# Neutrinos from another galaxy hit ice with black-hole force

If they're neutrinos – the scientists are being cautious about that, not yet having the six-sigma certainty that particle physics likes – they're rather exciting excited ones: two neutrinos believed detected at the IceCube detector in Antarctica have huge energy and probably came from outside our galaxy. The energy claimed for …

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#### How's it even possible

for El Reg to mention Cherenkov radiation without making a Dr. Manhattan reference?

#### Back-of-an-envelope calculation

The experiment detected two of these neutrino interactions in a volume of 1 cubic Km in two years, so a rate of about 1E-9 per year per m3

The global population is about 7E9, and let's say the volume of a human is about 0.07 m3 - so the global volume of human beings is roughly 5E8 m3

So you'd expect 5E8 * 1E-9 = 0.5 ultra powerful neutrino interactions with a human being per year, i.e. one every two years.

I read elsewhere that the energy of these neutrinos is about the same as a raindrop falling on your head - so every couple of years someone, somewhere will probably feel one of these cosmic neutrinos. Presumably they'll emit a small flash of blue light at the same time.

#### Re: Back-of-an-envelope calculation

I will rarely get a white with blue tinge light flash in one or the other eye at night when trying to sleep - it always startles me enough to prevent my going to sleep for a few minutes. It only happens a very few times a year, and my ophthalmologist says I have no eye condition that would cause it - my doctor says stroke symptoms are very different, and always look like a far off flash cube affect of pin point light - so this is very different. It seems to light up the entire fluid of one eye for a very brief flash - in a neon glow kind of way - I always immediately open my eyes to confirm that it isn't lighting or other external influence, but something like that should register in both eyes. I've always wondered if something like this could be happening. Of course I could just be having brain farts, or going crazy too - none-the-less it makes life fascinating!

#### pedantry

Cherenkov radiation is emitted directly by a neutrino travelling faster than the local speed of light - no collisions are necessary for this to happen. Compare with sonic booms of supersonic flight.

Simply detecting two in two years implies no collision rates with humans, only passing harmlessly through them.

Note: 1 PeV is approximately equal to 0.16 Joules - which is the amount of energy released when you let a mass of 16 grams drop vertically 1 metre to impact the ground under earth's gravity.

It might just be me, but that is far easier to comprehend than some nonsense about thousands of trillions times the energy of visible light. Could you have found a more obscure and ridiculous example?

#### Re: pedantry

Thanks for the illumination :)

I was wondering what the force of the impact was equivalent to...

That is a crazy amount of energy to be found in a single, sub-atomic, particle.

#### Re: pedantry

1 PeV is actually 1E-4 Joules, according to Wolfram Alpha [http://www.wolframalpha.com/input/?i=1+PeV+in+Joules]

WA's handy "Comparison as energy" for it is of the order of the amount of 1/62 x the amount of "acoustic energy contained in a whisper (~~ 0.01 J )".

I don't think you'd notice it if it did interact with your body.

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