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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #20 on: September 11, 2020, 10:24:02 PM »
This is a poor setup. The gravimeter is very sensitive to noise. Placing a mass on top of the gravimeter can change the dampening. .... This experiment should  be done with the mass suspended over the device without touching it.

Reading a little more carefully, you'll see two cabinets were placed either side of it to make a platform to support the weight above the SG and left for some hours to stabilise. The reduction in gravitational reading is, like the reduction by raising the SG on a lifting platform, difficult to square with Universal Acceleration. Indeed, if the methodology is so poor, why is it cited by a number of other scientific papers on applications of gravimeters? Scroll down your original link and you'll find them.

Show me.

It says:

Quote
4. Designed laboratory experiments

4.1. Monitoring mass change

In order to test the sensitivity of the iGrav, three boxes with
known weights were placed on top of the iGrav. Before doing
this experiment, we provided extra support (two cabinets) to
the platform
and let this situation become stabilized. The three
boxes with a total weight of 92.8 kg were then positioned
on the top of the platform, the height of which was 132 cm
from the ground.

It says they placed the weights on top of the gravimeter.

The cabinets were placed as extra support to the platform.

Then they took the weights off the gravimeter and put it onto the platform. The gravimeter readings returned to their original state.

From elsewhere in the document:

Quote
We put the iGrav on the platform of the lift table and measured the residual gravity without periodical effects (figure 9).

The 'platform' is something the gravimeter is resting on.
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #21 on: September 12, 2020, 01:26:20 PM »
For anyone else reading this, if you google laboratory calibration of gravimeter, you will find examples of measurements performed with a large mass suspended above a gravimeter, as Tom suggested, and there was a reduction in the observed 'pull' measured by the meter.

I would also point out that despite Tom's objections, the experimental measurements are exactly in line with the predictions of gravity. The experimental parameters also satisfied the researchers, the reviewers, and the journal associate editor.

If anyone wants to talk about the field measurements though, it's a really cool field of study and extremely useful in a wide range of investigations.
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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #22 on: September 12, 2020, 06:00:15 PM »
The first one we saw had a weight resting directly on the gravimeter.

I performed a google search on laboratory calibration of gravimeter. I got this:

Laboratory calibration of Lacoste-Romberg type gravimeters by using a heavy cylindrical ring

Quote
A ring with an inner diameter slightly bigger than the width of the instrument to be calibrated is raised and lowered over the gravimeter installed on a column.



The gravimeter is a device very sensitive to noise. We saw with the gravimeter in Sweden that most of the signal was due to noise and not the gravity signal. The gravity signal was a small component of it. Why should we believe that this large cylindrical ring with an inner diameter slightly bigger than the gravimeter wouldn't have an affect due to dampening of the environment?

They also claim that their results match a model:

Quote
For the purpose of the present study a special numerical solution has been proposed by Hajésy (1988) for the calculation of the gravity field of the optional rings. This numerical integration is based on linear combination of first and second type Chebyshev—Gauss quadratures.

So they are not using the same model as in the previous paper, but a "special numerical solution".

On Numerical Solutions, from quotes collected at https://wiki.tfes.org/Numerical_Solutions

Quote
The book Nuclear Astrophysics: A Course of Lectures tells us on p.259:

  “ Solutions generated by numerical methods are generally only approximations to the exact solution of the underlying equations. However, much more complex systems of equations can be solved numerically than can be solved analytically. Thus, approximate solutions to the exact equations found by numerical methods often provide far more insight than exact solutions to approximate equations that can be solved analytically. ”

The abstract of a medical research paper Simulation and air-conditioning in the nose says:

  “ In general, numerical simulations only calculate predictions in a computational model, e. g. realistic nose model, depending on the setting of the boundary conditions. Therefore, numerical simulations achieve only approximations of a possible real situation. ”

From a question posted on researchgate.net:

  “ Q. What kind of problem solutions do you rate higher: analytical or numerical? More problems can be solved numerically, using computers. But some of the same problems can be solved analytically. What would your preference be? ”

Mohammad Firoz Khan, Ph.D. responds:

  “ A researcher would like to solve it analytically so that it is clear what are premises, assumptions and mathematical rules behind the problem. As such problem is clearly understood. Numerical solution using computers give solution, not the understanding of the problem. It is quite blind. However, in emergency one may resort to this option. ”

Jason Brownlee, Ph.D., tells us on machinelearningmastery.com:

  “ An analytical solution involves framing the problem in a well-understood form and calculating the exact solution. A numerical solution means making guesses at the solution and testing whether the problem is solved well enough to stop. ”

University of Pittsburg - http://www.math.pitt.edu/~sussmanm/2071Spring09/lab02/index.html

  “ With rare exceptions, a numerical solution is always wrong; the important question is, how wrong is it? ”

"Numerical solutions" are not actually based on the underlying laws, and are constructed guesses. Is is analytical solutions which are based on the mathematical rules behind the problem.

Just because someone says that they can match something to a model, it doesn't mean that the solutions are directly connected to the mathematical rules of the problem.

https://www.uah.edu/images/people/faculty/howellkb/DEText-Ch9.pdf

An example of generating a slope field for a given first-order differential equation -

Quote
In this chapter, we will develop, use, and analyze one method for generating a “numerical solution” to a first-order differential equation. This type of “solution” is not a formula or equation for the actual solution y(x), but two lists of numbers,

{ x0 , x1 , x2 , x3 , ... , xN } and { y0 , y1 , y2 , y3 , ... , yN }

with each yk approximating the value of y(xk ). Obviously, a nice formula or equation for y(x) would be usually be preferred over a list of approximate values, but, when obtaining that nice formula or equation is not practical, a numerical solution is better than nothing.

The "numerical solution" in the above example is just a list of numbers which attempts to approximate the situation, and "a numerical solution is better than nothing". Hilarious. And that's exactly what these numerical solutions in these papers are - "better than nothing."

While this is amusing, it is frankly deception when people insist on numerical solutions as truth.
« Last Edit: September 12, 2020, 10:50:03 PM by Tom Bishop »
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #23 on: September 12, 2020, 06:14:30 PM »
Show me.

It says:

Quote
4. Designed laboratory experiments

4.1. Monitoring mass change

In order to test the sensitivity of the iGrav, three boxes with
known weights were placed on top of the iGrav. Before doing
this experiment, we provided extra support (two cabinets) to
the platform
and let this situation become stabilized. The three
boxes with a total weight of 92.8 kg were then positioned
on the top of the platform, the height of which was 132 cm
from the ground.

It says they placed the weights on top of the gravimeter.

The cabinets were placed as extra support to the platform.

Then they took the weights off the gravimeter and put it onto the platform. The gravimeter readings returned to their original state.

From elsewhere in the document:

Quote
We put the iGrav on the platform of the lift table and measured the residual gravity without periodical effects (figure 9).

The 'platform' is something the gravimeter is resting on.

Yes, the platform is something the gravimeter rests on, but beware of conflating two calibration experiments. The experiment you're questioning has the gravimeter on the ground – typically a concrete block – and cabinets either side of it. Here is the iGrav device loaded in the back of a Honda SUV:–



and this is the device set up for use:–



Now, the weights mentioned were placed "on top of" the iGrav at a height of 132cm above the ground. The iGrav is 102cm tall when set up, and its core sensor (in the middle of the device) is explicitly mentioned as being 52cm above the ground. So there was a gap between the top of the iGrav and the weights in the calibration experiment of up to 30cm (approx 1 foot). There is also nowhere to set heavy boxed weights directly on the device, so your objection is bogus.

All relevant sizes of the iGrav can be found on their website:– http://www.gwrinstruments.com/igrav-gravity-sensors.html#Ease-of-Operation-And-Portability

The other experiment I mentioned involved placing the iGrav on a liftable platform and when raised the device measured a reduction in gravitational deflection:–




UA cannot account for a reduction in gravity in such circumstances. Gravity has been investigated and demonstrated for some centuries, UA has not.

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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #24 on: September 12, 2020, 06:23:55 PM »
Quote
So there was a gap between the top of the iGrav and the weights in the calibration experiment of up to 30cm (approx 1 foot). There is also nowhere to set heavy boxed weights directly on the device, so your objection is bogus.

Incorrect. There is clearly material between that gap. See the red ovals:



And even if there was a gap, the support is connected directly to the platform (orange circles). Placing weights on that would be placing weight on the platform, changing its properties to vibration.
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #25 on: September 12, 2020, 06:40:59 PM »
Look up the word "conflate", Tom. You are applying the explanation of Experiment A to Experiment B, when they are not the same. Also, if you care to look up the iGrav manufacturer's information, you will see the sizes given include what you have circled, the "cold head" of the device. It's still only 102cm tall fully set up.

The connections to the platform you point out are not in fact bolted or screwed to it, they only rest on it. There's a handy video on the iGrav site on moving it which will show what all the pieces are.

« Last Edit: September 12, 2020, 06:48:23 PM by Longtitube »

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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #26 on: September 12, 2020, 06:57:35 PM »
Whether they used that blue platform for the gravimeter to rest on, or another one, the same criticism applies.

There is material between that gap at the top of the gravimeter you say exists. And it looks like significant material. It's not even possible for those wires at the top to lead into the gravimeter without some sort of material between the top component and bottom component. Even if it was the wires alone, that top part is still pushing the wires into the gravimeter.

The weights are also pressing against those side struts into the gravimeter's platform, of whatever that platform might be, causing a change in its properties to vibration.

None of this is demonstrating gravity in a decisive way. The guy sitting at that desk put some weights on a device very sensitive to noise and vibration and then wrote that paper when he saw a change, declaring that it must have been gravity with an overly complex equation he says it matches, which appears nowhere in Newton's Principia. This is the expected quality of work of such scientists, who produce works which you think is "fact".
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #27 on: September 12, 2020, 07:01:39 PM »
I know some people struggle with arithmetic, but I didn't think it was something that troubled you. The weighted boxes were 132cm above ground, the iGrav is 102cm tall. That makes a 30cm gap between the top of the assembled iGrav - the complete, all pipes and wires connected, iGrav – and the weighted boxes supported by cabinets placed either side of the iGrav and not shown in any photos from that research paper. 30cm is almost 12 inches. Big enough to get both hands through, easily.

Or perhaps you're doubting photographic evidence. Again.

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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #28 on: September 12, 2020, 07:10:03 PM »
The only person in denial here is you. It's fairly clear from that video you posted that the red top plate is attached to the gravimeter:



So this  assertion you posted:

Quote
So there was a gap between the top of the iGrav and the weights in the calibration experiment of up to 30cm (approx 1 foot). There is also nowhere to set heavy boxed weights directly on the device, so your objection is bogus.

Is bogus.
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #29 on: September 12, 2020, 07:27:36 PM »
Ah, I understand now! The manufacturer states the height of the iGrav is 102cm when fully assembled, but you have spotted a stray red plate that invalidates their measurements, completely. Obviously I should have seen that in the beginning – just can't trust manufacturer's data. Thank you so much.

edit: You can get a good idea of the physical size of the iGrav from the video. 102cm is around waist height, as may be seen in the video and 120cm is about armpit height on a six foot adult. 132cm is more like shoulder height on the same adult, noticeably taller than an assembled iGrav. That red plate is fixed to the Dewar – the flask of liquid helium. The coldhead gets bolted to the top of the Dewar via fixings in that red plate, which you will see if you watch the video through.
« Last Edit: September 12, 2020, 07:43:29 PM by Longtitube »

Re: Gravity - measurement and applications
« Reply #30 on: September 13, 2020, 12:32:25 AM »
Tom you keep saying that gravimeters only measure seismic noise, even though the example that YOU dug up and spend the first half of this thread discussing demonstrated that the noise that is measured is 4 orders of magnitude less than the signal it was measuring.

You write them off as measuring nothing but noise, then give another example,the lacoste and bromberg set up, where they do exactly the thing you complained the first paper's authors DIDN'T do, but then write off the data because you dont understand the math they used... I'm at a loss.

UA doesnt account for the observed changes in pull measured by gravimeters when different masses are near, whether that's beneath earth's surface or directly above the instrument.
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Offline RonJ

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Re: Gravity - measurement and applications
« Reply #31 on: September 13, 2020, 02:02:37 AM »
The current standard for sensitive gravimeters are the superconducting gravimeters, which operate by suspending a superconducting niobium sphere in an extremely stable magnetic field; the current required to generate the magnetic field that suspends the niobium sphere is proportional to the strength of the Earth's gravitational acceleration.[4] The superconducting gravimeter achieves sensitivities of 10–11 m·s−2 (one nanogal), approximately one trillionth (10−12) of the Earth surface gravity. In a demonstration of the sensitivity of the superconducting gravimeter, Virtanen (2006),[5] describes how an instrument at Metsähovi, Finland, detected the gradual increase in surface gravity as workmen cleared snow from its laboratory roof.

Here is an instance of an isolated mass above the gravimeter.  You have a snow mass causing a vector in opposition to the main vector caused by the earth below.  As the snow was removed the opposition vector became less & less and there was an expected increase in the main acceleration vector caused by the mass of the earth.  If universal acceleration was a valid argument in the flat earth theory then you wouldn't expect the gravimeter to react to the snow on the roof of the laboratory.  Any dampening of the vibrations of the gravimeter due to snow on the roof wouldn't be expected either.  The gravimeter should be well isolated from it's surrounding building structure.   
« Last Edit: September 13, 2020, 04:27:33 AM by RonJ »
For FE no explanation is possible, for RE no explanation is necessary.

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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #32 on: September 15, 2020, 04:05:05 AM »
Tom you keep saying that gravimeters only measure seismic noise, even though the example that YOU dug up and spend the first half of this thread discussing demonstrated that the noise that is measured is 4 orders of magnitude less than the signal it was measuring.

You write them off as measuring nothing but noise, then give another example,the lacoste and bromberg set up, where they do exactly the thing you complained the first paper's authors DIDN'T do, but then write off the data because you dont understand the math they used... I'm at a loss.

UA doesnt account for the observed changes in pull measured by gravimeters when different masses are near, whether that's beneath earth's surface or directly above the instrument.

Lets recap:

- The gravimeter is incredibly sensitive to noise.

From the lacoste and bromberg document:

    "The first experiments carried out in 1991 showed that
    the human presence near the calibration device during the
    measurements produces thermal anomalies, tilts, vibrations,
    etc., significantly influencing the results. To avoid these
    problems the automated version of the equipment operates
    by remote control."

Very sensitive. With this sort of sensitivity there would need to be sufficient and very compelling evidence that gravity actually plays a part in the results.

- From the SG in Sweden, we saw that most of the raw signal was noise.

- When placing a weight on top of the gravimeter, the gravity signal dampened.

- When placing a massive cylinder around the gravimeter over its sides, the gravity signal dampened.

- In one anecdote above, when the large area of the roof above was covered with a bunch of snow, the gravity signal was dampened.

So far, all of this is in line with the idea that the device could be reading noise. Mass dampens noise.

In order to demonstrate that the device is actually measuring gravity, we would need more and different tests. We would need to put a mass underneath the gravimeter. If the gravimeter is just reading how noise propagates, when a mass is put underneath the gravimeter the readings should dampen like the previous examples. If it is gravity, the pull of the mass should add to the pull of the Earth and the readings should increase.

You will have a difficult time finding someone who did that, however, as they aren't really trying to prove gravity, only to describe things under existing assumptions, which is why they aren't testing much in the determinative ways we are looking for. But fortunately we already have this experiment. In practice the gravimeter gives lower readings over the continents and mountains, and higher readings over the oceans. Additional mass below the device dampens the reading.

https://wiki.tfes.org/Gravimetry#Perplexing_Anomalies

Quote
Gravity Anomalies Contrary To Theory

Bouguer Anomalies Over The Continents and Oceans (Archive) in the Journal of the Geological Society of India tells us that the anomalies are greater over the ocean than over the land, which is contrary to gravity theory:

    "Why, in general, the Bouguer gravity anomalies are negative in continental areas and positive in oceanic areas? Extending the question further, why do the predominant negative and positive anomalies respectively correspond to the mountain peaks and ocean depths? Although the Bouguer gravity data are not brought on to an even datum, there is fairly a good inverse correlation of Bouguer anomalies with height/depth as well as seismic data. This obviously indicates the excess mass reflected as gravity lows and the deficit mass as gravity highs with respect to the geoid/ellipsoid surface. This is in contrast to the theory of the gravity field which is proportional to the excess or deficit mass. Mathematically speaking, the observed anomalies are proportional to the vertical gradient of gravity, indicating excess mass above the geoid as gravity lows and deficit mass below the geoid as gravity highs. If this were true, far reaching implications arise in the understanding of the theory and interpretation of Bouguer anomalies."

The anomalies are negative in continental areas and positive in oceanic areas. The anomalies are also negative in the mountains. These anomalies appear to go against the theory that the anomalies are due to the attraction of mass.

On discrepancies, one writer states:

    "On the basis of newtonian gravity, it might be expected that gravitational attraction over continents, and especially mountains, would be higher than over oceans. In reality, the gravity on top of large mountains is less than expected on the basis of their visible mass while over ocean surfaces it is unexpectedly high. To explain this, the concept of isostasy was developed: it was postulated that lowdensity rock exists 30 to 100 km beneath mountains, which buoys them up, while denser rock exists 30 to 100 km beneath the ocean bottom. However, this hypothesis is far from proven. Physicist Maurice Allais commented: ‘There is an excess of gravity over the ocean and a deficiency above the continents. The theory of isostasis provided only a pseudoexplanation of this.’ 15

    The standard, simplistic theory of isostasy is contradicted by the fact that in regions of tectonic activity vertical movements often intensify gravity anomalies rather than acting to restore isostatic equilibrium. For example, the Greater Caucasus shows a positive gravity anomaly (usually interpreted to mean it is overloaded with excess mass), yet it is rising rather than subsiding."

Bouguer Anomalies - Australia

We find the following depiction of Australia's Complete Bouguer Anomalies and Free Air Anomalies on a University of California Berkeley lecture on gravimetry (Archive) p.3, showing that the unfiltered anomalies are negative over continental areas and positive over oceanic areas:



Bouguer Anomalies - Alps of Germany

https://www.leibniz-liag.de/en/research/methods/gravimetry-magnetics/bouguer-anomalies.html (Archive)

    "This map shows the Bouguer anomalies over the whole of Germany and surrounding areas, in a detailed but still clear way.

    ...The resulting gravity anomalies vary across the mapped area from -170 mGal in the Alps to +40 mGal around the gravity low in the Magdeburg area."

The above shows that the anomalies are negative in the Alps of Germany.

So the continents and mountains act to dampen the gravity readings, rather than to increase them. This is the missing experiment that you needed to complete your theory, and the result is contradictory.
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #33 on: September 15, 2020, 12:16:09 PM »
That was a pretty misleading recap.
The noise in the experiment was 0.0001% of a typical signal, which are usually on the order of a few mGal.
You keep saying 'dampen' but you should be saying 'reduced'. The measured pull was reduced in the experiments when a large mass was placed above the gravimeters.
In your last proposition, your right, it is a good idea. In this case, the measured pull would be increased, due to the underlying mass (again, not dampened).

These are very sensitive instruments that measure noise within the signal. Depending on the magnitude of the signal you're measuring, that can become problematic something with a very low amplitude, like say, the pull from Jupiter, could potentially get lost within the ambient noise the device measures. Something with larger amplitudes, like buried valleys and ore deposits, are orders of magnitude larger than the noise.

We have thousands of measurements of local-scale (100'd of m to few km) gravity variations that are corroborated by the measurement of the properties of materials beneath our feet. Universal acceleration does not account for these variations.
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Re: Gravity - measurement and applications
« Reply #34 on: September 15, 2020, 09:37:31 PM »
The wiki entries Tom quotes should be read to avoid misunderstanding, in particular following the links within these entries. If you do this, you find the quotation

Quote
    "This map shows the Bouguer anomalies over the whole of Germany and surrounding areas, in a detailed but still clear way.

    ...The resulting gravity anomalies vary across the mapped area from -170 mGal in the Alps to +40 mGal around the gravity low in the Magdeburg area."

but if you read the source, it goes on as follows:–

Quote
The resulting gravity anomalies vary across the mapped area from -170 mGal in the Alps to +40 mGal around the gravity low in the Magdeburg area. In the mapped area they form local structures such as the salt diapirs of north Germany, as well as regional units such as the Rhine Graben. Previous inconsistencies along the former German-German border have been removed. Anomalies can be used to interpret the geological structure of the Earth's crust.

In short, the gravity anomalies can be used to work out what's going on beneath ground level, which is what Iceman2020 originally stated. Perhaps Tom sees the word "anomalies" as meaning something is wrong, which is rather short-sighted.

The wiki also quotes "one writer" on gravity – why not name this "one writer"? Could it be because the writer is one David Pratt who unquestioningly documents many cranks and frauds who have made "discoveries" which no-one can replicate and are openly mocked by engineers and scientists who actually work in the relevant fields? Perhaps this "one writer" is less than reliable in his own comments about gravity too.

The word "dampened" gives Tom great trouble, he must be thinking of "dampening down" a fire, a much-desired thing in the US West coast states at the moment. What is meant by "dampened" in instrumentation is removing noise or extraneous vibration. A modern speedometer has a dampened readout and reads a steady 88mph when you're doing 88mph, whereas an undampened needle might continually oscillate between 84 and 92mph. Dampening the readout does not reduce the readout, just steadies it.

If you examine the results of raising an iGrav gravimeter on a lifting platform and later lowering it to its original position, you'll see significant noise in the readout after raising the platform which soon dies away. Nearly 24 hours later the iGrav is returned to the lower position and more significant noise is encountered at first which soon dies away. In each case, for the most of a day afterwards the instrument recorded a pretty steady reading. This is an example of a dampened noise signal – the noise quickly dies away. The experimental results (of a lesser pull when the instrument is raised) stand.



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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #35 on: September 16, 2020, 02:59:52 AM »
> Appeals to geoscience

Funny that you think that gravimetry is a field of scientific certainty. It's not. It barely qualifies as a science, and must be used alongside other techniques, as gravimetry alone provides poor understanding of the earth.

https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-17-30673

    "Both negative and positive density contrasts can be modeled for any gravity survey target. The lower panel shows a cross-section through the ground. The circles represent denser (right) and less dense (left) regions. The upper panel shows the gravity that might be measured at the surface."

                 

    WARNING!

    "Gravity is a Potential Method, meaning that we try to interpret the sources that contribute to a total potential force (this is also true for magnetic surveying). As such, we can always find a variety of physical models that can produce the same observations. This means that no model based solely on gravity observations can be considered to be uniquely correct. Always, additional information is needed before confident interpretation of the gravitational data is possible."

    ~

    "Combining gravity models with other information – geologic, seismic, electromagnetic, will improve confidence in the results.  Gravity is a potential method, meaning that its results are ambiguous in isolation. Other information is always needed to interpret gravity anomalies with confidence."

http://www.science.earthjay.com/instruction/HSU/2016_spring/GEOL_460/lectures/lecture_07/geophysical_expoloration_gravity.pdf

    "The interpretation of potential field anomalies (gravity, magnetic and electrical) is inherently ambiguous. The ambiguity arises because any given anomaly could because by an infinite number of possible sources. For example, concentric spheres of constant mass but differing density and radius would all produce the same anomaly, since their mass acts as though located at the centre of the sphere. This ambiguity represents the inverse problem of potential field interpretation, which states that, although the anomaly of a given body may be calculated uniquely, there are an infinite number of bodies that could give rise to any specified anomaly."

https://doc.rero.ch/record/255651/files/00002456.pdf

    Gravity anomaly interpretation

    "Interpretation  of gravity anomalies  can be  made in two ways, directly  or by building a gravity model. Concerning the latter, the gravity anomaly generated by  the  model  will  be  compared  with  the  measured  gravity. In all cases the nature of the gravity makes its interpretation ambiguous, as several different bodies can induce the same anomaly as presented in figure 2.16. Therefore gravity is often used in combination with other geophysical methods to avoid or decrease the ambiguity."

https://www.mtholyoke.edu/courses/mpeterso/phys103/PhysicsInProportionI.pdf

    "A gravimeter is like a crude eye, looking into the Earth, but without any ability to focus, able to report only that there is something interesting nearby or there isn’t."
« Last Edit: September 16, 2020, 06:47:15 AM by Tom Bishop »
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #36 on: September 16, 2020, 03:04:17 AM »
You're describing things as if they're somehow a detriment. As I said from the beginning, the utility of the gravity measurements in exploration settings comes from the rigorous geoundtruthing and subsequent analysis of the physical properties of the materials that are intersected in boreholes/mines/excavations.

You can try to make is as abstract as you want, since gravity measurements are part of a potential field and, on their own, provide non-unique solutions...but the fact of the matter is that we go and check. Seismic reflection surveys delineate the geometry of units. Boreholes drilled allow us to measure the physical properties. Downhole geophysical tools all us to measure physical properties and take photos and videos of the materials in-situ.  The gravimeters record different pull forces in different places. The magnitude of the differences is much greater than the magnitude of the noise. We learn about what causes the changing pull forces by measuring the properties of the subsurface directly. Together, these data collectively tell us that areas with more mass create stronger  downward pull force. This is strong support that gravity is the pull force a gravimeter measures and the varying strength of gravity/ measured pull force is inexplicable within a framework involving uniform upward acceleration.
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Offline Tom Bishop

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Re: Gravity - measurement and applications
« Reply #37 on: September 16, 2020, 06:13:57 AM »
Let me get this straight:

- The gravimeter readings alone can't predict the result of core samples
- The gravity models can be adapted and interpreted to fit any result of the readings or core samples
- Other non-gravity techniques are actually required to predict the result of the core sample
- So you therefore think that the gravimeter readings are connected to the result of the core samples

lol

A quote above says "Both negative and positive density contrasts can be modeled for any gravity survey target." The gravimeter can read mass targets beneath it as positive or negative. And, of course, it is an established trend that mountains and continents are more negative than the oceans. What kind of large surveys have taken place to verify these unique mass configurations which causes negative readings in the presence of additional mass below the gravimeter? Isostasy explains that low density rock exists 30 to 100 km beneath mountains. Where have geoscientists dug that far "to go check"? They haven't.

This adds another variable for the core sample interpretation. You are not actually testing the entire environment. You are just posting here pretending that the environment is known. There is unknown data, loads of assumptions, models that can be fit to any interpretation, and it's a requirement that other non-gravitational techniques are used, making this quite a pseudo-scientific enterprise.
« Last Edit: September 16, 2020, 06:34:40 AM by Tom Bishop »
"The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is" — Pauline Barmby, Ph.D., Professor of Astronomy

Re: Gravity - measurement and applications
« Reply #38 on: September 16, 2020, 06:22:41 AM »
If you watch the reading of a barometer from a closed, windowless room you are unable to say confidently what the weather will be. Does that make the barometer an unscientific piece of junk? Hardly.

If you smell fungus growing in a spare room, does the damp meter used by the man investigating this tell you there’s a tile missing from the roof, or a big crack in the wall or does it pinpoint the leaking water pipe in your attic? It does none of these, but it does tell you the wall is damp in the area at the top of the far wall instead of the near left bottom corner. Obviously this makes it useless pseudoscience by your reckoning.

These are the grounds given for discounting gravimetric measurements, because Tom doesn’t believe in gravity. Not because it doesn’t work - geologists have used gravimeters for years as a valuable tool in their armoury - but because Tom doesn’t believe in gravity.

So tell us all - what valuable observation or prediction has UA ever made? There are none. 
« Last Edit: September 16, 2020, 09:39:14 AM by Longtitube »

Re: Gravity - measurement and applications
« Reply #39 on: September 16, 2020, 11:42:23 AM »
Your inability to understand how the process works - despite my numerous explanations above - does not invalidate it.

Collecting the field data within a given survey area in the form of mapping and sampling surface materials, conducting additional geophysical surveys, and drilling boreholes so we can measure the properties of different rock and sediment units, reduces the number of potential solutions to the gravity data to a point where we can confidently and accurately map the feature.

A gravity survey on it's own can give a good - but not unique - view of the distribution of mass beneath the ground. A good example is that a gravity survey on it's own can tell us where a buried valley is located (because theres less mass in the valley than on either side of it). But it doesnt tell us enough details on what's IN it. If I'm looking for new water supply for a city, the gravity data essentially tells me where to drill to look for an aquifer. If these gravity lows didnt always show geologists where valleys were, we would have stopped using the method decades ago. But it consistently works, so we keep using it.

Drillers comminly ask me what were going to go through in the next 5 feet down a borehole... I always tell them that if I knew for sure, we wouldn't have called them. Geologic data constrains geophysical interpretations. The more geologic data you have, the more accurate your geophysical interpretations can be.

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"Earth isnt round or flat. It's fucked."
- Ricky LaFleur