Guide Where The Light Is

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Then get a "coherent" light source, which only produces light of a particular wavelength: a laser will do nicely. Now shine the light through the two slits onto another surface. On that second surface, you might expect to see two bright vertical lines where some of the light has passed through the two slits. But when Young performed the experiment, he saw a sequence of light and dark lines rather like a bar code.

When the light passes through the thin slits, it behaves in the same way that water waves do when they pass through a narrow opening: they diffract and spread out in the form of hemispherical ripples. Where the "light ripples" from the two slits hit each other out of phase they cancel out, forming dark bars. Where the ripples hit each other in phase, they add together to made bright vertical lines.

Young's experiment was compelling evidence of the wave model, and Maxwell's work put the idea on a solid mathematical footing. Light is a wave. View image of Lightbulbs rely on substances that emit electromagnetic radiation Credit: In the second half of the nineteenth century, physicists were trying to understand how and why some materials absorbed and emitted electromagnetic radiation better than others. That may sound a bit niche, but the electric light industry was emerging at the time, so materials that could emit light were a big thing. By the end of the nineteenth century, scientists had discovered that the amount of electromagnetic radiation released by an object changed depending on its temperature , and they had measured these changes.

But no one knew why it happened.


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In , Max Planck solved the problem. He discovered that the calculations could explain those changes, but only if he assumed that the electromagnetic radiation was held in tiny discrete packets. Planck called these "quanta", the plural of "quantum". Physicists had discovered that a chunk of metal becomes positively charged when it is bathed in visible or ultraviolet light. They called this the " photoelectric effect ". The explanation was that atoms in the metal were losing negatively-charged electrons.

Apparently, the light delivered enough energy to the metal to shake some of them loose. But the detail of what the electrons were doing was odd. They could be made to carry more energy simply by changing the colour of light. In particular, the electrons released from a metal bathed in violet light carried more energy than electrons released by a metal bathed in red light.

You usually change the amount of energy in a wave by making it taller — think of the destructive power of a tall tsunami — rather than by making the wave itself longer or shorter. By extension, the best way to increase the energy that light transfers to the electrons should be by making the light waves taller: that is, making the light brighter.

Changing the wavelength, and thus the colour, shouldn't make as much of a difference. Einstein realised that the photoelectric effect was easier to understand by thinking of light in terms of Planck's quanta. He suggested that light is carried in tiny quantum packets. Each quantum packs a discrete energy punch that relates to the wavelength: the shorter the wavelength, the denser the energy punch.

This would explain why violet light packets, with a relatively short wavelength, carried more energy than red light packets, with a relatively longer one. A brighter light source delivers more light packets to the metal, but it doesn't change the amount of energy each light packet contains. Crudely speaking, a single violet light packet could transfer more energy to a single electron than any number of red light packets. Einstein called these energy packets photons, and these are now recognised as a fundamental particle.

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Visible light is carried by photons, and so are all the other kinds of electromagnetic radiation like X-rays, microwaves and radio waves. In other words, light is a particle. At this point physicists decided to end the debate over whether light behaved as a wave or a particle. Both models were so convincing that neither could be rejected. To the confusion of many non-physicists, the scientists decided that light behaved as both a wave and a particle at the same time.

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In other words, light is a paradox. Physicists, though, have no problem with light's split identity.

If anything, it makes light doubly useful. Today, building on the work of luminaries — literally "light-givers" — like Maxwell and Einstein, we are squeezing even more out of light. It turns out that the equations used to describe light-as-a-wave and light-as-a-particle work equally well, but in some circumstances one is easier to use than the other.

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So physicists switch between them, just as we use metres to describe our own height but switch to kilometres to describe a bicycle ride. Some physicists are trying to use light to create encrypted channels of communication: for money transfers, for instance. For them, it makes sense to think of light as particles.

This is because of another strange quirk of quantum physics. Two fundamental particles, like a pair of photons, can be "entangled". This means they share properties no matter how far apart they are from one another, so they can be used to communicate information between two points on Earth. Another feature of this entanglement is that the quantum state of the photons changes when they are read.

That means if anyone tried to eavesdrop on a channel encrypted using the quantum properties of light, they would, in theory, immediately betray their presence.

Others, like Goulielmakis, are using light in electronics. For them it is far more useful to think of light as a series of waves that can be tamed and controlled. View image of Is that shaft of light made up of a wave, or tiny particles? Modern devices called "light field synthesisers" can corral light waves into perfect synchrony with each other. As a result, they create light pulses that are far more intense, short-lived and directed than the light from an ordinary bulb. In Goulielmakis and his colleagues managed to produce incredibly short pulses of X-ray radiation.

Each pulse lasted just attoseconds, or quintillionths of a second. Using these tiny pulses like a camera flash, they managed to capture images of individual waves of visible light , which oscillate rather slower. They literally took photos of light waves moving. Seeing those individual light waves is a first step towards controlling and sculpting them, he says, much as we already sculpt much longer electromagnetic waves, like the radio waves that carry radio and television signals. A century ago, the photoelectric effect showed that visible light affects the electrons in a metal.

Goulielmakis says it should be possible to precisely manipulate those electrons, using visible light waves that have been shaped to interact with the metals in a carefully defined way. That could revolutionise electronics, leading to new generations of optical computers that are smaller and faster than those we have today. That is nothing new. Life has been harnessing light ever since the first primitive organisms evolved light-sensitive tissues. Human eyes are photon detectors that use visible light to learn about the world around us.

Modern technology is simply taking this idea even further. In , the Nobel Prize in Chemistry was awarded to researchers who built a light microscope so powerful, it was thought to be physically impossible. It turned out that, with a bit of persuasion, light would show us things we thought we would never see. Earth Menu. The Big Questions Physics What is a ray of light made of? Share on Facebook. Share on Twitter. Share on Reddit.

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    They experienced communication issues due to heavy cell phone use in the area, especially at rush hour. Dan Kohne was thinking about ways to draw more eyes toward Mount Wilson. It was, conceptually, a perfect fit. Wilson Observatory was founded in by George Ellery Hale, famed for his work studying the sun. And so Sunstar becomes both a reference to how the installation works as well as the history of its current location.

    Looking Where The Light Is

    Lijn has a different batch of colors in store for the presentation and the art will be accompanied by a wasteLAnd chamber music concert. Sun Day Star is November 11 from noon to 4 p. Holly St. Check the AxS Festival schedule for more opportunities to view Sunstar. Stay up to date with everything you need to know about L.

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