Slashdot Mirror
Black Holes and Hidden Dimensions
Slackware Geek writes "It is being reported in the Nature Science Update that a new observitory being built in Argentina to study cosmic rays could detect extra hidden dimensions if they exist. 'Cosmic rays could find holes in Standard Model of particle physics ...If the Universe contains invisible, extra dimensions, then cosmic rays that hit the atmosphere will produce tiny black holes. These black holes should be numerous enough for the observatory to detect.'"
Does anyone know how this works? Is this detecting the Hawking radiation from an evaporating hole, or is it detecting other effects?
In Soviet Russia, sig types you!
And every particle DOES have "simultaneous exact position and momentum," it's just that we aren't capable of determining both through observation. We can determine one or the other.
No, not exactly, though this is a common misconception.
Heisenberg's Uncertainty Principle has nothing to do with the act of observation. The actual uncertainty is fundamental to the quantum model. It's not that you can't measure both the position and the momentum at the same time, it's more that the particle's wave aspect cannot be constrained by both 'measurements' at the same time. Think of the particle like a water balloon on the position/momentum graph: if you compress it in one direction (measuring position) it spills out in the other (uncertain momentum).
The fun part is that you can actually use the uncertainty principle to make more accurate measurements. An experiment that was done years ago in Australia proved this. The idea is that a photon travelling here from a distant star has a very narrowly defined transverse momentum: it's heading almost directly towards us, so the uncertainty in its side-to-side momentum is directly related to how much space it takes up in the sky. (Since that defines the range of angles the photon could arrive from.) Since the transverse momentum is highly constrained, the transverse position must be highly spread out. So in theory the photon could be seen as a paper-thin pancake several miles across.
Now, from the standard double-slit experiments, you get an interference pattern as long as there is a possibility of the photon 'hitting' both slits at the same time. In this experiment, the slits were replaced with radio telescopes on train cars, on a long straight section of track. (Hence why this was done in the Australian outback.) So long as the telescopes are closer together than the uncertainty in the photon's position, you get an interference pattern. Once they're further apart than that, you revert to two seperate streams of photons.
So, you slowly move the telescopes apart, watching the star, until the interference pattern disappears. Presto, you have the 'size' of the photon, which gives the uncertainty of its transverse position. Back-calculating throug Heisenberg's inequality gives you a limit on its transverse momentum. And that gives you a good idea of the 'size' of the star in the sky, in fractions of an arc second.
This has been done, and gave answers that agreed with other observations of the stars. So the Uncertaintly Principle has, in this case, improved the accuracy of measurements.
And demonstrated that the HUP is a lot more fundamental than what you said. Particles simply do NOT have "simultaneous exact position and momentum."
-- Bryan Feir
Oh my God, I'm amazed - this is the observatory I actually WORK for, and it's on SLASHDOT, my God.
Forgive me for going completely crazy replying to everyone, but this is just too cool.
OK, so long as people promise not to Slashdot the server (heh, that was dumb) for anyone who wants more information, go to the main Auger website, or for even cooler information, go to the Auger site in Argentina.
Auger is actually a very interesting project, and it's not like anything you'd ever think of - it's a 1600 km^2 array of water Cerenkov detectors (10 cubic meters of water) spaced 1.5 km apart - the picture in the article is of the flourescence detector, which is more like what you think of for a standard detector, but due to the limitations of the flourescence method of detecting cosmic rays, its duty time is only 10%, as opposed to the 100% of the surface array.
The project is proceeding along... pretty well. We've basically finished the Engineering Array, a small-scale testbed to find all of the design flaws in the initial project (and boy, did we find them) and we've detected some cosmic rays which we believe to be ~10^19 eV. We've also demonstrated the hybrid design as well (events where the flourescence detector triggers as well as the surface detector).
The black hole stuff isn't the important goal of the project - the goal is to elucidate the spectrum of cosmic rays above 10^20 eV, because we have no idea where those particles come from - all of basic physics says they can't exist. This is one of the big questions in astrophysics in recent years, up there with gamma ray bursts and odd quantum states of matter.
It's way cool. And not just because I work on it...
Unfortunately, this argument isn't very likely. The main problem we have is how to accelerate particles to such high energies - 10^20 and above is impossible by any stretch of the imagination, but the 3 x 10^20 particle that slammed into Dugway, Utah appeared to have a slightly better imagination than humans.
Empty-space acceleration would have to be massive to counteract the utterly huge deceleration caused by energy loss in galactic/extragalactic magnetic fields, interaction with the interstellar medium, and, most importantly for extreme high energy cosmic rays (UHECRs), the GZK effect - photopion production by interaction with the cosmic microwave background radiation. It's simply not possible to accelerate particles like this in empty space - we would've seen it already in particle accelerators.
Seriously, physicists right now have no idea how these particles are accelerated. Supernovae? Not nearly enough energy, by any stretch of the imagination - fundamental arguments like conservation of energy kill you far below the 10^20 eV limit. Gamma-ray bursts? Maybe, but the distribution of cosmic-rays doesn't agree with GRBs as a possible source. Extragalactic? Not unless you throw away basic physics and ignore the GZK effect - there's no way they could propagate that far.
Basically, the one question that there have been tons upon tons of papers in the recent literature for is "where is this gigantic particle accelerator nearby us?"
You're right - they don't jive.
:) A black hole is completely described by its charge, mass, and angular momentum. It has no other properties (hence "black holes have no hair" - "hair" in this case is any other property).
So, to explain: black holes have three properties. They're the universe's most massive particles in that respect.
Charge does affect the event horizon's properties, basically in the same way that angular momentum does - it alters it massively. You can get very weird black holes, including ring singularities instead of point singularities (black hole donuts!).
In reality, it's very difficult to charge up a black hole. Most of the matter falling in is neutral, and a buildup of one charge will result in a preferential draw of the other charge (opposites attract, y'know) and therefore, an overall neutral black hole. In falls an electron, and a proton is drawn preferentially over another electron. You also need a ton of charge to change the event horizon significantly - but in theory, it is possible to tell.