Physics Archives

January 20, 2010December 24, 2015 by Jean Tate

What is the Boltzmann Constant?

There are actually two Boltzmann constants, the Boltzmann constant and the Stefan-Boltzmann constant; both play key roles in astrophysics … the first bridges the macroscopic and microscopic worlds, and provides the basis for the zero-th law of thermodynamics; the second is in the equation for blackbody radiation.

The zero-th law of thermodynamics is, in essence, what allows us to define temperature; if you could ‘look inside’ an isolated system (in equilibrium), the proportion of constituents making up the system with energy E is a function of E, and the Boltzmann constant (k or k_B). Specifically, the probability is proportional to:

e^-E/kT

where T is the temperature. In SI units, k is 1.38 x 10^-23 J/K (that’s joules per Kelvin). How Boltzmann’s constant links the macroscopic and microscopic worlds may perhaps be easiest seen like this: k is the gas constant R (remember the ideal gas law, pV = nRT) divided by Avogadro’s number.

Among the many places k appears in physics is in the Maxwell-Boltzmann distribution, which describes the distribution of speeds of molecules in a gas … and thus why the Earth’s (and Venus’) atmosphere has lost all its hydrogen (and only keeps its helium because what is lost gets replaced by helium from radioactive decay, in rocks), and why the gas giants (and stars) can keep theirs.

The Stefan-Boltzmann constant (?), ties the amount of energy radiated by a black body (per unit of area of its surface) to the blackbody temperature (this is the Stefan-Boltzmann law). ? is made up of other constants: pi, a couple of integers, the speed of light, Planck’s constant, … and the Boltzmann constant! As astronomers rely almost entirely on detection of photons (electromagnetic radiation) to observe the universe, it will surely come as no surprise to learn that astrophysics students become very familiar with the Stefan-Boltzmann law, very early in their studies! After all, absolute luminosity (energy radiated per unit of time) is one of the key things astronomers try to estimate.

Why does the Boltzmann constant pop up so often? Because the large-scale behavior of systems follows from what’s happening to the individual components of those systems, and the study of how to get from the small to the big (in classical physics) is statistical mechanics … which Boltzmann did most of the original heavy lifting in (along with Maxwell, Planck, and others); indeed, it was Planck who gave k its name, after Boltzmann’s death (and Planck who had Boltzmann’s entropy equation – with k – engraved on his tombstone).

Want to learn more? Here are some resources, at different levels: Ideal Gas Law (from Hyperphysics), Radiation Laws (from an introductory astronomy course), and University of Texas (Austin)’s Richard Fitzpatrick’s course (intended for upper level undergrad students) Thermodynamics & Statistical Mechanics.

Sources:
Hyperphysics
Wikipedia

January 18, 2010December 24, 2015 by Nancy Atkinson

Physicists Tie Beam of Light into Knots

The colored circle represents the hologram, out of which the knotted optical vortex emerges. Credit: University of Bristol

[/caption]
Imagine taking a beam of light and tying it in knots like a piece of string. Hard to fathom? Well, a group of physicists from the UK have achieved this remarkable feat, and they say understanding how to control light in this way has important implications for laser technology used in wide a range of industries.

“In a light beam, the flow of light through space is similar to water flowing in a river,” said Dr. Mark Dennis from the University of Bristol and lead author of a paper published in Nature Physics this week. “Although it often flows in a straight line – out of a torch, laser pointer, etc – light can also flow in whirls and eddies, forming lines in space called ‘optical vortices.’ Along these lines, or optical vortices, the intensity of the light is zero (black). The light all around us is filled with these dark lines, even though we can’t see them.”

Optical vortices can be created with holograms which direct the flow of light. In this work, the team designed holograms using knot theory – a branch of abstract mathematics inspired by knots that occur in shoelaces and rope. Using these specially designed holograms they were able to create knots in optical vortices.

This new research demonstrates a physical application for a branch of mathematics previously considered completely abstract.

“The sophisticated hologram design required for the experimental demonstration of the knotted light shows advanced optical control, which undoubtedly can be used in future laser devices,” said Miles Padgett from Glasgow University, who led the experiments

“The study of knotted vortices was initiated by Lord Kelvin back in 1867 in his quest for an explanation of atoms,” addeds Dennis, who began to study knotted optical vortices with Professor Sir Michael Berry at Bristol University in 2000. “This work opens a new chapter in that history.”

Paper: Isolated optical vortex knots by Mark R. Dennis, Robert P. King, Barry Jack, Kevin O’Holleran and Miles J. Padgett. Nature Physics, published online 17 January 2010.

Source: University of Bristol

January 5, 2010December 24, 2015 by Ryan Anderson

New Pulsar “Clocks” Will Aid Gravitational Wave Detection

This illustration shows a pulsar’s magnetic field (blue) creates narrow beams of radiation (magenta). Image credit: NASA

How do you detect a ripple in space-time itself? Well, you need hundreds of precision clocks distributed throughout the galaxy, and the Fermi gamma ray telescope has given astronomers a new way to find them.

The “clocks” in question are actually millisecond pulsars – city-sized, sun-massed stars of ultradense matter that spin hundreds of times per second. Due to their powerful magnetic fields, pulsars emit most of their radiation in tightly focused beams, much like a lighthouse. Each spin of the pulsar corresponds to a “pulse” of radiation detectable from Earth. The rate at which millisecond pulsars pulse is extremely stable, so they serve as some of the most reliable clocks in the universe.

Astronomers watch for the slightest variations in the timing of millisecond pulsars which might suggest that space-time near the pulsar is being distorted by the passage of a gravitational wave. The problem is, to make a reliable measurement requires hundreds of pulsars, and until recently they have been extremely difficult to find.

“We’ve probably found far less than one percent of the millisecond pulsars in the Milky Way Galaxy,” said Scott Ransom of the National Radio Astronomy Observatory (NRAO).

Data from the Fermi gamma-ray space telescope, which started collecting data in 2008, have changed the way millisecond pulsars are detected. The Fermi telescope has identified hundreds of gamma-ray sources in the Milky Way. Gamma rays are high-energy photons, and they are produced near exotic objects, including millisecond pulsars.

“The data from Fermi were like a buried-treasure map,” Ransom said. “Using our radio telescopes to study the objects located by Fermi, we found 17 millisecond pulsars in three months. Large-scale searches had taken 10-15 years to find that many.”

Ransom and collaborator Mallory Roberts of Eureka Scientific used the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) to find eight of the 17 new pulsars.

Right now astronomers have only barely enough millisecond pulsars to make a convincing gravitational wave detection, but with Fermi to help identify more pulsars, the odds of detecting these ripples in space-time are steadily increasing.

Ransom and Roberts announced their discoveries today at the American Astronomical Society’s meeting in Washington, DC.

(NRAO Press Release)

November 30, 2009April 26, 2016 by Nicholos Wethington

LHC Officially Becomes Most Powerful Accelerator

Well, they’ve done it: at 2028 GMT, 29 November 2009 the Large Hadron Collider officially became the most powerful particle accelerator ever built by humans. One of the proton beams in the LHC was powered up to 1.05 teraelectron volts (TeV) at that time, and three hours later both of the beams were powered to 1.18 TeV. This breaks the previous record held by the Fermilab accelerator in Chicago, which has held the record of .98 TeV since 2001.

Despite the initial problems that the largest scientific instrument ever built had this past year, things seem to be progressing smoothly. Last week, the proton-proton beams were collided for the first time. This latest record accelerated the protons to 0.9997 times the speed of light.

No new collisions were seen at this latest milestone, as it is just part of the process of powering up the beams to the projected 7 TeV needed for the first experiments of next year. Each beam will be powered up to 3.5 TeV to smash protons in order to re-create the conditions that existed near the time of the Big Bang, and help physicists understand the fundamental nature of matter. The 7 TeV goal should be reached by the end of December, and the first collisions at the amazing energies of the LHC will occur in early 2010.

Director-General of CERN Rolf Heuer said the recent progress has been fantastic. “However, we are continuing to take it step by step, and there is still a lot to do before we start physics in 2010,” he said. “I’m keeping my champagne on ice until then.”

The LHC, is a 27 km (17 mile) long circular tunnel composed of super-cooled, superconducting magnets that runs underneath the town of Geneva, Switzerland. By colliding protons together at such energetic speeds, some fundamental questions about what matter is made of, and what the conditions were like around the earliest times of our Universe may be answered.

You can follow further advancements of the LHC at CERN’s site, on Twitter or right here at Universe Today!

Source: CERN

November 23, 2009April 26, 2016 by Nancy Atkinson

First Collisions for the LHC

Screens showing two beams in the LHC. Credit: CERN

[/caption]

Two beams circulated simultaneously inside the Large Hadron Collider for the first time today, allowing for the first proton-proton collisions to take place. “It’s a great achievement to have come this far in so short a time,” said CERN Director General Rolf Heuer. “But we need to keep a sense of perspective – there’s still much to do before we can start the LHC physics program.”

The beams crossed at points where various detectors are stationed. The beams were made to cross at point 1, where the ATLAS all purpose detector is located, then at point five at the CMS (Compact Muon Solenoid) detector. Later, beams crossed at points 2 and 8, where the ALICE (heavy ion detector) and the LHCb (looking for heavy particles containing a bottom quark) are positioned.

The first collisions are allowing operators to test the synchronization of the beams.

“This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years’ work by the international community to build a machine and detectors of unprecedented complexity and performance,” said ATLAS spokesperson, Fabiola Gianotti at a press conference today.

“The events so far mark the start of the second half of this incredible voyage of discovery of the secrets of nature,” said CMS spokesperson Tejinder Virdee.

“It was standing room only in the ALICE control room and cheers erupted with the first collisions” said ALICE spokesperson Jurgen Schukraft. “This is simply tremendous.”

“The tracks we’re seeing are beautiful,” said LHCb spokesperson Andrei Golutvin, “we’re all ready for serious data taking in a few days time.”

The first collisions come just three days after the LHC restart. Since the start-up this weekend, the operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV (gigaelectron volts). The beam lifetime has gradually been increased to 10 hours, and today beams have been circulating simultaneously in both directions, still at the injection energy.

Next on the schedule is an intense commissioning phase aimed at increasing the beam intensity and accelerating the beams. If everything goes as planned, everyone at CERN hopes to obtain good quantities of collision data for all the experiments’ calibrations by Christmas, when the LHC should reach 1.2 TeV (terraelectron volts) per beam.

Source: CERN

November 19, 2009December 24, 2015 by Nancy Atkinson

Large Hadron Collider Could Re-Start This Weekend

Particle Collider — Today, CERN announced that the LHCb experiment had revealed the existence of two new baryon subatomic particles. Credit: CERN/LHC/GridPP

The Large Hadron Collider (LHC) could be re-started on this Saturday morning CERN officials said. Engineers are preparing to send a beam of sub-atomic particles around the 27km-long circular tunnel, which has been shut down since an accident in September 2008. Scientists hope to create conditions similar to those present moments after the Big Bang in search of the elusive Higgs particle to shed light on fundamental questions about the universe.

The massive “Big Bang Machine” as it’s been called is located on the French-Swiss border and is operated by the European Organization for Nuclear Research (CERN)

Watch an animated movie from CERN that explains how the LHC works.

1,200 superconducting magnets arranged end-to-end in the underground tunnel bend proton beams in opposite directions around the main “ring” at close to the speed of light.

At allotted points around the tunnel, the proton beams cross paths, smashing into one another. Physicists hope to see new sub-atomic particles in the debris of these collisions.

The LHC had only recently been turned when on Sept. 19, 2008 a magnet problem called a “quench” caused a ton of liquid helium to leak into the tunnel.

Liquid helium is used to cool the LHC to an operating temperature of 1.9 kelvin (-271C; -456F).

Low-energy collisions are expected a week or two after full beam. High energy collisions will take place starting in early 2010.

Source: BBC

November 9, 2009December 24, 2015 by Nicholos Wethington

Physicist Vitaly Ginzburg Dies at age 93

Vitaly Ginzburg, a Russian physicist and Nobel laureate, died yesterday of cardiac arrest. He was 93 years old. Ginzburg shared the 2003 Nobel Prize in physics for his work on superconductors, but contributed to many other fields of study, including quantum theory, astrophysics, radio-astronomy and diffusion of cosmic radiation in the Earth’s atmosphere. In addition, he is known for his contributions to the development of the Russian hydrogen bomb in the 1950s, for which he received the Stalin Prize.

Ginzburg was born in 1916, before the Bolshevik Revolution, to a Jewish family in Moscow. He lived through the hardships of his childhood to enter Moscow State University in 1933, where he took up the study of physics, he wrote in his autobiography for the 2003 Nobel Prize.

Ginzburg went on to work on the hydrogen bomb during the 1950s, for which he credits his escape from Stalinist purges and anti-Semitism of the period. He became a member of the Soviet Academy of Sciences in 1953. Ginzburg later bcame editor of a leading scientific magazine on theoretical physics, Uspekhi Fizicheskikh Nauk and the head of the P.N. Lebedev Physical Institute, Moscow, Russia.

Ginzburg shared the 2003 Nobel Prize in physics with Alexei A. Abrikosov and Anthony J. Leggett for their work in the field of superconductivity, the ability of materials to conduct electricity with little or no resistance. Ginzburg also authored a book on the subject, titled On Superconductivity and Superfluidity.

His position on his role of the development of the H-bomb for Stalinist Russia is best left in his own words. Ginzburg said just last week in an interview with Physics World :

We thought at the time that we were working to prevent a monopoly on the atomic bomb – Hitler’s monopoly if he got the bomb before Stalin. The thought of what would happen if Stalin had a monopoly on atomic weapons somehow never entered my head. Scary thought. Stalin would seek to subjugate the entire world. I admit this may betray stupidity, but this stupidity was, back then, a common way of thinking in the Soviet Union.

Ginzburg will be buried Wednesday in the Novodevichye Cemetery in Moscow. To read more about Ginzburg and his long life and incredible list of achievements, see this video interview on the Nobel Prize site, and read his autobiography.

Source: AP, Nobel Prize site, Physics World

November 6, 2009December 24, 2015 by Nancy Atkinson

Bread Dropped By Bird Causes Problems for LHC

[/caption]
Yes, this headline appears to be true. A bird dropping a piece of bread onto outdoor machinery has been blamed for a technical fault at the Large Hadron Collider (LHC) this week which saw significant overheating on parts of the accelerator. The LHC was not operational at the time of the incident, but the spike produced so much heat that had the beam been on, automatic safety detectors would have shut down the machine. This would put the LHC out of action for a few days while it was restarted, but there would be no repeat of the catastrophic damage suffered last September. That’s when an electrical connection in the circuit itself failed violently, causing a massive liquid-helium leak and subsequent damage along hundreds of meters of magnets.

Hmm. The idea of a time-traveling Higgs boson coming back to prevent its own discovery is seeming less and less far fetched!

Yes, this theory was recently proposed by a pair of physicists, who suggested the hypothesized Higgs boson, which physicists hope to produce with the collider, might be so abhorrent to nature that its creation would ripple backward through time and stop the collider before it could make the discovery, like a time traveler who goes back in time to kill his grandfather.

This most recent incident won’t delay the reactivation of the facility later this month, but exposes yet another vulnerability of the what might be the most complex machine ever built.

Source: PopSci

November 2, 2009April 26, 2016 by Nancy Atkinson

Solving the Mystery of Cosmic Rays’ Origins

What accelerates cosmic rays to nearly the speed of light? Astronomer have pondered that question for nearly 100 years, and now new evidence supports a theory held for two decades that cosmic rays likely are powered by exploding stars and stellar winds. “This discovery has been predicted for almost 20 years, but until now no instrument was sensitive enough to see it,” said Wystan Benbow, an astrophysicist at the Smithsonian Astrophysical Observatory who coordinated this project for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaboration.

Nearly 100 years ago, scientists detected the first signs of cosmic rays, which are actually not rays or beams but subatomic particles (mostly protons) that zip through space at nearly the speed of light. The most energetic cosmic rays hit with the punch of a 98-mph fastball, even though they are smaller than an atom. Astronomers questioned what natural force could accelerate particles to such a speed.

The rarest cosmic rays carry over 100 billion times as much energy as generated by any particle accelerator on Earth. Astronomers have devised ingenious methods for detecting cosmic rays that hit Earth’s atmosphere. However, detecting cosmic rays from a distance requires much more effort.

This representative-color figure shows the very-high-energy gamma-ray emission observed by VERITAS coming from the Cigar Galaxy, also known as Messier 82. The black star is the location of the active starburst region. The emission from M82 is effectively point-like for VERITAS, and the white circle indicates the size of a simulated point source. The entire galaxy would be contained within the circle. Credit: CfA/V.A. Acciari

VERITAS has found new evidence for cosmic rays in the “Cigar Galaxy,” also known as Messier 82 (M82), which is located 12 million light-years from Earth in the direction of the constellation Ursa Major, which strongly support the long-held theory that supernovae and stellar winds from massive stars are the dominant accelerators of cosmic-ray particles.

Galaxies with high levels of star formation like M82, also known as “starburst” galaxies, have large numbers of supernovae and massive stars. If the theory holds, then starburst galaxies should contain more cosmic rays than normal galaxies. The VERITAS discovery confirms that expectation, indicating that the cosmic-ray density in M82 is approximately 500 times the average density in our Galaxy, the Milky Way.

“This discovery provides fundamental insight into the origin of cosmic rays,” said Rene Ong, a professor of physics at the University of California, Los Angeles, and the spokesperson for the VERITAS collaboration.

Using gamma rays to infer cosmic rays

VERITAS could not detect M82’s cosmic rays directly because they are trapped within the Cigar Galaxy. Instead, VERITAS looked for clues to the presence of cosmic rays: gamma rays. Gamma rays are the most energetic form of light, far more powerful than ultraviolet light or even X-rays. When cosmic rays interact with interstellar gas and radiation within M82, they produce gamma rays, which can then escape their home galaxy and reach Earthbound detectors.

It took two years of dedicated data collection to tease out the faint signal coming from M82.

“We knew that the detection of M82 would have important scientific implications. As a result, we scheduled an exceptionally long exposure immediately after the experiment became fully operational” said Benbow. “The data needed to be meticulously analyzed to extract the gamma-ray signal, which is over a million times smaller than the background noise. Although the signal is only a tiny fraction of the data, we made many checks for possible bias and we are confident that the signal is genuine.”

“The detection of M82 indicates that the universe is full of natural particle accelerators, and as ground-based gamma-ray observatories continue to improve, further discoveries are inevitable.” said Martin Pohl, a professor of physics at Iowa State University who helped lead the study. A next-generation VHE gamma-ray observatory, the Advanced Gamma-ray Imaging System (AGIS), is already under development.

VERITAS is operated by a collaboration of more than 100 scientists from 22 different institutions in the United States, Ireland, England and Canada. Click here for more information on VERITAS.

Lead image caption: A composite of multi-wavelength images of the active galaxy M82 from Hubble, Chandra, and Spitzer. Credit: NASA, ESA, CXC, and JPL-Caltech

Source: Harvard Smithsonian Center for Astrophysics

October 28, 2009December 24, 2015 by Nancy Atkinson

Particles Injected into Large Hadron Collider

The first ion beam entering point 2 of the LHC, just before the ALICE detector (23 October 2009). Credit: CERN

[/caption]
The Large Hadron Collider reached an important milestone last weekend as a beam of ions was injected into the clockwise beam pipe. This is the first time particles have been inside the collider since September, 2008 when physicists were forced to shut down the system because of a massive failure. According to a CERN press release, lead ions were placed in the clockwise beam pipe on Friday October 23, but did not travel along the whole circumference of the LHC. CERN officials still hope for a restart in 2009, with the first circulating beam likely to be injected in mid-November, and the first high energy collisions occurring around mid-December.

CERN said that later last Friday the first beam of protons followed the same route — and then on Saturday protons were sent through the LHCb detector.

They reported all settings and parameters showed a perfect functioning of the machine. In the coming weeks, physicists hope to have the first circulating beam. Then hunt for the elusive Higgs particle will recommence.

Here is an interview with CERN director general Rolf-Dieter Heuer about the switch-on of the LHC.

Sources: CERN, Physics World