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‘It’s the perfect place’: London Underground hosts tests for ‘quantum compass’ that could replace GPS
(www.theguardian.com)
this post was submitted on 19 Jun 2024
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The article describes the device working in ways that violate relativity, but the actual technical description is a lot cooler.
It's not a quantum compass, really. It's a quantum accelerometer and gyroscope. The hope is that its accuracy will lend itself to long-term inertial guidance, which normally needs regular GPS updates to correct errors which accumulate over time.
ice what you did there
this is exactly what I got from the article: a more accurate inertial navigation. What part violates relativity?
These statements imply the device can know exactly where it is in space just by measuring some purely internal quantum effect, which conflicts with the principles of Lorentz invariance and relativity.
Both are constructed around the same idea that there's nothing special in the laws of physics that changes with where you are or how fast you're going. That observation is what led the conclusion that the speed of light is the same in every reference frame, and to Einstein developing the theory of relativity.
In reality, the device needs an external signal to learn its initial position. And it's unlikely to be perfectly accurate so it may still need periodic updates, just hopefully a lot less frequently.
The London Underground is actually kind of a dumb use-case because it's fixed infrastructure. You can just have something like RFID tags around the track that the train reads as it goes by. And there's going to be sensors in the track that report trains' presence to a central control room. It's just a good setting to test the device.
What it's really potentially quite useful for is nuclear submarines since they can stay underwater pretty much as long as their food supplies last, and knowing their position without using sonar or being able to receive GPS signals is quite important for navigation and obstacle avoidance. But the author was probably told to downplay potential military applications.
On the other hand it's a perfect test bed, because there's sufficient changes of direction and speed, and the fixed infrastructure lets you measure drift. Plus it being underground helps simulate GPS signal being weak or unavailable.
It would certainly make jamming of guided weapons quite difficult; missiles, drones, UAVs, etc.
You can’t use it to determine both your location and velocity at the same time. (/s)