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This is the most obvious practical application of my PhD topic. A Bose Einstein Condensate is an extremely sensitive detector of gravity- a nuclear submarine co
by jchallis 3y ago
This is the most obvious practical application of my PhD topic. A Bose Einstein Condensate is an extremely sensitive detector of gravity- a nuclear submarine could use it to make an ultra-accurate map of the world based on variations in the gravitational constant g. This would remove one of the primary reasons subs need to surface , in order to GPS lock.
It’s a naval chart that would not require surfacing.
A French postdoc in my lab swore this was the moneymaker for our entire subfield, and it seems he was on to something …
- deleted 3y ago[deleted]
- themodelplumber 3y agoFascinating. Q for you since you are so clued in. I am a ham radio operator and was thinking about novel forms of signal propagation. I landed on the idea of gravitons. Could gravitonic signal propagation be done somehow? While researching, I keep coming across familiar terms I know from radio land. Just curious if the fields here could be harnessed for communication. Thanks.
- HyperSane 3y agoGravity waves are way too hard to detect and generate to be used for communication. The waves we can just barely detect too 8 solar masses worth of energy to generate.
- multjoy 3y agoAnd people complained about next door's aerial farm!
- dumpsterdiver 3y ago[flagged]
- sph 3y ago> any stable solar system capable of sustaining life will emit a steady heartbeat, just like a living being What do you mean? What would be the source of the regular wave-like signal, and why only systems with life have one? Do you mean that actual hearts beating create gravitational waves?
- dumpsterdiver 3y ago> What do you mean? What would be the source of the regular wave-like signal The source of the signal would be a solar system that contains planets in a stable enough orbit to harbor life. > and why only systems with life have one? Solar systems that harbor life (our own, for example) are not the only stable solar systems. A stable solar system is however required to be the genesis grounds of life as we understand it, otherwise the building blocks of such potential life would be swallowed in the chaos and heat.
- sethammons 3y agoHow does stability lead to a wave? We can see wobble in stars to know they are getting tugged by planets. Are you expecting similar with gravity? I'm not a physicist nor astronomer. I wouldn't expect any gravity waves as I'd expect the star system to have a center of mass that stays in roughly the same space.
- dumpsterdiver 3y ago> How does stability lead to a wave? All gravitational events lead to a wave. A system emitting stable waves creates a "pattern".
- ilteris 3y agoIn the movie interstellar were they using gravitational communication to write the book? Can someone enlighten me?
- beders 3y ago> Here's what Chat-GPT4 has to say about the fidelity of "gravitational communication": Who was the original author?
- johndunne 3y agoRemember that that 8 solar mass gravity wave source is potentially 100’s millions of light years away. A sci-fi author could conjure up a ‘portable box’ containing a couple of orbiting micro-scopic black holes in a box to generate gravity wave signals someone somewhere in the solar system could pick up with a portable LIGO device. Consider this comment a patent on the idea :-)
- jchallis 3y agoThe big big downside of gravity waves is that they have no dipole radiators - with electric charge you have + and - and that allows very efficient propagation. For gravity there is only one charge ,and this allows only quadrupole radiation - making it extremely awful for transmission.
- yodon 3y agoYes, but there is no dispersion relation or absorption by the interstellar medium (not directly related to the quadrupole nature, but that which makes a radiation hard to detect also makes it hard to interfere with).
- _joel 3y agoThe detectors are such precision instruments it took over 10 years of calibration until they even had the first detection. Maybe some far off comms network could use them, but I doubt anytime soon. I wonder if you could use erasure codes with them too :)
- comboy 3y agoAccelerating star-like masses to 99% speed of light in a few seconds also seems somewhat less efficient than your typical FM transceiver.
- conradev 3y agoThe Three-Body Problem science fiction series involves gravitational waves. I’m not going to spoil it, but the series is a great read :) Not quite possible today, though, as others have pointed out
- JumpCrisscross 3y agoAren’t neutrinos holy grail for signals?
- andromeduck 3y agoYup and it's called is called Terrain Contour Matching! https://en.wikipedia.org/wiki/TERCOM https://en.wikipedia.org/wiki/TERCOM
- smilespray 3y agoIsn't this the old radar terrain mapping system codnamed FINGERPRINT? It's conceptually similar, but they didn't use quantum gravity mapping in the 50s.
- andromeduck 3y agoThink so? I don't find anything on Google. I thinkOme documentary said it was called SLAM on the tomahawk?
- abhayhegde 3y agoAs a fellow PhD student having a bit of idea on quantum metrology and sensing, I'd love to know more on your thesis! Kudos, by the way.
- rogers18445 3y agoWhat would you do with the g measurement to get your location? Can g deltas be matched to sea floor contour maps? Otherwise it seems like subs would have to be following g-mapped routes.
- etrautmann 3y agoWith a highly detailed map, it becomes a statistical fitting problem, to locate yourself based on an estimate of position history using intertidal measurements and your time history of gravitational measurements, starting from an initial position estimate. I would imagine this could be quite accurate.
- tehlike 3y agoPretty much a slam application.
- etrautmann 3y agoexactly - presumably a subset of the full SLAM challenge if a detailed map already exists and you're just localizing within it
- quickthrower2 3y agoDead reckoning with gravitational adjustments?
- etrautmann 3y agoOops fat fingers - s/intertidal/inertial
- unhammer 3y agowhat a strangely fitting typo though :-)
- jchallis 3y agoA typical sub drifts by only a few tens of meters per day - obviously this builds up . The point of the BEC gravity map is to reduce this inaccuracy an order of magnitude, thereby extending the subsurface range of the subs.
- snovv_crash 3y agoIsn't this the method used by the sub in Hunt for Red October? Or did they also use a gyroscopic and look for changes in the gravitational vector, not just its magnitude?
- jchallis 3y agoRed October used the usual gyroscopes approach that gets more and more inaccurate as it sails. I think a key plot point is that they need to surface to take a latitude / longitude , precipitating much suspense.
- DaiPlusPlus 3y agoI haven't read the book, but in the film the problem was the Red October was using the caterpillar-drive https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive (and not a propeller/impeller) but a chance detection by Dallas' sonar along with the ingenuity of Dallas' sonar operator, who figured out how to detect and track Sean Connery's boat. Nothing to do with gravity or gyroscopes at all.
- snovv_crash 3y agoYes, but Red October had some super accurate underwater gravity map of some kind that allowed them to navigate at speed through areas Dallas couldn't follow IIRC.
- deleted 3y ago[deleted]
- 1letterunixname 3y agoPassive sonar in the SOFAR channel.
- julienfr112 3y agoIs the gravity really constant ? I mean, big chunk of lava moving with different concentration of iron would make it change, wouldn't it?
- varjag 3y agoGravity is not magnetism, it does not care if it's iron or anything else.
- beerpls 3y agoUm how do you figure? Gravity cares about distance and mass, and as large parts of the planet move their density distribution shifts affecting both of those factors
- beerpls 3y agoLol this point is true but it’s downvoted. I love how the IQ of this place keeps spiraling downward.
- jh00ker 3y agoHis point was that lava density could have high-variability.
- thinkingemote 3y agoThere might be some confusion in these replies related to the gp's mixture of two terms. g = gravity of the earth which varies and the gravitational constant G which is a Constant and the same across the universe.
- deleted 3y ago[deleted]
- DaiPlusPlus 3y ago> big chunk of lava moving with different concentration of iron would make it change, wouldn't it Why do you think the concentration of iron in magma would not be evenly distributed throughout the mantle?
- otikik 3y agoA submarine itself is quite massive, and has big moving parts (e.g. the rotor). The crew has less mass, but it would be very close, and also in constant movement. Wouldn’t this interfere with those measurements? Would they need to stop the engine and play “frozen TikTok” while the measurement device is active?
- kryogen1c 3y ago> big moving parts (e.g. the rotor) The shaft and screw are confined to the end of the sub. A navigation instrument like this would not be in the engineroom.
- otikik 3y agoIt is still way closer to the instrument than the deep end of the sea, most of the time. Square of distance is a very potent thing. I am reminded of this: https://www.theguardian.com/science/2015/may/05/microwave-oven-caused-mystery-signal-plaguing-radio-telescope-for-17-years https://www.theguardian.com/science/2015/may/05/microwave-ov...
- RobotToaster 3y agoImagine spending 17 years to find the source of interference, and it's just Kyle with his chicken tenders.
- JumpCrisscross 3y ago> Wouldn’t this interfere with those measurements Towed sensors and multiple passes over known calibration zones?
- samus 3y agoSurely the influence of some of these sources of noise can be modeled and filtered out. A University of Vienna currently conducts experiments to measure the gravitational force at very small sales, and they already have to do this with things like crowds moving about the city during rush hours.
- 1nf_ 3y agoThe majority of INS platform drift is from a thing called "tilt error" - where the IRS initially misjudges the exact direction of the gravitational vector during alignment. All this will do is improve the accuracy of the accelerometers but will still have the drift caused in the INS itself. How will this make such a large improvement over what we have already?
- throwawaylinux 3y agoIt's not dead reckoning, it's continually fixing to a map.
- beambot 3y agoLet's use a magnetometer as an example. Inertial navigation system (INS) is just using the magnetometer as a compass, so errors in bearing accumulate over time. Instead, if you built a map of magnetic field strength, the slight spatial variation of field strength would let you precisely localize on the map. In robotics parlance, this is the difference between dead reckoning versus SLAM (simultaneous localization and mapping).
- mc32 3y agoThen it looks like underwater landslides, volcanoes and earthquakes could throw things off from time to time.
- Retric 3y agoTraditional dead reckoning is reasonably accurate over moderate timescales in the mostly empty ocean as subs are big/stable and relatively slow. Thus the existing approach of only occasionally surfacing for GPS. This is therefore more a supplement as being able to regularly recenter even a few times a day is good enough.
- fho 3y agoI would assume that you'd use that data in conjunction with others (sensor fusion / kalman filter). Wenn you know you were at location X 10 minutes ago and now one sensor tells you you are at Y ... You can reasonably assume that that sensor is wrong.
- jofer 3y agoIt's somewhat unlikely (but not impossible) that this method is based on navigating by matching patterns of the shape of the geoid (aka variations in g). We need accurate maps of the geoid for a lot of different reasons. (Military as well as civilian. Potential fields geophysics is super useful for all kinds of different geologic use cases, and regardless, if you want to target an ICBM, you need an accurate geoid.) However, a super precise gravimeter doesn't help much. We have more precision than we can use already. Rather ancient spring-based instruments from 100 years ago can actually still give more precision than we can use in many cases. Modern ship-borne gravity instruments work on different principles, but the signal is very noisy for the same external reasons. The biggest issue is that you also need to know absolute elevation very precisely to use the measurement of g that you get. A few millimeters of error in elevation significantly changes the anomaly measurement you make. Sure, submarines can get accurate hydrostatic measurements of depth, but those assume a lot of things and critically aren't absolute. The ocean has currents - that's another way of saying that the surface of the ocean isn't "sea level". Those vary through time and would require satellite information to correct for. However, once you get down in the weeds, it gets tougher still. Remember that we're dealing with an inverse square distance relationship. Things close by matter quite a lot. People nearby standing in different positions? That actually does affect things. Easy enough to mount the instrument away from people, though. Different distributions of mass in the submarine? Also affects the measurement. You can correct for all of these in various ways, though, so long as you have information on it. It's just more complexity and another source of noise. In the end, the "free air anomaly" measurement you'd be correcting things to is an bathymetry map, to the first order. If there's a landslide, that affects things quite a bit, and those happen all the time. Finally, you'd be matching a "fingerprint" time series measurement as you travel to a pre made map. That's a non unique relationship. You'd have heading/etc information to help the non uniqueness part significantly, but when things don't vary much (i.e flat topography and not a ton varying geologically), you don't have much of a unique signal to match to. At any rate, it's a very useful tool for many other things, but I'm skeptical it could be turned into a precise navigational aid. In combination with traditional gyroscopic/etc measurements of heading and distance, it could help constrain uncertainty, but it's not an independent measurement and it's relatively noisy. Now that I think about it, though, a fully passive "seamount proximity sensor" is rather useful, and that's something you'd get even with a noisy signal...
- narenkeshav 3y agoWould it be possible to replicate that on mobile phones? Or a special device is required? 1. trying to figure out the feasibility?
- thesz 3y agohttps://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensa... "n condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero (−273.15 °C or −459.67 °F)..." I guess, a special device is needed. The size of such device will be in thousands of mobile phones just in volume needed. Yet, it is feasible. ;)
- wongarsu 3y agoThere wasn't much money in miniaturizing them so far. Cooling down tiny amounts of matter is much easier than cooling down larger amounts, so maybe there's hope for a microchip sized BEC in 20 years.
- ClumsyPilot 3y agowhats the smalled device to contain a gradient of 300 degrees C? this is a but solly, like saying you will eventually have a fridge the size if a m9bile phone - us it usefull?
- thesz 3y agoLet us take a look at what boson is. https://en.wikipedia.org/wiki/Boson https://en.wikipedia.org/wiki/Boson "multiple identical composite bosons (in this context sometimes known as 'bose particles') behave at high densities or low temperatures in a characteristic manner described by Bose–Einstein statistics: for example a gas of helium-4 atoms becomes a superfluid at temperatures close to absolute zero." Helium leaks as nothing else, even more than hydrogen. Here's some leak rates of heilum: https://www.researchgate.net/figure/Comparison-of-the-helium-leak-rate-for-samples-with-different-bonding-materials_fig4_262953618 https://www.researchgate.net/figure/Comparison-of-the-helium... Let's say we have a um^3 of helium in the device proposed. Let's assume leak rate of 8*10^-9 of cm^3/sec. (1e-6/1e-2)^3/(8e-9) is equal to 1.2499999999999998e-4 - all helium will leak in 1/8 of microsecond in the device proposed. I hope this helps.
- alexpotato 3y ago> a nuclear submarine could use it to make an ultra-accurate map of the world based on variations in the gravitational constant g I believe in the book version of the Hunt for Red October by Tom Clancy, they mention that the Soviets did something similar but using a magnetometer. Super cool to see the newest versions of this are going from sci-fi to fact.
- EVa5I7bHFq9mnYK 3y agoCan it also be used for missile guidance, in case of GPS denial?
- deleted 3y ago[deleted]
- RobotToaster 3y agoCouldn't it also be used to detect submarines as well then? Given they're quite big.
- phkahler 3y agoThey have the same (average) density as water.
- hackernewds 3y agowhat a sad outcome it is that research such as this is funded for, and classified by military interests such that it is barred from public collaboration and societal progress
- fho 3y agoMay I ask: how sensitive? Sensitive enough to, say, detect the movement of something moving at a known frequency on the other side of the planet? Are we on the edge of gravitation based communication channels?
- white_dragon88 3y agoI would imagine that there is is an insane amount of gravitational noise from things like the planet’s asymmetry and events occurring all the way from the core to the crust, the ocean… to cut through that noise you need one big thumper.
- martopix 3y agoThe most obvious source of noise seems to me the fact that the submarine is moving and has therefore nonzero accelerations all the time
- andromeduck 3y agoMost obvious would be the phase of the moon.
- fho 3y agoThing is, you don't have to cut through the noise these days. Low energy/low bandwidth radio communication routinely sends messages below the noise floor. Depends on you application, but if you only send some bits of information ("stocks just crashed") having a big thumper with a very known impact profile is sufficient.
- hwillis 3y agoLocal surface gravity varies by up to a ten-thousandth, about .001 m/s: https://en.wikipedia.org/wiki/Gal_(unit) https://en.wikipedia.org/wiki/Gal_(unit) Sensitive detectors can measure differences in hundreds of millionths (10^-8 parts) or around .1 um/s^2. A 1 million tonne mass on the other side of the earth will create a TOTAL acceleration of 4*10^-16. Changes in that will not be detectable.
- punnerud 3y agoCan you also use it to detect other submarines? If they affect the gravitation
- dumbo-octopus 3y agoI wonder how close you'd need to be for any small-scale buoyancy differences to be detectable, given the entire object would clearly be neutrally-buoyant.
- awesometech 3y agoSubmarines do not have to surface to get a GPS lock. https://en.wikipedia.org/wiki/Submarine_navigation https://en.wikipedia.org/wiki/Submarine_navigation "On the surface or at periscope depth, submarines have used these methods to fix their position"...GPS being one of them. A submarine can also navigate by the stars without surfacing. https://www.usni.org/magazines/proceedings/2021/october/navigate-stars-beneath-waves https://www.usni.org/magazines/proceedings/2021/october/navi... "This is precisely the information required by the traditional method of celestial navigation, and it is accomplished without the need to surface or use a sextant!"
- deleted 3y ago[deleted]
- awesometech 3y agoWhy was I downvoted please? I provided facts to my counterpoint.
- wolverine876 3y agoNever attribute to malice what can be attributed to ignorance. Also, look up the HN guidelines on debating your downvotes. Welcome to HN!
- paulsutter 3y agoDoes this detect gravity as distinct from acceleration?
- digging 3y agoGravity isn't distinct from acceleration though - how would it?
- paulsutter 3y agoThats why I asked. And they are different. If you throw a baseball in an accelerating enormous elevator in a vacuum, the baseball will follow a parabolic arc. If you throw a baseball on the vacuum surface of a planet, it will almost (but not quite) follow a parabolic arc. The force of gravity is lower at the peak, unlike in the elevator where acceleration is constant everywhere in the elevator. Therefore, you can distinguish gravity from acceleration
- 5ersi 3y agoDoesn't magnetic pole shift due to fluid dynamics in Earth core? Wouldn't that also affect gravity field?
- rtkwe 3y agoYes it does but we also have satellites mapping those shifts so it could be accounted for. The big question is are those fine grained enough to resolve the errors in modern INSs.
- RationPhantoms 3y agoWouldn't that then require communication with those satellites to receive the shift/drift info? Doesn't that eradicate the point of a navigational system without reliance on GPS/satellites? Or is the drift is so minor that this quantum navigation system can operate for up to 6 months without sufficient core drift alignment calculation?
- rtkwe 3y agoNo idea but there are low bitrate coms available to submarines that could update that data maybe. The changes should be pretty slow at the bulk scale.
- comboy 3y ago> This would remove one of the primary reasons subs need to surface , in order to GPS lock. Huh? Wouldn't it be enough to send some small thing connected by thin wires or wirelessly to the submarine (lasers, ultrasound, whatever) that could aquire location and communicate it? Given military budgets it could probably even be disposable. Leaving beacons in areas of interest also seems like a good idea. With good encryption their signal could be indistinguishable from noise happening around it.
- dmos62 3y agoBoth these things are probably already being done to some extent. Submarine broadcast stations for navigation were definitely talked about a lot. Note that military submarines is a secretive field, so you ever know only so much.
- monocasa 3y agoYou don't want to send out beacons like that from your nuclear sub. Your adversaries can detect those, which negates the purpose of having a nuclear sub in the first place. Additionally if they communicate through radio, you're back to the same problem because it's the thousand feet of water that blocks most radio waves. If they communicate via ultrasound you've just tied your sub to a nearby active sonar source. If they communicate via laser you have to be very close otherwise the power of the laser creates sonar detectable variations in the water near the sub.
- baybal2 3y ago[dead]
- George83728 3y ago> Wouldn't it be enough to send some small thing connected by thin wires or wirelessly to the submarine (lasers, ultrasound, whatever) that could aquire location and communicate it? They do, using either tethered buoys or 'buoyant cable antennas' (the cable is the antenna and is itself buoyant) They can use these without coming to periscope depth, or even slowing down.
- vl 3y ago
- rtkwe 3y agoIt'd be interesting to see if they're sensitive enough to do the opposite detect the gravity anomaly that is the sub. There's a couple near future submarine warfare books where that's one of the devices used to attempt to find subs.
- QQ00 3y agoWould love to see a list of such books.
- rtkwe 3y agoThe main one I've read is Joe Buff's Deep Sound Channel series, found it after a recommendation from someone else on HN even so glad to continue the chain. Fell off it a bit in book 4 but that might have been me burning out on them, I ripped through the first 3 and focused too hard on them.
- QQ00 3y agoThank you so much, I love when people recommend good books to me.
- djyaz1200 3y agoI suspect that may be what these satellites are doing... https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO#:~:text=As%20the%20twin%20GRACE%20satellites,ahead%20of%20the%20trailing%20satellite https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO#:~:text=As%....
- earthscienceman 3y agoI love when HN commenters get out of water on topics. The GRACE retreivals to reconstruct mass changes for "mascons" that are several hundred kilometers in width\height take a month of static overpasses and incredible mathematics and signal processing. There is absolutely no way that their data could be used to locate a submarines, ever.
- L_226 3y agoYeah, and if you put one in some kind of "spy balloon" you could also use it to map secret underground structures that may or may not exist in certain parts of the US ;)
- sampo 3y ago> It’s a naval chart that would not require surfacing. Other sources say this is about inertial navigation, not based on charts. "Accelerometers measure how an object’s velocity changes over time. With this, and the starting point of the object, the new position can be calculated." https://www.imperial.ac.uk/news/188973/quantum-compass-could-allow-navigation-without/ https://www.imperial.ac.uk/news/188973/quantum-compass-could...
- George83728 3y agoWhat's the difference between measuring accelerations and measuring gravity? I think with any INS system, if you want to be very accurate you need charts of gravitational anomalies. So these seem like one and the same to me.
- rcxdude 3y agoThere isn't any inherent difference (indeed, you can do some coarse gravity surveys by basically watching the drift of an IMU relative to GPS), but there's a pretty big difference in terms of the parameters of your sensor. Most gravimeters don't make for good accelerometers and vice-versa. One of the biggest reasons being dynamic range: most gravimeters are only able to sense a very small range around 1g, which means they quickly saturate when there's any significant motion. I don't know if that's something which these quantum sensors can work around, however. (Also, you need a gyro good enough to go along with those accelerometers, which may still be a challenge)
- stealthcorp 3y agoVery interesting! What year did you complete your PhD? Care to share a link to your thesis?
- jedc 3y agoFormer submariner here with a quibble on this: > one of the primary reasons subs need to surface , in order to GPS lock While getting a GPS position is helpful, the primary reason a submarine goes to periscope depth regularly is for communications. The Navy needs to send information to submarines and know that they'll get it and take action within a certain timeframe. That's by far the primary driver.
- eyko 3y agoFrom layman to former submariner, a very silly question I've always wondered about and that I now have the rare chance to ask someone with some expertise: Do submarines mostly roam about or do they tend to stay relatively quiet/idle? I always imagined submarines constantly moving about but at the same time it feels like a waste of fuel.
- jwithington 3y agoFrench (& American and Royal Navy) submarines are nuclear powered. No fuel necessary. They do have measures of "nuclear fuel" remaining, but it lasts about 30 years (at least in the American boats) so generally doesn't impact day-to-day considerations.
- oynqr 3y agoLayman here as well, but there are probably no fuel concerns because the reactors are constantly running anyway.
- thatguy0900 3y agoI wonder what the fuel difference is between fighting the currents and generating electricity while staying in the same area VS just moving around
- jedc 3y agoThe main thing is that you need to be moving at least a few knots in order for your control surfaces (rudder, forward planes, stern planes) to work.
- paulmd 3y ago> A Bose Einstein Condensate is an extremely sensitive detector of gravity- a nuclear submarine could use it to make an ultra-accurate map of the world based on variations in the gravitational constant g it would seem the Total Perspective Vortex has obvious military applications https://www.urbandictionary.com/define.php?term=Total%20Perspective%20Vortex https://www.urbandictionary.com/define.php?term=Total%20Pers...
- crispyambulance 3y agoI don't understand how this would work. Do we somehow already have that super-accurate "map of g"? Wouldn't one already have to exist to be able to use quantum navigation? Moreover, would it not also require integration with a gyro and a lot of history to be able to know, for instance, which place it's at of many in any given ocean where g = 9.8100023? Does g really vary that much that you can figure out where you are with it with sufficient accuracy to do military stuff?
- andromeduck 3y agoYes, and yes. We've had the gravity maps for about a decade now, and the tech for recovering the location given such data was mastered in the late 80s, but no way to make accurate enough measurements while at sea until now. https://news.ycombinator.com/item?id=36223373 https://news.ycombinator.com/item?id=36223373