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Flat Earth Discussion Boards => Flat Earth Theory => Topic started by: Iceman on September 09, 2020, 07:11:38 PM

Title: Gravity - measurement and applications
Post by: Iceman on September 09, 2020, 07:11:38 PM
The gravity vs. Upward acceleration/ equivalency principle arguments are an interesting set of discussions. They commonly quote the constant value of 9.8 m/s2 for g. This is true enough for our every day lives.

The problem is that Earth's gravity is nowhere near that uniform once to start using more sensitive instruments in different areas - i.e. the significant digits after 9.8 become significant to the discussion. Gravitational strength varies based on a number of regional factors, like your latitude (because of the earth's rotation, you weigh very slightly less at the equator than you do at the poles, even though you're at a greater distance to the center of the earth).

Ignoring large regional effects, local variations in earth's gravity occur over as little as tens of meters! And in mapping out these changes, weve been able to discover geologic features like buried mineral deposits, oil and gas reservoirs, and buried bedrock valleys that may host large aquifers capable of supplying groundwater for large municipalities. (e.g. Greenhouse and Williams, 1986. A gravity survey of the Dundas buried valley west of Copetown, Ontario. Canadian Journal of Earth Sciences, v.23: 110-114 available free online)

Aside from the multi-billion dollar applications of gravity for exploration, understanding temporal variations in earth's gravity is becoming increasingly effective. The GRACE satellite system can now detect tiny changes in gravitational strength that relate to changes in water and ice storage on land on seasonal and multi-year timescales. These help measure climate change impacts and long-term over use of major aquifer systems that are causing subsidence problems in many cities (examples in California and Arizona are widespread in google searches https://lmgtfy.com/?q=land+subsidence+aquifers )

How do these measured changes in local acceleration due to gravity fit within a FE framework? The UA would induce an apparent acceleration of 9.8 m/s2 uniformly across earth's plane, and the equivalency principle is really only valid for local reference frames and cannot account for these local variations.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 09, 2020, 07:45:14 PM
Review these articles:

https://wiki.tfes.org/Weight_Variation_by_Latitude

The classic scale and weight diminution experiments show variations by latitude, but were not done in a vacuum chamber.

https://wiki.tfes.org/Gravimetry

The gravimeter is not measuring gravity directly, and is based on an indirect theory of underground density variations, which is why the anomalies are associated with seismic zones and have a negative association with mountains and continents. Latitude variations are corrections to the data, even for absolute gravimeters. The corrections are based on those original 300 year old weight diminution experiments from the first article which were not done in a vacuum chamber.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 09, 2020, 07:46:24 PM
Tom, thanks for providing the link to the wiki. It was an interesting read. My questions stemmed from that, and I will try to rephrase.

My issue is that the gravimeter readings of local changes in relative pull, as the wiki puts it, are supported by the subsequent drilling of boreholes and measurement of the properties from the subsurface materials. In mining camp settings, there are hundreds of boreholes drilled to provide the necessary ground-truthing.

I would argue that the wiki article misrepresents the density differences that are interpreted from the changing reading on gravimeters. It's really the total amount of mass beneath the meter (the relative densities of subsurface materials just influence the total mass because denser materials have more mass per unit volume).

The other issue is the seismometer-gravimeter comparison. The wiki article seems to argue that the fact that the two are variations of the same setup invalidates either of them. That's just not true because both are devices that measure acceleration. Why would they need to be different? The fact that they differ in precision and frequency is a function of the nature of the acceleration they are developed to measure at-large amplitude high frequency seismic waves vs. Low amplitude low frequency gravitational variations.

The wiki article does no seem to provide any explanation as to why the relative pull measured by a gravimeter would change over small areas, nor why temporal changes in gravitational strength are observed across large areas.

If you could provide further clarification to those last points that would be great!
Cheers

Edit, these variations are often in the interior portions of tectonic plates and far from mountains or other features
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 09, 2020, 08:06:52 PM
Quote
The wiki article does no seem to provide any explanation as to why the relative pull measured by a gravimeter would change over small areas, nor why temporal changes in gravitational strength are observed across large areas.

We are told to correct the data as we move.

http://www.geol-amu.org/notes/m10-1-4.htm


The anomalies are otherwise associated with the seismic zones. More seismic noise = greater gravity anomaly. There is always background seismic noise in the Earth. Some places stronger than others.

Quote
I would argue that the wiki article misrepresents the density differences that are interpreted from the changing reading on gravimeters. It's really the total amount of mass beneath the meter (the relative densities of subsurface materials just influence the total mass because denser materials have more mass per unit volume).

The other issue is the seismometer-gravimeter comparison. The wiki article seems to argue that the fact that the two are variations of the same setup invalidates either of them. That's just not true because both are devices that measure acceleration. Why would they need to be different? The fact that they differ in precision and frequency is a function of the nature of the acceleration they are developed to measure at-large amplitude high frequency seismic waves vs. Low amplitude low frequency gravitational variations.

The device isn't measuring gravity directly, and relies on the theory of underground density variations. A seismometer can also function as a gravimeter. The 'gravity tides' are found in the subseismic band.

Looking for the tides in the subseismic band with data analysis is a bit different than a direct experiment where a test mass is being pulled towards the Moon as it passes by overhead. If this is an indirect test of gravity, as you acknowledge, then the results may well be caused by something else which is not gravity.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 09, 2020, 08:23:55 PM
East-west profiles over short distances (1-3km) still register the local changes in gravimeter readings I'm talking about. This isnt just theory about density changes though. The subsurface properties are investigated by drilling and measurement of density/specific gravity etc.

You're 100% right that gravimeters dont measure gravity directly. They measure a pull on a mass.

BUT. Thousands of measurements spanning all the continents over many decades document changes in the pull over local scales. These are correlated with the observed properties of subsurface media (rocks, sediments, ice, water) in exploration settings, or with sun-moon positions, as you alluded to. Collectively, the local variations of the pull measured from all these gravimeters point to spatial and temporal variations in that pull. This collection of measurements and supporting ground truthing data is the evidence that gravity is the force exerting the pull, rather than a uniform upward acceleration.
Title: Re: Gravity - measurement and applications
Post by: fisherman on September 10, 2020, 12:19:28 AM
Quote
the equivalency principle is really only valid for local reference frames and cannot account for these local variations.

Its also only valid for objects in free fall.  Not everything that falls is free fall.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 10, 2020, 01:46:44 AM
Quote
BUT. Thousands of measurements spanning all the continents over many decades document changes in the pull over local scales. These are correlated with the observed properties of subsurface media (rocks, sediments, ice, water) in exploration settings, or with sun-moon positions, as you alluded to. Collectively, the local variations of the pull measured from all these gravimeters point to spatial and temporal variations in that pull. This collection of measurements and supporting ground truthing data is the evidence that gravity is the force exerting the pull, rather than a uniform upward acceleration.

Are you sure that the weight in a seismometer/gravimeter device isn't returning to its zero state in the raw readings of these gravity signals?

Look at the first graph in black called "SG Raw Gravity" here, from a superconducting gravimeter:

https://www.researchgate.net/figure/Raw-gravity-black-contains-all-signals-Residual-gravity-with-the-step-function-blue_fig2_264122117

(https://i.imgur.com/Zy8pFNC.png)

The first graph in black, labled "Raw Gravity" seems to be returning to a zero state. If the mass in the superconducting gravimeter device (suspended by magnetism) was being pulled upwards or downwards - and stayed that way - we should see something more like the step functions and residual graphs, constantly rising or lowering, rather than something that looks like a seismograph that returns to its zero state.

Here is a live reading from a gravimeter in Sweden:

http://holt.oso.chalmers.se/hgs/SCG/monitor-plot.html

(https://i.imgur.com/2ic1j7W.png)

The Observed Gravity (middle black) shows that there is a bunch of noise, labeled with a 'Typical noise level' range, and the thinner yellow line is the gravity signal.

So it looks like:

- There is a bunch of noise which dwarfs the gravity signal.
- The signal in the raw results returns to a zero or common state and the signal does not stay suspended or suppressed, except in step sizing algorithms and filters

The Sweden Gravimeter site also has a 24 hour gravity plot:

http://holt.oso.chalmers.se/hgs/SCG/daily-residual-plots.html

(https://i.imgur.com/SzmEkhd.png)

When gravity gets stronger, the yellow gravity signal grows thicker.

(https://i.imgur.com/eXwPH79.png)

The black is presumably still the noise like in the previous graph.

It gets vertically thicker because the earth is moving more violently up and down, like in a vertical component seismometer.

(https://i.imgur.com/T84QVal.jpg)

Of course, this 'violent' movement is very small.

It is telling that we have to look into noise to get the gravity signal. If the gravity signal is dwarfed by noise then the gravity signal could be a component of whatever else is causing that noise, such as seismic activity, which would explain why those gravity anomaly maps (https://wiki.tfes.org/Gravimetry#Seismic_Map_Similarities) on the gravimetery page are all associated with seismic zones.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 10, 2020, 02:35:24 AM
Hey Tom, thanks for the continued input. Interesting study you linked about the gravimeter calibration and apparent drift.

I would point out the scale on the y axis, and that the 'typical noise' range is 20 nm/s2... converted into standard g values, that's 2.039x10^-9 g in noise.... that's a lot of significant figures to carry around.

The bouguer gravity anomalies that define buried valleys and mineral deposits are about three orders of magnitude stronger (lower value of~1.5 mGal from the paper I cited earlier).

Again I emphasize that the readings are then ground truthed in exploration studies, so we can then verify whether the observed differences in pull match with the density contrasts of the rock/sediment beneath.
Title: Re: Gravity - measurement and applications
Post by: Longtitube on September 10, 2020, 06:32:51 AM
So the level of noise Tom’s talking about, compared to your survey data, is like the person behind you coughing in the middle of a ZZ Top concert. Or sniffling during Tchaikovsky’s 1812 overture as the cannons are fired?
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 10, 2020, 12:14:14 PM
To be fair, gravimeter measurements are noisy, and if you tried to take measurements during a seismic event, the additional accelerations would make it impossible. The instruments are so sensitive that we had a had time completing a survey along a busy road because any large trucks driving by created enough vibrations that we had to wait until they had passed.

But there are still large, pronounced responses that are observed in exploration surveys (whether that's for mineral deposits or groundwater incestigations) that we know with a very high degree of certainty are caused by varying properties of material beneath our feet, namely the different local distribution of mass.

 in the examples provided above, the noise level would be like repeatedly using one of those rolling distance measuring wheels to measure the distance around the curved part of a regulation Olympic sized track then plotting the difference in measurements you get in millimeters. You'll never get exactly 100 m, but you can get really close every time.

This just wasnt the discussion I wanted to have, but not that weve gone through the measurement and precision side of things, maybe we'll be able to move toward the issue at hand of the observed changes in force at different locations and at different times. I would argue that these data support the idea that the force is gravity and is problematic for a constant upward acceleration concept, but would happily consider other options to explain the phenomena that account for the observations
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 11, 2020, 03:26:09 AM
If the gravimeter is really detecting seismic waves, then when you move to a different area the waves need to transmit through different materials to get to the device in a new area. Seeing different readings would tell you that the material beneath you is different, as different materials might block or allow waves differently.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 11, 2020, 12:31:41 PM
If there were active seismic waves (I.e. from a major event that causes notable vibrations of the the earth) passing by, we wouldn't be able to get our readings. As I mentioned earlier, the passing of large trucks forced us to pause because the vibrations made it impossible to take a reading.

We actually do multiple types of seismic investigations as well. Seismic reflection surveys involve a seismic source (vibrator or shockwave) and a series of receivers (think micro phones). As you said, different media transmits seismic waves differently (denser media transmit the waves the fastest, and the energy of the wave is both reflected and refracted at interfaces between layers of different properties. By measuring the time and amplitude of the seismic energy reflected back upward to the receivers, we essentially get a picture of the geometry and layering of different materials beneath the surface.

 In exploration contexts, the gravity survey will tell us whether there is a valley beneath your feet, the seismic survey will gives you clues as to what's actually in filling the valley, and then drilling will allow you to measure the properties, test the chemistry, measure permeability etc..

Gravimeters are absolutely able to detect ground vibrations from seismic waves. The problem is that gravimeters are so sensitive that they cant actually read them.

Since they both do they same thing- measure acceleration  they are similar instruments, but the nature of the accelerations they measure  (the enormous differences in their amplitudes and frequencies) requires them to be built very differently.  I would say you can think of them like boats. Depending on where you want to go, you would want a different type of boat. A 12-foot aluminum boat is great for getting you up and down a flat stretch of river, but I wouldn't want to be caught in one in the middle of a big lake on a windy day!
Title: Re: Gravity - measurement and applications
Post by: Longtitube on September 11, 2020, 06:44:25 PM
It would help if we had some survey data of some sort to see what Iceman2020 is describing, whether a gravimeter can detect different densities of below-ground deposits. Happily, Tom has supplied a link to some: if you follow his link to the "SG Raw Gravity graph" etc, you can scroll down a little to a download of the full scientific paper – https://www.researchgate.net/publication/264122117_Detecting_small_gravity_change_in_field_measurement_Simulations_and_experiments_of_the_superconducting_gravimeter_-_IGrav/download

It's a very interesting read, investigating whether a superconducting gravimeter could be used to monitor in-ground storage of carbon dioxide for reducing global warming. The calibrating experiments include one where a heavy weight is placed directly above the gravimeter to see if any change in the downward, Planet Earth-induced force of gravity is found, plus another to measure any variation in gravity when the instrument is simply raised a short distance above the ground, but I won't spoil your enjoyment by posting spoilers. Suffice to say, the idea of Universal Acceleration struggles to explain the results found.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 11, 2020, 07:48:34 PM
Yeah fair point!

Here's another example that is available free:

conservancy.umn.edu/bitstream/handle/11299/60798/1/mgs-264.pdf
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 11, 2020, 08:01:17 PM
Paper from Canada:
nrcresearchpress.com/doi/pdfplus/10.1139/cjes-2016-0224

Others:
Gabriel et al. 2003 - geophysical investination of buried Pleistocene subglacial valleys in northern Germany

Moller et al 2007 - gravity field separation and mapping of buried quaternary valleys in Lolland Denmark. Journal of geo dynamics 43(2), 330-337.
The Scintrex operator manual from 1995 has some good examples of applications

Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 11, 2020, 09:05:34 PM
Quote
It would help if we had some survey data of some sort to see what Iceman2020 is describing, whether a gravimeter can detect different densities of below-ground deposits. Happily, Tom has supplied a link to some: if you follow his link to the "SG Raw Gravity graph" etc, you can scroll down a little to a download of the full scientific paper – https://www.researchgate.net/publication/264122117_Detecting_small_gravity_change_in_field_measurement_Simulations_and_experiments_of_the_superconducting_gravimeter_-_IGrav/download

It's a very interesting read, investigating whether a superconducting gravimeter could be used to monitor in-ground storage of carbon dioxide for reducing global warming. The calibrating experiments include one where a heavy weight is placed directly above the gravimeter to see if any change in the downward, Planet Earth-induced force of gravity is found, plus another to measure any variation in gravity when the instrument is simply raised a short distance above the ground, but I won't spoil your enjoyment by posting spoilers. Suffice to say, the idea of Universal Acceleration struggles to explain the results found.

(https://i.imgur.com/rYTal6w.png)

This is a poor setup. The gravimeter is very sensitive to noise. Placing a mass on top of the gravimeter can change the dampening.

Per the complex model they claim it matches, any phenomena can be made to match a model under any imagined assumption. Such a model could really be describing how mass stabilizes the readings of gravimeters, with gravity as the assumption, as an example.

This experiment should  be done with the mass suspended over the device without touching it.

Of course when you touch a device sensitive to noise, things are going to change. Ideally there would be multiple experiments conducted on the gravimeter in different ways to demonstrate the matter indisputably. Not a single experiment conducted on a device not designed for that procedure, with a claim that it matches a complex model and a conclusion. This is quite unsatisfactory.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 11, 2020, 09:13:35 PM
Tom, this is just one single paper that you dug up. These types of tests and calibrations have been done thousands of times in hundreds of settings, on dozens of different instrumental designs.

I would reiterate that this method is part of billions of dollars in exploration studies around the world, which in turn lead to discovery of mineral bodies, oil and gas reservoirs, and help us identify and understand groundwater systems. The signals they measure provide only insight into what is happening in the subsurface. These are clues as to areas that need to be followed up with other types of geophysical and geological investigations in order to fully understand what is happening beneath our feet. The resounding evidence that changes in the gravitational strength observed at a given location result from the changing  properties of the materials.

I realize that I probably wont be able to change your mind on this issue. And that's OK.  I can only hope that others reading this will use the resources provided to decide for themselves.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 11, 2020, 09:42:34 PM
Quote
I realize that I probably wont be able to change your mind on this issue. And that's OK.

There is a way to show that gravity exists. Unfortunately these papers aren't it. These authors are not trying to prove that gravity exists. They already assume that it exists and make complex models with an assumption of gravity's involvement for any particular observation. The goal is not to prove gravity. The goal is to describe with a set of assumptions, which makes most of these papers generally meaningless for the topic of FE vs RE.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 11, 2020, 09:46:37 PM
I already conceded that you dont need to believe a gravimeter directly measures gravity. It measures the magnitude of downward pull experienced at a given location.

Collectively, the detection of changes in that measured pull, and the strong correlation between those changes and the physical properties of the rocks which underlie them, providence evidence that the measured pull results from differences in mass at different locations locally. Those point to gravity as the best possible explanation.
Title: Re: Gravity - measurement and applications
Post by: Longtitube on September 11, 2020, 09:58:20 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.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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.
Title: Re: Gravity - measurement and applications
Post by: Iceman 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.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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 (https://academic.oup.com/gji/article/120/3/745/779022)

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.

(https://i.imgur.com/ZW7Pyom.png)

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 (https://books.google.com/books?id=7mdQDwAAQBAJ&lpg=PA259&pg=PA259#v=onepage&f=false) 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 (https://europepmc.org/article/med/20352565) 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: (https://www.researchgate.net/post/What_kind_of_problem_solutions_do_you_rate_higher_analytical_or_numerical)

  “ 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: (https://machinelearningmastery.com/analytical-vs-numerical-solutions-in-machine-learning)

  “ 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.
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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:–

(https://i.imgur.com/FDZ0npi.jpg)

and this is the device set up for use:–

(http://www.gwrinstruments.com/images/gravity-meters-large.jpg)

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:–

(https://i.imgur.com/HF4YV1K.jpg)


UA cannot account for a reduction in gravity in such circumstances. Gravity has been investigated and demonstrated for some centuries, UA has not.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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:

(https://i.imgur.com/Zb3Q2WQ.jpg)

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.
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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.

https://youtu.be/01J03Q2BAUE
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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".
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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:

(https://i.imgur.com/kDcXbs1.jpg)

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.
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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.
Title: Re: Gravity - measurement and applications
Post by: Iceman 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.
Title: Re: Gravity - measurement and applications
Post by: RonJ 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.   
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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:


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 (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwj35rvk0_jeAhVknuAKHU-rC7EQFjAAegQIGhAC&url=http%3A%2F%2Fwww.geosocindia.org%2Findex.php%2Fjgsi%2Farticle%2Fdownload%2F83944%2F64911&usg=AOvVaw2HzDoF7yD_h3qD27TuGMzb) (Archive (http://web.archive.org/web/20190315171539/http://www.geosocindia.org/index.php/jgsi/article/download/83944/64911)) 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: (https://web.archive.org/web/20190728080158/https://pdfs.semanticscholar.org/ae59/7456f647efb7155ac419edf5c9f38f240fb0.pdf)

    "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 (http://seismo.berkeley.edu/~rallen/eps122/lectures/L17.pdf) (Archive (https://web.archive.org/web/20190121230515/http://seismo.berkeley.edu/~rallen/eps122/lectures/L17.pdf)) p.3, showing that the unfiltered anomalies are negative over continental areas and positive over oceanic areas:

(https://wiki.tfes.org/images/6/61/Australia_Bouguer_Anomaly.png)

Bouguer Anomalies - Alps of Germany

https://www.leibniz-liag.de/en/research/methods/gravimetry-magnetics/bouguer-anomalies.html (Archive (https://web.archive.org/web/20190121230555/https://www.leibniz-liag.de/en/research/methods/gravimetry-magnetics/bouguer-anomalies.html))

    "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.
Title: Re: Gravity - measurement and applications
Post by: Iceman 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.
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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.


(https://i.imgur.com/HF4YV1K.jpg)
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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


                 (https://i.imgur.com/0OSkjOZ.png)


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


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


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

Title: Re: Gravity - measurement and applications
Post by: Iceman 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.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop 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.
Title: Re: Gravity - measurement and applications
Post by: Longtitube 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. 
Title: Re: Gravity - measurement and applications
Post by: Iceman 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.

Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 16, 2020, 05:32:32 PM
Look at the Complete Bougeur Anomaly and the cross section illustration of the low density root beneath the Rocky Mountains at the bottom of the diagram. Are we supposed to believe that inverse low-density root mirror images of the mountain form which correspond with the all of the mountain peaks of the Rocky Mountains?

https://www.researchgate.net/figure/Gravity-anomaly-profiles-on-a-West-East-transect-across-the-Rocky-Mountains-in-the-State_fig1_258829035

(https://i.imgur.com/ea3QUzy.png)

"Gravity anomaly profiles on a West/East transect across the Rocky Mountains in the State of Colorado. Note the change in vertical scales for the anomalies and the vertical exaggeration of the surface topography. The geological cross-section shows the sources of the modeled isostatic gravity anomaly."



http://earthsci.org/education/teacher/basicgeol/earthq/earthq.html

"Negative anomalies exist beneath mountain ranges, and mirror the topography and crustal thickness as determined by seismic studies. Thus, the low density continents appear to be floating on higher density mantle."

(https://i.imgur.com/JAqvbE7.jpg)

Amazing.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 16, 2020, 06:35:25 PM
I'm starting to worry that the flaws you perceive related only to your lack of understanding gravity, mass, and density... you seem to be implying that it's not plausible that something less dense can push down something more dense.  Ice is less dense than water. We know this because ice floats ...if you have a glass of water and place an ice cube into it, the ice cube doesnt sit on top of the water, it deforms it, displacing it around it.

That's obviously an oversimplification, but it still holds: for mountains, less dense rocks are thrust together and accumulate to greater thicknesses, thus adding more mass, which deforms the underlying mantle boundary downward. During glaciation, several kilometers of ice accumulates on top of the crust deforming/compressing it over thousands of years. As the ice melts and retreats, that mass is removed and the crust rebounds back to equilibrium.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 16, 2020, 07:46:10 PM
Pretty weird. All mountains don't form the same way. If the upper mantle/lower crust had this low density rock material I would expect that it builds up somewhere in the middle of fold mountains, or off to one side, not outlining the profile of the fold mountains.

https://www.quora.com/What-are-the-characteristics-of-famous-fold-mountains

(https://i.imgur.com/WurSCH3.jpg)

It outlines the profiles of the mountains every time? Come on.

There is another correlation too. The previous quote says that the inverse correlation also applies to crustal thickness:

"Negative anomalies exist beneath mountain ranges, and mirror the topography and crustal thickness as determined by seismic studies. Thus, the low density continents appear to be floating on higher density mantle."

(https://i.imgur.com/a8L9ebG.png)

So below the crust there is a mirror image of low density roots which masks and counters its thickness in regards to how thick it is too?

It's just one coincidence after another.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 16, 2020, 08:15:55 PM
You're right, not all mountain chains form in the same way.
This site is the only place I've seen the term 'fold mountains'
The upper mantle has high (not low) density material.
You "would expect..." what are you basing your expectations on? Logic? Common sense? Willful optimism?
That quote from quora(?) Mixes up continent-continent orogenic belts with subduction belt orogenies.
Those negative anomalies exist because when you pile up a bunch of low-density material, it pushes down the underlying high-density material, making the dense stuff relatively further away from the measuring device, creating a weaker observed pull.
It's not coincidence - its correlation.
Title: Re: Gravity - measurement and applications
Post by: Veritatisferebat09 on September 16, 2020, 11:21:50 PM
The gravity vs. Upward acceleration/ equivalency principle arguments are an interesting set of discussions. They commonly quote the constant value of 9.8 m/s2 for g. This is true enough for our every day lives.

The problem is that Earth's gravity is nowhere near that uniform once to start using more sensitive instruments in different areas - i.e. the significant digits after 9.8 become significant to the discussion. Gravitational strength varies based on a number of regional factors, like your latitude (because of the earth's rotation, you weigh very slightly less at the equator than you do at the poles, even though you're at a greater distance to the center of the earth).

Ignoring large regional effects, local variations in earth's gravity occur over as little as tens of meters! And in mapping out these changes, weve been able to discover geologic features like buried mineral deposits, oil and gas reservoirs, and buried bedrock valleys that may host large aquifers capable of supplying groundwater for large municipalities. (e.g. Greenhouse and Williams, 1986. A gravity survey of the Dundas buried valley west of Copetown, Ontario. Canadian Journal of Earth Sciences, v.23: 110-114 available free online)

Aside from the multi-billion dollar applications of gravity for exploration, understanding temporal variations in earth's gravity is becoming increasingly effective. The GRACE satellite system can now detect tiny changes in gravitational strength that relate to changes in water and ice storage on land on seasonal and multi-year timescales. These help measure climate change impacts and long-term over use of major aquifer systems that are causing subsidence problems in many cities (examples in California and Arizona are widespread in google searches https://lmgtfy.com/?q=land+subsidence+aquifers )

How do these measured changes in local acceleration due to gravity fit within a FE framework? The UA would induce an apparent acceleration of 9.8 m/s2 uniformly across earth's plane, and the equivalency principle is really only valid for local reference frames and cannot account for these local variations.






Without an oversimplification, God Created the heaven(firmament) and the earth(circle/compass). To that end, the fact that you go up and come back down is simply so you do not float to the top of the firmament dome..... ;D ;D ;D
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 18, 2020, 01:01:06 AM
Those negative anomalies exist because when you pile up a bunch of low-density material, it pushes down the underlying high-density material, making the dense stuff relatively further away from the measuring device, creating a weaker observed pull.
It's not coincidence - its correlation.

You are talking about the buildup of the mounain pushing down the higher density layers (circled in purple). You are saying that this mass buildup pushes down the higher density layers away from the gravimeter.

But there is also mass buildup pushing the mantle downwards elsewhere (circled in light blue).

(https://i.imgur.com/PQ1uz5T.jpg)

So why should this cause a negative gravity profile which matches the topside profile of the mountain peaks?

In this next one, why should the mass pushing down the mantle at the orange circle be distributed like the masses at the peaks?

(https://i.imgur.com/nir63XM.jpg)
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 18, 2020, 01:11:20 AM
We might be getting closer here, cause yeah that's exactly what isostacy says. And it's not nonsense at all... put enough mass of something and it will start to do work to something beneath it, regardless of their relative densities.

Think snowflakes slowly compressing underlying snow into denser glacier ice, sediments slowly compacting and lithifying underlying layers into rock, and ice cube in a glass of water, or a bunch of colliding low density continental crust deforming the contact with the underlying denser mantle (pictured above and circles in purple in your post)

I would just caution that the diagram is a 3D conceptual model and is no way drawn to scale, so in this case your blue circle isnt really meaningful.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 18, 2020, 02:11:39 AM
Quote
I would just caution that the diagram is a 3D conceptual model and is no way drawn to scale, so in this case your blue circle isnt really meaningful.

What? Many diagrams of mountain formation have continental plates stacked on top of each other, more so or differently on one side of the mountain range than the other.

If you won't trust the University of Bristol, why not show us how mountains really form.
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 18, 2020, 04:09:27 AM
I never said it was wrong, I said there was no scale. I have no issue with Bristol  - tons people there smarter than I am!

The conceptual drawings demonstrate plate tectonic theory accurately enough ( the second one you added later is probably better than the first one you had originally, but that's just my opinion). The maximum amount of downward deformation of the mantle contact will occur beneath the area that has the thickest accumulation of continental crust (your purple oval in the first and orange circle in the second).

I feel like this would be easier if, instead of pulling out individual slides from things, you read the whole documents. You could then include some references on the mountains and volcanoes page which currently has none.
Title: Re: Gravity - measurement and applications
Post by: Tom Bishop on September 18, 2020, 06:55:07 AM
All of the diagrams I've seen of mountain formation show unique mass distributions beneath the mountains to one side, so I don't really know where you are suggesting I look for these more accurate diagrams or information for mountain formation.

You like to use floating things as an example of isostasy, but how it is logical that the mass distribution beneath the surface would necessarily conform to the profile above the surface considering the multiple ways mountains can form?

From Dr. Narendranath Guria - https://www.researchgate.net/publication/336639287_Isostasy_Theory

(https://i.imgur.com/K9qdaUw.png)

Are you claiming that this iceberg would eventually morph to a form where the roots form a mirror image of the surface? Maybe we just need to throw around the word "eons" or something?

Why can't the topside and root profile have their own unique shapes so long as the ratio of floating material stays above the surface, per Archimedes' principle? If the top side or roots were flat, would the opposite side become flat?

If you are going to dismiss it because of its size, just imagine that it's the size of a mountain or two.
Title: Re: Gravity - measurement and applications
Post by: DuncanDoenitz on September 18, 2020, 08:01:59 AM
Are we missing the elephant in the room here? 

This thread has moved on ("gravitated", if you will) to discussion of hypotheses for the documented stable variations in gravity in different parts of the Earth under a RE model.  There is no sign of agreement, but there is at least one hypethesis. 

What is the FE/UA hypothesis, if the whole Earth is accelerating at the same rate?  Are some parts being left behind?   
Title: Re: Gravity - measurement and applications
Post by: Iceman on September 18, 2020, 11:40:36 AM
I'm not saying anything specific about the mass distributions beneath mountains.... but you seem to be claiming it would be a mirror image of the surface profile, but also has a unique mass distribution to one side.

I don't like using examples of floating things, but the do demonstrate clearly that the weight of non-dense things can induce deformation of underlying denser material, which seems the be the main issue you disagree with here ( I hope that doesnt over simplify your stance). In the case of that ice Berg, if the surface or subsurface morphology changes enough, the uneven mass distribution will cause the ice very to roll over, to find a new equilibrium.

Duncan's right though Tom, all this recent stuff should be on a different board, and we should go back to the examples of local-scale changes in measured pull over buried valleys, the references I provided, and whether UA can address those spatial variations.
Title: Re: Gravity - measurement and applications
Post by: Longtitube on September 19, 2020, 09:37:27 PM
Are we missing the elephant in the room here? 

This thread has moved on ("gravitated", if you will) to discussion of hypotheses for the documented stable variations in gravity in different parts of the Earth under a RE model.  There is no sign of agreement, but there is at least one hypethesis. 

What is the FE/UA hypothesis, if the whole Earth is accelerating at the same rate?  Are some parts being left behind?

What has happened here is what has happened so often in the past: someone asks a difficult question which the FAQ and wiki don't answer and someone, by muddying the water, avoids answering the question. Several pages of irrelevant discussion ensue and the original question is forgotten.

Variations in the strength of gravity are documented from many locations, so how does FE thinking account for these? Several answers are possible, including "We don't know" - or - "No idea, but this person (link supplied) should be able to answer your question" - or - "There are no variations, there's no such thing as gravity. Read up about Universal Acceleration, duh."

Instead, we have in order:–

(1) references to not measuring in a vacuum chamber. which is meaningless without context, and vague references to underground density variations affecting gravity (which the OP asked for an FE explanation of)

(2) attempt to dismiss gravity variations as seismic noise in the gravimetric signal, ignoring the great difference in the period of low-frequency gravity variations compared to much higher frequency seismic noise and quite ignoring the vast difference in gravity signal size compared to the noise level in the signal (signal to noise ratio exceeding 1000:1). Additional attempt to make out the gravimeter is only a seismometer by producing graphs from a scientific paper which the poster does not understand, confusing signal noise at  the nano scale with the main signal variations at a minimum of micro scale, again at least 1000:1 difference, often much more.

(3) challenged on grounds of evidence introduced by the FE responder, attempt to dismiss this evidence as crude experimentation, alleging weights are piled indiscriminately directly on to expensive, sensitive gravimetric equipment and affecting instrument's sensitivity. Simple arithmetic refuting this claim, using figures from that evidence and manufacturer's data, ignored.

(4) FE responder introduces another scientific paper on gravimetry to dismiss mathematical methods used in processing results in the paper as mere guesswork and deception. Note to responder: the complete lack of mathematical understanding demonstrated here is not just laughable, it's embarassing. Please, for your own sake, don't do that; you're only inviting ridicule.

(5) repeated misunderstanding of effect of changes in nearby masses or height on gravimeters.

(6) introducing Bouguer anomalies into response without any understanding of what these are, despite earlier quoting an article from the Aligarh Muslim University which explains them

(7) dismissing gravimeter as a crude tool whose results can be interpreted any way, ignoring the necessary field work which follows a gravimetric survey.

(8/) attempt to make theories of mountain building part of dismissal of gravimetry, using case of fold mountains – an archaic term not used in geology since the 19th century

(9) irrelevant squabble about symmetry in geological and iceberg formations, concluding with challenge to show how mountains form

That is how the original question is avoided, as the regulars here know all too well. By now we're at the end of three pages of increasingly muddy waters, none of which gives an FE explanation for the well-documented variations in gravity in many parts of the world.

Just what explanation does FE theory have for this variation? If there's currently none, just say so.