10 Discoveries Relativity Made Possible
10: The Expanding Universe
In 1924, Edward Hubble made a startling observation: Stars and galaxies move. By studying the redshifts of
distant galaxies, he found that as they move away from the earth, they increase in speed. In short, he demonstrated
that the universe is in a constant state of change and expansion.
Hubble based his calculations on the General Theory of Relativity, which made the idea of an expanding
universe possible. At first, Einstein rejected Hubble's conclusions. He preferred his cosmological constant idea, which
set out to prove the universe was static. Einstein was eventually forced to accept Hubble's findings, which were, after
all, based on his own theories of space and time.
Based on Hubble's initial discovery, three theories of the fate of our universe have been proposed: open, flat
and closed. In an open universe, expansion would go on forever. A flat universe would also mean indefinite expansion,
but the rate would eventually slow to zero. Perhaps the most disturbing is the "Big Crunch," or closed universe
scenario, in which the universe eventually stops expanding and collapses in on itself. The jury is still out on the fate of
our universe, but rest assured that we won't be around should the crunch come to pass.
9: The Big Bang Theory
The Big Bang theory is generally accepted as the most probable explanation of how our universe developed.
But where did the theory originate, and more specifically, how is it scientifically possible?
The General Theory of Relativity contains Einstein's 10 field equations (EFE). These equations have to do with
space-time (space and time are relative to one another), matter and energy. In 1922, a mathematician and
meteorologist named Alexander Friedmann found the solutions to the field equations, opening up the door to Georges
Lemaître's later proposal of what's now known as the Big Bang theory. Taking Friedmann's findings into account,
Lemaître hypothesized that our universe started out smaller than an atom, in a hot and extremely dense state. Over
millions of years, it expanded and cooled, resulting in what we know today.
One of the most radical ideas to emerge was the incredible age of our universe. At the time the theory came
about, the universe was thought to be more than 10 billion years old. (Scientists now believe it's more likely 13 billion
years of age.) Interestingly enough, Einstein was not a fan of this hypothesis, but he didn't dismiss it outright at the
time it was proposed. Astronomer and mathematician Fred Hoyle scoffed at Lemaître's idea, which directly conflicted
with his own thoughts on the subject. He mockingly nicknamed it the Big Bang, and the name stuck.
8: Time Travel
In 1895, H.G. Wells wrote "The Time Machine," one of the definitive science-fiction stories on time travel. In
the novella, a time traveler goes more than 800,000 years into the future to see what Earth is like at that time. His
findings are unusual to say the least. For hundreds of years, people have dreamed of hopping about among the years,
but outside of the fictional realm, it's been dismissed, for the most part, as folly. Ironically enough, we don't need to
jump into a time machine to get to the future. Technically we've already been there. While it's not a glamorous
experience, we're all time travelers in the sense that we move with time.
Don't be too disappointed -- time travel into the distant future is a theoretical possibility. Einstein's Special
Theory of Relativity, which relies on frames of reference to explain movement through space, demonstrates that time
is relative. There isn't one set hour that's universal for everyone and everything. Rather, time speeds up and slows
down depending on how fast one particular object is moving relative to another object. Oddly enough, the closer an
object travels to the speed of light, the slower time passes. If someone could travel at the speed on light, this "time
traveler" could, in theory, travel thousands of years into Earth's future and back again.
7: Black Holes
A black hole emerges from a seemingly sad event -- the death of a massive star. After its lights go out, so to
speak, all that's left is an extremely cold, extremely dense core. Einstein predicted the existence of black holes in
the field equations of his General Theory of Relativity. German physicist Karl Schwarzschild proved this prediction to
be correct. In a nutshell, a large mass affects space-time. In the region near a black hole, the gravitational pull is so
incredibly strong that anything nearby is pulled in, never to be seen again. Even light can't escape.
Black holes are extremely important for several reasons. They demonstrate that matter can be hidden. As we
will see later, they may contribute to gravitational waves. But the big whopper is this: The behavior of black holes
helps prove that Einstein's theories on gravity and space are fundamentally correct.
6: Gravitational Waves
A gravitational wave is a change in the shape or curvature of space-time. It occurs when two large, moving
masses interact. For example, when two neutron stars orbit each other, their motion creates ripples or vibrations in
space-time. These waves, which are relative to the size of the masses, are quite strong at the source but diminish as
they move outward. Think of it as a bird landing in a pond. Big splash on impact, little ripples rolling across the water.
What makes their possible existence so exciting? Much like black holes, the existence of gravitational waves
was predicted in Einstein's General Theory of Relativity, and proving their existence would support the validity of the
theory. Scientists also hope to use them to understand large-scale events in space, like the death of large stars and
the emergence of black holes. It's suspected that gravitational waves remain the same, even when objects pass
through them. This means they could carry important messages about the universe across the vastness of space.
5: Gravitational Lensing
Gravitational lensing sounds like a game you'd play in a physics lab with a particle laser and some goggles. In
actuality, it's yet another thing made possible with Einstein's relativity laws. Gravitational lensing is the bending of
light by massive objects in space. It's often referred to as "Einstein's Telescope," because in essence, it's a
telescope. There are two types of gravitational lensing: strong and weak. Strong lensing occurs when the gravitational
field of one object distorts the light from the object directly behind it. The distortion results in the projection of an
image of that object that can be magnified or multiplied depending on the position of the "lensing mass." Weak lensing
occurs when light from a galaxy passes another massive galaxy, galaxy cluster or dark-matter concentration. It's
much, much harder to see. In fact, astronomers must rely on patterns in galaxies to spot it, and doing so enables them
to create 3-D maps of matter.
Scientists are using gravitational lensing to research dark matter, which is all that we can't see in the
universe. Weak lensing via galaxy clusters is helping scientists look 13 billion years back in time to metaphorically visit
some of the very first galaxies to determine the distribution of matter. Being able to measure how wide matter has
spread will illustrate how the universe has expanded.
4: Reverse Gravitational Lensing
Quasars are extremely bright powerhouses that glow thousands of times more luminously than a galaxy
containing billions and billions of stars. Presumed to be energized by gigantic black holes, they've been used as tools
to study distant galaxies for decades. There's one slight problem: They're so luminous that little information can be
collected on the host galaxies where they live. Until now, that is.
Using two 10-meter (33-foot) telescopes at the W.M. Keck Observatory in Hawaii, researchers from Cal Tech
and the Ecole Polytechnique Federale de Lausanne (EPFL) have recently made an amazing discovery: Certain quasars
can be used as "reverse" gravitational lenses. What this means is that a faraway or "background" galaxy can be
magnified or "lensed" by the huge host galaxy of a foreground quasar. After narrowing down quasar candidates, they
hit upon one 1.6 billion light years away from Earth that's lensing a galaxy approximately 7.5 billion light years away.
Reverse gravitational lensing will help astronomers to learn and possibly identify the mass of a far-off galaxy. It will
also provide information about the relationship between quasars and their host galaxies, and perhaps provide clues
into their co-evolution .
3: Atomic Energy
E=mc2 is possibly the most recognizable scientific equation. With it, Einstein showed how a very sizable and
very powerful amount of energy could be released from an extremely small amount of matter. Enter atomic energy,
which is energy of an atom, the basic unit of all matter. In many ways, atomic energy is a catch-22. Its discovery
heralded an age of innovation and is also responsible for two of the most controversial and dangerous technologies of
the modern age: nuclear power and nuclear weapons.
The debates on the topics of nuclear energy and nuclear weapons have raged on for years. Nuclear power is a
clean energy source because it doesn't burn fossil fuels or emit colossal amounts of carbon dioxide into the air. It
does, however, leave nuclear waste in its wake, and nuclear weapons are a moral and political argument unto
themselves.
Those two very large issues aside, atomic energy is used in everyday things, like the cost-effective and
accurate ionization smoke detector. Have you gone to the dentist recently and gotten an X-ray? You've experienced
atomic energy at work. It's used in other areas of the medical field, as well, such as cancer treatments and research.
It's also being used in the growing field of nanotechnologies, particularly in boosting energy production from nuclear
power plants.
2: The Neutron Dance
What's really, really old, the result of a catastrophic supernova, and puts the theory of general relativity to
the test? Neutron stars, of course. Though usually small in diameter (less than 20 miles in most cases), these little
guys are dense. In fact, the only thing denser is a black hole. But as neutron stars have the advantage of luminosity,
we know quite a lot about them.
Neutron stars spin very fast. The recently discovered J1614-2230 makes a dizzying 317 revolutions per
second. With its white dwarf friend in orbit, J1614-2230 sends radio waves back to Earth. As these waves pass
through, their timing changes, supporting the idea that space and time are not constants. Neutron stars seem quite
friendly to us Earthlings. Over 1,500 spend their time blinking at us. Those that emit this pulsing light are aptly named
pulsars. Pulsars that have very precisely timed pulses are called millisecond pulsars. As pulsars age, they move away
from our galaxy and will eventually disappear for good. But before they go, scientists are using millisecond pulsars to
understand the mass and motions of planets, detect gravity waves and even improve clock accuracy on Earth.
1: Quantum Physics
Albert Einstein alone didn't invent quantum physics. Protons, electrons, photons and the like obviously existed
on their own for quite some time before he and Max Planck, the German physicist who first introduced quantum
theory, came along. What Einstein did do was build upon Planck's work, taking the theory of light to the next step.
To make a long story much shorter, Planck proposed that light energy exists not as continuous waves, but as a
stream of miniscule quanta particles or units. This theory, however, didn't explain the photoelectric effect. Using
Planck's calculations, Einstein proved that light energy striking a metal surface releases a flurry of electrons. This
solidified Planck's quantum theory, and the field of quantum physics came into being.
Quantum physics, also known as quantum mechanics, has had a startling impact on the scientific world. Particle
accelerators, which are unraveling the mysteries of matter and deepening our understanding of the universe, would
have been impossible without it. Technology -- like microchips, USB drives and computers -- relies on our
understanding of quantum physics, as well. Quantum physics is responsible for our understanding of the universe from
the smallest bits on up.