Oh-My-God particle | Hacker News Reader

Oh-My-God particle

en.wikipedia.org

165 pointsmarkmassie42 comments

I worked on the child and grandchild of this experiment, HiRes and Telescope Array as an undergraduate and a bit as a postgraduate at the University of Utah. Currently I work with the Fermi Gamma-Ray space telescope as a "science janitor".

The reason it's called the Oh-My-God particle is because it kind of smashed through the GZK limit ( http://en.wikipedia.org/wiki/Greisen%E2%80%93Zatsepin%E2%80%... )

There's a few particles near this energy hitting the earth every day, the flux is just very, very low. This is why the follow up experiments to HiRes and AGASA, the Auger and Telescope Array experiments, are very, very large.

Most research has started to gravitate towards the lower energy cosmic rays, near 10^17 eV.

I can talk more about this but I got to go for now.

Experiments involved in UHECR research:

http://en.wikipedia.org/wiki/Telescope_Array_Project

http://en.wikipedia.org/wiki/High_Resolution_Fly%27s_Eye_Cos...

http://en.wikipedia.org/wiki/Pierre_Auger_Observatory

http://en.wikipedia.org/wiki/Akeno_Giant_Air_Shower_Array

Fun facts about Dugway, home of Fly's Eye and HiRes:

Some jets at Dugway once bombed a prototype detector.

One of the HiRes detectors was just past some German Village buildings, which was a mock-up of a German village in the Utah desert used for weapons research in WWII.

> I can talk more about this but I got to go for now.

please do...

The fact that the earth has seen these bombarding us regularly for millions of years does rather imply that the whole "OMG the LHC will make a black hole" panic was unfounded

The best explanation of the LHC black hole issue I have ever seen was a The Daily Show interview which pegged the odds at 50/50:

Either it will. Or it won't.

The best part is around 3:00 in. http://thedailyshow.cc.com/videos/hzqmb9/large-hadron-collid...

while I agree with the general sentiment that the idea that the LHC will create a blackhole is silly, surely there is a difference between creating such a particle and simply being in the trajectory of a particle that has already been created.

The idea that it would create a black hole isn't silly, it could well do. The silly bit is the thought that it would be dangerous if it did, given particle collisions at higher energies than the LHC happen regularly in the atmosphere and there is nothing particularly special about the LHC ones, bar the fact they are in a massive detector.

Note: I also think the public's LHC worries were unfounded.

One way that the LHC collisions differ from cosmic ray impacts is that the center of mass velocity is much lower. If high energy collisions created small black holes, cosmic rays could make ones that simply zip past at escape velocity (because (lots+0)/2 is still lots) while the LHC ones are captured (because (lots+-lots)/2 can be tiny).

I don't think that follows. The LHC is many, MANY orders of magnitude too weak to produce this kind of thing, but it can produce beams of many protons or, alternatively lead nuclei. Thus, it could conceivably create entirely different effects.

Actually, it does follow. If there are particles of the energy described in the original link, there are many more particles of lower energies also hitting the Earth's atmosphere, including energies accessible at the LHC. And none of these resulted in the Earth's destruction.

The same logic applies to the argument that any black-holes or otherwise dangerous particles would simply zip by the Earth (stated in a sibling comment to yours). Particles of slightly lower momenta come in higher numbers, so these would produce the dangerous particle, but not retain enough momentum to escape. Since the Earth has not been destroyed, there are no particles produced at low enough energies for us to destroy ourselves.

If I understand you correctly, your argument is based on the assumption that particle energies have some sort of continuous distribution. That's not necessarily true.

It's based on the fact that particle energies follow a continuous distribution.

See, for example: http://www2.astro.psu.edu/users/nnp/cr.html.

The article kinda lackluster in regards to information. Is there any more information on where this type of particle originated(s) from? It says from space, but supernova, black hole, stars, aliens?

This wasn't a bad round up I thought.

http://phys.org/news/2011-06-oh-my-god-particles.html

"They propose that extragalactic cosmic rays are spun up in supermassive black hole accretion disks, which are the basis of active galactic nuclei. Furthermore, they estimate that nearly all extragalactic cosmic rays that reach Earth come from Centaurus A. So, no huge mystery – indeed a rich area for further research. Particles from an active supermassive black hole accretion disk in another galaxy are being delivered to our doorstep."

Better link would be to http://en.wikipedia.org/wiki/Ultra-high-energy_cosmic_ray which gives some speculation as to what causes them.

Nobody knows, it's a big mystery. It's mysterious partly because it shouldn't exist. If you do the math a very high energy proton should have a reasonable upper energy limit. Because protons are charged and at high enough speeds the cosmic microwave background actually slows them down (because it becomes significantly blue shifted). So that means either this particle came from our own galaxy over a short distance or something else is going on that we haven't accounted for.

There are candidates for what would give rise to such a particle, but observations are sparse so we haven't had much chance to test any theories.

Considering it's practically the speed of light, one needs only to figure out the direction the particle was travelling in and point a telescope in the opposite direction. You will be able to see whatever it was that created it within 3 microseconds of the particle's creation.

EDIT: calculation error

On the other hand, if it was created in an ephemeral event you have an absolute maximum of 300 nanoseconds to point your telescope at it :) (taking your number on faith)

Oops, I did it wrong. I skipped a zero.

They state that the particle differs from light by 1 cm every 220,000 years. Considering the age of the universe is about 14 billion years, that works out to 63636 cm. It takes light 2210 nanoseconds to cover that distance.

https://www.wolframalpha.com/input/?i=light+over+%2814+billi...

From the phys.org link in a sibling comment:

"It’s difficult to determine their exact source as the magnetic fields of the galaxy and the solar system alter their trajectories so that they end up having a uniform distribution in the sky – as though they come from everywhere."

We have absolutely no idea. Really.

My favorite particle: https://en.wikipedia.org/wiki/Oops-Leon

Okay, so what kind of cosmic phenomena causes a particle with mass to accelerate to such a ridiculous speed?

That seems like the more interesting point not touched by the article.

What happens when two Oh-My-God particles collide?

If you could record the collision it could give you a glimpse into the string theory. Wouldn’t that be something!

What would happen to someone if it hit their skin?

"kinetic energy equal to that of ... a 5-ounce (142 g) baseball traveling at about 100 kilometers per hour (60 mph)"

Probably wouldn't notice a thing. You're mostly empty space (on a subatomic level), odds are it wouldn't hit anything, and would just release no more energy than getting hit by a baseball if it did. Sure it's a stunning amount of energy for such a small object, but not much on a human scale. Compare getting hit with a bullet: penetration is damaging only because of what it tears up in the process, when the energy involved (demonstrated by getting shot while wearing a bulletproof vest) is little more than a solid kick. A "hole" of subatomic width doesn't do much damage.

The energy content is significant, but it would have to be both transferred and absorbed.

As you note, odds of it interacting with some bit of you are relatively low. I disagree with your baseball comparison, as the result of the collision would be a cascade of secondary particles. Each of which would likely have only a small chance of interacting with yet another bit of you before exiting your body.

The net result would be something like firing a cannonball (or bullet) at a series of bead curtains. Most of the time, the bullet would miss. Occasionally it might strike one or more beads. Those then would also mostly miss the other beads within the curtain, though some might strike and cause secondary effects. Most of the energy would simply transit the curtain system as a whole. Or maybe even at sheets of laced (punched-out) tissue paper. The target simply doesn't have the capability to absorb the energy of the particle.

A more accurate answer would require some subatomic particle modeling, past my pay grade.

Total energy is not the only factor in determining damage. The rapid movement of a bullet through flesh does extra damage due to the shockwave it creates.

Similarly, if you drop a hard drive on carpet it's probably okay, but if you drop it on concrete, you're likely to have damaged it and even deformed the case, even though in both cases the total energy to stop the drive is the same.

Here's the story of one guy who's head was in the path of a proton particle beam:

http://boingboing.net/2011/02/22/what-happens-when-yo-6.html

"The radiation absorbed by his head was in the region of 1000 gray. 5 gray worth of X-rays is generally considered fatal, but Bugorski survived and went on to complete his PhD (a proton beam moving near the speed of light has different characteristics from an X-ray!). The side of his face that was burned by the beam's exit has not visibly aged in the years since the accident. "

Note that such a beam contains millions (or a few orders of magnitude more?) of protons. I can't say whether millions of protons with a millionth of the energy as this particle do more or less damage.

Virtually nothing, I think. I'm not a physicist but 7.5×10^14 eV converts to 120 microjoules. Wikipedia says that one Joule is the energy in a tennis ball moving at 23 km/h (14 mph). Another comparison I've heard is that a joule is about the energy in a strong handclap. This would be about a ten-thousandth of that.

Wolfram Alpha also gives the helpful comparison "0.06 times the mechanical work done pressing a key on a keyboard" so if that helps?

http://www.wolframalpha.com/input/?i=7.5%C3%9710%5E14+eV+to+...

Wikipedia actually says the kinetic energy of the particle is 50 Joules (3*10^20 eV) or equivalent to slightly over quarter pound ball (142 grams) traveling at about 100 km/h.

Deleted comment

I was using the number given at the end of the article for available energy in a particle collision.

The article says the collision energy is only 7.5×10^14 eV.

See the case of Anatoli Bugorski:

http://en.wikipedia.org/wiki/Anatoli_Bugorski

He put is head in a proton beam of a particle accelerator and survived. It wasn't pretty but he got hit by a lot more than one proton.

Close to nothing would happen. The relevant quantity to understand is the stopping power (usually referred to by us physicists as dE/dx). Stopping power drops significantly as energy of the charged particle increases. So for very large energies, very little of that energy is deposited over a given distance (in an absolute sense).

This principle is how some radiation therapies work to treat cancer. Because the stopping power curve for protons is well understood, a proton beam can be tuned to deposit all of its energy is a fairly small area.

Aside/Rant: this question clearly can be answered by someone with expertise in the field. So why did people feel the need to speculate about it instead of just waiting for someone who knows how to answer it?

They would become Starman.

this site is so full of pussies who dont get a joke

so what happens when this particle collides? Can you access the 60mph baseball energy and take out a bird? Just extremely unlikely.

Cool name!

These are emanations from vulcan warpships travelling through our solar system.

Don't be silly. It's probably Romulan ships with a faulty waveguide around the artificial singularity core. Vulcan warp signatures look entirely different, and mostly radiate into subspace.

Reply on news.ycombinator.com