-
3845 - LIGHT
- mysteries beyond
comprehension? Light is both particle
and wave, and it is the fastest thing in the universe. It carries with it the
secrets of reality in ways we cannot completely understand. But understanding
its duality was an important step for our perplexed minds.
--------- 3845 - LIGHT - mysteries beyond comprehension?
- Light is the most mysterious of all things we
know exist. Light is not matter, but ,
it is both wave and particle, and it's the fastest thing in the
Universe.
-
- Light is a paradox. The nature of light is a mystery. Quantum physics has been essential along this
path, changing the way we describe light.
-
- If we traveled back to the 17th century, we
could follow Isaac Newton’s disagreements with Christiaan Huygens on the nature
of light. Newton would claim that light is made of tiny, indivisible atoms,
while Huygens would counter that light is a wave that propagates on a medium
that pervades all of space: “the ether“.
-
- They were both right, and they were both
wrong. If light is made of particles, what particles are these? And if it is a
wave propagating across space, what’s this weird ether?
-
- We now know that we can think of light in
both ways, as a particle, and as a wave. But during the 19th century the
particle theory of light was mostly forgotten, because the wave theory was so
successful, and something could not be two things.
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- In the early 1800s Thomas Young, who also
helped decipher the Rosetta Stone, performed beautiful experiments showing how
light diffracted as it passed through small slits, just like water waves were
known to do. Light would move through the slit and the waves would interfere
with one another, creating bright and dark fringes. Atoms couldn’t do that.
-
- But then, what was the ether? All great
physicists of the 19th century, including James Clerk Maxwell, who developed
the beautiful theory of electromagnetism, believed the ether was there, even if
it eluded us. After all, no wave could propagate in empty space.
-
- But this ether was quite bizarre. It was
perfectly transparent, so we could see faraway stars. It had no mass, so it
wouldn’t create friction and interfere with planetary orbits. Yet it was very
rigid, to allow for the propagation of the ultra-fast light waves.
-
- Maxwell had shown that if an electric charge
oscillated up and down, it would generate an electromagnetic wave. This was the
electric and magnetic fields tied up together, one bootstrapping the other as
they traveled through space. And more amazingly, this electromagnetic wave
would propagate at the speed of light, 186,282 miles per second. You blink your
eyes and light goes seven and a half times around the Earth.
-
- Light is an electromagnetic wave, and the
distance between two consecutive crests is a wavelength. Red light has a longer
wavelength than violet light. But the speed of any color in empty space is
always the same. Why is it about 186,000 miles per second? No one knows. The
speed of light is one of the constants of nature, numbers we measure that
describe how things behave.
-
- A crisis started in 1887 when Albert
Michelson and Edward Morley performed an experiment to demonstrate the
existence of the ether. They couldn’t prove a thing. Their experiment failed to
show that light propagated in an ether. It was chaos. Theoretical physicists
came up with weird ideas, saying the experiment failed because the apparatus
shrunk in the direction of the motion. Anything was better than accepting that
light actually can travel in empty space.
-
- Then Albert Einstein in 1905, the 26-year-old
patent officer wrote two papers that completely changed the way we picture
light and all of reality. The second paper was the “special theory of
relativity”.
-
- Einstein showed that if one takes the speed
of light to be the fastest speed in nature, and assumes that this speed is
always the same even if the light source is moving, then two observers moving
with respect to each other at a constant speed and making an observation need
to correct for their distance and time measurements when comparing their
results.
-
- So, if one is in a moving train while the
other is standing at a station, the time intervals of the measurements they
make of the same phenomenon will be different. Einstein provided a way for the
two to compare their results in a way that allows these to agree with each
other. The corrections showed that light could and should propagate in empty
space. It had no need for an ether.
-
- Einstein’s other paper explained the
“photoelectric effect“, which was measured in the lab in the 19th century but
remained a total mystery. What happens if light is shined onto a metal plate?
It depends on the light. Not on how bright it is, but on its color, or more
appropriately stated, its wavelength.
-
- Yellow or red light does nothing. But shine
a blue or violet light on the plate, and the plate actually acquires an
electrical charge, the term photoelectric.
How could light electrify a piece of metal? Maxwell’s wave theory of
light, so good at so many things, could not explain this.
-
- The young Einstein, bold and visionary, put
forth an outrageous idea. Light can be a wave, sure. But it can also be made of
particles. Depending on the circumstance, or on the type of experiment, one or
the other description prevails. For the photoelectric effect, we could picture
little “bullets” of light hitting the electrons on the metal plate and kicking
them out like billiard balls flying off a table.
-
- Having lost electrons, the metal now holds a
surplus positive charge. Einstein even provided a formula for the energy of the
flying electrons and equated it to the energy of the incoming light bullets, or
photons.
-
- The energy for the photons is E = h*c/L,
where c is the speed of light, L its wavelength, and h is Planck’s constant.
The formula tells us that smaller wavelengths mean more energy.
-
- Einstein essentially suggested what we now
call the wave-particle duality of light, showing that light can be both
particle and wave and will manifest differently depending on the circumstance.
The photons are the quanta of light, the smallest light packets possible.
Einstein thus brought quantum physics into the theory of light, showing that
both behaviors are possible.
-
- These are the photons that Bohr used in his
model of the atom. Light is both
particle and wave, and it is the fastest thing in the universe. It carries with
it the secrets of reality in ways we cannot completely understand. But
understanding its duality was an important step for our perplexed minds.
-
January 26, 2022 LIGHT
- mysteries beyond comprehension? 3845
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“Jim Detrick” -----------
--------------------- --- Thursday, January 26, 2023 ---------------------------
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