The enemy is constrained by size, cost, power, and heat dissipation. What can be done on the ground is not the same as what can be done in a fighter plane, and that isn't the same as what can be done in a small-diameter missile, and that isn't the same as what can be done in an anti-aircraft shell.
The enemy might be able to briefly detect at close range, reliably track at long range, or anything in between.
Because of this, stealth is not simply defeated, and it does not suddenly become 100% useless.
Which was the genius idea behind Track-via-Missile in the Patriot SAM
Instead of having the missile work-out the best interception based on what it can detect, it relays its view of the World back to the ground station which returns its recommended geometry. Constantly and at high frequency.
And since the ground station is more powerful and can be upgraded more easily than the missile's electronics, Patriot has made huge improvements since the 1991 Scud incidents.
In an anti-stealth context having each missile 'see' from a different angle and being able to fuse that I to one picture is also useful in defeating shaped reflections. It's like a network of remote, lethal sensors.
Can't the missile jam the signal?
The worst part is that misfiring telephone poles have killed about as many Gazans as Israelis.
And also it's not just about the technology in the design of the aircraft. It's a combined strategy such as knowing where the radar stations are and flying a path to minimise exposure.
I remember seeing a visualisation of what ISTR was a stealth flightpath into Iraq giving an idea of how they maintained their extremely low visibility. I've just has a search but can't find it at the moment.
 Skunk Works: A Personal Memoir of My Years at Lockheed by Ben R. Rich and Leo Janos (page 101 on my copy)
The relevant Wikipedia article also mentions the system, but in less detail: https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk#Avion...
Radars, even quantum radars, each have their issues. The most powerful stealth tech isn't defeating a radar but understanding it well enough to leverage its defects in coverage or operating range. The f-117's real trick was the preflight planning based on a deep understanding of the threat environment. A radar avoided need not be defeated.
Why do they need to be entangled? Aren't there other ways of checking if the photons coming back are the ones you sent?
I'm guessing that this might be more effective at very small returns, where the reflection is so small that it suffers from shot noise - the fact that the energy comes in discrete packets makes it hard to correlate. This is another way to verify that the photons received are the same ones sent out (and not background noise)
What it can't do is generate photons which are entangled with another photon you already have, so it kind of cuts through all the incremental stuff you could otherwise do (and which has been done already).
At least, that's how I understand the physics involved at a fairly superficial level.
This sounds like it's a long way away from being useful though, that slight issue of not having an abundant source of entangled photons is a huge blocker.
It's really an idea not a complete system, needing a way to quickly entangle photons on-demand. Cool idea, definitely!, but not yet completed.
Most stealth systems are designed to either absorb or reflect millimetric point source radar. HF long wavelength systems reflect nicely off the top surfaces of the aircraft, which aren't designed to dissipate and absorb those frequencies. To one of those systems a stealth aircraft shows up brighter than a 747...
So while this is neat science, it's not economical compared to the systems currently in use. The only real downside of OTHR systems is that you need a couple of miles space for the transmit antenna and a big empty space for the receiver; plus plenty of CPU to process the data.
That's just a usual FUD stuff from Russians.
Chinese "quantum radar" is a thing that cannot exist
According to an article I read, they should be able to gravimetrically image the volume of earth to within about a cubic centimeter resolution.
At that point it becomes very hard to hide high-density materials, like concentrations of U or Pu, anywhere.
However, a larger array of more sensitive detectors that are immune from the tremendous amount of terrestrial noise might make short work of it.
assume the fission event to occur in empty space, assume the liberated energy is isotropically radiated, and assume all the energy is thus expanding spherically, then the mass/energy that was initially in the mother isotope is now after some time distributed on a spherical surface.
As long as the observer is outside of the shell of escaping energy, to the observer the gravitational field looks like all the mass is concentrated at the center of the expanding shell of energy, exactly where the mass/energy originally was, and hence gravitationally undetectable.
After a while the expanding surface has past the observer, and the observer is inside a spherically symmetric shell of mass/energy. Even if the observer is not at the center there will no gravitational field at all according to the observer. (consult any physicist or physics textbook, or do the exercise for the gravitational field in a 'hollow earth'). So to the observer this looks like a bit of disappearing mass at the location of fission event.
It seems extremely difficult to me to actually measure such an event gravitationally though..
1 - nuclear explosion involves the conversion of a tiny amount of mass into rapidly expanding cloud of energy conveyed by various particles. The significance being the drastic density difference before and after it’s blown to bits. This difference is equivalent to a sudden moment of regular mass since energy and mass are equivalent and energy has gravitational attraction. This is roughly the same as attempting to catch the gravitational waves theorised to be produced by a supernova. We can’t catch these yet due to insufficient sensitivity, but despite the nuclear explosion being ridiculously tiny compared to a supernova, we are also ridiculously close compared to the supernova, so the proximity to the event may “win” and make it strong enough for the detectors to see it.
2 - the equivalence of nuclear explosions to earthquakes in terms of energy displacement into the earths crust, and in particular underground tests of them, has been established. (This is obviously dependent on the size of the explosion and if it’s an underground test or not, since underground tests dump basically all their energy into the surrounding geology they make it a “more effective earthquake”). Earthquakes can speed up or slow down the earths rotation, which has tidal effects which involve the moon, so between the seismic and seismically induced tidal changes, we get to affecting the moons orbit and consequently we get a tiny gravitational wave which once again is detectable only because of how much closer we are to the source compared to the things we built LIGO to detect.
Of course I might be wrong on both of these. They were just fun to think about on my ride home from work. :-)
Entanglement is one of the main phenomena that permit quantum hardware to do things infeasible on classical hardware. In the context of communication it permits quantum key distribution, whose security depends only on quantum mechanics being a not-too-wrong description of nature (while classical schemes depend on less tested computational complexity conjectures). In the context of computing, it is an integral component of many of the "fault-tolerant error correcting" schemes, necessary in order to protect the extremely fragile qubits (similar to what ECC RAM does for classical computing).
In the context of sensing, it does permit some cool unbelievably sensitive detectors (the case discussed in the article), but it is only one of the avenues of intense research.
And it seems that detection is always easier and cheaper. I wonder wether radar and quantum "noise"-bombs that basically spam the enemy detection methods would be a cheaper approach.
Of course, overloading the receiver may be an attack worthy of investigating.
That's the fate of most military technologies throughout history, why would stealth be different?
I'm getting quantum sick.
RF photonics is barely even a thing, and no one is going to get much joy from more comfortably photonic frequencies operating in the Earth’s atmosphere.
Besides, entangled states are very delicate and disappear after any environmental interaction. So I’m not entirely clear how you’re supposed to maintain an entangled state while bouncing photons off a large object.
Even the actual scientist who formulated Quantum Electrodynamics didn't quite understand what quantum is and what to make of it, nor did he find a way to properly explain it. This term and the theories behind it were used just to explain some connections in phenomena, not to invent new ones! Quantum laser, quantum liquid, quantum crystals, quantum nose, quantum ass!
There was a post here somewhere, discussing that science isn't exactly science anymore when it very closely resembles its own stereotype. A philosopher for example today isn't someone who actually thinks, but rather a person who writes non-sense papers just for the sake to be published in a major journal, because otherwise they can't find a job. So, it's not the scientists who publish science-y papers who deserve credit. I don't know who deserves any credit anymore. Academia makes me sick to my stomach.
Instead of relying on hearsay to reinforce your beliefs, I implore you to challenge them and read an intro science textbook on quantum mechanics. It is that theory of nature that permitted us to build the day-to-day electronics that powers our lives and our civilization, and it is empowering to understand it. "Theoretical Minimum" is a good set of free courses with video lectures for instance.
Or if you prefer you can just continue with your self-aggrandizing pity and willful ignorance. It is true that there is a rat race in the sciences, but that does not devalue the amazing advances that science has nontheless given us.
Edit: for the more advanced I would suggest reading the first few chapters of Sakurai's or Griffiths' Quantum Mechanics textbook - if you know math they explain how quantum mechanics works quite well. Or Aaronson'a Quantum Computing since Democritus if you are more interested in computational complexity.
This was because the Radar battery were using a different frequency.
You don't need a direct hit with a missile, just be close enough when you explode it.
Also, all the "shared battle information" is done via radio, which with passive radar will give wonderfully accurate positioning with cheap off the shelf hardware.
And passive radar isn't a thing. There's passive radio sensors, that can theoretically detect a transmitter, but frequency hopping etc make that tough.
it works by using known radio sources (ie tv transmitters) which has the advantage of being powerful , continuous and reasonably unique signal pattern (for timing)
radio sniffing is where you listen for the aircraft directly, and there are a number of offerings on that front too. Phased array antenna with SDR front ends, are smashing bits of kit.
now frequency hopping spread spectrum means you need more DSP to find the signal, but its still there. In fact it provides nice timing signals because they hop frequency so much. There is more, but thats for another time
In theory the frequency hopping can be random, but that requires a shared random source, which is hard to sync.
Passive and active are both valuable in their own regimes, but they're not the same.
> According to Dani in a 2007 interview, his troops spotted the aircraft on radar when its bomb-bay doors opened, raising its radar signature.