An easier yes is that in fact we do it all the time – by letting the light pass through a transparent medium. It’s the “speed of light in a vacuum” that is relevant to relativity.
Okay. I am starting to remember high school physics class and those NOVA specials I use to watch (maybe I should rewatch them).
So here is my last question. If light is massless, why does it not pass through other matter? Why can neutrinos do this and not light?
It just seems to me that something without mass could not interact with other matter in a way that it would reflect back. Maybe this has something to do with quantum physics and small particles behaving in a wave-like manner?
I’m really not the best person to ask about this-- I just encountered it somewhere as a tidbit of factoid, and don’t really have any expertise on eyes or neutrino cross-sections. Feel free to start a new thread, though.
IAmError403, the low interaction rate between neutrinos and matter really has nothing to do with their mass. It’s just because they only interact via the weak force, which is weaker than the electromagnetic force.
The Kamioka II detector saw 11 neutrinos, and has 3000 tons, or 2.7 billion g, of water.
Eyeballs are mostly water, and I’ll assume each eyeball has 2 cubic cm of volume that might intercept a neutrino. There were about six billion people then, or 24 billion grams of eyeball detector juice. So you’d expect about 100 neutrinos interacting with human eyes from the supernova. Give or take a factor of 3 or 4, because that 2 cc per eye is pretty rough, and because I didn’t account for people sleeping, or looking the wrong way.
Not sure how to get to only one or two people seeing a flash from there.
Looking the wrong way?
The Cherenkov photons produced by a neutrino interaction travel in mostly the same direction as the neutrino itself. So if the neutrino entered from the back, the photon would go forward in the eye and miss the retina.
If the supernova is behind your head, a neutrino interacting with the clear portion of your eyeball will send photons away from the retina. If it interacts behind the retina, the light would, I assume, be absorbed by other tissue and not reach the retina.
Also, I forgot to account for people with their eyes closed.
(That’s a joke.)
:smack:
For some reason reading this I thought we were talking about interactions happening in the retina itself, but if it’s the fluid of the…yeah makes sense.
<hijack>
Say we were to discover something that could block or absorb neutrinos.
Aside from trying to figure out why it has that property, what would be the practical value of such a thing? Would absorbing neutrinos necessarily entail huge amounts of energy?
About a third of the planet’s population would be asleep at any given time.
The optic nerve takes up, as a generously liberal estimate, maybe a third of the circumfrence of the eye.
Countless events take place which make an impression on our optic nerve which never make it to the actual “seeing” stage–fraction here I couldn’t speculate about, though.
But we’re down to less than 10, I think.
Here’s an interesting comment from The Register that I am not qualified to analyze:
Actually, if one views this through the SME framework, in particular, the Puma model, one CAN have superluminal neutrinos via Lorentz violation neutrinos. It’s a bit out there and not well modeled, but it COULD be an explanation.
My money is still on an experimental error though, else we should get type 1a neutrino events years in advance of the light from the event, rather than hours before, as is typical, as the entire star is “blowing out” before the light from the core fusing could escape the core.
Actually, the Puma model is one I was reading about earlier today, it predicts possible Lorentz violation neutrinos, with potential superluminal neutrinos, during oscillation. It’s one of the Standard Model Extensions being theorized and tested now.
Light is slowed whenever it goes through a transparent medium, such as water or glass. It’s even been stopped in a Bose-Einstein condensate, under some really complex conditions.
But, light is electromagnetic governed. Neutrinos are weak force governed, they ignore electrons, so to cause a neutrino to interact with an atom, it has to manage to slam into a nucleus of an atom and actually strike a particle within that nucleus. A near miss would only trigger oscillation of its flavor. They’re THAT small.
And what would that person see? IF an optic nerve cell or retina receptor (rod OR cone) were excited, a small dot sized flash, of the briefest possible time, hence probably wouldn’t even be noticed.
The brain is REAL good at filtering out noise.
Had he read the paper that was published on the experiment, he’d know that they calibrated the equipment to properly ensure no such artifact would be introduced.
I’m generally familiar with those units, one CAN introduce a delay in the processing path, but preventing such a delay is trivially easy to accomplish.
The scientists did their very best to shoot their own results down all by themselves and couldn’t, hence the publication that is essentially begging for someone to find a flaw in the results. Or for someone to reproduce the results.
Well it’s a pretty good link because you can follow it through to see that it’s a WAG from some guy, and the processing delays he’s talking about would be irrelevant. And here’s the manual for the CERN High Performance Time to Digital Convertor (HPTDC) , or what most people would call a really good clock. It’s accounting for temperature sensitivity, and it’s a relatively simple device. The FPGAs mentioned originally were data-processing devices whose operation would not have affected anything unless they couldn’t count, and that problem, and/or any inaccuracies in the TDC could be easily discovered with simple tests.
If the fluid in the eye were to flash, it would go unnoticed, it would come and go too fast for the retina to register. It’s not like a xenon flash. You’re talking about ONE atom releasing a photon.
Absorbing neutrinos? Simplicity itself! You use a block of neutronium. That said, I have no idea HOW you KEEP it neutronium, as when you remove it from the neutron star, gravity won’t be holding those neutrons together… 
Not at all. The Cosmic Speed Limit is exactly that. If photons are massless then they can and so will travel at the CSL, which perforce becomes the same as the Speed of Light. But there’s nothing magical about light that says nothing can ever travel faster than it, per se, it is just a convenient and common phenomenon to use as a stand-in for the CSL. If photons (and neutrinos) have mass then they CANNOT travel at the CSL, and so the speed of light is no longer “as fast as it is even theoretically possible to go”. One possible interpretation of this measurement is that neutrinos have some mass but less than photons do, and consequently are permitted to travel faster that light while still not exceeding the CSL.
You can, just look through a pane of glass. Experimentally, scientists have slowed (the average speed of photons in) a particular beam of light to almost a standstill.
Thanks. This video helped me understand a little better as well:
Wait, so I was right before and I was premature in throwing in a :smack :
?
For the purpose of the hypothetical, it doesn’t matter how we manage to block neutrinos.
Let’s say…I’m doing some sewing and I discover that a particular kind of weave has the curious property that it refracts neutrinos, and can be arranged to block them altogether.
Obviously scientists would be very excited by trying to figure out why it has that wtf property. But other than that, would it have any use?
Is there anything which is impractical to do now, which that discovery would make practical?
It’s valid to say “I don’t know. I’ve never thought about it before because…why would I?”. I’m just wondering if anything comes to mind.