Photon
hideIn physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons are governed by quantum mechanics and will exhibit wave-particle duality – they exhibit properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference, but also act as a particle giving a definite result when its location is measured.
The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation, that other physicists, most notably Max Planck, had sought to explain using semiclassical models, in which light is still described by Maxwell's equations, but the material objects that emit and absorb light are quantized. Although these semiclassical models contributed to the development of quantum mechanics, further experiments proved Einstein's hypothesis that light itself is quantized; the quanta of light are photons.
In the modern Standard Model of particle physics, photons are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of photons, such as charge, mass and spin, are determined by the properties of this gauge symmetry.
The photon concept has led to momentous advances in experimental and theoretical physics, such as lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers and for sophisticated applications in optical communication such as quantum cryptography.
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News tagged with photon
JQI researchers create entangled photons from quantum dots
Nov 18, 2009 |
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To exploit the quantum world to the fullest, a key commodity is entanglement—the spooky, distance-defying link that can form between objects such as atoms even when they are completely shielded from one another. Now, physicists ...
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Using lasers to cool and manipulate molecules
Dec 07, 2009 |
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(PhysOrg.com) -- "For years, we have been using laser cooling to trap and manipulate atoms," David DeMille tells PhysOrg.com. "This has been very useful for both basic science and many applications. Recent ...
The how and why of freezing the common fruit fly
1hour ago |
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Using a microscope the size of a football field, researchers from The University of Western Ontario are studying why some insects can survive freezing, while others cannot.
New structure could produce efficient semiconductor laser sources
Dec 14, 2009 |
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(PhysOrg.com) -- University of Wisconsin-Madison researchers have achieved a nanoscale laser structure they anticipate will produce semiconductor lasers in the next two years that are more than twice as efficient ...
Lifelong memories linked to stable nerve connections
Medicine & Health / Neuroscience
Dec 03, 2009 |
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Our ability to learn new information and adapt to changes in our daily environment, as well as to retain lifelong memories, appears to lie in the minute junctions where nerve cells communicate, according to ...
Researcher studies the universe through quantum electrodynamics
18 hours ago |
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(PhysOrg.com) -- Fundamental constants, such as the standards for length and mass, are a given in our society. However, research has shown that these constants might be changing slightly with the expansion of the universe.
Clearing the way for detecting pulmonary embolism
Dec 01, 2009 |
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When it comes to diagnosing pulmonary embolism—a sudden blockage in the lung artery that could be deadly if not treated—which technique is the most effective? Research published in the December issue of The Journal of Nu ...
Fermi Telescope Peers Deep into Microquasar (w/ Video)
Nov 27, 2009 |
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(PhysOrg.com) -- NASA's Fermi Gamma-ray Space Telescope has made the first unambiguous detection of high-energy gamma-rays from an enigmatic binary system known as Cygnus X-3. The system pairs a hot, massive ...
Unique Uranium Source in Naturally Bioreduced Sediment
Nov 18, 2009 |
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(PhysOrg.com) -- A recently published Pacific Northwest National Laboratory study of a naturally bioreduced sediment sample from a former uranium mill tailings site reveals insights that enhance understanding ...
Study shows new brain connections form rapidly during motor learning
Medicine & Health / Neuroscience
Nov 29, 2009 |
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(PhysOrg.com) -- New connections begin to form between brain cells almost immediately as animals learn a new task, according to a study published this week in Nature. Led by researchers at the University of Cal ...
Caltech scientists film photons with electrons
Dec 16, 2009 |
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(PhysOrg.com) -- Techniques recently invented by researchers at the California Institute of Technology -- which allow the real-time, real-space visualization of fleeting changes in the structure of nanoscale ...
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