- 4618 -
LIGHT - is it a particle or a wave? From the most distant stars in the sky
to the screen in front of your face, light is everywhere. But the exact nature
of light, and how it travels, has long puzzled scientists. One question in
particular has vexed thinkers from Issac Newton to Albert Einstein: Is light a
particle or a wave?
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------------------------------------- 4618
- LIGHT - is
it a particle or a wave?
-
- As a species, we seem driven to understand
the fundamental nature of the world around us, and this particular puzzle kept
19th-century scientists busy. Today,
there's no doubt about the answer: Light is both a particle and a wave. But how
did scientists reach this mind-bending conclusion?
-
- The starting point was to scientifically
distinguish between waves and particles. You would describe an object as a
particle if you can identify it as a point in space. A wave is an object that you don't define as
a point in space and you need to give a frequency of oscillation and distance
between maximum and minimum for the wave/
-
- The first conclusive evidence of the wave
nature of light came in 1801, when Thomas Young performed his now-famous
double-slit experiment. He placed a screen with two holes in front of a light
source and observed the behavior of the light after it had passed through the
slits. The light hitting the wall showed a complicated pattern of bright and
dark bands, known as interference fringes.
-
- As the light waves passed through each hole,
they generated partial waves that radiated spherically, intercepting each other
and adding or subtracting to the final intensity. If the light was a particle, you would have
ended up with two bunches on the other side of the screen. But we have interference, and we see light
everywhere after the screen, not just at the position of the holes. That's
proof that light is indeed a wave.
-
- Eighty-six years later, Heinrich Hertz
became the first to demonstrate the particle nature of light. He noticed that
when ultraviolet light shone on a metal surface, it generated a charge, a
phenomenon called the “photoelectric effect”. However, the significance of his
observation wasn't fully understood until many years later.
-
- Atoms contain electrons in fixed energy
levels. Shining light on them is therefore expected to give the electrons
energy and enable them to escape from the atom, with brighter light liberating
electrons faster. But in experiments following Hertz's work, several unusual
observations seemed to completely contradict this classical understanding of
physics.
-
- It was Einstein who finally solved this
puzzle, for which he was awarded a Nobel prize in 1921. Rather than absorbing
light continuously from a wave, atoms actually receive energy in packets of
light called “photons”, explaining odd observations such as the existence of a
cutoff frequency.
-
- But what determines whether light behaves as
a wave or as a particle? Light is not
sometimes a particle and sometimes a wave.
It is always both a wave and a particle. It's just that we highlight one
of the properties depending on which experiment we do.
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- In day-to-day life, we mostly experience
light as a wave, and it's this form that physicists find most useful to
manipulate. There's a full field called
metamaterials, by shaping a material with the same features as light, we can
enhance the interaction of light with the material and control the waves. For example, we can make solar absorbers
that can absorb light more efficiently for energy generation or metamaterial
MRI probes which are much more effective.
-
- However, light's double nature, known as
wave “particle duality”, is absolutely fundamental to the existence of the
world as we know it. This strange twinned behavior also extends to other
quantum particles, like electrons.
-
- You could not have an atom be stable if you
didn't have quantum mechanics with the electrons in specific states. If you remove the fact that it is a
particle, you remove the fact that it has a specific energy and life could not
exist.
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November 23, 2024 LIGHT - is
it a particle or a wave? 4618
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------ “Jim Detrick” -----------
--------------------- --- Sunday, November 24,
2024
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