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Do you look around the natural world and wonder? Wonder why things work the way they do, why things are the way they are?
Physics is all around us. When light from an object enters your eyes, your brain forms an image by tracing that light directly away from you along a straight line. For example, when light from the sky way out in front of you comes directly to your eyes, your brain traces that light straight back and lets you know that the sky is, well, way out in front of you. But not every object you see is located directly along the direction in which you see it. Perhaps you have been frustrated by reaching into the surf for a smooth pebble resting on the bottom, only to close your fingers on a fistful of water.
Or tried over and over to scoop up a pesky leaf in your swimming pool, always missing it. The light reflecting off the pebble and the leaf changes direction as it exits the water. Neither the pebble nor the leaf — nor the net at the end of the pole — is where you see it. You can experience a mirage as you drive. Some light is heading down toward the road in front of you. But the direction of that light can change as it travels through the air. The speed that light travels through a medium depends on its density.
The quantum electrodynamics explanation is that photons always take the path of minimum time when traveling from one point to another. In order to get from one point to another in a minimum time, photons will take "shortcuts" even though the length of the path is curved and it covers a longer distance than the direct route. Mirages are a direct result of photons taking the path of minimum time in vertical temperature gradients.
Ideal conditions for a mirage are still air on a hot, sunny day over a flat surface that will absorb the sun's energy and become quite hot. When these conditions exist, the air closest to the surface is hottest and least dense and the air density gradually increases with height.
Incoming photons take a curved path from the sky to the viewer's eye. The illusion comes from the fact that quantum electrodynamics is not intuitive and the human brain assumes that light travels in a straight line. A viewer looking at, say, the road ahead on a hot, still, day will see the sky because photons from the sky are taking the curved path that minimizes the time taken.
The brain interprets this as water on the road because water would reflect light from the sky in much the same way that a vertical temperature gradient does.
A simple experiment can demonstrate the manner in which a light beam bends in a vertical density gradient. Fill a long glass tank with water, dissolve sugar in the water and shine a laser beam in one end. Polar explorers and sailors in the polar regions have told tales of flying ships or coastal cities in the sky for centuries. Although superior mirages are far more rare than inferior mirages, they remain consistent because cold air does not generally rise and hot air generally does not come downward.
However, they can be seen in deserts as well as large bodies of water, such as lakes and oceans, in hot weather. As the light rays bend toward the curvature of the Earth, unique optical illusions come to life creating images that appear to be so real and amaze all who witness the deception.
The content on this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.
Why do we see mirages?
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