Human beings have always been fascinated by the celestial sphere above, whose twinkling lights have inspired many theories and artistic endeavors.This Blog would like to show the mysteries of the universe and the technologies searching to provide the answers.Any material or informations of this blog has been taken from the Internet.
This artist's illustration shows the evolution of the universe over time, starting with the Big Bang (left).(Image credit: NASA)Was the universe created with a Big Bang 13.7 billion years ago, or has
it been expanding and contracting for eternity? A new paper, inspired by
alternative explanations of the physics of black holes, explores the
latter possibility, and rejects a core tenet of the Big Bang hypothesis.
The universal origin story known as the Big Bang postulates that,
13.7 billion years ago, our universe emerged from a singularity — a
point of infinite density and gravity — and that before this event,
space and time did not exist (which means the Big Bang took place at no
place and no time).
There is ample evidence to show that the universe did undergo an early period of rapid expansion — in a trillionth of a trillionth of a trillionth of a second, the universe is thought to have expanded by a factor of 1078
in volume. For one, the universe is still expanding in every direction.
The farther away an object is, the faster it appears to move away from
an observer, suggesting that space itself is expanding (rather than
objects simply moving through space at a steady rate). [Big Bang Theory: 5 Weird Facts About the Universe's Birth].
The afterglow of the Big Bang reveals the geometry of the universe.
Einstein’s field equations describe gravity not as a force, but rather a
property of space-time — the fabric of the universe. Earth travels
around the Sun in a circular orbit because the Sun’s mass deforms the
space-time around it like a bowling ball
on a trampoline.
In ancient times, scholars such as Aristotle thought that heavy objects
would fall faster than lightweight objects under the influence of
gravity. About four and a half centuries ago, Galileo Galilei decided to
test this assumption experimentally. He dropped objects of different
masses from the Tower of Pisa and found that gravity actually causes
them all to fall the same way. More than 300 years later, Albert
Einstein was struck by Galileo’s finding. He realized that if all
objects follow the same trajectory under gravity, then gravity might not
be a force but rather a property of space-time — the fabric of the
universe, which all objects experience in the same way.
In one of the most important advances in modern physics, Einstein
recognized that when space-time is curved, objects do not follow
straight lines. He reckoned that Earth, for example, orbits the Sun in a
circle because the Sun curves space-time in its vicinity. This is
similar to the path of a ball on the surface of a trampoline whose
center is weighed down by a person.
In November 1915, Einstein published the mathematical equations that
established the foundation for his general theory of relativity. These
equations describe the link between matter and the space-time in which
it resides, showing that mass deforms space-time and influences the path
of matter. In the words of physicist John Wheeler: “Space-time tells
matter how to move and matter tells space-time how to curve.”
Artistic conception of gravitational waves. Public Domain Image, source: R. Hurt/Caltech-JPL.
Yes, gravity can forms waves. Gravitational waves are ripples in
spacetime that travel through the universe. If you think of gravity as a
force acting at a distance, it is difficult to visualize how
gravitational waves could form. However, if you use the more accurate
description of gravity that was developed by Einstein in his general
theory of relativity, these concepts become more logical.
General relativity describes gravity as a warping or curvature of
space and time. All objects warp spacetime. When other objects travel
through this warped spacetime, they end up traveling along curved paths.
These curved paths look like they result from a force being exerted on
the objects, when in reality they result from spacetime itself being
warped. For instance, when you throw a baseball to your friend, it
follows a smooth parabolic trajectory under the influence of gravity.
Isaac Newton's laws would say that earth's mass is creating a
gravitational force which acts on the baseball, gradually pulling the
baseball down from straight-line motion. However, the more accurate
description goes like this: The earth warps space and time. The baseball
is actually traveling in a straight line relative to spacetime, but
since spacetime itself is curved, this straight line becomes a curve
when viewed by an external observer. In this way, there is not really
any direct force acting on the baseball. It just looks that way because
of the spacetime warpage. If all of this sounds too strange to be
believed, you should know that Einstein's general relativity has been
mainstream science for over a hundred years and has been verified by
countless experiments.
In principle, all objects warp spacetime. However, low-mass objects
such as houses and trees warp spacetime to such a small extent that it's
hard to notice their effects. It takes high-mass objects such as
planets, moons, or stars in order for the gravitational effects to be
noticeable. The more mass an object has, the more it warps spacetime,
and the stronger its gravitational effect on other objects. For
instance, a black hole has such a high amount of mass in such a small
volume that even light cannot escape. Inside the event horizon of a
black hole, spacetime is so strongly warped that all possible paths that
light can take eventually lead deeper into the black hole.
Since spacetime warpage is caused by mass, the warpage travels along
with the mass. For instance, earth warps the surrounding spacetime into
an inward-pinched shape (roughly speaking). As the earth travels around
the sun in its year-long orbit, this pattern of spacetime curvature
travels along with the earth. An observer that is stationary relative to
the sun and is at a point close to earth's path would see the earth get
closer and then farther away, closer and then farther away, in one-year
cycles. Therefore, this observer would see earth's pinched spacetime
pattern come closer and then farther away, closer and then farther away,
in one-year cycles. Because the observer himself sits in spacetime and
experiences it, the observer therefore sees his own local spacetime as
being pinched, and then not pinched, pinched and then not pinched, in
one-year cycles. The observer is therefore experiencing an oscillation
of spacetime curvature that is traveling outward from the earth, i.e. a
gravitational wave. This actually happens in the real world. However, in
practice, gravitational waves are so incredibly weak that they have no
significant effect on daily life. The oscillating spacetime warpage of a
passing gravitational wave is far too weak for humans to notice or
feel. Only very sensitive, expensive, modern equipment is able to detect
gravitational waves. In fact, it took a hundred years after Einstein
predicted the existence of gravitational waves for technology to improve
enough to be able to detect them.
This idea of periodically-pinched spacetime is over-simplified. If
you apply the full mathematics of general relativity, you find that an
observer experiencing a passing gravitational wave does not
experience a cycling pattern of spacetime pinching and no pinching.
Rather, the observer experiences a cycling pattern of stretching in the
sideways directions with pinching in the other sideways directions, and
then pinching in the first sideways directions with stretching in the
other sideways directions. For instance, suppose a gravitational wave
from a distant star traveled straight down toward earth's surface right
where you sit. If the gravitational wave were a thousand trillion times
stronger than it can actually get in the real world, then you would see a
ruler that is aligned with the east-west directions momentarily become
shorter while a ruler that is aligned with the north-south directions
momentarily become longer. And then a moment later, the east-west ruler
would become longer while the north-south ruler would be shorter. Each
ruler would continue to get periodically longer and shorter until the
gravitational wave has passed. There is nothing wrong with the rulers.
Spacetime itself is warping and everything in spacetime experiences the
warping.
Although this effect is very weak, it actually happens. A
gravitational wave detector is effectively just a very long ruler with
the ability to measure the length of the ruler very accurately. For
instance, each arm of a LIGO detector is 2.5 miles long and uses lasers
to accurately measure lengths. Even with large, modern, expensive
detectors, gravitational waves are so weak that only the largest waves
can currently be detected. The current detectors cannot pick up the
gravitational waves generated by planets orbiting stars or moons
orbiting planets. The largest gravitational waves are generated when two
black holes orbit each other rapidly immediately before falling
together and merging. Large waves are also generated when two neutron
stars orbit each other, or when a black hole and a neutron star orbit
each other, immediately before merging. These are the only types of
gravitational waves that have been detected so far.
In general, a gravitational wave is created any time a mass
accelerates. Traveling along a circular path is only one type of
acceleration. If an object with mass speeds up along a straight path,
this is also a type of acceleration, and therefore it should create
gravitational waves. Similarly, an object with mass slowing down along a
straight path should also create gravitational waves. However, on the
astronomical scale, an object traveling steadily along a circular orbit
is far more common than an object violently slowing down or speeding up.
Another point to keep in mind is that the gravitational waves created
by the earth in its yearly orbit are not only extremely weak, they also
have a period of one year. This means that a gravitational wave
detector on another planet would have to watch for several years in
order to pick up the oscillatory shape of the gravitational waves
generated by earth's orbital motion. In contrast, immediately before two
black holes merge, they orbit each other so rapidly that it only takes a
fraction of a second for each to complete an orbit. This is another
factor that makes these types of gravitational waves easier to detect.
Earth, our home planet, is a world unlike any other. The third planet
from the sun, Earth is the only place in the known universe confirmed
to host life.
With a radius of 3,959 miles, Earth is the fifth
largest planet in our solar system, and it's the only one known for sure
to have liquid water on its surface. Earth is also unique in terms of
monikers. Every other solar system planet was named for a Greek or Roman
deity, but for at least a thousand years, some cultures have described
our world using the Germanic word “earth,” which means simply “the
ground.”
Our dance around the sun
Earth orbits the sun once every
365.25 days. Since our calendar years have only 365 days, we add an
extra leap day every four years to account for the difference.
Though
we can't feel it, Earth zooms through its orbit at an average velocity
of 18.5 miles a second. During this circuit, our planet is an average of
93 million miles away from the sun, a distance that takes light about
eight minutes to traverse. Astronomers define this distance as one
astronomical unit (AU), a measure that serves as a handy cosmic
yardstick.
Earth
rotates on its axis every 23.9 hours, defining day and night for
surface dwellers. This axis of rotation is tilted 23.4 degrees away from
the plane of Earth's orbit around the sun, giving us seasons. Whichever
hemisphere is tilted closer to the sun experiences summer, while the
hemisphere tilted away gets winter. In the spring and fall, each
hemisphere receives similar amounts of light. On two specific dates each
year—called the equinoxes—both hemispheres get illuminated equally.
Many layers, many features
About
4.5 billion years ago, gravity coaxed Earth to form from the gaseous,
dusty disk that surrounded our young sun. Over time, Earth's
interior—which is made mostly of silicate rocks and
metals—differentiated into four layers.
At the planet's heart lies
the inner core, a solid sphere of iron and nickel that's 759 miles wide
and as hot as 9,800 degrees Fahrenheit. The inner core is surrounded by
the outer core, a 1,400-mile-thick band of iron and nickel fluids.
Beyond the outer core lies the mantle, a 1,800-mile-thick layer of
viscous molten rock on which Earth's outermost layer, the crust, rests.
On land, the continental crust is an average of 19 miles thick, but the
oceanic crust that forms the seafloor is thinner—about three miles
thick—and denser.
Like Venus and Mars, Earth has mountains, valleys, and volcanoes. But
unlike its rocky siblings, almost 70 percent of Earth's surface is
covered in oceans of liquid water that average 2.5 miles deep. These
bodies of water contain 97 percent of Earth's volcanoes and the mid-ocean ridge, a massive mountain range more than 40,000 miles long.
Earth's
crust and upper mantle are divided into massive plates that grind
against each other in slow motion. As these plates collide, tear apart,
or slide past each other, they give rise to our very active geology.
Earthquakes rumble as these plates snag and slip past each other. Many
volcanoes form as seafloor crust smashes into and slides beneath
continental crust. When plates of continental crust collide, mountain
ranges such as the Himalaya are pushed toward the skies.
Protective fields and gases
Earth's
atmosphere is 78 percent nitrogen, 21 percent oxygen, and one percent
other gases such as carbon dioxide, water vapor, and argon. Much like a
greenhouse, this blanket of gases absorbs and retains heat. On average,
Earth's surface temperature is about 57 degrees Fahrenheit; without our
atmosphere, it'd be zero degrees. In the last two centuries, humans have added enough greenhouse gases to the atmosphere to raise Earth's average temperature by 1.8 degrees Fahrenheit. This extra heat has altered Earth's weather patterns in many ways.
The
atmosphere not only nourishes life on Earth, but it also protects it:
It's thick enough that many meteorites burn up before impact from
friction, and its gases—such as ozone—block DNA-damaging ultraviolet
light from reaching the surface. But for all that our atmosphere does,
it's surprisingly thin. Ninety percent of Earth's atmosphere lies within just 10 miles of the planet's surface.
We also enjoy protection from Earth's magnetic field, generated by
our planet's rotation and its iron-nickel core. This teardrop-shaped
field shields Earth from high-energy particles launched at us from the
sun and elsewhere in the cosmos. But due to the field's structure, some
particles get funneled to Earth's Poles and collide with our atmosphere,
yielding aurorae, the natural fireworks show known by some as the
northern lights.
Spaceship Earth
Earth is the planet we
have the best opportunity to understand in detail—helping us see how
other rocky planets behave, even those orbiting distant stars. As a
result, scientists are increasingly monitoring Earth from space. NASA
alone has dozens of missions dedicated to solving our planet's mysteries.
At
the same time, telescopes are gazing outward to find other Earths.
Thanks to instruments such as NASA's Kepler Space Telescope, astronomers
have found more than 3,800 planets orbiting other stars, some of which are about the size of Earth,
and a handful of which orbit in the zones around their stars that are
just the right temperature to be potentially habitable. Other missions,
such as the Transiting Exoplanet Survey Satellite, are poised to find
even more.
If you were to list the imperfections of the standard model –
physicists’ remarkably successful description of matter and its
interactions – pretty high up would have to be its prediction that we don’t exist.
According to the theory, matter and antimatter were created in equal
amounts at the big bang. By rights, they should have annihilated each
other totally in the first second or so of the universe’s existence. The
cosmos should be full of light and little else.
And yet here we are. So too are planets, stars and galaxies; all, as
far as we can see, made exclusively out of matter. Reality 1, theory 0.
There are two plausible solutions to this existential mystery. First,
there might be some subtle difference in the physics of matter and
antimatter that left the early universe with a surplus of matter. While
theory predicts that the antimatter world is a perfect reflection of our
own, experiments have already found suspicious scratches in the mirror.
In 1998, CERN experiments showed that one particular exotic particle,
the kaon, turned into its antiparticle slightly more often than the
reverse happened, creating a tiny imbalance between the two.
That lead was followed up by experiments at accelerators in California and Japan,
which in 2001 uncovered a similar, more pronounced asymmetry among
heavier cousins of the kaons known as B mesons. Once the LHC at CERN is
back up and running later this year, its LHCb experiment will use a 4500-tonne detector to spy out billions of B mesons and pin down their secrets more exactly.
But LHCb won’t necessarily provide the final word on where all that
antimatter went. “The effects seem too small to explain the large-scale
asymmetry,” says Frank Close, a particle physicist at the University of
Oxford.
The second plausible answer to the matter mystery is that
annihilation was not total in those first few seconds: somehow, matter
and antimatter managed to escape each other’s fatal grasp. Somewhere out
there, in some mirror region of the cosmos, antimatter is lurking and
has coalesced into anti-stars, anti-galaxies and maybe even anti-life.
“It’s not such a daft idea,” says Close. When a hot magnet cools, he
points out, individual atoms can force their neighbours to align with
magnetic fields, creating domains of magnetism pointing in different
directions. A similar thing could have happened as the universe cooled
after the big bang. “You might initially have a little extra matter over
here and a little extra antimatter somewhere else,” he says. Those
small differences could expand into large separate regions over time.
These antimatter domains, if they exist, are certainly not nearby.
Annihilation at the borders between areas of stars and anti-stars would
produce an unmistakable signature of high-energy gamma rays. If a whole
anti-galaxy were to collide with a regular galaxy, the resulting
annihilation would be of unimaginably colossal proportions. We haven’t
seen any such sign, but then again there’s a lot of universe that we
haven’t looked at yet – and whole regions of it that are too far away
ever to see.
Finding anti-helium or other anti-atoms heavier than hydrogen would
be concrete evidence for an anti-cosmos. It would imply that anti-stars
are cooking up anti-atoms through nuclear fusion, just as regular stars
fuse normal atoms.
Until now, researchers have believed that dark energy accounted for
nearly 73 percent of the ever-accelerating, expanding universe.
For
many years, this mechanism has been associated with the so-called
cosmological constant, developed by Einstein in 1917, that refers to an
unknown repellant cosmic power.
But because the cosmological constant—known as dark energy—cannot
be measured directly, numerous researchers, including Einstein, have
doubted its existence—without being able to suggest a viable
alternative.
Until now. In a new study by researchers at the University of Copenhagen, a model was tested that replaces dark energy with a dark matter in the form of magnetic forces.
"If what we discovered is accurate, it would upend our belief that what we thought made up 70 percent of the universe
does not actually exist. We have removed dark energy from the equation
and added in a few more properties for dark matter. This appears to have
the same effect upon the universe's expansion as dark energy," explains
Steen Harle Hansen, an associate professor at the Niels Bohr
Institute's DARK Cosmology Centre.
The universe expands no differently without dark energy
The usual understanding of how the universe's energy is distributed
is that it consists of five percent normal matter, 25 percent dark
matter and 70 percent dark energy.
In the UCPH researchers' new model, the 25 percent share of dark
matter is accorded special qualities that make the 70 percent of dark
energy redundant.
"We don't know much about dark matter other than that it is a heavy
and slow particle. But then we wondered—what if dark matter had some
quality that was analogous to magnetism in it? We know that as normal
particles move around, they create magnetism. And, magnets attract or
repel other magnets—so what if that's what's going on in the universe?
That this constant expansion of dark matter is occurring thanks to some
sort of magnetic force?" asks Steen Hansen.
Computer model tests dark matter with a type of magnetic energy
Hansen's question served as the foundation for the new computer
model, where researchers included everything that they know about the
universe—including gravity, the speed of the universe's expansion and X,
the unknown force that expands the universe.
"We developed a model that worked from the assumption that dark
matter particles have a type of magnetic force and investigated what
effect this force would have on the universe. It turns out that it would
have exactly the same effect on the speed of the universe's expansion
as we know from dark energy," explains Steen Hansen.
However, there remains much about this mechanism that has yet to be understood by the researchers.
And it all needs to be checked in better models that take more factors into consideration. As Hansen puts it:
"Honestly, our discovery may just be a coincidence. But if it isn't,
it is truly incredible. It would change our understanding of the
universe's composition and why it is expanding. As far as our current
knowledge, our ideas about dark matter with a type of magnetic force and the idea about dark energy
are equally wild. Only more detailed observations will determine which
of these models is the more realistic. So, it will be incredibly
exciting to retest our result.
