Oh-My-God Particle

> The Greisen–Zatsepin–Kuzmin limit (GZK limit or GZK cutoff) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy. The limit is 5×1019 eV (50 EeV), or about 8 joules (the energy of a proton travelling at ≈ 99.99999999999999999998% the speed of light). The limit is set by the slowing effect of interactions of the protons with the microwave background radiation over long distances (≈ 160 million light-years).

The very highest energy cosmic rays are theorized to come from Active Galactic Nuclei (very hot stuff around the giant black hole at the center of galaxies) or supernovae (large exploding stars), or even from the magnetic fields of galaxies themselves, all which are mostly outside the Milky Way. The implication is that some of these particles could be coming from smaller, closer sources, close enough to not be slowed by the MBR. This is unusual because it seems like closer phenomenon shouldn't be able to accelerate a proton that much.

note: not a physicist so my understanding may be off.

It’s more like getting punched. Really hard.

https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy)

For comparison a typical professional baseball pitch is around 90mph. At 63mph I guess it might not break your face, but it would certainly leave a bruise (if it was actually a baseball -- who knows what the actual particle would do to flesh and bone). I know people are pretty derisive about using swimming pools or whatever for measurement, but I think this one is pretty good for bringing incomprehensible numbers into the realm of lay-understanding.

As others have noted, the total energy equivalent is that of a moderately-fast baseball throw, which, in the case of a baseball is perceptible but generally not harmful.

The transmission mechanism for the baseball is the electromagnetic force, where the individual molecules of the baseball are interacting with the individual molecules of your body, and the imposed and reactive forces are roughly equivalent.

In the case of the OMG particle, as a proton it would exert a positive charge, and might steal an electron (becoming a hydrogen atom in the process), or interact directly with a nucleus, though likely splitting that. The atoms of your body are principally carbon, hydrogen, oxygen, and nitrogen, atomic numbers 1, 12, 14, and 16, respectively. The result of such an interaction might be isotopes of: H, He, Li, Be, or B, numbers 1--5 inclusive. There would likely be a chain of such interactions depending on the effective cross-section of the incident particle, atoms in your body, and any collision particles, though this is pretty much where my physics knowledge abandons me.

Online sources suggest that this is pretty accurate: the particle would pass straight through you:

<https://www.technology.org/how-and-why/if-proton-nearly-at-l...>

Presuming there is a collision within your body, at this point you have a particle stream, interacting with other material through electromagnetic and nuclear (strong and weak) forces. Again, you're dealing with exceedingly high energies, and it seems likely to me that those particles would tend to exit your body and have further interactions with the surrounding region (air and solid matter), which would result in some local ionisation and light heating. The question is the interaction cross-section of the incident particle, atoms within your body, and any collision and decay products.

Point being that you don't want to necessarily direct the maximum energy at a target, but the energy that will disrupt or interact with that target in the manner in which you intend.

Cosmic rays are striking your body all the time, though at lower energies. The effects tend to be local ionisation and, most critically, damage to genetic material. The latter is the most significant from a biological perspective.

> Instead, theorists generally expect that the most energetic cosmic rays rev up over millions of years in unidentified accelerators the size of galaxies.

> Physicists think that the highest energy cosmic rays cannot come from more than 500 million light-years away, as interactions with lingering radiation from the big bang ought to snuff out cosmic rays from more distant sources. But no obvious candidate for a nearby cosmic accelerator lies directly in line with the hotspot, Sokolsky says. He notes, however, that in that region a filament of galaxies kinks toward Earth and speculates that magnetic fields in that string might help rev up particles.

About one nanometer per week in case that is more relatable.

Though, to me it seems that the article's explanation is the ELI5 of your equation, not the other way around...

The kinetic impact alone would get your attention.

<https://news.ycombinator.com/item?id=37793828>

- Repeated observations.

- Simultaneous independent observations: multiple devices/instruments.

- Observation of primary and corresponding secondary events, e.g., an initial interaction with the atmosphere and further observations consistent with collision / decay particles arising from an initial interaction.

Put another way: if you see a bright flash (visual sensation), and some seconds later hear a heavy rumble (audio sensation), and within a few minutes observe heavy rain, odds are quite strong that the initial observation was lightning. This is based on multiple independent channels of information.

If you and multiple other people see the same flash at the same time, you have independent observations, and can validate the initial observation by that means.

In a world of increasingly high-plausibility generative tools (images, audio, text, video), the ability to show multiple independent observations of a given event becomes far more critical than the emergence of any one high-detailed, realistic document (where document refers to a record in text, audio, image, video, etc.).