This laser apparatus used to test the size of the proton found that the particle's radius is about 4 percent smaller than thought.

How many protons can dance on the head of a pin? The answer is nowhere near as straightforward as one may think — and it might offer new insights into one of the most well-tested theories in physics.

An international team of scientists recently tried to find out the actual size of a proton, one of the ingredients (along with neutrons and electrons) of the atoms that make up our bodies and the world around us.

Reporting this week in the journal Science, the researchers found that the particle's radius is 0.84087 femtometers. A femtometer is a billionth of a billionth of a meter, or so small that the wavelength of gamma radiation is 100 times longer. The new measurement is about 4 percentsmaller than the currently accepted radius of 0.8768 femtometers, and that small difference presents a puzzle.

If the smaller size is correct, then there's something missing in physicists' understanding of quantum electrodynamics, which governs how light and matter interact.

Proton error?

Aldo Antognini, a physicist at the Swiss Federal Institute of Technology and first author of the paper, told Livescience the difference could mean one of three things.

First, that there is some error in the earlier work, though that isn't likely given how many times various experiments were repeated.

The second possibility is that some piece of the calculations for the proton's size is missing. "Maybe we don't understand fully proton structure," Antogninisaid.

The third explanation is that the current theories of quantum electrodynamics are wrong, though chances of that seem slim given that the theory works very well and it has been tested many times. [Wacky Physics: The Coolest Little Particles in Nature]

This result isn't the first time a discrepancy has shown up. In 2010, Antognini, working with aninternational team led by Randolf Pohl of the Max Planck Institute of Quantum Optics in Garching, Germany, found the proton radius seemed to be 0.84185 femtometers.

How to measure a proton

To find the size of a proton scientists have used three methods. One is electron scattering: firing negatively charged electrons at positively charged hydrogen nuclei (protons) and measuring how they are deflected. The scattering pattern can then give an idea of how big the region of positive charge is.

The second method is to measure how much energy it takes to get an electron to move to different orbital regions around a nucleus. Electrons usually stay in regions that are a certain distance from the nucleus. Increase their energy and they become excited, and move to a different region, called an orbital. The electrons then fall back into their unexcited states and emit a photon. By looking closely at how much energy it takes to move an electron from one orbit to a higher-energy one, and the wavelength of the photon emitted when the electron drops back to its lower-energy orbital, it's possible to estimate a proton's size.

Last, the method used in the latest set of experiments, involves muonic hydrogen, which is a protonwith a muon, rather than an electron, orbiting around it. Like electrons, muons are negatively charged, but they are 207 times heavier. That means they fly closer to the proton, and it takes more energy to move them to higher-energy orbitals. The greater energy differences make measuring them easier. Firing a laser at the muonic hydrogen excites the muon, moving it to a different orbital. The muon then falls back to its lower-energy state, emitting an X-ray photon.

The first two methods, used over decades, had come up with the larger value for the proton's radius. The latter method, which scientists say has a smaller uncertainty, found the smaller one. These calculations, though, are quite complex.

New proton measure

Antognini's team, carrying out experiments at the Paul Scherrer Institute in Switzerland, not only did the muonic hydrogen experiment a second time, they also took steps to ensure a more accurate measurement. The discrepancy remained. "Maybe there is something in [proton] structure only highlighted by muons," Antognini said. [Weird: Top 10 Unexplained Phenomena]

That's why the new value is proving such a mystery. Quantum electrodynamics (QED) is probably right, and it's also not likely that the earlier experiments were that far wrong due to simple errors, experts say.

"There might be some missing terms in the calculations," said Helen Margolis, a research scientist at the National Physical Laboratory in the U.K., who was not involved in the research. "QED has been tested to incredible levels so far, but the mathematical foundation is not as secure as you might like."

Chad Orzel, an associate professor of physics and astronomy at Union College and author of "How to Teach Physics to Your Dog" (Scribner, 2010), said the results are good for physics generally, because of the questions they raise. "It's really boring when all the measurements and theory agree with each other. This kind of disagreement gives us something to talk about that isn't the Higgs boson."

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Photo Credit: The Sierra Club

Doubts raised about fairness of Delhi rape trial

FILE – In this Saturday, Dec. 22, 2012 file photo, Indian students hold placards and shout slogans during a protest rally against the gang rape of a 23-year-old student on a moving bus in New Delhi, in Gauhati, India. In the court of public opinion, the men being tried in the gang rape of the Indian university student should be hanged in a public square. The demand for swift justice might make it impossible for them to get a fair trial in a court of law, with even a local bar association stopping its members from representing the men citing the heinous nature of the crime. (AP Photo/Anupam Nath, File)

FILE – In this Saturday, Dec. 22, 2012 file photo, Indian women shout slogans from top of a flag post during a protest against the gang rape of a 23-year-old student on a moving bus in New Delhi, India. In the court of public opinion, the men being tried in the gang rape of the Indian university student should be hanged in a public square. The demand for swift justice might make it impossible for them to get a fair trial in a court of law, with even a local bar association stopping its members from representing the men citing the heinous nature of the crime. (AP Photo/Altaf Qadri, File)

NEW DELHI (AP) — In the court of public opinion, the men being tried in the gang rape of an Indian university student should be hanged in a public square.

That demand for swift justice might make it impossible for them to get a fair trial in a court of law. Already, there are plenty of portents.

Amid the heightened emotions that have surrounded this case a local bar association has stopped its members from representing the men citing the heinous nature of the crime. The three grandstanding lawyers who have rushed in to represent the accused spent weeks taking potshots at each other instead of coordinating a defense. Two lawyers fought for days over which one was representing one of the defendants.

And the case is being heard by a brand new fast track court, set up in the wake of the rape to deal with sexual assaults in the capital, that is under pressure to reach a verdict within weeks. Finally, whatever is said or submitted in court has to stay in the room -- a gag order by the judge prevents the media from reporting anything about the case.

"However wicked and depraved society may perceive a person to be, he deserves a fair trial. He deserves a good defense," said Markandey Katju, a retired judge of India's Supreme Court.

"That some of those charged are the real culprits and some are innocent ... that is a very real possibility," he said, adding that in India the police "spreads its net wide."

As details of the attack have emerged Katju said he feared the trial may be overrun by emotion rather than the calm voice of reason.

"You can't decide cases on sentiment. That's lynch law."

The specifics of the gang rape are horrifying. According to the police report, the attack lasted at least 45 minutes. There were six attackers, one of whom claims to be a juvenile and is being tried separately. Each of the men raped the 23-year-old woman, with at least two taking turns driving the bus. They penetrated her with two metal rods, causing such severe internal injuries that doctors later found parts of her intestines floating freely inside her abdomen.

The battered woman and her badly beaten male friend were then thrown out of the moving bus and lay naked and bleeding on the side of a busy road on a cold December night.

The attack was so brutal that the woman died two weeks later in a Singapore hospital.

Within two days of the attack the police arrested the six accused. According to the police all six confessed their crimes. The police report said that DNA evidence from the men tied all of them in the rape and murder. According to police documents blood and saliva swabs from the accused matched the DNA found on the victim's injuries. The victim's blood was also found on the clothes, underwear and slippers of the accused.

The attack in the heart of New Delhi brought protesters into the streets demanding the government protect women and ensure those attacked get justice. In response, the city government set up five fast track courts to swiftly handle those cases, keeping them out of India's overburdened regular court system, where trials can drag on for years if not decades.

As the police framed charges against the men and prepared for trial the bar association of Saket, the district where the case is being heard, declared that their members would not represent the men. They were following a precedent set by lawyers' groups across India over the last few years, which have banned their members from representing those accused of terrorism and other heinous crimes.

"This is completely unconstitutional and unethical," said Katju. "Right minded lawyers should defy and ignore such rulings."

Outside the courtroom the cries for a quick trial and execution of the five men have persisted.

"They should be handed over to the public and hanged," said Prakash, a 51-year-old gardener who had come to court on a personal matter but waited to get a glimpse of the accused being whisked into court. She uses only one name.

The three men who rushed forth to represent the accused were not members of the local bar and have spent more time fighting each other than putting up a defense.

One insisted he would ask the Supreme Court to move the trial out of Delhi because emotions were too high to hold a fair trial here. But when a second lawyer made a similar appeal, the first changed his mind and vehemently opposed it.

One lawyer, M.L. Sharma, has accused police of planting the other two defense lawyers to ensure a guilty verdict.

"I'm the only hurdle standing in their way," Sharma said earlier this week. Even as he made his allegations, fellow defense counsel V.K. Anand stepped up to say that Sharma's client had decided to fire his lawyer — and hire him.

The dispute over who would represent the defendant was only resolved Thursday — the day the trial started. Sharma dropped out of the trial, saying he feared his client would be tortured to get him to change his lawyer. Anand replaced him.

Sharma has accused police of beating all five men to extract their confessions, then later amended that to say only his client was beaten. He also made unsubstantiated accusations that the victim's male friend was somehow responsible for the deadly assault, only to backtrack later.

Another lawyer, A.P. Singh, said the only reason he agreed to represent two of the accused was because their families had begged his mother for help.

"My mother has a kind heart and an order from her is like an order from God," he said, posing dramatically for the cameras.

Anand hasn't spoken about his strategy, but both Sharma and Singh have claimed at least once that their clients were not even on the bus during the attack.

In the past, courts across the country have criticized the police for coercing confessions and even planting evidence to get convictions.

"We set so little store by how the police functions in this country. There's no reason to accept the police's version of events in this case without thorough legal scrutiny," said Jawahar Raja, a lawyer and activist.

The defense is made even more complicated by the fact the case is being tried in a fast track court. As a result the police has put together its case at rapid speed. The trial has started even as defense lawyers are falling into place.

"Justice takes some time. It's all very easy to talk about fast track courts," said Katju, adding that cases should be tried quickly and efficiently but without a looming deadline.

"A judge has to read all the documents, hear the lawyers, apply his mind. It's not a magic lamp that with a swish you can dispose of a case."

French forces take airport, bridge in Gao, Mali

SEVARE, Mali (AP) — French forces took control of the airport and a key bridge in the radical Islamist stronghold of Gao under the cover of darkness early Saturday, marking a significant inroad into the heart of territory held by the al-Qaida-linked extremists.

The move comes just two weeks after France launched its military offensive to rout the Islamists from power in northern Mali. It is unclear what kind of resistance they will face in the coming days

French and Malian forces came under fire in the morning and continued to face sporadic "acts of harassment," in the afternoon, said Col. Thierry Burkhard, a French military spokesman in Paris. He had no immediate estimate on casualties.

The Islamists first seized control of Gao and two other northen provinicial capitals — Timbuktu and Kidal — in April last year during the chaotic aftermath of a coup in the distant capital.

French Defense Minister Jean-Yves Le Drian announced in a statement from his ministry Saturday that jihadist fighters who encountered the advancing French and Malian troops "saw their means of transport and their logistics sites destroyed."

Nouhoum Maiga, a deputy mayor in Gao, confirmed Saturday that the French had come by land and air late Friday.

Gao has been under the control of the al-Qaida-linked Movement for Oneness and Jihad, or MUJAO, for months.

On Friday in a show of might, the Islamist radicals destroyed a bridge near the Niger border with explosives, showing that the extremists still remain a nimble and daunting enemy.

Since France began its military operation two weeks ago with a barrage of airstrikes followed by a land assault, the Islamists have retreated from three cities in central Mali: Diabaly, Konna and Douentza.

The Islamists, though, have maintained control of the majority of the territory in Mali's north, most importantly the cities of Gao, Kidal and Timbuktu.

The announcement that Gao's airport had been taken marked the first official confirmation that French and Malian forces had reached the city. Previously the closest they had been was Hombori, a town some 155 miles (250 kilometers) away.

The French currently have about 2,500 forces in the country and have said that they will stay as long as needed in Mali, a former French colony. However, they have called for African nations to take the lead in fortifying the Malian army's efforts.

There are currently some 1,750 troops from neighboring African countries, including Togo, Nigeria, Burkina Faso, Benin, Senegal, Niger and Chad.

The French-led mission began after the Islamists surged the farthest south yet and took the town of Konna. On Saturday, the Malian military allowed international journalists to enter the town for the first time since the conflict began.

Residents described the civilian casualties that took place during the French air strikes, including one that left three women and a child dead. Officials have said at least 11 Malians died in the military effort to retake the town.

Souleymane Maiga said the women were preparing food in the courtyard underneath a mango tree when he heard the helicopters overhead.

"I ran and hid between the walls of our courtyard," he said. "After it was over, I went to the house and I opened the door and that's when I saw that they were dead."

Only a toddler survived, Maiga said.

"They were one on top of the other. The baby was crying," he said. "I tried to feel for a pulse to see if there was any life, but I found that they were all dead."

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Keaten reported from Dakar, Senegal. Associated Press writers Rukmini Callimachi and Baba Ahmed contributed to this report from Konna, Mali.

Iraqi insurgents try to harness opposition rage

BAGHDAD (AP) — Iraqi insurgents are trying to capitalize on the rage of anti-government protesters and the instability caused by rising civil unrest, complicating the government's efforts to stamp out a resurgent al-Qaida and other militants.

Organizers of the protests attracting minority Iraqi Sunnis insist they have no links to terrorist groups. Yet Iraqi and U.S. officials have expressed concern that violent extremists could benefit from the demonstrators' feelings of alienation and hostility toward the Shiite-led Iraqi government.

And tensions are rising.

At least five protesters were killed and more than 20 were wounded on Friday when soldiers opened fire at stone-hurling demonstrators near Fallujah, a former al-Qaida stronghold where tens of thousands took to the streets. Some in the crowd waved black banners emblazoned with the Muslim confession of faith.

They were the first deaths at opposition rallies that have been raging around the country for more than a month. Two soldiers were later killed in an apparent retaliatory attack.

Protesters also have staged demonstrations in other areas with large concentrations of Sunni Arabs, who feel discriminated against by the government. Their list of demands includes the release of detainees and an end to policies they believe unfairly target their sect.

For now, the American Embassy has no indication that al-Qaida is gaining support from the demonstrations. But the fear remains, particularly as the security situation deteriorates in neighboring Syria.

An embassy official said the U.S. had expressed concern that the protesters' peaceful expression of their viewpoints must not be usurped by extremists trying to provoke violence. The official spoke on condition of anonymity because he was not authorized to speak publicly about the matter.

Sectarian violence that once pushed Iraq to the brink of civil war has ebbed significantly, though violent attacks aimed mainly at Iraq's Shiite majority, security forces and civil servants still happen frequently.

Insurgents have managed to mount large, mass-casualty bombings of the type favored by al-Qaida on at least five days this month. In another attack, a suicide bomber killed a total of seven when he assassinated a prominent politician who played a leading role in the fight against al-Qaida.

The extremist group later claimed responsibility for the latter bombing and other unspecified attacks.

At least 170 people have been killed in insurgent violence since the start of the year, making January already the deadliest month since September.

Protest organizers and the politicians who support them are eager to distance themselves from extremist rhetoric.

Sunni lawmaker Ahmed al-Alawani recently urged Iraq President Nouri al-Maliki to meet demonstrators' demands so al-Qaida and other militant groups could not exploit their frustration.

That was a sentiment echoed by protest organizer and spokesman Saeed Humaim in Ramadi, a city in western Iraq that has been the focus of daily sit-ins and frequent mass rallies. He said protesters have no intention to take up arms, but will defend themselves if attacked by government security forces.

Still, many Iraqi Sunnis have little doubt that the protests strengthen militant groups.

"I don't think the al-Qaida people would miss an opportunity to move freely when the government and security forces are busy handling these spreading protests," said Ayad Salman, 42, who owns a shoe store in northern Baghdad. "The country is slipping toward a new round of civil war, or at least some groups are planning and pushing for this."

The rallies broke out just over a month ago in Iraq's western Sunni heartland of Anbar following the arrest of guards assigned to the Iraqi finance minister, a Sunni who hails from the province. The vast desert territory on Syria's doorstep was the birthplace of the Sunni insurgency that erupted after the 2003 U.S.-led invasion, and where Iraqi officials believe al-Qaida's Iraq arm is regrouping.

In an interview aired late Thursday, the Iraqi prime minister suggested that al-Qaida and members of Saddam Hussein's ousted regime have a hand in the demonstrations.

"I hope that these protests would not turn violent ... and drag the country to a sectarian war," he told al-Baghdadiya TV.

Al-Qaida's local affiliate this week posted a statement praising the protesters, saluting what it called "the true Muslims who revolted in defense of their honor and religion."

A senior Iraqi security official who specializes in terrorist activities said al-Qaida is making use of the resentment in predominantly Sunni provinces, where local residents who used to provide authorities tips about terrorist activities are growing much more reluctant to snitch.

He and another senior security official said al-Qaida fighters now have more freedom to move around. That is partly because state security forces' movements are being restricted in Sunni areas so they cannot be accused of unfairly targeting the Muslim sect, they said.

The second official said the demonstrations give extremists a good opportunity to try to mobilize Sunni opposition and portray themselves as the only groups who can safeguard the rights and interests of the Sunni minority.

The Iraqi officials insisted on anonymity because they were not authorized to discuss security operations with the media.

The local wing of al-Qaida, known as the Islamic State of Iraq, generally does not operate beyondIraq's borders. But al-Qaida leader Ayman al-Zawahri last year urged Iraqi insurgents to support the Sunni-based uprising in neighboring Syria against President Bashar Assad, whose Alawite sect is a branch of Shiite Islam.

Iraqi officials believe Sunni fighters aligned with al-Qaida's Iraq franchise are moving back and forth across the Syrian border to help Sunni rebels overthrow Assad.

Rebel gains in Syria are giving Iraq's Sunni protesters and insurgents alike a sense that their fortunes may be shifting too.

"Sunnis seem ascendant in Syria. That is a major psychological boost to the Sunnis in Iraq," said Kamran Bokhari, an expert on Mideast issues for the global intelligence company Stratfor. "They're trying to capitalize on that."

Other militants are trying to tie their fight to the protests too.

Earlier this month, uniformed members of the Naqshabandi Army appeared in an online video urging Iraqis to continue their protests, sit-ins and acts of civil disobedience. It called on security forces to turn their weapons on the "traitors and foreign agents" — a likely reference to what many Sunnis see is Shiite powerhouse Iran's influence over the government.

The group, a network of former Iraqi military officers and jihadists, frequently claims responsibility for attacks on government security forces.

The highest ranking member of Saddam's regime still at large, Izzat Ibrahim al-Douri, has separately lent his support to the demonstrators. Al-Douri, who is suspected of having ties to the Naqshabandi Army, is thought to have played a key role in financing Sunni insurgents seeking to undermine Iraq's post-Saddam government.

Another small jihadist group, the 1920 Revolution Brigades, put out a statement of its own backing the protest movement.

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Associated Press writers Qassim Abdul-Zahra and Sameer N. Yacoub contributed reporting.

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