Astronomers announced on Wednesday that a race halfway across the universe had ended in a virtual tie. And so the champion is still Albert Einstein — for now.
The race was between gamma rays of differing energies and wavelengths spit in a burst from an exploding star when the universe was half its present age. After a journey of 7.3 billion light-years, they all arrived within nine-tenths of a second of one another in a detector on NASA’s Fermi Gamma-Ray Space Telescope, at 8:22pm, Eastern time, on May 9.
Astronomers said the gamma-ray race was one of the most stringent tests yet of a bedrock principle of modern physics: Einstein’s proclamation in his 1905 theory of relativity that the speed of light is constant and independent of its color, energy, direction or how you yourself are moving.
“I take it as a confirmation that Einstein is still right,” Peter Michelson of Stanford, principal investigator for Fermi’s Large Area Telescope and one of 206 authors of a paper published online on Wednesday in the journal Nature, said in an interview.
There is no evidence so far that the energy or wavelength of light affects its speed through space. That is important because of what it could say about the structure of space-time. Some theorists have suggested that space on very small scales has a granular structure that would speed some light waves faster than others — in short, that relativity could break down on the smallest scales.
Michelson and others said that while the new Fermi results did not yet eliminate the prospect, further observations with more gamma-ray bursts could eventually verify or refute the hypothesis. That would have a major effect on physicists’ efforts to unify the Einsteinian gravity that governs outer space with the weird quantum laws that govern the inner space of the atom.
Mario Livio, an astronomer at the Space Telescope Science Institute in Baltimore, called the Fermi results an interesting effect, but not revolutionary by any stretch.
“The beauty of the experiment is not as much in what it achieves,” Livio said, “as in the fact that you can use astronomical observations to place some interesting limits on very fundamental physics.”
Quantum theory, as Einstein discovered to his chagrin, reduces life on subatomic scales to a game of chance in which elementary particles can be here or there, but not in between. One consequence is that space-time itself should become discontinuous and chaotic when viewed at very close distances, the way an ocean that looks smooth from an airplane appears choppy and foamy up close.
This, the story goes, could have an effect on the propagation of light — or photons, as they are called in quantum-speak — slowing light with short wavelengths relative to light with longer wavelengths. The higher the energy of a photon, the shorter is its wavelength. One way to think about it is to envision the photons as boats on this choppy sea. The small ones, like tugboats, have to climb up and down the waves to get anywhere, while the bigger ones can slice through the waves and bumps like ocean liners, and thus go a little faster.
Until now such quantum gravity theories have been untestable. Ordinarily you would have to see details as small as 10cm to 33cm — the so-called Planck length, which is vastly smaller than an atom — to test these theories in order to discern the bumpiness of space. Getting that kind of information is far beyond the wildest imaginations of the builders of even the most modern particle accelerators, and that has left quantum gravity theorists with little empirical guidance.
“What’s really lacking,” Michelson said, “is a laboratory experiment that tells us anything. So we have to use cosmology: We use the universe as the lab.”
The photons from GRB 090510, detected on May 9, ranged from 10,000 electron volts — the energy unit of choice in physics — to 31 billion electron volts, a factor of more than 1 million, in seven brief bursts over about two seconds.
The spread in travel time of 0.9 second between the highest and lowest-energy gamma rays, if attributed to quantum effects rather than the dynamics of the explosion itself, suggested that any quantum effects in which the slowing of light is proportional to its energy do not show up until you get down to sizes about eight-tenths of the Planck length, said the Nature paper, whose lead author was Sylvain Guiriec of the University of Alabama.
With the midday sun blazing, an experimental orange and white F-16 fighter jet launched with a familiar roar that is a hallmark of US airpower, but the aerial combat that followed was unlike any other: This F-16 was controlled by artificial intelligence (AI), not a human pilot, and riding in the front seat was US Secretary of the Air Force Frank Kendall. AI marks one of the biggest advances in military aviation since the introduction of stealth in the early 1990s, and the US Air Force has aggressively leaned in. Even though the technology is not fully developed, the service is planning
INTERNATIONAL PROBE: Australian and US authorities were helping coordinate the investigation of the case, which follows the 2015 murder of Australian surfers in Mexico Three bodies were found in Mexico’s Baja California state, the FBI said on Friday, days after two Australians and an American went missing during a surfing trip in an area hit by cartel violence. Authorities used a pulley system to hoist what appeared to be lifeless bodies covered in mud from a shaft on a cliff high above the Pacific. “We confirm there were three individuals found deceased in Santo Tomas, Baja California,” a statement from the FBI’s office in San Diego, California, said without providing the identities of the victims. Australian brothers Jake and Callum Robinson and their American friend Jack Carter
Le Tuan Binh keeps his Moroccan soldier father’s tombstone at his village home north of Hanoi, a treasured reminder of a man whose community in Vietnam has been largely forgotten. Mzid Ben Ali, or “Mohammed” as Binh calls him, was one of tens of thousands of North Africans who served in the French army as it battled to maintain its colonial rule of Indochina. He fought for France against the Viet Minh independence movement in the 1950s, before leaving the military — as either a defector or a captive — and making a life for himself in Vietnam. “It’s very emotional for me,”
The Chinese Communist Party’s (CCP) Central Committee is to gather in July for a key meeting known as a plenum, the third since the body of elite decisionmakers was elected in 2022, focusing on reforms amid “challenges” at home and complexities broad. Plenums are important events on China’s political calendar that require the attendance of all of the Central Committee, comprising 205 members and 171 alternate members with Chinese President Xi Jinping (習近平) at the helm. The Central Committee typically holds seven plenums between party congresses, which are held once every five years. The current central committee members were elected at the