Submarine detection by gravitational anomaly

[spot]

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.

[LarsMac]

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.

[Bryn Mawr]

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.

[FourPart]

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.

[spot]

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.

[FourPart]

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.

[spot]

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".

[FourPart]

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.

[spot]

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?