Problems with G (split from history of astronomy)

[swansont]

swansont re your post#22.

In which u ask me to explain the physics behind my statement that if a pendulum cannot be trusted to measure time, ie g, then it cannot be trusted to measure the stability of G.

It is well known that a pendulum might change its beat if moved, ie due to a change in g due to position or altitude. But, if not moved, the beat might also change due to temperature or air pressure or vibration. Bearing in mind that we are talking mainly about a Grandfather clock here.

The note in Einstein's paper refers to a comparison of a clock on the equator to a clock on the pole of a rigid spinning body. It is not a statement of a pendulum clock not being trusted to tell the time, it is a matter of why a direct comparison of those two clocks would not demonstrate the time dilation effect (in principle)

 

It is because you are grabbing statements and making incorrect assertions that you need to explain the physics behind your reasoning, so that others might comment on it. If you aren't doing that, you aren't engaging in science, and this is a science discussion board.

 

 

Which reminds me that when John Cuthber made his statement that "we have Grandfather clocks that are good enough to disprove that idea" (regarding my statement that Russians found a curious change in G of 0.7% over time), no-one asked him to explain the physics. That doesn't bother me much, what bothers me more is that no-one pointed out the lack of logic that any fresh measurements anywhere with any sort of apparatus could possibly disprove that the Russians did actually measure a 0.7% change at a particular place at a particular time.

As I stated before, it's generally not required when someone who has passed first-semester physics could derive it. After all, you are discussing more advanced concepts. A certain background is assumed to be in place.

 

If you can't see how a pendulum could be used to measure changes in G, maybe you should open up a thread and ask how it could be done. Also consider that you're in over your head if you lack the background that would allow you to figure this out.

 

Nextly, there doesn't appear to be any reference on Google that a pendulum has ever been used to measure G.

That's funny, I found several when I googled for such examples yesterday.

 

If u are correct that Einstein had no doubts about a pendulum's suitability for measuring time, then it must have been the Editor who authored Note 7 in Einstein's book (see earlier postings). Possibly the Editor of the English version (1920 here).

The note doesn't mean what you are asserting it means. There's a pretty obvious reason why a pendulum clock would not give a valid comparison in the case the footnote refers to.

 

One little problem, Einstein said (somewhere??) that a clock at a low altitude was slower than a clock at a higher altitude. But, i reckon that a pendulum clock beats faster at a lower altitude.

Is that a problem, that there would be two different effects?

[madmac]

Strange.

The equations (that i see on Google) for a pendulum suggest that the period will halve if g increases by 4. And the equations don't allow for GR, nor SR. I guess that they accept that pendulums are never going to go to the Moon.

[studiot]

 

madmac post#24

Nextly, there doesn't appear to be any reference on Google that a pendulum has ever been used to measure G. Cavendish used a torsion apparatus in say 1790, & he was the first, despite good pendulums being around since say 1690. Perhaps a pendulum can be used to measure G, armed with a good equation for that pendulum, & using Newton's inverse square equation for gravity, so why hasn't it ever been done (or has it?).

 

Congratulations, you actually asked a question instead of proclaiming your gospel.

 

And wow, swansont quickly gave you a helpful answer +1

 

Let me offer you two pieces of advice.

 

Firstly Einstein's clocks and thought experiments all refer to perfect or ideal clocks and other apparatus and perfect observers.

 

Nevertheless secondly, you need to distinguish between practical difficulties and theoretical ones.

It is the practicalities that cause difficulties with simple pendulum clocks.

 

However this thread is about the measurement of G and perhaps g, not the measurement of time.

I suggest starting another thread if you want to discuss that.

Now that you have found out how to get help from swansont ask plenty of questions, he is a real expert in the area of time measurement.

[madmac]

swansont.

I plead innocent to the charge that i cant see how a pendulum can be used to measure changes in G. I have always said that it could. But, i might have raised the question of accuracy. And not forgetting that it would need a balance-clock (or a modern clock) sitting near the pendulum clock to tell true time. At least i would if we are talking about a Grandfather clock.

 

And yes i have found references to a pendulum being used to measure G. I can see how this is possible, using Newton's inverse square gravity equation. But, this appears to be a very modern thing, using a super accurate pendulum, with amazingly accurate measurement apparatus, supposedly giving G to umpteen places. I wonder what the error estimates might be for a Grandfather clock. John Cuthber inferred that they would be much better than the 1% (or 0.7%) that i was alluding to.

 

Re two different effects, it might be a problem. One that comes to mind is what if Einstein simply used pendulum clocks for all of his SR & GR imaginings & equations. When he got to his rotating-disc-thought-experiment, the outer clock would be ticking faster than the inner clock at the axis, & i hate to think where things would go after that.

Edited February 8, 2017 by madmac

[swansont]

swansont.

I plead innocent to the charge that i cant see how a pendulum can be used to measure changes in G. I have always said that it could. But, i might have raised the question of accuracy.

The question of accuracy and or precision is not the same as the possibility of making the measurement.

 

And not forgetting that it would need a balance-clock (or a modern clock) sitting near the pendulum clock to tell true time. At least i would if we are talking about a Grandfather clock.

I should find some pictures of the Naval Observatory's original clock vault where they used to keep the pendulum clocks used to tell time ca 100 years ago. I think it would be news to my colleagues that a balance clock worked better. Shortt and Riefler clocks were state-of-the-art a century ago.

 

https://en.wikipedia.org/wiki/Shortt–Synchronome_clock

 

"[shortt clocks] were the most accurate pendulum clocks ever commercially produced,[3][4][5][6][7] and became the highest standard for timekeeping between the 1920s and the 1940s"

 

 

[Strange]

Strange.

The equations (that i see on Google) for a pendulum suggest that the period will halve if g increases by 4. And the equations don't allow for GR, nor SR. I guess that they accept that pendulums are never going to go to the Moon.

Or maybe they are only concerned with non-relativistic effects.

This might be of interest. A 240 year old pendulum clock that is accurate to better than 1 in 8000000 (that is about 5 orders of magnitude more stable than your sloppy Russian friends)

 

http://wornandwound.com/the-240-year-old-pendulum-clock-thats-more-accurate-than-your-watch/

[swansont]

Or maybe they are only concerned with non-relativistic effects.

This might be of interest. A 240 year old pendulum clock that is accurate to better than 1 in 8000000 (that is about 5 orders of magnitude more stable than your sloppy Russian friends)

 

http://wornandwound.com/the-240-year-old-pendulum-clock-thats-more-accurate-than-your-watch/

 

 

The link I provided points out that a Shortt clock was good to a few parts in 10^9 (200 microseconds/day), measured against atomic clocks, and could discern tidal effects (Loomis had done a similar measurement in the early 1930's, comparing pendulum clocks with quartz clocks)

[madmac]

swansont.

My comment about having a balance-clock next to the Grandfather clock wasn't to do with the accuracy of the Grandfather.

The Grandfather feels any change in G, good, that is what we were originally talking about, & my idea of having a balance-clock next to the Grandfather was because the balance-clock is immune from the effects of G, & hencely makes it easy to use the Grandfather to find-measure changes in G (if any, which i doubt, despite the Russians). Such use of a balance-clock would give a bunch of numbers that would be easier to crunch than the case of having the Grandfather on its own (which would then require ultra accurate measurements of mass & L etc of the Grandfather, not needed if one has the help of the balance-clock, all of which is just my personal observation, i didn't read it anywhere).

 

The Shortt pendulum is very interesting. I am thinking that the next step in improving that concept would be to have 2 identical pendulums in that partial vacuum chamber, each swinging towards & away from the other in unison (ie for vibrational reasons). I think that the modern pendulum tests of G look like that (not sure).

Strange.

Thanx for that link to Harrison's pendulum. i remember seeing the sad saga of his treatment by the Royal Society on TV. One of the first cases of censorship i guess.

 

But, everyone is still missing one of my points -- no matter how accurate your timepiece or test for G, the Russian advice that their G varied by 0.7% was meant to be a statement about G, & while it is fair enough to start off by questioning their apparatus, u can bet that their apparatus was state of the art.

 

All the same, something stinks. Either G stinks, or their ultra accurate apparatus has a source of error. I will look into it.

 

Wait a minute. I remember a sister-thread from a few months ago where a poster advised that he had calculated that a Cavendish Test that treated the wts as point-wts can lead to an error of perhaps 0.3%. Weights (& planets) should only be treated as points if at long range (it seems). I will look into it.

 

This might partly explain the 1% range of values found for G. But it wouldn't explain the Russian finding about their variation of G. I will look into it.

[hoola]

what about gravity waves passing through the test apparatus? Would a low freq wave lasting through the duration of a test skew the expected value of G at a particular point in time? Could gravity wave noise coming in from the universe affect the result depending on the frequency, intensity, duration, polarity and direction the wave might be coming from? One would presume that the effects would be too small to skew a result, with the difficulty of detecting even large waves from colliding black holes. I am only mention it to eliminate it as a credible possibility of the fluctuating test results.

Edited February 9, 2017 by hoola

[Strange]

But, everyone is still missing one of my points -- no matter how accurate your timepiece or test for G, the Russian advice that their G varied by 0.7% was meant to be a statement about G,

 

 

Or maybe it is a statement about their experimental technique. Or the analysis of their results. Or ...

 

 

 

makes it easy to use the Grandfather to find-measure changes in G (if any, which i doubt, despite the Russians).

 

If you doubt their results (which is quite reasonable) then why keep banging on about it?

 

 

 

Wait a minute. I remember a sister-thread from a few months ago where a poster advised that he had calculated that a Cavendish Test that treated the wts as point-wts can lead to an error of perhaps 0.3%. Weights (& planets) should only be treated as points if at long range (it seems). I will look into it.

 

There was someone with their crackpot gravity theory. He insisted that using cylindrical weights would introduce an error (I have no idea if the error would be as large as he claimed, nor if any such error was taken into account in the experiments). He also insisted that if spherical weights were used then a different result would be obtained. He went a bit quiet after all the experiments using spherical weights (and getting consistent results for G) were pointed out to him.

what about gravity waves passing through the test apparatus?

 

Given that gravitational waves can barely be detected using a highly sensitive interferometer with 4km long arms, I think the answer is a pretty definitive, no.

 

(p.s. gravity waves are something else entirely, and would only be relevant if the lab was flooded!)

[madmac]

hoola.

Yes what could possibly change measurements of G?? Here are some candidates, not including the crankiest.

1. Gravitational Waves. The type found by LIGO. Due to stars orbiting each other, in extreme cases merging.

2. Gravitational Waves. Due to loss of mass by stars. Possibly due to an explosion.

3. Gravitational Surge. Due to reverberation of gravitational attraction forces to & from planets & stars. This lends itself moreso to aether theory, but might also be found in Eiinsteinian space-time, & even in a Newtonian world. Might be a cause of the Shnoll Effect.

4. Gravitational Turbulence. Found by Prof Reg Cahill (see posting #4). This too is probably a cause of the Shnoll Effect.

5. Tidal Changes in Gravity. Due to orbits, of Moon mainly.

6. Tidal Changes to Gravity. Due to the change in position of ocean water, & the atmosphere. Gravity Waves are ocean waves, which are good for surfing, but would have little effect on G.

7. Centrifugal forces due to Earth's spin. This pseudo-gravity effect needs to be allowed for, if not, calculations of G might be understated. I suppose that this refers to drop tests, not Cavendish tests.

8. Bad apparatus, & bad logic, & bad equations, & bad errors. Which show a false change in G.

9. A mistake in the simple Newtonian inverse square equation of gravitational attraction. Apart from the known mistake of not being correct at high speeds.

 

There are three possible types of change in G i think.

A. Where G at one site appears to change over time. Perhaps periodically. The Russians say they have measured a change.

B. Where G has a constant value at one site, & at another site, but the values are different. Probably involving two different teams.

C. Where G at one site has different values on the same day, due perhaps to a team using a number of different types of apparatus, or due to a number of teams using the same or different apparatus etc. (i don't know of any such cases).

D. I will add one more, it belongs in B, but i think it deserves its own mention. It is the borehole-anomaly. Underground, g is less than expected. Everyone blames Newton's equation, but if the equation is ok then it means that G is different underground (this wording is bad, but it will have to do for now).

Edited February 9, 2017 by madmac

[Strange]

Perhaps you could quantify those and show that they could have a measurable effect (never mind changes of 1%).

And you forgot the possible effect of invisible pink unicorns flapping their wings near the apparatus.

[madmac]

Strange.

That business about Cavendish tests & assuming that wts can be considered to act at a point (ie the central point) is interesting.

But all of this still leaves us no closer to understanding why.....

...... tests for G are on the one hand claimed to be accurate to umpteen places,

...... yet on the other hand some teams cannot get within much better than plus 0.7% or minus 0.3%,

...... & some variations in G are 10 times larger than the estimated errors, & up to 40 times even,

...... & we have a serious borehole anomaly,

...... & the Russians measure changes over time at one site (i think).

Strange.

Unicorns are rhinoceros. But the old reports were stretched & altered. Couldn't happen nowadays.

 

A change of 1% in G equates i think to a 1% change in g. I will certainly be looking into all of this.

 

Should any of this throw doubt on the equivalence of inertial mass & gravitational mass?? I wonder.

I daresay that some tests are inertial, & others are not. Has anyone ever done a comparison along those lines?? I wonder.

Edited February 9, 2017 by madmac

[Strange]

As you refuse to provide a link to this Russian work, or even name the scientists, it is hard to comment.

Re boreholes, this was the first result I found on Googling it: http://www.sciencedirect.com/science/article/pii/037026938991397X
So it seems to be fully accounted for.

Regarding the Allias Effect. It has never been properly confirmed and the most recent experiment found no effect:
Kuusela T., Effect of the solar eclipse on the period of a torsion pendulum, Phys. Rev. D 43, 2041–2043 (1991)
"Contrary to previous experiments, no increase in the period was observed"

[swansont]

what about gravity waves passing through the test apparatus? Would a low freq wave lasting through the duration of a test skew the expected value of G at a particular point in time? Could gravity wave noise coming in from the universe affect the result depending on the frequency, intensity, duration, polarity and direction the wave might be coming from? One would presume that the effects would be too small to skew a result, with the difficulty of detecting even large waves from colliding black holes. I am only mention it to eliminate it as a credible possibility of the fluctuating test results.

 

 

Gravitational waves? Way too small of an effect

[studiot]

madmac

 

OK in post#14 I tried to point this thread towards a more scientific footing and was disappointed by your lack of acknowledgement.

 

The latest twaddle in your posts #36 and #38 with no proper analysis make this the last time I will try here.

There are more rewarding threads to spend time on.

 

For instance tides do not affect gravity.

Gravity affects tides.

 

I did in fact refer you to a reference that offered a summary of the several physical factors that might have affected gravity and the experiments that were made to

study this.

 

So I will leave you with a simple example evaluation of the issue, of the type that you should have carried out at the beginning.

 

Newton's Law of Gravitation states

 

[math]F = G\frac{{Mm}}{{{d^2}}}[/math]

Where F is the force between two bodies of mass M and m respectively, di is the separation of their centroids and G is a universal constant.

If we let M be the mass of the Earth and m be the mass of a 1kg pendulum or other test mass then

The force on the mass (at the surface of the Earth) is given by F and using Newton's Second Law we have

[math]mg = G\frac{{Mm}}{{{d^2}}}[/math]

Since the mass is at the surface, d = the radius, R so this reduces to the relation between little g and big G

 

[math]g = G\frac{M}{{{R^2}}}[/math]

Replacing M by volume times density we have

[math]g = G\frac{1}{{{R^2}}}4\pi {R^3}\rho [/math]

Which reduces to

[math]g = 4\pi R\rho G[/math]

Where rho is the density.

So a change in G referred to a change in g is

[math]\Delta G = \frac{{\Delta g}}{{4\pi R\rho }}[/math]

That is delta g divided by a very large number.

Putting in some numbers

The radius of the Earthis

[math]R = 6.4x{10^6}metres[/math]

and the density is

[math]\rho = 5.5x{10^3}kg/{m^3}[/math]

So the variation of G measurable as a variation in g is given by

[math]\Delta G = \frac{{\Delta g}}{{4\pi *6.4*{{10}^6}*5.5*{{10}^3}}} = 2.3x{10^{ - 12}}(\Delta g)m/{s^2}[/math]

You should compare this with the magnitude of other reasons for g varying.

It also accounts for the difficulty in making measurements of G.

Edited February 9, 2017 by studiot

[swansont]

 

madmac

 

OK in post#14 I tried to point this thread towards a more scientific footing and was disappointed by your lack of acknowledgement.

 

The latest twaddle in your posts #36 and #38 with no proper analysis make this the last time I will try here.

There are more rewarding threads to spend time on.

 

For instance tides do not affect gravity.

Gravity affects tides.

 

I did in fact refer you to a reference that offered a summary of the several physical factors that might have affected gravity and the experiments that were made to

study this.

 

So I will leave you with a simple example evaluation of the issue, of the type that you should have carried out at the beginning.

 

Newton's Law of Gravitation states

 

[math]F = G\frac{{Mm}}{{{d^2}}}[/math]

Where F is the force between two bodies of mass M and m respectively, di is the separation of their centroids and G is a universal constant.

If we let M be the mass of the Earth and m be the mass of a 1kg pendulum or other test mass then

The force on the mass (at the surface of the Earth) is given by F and using Newton's Second Law we have

[math]mg = G\frac{{Mm}}{{{d^2}}}[/math]

Since the mass is at the surface, d = the radius, R so this reduces to the relation between little g and big G

 

[math]g = G\frac{M}{{{R^2}}}[/math]

Replacing M by volume times density we have

[math]g = G\frac{1}{{{R^2}}}4\pi {R^3}\rho [/math]

Which reduces to

[math]g = 4\pi R\rho G[/math]

Where rho is the density.

So a change in G referred to a change in g is

[math]\Delta G = \frac{{\Delta g}}{{4\pi R\rho }}[/math]

That is delta g divided by a very large number.

Putting in some numbers

The radius of the Earthis

[math]R = 6.4x{10^6}metres[/math]

and the density is

[math]\rho = 5.5x{10^3}kg/{m^3}[/math]

So the variation of G measurable as a variation in g is given by

[math]\Delta G = \frac{{\Delta g}}{{4\pi *6.4*{{10}^6}*5.5*{{10}^3}}} = 2.3x{10^{ - 12}}(\Delta g)m/{s^2}[/math]

You should compare this with the magnitude of other reasons for g varying.

It also accounts for the difficulty in making measurements of G.

 

 

 

This clouds the issue little, since we would be looking at fractional changes in G. Sure, it's ~10^-12 the change in g, but the value of G is also ~10^-12 the size of g. A 1% change in G results in a 1% change in g. That's the important thing.

[studiot]

 

 

This clouds the issue little, since we would be looking at fractional changes in G. Sure, it's ~10^-12 the change in g, but the value of G is also ~10^-12 the size of g. A 1% change in G results in a 1% change in g. That's the important thing.

 

Perhaps it does, but the first 8 posts wandered around the subject of the accuracy of measurement of G itself, before digressing to a discussion of the measurement of time.

 

I certainly gained the impression that the OP considered the current value of G stated as being a pretty poor quality measurement.

 

I would observe that considering the small magnitude of the G, the question should not have been "Why was it so bad?" but, "How the hell did they get it so damn good?"

 

My analysis was deliberately stopped because it leads into the question of what do we have to measure accurately (and how accurately) to measure G? Does it matter if we get the density wrong say 4.5 or 6.6? What about the radius?

 

As I said a proper mathematical assessment of this should been undertaken at the outset, and I still don't see one.

 

I take my hat off the these guys of old who could not simply ask Google, as I did, what is the size, mass and density of the Earth etc, when attempting such fine measurement.

Edited February 9, 2017 by studiot

[swansont]

 

Perhaps it does, but the first 8 posts wandered around the subject of the accuracy of measurement of G itself, before digressing to a discussion of the measurement of time.

 

I certainly gained the impression that the OP considered the current value of G stated as being a pretty poor quality measurement.

 

I would observe that considering the small magnitude of the G, the question should not have been "Why was it so bad?" but, "How the hell did they get it so damn good?"

 

My analysis was deliberately stopped because it leads into the question of what do we have to measure accurately (and how accurately) to measure G? Does it matter if we get the density wrong say 4.5 or 6.6? What about the radius?

 

As I said a proper mathematical assessment of this should been undertaken at the outset, and I still don't see one.

 

I take my hat off the these guys of old who could not simply ask Google, as I did, what is the size, mass and density of the Earth etc, when attempting such fine measurement.

 

 

Since the value depends on r and m, any limitations on the accuracy and precision of those values will affect the precision and accuracy of any determination of G this way.

 

However, IMO the main problem of the OP has been the credulous embracing of every anomalous measurement rather than an investigation into the quality of the research. And that also ties in with your observation — there are undoubtedly methods that will inherently have higher or lower accuracy and/or precision, depending on what needs to be measured. But you can't condemn all measurements (as the OP seems to have done) simply because some groups tried a poorer way of making the measurement, or executed their experiment badly.

 

Put another way: "Can I do the measurement this way?" is different question from "is this the best way to do the measurement?"

[madmac]

studiot.

Thanks for the equations linking delta G & delta g by a factor near 10 to the minus 12 (i haven't seen these, not recently).

It did cross my mind that nonetheless my statement that a 1% change in G possibly equals a 1% change in g is ok, because G is itself down near 10 to the minus 11 (& later i read swansont's posting saying as much). And i suspect that there is much chicken & egg involved in G & M & m & g, apart from the simpler worry of using an accurate R etc.

 

If G is 6.674 08 (by 10^-11), & if the standard uncertainty is 0.000 31, then that is 1 in 21,529. Whereas plus 0.7% (New Zealand team i think) is 1 in 142.86, which is 150.7 times larger than 21,529. For sure this needs a closer look at the tests, & for sure i will try, if nobody beats me to it.

 

Thanks for the link to Kim's paper explaining errors leading to the borehole anomaly. I did manage to find a free copy. However i notice that this is dated 1989, & i feel sure that some of the anomalies have come up since. If so, & if the teams were aware of Kim's explanation, then we still have a problem. I will look into this, it might take a while, there is almost nothing in Google about any of this.

Edited February 9, 2017 by madmac

[zztop]

 

 

There is always a future for you in agriculture with all this experience of cherry picking ...

I wish I could have given you +10 for this!

 

 

!

Moderator Note

If you keep ignoring the requests that your claims need to be supported, this will not end well. IOW, explain they physics behind this, don't just assert it.

This one deserves a +10 as well. Unfortunately, I could only give you a +1 only. Why is "madmac" still here?

Bender.

Make that 2 digits.

Some sources report plus 0.7%, some minus 0.2%.

A borehole analysis gave plus 1%.

A Russian source found a curious variation of up to 0.7% over time.

 

Prof Reg Cahill has measured turbulence of up to 20% (of speed or something) in what he calls Dynamic Space. And says that measurements of G (not by him) produce values that differ by nearly 40 times their error estimates. All of Cahill's 40 or so papers on Process Physics can be found in various sites on google, including Flinders University, & Mountain Man Graphics, & Physics arXiv. The one i was reading just now was Gravity as Quantum Foam Inflow (2003).

 

Cahill says that Newton's inverse square law is only applicable for spherical symmetry & is therefor inapplicable to say spiral galaxies & Cavendish type experiments. Not forgetting the wild swings due to turbulence.

Reg Cahill is a well known crank (coming from your part of the world). Why do you keep polluting this forum by posting utter rubbish? Read here and stop posting rubbish.

Edited February 9, 2017 by zztop

[madmac]

zztop.

Thanks for that wiki link. It mentions & demolishes a claim by Anderson re a supposed periodic change in G, but i hadn't heard of Anderson & his claim. It appears that Anderson's stuff is indeed rubbish, but i doubt that Anderson's rubbish has any bearing on the Russian's 0.7%.

 

And i see in that wiki article that G*m is indeed used in orbital work, & is considered accurate to many more places than G itself (which is what i said in an earlier posting, was it on this thread or another, i mentioned it because i had read about G*m (for Earth) many years ago).

 

U mention Cahill. This reminds me that Cahill says something about Cavendish & G, i don't understand it, but i think it might mean that a G deduced from a spherical lead ball cant be used for a spiral galaxy (hencely dark matter). This ties in with my earlier posting re a similar claim on this forum, that goes one stop further (i think) claiming in effect that a lead ball shouldn't be considered to be at a point, if at close range. I am not sure whether these are the same thing, or two separate problems.

[Strange]

U mention Cahill. This reminds me that Cahill says something about Cavendish & G, i don't understand it,

 

 

It doesn't matter if you understand it or not, it is almost certainly nonsense.

 

 

 

This ties in with my earlier posting re a similar claim on this forum, that goes one stop further (i think) claiming in effect that a lead ball shouldn't be considered to be at a point, if at close range.

 

Can you support his claim? Or is it just another random guess that you would like to be true? (My money is on the latter.)

 

 

With regard to the difficulty of properly accounting for the Earth's mass distribution in things like the borehole "anomaly" and similar measurements, you might be interested in the Potsdam Gravity Potato: http://www.universetoday.com/116801/the-potsdam-gravity-potato-shows-earths-gravity-variations/

 

Their measurements are now accurate enough to track changes in gravity as the oceans move.

Edited February 10, 2017 by Strange

[swansont]

 

U mention Cahill. This reminds me that Cahill says something about Cavendish & G, i don't understand it, but i think it might mean that a G deduced from a spherical lead ball cant be used for a spiral galaxy (hencely dark matter). This ties in with my earlier posting re a similar claim on this forum, that goes one stop further (i think) claiming in effect that a lead ball shouldn't be considered to be at a point, if at close range.

 

 

The issue around dark matter is the opposite of this. You determine G using normal matter, implying that dark matter exists. If one is suggesting that the galactic rotation curves are due to a variable G, then they are proposing new physics, rather than Newtonian gravity.

 

Being able to determine G from a uniform sphere is completely consistent with Newtonian gravity. Arguing that you can't treat it as a point is the same as saying Newtonian gravity is wrong, which immediately raises the question of what evidence one has for this.

[madmac]

Today i read -- Searching for the Ether -- 2011 -- DIO 17 -- The International Journal of Scientific History.

In Section K7 (page 25) -- Local Comparison Between Pendulum Clocks and Chronometer -- it mentions Courvoisier's experiment.

 

In Section H1 on page 19 -- it mentions another experiment where Courvoisier supposed that Lorentz contraction changed the shape & radius & local vertical of the Earth periodically with sidereal time.

 

This is slightly relevant to my post#33 where i mentioned the possible use of a pendulum clock together with a balance clock to determine changes in big G, & i said that i didn't read it anywhere. Well now i have (although for a different experiment).

 

And it is slightly relevant to post#18 by Strange where he says --

.................. it is entirely possible that the radius &/or mass of the Earth varies when G changes in order to keep pendulums swinging at the same rate.

 

I will have to have a think about all of this, ie whether Lorentz contraction changes Earth's radius & the local vertical, & hencely measurements of g, & hencely some types of measurements of big G.

It would affect pendulum tests, & drop tests (gravity tests), but wouldn't affect torsion-wire tests (inertia tests).

But in these sorts of cases every local thing is surely contracted too, ie the standard meter, the shape of the observer, the shape of the observer's eye, & to some extent we might have a change in time dilation.

 

I cant think of any Einsteinian answers, ie using SR & GR. Perhaps a bit of time dilation. Change in mass??????

Edited February 28, 2017 by madmac