Nanocluster Collision Simulation

This result would be incredible it it were to occur on a macro-scale - It would be breaking one of the fundamental laws of physics. However, at the micro-scale, one has to take the effect of having so few atoms and having the wavefunctions of these atoms so close together in to account. Also, this “super-rebound” effect has been observed in several systems.

Resources:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PLEEE8000079000003031309000001&idtype=cvips&gifs=Yes
http://www.sciencenews.org/view/generic/id/42877/title/Nanoclusters_seem_to_skirt_physics_law

The softcore link: Lagrangian points L4 and L5 to be Explored by Twin Spacecraft

http://www.sciencedaily.com/releases/2009/04/090409153020.htm

hardcore: Predicted Exotic Gravitational Lenses

http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.1454v1.pdf

Because details are scarce in all news reports of the laser test, it is hard to say what type of laser it is. In the past chemical lasers have been the most powerful tested for military application. A friend of mine did work on something like this at Research Electro Optics - an optical component manufacturer. He took part in the manufacturing process for stackable scaling laser amplification crystals with specially design thin film coatings (applied in house). They were supposedly in the 3rd stage of testing out of 4. This particular stage focused on creating and testing a 200kW output laser using these laser amplification crystals. Although… this seems like a rather high output when considering other literature on these types of lasers.

Check out that video, though.

Apparently the reason for military investigation of this phenomenon is a funding proposal from a company called GravWave (imaginative name!), which claimed that gravitational waves of significance could be produced by humans using the Gertsenshtein effect. The Gertsenshtein effect, explained in “Wave resonance of light and gravitational waves,” by M. E. Gertsenshtein, shows how it is possible to convert electromagnetic waves into gravitational waves given a strong enough magnetic field. The resultant gravitational waves would be weak, but easy to control because the frequency is the same as that of the electromagnetic input waves.

The report, despite being a waste of time and resources, confirmed the long-held belief that “these proposals belong to the realm of pseudo-science, not science.” See the report in full, linked from the sources below.

However, any physicist remotely familiar with gravitational waves or some of our current experiments just to detect them could have told one this. Reminiscent of the “hafinum bomb” incident in the early 2000’s, military wastes in resources like this are drawing more and more criticism: A quick phone call to a physicist would have been more than sufficient, explained David Shoemaker from MIT. If more physicists were involved in day-to-day government and military operations, then surely wastes like this could be prevented.

Source:
http://www.fas.org/irp/agency/dod/jason/gravwaves.pdf
Gertsenshtein, M. E., “Wave resonance of light and gravitational waves,” Soviet Physics JETP, 14, No. 1, 84-85, (1962).
http://www.newscientist.com/article/dn16306-us-investigation-into-gravity-weapons-nonsense.html

Neutron Detector

An MIT team led by Jocelyn Monroe has found a new, more efficient method of detecting the weakly-interacting massive particle (WIMPs) that are thought to make up dark matter, which comprises up to 23% of the Universe’s total mass.

Dark matter has been an area of research recently. In particular, many are working to identify and detect the common yet elusive particles that are thought to make up the majority of it. Some scientists work from the theoretical side, producing and analyzing models that describe and put constraints on dark matter. Others are trying to observe these particles using various experiments.

The experiments that are currently underway work by detecting the light that results from dark matter colliding with normal matter. However, these flashes of light are rare and hard to differentiate from collisions of purely normal matter. That is why large tanks of liquid, usually some sort of fluorine or chlorine based molecule, are set deep underground with a surrounding field of photomultipliers. When a dark matter particle reacts with the liquid, the photomultipliers detect the resultant flash. While most normal matter particles with interact with other normal matter particles in the ground around the tank, a few make it through and interact with the liquid to produce a false detection. These few particles far outnumber the dark matter particles, though: “…ordinary collisions should happen about 10 billion billion times (19 orders of magnitude) more often than the dark-matter collisions.”

That is why Monroe’s team proposes placing a second detector, which only detects neutrons from normal matter collisions, to characterize the background. This background noise is then compared to the collisions detected by the large tank of liquid and photomultiplier tubes, and all collisions due to normal matter are subtracted from the data. This then allows one to count only those collisions due to dark matter.

Although there are many dark matter particle candidates, experimentalists have yet to directly observe such a candidate in one of these detectors. The few possible observations of dark matter collisions that have occured are as of yet unconfirmed. However, Monroe stated, “I think probably in the next five years, someone will see a candidate.”

Sources:
http://web.mit.edu/newsoffice/2008/dark-matter-tt1210.html

However, the possibilities of many of the 331 detected exoplanets being habitable remains low, mostly due to these and accompanying characteristics. A new hypothesis paper by Bloh W. et al (nice names, source at bottom), suggests there is a much greater probability than previously thought. In their astrobiology paper they propose a thermal evolution model based on a star similar to the Sun and a planet with 10 times Earth mass.

Their model describes the photosynthetic biomass production (PBP) for the planet from a main sequence star like the Sun that becomes a red giant in its later life. They examined biogeochemical, geodynamical, and climatological processes that contribute to PBP. In particular, they paid special attention to all carbon processes, like the carbon-silicate one that is so important to homeostasis on Earth. They make extensive use of previous models, with slight modifications.

They found, like some other previous models, that planetary characteristics like overall continental area were the most important factors in habitability and PBP. Bloh et al state, “Habitability was found most likely for water worlds.” This is apparently the case for both pre red giant and red giant Sun like stars. For stars with a mass greater than that of the Sun, they found that the evolution will occur more rapidly, resulting in stricter temporal and spatial constraints on habitability, especially in the red giant phase.

Personally, I’m pretty hopeful for the widespread existence of life throughout the Universe. This paper puts together a good comprehensive model with conclusions that lean toward my hope. Check out the paper below, on arXiv.

Source:
Bloh W., Cuntz M., Schroder K.P., Bounama C., Fracnk S. Habitability of Super-Earth Planets around Other Suns: Models including Red Giant Branch Evolution. arXiv.org 12/4/08.

A direct consequency of the theory of general relativity, GWs are small perturbations in space-time. Because nothing travels faster than light, changes in a gravitational field must also propagate at or below this speed. These waves are analogous in many ways to electromagnetic waves, leading many to talk about them as the theory of gravitational radiation. GWs have not been directly observed to date, but are a subject of intense research and debate amongst the scientific community. Many are excited because they think we are close to detecting these GWs. Several experiments that are currently underway to accomplish this goal:

LIGO - Laser Interferometer Gravitational Wave Observatory

VIRGO - kilometer scale Michelson interferometer with Fabry-Perot arms in Italy

GEO - German/UK experiment

LISA - Laser Interferometer Space Antenna

While many sources of GWs are subject to investigation, those that are generated by rotating neutron stars are some of the most promising.

A paper by Worley, Krastev, and Li entitled Nuclear Constraints on gravitational waves from rapidly rotating neutron stars, recently submitted to Arxiv, explores what these GWs would be like. In particular, they determine a theoretical upper limit on the strain-amplitude of GWs emitted by rapidly rotating neutron stars. For a full explanation of strain-amplitude, see source number 2.

Their establishment of the upper limit of this property makes it easier to predict what GWs will look like in the vicinity of Earth for the fastest pulsars currently known of. They end their paper by saying, “These predictions serve as the first direct nuclear constraint on the gravitational waves from rapidly rotating neutron stars.” With a little luck and a lot more hard work, gravitational waves from all types of sources will soon be directly observed.

Sources:
1. Worley A., Krastev P.G., Li Bao-An. Nuclear Constraints on Gravitational waves from rapidly rotating neutron stars. Arxiv December 2, 2008
2. Plamen G. Krastev, Bao-An Li, and Aaron Worley, Phys. Lett. B 668, 1 (2008).

Diagram of experimental setup, Credit: Noginov et al.

Metamaterials are engineered media that have many unique electromagnetic properties. Among these exotic properties is the possibility of a negative index of refraction, while most materials have a positive index of refraction. This leads to several interesting implications:

The doppler shift is reversed

Wave fronts move opposite to the flow of energy

Snell’s law is reversed

Because of these unusual properties, several potential applications have been proposed, such as

Optical Cloaking

Nanolasers

Subdiffraction resolution imaging (very precise microscopes)

However, most metamaterials constructed this far have been fundamentally limited by the amount of absorption loss they exhibit. This means that most of the light does not make it through, rendering these metamaterials unsuitable for application. Recent publications have shown that one solution to this problem is to add a dielectric material with an optical gain adjacent to the metamaterial [1]. However, this wasn’t experimentally verified until now.

Just published in Physical Review Letters is a paper entilted Stimulated Emission of Surface Plasmon Polaritons by M. A. Noginov et al. In it they report upon the experimental observation of compensation for absorption loss via stimulated emission of surface plasmon polaritons.

Surface plasmon polaritons are quasiparticles generated by the coupling of light with surface plasmons. Surface plasmons are quantum of plasma oscillations, analagous to the quantized portions of light called photons, that are confined to the surface of a material. When these surface plasmons interact with light, they create the polaritons. These polaritons, described by Noginov et al as “electromagnetic waves coupled to oscillations of free-electron plasma,” are emitted at optical frequency. This is the mechanism utilized for optical gain in the adjacent dielectric.

They conclude their paper by saying, “The demonstrated phenomenon adds a new stimulated emission source to the toolbox of nanophotonic materials and devices..” Not only does this experimental demonstration allow the possibility of future applications of metamaterials to take advantage of the previously mentioned properties, but it has significantly improved understanding fo the proposed theories behind the phenomenon. For more information, see the paper listed below [2].

Sources:
[1] I. Avrutsky, Phys. Rev. B 70, 155416 (2004).
[2] M.A. Noginov et al, Stimulated Emission of Surface Plasmon Polaritons. PRL 101, 226806 (2008).

A new paper by Leonid Marochnik, Daniel Usikov, and Grigory Vereshkov suggests that dark energy maybe be the third macroscopic quantum effect, after superfluidity and superconductivity. Dark energy is a theoretical form of energy that causes the rate of expansion of the Universe to speed up. In terms of total mass-energy present in the Universe, it is thought to account for up to 74% of it.

Current models that attempt to explain dark energy include Lambda-CDM (Cold Dark Matter) and Quintessence. Lambda-CDM includes a cosmological constant that describes this dark energy as a vacuum energy that fills fills all space. It is called the standard model of cosmology, as it is the most widely accepted model. Quintessence, on the other hand, explains dark energy as a scalar field with density and equation of state that varies throughout spacetime. Neither, however, have been proven to a satisfactory degree of validity. Also, neither can explain exactly why dark energy exists.

Marochnik, Usikov, and Vereshkov dub their theory “Lambda-GCDM” where the added G stand for gravity. Gravity is incorporated into the existing Lambda-CDM model by interpolating exact solutions of one-loop quantum gravity. Loop quantum gravity is a proposed theory that attempts to reconcile quantum mechanis with general relativity.

While their 92-page paper covers many possibilities and makes many points, they clearly express the view that their calculations point towards dark energy consisting of a “graviton-ghost condensate,” and that “a graviton-ghost condensate played a measurably significant part in shaping global cosmological dynamics.” Identifying this component of dark matter is critical, they say, and could be accomplished by exploring the area of possible transition in differing red-shifts. This is the point at which any graviton-ghost condensate would change from it’s pre-asympotitc state to its asymptotic state. More on this later, once I learn exactly what it entails…

They are able to show that their model is consistent with existing observational data on dark energy extracted from the Hubble diagram for supernovae SNIa. They also argue that their model has several advantages over Lambda-CDM. However, they concluded by saying the next step in determining their theory’s viability will be to conduct numerical experiments with the BBGKY(Born, Bogoliubov, Green, Kirkwood, and Yvon) chain, taking into account non-relativistic matter. This modification and expansion of currently accepted models could be a great step forward, depending on peer reviews of it.

Actual paper in sources below.

Sources:
Marochnik L, Usikov D, Vereshkov G. Graviton, Ghost and instanton condensation on horizon scale of the Universe. Dark energy as Macroscopic Effect of Quantum Gravity. Arxiv.org Nov 27, 2008
http://www.astronomytoday.com/cosmology/quintessence.html/

Dark Matter Particle Candidates

No one knows what dark matter is exactly. Whatever dark matter is, though, we do know that it is affecting everything on a universal scale. Dark matter interacts gravitationally with other particles in the universe, but does not interact with electromagnetic radiation (light). This makes it impossible to observe directly. At the moment there are a large number of current theories as to what dark matter is, most involving some combination of MAssively Compat Halo Objects (MACHOs) and/or Weakly-Interacting Massive Particles (WIMPs). These WIMPs are thought to make up most of the dark matter throughout the Universe currently.

A new theoretical framework that explains the types of particles that comprise dark matter in our universe has been proposed by Johnathan Feng and Jason Jumar from the University of California, though. Their paper, Dark-Matter Particles without Weak-Scale Masses or weak Interactions, detailing their elegant model, was released in the most current edition of Physical Review Letters.

While their model’s theoretical particles have the correct thermal relic density, they don’t have weak-scale masses or weak interactions, making it very different from many current models. For this reason they dub it “WIMPless dark matter.” The proposed framework allows for particles masses from 10 MeV to 10 TeV with associated interaction strengths from gravitational to strong.

More traditional theory places the mass of particles comprising dark matter at 100 GeV up to 1 TeV, interacting via a weak-scale force. Because of the greater allowed range in Feng and Jumar’s framework, there is a good possibility that dark matter experiment prospects are much better than initially believed. The last part of their paper examines these different detection prospects with cross sectional scattering theory. The figure above shows several of these proposed detection prospects, plotted on a graph of J, a constant characterizing dark matter halo structure, and GeV, the mass (in energy) of the proposed particle.

They also state that, “LHC evidence .. would exclude neutralino dark matter, but favor WIMPless scenarios.” Meaning theoretical particles described in this theory would be more easily detected. However, they are only optimistic to the point of caution, saying that future experiments at the Tevatron and/or LHC could easily either favor or disfavor their model. The LHC, in particular, is poised to make big discoveries regarding so-called “4th generation” quarks and leptons, which would be a large deciding factor on this theory’s validity. Look for the confirmation when the LHC starts up again, hopefully next year.

Sources:
Feng J., Jumar J. Dark-Matter Particles without Weak-Scale Masses or weak Interactions. Phys. Rev. Lett. 101, 231301