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Is There a Fourth Neutrino Out There in the Universe? (medium.com)
128 points by breadbox 19 days ago | hide | past | web | favorite | 41 comments

I thought Joachim Kopp's article at https://physics.aps.org/articles/v11/122 was an even better explanation in some ways. It was buried as a link in the middle of the medium.com article.

I found Kopp's article easier to follow after reading Siegel's, myself. YMMV




Your Neutrino May Oscillate — physics humour

I'll believe you, but a google search for that phrase brings up nothing.

Well, neutrino detection is hard...

Right. I'll show myself out.

> I’ll show myself out.

We hadn’t even confirmed you’d arrived.

I thought that you were just passing through.

I wonder if solar neutrino detection could be done on a satellite heading towards the sun. Seems like the signals may vary over distance from the sun (guessing here) perhaps providing some insight.

The problem with that at present is our only way to detect neutrinos is by using loads of mass, usually ice, water, or xenon. It’s going to be tough to launch a glacier or a vast tank of xenon to make up the body of a detector. We’d need some novel form of detection that isn’t dependent on the occasional reaction of a neutrino as it passes theough a huge body of something. Sadly, that isn’t on the horizon and would ironically require a better understanding of neutrino interactions before it could be done, if it could be done.

Even worse, most neutrino detectors rely on being under thick masses of rock to filter out things like cosmic rays, which would otherwise completely flood the detectors.

So what you're saying is we need to capture an icy asteroid and stick a probe in it?

The ice would need to be very clear, surrounded by a grid of detectors, and all of that surrounded by a minimum of several hundreds of metres of rock on all sides.

The reason it needs to be clear is the detector watches for flashes of Cherenkov radiation.

cough .... IceCube .... cough

IceCube uses the entire earth as a shield. Basically only neutrinos going up through the detector is considered.

I guess that depends on how you define 'up' (are you looking at the entire planet or standing on the pole)

As I understand it these days they grab all samples and are now able to distinguish 'downward' coming neutrinos from cosmic rays in software

And somehow not have it melt next to the sun.

That would actually be the least of your worries. Ice is actually a pretty good insulator because it doesn't convect. Comets are giant snowballs. They regularly venture close to the sun and only lose a small percentage of their mass.

How flooded are we talking? A detector in orbit would regularly have an earth sized mass of rock between it and the sun so the difference could be teased out statistically for low values of flooded.

Don't we use water/xenon for it's combination of density and transparency? I wonder if there are other things we could use to shrink detectors at the expense of missing many wavelengths produced by collisions?

A large detector also has the advantage of being a large target. Even if you managed to make a detector a thousand times smaller while keeping it just as sensitive as our current ones, you'd still detect a thousand times fewer neutrinos.

The article makes it clear that the effect doesn't need a solar observatory to be visible.

The fact that it's easy to replicate with relatively small experiments is one of the things that makes it so striking.

This could be measured to some extent without leaving the earth, since the distance to the sun varies by about 3% between perihelion and aphelion.

I doubt our detectors are sensitive enough to pick that up, but it’s a good point.

Radiation flux varies as the square of the distance so a 3% change in distance produces a 6% change in flux. That seems to me like it should be detectable (but IANAP).

Please note: Unrelated to article content.


Medium's viewport is now about an inch tall on my phone, unless I carefully click 3 different 1sqmm X's. That's... Gross.

Even on my laptop, I'm no longer able to browse without a bookmarklet handy to remove sticky position elements. Vertical space is at enough of a premium just from the prevalence of widescreen aspect ratios; we don't need so many inch-tall menu bars and overlays getting in the way of the real content.

"An app designed for readers." Ironic.

I can read every word in that screenshot!

The only words I can't read are the words not visible in the screenshot.

Medium annoys me so hard I just give up on reading content and close the page.

I do the same. I feel this was not always the case but now the banners are so annoying I have just given up on medium-hosted content.

I've switched all of my mobile browsing to Firefox with ublock origin. I've got the "annoyance" filters enabled. It's a game changer.

Medium seems to be a poor webhost from my POV.

Works beautifully without JS.

I set this flag in Chrome so I always get the "Show Simplified View" prompt. It can sometimes get in the way, but it's generally nice to have. Wish it was simply a menu option.


:o It seems I don't have this flag. I'm running chrome Version 71.0.3578.98 (Official Build) (64-bit.

edit: Ah mobile only I see..

Yeah. I have the sticky header bookmarklet saved first in my bookmarks so I can hit it whenever I browse Medium on mobile.

This sounds useful, would you mind sharing?

javascript:(function()%7B(function () %7Bvar i%2C elements %3D document.querySelectorAll('body *')%3Bfor (i %3D 0%3B i < elements.length%3B i%2B%2B) %7Bif (getComputedStyle(elements%5Bi%5D).position %3D%3D%3D 'fixed') %7Belements%5Bi%5D.parentNode.removeChild(elements%5Bi%5D)%3B%7D%7D%7D)()%7D)()

you could just use greasemonkey or whatever the chrome equivalent is instead

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