Real Life Races Ahead of the Tech Level Again!

[Fred Brackin]

Originally Posted by johndallman

. 50MW of decay heat in a reactor raises the neutrino flux at 1000 metres by about 1% of the solar flux - which is not small, it's just that the probability of interaction is really low.

Yeah, what I remember about RW neutrino detectors is that the number of hits from the Sun may be be less than 20/year.

So to invert what Dataweaver said the real key to a compact neutrino detector might be a ^ force field that interacted with neutrinos _only_(and with much greater frequncy than solid matter).

[Kromm]

Yeah, the relevant passage is this one:

Originally Posted by GURPS Ultra-Tech, p. 45

Neutrino transmission uses specialized particle accelerators; at TL11, these are fairly compact. However, at nonsuperscience TLs, neutrino detection requires massive installations. At TL8, a typical detector contains several hundred thousand gallons of industrial cleaning liquid and is buried nearly a mile underground. Using superscience, much more compact receivers are available, using force fields or hyperdense matter.

Note the text I've put in boldface. The superscience isn't in using neutrinos for comms; the superscience is in force fields and hyperdense matter. The neat trick is in improving the neutrino cross section well enough to have lossless transmission at 230 times the bandwidth of our fastest theoretically possible TL8 wi-fi, at 640 times the plausible range for that TL8 wi-fi, using a pair of 0.05-lb. earbud thingies of essentially negligible size (Ultra-Tech, p. 45). Managing that with ordinary radio would be superscience, for that matter!

[dataweaver]

Originally Posted by johndallman

The energy consumption of your neutrino source may become impractically large. I did the sums recently for detecting nuclear submarines by their neutrino emissions. 50MW of decay heat in a reactor raises the neutrino flux at 1000 metres by about 1% of the solar flux - which is not small, it's just that the probability of interaction is really low.

And neutrinos obey the inverse-square law. I think a 400lb device for two-way communication at 100,000 miles still has its ^.

You're right about the inverse-square law; but it seems to me that a particle accelerator would have an advantage that a nuclear submarine would not: namely, its neutrino flux would be directional. If that 50MW of neutrino flux generation is concentrated in a 20° arc, then at 1km it will match the solar flux; narrow the beam to a 2° arc, and you can reach a 10km range before the beam's neutrino flux is no stronger than the solar flux. If we say that the neutrino sensor can detect variations in the neutrino flux of, say, 1%, then a 50MW neutrino beam concentrated across a 2° arc should be detectable at roughly 100km. (That said, the sensitivity of the receiver depends greatly on the variability of the solar flux: if the solar flux regularly varies by, say, 10%, then looking for a 1% variation is probably too much to ask for.)

But you're right that the TL^ marker is still appropriate for the UT neutrino sensor: cranking up the signal strength to the point that you can generate a beam strong enough to be detected a thousand times as far away as the above while keeping the combined mass of the beam generator and receiver under a fifth of a ton just doesn't work.

[Anders]

Originally Posted by Kromm

Note the text I've put in boldface. The superscience isn't in using neutrinos for comms; the superscience is in force fields and hyperdense matter. The neat trick is in improving the neutrino cross section well enough to have lossless transmission at 230 times the bandwidth of our fastest theoretically possible TL8 wi-fi, at 640 times the plausible range for that TL8 wi-fi, using a pair of 0.05-lb. earbud thingies of essentially negligible size (Ultra-Tech, p. 45). Managing that with ordinary radio would be superscience, for that matter!

But what do you think of this experiment? Is it cool?

[Kromm]

It's a good consistency test for neutrino physics, in that if the physics didn't work as currently understood, some part of the process would likely have failed.

[Flyndaran]

Originally Posted by Kromm

It's a good consistency test for neutrino physics, in that if the physics didn't work as currently understood, some part of the process would likely have failed.

The old experiment in which if every goes perfectly as planned, the scientists giggle, but if it fails and after every test for screw up is done, the scientists giggle louder?

[Phil Masters]

Originally Posted by dataweaver

The trick to detecting neutrinos lies in the need to filter out everything else.

That assumes that the only way to detect neutrinos is the one currently being used at TL8. That may possibly indicate insufficient imaginative flexibility.

However, coming up with an alternative is a little tricky. (Which may just be a way of saying "We're at TL8".) Any answer involving unspecified "force fields" takes us straight back into the superscience zone. The only hard SF attempt that I've seen was from Greg Egan (naturally), in "Wang's Carpets", subsequently incorporated into Diaspora:

"Nuclei in the detectors were excited into unstable high-energy states, then kept there by fine-tuned gamma-ray lasers picking off lower-energy eigenstates faster than they could creep into existence and attract a transition. Changes in neutrino flux of one part in ten to the fifteenth could shift the energy levels far enough to disrupt the balancing act."

Don't ask me if it'd work. It's probably GURPS TL11, anyway.

[Flyndaran]

I feel like a grumpy guss saying, "Back in my day, we had radio satellites. And we were grateful about it!"
No matter how high tech you get, I don't see it being useful for anything other than scientific study and a very few military applications.

[dataweaver]

Well, why is it that neutrinos are so elusive in the first place? My understanding is that a big part of it is that they're electromagnetically inert; but then, so are neutrons, right? OTOH, neutrons aren't fundamental particles; they're composed of quarks, which aren't electromagnetically inert. So maybe that's it. But if neutrinos don't interact with anything electromagnetically, how do they interact with things? The only options left are the strong and weak nuclear forces and gravity; and given that neutrinos are massless (or, depending on who you ask, very nearly so), I think we can discard gravity as a factor here.

That leaves only the strong and weak nuclear forces. And this is where my knowledge of particle physics gets really sketchy: my understanding is that the Strong Nuclear Force is the thing that binds quarks together; anything that interacts via that force will have a "color charge", and will thus exist strictly within bundles of other "strong force-active" particles with complementary color charges. AFAIK, neutrinos don't have "color charges". So: if I'm understanding this correctly, the only way that neutrinos can interact with anything else is by means of the Weak Nuclear Force. Would I be right about this? And if so, what else interacts via the WNF? (My knowledge of the WNF is severely limited, and amounts to "it plays a part in some forms of particle decay".)

If I'm right about this, the only method of detecting neutrinos that doesn't rely on superscience and doesn't require filtering out "noise" would be something that exploits differences between the weak nuclear force and the other three forces.

[Kromm]

Neutrinos are hard to detect because they only interact with the universe via gravity and the electroweak force. Their mass is so small (once thought to be exactly 0 on fundamental grounds . . . that small) and gravity is so weak (about 10^-25 times the strength of the weak force at subatomic scales) that gravity isn't terribly useful here. That leaves electroweak, which here really means weak, because neutrinos have no electric charge with which the electromagnetic force can interact. The weak force has about 10^-11 times the strength of electromagnetism on the relevant scale. All this could be summed up by saying that because neutrinos are electrically neutral and have extremely low mass, their effective "radius" for interaction is minuscule, and only pertinent for a fundamental interaction that's hard to see directly and that TL8 science is not up to manipulating directly with some sort of "force-field generator."

Possible dodges:

1. There are other fundamental interactions besides strong, electromagnetism, weak, and gravity, and neutrinos interact powerfully with these for some reason. (Possible, but given that we haven't detected this force, it would be fair to assume that it's very, very weak and no more useful than the ones we know.)
   
   
2. Our grasp of the weak interaction is flawed and in fact there are ways to manipulate it that we haven't learned yet. (Our grasp would have to be really flawed, though, because electroweak theory is well-tested and relatively solid.)
   
   
3. Our model of physics is incomplete, and neutrinos are somehow entangled with some as-yet-unseen artifact of symmetry or topology or probability, which could be used as the real basis of interaction. (Though I cannot think of anything that wouldn't fall into one of the two cases above.)

In all three cases, my parentheses amount to saying "We're at TL8" in the sense Phil Masters used it above.

It's theoretically possible to link the weak interaction to something stronger – that's what electroweak theory does, and ultimately what the Standard Model does – but that's a nonstarter for applications in the world at large. Such links exist at extremely early times in the universe and excessively high energy regimes. Even if you come up with some amazing GUT that has huge numbers of strange cross-terms in the Lagrangian, symmetry-breaking will freeze out any useful, interesting interactions under conditions outside of machines that would require energies that our current understanding deems impossible. And if you have that kind of energy, it opens up far better communications media than neutrinos.