1: Heisenberg's Uncertainty Principle
Einstein's broader
theory of relativity told
us more about how the universe works and helped to lay the foundation for
quantum physics, but it also introduced more confusion into theoretical
science. In 1927, this sense that the universe's laws were, in some contexts,
flexible, led to a groundbreaking discovery by the German scientist Werner
Heisenberg.
In postulating his Uncertainty
Principle, Heisenberg realized that it was impossible to
simultaneously know, with a high level of precision, two properties of a
particle. In other words, you can know the position of an electron with a high
degree of certainty, but not its momentum and vice versa.
Niels Bohr later made a discovery that helps to explain
Heisenberg's principle. Bohr found that an electron has the qualities of both a
particle and a wave, a concept known as wave-particle
duality, which has become a cornerstone of quantum physics. So
when we measure an electron's position, we are treating it as a particle at a
specific point in space, with an uncertain wavelength. When we measure its momentum,
we are treating it as a wave, meaning we can know the amplitude of its
wavelength but not its location.
2: Theory of General Relativity
Albert Einstein's theory of general relativity remains an important and essential
discovery because it permanently altered how we look at the universe.
Einstein's major breakthrough was to say that space and time are not absolutes
and that gravity is not simply a force applied to an object or mass. Rather,
the gravity associated
with any mass curves the very space and time (often called space-time) around
it.
To conceptualize this, imagine you're traveling across theEarth in
a straight line, heading east. After a while, if someone were to pinpoint your
position on a map, you'd actually be both east and far south of your original
position. That's because the Earth is curved. To travel directly east, you'd
have to take into account the shape of the Earth and angle yourself slightly
north. (Think about the difference between a flat paper map and a spherical
globe.)
Space is pretty much the same. For example, to the occupants of
the shuttle orbiting the Earth, it can look like they're traveling on a
straight line through space. In reality, the space-time around them is being
curved by the Earth's gravity (as it would be with any large object with
immense gravity such as a planet or a black hole), causing them to both move
forward and to appear to orbit the Earth.
Einstein's theory had tremendous implications for the future of
astrophysics and cosmology. It explained a minor, unexpected anomaly in
Mercury's orbit, showed how starlight bends and laid the theoretical
foundations for black holes.
3: Evolution and Natural Selection
Now that we've established some of the fundamental concepts of
how our universe began and how physics play out in our daily lives, let's turn
our attention to the human form and how we got to be the way we are. According
to most scientists, all life on Earth has
a common ancestor. But in order to produce the immense amount of difference
among all living organisms, certain ones had to evolve into
distinct species.
In a basic sense, this differentiation occurred through
evolution, through descent with modification [source: UCMP].Populations of organisms developed different
traits, through mechanisms such as mutation. Those with traits that were more
beneficial to survival such as, a frog whose brown coloring allows it to be
camouflaged in a swamp, were naturally selected for survival; hence the term natural selection.
It's possible to expand upon both of these theories at greater
length, but this is the basic, and groundbreaking, discovery that Darwin made
in the 19th century: that evolution through natural selection accounts for the
tremendous diversity of life on Earth.
4: Archimedes' Buoyancy Principle
After he discovered his principle of buoyancy, the ancient Greek
scholar Archimedes allegedly yelled out "Eureka!" and ran naked
through the city of Syracuse. The discovery was that important. The story goes
that Archimedes made his great breakthrough when he noticed the water rise
as he got into the tub [source: Quake].
According to Archimedes'
buoyancy principle, the force acting on, or buoying, a
submerged or partially submerged object equals the weight of the liquid that
the object displaces. This sort of principle has an immense range of
applications and is essential to calculations of density, as well as designing
submarines and other oceangoing vessels.
5: Laws of Thermodynamics
The British physicist and novelist C.P. Snow once said that a
nonscientist who didn't know the second law of thermodynamics was like a
scientist who had never read Shakespeare [source: Lambert].
Snow's now-famous statement was meant to emphasize both the importance of
thermodynamics and the necessity for nonscientists to learn about it.
Thermodynamics is the study of how energy works in a
system, whether it's an engine or the Earth's core.
It can be reduced to several basic laws, which Snow cleverly summed up as
follows [source: Physics Planet]:
·
You can't win.
·
You can't break even.
·
You can't quit the game.
Let's unpack these a bit. By saying you can't win, Snow meant
that since matter and energy are conserved, you can't get one without giving up
some of the other (i.e., E=mc²). It also means that for an engine to produce
work, you have to supply heat, although in anything other than a perfectly
closed system, some heat is inevitably lost to the outside world, which then
leads to the second law.
The second statement -- you can't break even -- means that due
to ever-increasing entropy, you can't return to the same energy state. Energy
concentrated in one place will always flow to places of lower concentration.
Finally, the third law -- you can't quit the game -- refers to
absolute zero, the lowest theoretical temperature possible, measured at zero
Kelvin or (minus 273.15 degrees Celsius and minus 459.67 degrees Fahrenheit).
When a system reaches absolute zero, molecules stop all movement, meaning that
there is no kinetic energy, and entropy reaches its lowest possible value. But
in the real world, even in the recesses of space, reaching absolutely zero is
impossible -- you can only get very close to it.
6: Newton's Laws of Motion
As long as we're talking about one of the greatest scientists who ever
lived, let's move on to Newton's other famous laws. His three
laws of motion form an essential component of modern physics. And like many
scientific laws, they're rather elegant in their simplicity.
The first of the three laws states an object in motion stays in motion
unless acted upon by an outside force. For a ball rolling across the floor,
that outside force could be the friction between the ball and the floor, or it
could be the toddler that kicks the ball in another direction.
The second law establishes a connection between an object's mass (m)
and its acceleration (a), in the form of the equation F = m × a. F represents
force, measured in Newtons. It's also a vector, meaning it has a directional
component. Owing to its acceleration, that ball rolling across the floor has a
particular vector, a direction in which it's traveling, and it's
accounted for in calculating its force.
The third law is rather pithy and should be familiar to you: For every
action there is an equal and opposite reaction. That is, for every force
applied to an object or surface, that object pushes back with equal force.
7: Universal Law of Gravitation
We may take it for granted now, but more than 300 years ago Sir Isaac Newton proposed a revolutionary idea: that
any two objects, no matter their mass, exert gravitational force toward one another. This law is
represented by an equation that many high schoolers encounter in physics class.
It goes as follows:
F = G × [(m1m2)/r²]
F = G × [(m1m2)/r²]
F is the gravitational force between the two
objects, measured in Newtons. M1 and m2 are the masses of the two objects,
while r is the distance between them.G is the gravitational constant, a
number currently calculated to be 6.672 × 10-11 N m² kg-2 [source:Weisstein].
The benefit of the universal law of gravitation is that it
allows us to calculate the gravitational pull between any two objects. This
ability is especially useful when scientists are, say, planning to put a satellite in orbit or charting the course of the moon.
8: Kepler's Laws of Planetary Motion
For centuries, scientists battled with one another and with religious
leaders about the planets' orbits, especially about whether they orbited our
sun. In the 16th century, Copernicus put forth his controversial concept of a
heliocentric solar system, in which the planets revolved around the sun -- not
the Earth. But it would take Johannes Kepler, building on work performed by
Tyco Brahe and others, to establish a clear scientific foundation for the
planets' movements.
Kepler's three laws of planetary motion -- formed in
the early 17th century -- describe how planets orbit the sun. The first law,
sometimes called the law of orbits, states that planets orbit the
sun elliptically. The second law, the law of areas, states that a
line connecting a planet to the sun covers an equal area over equal periods of
time. In other words, if you're measuring the area created by drawing a line
from the Earth to the sun and tracking the Earth's movement over 30 days, the
area will be the same no matter where the Earth is in its orbit when
measurements begin.
The third one, the law of periods, allows us to establish a
clear relationship between a planet's orbital period and its distance from the
sun. Thanks to this law, we know that a planet relatively close to the sun,
like Venus, has a far briefer orbital period than a distant planet, such as
Neptune.
9: Hubble's Law of Cosmic Expansion
Let's stick with Edwin Hubble for a second. While the 1920s roared past
and the Great Depression limped by, Hubble was
performing groundbreaking astronomical research. Hubble not only proved that
there were other galaxies besides theMilky
Way, he also discovered that these galaxies were zipping away from
our own, a motion he called recession.
In order to quantify the velocity of this galactic movement, Hubble
proposed Hubble's Law of Cosmic Expansion, aka Hubble's law, an
equation that states: velocity = H0 ×distance. Velocity represents
the galaxy's recessional velocity; H0 is the Hubble
constant, or parameter that indicates the rate at which the universe is
expanding; and distance is the galaxy's distance from the one
with which it's being compared.
Hubble's constant has been calculated at different values over time, but
the current accepted value is 70 kilometers/second per megaparsec, the latter
being a unit of distance in intergalactic space [source:White]. For our purposes, that's not so
important. What matters most is that Hubble's law provides a concise method for
measuring a galaxy's velocity in relation to our own. And perhaps most
significantly, the law established that the universe is made up of many
galaxies, whose movements trace back to the big bang.
10: Big Bang Theory
If you're going to know one scientific theory, make it the one that
explains how the universe arrived at its present state. Based on research
performed by Edwin Hubble, Georges Lemaitre and Albert Einstein, among others,
the big bang theory postulates
that the universe began almost 14 billion years ago with a massive expansion
event. At the time, the universe was confined to a single point, encompassing
all of the universe's matter. That original movement continues today, as the
universe keeps expanding outward.
The theory of the big bang gained widespread support in the scientific
community after Arno Penzias and Robert Wilson discovered cosmic
microwave background radiation in 1965. Using radio telescopes, the
two astronomers detected cosmic noise, or static, that didn't dissipate over
time. Collaborating with Princeton researcher Robert Dicke, the pair confirmed
Dicke's hypothesis that the original big bang left behind low-level radiation
detectable throughout the universe.
