3 ms·

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 th

by GuB-42 2y ago

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.

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dahousecat 2y ago
Sounds like a great topic for an xkcd video
- bauruine 2y ago
  There is a what if about it. https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/
antognini 2y ago
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 2y ago
  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 2y ago
    More like 100 km I'd think but yeah, the neutrino nucleon cross section gets much bigger at high energies
queuebert 2y ago
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.
mppm 2y ago
> 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.

by GuB-42 2y ago

deleted 2y ago

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dahousecat 2y ago

Sounds like a great topic for an xkcd video

bauruine 2y ago
There is a what if about it. https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/

antognini 2y ago

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 2y ago
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 2y ago
  More like 100 km I'd think but yeah, the neutrino nucleon cross section gets much bigger at high energies

queuebert 2y ago

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.

mppm 2y ago

> 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.