13.7 billion years ago, an event occurred. Space itself swelled terrifically into being. Suddenly, there appeared a burgeoning cosmos where before there had been nothing. The explosion left behind a molten sea of charged particles that would eventually give life to everything in the universe. The churning plasma expanded along with space for 300,000 years until its constituent protons and electrons had finally cooled enough to combine. Consequently, the entire universe was soon clouded by neutral hydrogen gas. Such gas absorbs radiation exceptionally well, and so space was plunged into darkness for another billion or so years.
At this point, it was gravity that dispelled the haze. Clumps of gas soon condensed under its influence, slowly becoming dense furnaces for nuclear fusion. The high energy UV radiation emitted by these young stars leaked out across the universe, heating the surrounding gas to temperatures they had not faced since the big bang. Electrons that had been trapped within the nuclei of light atoms were suddenly released, reionizing hydrogen and rendering space transparent once more. As the universe expanded, overdense regions of structure contracted under gravity. Over the course of a few billion years, a familiar cosmos took shape. Stars came together into galaxies, galaxies came together into clusters, wacky objects like quasars came and went, supernovae went off, our Solar System formed, and the universe painstakingly plodded into its current configuration.
You may have noticed that some details are a little murky. As of yet, astronomers have no idea how the first stars formed out of the ambient fog. One pair of scientists is now hoping to change that. Alan Rogers of MIT and Judd Bowman of Arizona State University have developed a method using the 21cm spectral line of hydrogen. This line appears in the spectra of hydrogen atoms that have undergone an excitation. According to Rogers and Bowman, the specific way in which the radio spectrum of hydrogen evolves with time tells us that reionization itself lasted about 5 million years. Thus, the first stars and galaxies were most likely born during this time. Understanding the stellar mechanics that occurred during reionization is one of the most active quests in cosmology today. The team hopes to learn more with future observation and fine-tuning of their instrument, the EDGES antenna at the MIT Haystack Observatory.
Showing posts with label hydrogen. Show all posts
Showing posts with label hydrogen. Show all posts
Saturday, January 15, 2011
Wednesday, July 7, 2010
A tiny mistake.
The proton is one of nature's most famous elementary particles. Solid, stable and always positive, this subatomic celebrity is, quite literally, at the center of everything in the universe. But new research suggests that the proton may actually be smaller than previously thought. If this turns out to be true, the laws of physics will definitely need some rehabilitation.
Excepting dark matter and dark energy, the entire universe is made up of atoms. In the center of each is a small positively-charged core called a nucleus, which is made up of protons and neutrons held together by the strong force. Like a swarm of bees, electrons buzz around the nucleus in different "shells", or energy states. Hydrogen, the lightest and most abundant element, has been exploited by scientists for centuries due to its extraordinarily simple structure: one proton orbited by one electron.
Ionized clouds of hydrogen. Image courtesy of UC Astronomy Dept.
Most recently, researchers at the Max Planck Institute used our atomic minimalist to probe some choice principles of Quantum Electrodynamics (QED), a theory that merges Einstein's theory of special relativity with quantum mechanics. According to QED, an electron orbiting the hydrogen nucleus in the 2S shell will have a different energy than it would if it were orbiting in the 2P shell. This difference is called the Lamb shift, and it contradicts Paul Dirac's original prediction that the 2S and 2P shells should have the same energy. In order to learn more about the Lamb shift, the team at Max Planck replaced the electron in hydrogen with its cousin the muon, a particle that is 200 times as massive and far less stable. When researchers observed the newly created muonic hydrogen, they found that the massive muon orbited the central proton far more closely than the electron did, and was therefore far more sensitive to its size. The team's calculations assign the proton a radius of 0.84184 femtometers (0.00000000000000084184 meters), a number that is 4% smaller than its previously accepted value of 0.8768 femtometers.
4% may not seem like a whole lot, but this tiny miscalculation could have enormous implications for particle physics. If this new result turns out to be accurate, QED and the Standard Model will have to be completely rewritten. No easy task for the most relied-upon theory in modern physics. Quite frankly, scientists may have a revolution on their hands.
Excepting dark matter and dark energy, the entire universe is made up of atoms. In the center of each is a small positively-charged core called a nucleus, which is made up of protons and neutrons held together by the strong force. Like a swarm of bees, electrons buzz around the nucleus in different "shells", or energy states. Hydrogen, the lightest and most abundant element, has been exploited by scientists for centuries due to its extraordinarily simple structure: one proton orbited by one electron.
Ionized clouds of hydrogen. Image courtesy of UC Astronomy Dept.
Most recently, researchers at the Max Planck Institute used our atomic minimalist to probe some choice principles of Quantum Electrodynamics (QED), a theory that merges Einstein's theory of special relativity with quantum mechanics. According to QED, an electron orbiting the hydrogen nucleus in the 2S shell will have a different energy than it would if it were orbiting in the 2P shell. This difference is called the Lamb shift, and it contradicts Paul Dirac's original prediction that the 2S and 2P shells should have the same energy. In order to learn more about the Lamb shift, the team at Max Planck replaced the electron in hydrogen with its cousin the muon, a particle that is 200 times as massive and far less stable. When researchers observed the newly created muonic hydrogen, they found that the massive muon orbited the central proton far more closely than the electron did, and was therefore far more sensitive to its size. The team's calculations assign the proton a radius of 0.84184 femtometers (0.00000000000000084184 meters), a number that is 4% smaller than its previously accepted value of 0.8768 femtometers.
4% may not seem like a whole lot, but this tiny miscalculation could have enormous implications for particle physics. If this new result turns out to be accurate, QED and the Standard Model will have to be completely rewritten. No easy task for the most relied-upon theory in modern physics. Quite frankly, scientists may have a revolution on their hands.
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