Sound Science Bite: August 19. The Old Man and the Sea
There is a puzzle about how some microorganisms in the ocean manage to get the nutrients they need. Take the bacterium Prochlorococcus marina for example. This photosynthetic microbe is responsible for producing about 25% of the oxygen released to the atmosphere – not an insignificant contribution to life on the planet. The problem: It needs to absorb 400 million molecules of ammonium ions a day to get the nitrogen necessary to divide and reproduce, but the volume of seawater that holds that many ions is hundreds of millions of times its size. Even if it were to swim at a rapid pace for a microorganism, it would never be able to encounter that many ions.
Enter Einstein. He proved the existence of atoms and molecules to the satisfaction of the majority of scientists by studying Brownian motion. Although he didn't discover this motion (three guesses for the name of the person who did and the last two don't count), he was able to characterize it statistically to show that it could be explained by the existence of molecules. Brownian motion involves how dust particles seen under a microscope can be jiggled and moved around by collisions with molecules. Dust particles are small enough that they normally get more collisions from one direction than from another.
An article in the 2017 August 18 issue of the journal Science by Jonathan Zehr, Joshua Weitz, and Ian Joint points out that this motion solves the problem of how microbes like P. marina can get the nitrogen they need. By being jostled around by molecular collisions, these little guys can encounter four times the amount of ammonium ions necessary for reproduction. Brownian motion is important for other microbial life in the ocean also. As Zeir, Weitz, and Joint write, "[Brownian motion] alone can fuel the growth and reproductivity of abundant, free-living unicellular microorganisms in the open ocean." (Note: Einstein wasn't old but actually quite young when he published his work on Brownian motion.)
Index of Previous Sound Science Bites
Science News from the American Association for the Advancement of Science
I-10, On Road To Big Bend
Thrust Fault On Us 90
South Rim Trail - Intruded Sediments
South Rim - Igneous Intrusions
Boquillas Canyon Fault
Fossil Near Hot Springs
Volcanic Rock In Tuff Canyon
Rio Grande Terraces
Burro Mesa Pouroff
Inside A Thrust Fault At Dog Canyon
Faulted Fold At Persimmon Gap
Lava Flow Over Alluvium, Rancherias Canyon
Sitting On A Dike By A Fault Scarp- Lost Mine Trail
Native American Petroglyphs - Chimneys
Oak Creek Pouroff - Only Water Outlet From The Basin
Carousel Mountain - Dodson Trail
Del Rio Clay On Santa Elena Limestone - Ernst Tinaja
Calcite Crystals - Near Mule Ear Peaks
On Mesa De Anguila
Pliocene-Miocene Contact - Estufa Canyon
"Hitchcock Rock" - Blue Creek Canyon
Outcrop - Telephone Canyon
Septarian Concretions - Banta Shut-In
Giant Dagger at Devils Den
Mule Ear Peaks
Thrust Fault Drag Folds - Strawhouse Trail
Dike Swarm Radiating from Dominguez Mountain
"You can have my rock hammer when you pry it from my cold, dead fingers."
I am in the process of adding new material and revising most if not all of the virtual field trips now that the new USGS geological map has been published.
Redfern, F. Eur. Phys. J. D (2017) 71: 325.
Magnetic coils in electric fields contain no hidden momentum.
There is no charge separation on a moving magnetic dipole. The apparent presence of charge is due to the relativity of simultaneity. An electric dipole does not appear on a moving magnetic dipole and a magnetic dipole does not appear on a moving electric dipole. I argue that the magnetization-polarization tensor is not a genuine four-tensor and is not a valid way to find transformed fields. Only the Lorentz transformation of fields directly can give the correct transformed fields.
Redfern, F. Eur. Phys. J. D (2017) 71: 163.
In 1967 Shockley and James addressed the situation of a magnet in an electric field. The magnet is at rest and contains electromagnetic momentum, but there was no obvious mechanical momentum to balance this for momentum conservation. They concluded that some sort of mechanical momentum, which they called “hidden momentum”, was contained in the magnet and ascribed this momentum to relativistic effects, a contention that was apparently confirmed by Coleman and an Vleck. Since then, a magnetic dipole in an electric field has been considered to have this new form of momentum, but this view ignores the electromagnetic forces that arise when an electric field is applied to a magnet or a magnet is formed in an electric field. The electromagnetic forces result in the magnet gaining electro- magnetic momentum and an equal and opposite amount of mechanical momentum so that it is moving in its original rest frame. This moving reference frame is erroneously taken to be the rest frame in studies that purport to show hidden momentum. Here I examine the analysis of Shockley and James and of Coleman and Van Vleck and consider a model of a magnetic dipole formed in a uniform electric field. These calculations show no hidden momentum.
Physica Scripta, Volume 91, Number 4.
In 2013 an article published online by the journal Science declared that the paradox proposed by Masud Mansuripur was resolved. This paradox concerns a point charge-Amperian magnetic dipole system as seen in a frame of reference where they are at rest and one in which they are moving. In the latter frame an electric dipole appears on the magnetic dipole. A torque is then exerted upon the electric dipole by the point charge, a torque that is not observed in the at-rest frame. Mansuripur points out this violates the relativity principle and suggests the Lorentz force responsible for the torque be replaced by the Einstein–Laub force. The resolution of the paradox reported by Science, based on numerous papers in the physics literature, preserves the Lorentz force but depends on the concept of hidden momentum. Here I propose a different resolution based on the overlooked fact that the charge-magnetic dipole system contains linear and angular electromagnetic field momentum. The time rate of change of the field angular–momentum in the frame through which the system is moving cancels that due to the charge-electric dipole interaction. From this point of view hidden momentum is not needed in the resolution of the paradox.
A discussion of this paradox and momentum flow
I show that the usual harmonic plane-wave equation can be derived from kinematic principles only; that is, requiring the wave to propagate without changing shape in a non-dissipative medium. Not only can the usual second order wave equation be acquired this way, but also an equation that is quadratic and of first order. These equations have a common set of solutions. The second-order equation corresponds to the restoring forces of a physical medium whereas the first-order quadratic equation corresponds to energy in a conservative medium. Properties of electromagnetic waves, including energy conservation (Poynting's theorem) and radiation pressure can be obtained from this kinematic approach.