I recently discovered that there is a neutrino detector a few kms under the sea not too far from where I live - which is kind of cool.
I’m writing a guidebook to the area and want to explain what it does in layman’s terms. I’ve looked at the website and the Wikipedia article on neutrinos but it’s all a bit much for me. What would be really good would be to know what they hope to discover - i.e. more about the big bang, the ToE or whatever?
Sorry for being stupid and thanks in advance.
The thing about neutrinos is that they are fantastically intangible, barely interacting with normal matter at all. There’s some couple of trillions going through your body right now, and you’re none the wiser. This, of course, makes them extremely hard to detect (which is why we need those big ‘water basin’ type detectors – basically, you’ll need a lot of stuff to observe at least a few interactions), but also comes with a great bonus – because they’re virtually unimpeded by matter in their propagation (technically, they have a small reaction cross section), they can be used to probe regions of the cosmos from where photons, for instance, could not reach us, being blocked by matter in between. For instance, a photon generated in the core of the sun would take some ten thousand years to reach the surface, while a neutrino is likely to traverse that distance at near light speed, delivering potentially valuable information. Even more importantly, neutrinos are generated in abundance in supernovae, and thus, the neutrinos released can be utilised as a probe of the exact nature of those events even when they’re otherwise inaccessible.
Also, there exist models that neutrinos with a small, but non-zero mass may form part of the ever-elusive dark matter we need to glue our galaxies together. There may be some connection to a possible ToE because of the neutrinos being stable particles that are only susceptible to gravity and weak interaction, eliminating a lot of what would usually obfuscate attempts at measuring quantum gravity effects (of course, this might be offset by them being difficult to detect due to the same properties).
Perhaps the wiki article on neutrino astronomy might be of some interest.
I think this was the piece of the puzzle I was missing - that makes sense to me, thanks.
On a more mundane level, what are the scientists involved in this actually doing day-to-day? There seems to be a cable to the detector, linking it to the town of Methoni. Are their a team of crack, international physicists sitting in a room there hunched over a screen waiting for a result, or is it just a computer recording occasional blips? Methoni is lovely, and has a great castle, but doesn’t seem the kind of place for crack, international physicists.
I have no specific knowledge of NESTOR (this neutrino telescope) but the normal way with these sort of collaborations is that there will be a small team on site actually looking after the equipment with all the data being fed back to the home labs in Greece, Germany, Russia, etc. The researchers will get the results directly on their computers in their offices and it will be the computers doing the waiting for an occassional blip!
Incidently, physicists aren’t daft - if they can find a pausible reason why their research has to be done in an exotic and interesting location, they’ll go for it. So don’t be that surprised to find that a number of them have to make site visits to Methoni 
That’s about what I’d figured.
I’ve also just been told the hotel the physicists stay in when they visit, so I will go and hang out there!
Or Sudbury!
I couldn’t possibly comment on the relative merits of southern Greece or the middle of Ontario in winter!
Given the reason for your interest, if you phone the Institute or drop them an email explaining the circumstances there’s a reasonable chance they’ll arrange a visit to their Methoni base for you. It doesn’t look big enough to have an actual press officer, but physicists are usually eager to talk about their work given half a chance and the slightest expression of interest. I can imagine a grad student being rummaged up to show you round the Institute and explain what they’re doing. Worth a try at least.
Yup, good notion. I had been thinking I’d do this.
Neutrinos pass through all matter unless they happen to directly impact an atomic nucleus*. So neutrino detectors are usually put in dark places, and they work by watching for the faint flashes of light that occur when a neutrino happens to smack into a nucleus. So most neutrino detectors are installed in places deep underground or underwater or under ice, where the earth or the water or the ice screens out all of the normal cosmic radiation and the like, so only neutrinos can make it through, and with each flash they say “Hey, a neutrino.” At least, that’s how the detectors in Sudbury (buried deep in an old nickel mine with naturally low background radiation) and the Antarctic (buried deep under the ice) work, IIRC. If I don’t RC, hopefully somebody will correct me.
It’s more complicated than this: They can interact with electrons about as easily as they can interact with nucleons. It’s just that they don’t interact with anything very well. You can’t really model the interactions of subatomic particles as colliding billiard balls, but if you try to stretch that weak analogy, you end up coming to the conclusion that, from a neutrino’s point of view, particles are smaller than they are from other non-neutrino particles’ points of view.
The same is true, but to an even greater degree, of gravitational radiation. This is part of the reason why cosmologists are so excited about the possibility of detecting gravitational waves: With light, you absolutely can’t see anything from earlier in the Universe than about 300,000 years after the Big Bang, since the Universe was opaque before that time. With neutrinos, you can push that back to about 200,000 years, and therefore “see” things that you can’t see with light. With gravitational waves, though, we expect to be able (in principle) to “see” back to about 10[sup]-32[/sup] seconds after the Big Bang.
The flip side, of course, is that in the same way that neutrinos’ low interaction rates means that it’s difficult to build detectors for them, gravitational waves’ much lower interaction rates mean that it’s even more difficult to build detectors for them. In fact, no instrument has yet succeeded in directly observing gravitational waves (though we think we’re only a few years away from being able to do so), and it would probably take an instrument several generations more advanced than the ones currently being worked on to attempt to pick up signals from the very early Universe. But if we can build the detectors, the waves are presumably out there to be detected.
Wow, thanks for the clarification, Chronos. I didn’t realize they could interact with electrons at all. That leads me to ask: Can neutrinos pass through a neutron star? I always assumed they couldn’t, since all those neutrons packed tightly together would (I assumed) be like one big atomic nucleus and would block a neutrino effectively. But if the individual neutrons appear smaller to a neutrino than normal, maybe they can still slip through even something that dense.
Thanks for all contributions.
Well, nothing is ever totally opaque or totally transparent to anything, so the short answer is that some will and some won’t-- It’s really just a question of how many of each. And certainly a neutron star will do a better job of stopping neutrinos than almost anything else will. We don’t know too much about the internal structure of neutron stars, but assuming that the interaction cross-sections aren’t too wildly different from normal matter, the mean free path of a neutrino through them will be inversely proportional to the density. A neutron star has about 10[sup]14[/sup] times the density of lead, and the mean free path of a neutrino through lead is about a lightyear, so the mean free path of a neutrino through a neutron star is about 100 m. A neutron star has a size of about 10 km, so almost no neutrinos would be able to make it all the way through, but if you had a bright enough neutrino source on the other side, a few might still be able to make it.