What a photon it was: a 31GeV gamma ray picked up by the orbiting Fermi Telescope. Because of the timing of its arrival, an entire class of quantum gravity models suddenly seems unlikely. More data of this sort may be coming soon, as scientists have now confirmed the oldest supernova yet detected, dating from just 630 million years after the big bang.
One of the awkward aspects of modern physics is that its two most successful fields, relativity and quantum mechanics, are fundamentally incompatible, as things happen in the quantum world that relativity says should not be possible. That’s left physicists looking for a way to harmonize the two, with two primary contenders: string theories, and quantum gravity theories. Testing either of them has been a bit challenging, but researchers have now managed to use a single, intensely powerful photon detected by the Fermi Telescope to significantly limit the number of viable quantum gravity theories.
The Fermi Gamma-ray Space Telescope has only been operational for about a year, but results from its observation have already been appearing in a number of significant publications. The observatory is designed to detect the highest energy radiation, which is only produced by the most energetic events in the universe, such as supernovae. In this case, the key observation was of a single photon produced by the gamma-ray burst GRB 090510, which came in at an extremely energetic 31GeV.
That photon allowed researchers to test some forms of quantum gravity against the predictions of relativity. According to relativity, the speed of light obeys Lorentz Invariance: it’s the same for all observers and all energies of light. Some theories of quantum gravity, however, suggest that Lorentz Invariance may break down near the Planck length, 1.62 x 10-33cm, causing high-energy photons to travel at different speeds than their low-energy peers. Unfortunately, the effects are small, meaning you need something very high energy that’s travelled for a very long distance before you could detect them.
That’s why this gamma ray burst turned out to be so useful. GRB 090510 was found to have a redshift of z=0.9, which places it about 10 percent of the way across the observed universe, which gives it the sort of distance required. The 31GeV gamma ray has the sort of energy needed to see a difference between it and some of the lower-energy photons detected at the same time, and the event was short-lived, with most of the high-energy photons arriving within a single second of each other. If high energy photons moved at a different speed, we should be able to detect it.
We don’t. There’s a degree of imprecision when it comes to the time window in which the high-energy photons arrive, and the authors spend most of the paper considering different scenarios, like the probability that high-energy photons might be generated earlier than their low-energy peers (the authors’ conclusion: this seems very unlikely). In the end, they conclude that if there is a quantum influence on the speed of light, it can only operate at distances of less than 1.2 times the Planck length.
A value this close to the Planck length means that quantum gravity models in which there’s a linear relationship between photon energy and speed are “highly implausible.” That leaves other quantum gravity options open, including those in which the the relationship is non-linear. Hopefully, theoreticians will be able to devise real-world tests for some of these.
Of course, it remains possible that some of the timing assumptions made by the authors are wrong. Fortunately, it looks like we may have other opportunities to test things at much greater distances. The same issue of Nature contains two papers that describe another gamma-ray burst, GRB 090423, which was detected earlier this year. Preliminary results suggested that it was the most distant item of this sort ever detected, and the papers confirm this: z = 8.2, which corresponds to an origin at the time when the Universe was only 630 million years old.
The discovery suggests that massive stars were being born and exploding in very short order after the birth of the universe. The similarity of the burst with more modern ones suggests that, on some levels, the early universe wasn’t entirely different from its current state. It also raises the prospect that we can use further bursts of this age to study the Cosmic Dark Ages, when the gasses that make up much of the visible matter of the universe had cooled enough to form neutral atoms, absorbing much of the light. This period ended as the first stars started re-ionizing these atoms, allowing light to propagate across the Universe. This era started at about 800 million years post-big bang, so GRB 090423 may provide a window into the era.
for billy. i hope i’m not too late to stop you from doing something you might regret.
A company called ASPEX, who bill themselves as “a leading producer of benchtop SEM (scanning electron microscopes, is offering readers a chance to send in a sample of anything and see what it looks like in extreme close-up.
To take them up on the offer, download and fill in this form from the ASPEX website and send it (along with the sample you want scanned) to:
ASPEX Corporation Free Sample Submissions 175 Sheffield Dr. Delmont, PA 15626
It’ll take them about two weeks to complete the scan. Once they’re finished, they’ll notify you by email and post the images and the report on their website.
A team led by physicists at the Science and Technology Facilities Council (STFC) and Brookhaven National Laboratory (BNL) have resolved a decade-long puzzle that is set to have huge implications for use of one of the most versatile classes of materials available to us for future technology applications: copper oxide ceramics.
The 2009 Nobel Prize in Physics has been awarded for “two revolutionary optical technologies.”
Charles K. Kao, who discovered how to transmit light through fiber optics, and the team of Willard S. Boyle and George E. Smith, who designed the first digital-imaging sensor, split the Nobel Prize, announced by the Nobel Foundation on Tuesday.
Born in Shanghai, Charles K. Kao made a discovery in 1966 that would lead to today’s fiber optics. A man ahead of this time, Kao calculated how it would be possible to transmit light over 100 kilometers (62 miles), compared to only 20 meters (65 feet) for the fiber cables available in the ’60s. He discovered that by removing impurities and creating a more pure type of glass, the fiber could be made more efficient and absorb less of the light over great distances.
Kao’s research stimulated other scientists to join the effort, leading to the first ultrapure fiber cable created in 1970.
Another breakthrough in technology was the invention of the first successful digital-imaging sensor, used today in everything from consumer cameras to surgical devices.
Working at Bell Labs in New Jersey in 1969, Willard S. Boyle and George E. Smith built the first CCD (Charge-Coupled Device). Using the photoelectric effect theorized by Albert Einstein, the sensor transforms light into electric signals. The team’s major hurdle was determining how to gather and read out those signals into a large number of pixels in a short burst of time.
The first consumer camera with a CCD was designed in 1981, leading to a revolution in digital photography.
"When combined with the laser and the transistor, the invention of an efficient, low-loss optical fiber has made nearly instantaneous communication possible across the entire globe," said H. Frederick Dylla, director of the American Institute of Physics. "This mode of communication is essential for high-speed internet and forms the optical backbone of 21st century commerce. The CCD sensor has revolutionized technical, professional, and consumer photography in the last few decades. Taken together these inventions may have had a greater impact on humanity than any others in the last half century."
Kao will take home one half of the award prize of 10 million Swedish kronor ($1.4 million) with the team of Boyle and Smith splitting the other half. Awarded by the The Royal Swedish Academy of Sciences, Nobel prizes are given each year for achievements in science, literature, and economics.
New York Times readers now have the once-in-a-generation chance to help do just that. Partly buoyed by $53 million from the economic stimulus package, aka the American Recovery and Reinvestment Act, the Fermi National Accelerator Laboratory, aka Fermilab, has embarked on a plan to build a new machine for accelerating protons.
For now, it goes by the name of Project X, but Fermilab would like to come up with a zippier, more descriptive name before this one gets cemented into place by the press. The new machine would replace an aging linear accelerator that now feeds the Tevatron, the world’s biggest particle collider for at least another two months, before the giant Large Hadron Collider in Europe takes over. The Tevatron is due to be shut down in 2011; Project X, or whatever name it eventually gets, is a step toward insuring that Fermilab has a future in high energy physics.
So send in your suggestions to Dr. Kim at email@example.com. You can see previous suggestions here.
Researchers of Eindhoven University of Technology and the Radboud University Nijmegen in The Netherlands show for the first time why ordinary graphite is a permanent magnet at room temperature. The results are promising for new applications in nanotechnology, such as sensors and detectors. In particular graphite could be a promising candidate for a biosensor material.
Graphite is a well-known lubricant and forms the basis for pencils. It is a layered compound with a weak interlayer interaction between the individual carbon (graphene) sheets. Hence, this makes graphite a good lubricant.
It is unexpected that graphite is ferromagnetic. The researchers Jiri Cervenka and Kees Flipse (Eindhoven University of Technology) and Mikhail Katsnelson (Radboud University Nijmegen) demonstrated direct evidence for ferromagnetic order and explain the underlying mechanism. In graphite well ordered areas of carbon atoms are separated by 2 nanometer wide boundaries of defects. The electrons in the defect regions (the red/yellow area in picture 1) behave differently compared to the ordered areas (blue in picture 1), showing similarities with the electron behaviour of ferromagnetic materials like iron and cobalt.