
The “Oh-My-God Particle” - jamesash
https://en.wikipedia.org/wiki/Oh-My-God_particle
======
nategri
Hey this is the field I did my PhD in!

Some fun facts:

* The flux of particles in this energy regime is so low that you get about 1 per square kilometer per century, so studying them necessitates doing really wild stuff like instrumenting a patch of land the size of Rhode Island.

See:
[https://en.wikipedia.org/wiki/Pierre_Auger_Observatory](https://en.wikipedia.org/wiki/Pierre_Auger_Observatory)

* These particles are so energetic that in their frame the nominally low-energy photons that comprise the cosmic microwave background appear as an impenetrable gamma ray wall thats prevents them from traveling more than about 100 million lightyears. This seems like an incredible distance but in astronomical terms this means that whatever is producing them is "nearby." We also know they don't come from our own galaxy because arrival directions don't correlate to the galactic plane.

* Current consensus says that these particles probably come from very large and active black holes in the center of certain galaxies. These objects are called active galactic nuclei (AGN).

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legohead
What would happen if this particle hit a person?

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smueller1234
Arg. Had a moderately long, not quite Randall Munroe worthy explanation
written up but it got lost by accident. Sorry. :(

In a nutshell, that'll never happen. You'd have to be the unluckiest astronaut
to ever live. These particles reach Earth at a rate less than 1 per century
per square kilometer. So you'd have to hang out in space for like a hundred
million years...

The original particle never reaches the ground. It gets annihilated in a
collision some tens of kilometers up in the atmosphere.

If you were hit, I'm not sure the cascade would do significant damage before
it exited your body on the other side.

~~~
tlb
If it wasn't for the atmosphere, with 7.6B people each presenting 𝜋/4 m² cross
sectional area, 60 people per year should get hit.

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Jun8
Not on this particle but relevant if you're interested in cosmic particles:
For my son's 5th grade Science Fair project we are building a cloud chamber to
detect cosmic particles! As crazy as that sounds we've decided on this project
after watching videos showing how _ridiculously_ easy it is to build one, e.g.
see this one:
[https://www.youtube.com/watch?v=pewTySxfTQk](https://www.youtube.com/watch?v=pewTySxfTQk).
Most designs call for dry ice (cheap, ~$10 for 10 lbs but may be hard to find
a local store) but you can also build one using an air duster:
[https://www.youtube.com/watch?v=QCAVlMTBMe0](https://www.youtube.com/watch?v=QCAVlMTBMe0)!

Fun fact that I've learned from him during research: humans are exposed to
cosmic radiation which is on average equivalent to 10 chest x-rays per year.
It would be interesting to look at the impact of this on, e.g. cancer rates
among people living at sea level versus cities with high elevation, e.g. Quito
in Ecuador.

~~~
Varcht
Volume/time - pour slowly into a funnel and it works, pour too fast the funnel
overflows and you get cancer. People accustomed to high altitudes likely have
bigger funnels.

~~~
IntronExon
What isn’t known about the relationship between exposure regimes and poor
outcomes could fill the complete OED. Is it really a hormesis model? Linear No
Threshold? Linear? Supra-linear? Linear-quadratic?

We don’t know, and generally speaking it would be unethical to try and find
out using humans.

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neor
"In the particle's reference frame, the photon would move away from it at the
speed of light."

For some reason I've never been able to wrap my head around this. Anyone know
a good explanation for this stuff?

~~~
lisper
Imagine you were driving a car with a stuck accelerator an no brakes. The car
always moves at 100 MPH. So you can't change the car's speed, but you can
change its direction. So you can drive north, at which point your east-west
velocity is zero, or you can drive east, at which point your north-south
velocity is zero, or you can drive in some other direction, which will give
you a mix of north-south and east-west velocities. The faster you move east-
west, the slower you move north-south and vice versa.

You are kind of like that car. You (and everything else) are always moving at
the speed of light, but through spaceTIME, not through space. When you move
through space you are not changing your speed through spacetime, you are only
changing your direction. The faster you move through space, the slower you
move through time, and vice versa.

~~~
whatshisface
The bug in your explanation is that turning the steering wheel performs a
rotation (which moves vectors along the edges of circles) on your velocity
vector, but in spacetime that would be a hyperbolic rotation (which moves
vectors along hyperbolas). The result of this is:

If I am an outside observer measuring your position with a very long ruler and
your time with my wristwatch, all while watching your dashboard clock, I have
access to three numbers. (Your clock, my watch, your position on my long
ruler.)

There are three ways to compare these numbers. If I compare my watch to your
position down the ruler, I will obtain "classical speed." The behavior of this
number is very confusing when it is high.

I may also compare your dashboard clock with my ruler position, or your
dashboard clock with my watch. Both of these can lead to a "speed," in the
sense of one number changing at a certian rate with respect to another.

If Vx is the rate of change of the ruler position with respect to your
dashboard clock, and Vt is the rate of change of my wristwatch with respect to
your dashboard clock, and c is the speed of light, then it turns out to be
always true that c^2*Vt^2 - Vx^2 = c^2. If you graph this you will see that it
is a hyperbola.

In the parent's example, the car situation would obey V(north)^2 + V(south)^2
= 100mph^2. If you graph that it is a circle, as it differs from the above by
the minus sign.

~~~
lisper
Yes, I know that, but I think this inaccuracy is a price worth paying to
achieve an initial intuitive understanding. As a student reflects more deeply
on what it can possibly mean to "move more slowly through time" the negative
sign on the time dimension can be introduced. But as an initial intuitive
picture to get a student out the the Galilean rut I think the circular
rotation works well.

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api
My favorite speculation is that it's the jet wash from someone's interstellar
antimatter rocket. Unlikely, but fun. :)

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lloeki
It's too bad there's no anecdote in the article as to how the particle came to
be such named.

Compare with the Wow! signal[0] for what I mean. I bet something similar
happened.

[0]:
[https://en.wikipedia.org/wiki/Wow!_signal](https://en.wikipedia.org/wiki/Wow!_signal)

~~~
tgb
I assume it was an intentional play on the "God particle" nickname for the
Higg's boson.

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zaarn
To make it a bit more graspable; A baseball at 90% the speed of light will
cause a fairly large nuclear detonation. [0]

This particle moved at 99.99999999999999999999951% the speed of light. IIRC
from when I worked it out a month ago or so (baseball with that speed), it was
in the region of 10^25 J, pretty close the energy the entire sun is outputting
each second or a couple million nuclear bombs. (10^25 particles, 4.8 joule per
particle)

[0]: [https://what-if.xkcd.com/1/](https://what-if.xkcd.com/1/)

~~~
Parcissons
If such a particle interacts with the water of my brain- would i drop dead?

~~~
icebraining
[https://www.reddit.com/r/askscience/comments/7dqqsh/what_wou...](https://www.reddit.com/r/askscience/comments/7dqqsh/what_would_happen_if_you_were_hit_by_the_ohmygod/)

[https://www.reddit.com/r/askscience/comments/3o16ut/what_wou...](https://www.reddit.com/r/askscience/comments/3o16ut/what_would_happen_if_the_ohmygod_particle_had_its/)

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dropspace
So we don't know what particle this is?

Do we know that it's not any of the particles we already know about? As in, is
it a new kind of particle, for sure?

Or is it just an energised photon or something?

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bitwize
So did the detector get clobbered by this particle?

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al2o3cr
The detector used doesn't interact directly with the particle - it observes
the light emitted as the particle (& the subsequent shower) interacts with the
atmosphere.

~~~
madaxe_again
They're called Air Showers -
[https://en.m.wikipedia.org/wiki/Air_shower_(physics)](https://en.m.wikipedia.org/wiki/Air_shower_\(physics\))

~~~
Nicksil
Non-mobile link:
[https://en.wikipedia.org/wiki/Air_shower_(physics)](https://en.wikipedia.org/wiki/Air_shower_\(physics\))

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olskool
Interested to know what the kinetic energy of a near Planck particle would be.

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vectorEQ
this particle physics is just silly and it will never lead to anything but
more tiny and faster particles which do inexplicable things. such useful
science ... really...

Here's something actually interesting >.> but no one care about it....
[http://aip.scitation.org/doi/abs/10.1063/1.2423240](http://aip.scitation.org/doi/abs/10.1063/1.2423240)

~~~
staplers

      and it will never lead to anything
    

Which particle physicist hurt you?

~~~
zaroth
Well they are certainly very good at building big honking machines with our
tax dollars! :-)

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ppaattrriicckk
Without being an expert on the subject, I hope some of what is learned from
the engineering of those big honking machines might be relevant for attempts
at sustainable fusion.

Plus:
[https://en.wikipedia.org/wiki/Particle_physics#Practical_app...](https://en.wikipedia.org/wiki/Particle_physics#Practical_applications)

