So, the boys (and probably some girls) at the CERN lab in Geneva are worried about the unclean vacuum. They're building a new particle accelerator. Why? Because it's going to accelerate really heavy atoms to really high energies. Their new toy is called the Large Hadron Collider (LHC).
And why are they worried? Well, because then need to economize on tremendous amounts of electricity. So, they build their electro-magnets out of superconductors that take a lot less electricity. But to be superconducting, they need to be super-cooled. But the electro-magnets need to be right up next to the beam of particles (those heavy lead atoms) so the beam can be easily (and cheaply) controlled. The beams are in their own tube, or pipe, so that all the air can be gotten out of the beam's way -- a vacuum. The magnets keep the beam centered in the pipe so that beam atoms don't accidentally collide with the pipe walls.
So, what's the problem? Nothing. Nasty nothing. The nasty nothing that is a vacuum.
See, when the beam particle energies get high enough, sometimes a beam particle will reach into that vacuum like it was a closet and pull out a pair of brand new particles (an oppositely charged particle/anti-particle pair, usually an electron-positron pair). This is a well-tested effect of what's called the quantum vacuum energy, first predicted by Georges Lemaître in 1934. Usually, such a brand new pair of particles will annihilate themselves without any release of energy -- effectively going home, back into that vacuum closet.
Now here's the nasty part. In a beam environment like the LHC, the boys worried that when a new pair was pulled out of the closet the positron would immediately fly off (and not be much of a problem, it's too light). But the electron would glom onto one of the beam particles. That would change the particle's charge. That would change the particle's direction, and it too would fly off -- hitting the beam pipe. And with a heavy particle, that would cause the pipe to heat up a tiny amount. So, what's nasty? The number of beam particles that this would happen to. The amount of heating. If there is a bit too much, then the super-cooled superconductors no worky. And the plan is to have them at 1.9 K -- super-cold.
To figure out how much heating (or whether they were just screwy wrong), the boys at LHC took a trip to visit the boys at the Brookhaven Lab on Long Island where the fairly new Relativistic Heavy Ion Collider (RHIC, "Rick") lives. The RHIC beam isn't as powerful as CERN's LHC will be. They found the heating -- a minuscule amount. But that was with a beam of middling weight copper atoms.
The bad news is that the vacuum closet's propensity to open up scales as the seventh power of Z (i.e., Z times Z times Z times Z times Z times Z times Z), the number of protons in the nucleus. Copper's Z is 29. Lead's Z is 82. That means about a 1,500 times bigger effect. The vacuum closet also opens easier with higher energies. LHC will be running about 100 times higher energy beams than RHIC. So the boys expect over 100,000 times more heating than seen at RHIC.
What does it all mean? The LHC boys will have to add extra cooling, because of something from nothing.[Ed.: Click on the title to see the full post]
Thursday, February 14, 2008
Something From Nothing
4 comments:
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Man, I really haven't kept up properly. I wasn't aware of spontaneous paired particle creation without a collision or a near-collision.
ReplyDeleteTrue, I had heard of such a thing near a super-heavy nucleus, such as you get briefly from low-energy collisions of heavy normal nuclei, such as two lead atoms, but I figured that was more due to the changing field densities in the collision, and not something that would happen anyway if such a thing were able to exist for more than the briefest of timespans.
Wayne, Now that my brother has retired from teaching (Astronomy) he has more time for my endless questions. I am constantly amazed at the State of the discussion in the last year or two. Hawking is using phrases like "Philosophical Physics", Einstein of course used words like spooky and Magic, particle Physics and cosmology are so seductive and amazing. Jack tells me that thanks to Hubble, regions of our universe are "visible" that indicate there are vast expanses of matter traveling far faster than the speed of light, and the universe is not only expanding, its expansion is Accelerating. He also tells me that creating mass in an accelerator is pretty old hat and that to best understand some of what is being done, it is important to entertain consciousness theories. Some folks are using this new data in some pretty interesting discussions about, well, God.
ReplyDeleteNow, see I knew that matter/antimatter creation was old news (I think it was first proven in '50s, but maybe even sooner), but I've only ever read about it being in conjunction with either a high-energy collision between particles, or the "decay" of a high-energy photon, and even that was usually in the vicinity of another particle, so that an interaction of electromagnetic fields was involved. I just hadn't heard about it happening randomly to high velocity particles without interacting with another particle in some way.
ReplyDeleteRegarding the matter traveling faster than light - I didn't get far enough in my studies (or I would be a Particle Physicist right now), so mathematically I'm not up to verifying it, but I'm skeptical of being able to observe anything that is traveling faster than light, even from the side. I suppose that if it created a disturbance in its passing, we might be able to see the effects of its passing, though.
Wayne- the part that is "new" I think is that given a high energy collision, the "creation" of new MATTER is observed, and needn't be in proximity to the collision at all; it is the "creation" that involves ethicists, physicists, and heretofore the AUDIENCE. It is unbelievably complex and incredibly simple, depending on your level of TRUST. I don't want to sound NEW AGE, it has NOTHING to do with that crap. I have about 2% figured out, or the whole thing, depending whether I'm in "church" or not.
ReplyDeleteFaster than "c" is only inferred by the observations, Wayne, sorry.