Einstein figured out that everything always moves at the speed of light, not through space, but through
spacetime. For example, even if you’re just sitting in a chair, and it seems like you’re not moving, in fact
you’re moving through time—hurtling into the future at the speed of light. Einstein unified the ideas
of motion through space, and motion through time, ultimately leading to E=mc2. This understanding
of the equivalence of energy and mass might one day provide abundant, clean energy for the rest of
humankind’s existence on earth. Explore the wonder and power of Einstein’s ideas!
What’s the big idea?
You measure space with a ruler and time with
a clock. Einstein’s special relativity idea unified
space and time into something called spacetime.
Like different sides of a cube, space and time are
now understood as just different sides of a single
thing—spacetime. To see this unity, consider that
both space and time can be measured with the
same instrument—a clock. How do you measure
space with a clock? Just time how long it takes
light to travel from here to there, and multiply
by the speed of light. For example, one lightsecond is the distance light travels in one second.
If you think this is trivial, you’re right. Until you
throw in the idea that our universe has a speed
limit, and that light always moves at this maximum
possible speed.
A speed limit? Nonsense! If you’re in a spaceship
zipping past a speed limit sign at almost the
speed of light, and I’m doing the same but in the
opposite direction, surely we will see each other
zip by at faster than the speed limit! Actually,
we won’t, and that’s because space and time are
relative. This means that, because of our relative
motion, I will experience your “spacetime cube”
as rotated relative to mine. What’s space for me
will be space and time for you, and vice versa, in
a remarkable way that guarantees that nothing
ever exceeds Einstein’s universal speed limit.
For example, let’s think of the Special Relativity
animation as showing me zipping past you, from
your point of view. The two clocks in my hands
are synchronized—they read the same time for
me, but not for you (I’m not kidding). As they
zip by, if you were to momentarily touch my two
clock faces at the same instant for you, the clock
you touch with your left hand would be in my
future, relative to the clock you touch with your
right hand. I would see you touch the clock in my
left hand first, then a short time later, the clock in
my right hand. And you would actually feel, with
your fingers, the different positions of the hands
of my two clocks. This is not an optical (or any
other kind) of illusion.
You would also notice that at the instant you
touched both of my clocks, your hands would
be unusually close together. I would physically
occupy less of your space than my own space
(notice in the animation how my width is
contracted). What’s space for you—the distance
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between your hands, is space and time for me:
space as in the distance between your hands
from my point of view (which is contracted by
the same factor by which you see my width
contracted!), and time as in the delay between
when your hands touch my left and right clocks.
This remarkable unification of space and time
quickly led Einstein to an even more surprising
unification: energy and mass are, in essence,
the same thing, as is expressed in his famous
equation E=mc2. This equation explains, for
example, the fusion process at the heart of
how the sun and stars work. It thus provides
the basic knowhow to construct an artificial
sun, a potential future technology that may one
day help solve the world’s energy and related
environmental problems once and for all. This is
the power of ideas!
What’s it good for?
Expanding Research Opportunities
Three hundred thousand kilometres in one
second—that is the speed limit of our universe,
and the idea at the heart of the unification of
space and time. Interesting things happen when
particles like electrons are accelerated to close
to this speed. For instance, at the Canadian
Light Source, electrons whizzing around a large
ring at 99.999687% the speed of light emit a
special type of light called synchrotron radiation.
Pouring out from as many as 19 “faucets,” this
extremely bright light is supplying industry,
academic, and government researchers with
an exceptionally fine-tuned probe to answer
questions in medicine, mining, and advanced
materials. Designing a research tool like this,
with twice as many control points as a nuclear
Candu reactor, relies on innovative engineering
and the physics of special relativity. Imagine:
Einstein’s ideas about space and time have led
to the creation of a machine that generates
beams of light billions of times brighter than
sunlight, a tool that’s helping researchers create
a brighter tomorrow.
Mass and Energy
E=mc2. This simple mathematical statement
has profound implications—energy and mass
are, in essence, the same. It means that a cup
of hot coffee weighs more than the same
cup after it has cooled, giving off some of its
energy, even though the mass difference in
our coffee example is too small to measure.
The same mass-energy conversion happens in
every chemical reaction, from baking cookies
to burning fossil fuels. But it is not until the massenergy conversions involve the nucleus of an
atom that the true power of Einstein’s idea shows
itself clearly. Fission—the splitting of large atomic
nuclei—is one example of this idea in action,
currently providing energy for cities all over
the world. Fusion—the joining of small atomic
nuclei—is another, and may one day help solve
the world’s energy and related environmental
problems. Small idea. Big impact!
National Lab System
During the early years of the 20th century
theoretical physics underwent a revolution, and
the implications of that revolution—in particular
special relativity and E=mc2—led to a new
model for how successful science can be done.
The Manhattan Project to build the world’s
first atomic bomb brought together some of
the greatest physics minds of the time. It was
a government-funded high concentration of
intellectual and experimental resources. And
it worked. After the war, it eventually led to the
national laboratory system in the United States,
one of the largest scientific research systems
in the world. The research covers a wide range
of questions in physics, chemistry, materials
science, and other areas of the physical sciences,
for instance finding solutions to the world’s
energy and environmental problems, two of the
most important concerns facing humanity today.
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