Tom has made the case for gravity very nicely with all the colored charts. Gravity manifests itself by producing a measurable force between two masses separated by a distance. The earth is not a perfect sphere and is not perfectly homogeneous. The density of the earth is also quite variable. That means that there will be variations in mass as you travel across the surface of the globe. Those density variations are certainly not consistent since the earths crust has a consistency more like a Mulligan Stew. Those inconsistencies in mass are being manifested in fluctuations of gravity that’s being accurately measured by the traveling gravimeters. Thank you, Tom, for showing us all the nice colored encoded charts of all those gravity anomalies that perfectly illustrate the inconsistencies of the density (and mass) of the earth’s crust.
Correct.
This explains. Briefly:
1. We start with the observed acceleration. Note acceleration, not gravity. In effect, we drop an object from a height, measure how long it takes to travel a certain distance, then work out acceleration from the well-known formula using time and distance.
This measurement will give the same result whether we are on a globe with ‘gravity’, or whether a flat earth with UA. It is 'theory neutral'.
2. Then
separately we work out, using latitude, elevation above sea level, facts about the terrain etc, what the theoretical gravity should be, i.e. the acceleration
due to gravity.
3. So we have two measurements which are quite separate, namely observed acceleration (which might have been caused by anything, including UA) and theoretical acceleration (which is specifically attributable to gravity).
4. We subtract the theoretical number from the observed number. This is the ‘anomaly’, i.e. the difference or anomaly between theory and practice.
5. The anomaly is what the coloured charts are showing. The received wisdom is that the anomaly is due to the higher density of rocks around mountain ranges and volcanic regions.
edby, I will come back to your questions later in the day.
I will answer it now. I suspect you thought the equator should be coloured red according to RE because it ‘bulges out’ according to RE. Wrong. This is not what the red is measuring at all. The bulge has already been corrected by the theoretical calculation for latitude.
standard gravity = 978.03185 (1+Asin^2(lat) – Bsin^2(2 lat))
A, B = fitted to observed data in 1967 agreement
The red is simply measuring the difference between the theory and the practice. There is a good fit around the equator. There is not such a good fit around the plates, because of the density. Nothing to do with ‘bulge’.