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Title: Least-time paths of light
Authors: Arto Annila

The variational principle in its original form á la Maupertuis is used to delineate paths of light through varying energy densities and to associate shifts in frequency and changes in momentum. The gravitational bending and Doppler shift are in this way found as mere manifestations of least-time energy dispersal. In particular, the general principle of least action due to Maupertuis accounts for the brightness of Type 1a supernovae versus redshift without introducing extraneous parameters or invoking conjectures such as dark energy. Likewise, the least-time principle explains the gravitational lensing without the involvement of additional ingredients such as dark matter. Moreover, time delays along curved geodesics relative to straight paths are obtained from the ratio of the local to global energy density. According to the principle of least action the Universe is expanding uniformly due to the irrevocable least-time consumption of diverse forms of bound energy to the lowest form of energy, i.e. the free electromagnetic radiation.

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Scientists around the world are working on the building blocks that could be linked up to create a useful quantum computer.
Single photons are at the heart of many of these schemes and, at first glance, seem like ideal information carriers: once encoded they are able to travel across galaxies and bend around suns without this information being lost.
Yet the quality that makes them such safe information carriers - the fact that they interact only very weakly with their environment - is exactly what makes them difficult to work with.
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Blobrana


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Light Speed



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Time travel: Light speed results cast fresh doubts

The speed of light in vacuum is the Universe's ultimate speed limit, but experiments in recent years suggested that single photons might beat it.
If they could, theory allows for the prospect of time travel.
Now, a paper in Physical Review Letters shows that individual photons too are limited to the vacuum speed limit.
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The Properties of Light as it Relates to Astronomy



Join Dr. Ken Boyer and Jonathan Bergmann as they continue their astronomy series: The Properties of Light

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Blobrana


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'Tractor beam' is possible with lasers, say scientists

A laser can act as a "tractor beam", drawing small objects back toward the laser's source, scientists have said.
It is known that light can provide a "push", for example in solar sails that propel spacecraft on a "wind of light".
Now, in a paper on the Arxiv server, researchers from Hong Kong and China have calculated the conditions required to create a laser-based "pull".
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Chilled light enters a new phase

The fuzzy dividing line between light and atoms has been blurred even further. Quantum physicists have created the first Bose-Einstein condensate using photons--a feat until now suspected to be possible only for atoms. The technique could be used to increase the efficiency of solar cells and lasers.
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A Phase Transition for Light

When a laser beam is intense enough, it can interact with the air around it in ways that lead to surprising effects. According to computer simulations to be published in the 12 November Physical Review Letters, the beam can act like a gas of quantum particles (fermions) or like a liquid droplet--and switch between the two as intensity is increased. Observing this transition in the lab would help researchers confirm that they understand the behaviour of high intensity lasers in air, which they hope to use for improved transmission of signals across long distances.
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The man who first measured the speed of light died 300 years ago this week. That's right, 300 years. By the time Einstein published his Special Theory of Relativity in 1905, the speed of light -- that's the C in E=MC{+2} -- was old news.
A Danish astronomer, Ole Romer, figured out how to calculate it in 1676, using just a telescope and a clock.
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Title: Spectroscopic Test of Bose-Einstein Statistics for Photons
Authors: D. English, V. V. Yashchuk, and D. Budker

Using Bose-Einstein-statistics-forbidden two-photon excitation in atomic barium, we have limited the rate of statistics-violating transitions, as a fraction of an equivalent statistics-allowed transition rate, to <4.0 x 10-11 at the 90% confidence level. This is an improvement of more than 3 orders of magnitude over the best previous result. Additionally, hyperfine-interaction enabling of the forbidden transition has been observed, to our knowledge, for the first time.

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