[GuB-42]

Now, what will happen if you get hit by a ping-pong ball mass of 120 PeV neutrinos? 120 PeV is about 2e-16 grams, so a ping-pong ball will have about 1e16 of them.

From nothing, to detectable, to lethal, to big boom?

My intuition would be "detectable" but I don't know enough to do the maths.

And by the way, I am using the mass-energy, not proper mass, because the question is crazy enough not to even consider what would be the mass of a neutrino.

[antognini]

The mean free path of neutrinos through lead is around one light-year. So, taking the thickness of the body to be 1/2 a meter, you would expect the probability of any individual neutrino to interact with the body to be ~5 x 10^-17. So you'd ballpark have around a 20--40% chance that a single neutrino interacts with your body. It would probably cause a localized radiation burn. Detectable, but probably not lethal unless you got really unlucky with where it hit you.

[pfdietz]

The mean free path of much lower energy neutrinos in lead is about a light year.

The MFP of a 120 PeV neutrino in lead would be something like 10 kilometers, I think.

[cozzyd]

More like 100 km I'd think but yeah, the neutrino nucleon cross section gets much bigger at high energies

[mppm]

> big boom

The probability of interaction of neutrinos with matter increases with the energy. I've asked o1 to estimate the mean free path of a 120 PeV neutrino in water and it came up with 1000km. So let's say, conservatively, that 10^-7 of the total energy gets deposited in your body when the beam goes through. The mass equivalent of a ping pong ball is about 2.5x10^14 J, which gives us 2.5x10^7 J total, or about 6kg TNT equivalent. This is only an order-of-magnitude estimate, but it would definitely not be healthy.

[queuebert]

Total energy of impact would be 120 PeV x 10^16 = 120 x 10^31 eV = ~60 kilotons TNT, or 4 Hiroshimas.

So BIG boom.

Since the velocity is so close to the speed of light, you can think of this like the energy released by annihilating a ping pong ball made of antimatter.

Edit: Commenter asked what would happen if they "hit", so I'm assuming a hypothetical 100% collision. But yes to stop 1/e of a neutrino beam with normal matter, you'd need a light year of lead.

[dahousecat]

Sounds like a great topic for an xkcd video

[bauruine]

There is a what if about it. https://what-if.xkcd.com/73/