Assorted links

Comments

Considering that E&M is easily formulated in a manifestly Lorentz-invariant way, it most certainly does not contradict special relativity. Perhaps some textbook statement disagrees because it's oversimplified or wrong. But E&M can be considered to define special relativity, as far as I'm concerned.

There's no way Tyler does his own grocery shopping - at the rate at which he posts on MR, how does he have the time????

In the not so distant future, we will find that Tyler is a Robot and his 'eating' is really just chemical compound derivation.

He has a time machine. But he only uses it to get fresh baguettes.

I looked at the write-up and indeed no one is claiming a violation between electromagnetism and special relativity. The question seems to involve how we describe the electromagnetic interactions of macroscopic objects: these aren't really derived directly from the theory but involve some additional assumptions (stemming from the simple fact that macroscopic objects have trillions and trillions of particles and we can't solve so many equations at once). Perhaps there is some issue with some of those assumptions, though I'm skeptical even of that, given the extent to which electromagnetism has been studied and used in the lab and day-to-day applications.

I have not read the article yet. In that area there is a lot of room for arguing about nothing because there is no one right way to divide up energy and momentum between the EM field and the medium. Is the momentum of a photon in a material n*h/lambda_vac or h/n*lambda_vac? Both are right depending on how you define things.

And to think I read the physics article to get away from all the econ blogosphere debate about micro foundations of macro phenomena...

" “The microscopic picture of electrodynamics is clear,” James says, “and if the macroscopic picture of electrodynamics doesn't follow from that, I'd be surprised.” Somehow, the Einstein-Laub equation for macroscopic materials must follow from the Lorentz force applied on the microscopic level, he says. Barnett says “there's going to be a heated debate about this result.” Undoubtedly."

For people outside of university interwebs, the link for #2 seems to be http://arxiv.org/abs/1205.0096

@MPS: the claim in the abstract is that there is a flaw in the Lorentz Force law. F=qE + v x B is hardly explicitly covariant so maybe there is a subtle flaw. Indeed talking about forces on point particles like this always seems a bit dodgy. I would say the "real" force law the relations between currents densities, fields and their energy-momentum tensors.

Thanks for the link.

I've had those hooks for years. If you use plastic grocery bags, perfect. If you're one of those people that re-uses fabric bags, you'll find those have handles that are often too long to work with the hook as you'll be dragging your bags on the ground. So you'll have to decide which is more important - the ability to haul lots of groceries on a single walking trip, or the environment. :)

2. That's interesting, a scientist in his 70s named Johann Prins who worked for DeBeers and claims to have found a way to make superconducting diamond has made a similar claim.

FYI, the full paper is available at http://arxiv.org/abs/1205.0096

After reading the paper, and with my limited understanding of EM fields (BA in electrical engineering), it seems plausible, but like Tyler, I had a little trouble following the details. The gist of Mansuripur's argument is that there are scenarios of charge + EM field that, using the Lorentz formula, generate a torque in a stationary frame of reference that do not generate a torque in a frame of reference that moves with the charge and EM field. This extra torque is a violation of relativity.

Mansuripur also notes in his paper, that there is some experimental evidence against the formulation he proposes, but that the type of measurements required are notoriously difficult to make.

I recall seeing the hooks many moons ago on Letterman with "kid inventors." Not sure if the kid/parent cashed in, or someone watching did.

I was surprised to see this in the financial times:

http://www.ft.com/intl/cms/s/0/ab2ac432-92ea-11e1-b6e2-00144feab49a.html#axzz1tq5amMxp

I wasn't impressed by Ron Paul in the Krugman debate...but in this op-ed he destroys any Krugman article I have ever seen.

Ron Paul was impressive in his debate with Paul Krugman in that Ron Paul has thought about a small piece of the puzzle that Paul Krugman is a one-trick pony in (liquidity trap). PK thinks he knows the only thing he needs to know about money (liquidity trap) and thus they really had nothing to debate.

The paper looks fishy to me just on purely formal criteria. Out of a total 23 citations, 9 are his own works, most of them solo and published in obscure journals, and 5 are textbooks. He cites Einstein. He talks about hidden momentum and cites Shockley, but does not cite Comay (1996) which resolves the hidden momentum paradox and which I found online in under 2 minutes by googling "hidden momentum". He explains at length stuff that does not need to be explained, like properties of delta functions. His notation is archaic. Preliminary diagnosis: a typical case of elderly applied physicist's fundamentalitis.

Agreed! All very good observations! The form and language of sensational papers are a good heuristic to sniff out the wackos.

The paper is "correct", but it actually finds a notational problem already discovered many years ago. Maxwell's equations in a medium tend to be written in a metric-less form in most textbooks -- by doing so there is an implicit assumption that the polarizing medium is at rest. A fully covariant treatment adds in the fact that the E, B fields form a 2nd rank covariant tensor while the D, H fields form a 2nd rank contravariant tensor density of weight +1 (and thus it a factor of the metric that cancels the inconsistency when Mansuripur goes from one frame to another). There is a cool paper that explains this really well ...

http://rmp.aps.org/abstract/RMP/v39/i2/p475_1

Read MPS and Adrian Ratnapala above for comments that I also agree with, but unlike many contrarian physics claims of late, there may actually be something interesting here!

Maxwell's equations in matter were formulated in the 1860s or shortly thereafter, and included a Lorentz force. Einstein comes along in 1905 with special relativity (SR). Someone could have piped up back then and done the calculation in Mansuripur's paper from 2012 and said: look at this incompatibility! Like the ultraviolet catastrophe for atoms + E&M, the violation of SR + E&M (in matter) implies the existence of some underlying theory (quantum field theory -- required for the existence of point-like neutral electric dipoles that violate PT symmetry; fundamental magnetic dipoles [spin] imply the existence of antimatter via Dirac).

But instead we have things discovered in a different order: Maxwell's equations in 1865, Planck's quanta from 1900, special relativity and photoelectric effect (photons) in 1905, full quantum mechanics in the 1920s, quantum field theory by the 40s and 50s and finally coming to Mansuripur's paper in 2012. The result? Ho hum. We know that there are more fundamental physical laws so this is probably a result of making some implicit assumption.

** I do want to note that there does not appear to be a flaw coming from using the nonrelativistic formulation. Even starting from the tensor notation
[ http://en.wikipedia.org/wiki/Lorentz_force#Field_tensor ] you would still have a problem since the inconsistency likely derives from introducing a field that consists of fundamental magnetic dipoles (made of particles with spin). So the H field source could not be completely general since it does not contain spin-1/2 particles and spin-1/2 particles combined with relativity gets you things like the Dirac equation and antimatter. Interestingly spin-1/2 particles are what is required for matter to exist -- bosons in atoms would drop down into the lowest levels and we'd have no chemistry. Maybe we could say that Maxwell's equations in matter with special relativity imply the existence of matter!

IIf this is right, there should be another paper and another formulation of the inconsistency where there is an electric dipole; a field of fundamental electric dipoles violates PT symmetry and hence implies CP violation also requiring quantum field theory to treat properly.

It appears you don't need to resort to an underlying theory to explain the problem. Maxwell's equations in matter are not relativistically invariant since they make the implicit assumption that the medium is at rest and the assumption that D = E and H = B in free space represents this preferred choice of frame.

Mathematically, the E & B fields form a covariant tensor, while the D & H fields form a contravariant tensor density of weight +1. There is a factor due to the metric (from the tensor density) that removes the difference between the calculations in one frame vs another. The statement: "Two other 2nd rank tensors that obey the Lorentz transformation rules are the field tensors, one formed by E and B, the other by D and H [1, 3, 4]." in the paper is false.

Specifically, the problem set up should exactly demonstrate this deficiency: a dipole in a moving frame while the observer is at rest.

Interestingly, this is important in the Sagnac effect.

http://rmp.aps.org/abstract/RMP/v39/i2/p475_1

Re: the grocery bag holders. I coincidentally spoke to the manager of a retail chain recently who has had a patent troll force them to remove them from the shelves.

So funny. On the silly site they posted you cut a slit in some 3/4" PVC pipe. Of course the problem is having the mental bandwidth to remember to have these things on hand, but I've made this kind of handle for buckets and the like before. Patents really have jumped the shark.

Then there are these.

http://www.harborfreight.com/8-inch-jumbo-aluminum-hook-95327.html

My wife got a set of the bag carriers some years back. They're great.

By the way, we have a really high demand for gold right now.

Is that demand for gold causing our current recession, or is it an effect?

Comments for this post are closed