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That's what the BBC reporters claim anyway.Not surprisingly, militaries across the world are also backing research in to quantum sensing.

Gravimeters in particular offer the potential for detecting your opponent's submarines, for instance. Gravity may be a weak force, but you can't shield against it.

So while stealth technology may hide your radar signature, it won't hide you from a quantum gravity sensor.

https://www.bbc.co.uk/news/business-47294704




Bosh. Bogus nonsense. How on earth is that true.

Your underwater submarine displaces its exact weight of water. If it didn't it would sink. The principle of buoyancy applies. So how is a gravity measurement, either from the sea floor or the surface, going to twitch in the vicinity of a submerged submarine, quantum or otherwise.

I am, of course, as always, eager to be corrected.

I'll do some calculations and get back to you..

Curious.

Surely a submarine mass will be different than that of whatever water it has displaced.

Especially if the thing is moving.

LarsMac;1522638 wrote: Curious.

Surely a submarine mass will be different than that of whatever water it has displaced.

Especially if the thing is moving.


It will have a variable density, but why would the mass differ?

LarsMac;1522638 wrote: Curious.

Surely a submarine mass will be different than that of whatever water it has displaced.

Especially if the thing is moving.


In order for it to float they have to adjust the mass using the buoyancy tanks so that it is exactly equal (OK, technically they could take up some slack whilst they are moving using the trim planes but why would they when they'd have to readjust whenever they stop?).

Surely the way to detect a sub would be the magnetic anomaly, not the gravitational one.

Bryn Mawr;1522642 wrote: In order for it to float they have to adjust the mass using the buoyancy tanks so that it is exactly equal (OK, technically they could take up some slack whilst they are moving using the trim planes but why would they when they'd have to readjust whenever they stop?).

Surely the way to detect a sub would be the magnetic anomaly, not the gravitational one.


I understand all that, but the variations in mass due to metal versus air will likely appear as at least an anomaly. It will likely depend on the range from sensor to object.

I am pretty sure that the water would be not unlike similar readings in air. Water is simply an atmosphere of H2O molecules all wandering about on their own so not likely to appear as a single mass.

Any object in the water will likely cause a much different reading than the water, itself.



And again, I suspect the movement of the thing is going to create detectable anomalies, as well.

I agree with you that there will be all sorts of detectable anomalies between a submarine and the equivalent mass of water. The question is whether any of those will be gravitational and I still see no reason to think they could be.

The earth, for example, when considered from any position outside its surface, behaves as a point source at its centre of mass seen from that position. So would the submarine. So would the mass of water in the absence of the submarine. How do those two point sources differ?

LarsMac;1522644 wrote: I understand all that, but the variations in mass due to metal versus air will likely appear as at least an anomaly. It will likely depend on the range from sensor to object.

I am pretty sure that the water would be not unlike similar readings in air. Water is simply an atmosphere of H2O molecules all wandering about on their own so not likely to appear as a single mass.

Any object in the water will likely cause a much different reading than the water, itself.



And again, I suspect the movement of the thing is going to create detectable anomalies, as well.


The problem here is the resolution. The current gravity maps are out by two or three orders of magnitude from the level they'd need to be to detect anomalies of the size involved in a sub. Then you have the rate of mapping - given a moving target it would all be a blur.

As gravity is a weak force I don't see that anyone can improve the detectors quickly enough to catch up given the improvements in concealment that would inevitably happen should such a technology race start.

Bryn Mawr;1522647 wrote: the improvements in concealment that would inevitably happen


I'm listening. Aluminium hull? Plywood partitioning? Helium buoyancy tanks?

Even a fridge magnet is stronger than the earth's gravity. The fact that it sticks to the fridge door instead of submitting to the gravitational force & falling to the earth is proof of that.

FourPart;1522651 wrote: Even a fridge magnet is stronger than the earth's gravity. The fact that it sticks to the fridge door instead of submitting to the gravitational force & falling to the earth is proof of that.


Something to do with the proximity of the fridge perhaps. Put the magnet a foot away from the fridge and let go, see which wins then.

Bryn Mawr;1522647 wrote: The problem here is the resolution. The current gravity maps are out by two or three orders of magnitude from the level they'd need to be to detect anomalies of the size involved in a sub. Then you have the rate of mapping - given a moving target it would all be a blur.

As gravity is a weak force I don't see that anyone can improve the detectors quickly enough to catch up given the improvements in concealment that would inevitably happen should such a technology race start.


From reading the article, I suspect "gravity maps" will change rather rapidly as this kind of technology matures.

Remember that in the early days of Radar and Sonar, what the receiver got was a "Blip" on a CRT screen.

The newer SONAR can give one a fairly well-defined image, depending, of course on range and relative velocity.

I didn't get that this might be a satellite-based technology, but in time that could be possible.

LarsMac;1522653 wrote: From reading the article, I suspect "gravity maps" will change rather rapidly as this kind of technology matures.

Remember that in the early days of Radar and Sonar, what the receiver got was a "Blip" on a CRT screen.

The newer SONAR can give one a fairly well-defined image, depending, of course on range and relative velocity.

I didn't get that this might be a satellite-based technology, but in time that could be possible.


I’m not convinced that they will improve quickly enough to be significant, remember, the closer the sub approaches an empty shell density wise the less detectable it will be until your resolution gets down to less than a foot. The hull and any horizontal decks would be invisible gravimetricly.

The main problem would be the engine / power plant and that is highly likely to give a magnetic anomaly which would be far easier to detect.

spot;1522652 wrote: Something to do with the proximity of the fridge perhaps. Put the magnet a foot away from the fridge and let go, see which wins then.


Put the fridge magnet on the ground so that it's in contact with the earth, held there by gravity. Hold a fridge door (or any piece of ferrous based metal), above it & see which overpowers it then.

FourPart;1522661 wrote: Put the fridge magnet on the ground so that it's in contact with the earth, held there by gravity. Hold a fridge door (or any piece of ferrous based metal), above it & see which overpowers it then.


You glide over the fact that the gravitational attraction isn't the floor, it's centred four thousand miles below the magnet. Half the earth is further and half is less far, the effect is of having the earth's mass four thousand miles distant. If you replaced the earth with a point source black hole four thousand miles away the gravitational attraction would be the same. If you put the fridge four thousand miles away, the magnet might reach it after a hundred years of very slow acceleration. The force of that electromagnetic attraction is trivially minuscule by comparison.

spot;1522662 wrote: You glide over the fact that the gravitational attraction isn't the floor, it's centred four thousand miles below the magnet. Half the earth is further and half is less far, the effect is of having the earth's mass four thousand miles distant. If you replaced the earth with a point source black hole four thousand miles away the gravitational attraction would be the same. If you put the fridge four thousand miles away, the magnet might reach it after a hundred years of very slow acceleration. The force of that electromagnetic attraction is trivially minuscule by comparison.


I imagine if you scaled up the size of the magnet to the size of the earth there would be a big difference. Gravity is based on Mass. The greater the Mass, the greater the Gravity. Of course, if the magnet were scaled up it would have its own Gravity but if you disregard that, as a hypothetical situation you would be comparing like with like.

FourPart;1522684 wrote: I imagine if you scaled up the size of the magnet to the size of the earth there would be a big difference.
We seem to have strayed a long way from "a fridge magnet is stronger than the earth's gravity".

spot;1522686 wrote: We seem to have strayed a long way from "a fridge magnet is stronger than the earth's gravity".


You moved a long way from fridge magnets to Black Holes.

FourPart;1522688 wrote: You moved a long way from fridge magnets to Black Holes.


I was talking about gravity. What form the mass takes is immaterial.

How about if I quote from a respectable source...

as two objects get far apart, the gravity between them goes down by a factor of four when you double the distance, but the magnetic force goes down by (at least) a factor of sixteen. On the scale of the solar system, with planets far apart, gravity is much more important than magnetism.

https://van.physics.illinois.edu/qa/listing.php?id=225




Does that help at all?