I remember doing laser cooling of rubidium atoms in physics class. It's really cool how it works:
* Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum.
* Shine laser light at it from all directions but at a wavelength slightly longer than the wavelength at which it will absorb. Now, if the rubidium atom is moving, the light hitting it head on will be Doppler shifted into the wavelength that it absorbs, slowing it down, whereas the other light wouldn't affect it. So, no matter how it is moving, it will slow down.
Rubidium is a good material since it has an S shell on the outside as though it were a big hydrogen atom, but it is so massive that it is a lot nicer to work with for this application.
If I understood this correctly, would this allow you to make an extremely good estimation of direction of velocity? If you want to use dead reckoning to estimate position, how would you know the abs of the velocity?
I'm way out of my depth here but I believe this would function as a very sensitive accelerometer. The rubidium would be still relative to the lasers so when you accelerated, it would have inertia and take some time to catch up with the rest of the device. You'd then integrate the acceleration to find the velocity and integrate that to find position.
Yeah, it is an extremely sensitive accelerometer which it calls out about halfway through the article.
"At the heart of the quantum compass – which could be ready for widespread use in a few years – is a device known as an accelerometer that can measure how an object’s velocity changes over time."
>Now, if the rubidium atom is moving, the light hitting it head on will be Doppler shifted into the wavelength that it absorbs, slowing it down, whereas the other light wouldn't affect it
Spooky.
It's like having a Maxwell's demon for photons sitting on top of every atom!
Maybe I'm missing something but hitting a gas just above absolute zero with lasers from every direction doesn't sound as something that could be miniaturised.
Most technology has a limit like this (for instance CPU transistor size in the past). However once this is a proven technology, money will be invested in solving these issues.
Maybe not down to a pea size, but possibly down to an orange size. Lasers are tiny, and "every direction" does not involve many of them, it involves some fiber optics, I suppose. The bulk of the device would be thermal insulation, and a volume for liquid helium + some piping to let it evaporate, and to replenish it.
You don't need any helium or nitrogen here, cooling happens only by laser cooling and evaporative cooling from magnetic or optical traps. The atoms are perfectly insulated in an ultra high vacuum.
Electronics still take the bulk of the volume here, as does the laser system. While the lasers themselves are tiny indeed, the light needs to be manipulated before reaching the atoms.
And yes, it involves quite a lot of fiber optics :-).
It's pretty amazing what's slowly but surely becoming possible. This company, for example, has successfully made chip-scale "fiber" ring gyros with incredible performance that would have been very large heavy units 5-10 years ago: https://www.anellophotonics.com/products/x3
US ICBMs been inertially guided for decades. They predate GPS. Once launched, they have no radio inputs.
Some weapons do use GPS. The Joint Direct Attack Munition, the US's most common "smart bomb", is GPS-dependent. There's an inertial backup, but it's not that good. With GPS, it can hit a bunker or an artillery emplacement or a parked vehicle. Without GPS, small targets are out.
DARPA has been working on small, low-cost inertial systems with enough accuracy to remove GPS dependence. Exactly how good those systems are and which weapons systems now use them is not talked about much. Here's the project poster.[1] This is an improved form of MEMS accelerometers and gyros, not new physics. DARPA has a project for that, too, but the near term goal is small, cheap, and disposable for munitions.
There's much current interest in weapons which combine gun, bomb, and missile technology to boost range. Bombs with a small jet engine and wings for extra range exist. Both the US and Russia have them. Artillery rounds with a rocket upper stage are becoming available. The general idea is to have stuff you can shoot into heavily defended territory.[2]
Is this the one technology used by Russia to bomb Ukraine. As it is so cheap the missile defend system is useless as it is just too expensive to fight it. The f16 is starting to prevent the airplane that throw the bomb with some gps guidance system.
> US ICBMs been inertially guided for decades. They predate GPS. Once launched, they have no radio inputs.
That's how the original Third Reich V-rockets worked as well, and they were shockingly inaccurate. It didn't matter for the Nazis, as their intention was to spread terror among the British population instead of actually hitting specific military targets, but in a modern war waged under the rules of war, "collateral damage" can actually be a war crime, and even if not, it will provoke significant opposition.
This can at the moment be seen in Ukraine, where Ukraine regularly (and rightfully, IMHO) claims that Russia's strikes violate the rules of war by hitting civilian infrastructure en masse, and where Ukraine's strike capability against Russia is severely impeded by Russian GPS jamming (that also causes serious safety issues for civilian airlines [1]), but also in the current Israel/Palestine war, where Hamas regularly claims that Israeli strikes are too imprecise [2] or unguided [3], while Israel claims it hits hidden weapons caches that subsequently explode and cause a lot of secondary damage [4].
While the V2 made use of a key element of inertial navigation systems (the Pendulous Integrating Gyroscopic Accelerometer [1]), it was apparently only used to cut off the motor when the desired velocity was reached (the other elements of the control system guided it on a trajectory which curved from vertical to 74 degrees as a function of time, with the azimuth determined by the positioning of the rocket on its launch stand prior to firing.) Consequently, the performance of modern inertial navigation cannot be deduced from V2 accuracy (or, rather, the lack thereof.)
ICBM is likely to deliver a nuke. Which will probably take out a 20 km radius circular area. It is not going to be used to target a base with 100 soldiers.
It is if the goal is to deter without launching a city roast fest. That’s one possible step to e.g. answer a first limited strike without starting a disastrous exchange. And US nukes can be set to low yield.
If NATO ever has any intention of deterrence through detonating a nuke, it will be done in exactly the way it's been specifically planned and openly explained: France has a specific nuclear policy, one of the only ones, that allows them to use nukes before an adversary does. They have a specific nuclear missile fired by plane that will be used as essentially a giant warning shot.
Nobody would fire a warning shot using an ICBM, because if things are hot enough to require a warning shot, that leaves a whole lot of interpretation up to your adversary who is quite likely to respond with their own ICBMs, before finding out yours were loaded with conventional munitions to make a point.
There are however, shorter range ballistic missiles, Russia has a lot of them (the US mostly gave up mid range ballistic missiles in a nuclear treaty) and has even launched a few with concrete "nuclear warhead simulation masses" at Ukraine.
Precision is, counterintuitively, still a big deal in the logic of nuclear weapons strategy. Nuking Moscow is easy, nuking hardened targets can be a lot harder.
> Before the invention of this new fuzing mechanism, even the most accurate ballistic missile warheads might not detonate close enough to targets hardened against nuclear attack to destroy them. But the new super-fuze is designed to destroy fixed targets by detonating above and around a target in a much more effective way. Warheads that would otherwise overfly a target and land too far away will now, because of the new fuzing system, detonate above the target...
> As a consequence, the US submarine force today is much more capable than it was previously against hardened targets such as Russian ICBM silos. A decade ago, only about 20 percent of US submarine warheads had hard-target kill capability; today they all do.
But importantly, making sure a nuke can still hit Moscow despite geolocation countermeasures has lots of worrying consequences for normal people that are in normal cities. If nukes are hitting random countryside then a lot less people die.
But when it's the difference between hitting a hardened target or being off by 200 meters, that doesn't really affect normal people.
> has lots of worrying consequences for normal people that are in normal cities.
Which is precisely why even the mere ownership of nuclear weapons was ruled by the ICJ to be illegal: a violation of inter alia the Hague [1907], UN Charter and Geneva Conventions.
Specifically the Geneva Convention Protocol I (1977) states that ‘the civilian population shall not be the object of attack’.
The 1977 Geneva Protocol was ratified by the USA, so its not even that mystical international law thing - its domestic law.
The nuclear powers have spent the next 25 years trying to lobby and bully their way out of this inconvenient bit of international law. Expect to see some in the comments.
The US does not belong to the ICJ, so that judgement would only be valid if the US Supreme court would say so. I dislike a lot nuclear weapons but they are an escalation deterrent like the humanity never had[1]. I hope they continue to be a deterrent but never ever launched in war.
[1] If Ukraine kept the nuclear weapons post USSR collapse we probably would not have the war on Ukraine, lots of dangerous threats but nothing else.
> If Ukraine kept the nuclear weapons post USSR collapse we probably would not have the war on Ukraine, lots of dangerous threats but nothing else.
If Ukraine tried to keep the nuclear weapons they would have been invaded within half an hour of that becoming apparent in or around 1994. They had no meaningful operational control over them, thus it would not have acted as a deterrent against that invasion.
Yes, nukes are really potent deterrent. Ukraine's case is not the right one to show this.
If you are looking for an example where nuclear deterrent works Russia's case is much better. They are badly bogged down in Ukraine. The reason why nobody dares to escalate and turn Moscow to rubble is because they have the nukes as a credible deterrent. All the tiptoeing around the range of missiles given to Ukraine and the constraints they have on not targeting Russia directly with them is due to that.
And even if they'd held onto them, keeping them operational for three decades without a nuclear weapons program of their own would have been impossible. They would have had to spend a huge amount of money they didn't have to build the infrastructure to do it.
The USA does belong to the ICJ and has since its inception (the USA not a member of the ICC - different court).
Its just that after the invasion of Nicaragua in 1984 it decided to abide by the court "on a case to case basis". Russia also decided to ignore the ICJ in 2022.
FWIW I agree that everyone should have nukes, there would be a lot fewer military adventures. But that's not the _current_ USA/UK/FR domestic* and international law.
I'm not sure there are much in the way of geolocation countermeasures against ICBMs anyway, they're inertially guided. Unless you can generate localized gravity anomalies at will, I guess.
And if that's not enough, I'm sure you could get the rest of the way with cameras and AI. In 2024, it can't be too challenging to train a machine to recognize Moscow.
* Rubidium will absorb photons of a certain wavelength and re-emit it in a random direction. Since photons have momentum, it will get some net momentum change from absorbing photons all coming from a particular direction, but the re-emissions are in random directions so they have net zero momentum.
* Shine laser light at it from all directions but at a wavelength slightly longer than the wavelength at which it will absorb. Now, if the rubidium atom is moving, the light hitting it head on will be Doppler shifted into the wavelength that it absorbs, slowing it down, whereas the other light wouldn't affect it. So, no matter how it is moving, it will slow down.
Rubidium is a good material since it has an S shell on the outside as though it were a big hydrogen atom, but it is so massive that it is a lot nicer to work with for this application.