New laser could cram GPS alternative into a shoebox

We’ve had other discussions of these sort of quantum compass ideas, see

https://news.ycombinator.com/item?id=40692333

for example.

I can never quite wrap my head around it or figure out if they are all the same idea, or what, and what exactly the idea is.

In particular, the article soften describe something that “could replace GPS.” But then they start taking about compasses, and things that sound a lot like IMUs. Integrating accelerations is well known as a bad way of keeping track of position over longer timescales due to catastrophic cancellation. A more accurate IMU might let you do it for a little longer, but eventually you need an absolute reference point to correct your drift.

But then, sometimes there are references to making very careful measurements of the change in the gravitational field. So maybe those could act as landmarks or something?

I wish there was an article for people who, like, had a control theory or signal processing class, but it was too early in the morning and not very interesting.

Nuclear arms doesn't need as much accuracy as other weapons though: when using a cruise missile or a glide bomb with a few hundreds of kilograms of explosives, you need metric precision to get the military effect, when the payload is a 100kt bomb, then 100m is accurate enough.

Unlike other bombs it must absolutely be 100% resilient to any kind of spoofing though, for obvious reasons, hence GNSS is a nonstarter for those when they are the default guidance system for other weapons (with backups, for cruise missile).

I wonder if we are within a century of having pulsar detection on a chip.

Document enough millisecond pulsars and find your position anywhere in the galaxy.

When signal reception and computing power get powerful enough, put it on your wrist.

Points on the Earth's surface are experiencing an acceleration- after all, after 12 hours their velocity has changed direction by ~180 degrees.

You can detect Earth's rotation with a sufficiently large pendulum[0] or a good gyroscope. Something with enough inertia will tend to refuse to rotate with the planet, which lets you compare the two and infer the absolute rotational speed of the planet.

https://en.wikipedia.org/wiki/Foucault_pendulum

> Could one derive the Earth's rotation? The motion of the solar system?

It's not a motion sensor; it's an acceleration sensor. That's an important distinction because the primary problem with IMUs is that they work of changes in velocity, and error in those measurements slowly accumulate - so they almost always need external references to correct for accumulated drift.