LIGO detects first ever gravitational waves

gravitational waves
The first ever direct detection of gravitational waves has been made by researchers working on the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) in the US. The breakthrough - announced today at a news conference in Washington, DC - ends a decades-long hunt for these ripples in space-time. This monumental observation marks the beginning of the era of gravitational-wave astronomy and provides evidence for one of the last unverified predictions of Einstein's general theory of relativity.

The waves were produced from the collision of two black holes of 36 and 29 solar masses, respectively, which merged to form a spinning, 62-solar-mass black hole, some 1.3 billion light-years (410 mpc) away in an event dubbed GW150914. The detection was made on 14 September last year and was measured while the newly upgraded aLIGO detectors - one in Hanford, Washington, and the other in Livingston, Louisiana - were being calibrated before the first observational run began four days later.


Can four neutrons tango?

Can four neutrons tango?
Evidence that the four-neutron system known as the tetraneutron exists as a resonance has been uncovered in an experiment at the RIKEN Radioactive Ion Beam Factory.

The fundamental ingredient for constructing a nucleus from scratch is the force between two nucleons. The most attractive interaction occurs between the proton and neutron, as evidenced by the ground state of the deuteron, which is bound by 2.2 MeV. In contrast, bound states of two protons ( 2He) or the "dineutron" ( 2n) do not exist, although the latter falls short by only some 100 keV. Intriguingly, however, theoretical models have revealed in recent years the importance of three-body and other multinucleon forces in binding light nuclei. As such, the question of whether a four-neutron system, or "tetraneutron", exists may be posed. Tantalizing evidence for the tetraneutron, in the form of a resonant, or unbound, state, has been uncovered in an experiment performed at the RIKEN Radioactive Ion Beam Factory (RIBF), in Saitama, Japan . Confirming this finding has the potential to change our understanding of nuclear interactions and provide a new window into the physics of few-body systems.


Pure quantum-mechanical mixture of electrons and photons demonstrated in bismuth selenide

Nano microchip from bismuth selenide
In 2013, MIT physicists showed for the first time that shining powerful mid-infrared laser light on solid bismuth selenide produces Floquet-Bloch states, which are characterized by replicas of electronic energy states inside a solid with gaps opening up at crossing points of replica states. The same external light also interacts with free electron states immediately outside the solid producing a competing state, called the Volkov state, which is gapless.

Now, researchers led by Nuh Gedik, the Lawrence C. (1944) and Sarah W. Biedenharn Career Development Associate Professor of Physics, have shown that changing the light's polarization eliminates competition from Volkov states, yielding pure Floquet-Bloch states.


Researchers discover new fundamental quantum mechanical property

new fundamental quantum mechanical property
Nanotechnologists at the University of Twente research institute MESA+ have discovered a new fundamental property of electrical currents in very small metal circuits. They show how electrons can spread out over the circuit like waves and cause interference effects at places where no electrical current is driven. The geometry of the circuit plays a key role in this so called nonlocal effect. The interference is a direct consequence of the quantum mechanical wave character of electrons and the specific geometry of the circuit. For designers of quantum computers it is an effect to take account of. The results are published in the British journal Scientific Reports.

Interference is a common phenomenon in nature and occurs when one or more propagating waves interact coherently. Interference of sound, light or water waves is well known, but also the carriers of electrical current - electrons - can interfere. It shows that electrons need to be considered as waves as well, at least in nanoscale circuits at extremely low temperatures: a canonical example of the quantum mechanical wave-particle duality.


A new way of defining temperature?

caesium atoms
Atoms wriggle - they can't help themselves. And the warmer they are, the faster they writhe. By using lasers to measure how fast atoms of the element caesium zip around a vacuum chamber, Australian scientists have shown they can calculate the sample's temperature. The super-accurate technique could be adopted as the basis of a new definition for the standard unit of temperature, the Kelvin. The work was reported in Nature Communications in October.

The International Bureau of Weights and Measures has for decades sought to redefine the seven key units of scientific measurement - a group that includes the kilogram and the metre, as well as the Kelvin - based on fundamental constants. Traditionally, many such measurements have been based on a physical object. The definitive metre, for example, was a metal bar kept by the International Bureau of Weights and Measures in Paris. But that method of defining a metre was inconvenient for anyone trying to calibrate a metre ruler elsewhere in the world. Today the metre is defined as the distance light travels in a vacuum in 1/299,792,458 of a second - a measurement many modern labs can carry out.


Physicists struggle to squeeze new particles from the LHC

Large Hadron Collider
It's a fairly silent night as the Large Hadron Collider shuts down for the holidays. Particle physicists at CERN today presented the first results since the LHC was switched back on for its second run, but had no discoveries to report.

Instead, early hints of new physics from the end of the LHC's first run seemed to drop away. But there is one glimmer of hope: a glimpse of a possible new particle.

With rumours of new particles flying around earlier in the week, physicists were crammed into the main lecture hall at CERN - the location of the announcement of the Higgs boson discovery in 2012. But this time there were no early Christmas presents.


Fifty shades of black

Fifty shades of black
Creating dark materials that prevent reflections has become hot competition recently, with Guinness World Records having to keep revising the darkest substance yet created. But depending on who's asking, the best black may not be the blackest black, as Jon Cartwright discovers/

For domestic use, options abound. Pitch black, jack black, lamp black, fine black, velour black, onyx black, blackboard black, black fossil, charcoal, soot, smoke, sinner, black stillness, off black, little black dress, penny black, deep black and - should you want to be left in no doubt - black black.

There are probably 50 shades of black, if not more. But sometimes, and especially where physicists are concerned, even the blackest black isn't black enough.


Electron lifetime is at least 66,000 yottayears

The best measurement yet of the lifetime of the electron suggests that a particle present today will probably still be around in 66,000 yottayears (6.6 x 1028 yr), which is about five-quintillion times the current age of the universe. That is the conclusion of physicists working on the Borexino experiment in Italy, who have been searching for evidence that the electron decays to a photon and a neutrino; a process that would violate the conservation of electrical charge and point towards undiscovered physics beyond the Standard Model.

The electron is the least-massive carrier of negative electrical charge known to physicists. If it were to decay, energy conservation means that the process would involve the production of lower-mass particles such as neutrinos. But all particles with masses lower than the electron have no electrical charge, and therefore the electron's charge must "vanish" during any hypothetical decay process. This violates "charge conservation", which is a principle that is part of the Standard Model of particle physics. As a result, the electron is considered a fundamental particle that will never decay. However, the Standard Model does not adequately explain all aspects of physics, and therefore the discovery of electron decay could help physicists to develop a new and improved model of nature.