Or is there some creepy, unknown substance surrounding us that we simply don't perceive or understand?
By Nathan Chandler. Scientists are using 3-D printers to make human corneas, an advancement that could end the perennial shortage of corneas from donors. By Laurie L. Why do we love looking at a perfectly stacked display of soup cans or six flower petals around a stamen? Our brains seem wired for it -- but why?
By Dave Roos. If you're one of those people who chooses invisibility as your desired superpower, it could mean you have a dark side. By Alia Hoyt. Light-reflective glasses promise to foil CCTV cameras. Here's how. By Michelle Adelman. Helicopters, ceiling fans, even tricked-out car tire rims: Sometimes they can even look like they're going backward, or bending.
A wall of Lego-like bricks creates the illusion of hyper-vivid, three-dimensional audio, altering sound waves much like a hologram does visible light.
By Patrick J. It's a young lady! It's an old woman! It's a blue dress! No, it's gold! Why are we fooled by optical illusions and what do they tell us about how the brain works? By Meisa Salaita. Whereas the majority of sighted people see a world with just a million colors, or fewer if you're color-blind. By Kate Kershner. Cosmological redshift: sounds like the latest blockbuster coming to a theater near you, doesn't it?
In reality, it has to do with how light itself travels -- and understanding how it works is essential to advanced space telescope technology. What if there are colors within the visible spectrum that our brains can't perceive? In fact, there are. They're called impossible colors. But some researchers think they've discovered a way to see the impossible.
Light travels pretty rapidly, but when it comes to faraway galaxies, that light takes a while to reach our telescopes. In fact, the light you see might actually be from billions of years ago. Our day to day experience with light suggests that it travels, for the most part, in straight lines. If we make the gap smaller within limits, discussed below , the stream gets narrower, but remains a stream of light.
Early optics researchers used geometry to model this view of light. Light is postulated to travel along rays — line segments which are straight in free space but may change direction, or even curve, when encountering matter.
Two laws dictate what happens when light encounters a material surface. The law of reflection , evidently first stated by Euclid around BC, states that when light encounters a flat reflecting surface the angle of incidence of a ray is equal to the angle of reflection.
The law of refraction , experimentally determined by Willebrord Snell in , explains the manner in which a light ray changes direction when it passes across a planar boundary from one material to another. From the laws of reflection and refraction, one can determine the behavior of optical devices such as telescopes and microscopes. This is in fact the most important use of geometrical optics to this day: the behavior of complicated optical systems can, to a first approximation, be determined by studying the paths of all rays through the system.
A simple illustration of this is the action of a clear glass lens on a collection of parallel rays, shown in the figure below. A collection of rays incoming from the left are refracted twice by the lens, once on entry and once on exit, and the net result is the accumulation of all rays at a focal point on the right.
In principle, there are an infinite number of parallel rays in the picture; we obviously draw only a few of these. The brightness of the light field at any particular point in space is proportional to the density of rays how closely spaced they are at that point. The focusing action of the lens therefore results in a bright spot at the focal point. Physical optics. Looking again at the ray picture of focusing above, we run into a problem: at the focal point, the rays all intersect.
The density of rays at this point is therefore infinite, which according to geometrical optics implies an infinitely bright focal spot. Obviously, this cannot be true. If we put a black screen in the plane of the focal point and look closely at the structure of the focal spot projected on the plane, experimentally we would see an image as simulated below:.
There is a very small central bright spot, but also much fainter augmented in this image rings surrounding the central spot. These rings cannot be explained by the use of geometrical optics alone, and result from the wave nature of light.
Though people had long suggested that light has wavelike properties, direct evidence was lacking note the size of the focal spot in the picture above: the rings are quite difficult to see with the naked eye until the early s.
A number of scientists provided the theoretical and experimental framework to demonstrate that light has wavelike properties, notable among them Thomas Young, Josef Fraunhofer and Augustin Fresnel. From this work, the field of physical optics was born. Physical optics is the study of the wave properties of light, which may be roughly grouped into three categories: interference, diffraction, and polarization.
Interference is the ability of a wave to interfere with itself, creating localized regions where the field is alternately extremely bright and extremely dark. Polarization refers to properties of light related to its transverse nature. We will cover all these terms in more detail in subsequent posts. The wave nature of sound can be readily determined by anyone even without special scientific apparatus. The sound waves from your friend partially wrap around the corners of the building, allowing you to hear him or her.
This may be considered an example of diffraction. The wave nature of light is not as readily apparent. The reason for this discrepancy has to do with the wavelength of the waves in each case.
For our purposes, the wavelength may be considered a distance over which wave effects are typically apparent. For audible sound, wavelengths range from millimeters to 20 meters, while for visible light the wavelength is on the order of 0.
Quantum optics. We return to the picture of the focal spot illustrated above and now imagine that the light source which produces the focal spot is on a very precise dimmer switch. What happens as we slowly turn the dimmer switch down to the off position?
Physical optics predicts that the shape of the focal spot will remain unchanged; it will just grow less bright. If we keep a running tally of how many squirts hit at each location, we can slowly build up an average picture of where light energy is being deposited; this is illustrated in parts b and c of the figure below. Remarkably, we find that the average spatial distribution of squirts results in exactly the ring pattern predicted by the wave theory of light!
The squirts of energy are now known in fact to be individual particles of light, called photons. The photoelectric effect is a phenomenon in which electrons can be ejected from a metal surface by shining a beam of light upon the surface. The effect had a number of curious features which Einstein demonstrated were most readily explainable by considering light as a stream of particles.
The reality is that light has both wavelike and particlelike properties, depending on the circumstances of measurement. But a new study finds that water bears propel themselves through sediment and soil on eight stubby legs, in The researchers measured the spontaneous emission of fast Now they're building the hardware for Hidden Behavior of Supercapacitor Materials Nov.
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