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>>> For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources Hold on how does that wo

>>> For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources Hold on how does that work? I have had a sort of sci-fi idea that sufficiently sensitive gravitational field measurements coukd detect the passing of submarines (I am not sure on the maths tbh) - which would render a lot of nuclear strategy moot. Just need to get a grasp on the maths

meindnoch 3y ago
https://apps.dtic.mil/sti/pdfs/AD1012150.pdf https://apps.dtic.mil/sti/pdfs/AD1012150.pdf Gravitational Detection of Submarines, PM Moser 1989
- moffkalast 3y ago
  That then makes single SLBM drone swarms the new meta. Spread them over a large enough area and it'll just seem like tectonic activity.
- perihelions 3y ago
  Look at what paper actually says: flat "not achievable" in the abstract; and the scaling laws on page 4 are third- and fourth- inverse powers of distance (!!!!); and on page 7 they're considering ranges of the same length scale as a submarine itself (few hundreds of meters), and even there it's hopeless. This one's never going to happen. Geologic mass concentrations are an entirely different story: you get a gravitational monopole, which is a more reasonable inverse square law. (No monopoles for a submarine, because by design they have a mean density equal to water—as the paper explains).
  - Eliezer 3y ago
    What an excellent retrospectively obvious point!
rpastuszak 3y ago
Check out quantum navigation systems. They're not used to track submarines, but rather as an alternative to GPS for submarines (using tiny differences in the Earth's gravitational field to determine position). (IIRC) Royal Navy trialed it (officially) for the first time last year.
fodkodrasz 3y ago
Actually the method of detecting mineral deposits by mapping gravitational field is already in use since a long time! The Eotvos pendulum (an instrument aka. Eotvos torsion balance) designed in 1888 started this kind of measurement. It was used commonly by the 1920s by geophysicist for mapping underground deposits by measuring the gradient of the gravitational field very precisely. This instrument was deprecated later by even better tools for surveying. The instrument was initially constructed for the experiment showing that inertial and gravitational mass are the same (well, linearly correlated) to a great precision: https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment https://www.nature.com/articles/118406a0 https://www.nature.com/articles/118406a0 (pretty useless link, but a famed periodical) Detecting submarines is way harder, practically impossible. as others have already pointed out.
limbicsystem 3y ago
Sufficiently accurate clocks can act as 'relativity sensors' - measuring changes in the 'time' bit of spacetime due to small changes in gravity.
MadnessASAP 3y ago
If you didn't know, deflections in earth's magnetic field are already used to detect submarines, amongst other things. Any large ferrous object will cause a small but detectable deflection in the magnetic field. Range is pretty short but still large enough that you can do it from an airplane flying over.
noqc 3y ago
Submarines are basically exactly the same mass as the water they displace.
bobmcnamara 3y ago
Does the average density of most submarines approaching the density of water make that more difficult? Are you looking for density variation between the parts and airspaces of a submarine?

meindnoch 3y ago

https://apps.dtic.mil/sti/pdfs/AD1012150.pdf https://apps.dtic.mil/sti/pdfs/AD1012150.pdf Gravitational Detection of Submarines, PM Moser 1989

moffkalast 3y ago
That then makes single SLBM drone swarms the new meta. Spread them over a large enough area and it'll just seem like tectonic activity.
perihelions 3y ago
Look at what paper actually says: flat "not achievable" in the abstract; and the scaling laws on page 4 are third- and fourth- inverse powers of distance (!!!!); and on page 7 they're considering ranges of the same length scale as a submarine itself (few hundreds of meters), and even there it's hopeless. This one's never going to happen. Geologic mass concentrations are an entirely different story: you get a gravitational monopole, which is a more reasonable inverse square law. (No monopoles for a submarine, because by design they have a mean density equal to water—as the paper explains).
- Eliezer 3y ago
  What an excellent retrospectively obvious point!

rpastuszak 3y ago

Check out quantum navigation systems. They're not used to track submarines, but rather as an alternative to GPS for submarines (using tiny differences in the Earth's gravitational field to determine position). (IIRC) Royal Navy trialed it (officially) for the first time last year.

fodkodrasz 3y ago

Actually the method of detecting mineral deposits by mapping gravitational field is already in use since a long time! The Eotvos pendulum (an instrument aka. Eotvos torsion balance) designed in 1888 started this kind of measurement. It was used commonly by the 1920s by geophysicist for mapping underground deposits by measuring the gradient of the gravitational field very precisely. This instrument was deprecated later by even better tools for surveying. The instrument was initially constructed for the experiment showing that inertial and gravitational mass are the same (well, linearly correlated) to a great precision: https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment https://www.nature.com/articles/118406a0 https://www.nature.com/articles/118406a0 (pretty useless link, but a famed periodical) Detecting submarines is way harder, practically impossible. as others have already pointed out.

limbicsystem 3y ago

Sufficiently accurate clocks can act as 'relativity sensors' - measuring changes in the 'time' bit of spacetime due to small changes in gravity.

MadnessASAP 3y ago

If you didn't know, deflections in earth's magnetic field are already used to detect submarines, amongst other things. Any large ferrous object will cause a small but detectable deflection in the magnetic field. Range is pretty short but still large enough that you can do it from an airplane flying over.

noqc 3y ago

Submarines are basically exactly the same mass as the water they displace.

bobmcnamara 3y ago

Does the average density of most submarines approaching the density of water make that more difficult? Are you looking for density variation between the parts and airspaces of a submarine?