Einstein's
Equation E=mc²
What does Einstein's
famous equation really mean?
BY ROBERT LAMB
Einstein's
equation E=mc² pops up on everything from baseball caps to bumper
stickers.
It's
even the title of a 2008 Mariah Carey album.
But
what does Albert Einstein's famous equation really mean?
For
starters, the E stands for energy and
the m stands for mass, a measurement of the
quantity of matter.
Energy
and matter are interchangeable.
Furthermore,
it's essential to remember that there's a set amount of energy/matter in the
universe.
If
you've ever read Dr. Seuss's children's book "The Sneetches," you
probably remember how the yellow, birdlike characters in the story go through a
machine to change back and forth between "star-bellied sneetches" and
"plain-bellied sneetches."
The
number of sneetches remains constant throughout the story, but the ratio
between plain- and star-bellied ones changes.
It's
the same way with energy and matter. The grand total remains constant, but
energy regularly changes form into matter and matter into energy.
Now
we're getting to the c² part of the equation, which serves the same purpose as
the star-on and star-off machines in "The Sneetches."
The c stands
for the speed of light, a universal constant, so the whole equation
breaks down to this: Energy is equal to matter multiplied by the speed of light
squared.
Why
would you need to multiply matter by the speed of light to produce energy?
The
reason is that energy, be it light waves or radiation, travels at the
speed of light.
That
breaks down to 186,000 miles per second (300,000 kilometers per second).
When
we split an atom inside a nuclear plant or an atomic bomb, the resulting energy
releases at the speed of light.
But
why is the speed of light squared?
The
reason is that kinetic energy, or the energy of motion, is
proportional to mass.
When
you accelerate an object, the kinetic energy increases to the tune of the speed
squared.
You'll
find an excellent example of this in any driver's education manual: If you
double your speed, the braking distance is four times longer, so the braking
distance is equal to the speed squared [source: UNSW Physics: Einsteinlight].
The
speed of light squared is a colossal number, illustrating just how much energy
there is in even tiny amounts of matter.
A
common example of this is that 1 gram of water -- if its whole mass were
converted into pure energy via E=mc² -- contains as much energy as 20,000 tons
(18,143 metric tons) of TNT exploding.
That's
why such a small amount of uranium or plutonium can produce such a massive
atomic explosion.
Einstein's
equation opened the door for numerous technological advances, from nuclear
power and nuclear medicine to the inner workings of the sun.
It
shows us that matter and energy are one.
About Robert Lamb
As a child, Robert Lamb dreamed of becoming a mad
scientist when he grew up. As this profession proved to be largely fictional,
however, he swallowed his heartbreak and turned his attention to the written
word instead. He earned his bachelor's degree in creative writing from the
University of Tennessee in Knoxville, which launched him on a career path
through high school English classrooms, small-town newsrooms and finally into
the offices of HowStuffWorks.
As a senior writer and podcaster for Stuff
to Blow Your Mind, Robert now spends his days
sifting through all the scientific wonders that make the world so mad and
amazing. He currently lives in Atlanta with his lovely wife and their beautiful
one-eyed cat. When he's not researching the apocalypse or the miracle we call a
space toilet, he enjoys listening to electronic music, painting the odd
miniature and writing fiction.
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