show that in all cases a fringe shift is in fact detected, only its value is less than expected. They provide an excellent explanation for the differences, based on previous work by Kitto and Cahill, which goes back to Fresnel and the Fresnel drag coefficient.

I mention all this in this context due to a number of reasons:
- Consoli & Constanzo show that ether drag is dependant on the refractive index of the medium, and that this is the explanantion for the diverging results of the various interferometry experiments.
- They talk about a small similar effect caused by gravity, which resembles Fresnel drag, that will be equivalent to what you're proposing in your paper for 2/3 of the geodetic effect.

You might be interested also in this http://en.wikipedia.org/wiki/Aether_drag_hypothesis
and the linked references and papers. In particular those by D. Gezari.

Regards,
Mauro
 P: 29 Hello, Thanks for the references, if we discuss it in detail it should be elsewhere (or we'll find ourselves there anyway!). But to make something clear - I don't believe in an ether, that was disproved. The original ether was thought to behave rather like matter behaves - unconventional 'ethers' have carried on, but they're so different they shouldn't be called that. The electromagnetic field is an example. PSG is a gravity theory that comes out of a theory of time, and has a conceptual basis that's different from others I've seen. The visual picture that led to both is in a book 'Motion through time: the missing piece of the puzzle'. Initially it looks at the question of whether the future is decided or undecided, and points out that relativity and quantum theory tell us opposite things on that. My solution does overlap with some other theories, including refractive medium theories, which according to mine are incomplete. Incidentally, my view has special relativity entirely right, except in the interpretation, which is incomplete anyway. To answer your question about the axial rotation of the planets - although most of them rotate in the right direction, I doubt if either version of the geodetic effect could slowly spin up the planets. But if mine could then it's likely the GR version could as well, so the question lands comfortably within standard physics, and the best thing is probably to ask Garth.. Jonathan
P: 23
 Quote by JonathanK Hello, Thanks for the references, if we discuss it in detail it should be elsewhere (or we'll find ourselves there anyway!). But to make something clear - I don't believe in an ether, that was disproved. The original ether was thought to behave rather like matter behaves - unconventional 'ethers' have carried on, but they're so different they shouldn't be called that. The electromagnetic field is an example.
Oh, I don't believe either in a mechanical and material ether.
But in fact, I certainly do believe that reality is composed by more than matter. Particularly, I believe that there are fields and "forces" that have no material cause, but that interact with and affect matter.
Moreover: matter is just a manifestation of these fields and forces(a kind of condensation), under the right circumstances.
We may not know and observe these fields and forces today in a direct way, but we can start to know them by their effects. And the day will come when we'll be able to observe them directly again, in all their magnificence and harmony.
I also firmly believe that Science, in the great name and tradition that represents, must (and certainly will) study and incorporate these fields and forces into its subjects of study. And when I say Science I mean all the sciencies, from Physics to Biology, from the study of the mineral to the study of the living. Also the social sciences; and the most important study of all: the clear and real understanding of the human being and its true nature.
 Sci Advisor PF Gold P: 3,273 Just a point: the geodetic effect is tiny unless you are dealing with an intense gravitational field, when the frame dragging effects would overwhelm it in the case of a rotating black hole, for example. It is not responsible for the spinning up of the planets; that is due to the simply the conservation of angular momentum. Unless a theory makes a specific prediction that is being tested by the GP-B experiment please post elsewhere. Garth
P: 23
 Quote by Garth Just a point: the geodetic effect is tiny unless you are dealing with an intense gravitational field, when the frame dragging effects would overwhelm it in the case of a rotating black hole, for example. It is not responsible for the spinning up of the planets; that is due to the simply the conservation of angular momentum.
That can't be so simple, or it is incomplete, considering by example that Venus is slowly spinning in the opposite direction.
Electromagnetic effects will have to be taken into account, sooner or later, to explain this solar system anomaly, and also others.
 Sci Advisor PF Gold P: 9,172 Not at all, Venus could easily have been 'flipped' as the result of a past collision. The rotational axis of Uranus is similarly goofy, it points almost directly at the sun [re: http://www.windows2universe.org/our_...ts_table.html] and also has a slightly retrograde rotation. The former planet Pluto also suffers from this condition. Their current axial orientation is unrelated to how the planets acquired spin.
P: 23
 Quote by Chronos Not at all, Venus could easily have been 'flipped' as the result of a past collision. The rotational axis of Uranus is similarly goofy, it points almost directly at the sun [re: http://www.windows2universe.org/our_...ts_table.html] and also has a slightly retrograde rotation. The former planet Pluto also suffers from this condition. Their current axial orientation is unrelated to how the planets acquired spin.
"Simply". "Easily". I'm dismayed by your fondness for "easy" explanations. "Easy" meaning, of course, that you can explain things (independently of how improbable these explanations really are) using standard physics and models.

Venus has a super-rotating atmosphere. That atmosphere circles the planet in around 4 (earth) days in a westward (Earth's west) direction. That is, most likely, the cause of the planet anomalous spin. The westward(Earth) spinning atmosphere gradually slowed down, and eventually reversed, the spin of the underlying solid planet, due to friction based momentum transfer.

Now, (and this independently if it is the cause of Venus's actual spin or not), we have to explain the reason for the atmosphere's super rotation. And to explain that it will be unavoidable to reckon with and take into account electromagnetic effects.

References:
http://en.wikipedia.org/wiki/Atmosphere_of_Venus
http://www.esa.int/SPECIALS/Venus_Ex...GQEFWOE_0.html
http://www.physorg.com/news194504586.html

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