New experiments challenge fundamental understanding of electromagnetism

Phys.org ^ | November 28, 2012 | NA

[neverdem]

A cornerstone of physics may require a rethink if findings at the National Institute of Standards and Technology (NIST) are confirmed. Recent experiments suggest that the most rigorous predictions based on the fundamental theory of electromagnetism—one of the four fundamental forces in the universe, and harnessed in all electronic devices—may not accurately account for the behavior of atoms in exotic, highly charged states.

The theory in question is known as quantum electrodynamics, or QED, which physicists have held in high regard for decades because of its excellent track record describing electromagnetism's effects on matter. In particular, QED has been especially useful in explaining the behavior of electrons, which orbit every atomic nucleus. But for all of QED's successes, there are reasons to believe that QED may not provide a complete picture of reality, so scientists have looked for opportunities to test it to ever-increasing precision.

One way to test parts of QED is to take a fairly heavy atom—titanium or iron, for example—and strip away most of the electrons that circle its nucleus. "If 20 of titanium's 22 electrons are removed, it becomes a highly charged ion that looks in many ways like a helium atom that has been shrunk to a tenth its original size," says NIST physicist John Gillaspy, a member of the research team. "Ironically, in this unusual state, the effects of QED are magnified, so we can explore them in more detail."

Among the many things QED is good for is predicting what will happen when an electron orbiting the nucleus collides with a passing particle. The excited electron gets bumped up momentarily to a higher energy state but quickly falls back to its original orbit. In the process, it gives off a photon of light, and QED tells what color (wavelength) that photon will have...

[SunkenCiv]

Oooh, hey, it's one of *those* topics, but in a different sense.

Thanks neverdem.

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[SunkenCiv]

"Ere many generations pass, our machinery will be driven by a power obtainable at any point in the universe. This idea is not novel... We find it in the delightful myth of Antheus, who derives power from the earth; we find it among the subtle speculations of one of your splendid mathematicians...Throughout space there is energy. Is this energy static or kinetic? If static our hopes are in vain; if kinetic -- and this we know it is, for certain -- then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature." -- Nikola Tesla, American Institute of Electrical Engineers address, 1891

[SunkenCiv]

I was going to post a graphic from Snorgtees, which illustrates Red Badger's joke, but found this first and liked it better.

[grey_whiskers]

Removing the electrons does not affect the *nucleus*.

Think of your atom from your basic corporate logo or whereever:

The electrons are those grey things orbiting around; the red and blue balls in the center are the neutrons and protons.

Electrons have a -1 charge; each proton a +1 charge; and the neutrons are neutral (hence the name).

In any element -- that is, when left to itself, you haven't reacted it or ionized it or anything -- the atom has a 0 charge, since the number of protons and electrons is identical.

Isotopes (like the deuterium in heavy water, or like Carbon-14) differ from the ordinary element because they weigh more: but the extra weight comes from extra neutrons in the nucleus, so they are still neutral.

The trick is, when you pull away so many electrons from iron or titanium, the charge of the nucleus is still the same: so you have a whole bunch of positive charge in the middle, pulling in on just a couple of electrons: since opposites attract, the electrons move in closer to the nucleus, so the atom is "smaller" -- kind of like as the Solar System would be smaller if you got rid of every planet past Mars. (Conceptually, not mathematically, that is, since the planets are attracted by gravity, not charges...)

Full Disclosure: I have a PhD in molecular physics.

Cheers!

[grey_whiskers]

Does QED allow for relativistic effects? I recall hearing at a theoretical chemistry conference, that the color of gold was due to relativistic effects on the inner electrons; presumably, using a similarly heavy highly ionized species to "mimic" helium by drawing in the electrons, would result in very high orbital velocity; hence, room for relativistic effects?

Cheers!

[grey_whiskers]

It's not a perturbation from that perspective, and a perturbation approach wouldn't be done that way: the perturbation would treat the atom as a hydrogenic atom with Z=22, and one electron. The second electron is then added as a perturbation. Just one additional electron is still a very large effect.

I thought perturbation theory for electronic structure was supplanted by configuration interaction; and that people generally liked to use Density Functional Theory rather than actually solving for the wavefunction explicitly.

Or am I just having a senior moment?

Cheers!

[Cyber Liberty]

Just realign the Flux Capacitor and you’ll be fine....

[neverdem]

Text of Divisive Psychiatric Manual Finalized

New Bacteria Raises Concern

Making a Flu Vaccine Without the Virus

U.S. Plans for New H5N1 Science Reviews Ruffle Researchers

FReepmail me if you want on or off my health and science ping list.

[neverdem]

Thanks for the link.

[FredZarguna]

No, you are correct. DFT is preferred these days.

I was taking his observation at face value: if you regard this as a perturbation how would you approach it.

However, for hydrogenic state vectors DFT is not needed; as you know, there's an exact solution, and for helium a perturbation is OK. I haven't taught it for a long time, but IIRC, the trick is usually tuning a Z_eff for each principal quantum number (n) then the two particle wave function "isn't too bad" even for angular momentum quantum numbers that have significant penetration into the inner shells.

Of course, that starts to crap out very quickly -- like, at Lithium -- so there isn't much of even pedagogic value for multiple electron systems in perturbation theory.

[FredZarguna]

QED is fully relativistic. Historically it derived from second quantization of the Dirac equation. Recall that anti-matter came out of the Dirac equation for the electron. So did spin. In the Schroedinger/Heisenberg version of quantum mechanics neither of those things really exist. Spin was just thrown in ad hoc because it was known to be there. But you can't produce it from first principles without relativistic treatment. Anti-matter kinda surprised even Dirac. But he stuck to his guns. You can't really do pair-production, negative energy, or virtual particles in QED without a relativistic basis.

Nobody likes to remember "second quantization" anymore; it's like the Klingons in the original Star Trek. Kind of embarrassing to High Energy guys these days. I was never a High Energy Physicist. I just found it interesting. Naturally my adviser regarded courses beyond the candidacy exam not related to my field as a waste of time.

Gold. Now you are really testing my memory. But ... I do not think so. I seem to recall that if you actually do a wild-ass guess (that works surprisingly well, kind of like that neutron/proton stability model that comes from viewing the nucleus as a particle-in-a-box) you find that the inner electrons in all elements from the Lanthanides and beyond have enough energy that they have to be treated relativistically.

Gawd that is a long time ago... anyway, no, color in pure metals is a result of band theory. I believe for most metals, there are so many energy levels so close at the top of the conduction band that they radiate essentially continuously (thus appear silver, as most metals do.) Copper and Gold have some weirdness in the Fermi-levels near the top of their conduction bands that cut-off blue light.

I'll see if I can dig up a web page in a while; must help daughter with math.

[DustyMoment]

Thank you. While I grasp the concept of the nucleus remaining the same without all of those electrons that have been pulled out (I squeaked through high school chemistry, but a few lessons stuck! LOL!), what ultimately changes in the atomic structure as the result of those missing electrons? Is it less able to bond with other atoms in a molecular structure, or did I sleep through that part of ny high school chemistry class?

[FredZarguna]

Its bonding properties change. In this particular case with so many electrons gone it is going to become strongly electronegative. Like a super-duper Oxygen or Florine. It will be pulling electrons away from everything within reach.

[FredZarguna]

Oh geez. You are 100% correct! I had forgotten that the Dirac equation leads to a completely different aufbau than the Schrodinger/Heisenberg one. In addition to the Lanthanide contraction caused by relativistic effects (at least I remembered that part correctly) in Au there is an additional contraction of the 6s orbital so the 5d -> 6s transition (into the conduction band) is so small it absorbs in the blue, rather than UV and higher as is the case of the bound electron orbitals in most metals. Have a go: http://voh.chem.ucla.edu/vohtar/fall02/classes/172/pdf/172rpint.pdf.

A more lay accessible treatment is here: http://www.fourmilab.ch/documents/golden_glow/. Which has some errors (the transition is 4d->5s in Ag, not Au) but omits the complexity of band theory altogether; and seems "correct enough."

Now, that still doesn't explain Cu, and I sure don't remember any more. No time tonight, though.

Thanks. That was fun.

[thecodont]

Thanks for the fun “golden glow” link from Fermilab! I have a “Periodic Table of the Elements” calendar for 2012, and December features — what else — Au, gold.

[outofsalt]

“...still have a lot to learn about this basic force.”

I’m still trying to figure out women and, after a lifetime of study, I’m no closer to understanding them.

[DustyMoment]

Ok, I’m staying up with you so far (and removing a LOT of dust that settled on the high school chemistry information!), but I keep getting hung up on the atomic weight. Is the atomic weight based solely on the nucleus? Do the atoms have zero weight or is it too negligible to make any difference?

BTW, thanks for your patience in helping me understand this stuff. I really enjoy learning new things, no matter how many times I have learned it before!!

LOL!!

[FredZarguna]

The neutron and proton masses are both close to 940 MeV/c^2. [Neutron is actually slightly heavier.] The electron is 0.512 MeV/c^2. So, it takes ~2000 electron masses to make a nucleon mass. Since the most massive element has only slightly more than 100 electrons, the electron mass is always negligible compared to nuclear mass (in chemistry.) The biggest variation in nuclear masses actually come from averaging isotope species and (to a much smaller extent) differences in binding energy.

[RinaseaofDs]

“I’m not an electrician but it’s always seemed to me
to be somewhat anachronistic to use atomic power to
run a steam turbine to make electricity.”

Bingo. The giant energy problem of the next decade(s) ISN’T where are we going to find stuff to burn.

The problem is: Where, on a planet where only one percent of the water on it is fresh water, are we going to find sufficient water for both energy exploration AS WELL AS production.

Consider this, however:

A generator is nothing more than a piece of iron spinning inside a magnetic field. The core of the earth is made up of nickel and iron. It rotates within a giant magnetosphere. Where does that electrical current manifest itself? Does that current require water to produce?

[DustyMoment]

Thanks, again, Dr. That helps push me past the electron weight and significance issue.

Having worked in high-tech communications for decad . . . . . er, a few years, I understand some of the broader concepts of atomic theory and rudimentary physics at about a 50,000 ft. level.

While I’m not the sharpest knife in thew drawer on these issues, I’m always looking for a knife sharperner!!

:-)