Cosmic
light horizon
In
astronomy, the cosmic light horizon is a "horizon" which marks the
edge of the visible universe. This horizon is the edge of a sphere,
centered upon Terra, which is ~14-15B light years in radius; this
figure is sometimes referred to as the "lookback distance" (because
astronomers, who view distant objects, are "looking back" into the
history of the universe -- see: speed of light). The general homogeneity
of temperatures, at the edge of the cosmic horizon, is part of the
evidence for the "Big Bang".The universe as we know it was initially
almost uniformly filled with energy and extremely hot. As the distances
in the universe rapidly grew, the temperature dropped, leading to
the creation of the known forces of physics, elementary particles,
and eventually hydrogen and helium atoms in a process called Big
bang nucleosynthesis.
Over time,
the slightly denser regions of the almost, but not quite, uniformly
distributed matter were pulled together by gravity into clumps,
forming gas clouds, stars, galaxies, and the other astronomical
structures seen today. The details of how the process of galaxy
formation occurred depends on the type of matter in the universe,
and the three competing pictures of how this occurred are known
as cold dark matter, hot dark matter, and baryonic matter. These
three models have be tested through computer simulations and observations
of galactic correlation functions. |
Hubble's
law
is the statement in astronomy that galaxies
move away from each other, and that the velocity with which they
recede is proportional to their distance. It leads to the picture
of an expanding universe and, by extrapolating back in time, to
the Big Bang theory. The law was first formulated by Edwin Hubble
in 1929. Hubble compared the distances to nearby galaxies to their
redshift, found a linear relationship, and interpreted the redshift
as caused by the receding velocity. His estimate of the proportionality
constant, now known as Hubble's constant, was however off by a
factor of about 10. Furthermore, if one takes Hubble's original
observations and then use the most accurate distances and velocities
currently known, one ends up with a random scatter plot with no
discernable relationship between redshift and velocity. Nevertheless
the relationship was confirmed by observations after Hubble.
The National Aeronautics
and Space Administration (NASA) is the government
department responsible for the United States of America's space
program and long-term general aerospace research. NASA's predecessor
was the National Advisory Committee on Aeronautics (NACA), which
was formed in 1915 to promote aeronautical research and development
in the United States. In 1959, the department was reorganized
and given control of the space program, which had previously been
undertaken separately by different branches of the military. Some
of its most notable achievements are sending the first men to
the moon in 1969, the ongoing space shuttle program, contributions
to the international space station, and the launching of various
space probes and satellites. Its activities have led to a wealth
of scientific discoveries, many of which have led to important
military and commercial applications. In recent years, its strategy
has begun to shift from pursuing a few high-cost projects, to
pursuing a number of smaller and lower-cost projects ("faster,
better, cheaper"), including the use of unmanned rockets, probes
and robots. NASA space missions * Manned space missions o Mercury
program o Gemini program o Apollo program o Skylab o Space Shuttle
o International Space Station * Unmanned space missions o Mariner
program o Surveyor program o Viking program o Voyager program
o Mars Pathfinder o COBE NASA has also collaborated with the ESA
on some missions: * Hubble Space Telescope * Ulysses Field installations
There are 12 NASA field installations: * John F. Kennedy Space
Center, Florida * Ames Research Center, Moffett Field, California
* Dryden Flight Research Center, Edwards, California * Goddard
Space Flight Center, Greenbelt, Maryland * Jet Propulsion Laboratory,
near Pasadena, California * Lyndon B. Johnson Space Center, Houston,
Texas * Langley Research Center, Hampton, Virginia * Glenn Research
Center, Cleveland, Ohio * George C. Marshall Space Flight Center,
Huntsville, Alabama * Michoud Assembly Facility, New Orleans,
Louisiana * John C. Stennis Space Center, Bay St. Louis, Mississippi
* Wallops Flight Facility, Wallops Island, Virginia
Groups and clusters of galaxies
Matter throughout the visible
Universe has, over the course of the Universe's history, aggregated
into a range of large-scale structures under the influence of
gravity. Groups of galaxies Groups of galaxies are the smallest
aggregates of galaxies. They typically have the following properties.
* They contain less than 50 galaxies. * They have a diameter of
about 2 megaparsec (Mpc) (see 1 E22 m for distance comparisons).
* Their mass is approximately 1013 solar masses. * The spread
of velocities for the individual galaxies is about 150 km/s. Clusters
of galaxies Clusters are larger than groups, although there is
no sharp dividing line between a group and a cluster. When observed
visually, clusters appear to be collections of galaxies held together
by mutual gravitational attraction. However their velocities are
too large for them to remain gravitationally bound by their mutual
attractions, implying the presence of an additional invisible
mass component. X-ray studies have revealed the presence of large
amounts of intergalactic gas. This gas is very hot, around 108K,
hence emits X-rays. The total mass of the gas is greater than
that of the galaxies by roughly a factor of two. However this
is still not enough mass to keep the galaxies in the cluster.
Since this gas is in approximate equilibrium with the overall
cluster gravitational field, its distribution in the cluster traces
out the overall cluster gravitational field, and therefore allows
calculation of the total mass distribution in the cluster. It
turns out the total mass deduced from this measurement is much
larger than the mass of the galaxies or the hot gas. The missing
component is known as dark matter and its nature is unknown. In
a typical cluster perhaps only 5% of the total mass is in the
form of galaxies, maybe 10% in the form of hot X-ray emitting
gas and the remainder is dark matter. Clusters typically have
the following properties. * They contain 50 to 1000 galaxies,
hot X-ray emitting gas and large amounts of dark matter * The
distribution of these three components is approximately the same
in the cluster. * They have total masses of 1014 to 1015 solar
masses. * They typically have a diameter of 8Mpc (see 1 E23 m
for distance comparisons). * The spread of velocities for the
individual galaxies is about 800-1000 km/s. * The average distance
between clusters is approximately 10 Mpc. Note: clusters of galaxies
should not be confused with star clusters such as globular clusters
and open clusters, which are structures within galaxies. Superclusters
Groups, clusters and some isolated galaxies form even larger structures,
the superclusters. At the very largest scales of the visible universe,
matter is gathered into filaments and walls surrounding vast voids.
This structure resembles a foam. See large-scale structure of
the cosmos. List of some close groups and clusters * Local Group
* Maffei Group * Sculptor Group * M81 Group * NGC 5128 Group *
Canes I Group * NGC1023 Group * M101 Group * Leo I Group * Canes
II Group * Virgo cluster * Fornax cluster
Cosmology is the study of the large-scale
structure and history of the universe. In particular, it deals
with subjects regarding its origin. It is studied by Astronomy,
Philosophy, and Religion.
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MATTER
The definition pursued here
is of matter as whatever the smallest, most fundamental entities
in physics seem to be. Thus matter can be seen as material consisting
of particles which are fermions and therefore obey the Pauli exclusion
principle, which states that no two fermions can be in the same
quantum state. Because of this principle, the particles which comprise
matter do not all end up in their lowest energy state, and hence
it is possible to create stable structures out of fermions. In addition,
the Pauli exclusion principle insures that two pieces of matter
will not occupy the same location at the same time, and therefore
two pieces of matter in which most energy states are filled will
tend to collide with each other rather than passing through each
other as with energy fields such as light.
Creative Notions
People seem to have the misconception that only a select few are
able to unleash a steady flow of creative genius. That is not true
at all. The fact is, creativity is very much like a muscle that
needs to be exercised in order to consistently give out great results.
If you don't practice harnessing creative thinking, this skill will
very much atrophy into inexistence. But keep working and this skill
will soon come to you in a snap.
So how do you unleash your creative thinking?
Well, the first thing is to become a human leech. No, we're not
talking about just sucking the blood out of every living being available,
we're saying that you should take in as much knowledge and learning
you can find. Read everything available -- good and bad, and keep
your mind open to the infinite possibilities of the universe. The
more you know, the more you'll want to know, and the more your faculty
of wonder will be exercised. Prepare to be amazed at little facts
that add a bit of color into your life.
Focus on a creative activity everyday. Yes, it's an effort. Even
doodling is a creative activity. Don't let anything hinder you.
Mindlessness may be a creative activity, but for people who are
just starting out to unleash a little bit of creative thinking in
their lives, it is helpful and encouraging to have concrete evidence,
that, "hey, what I'm doing is getting somewhere." So why
don't you try it. Practice drawing for a couple of minutes each
day. Bring out your old camera and start snapping photos like crazy.
Keep a journal and make a point to write in it religiously. Another
cool idea is to write by describing something with your five senses.
Try to avoid vague adjectives like "marvelous," "amazing,"
and "delicious." Before you know it, you'll have built
yourself a tiny portfolio, and you'll be amazed at the growth you've
undertaken after amassing all those works of art. Who knows, you
might actually take to liking those things you do everyday. Pretty
soon those things will become a part of you and you'll be addicted
to these creative exercises.
Think out of the box -- or don't. Sometimes, constraints are actually
a good thing. Limitations discipline you to work within your means.
It enables you to be more resourceful. Creative freedom is great,
but limitations enforce discipline.
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Try something new everyday and let your experiences broaden your
perspective. Explore a new district in your neighborhood. Spend
an afternoon in a museum to which you've never been before. Chat
up someone on the bus. Open up to the people around you. As you
thrust yourself out of your comfort zone more and more each day,
your sense of adventure grows and so does your zest for life. Think
about it. When was the last time you did something for the first
time? If it's been a while, I tell you, you've been missing out
on a whole lot of experiences that could've added to your growth,
emotionally, mentally, physically, or spiritually. Why don't you
try bungee jumping today? Not only will you learn, but you will
also have plenty of stories to share, enabling you to practice your
storytelling skills and making you the life of the party.
Embrace insanity. No, not to the point of practically admitting
yourself into the mental ward. As John Russell once said, "Sanity
calms, but madness is more interesting." Exactly! Every creative
thought was once deemed insanity by other "normal" people
at one time or another. Luckily, that didn't stop the creative geniuses
from standing by them. The thing is, sanity or being normal confines
people to think... well, normally. Withink limits. Creativity is
essentially breaking through barriers. Yes, this includes the bizzarre
and the downright strange. I'm not saying that you yourself should
develop a creative personality. That might go haywire. An example
of a creative personality would be George Washington, who often
rode into battle naked, or James Joyce, who wrote "Dubliners"
with beetle juice for an intense fear of ink, or Albert Einstein,
who thought his cat was a spy sent by his rival (or in thinking
creatively in this case, the term could probably be "archnemesis.")
It's important that your creativity doesn't get you detached from
the real world completely.
I hope this article has inspired you to start thinking beyond your
"limits." If you follow these steps pretty soon you'll
be living a life full of interesting adventures. Unleashing your
creative thinking will bring about a new zest for living life.
History
is often used as a generic
term for information about the past, such as in "geologic history
of the Earth". When used as a field of study, history refers to
human history, which is the recorded past of human societies. The
term "history" comes from the Greek historia, "an account of one's
inquiries," and shares that etymology with the English word story.
It does not come from the word his; however, some feminists have
coined the term herstory to refer to history from a female perspective.
The central lesson of general relativity is that spacetime cannot
be a fixed background, but is rather a network of evolving relationships.
A spacetime interval between two events is the frame-invariant quantity
analogous to distance in Euclidean space. The spacetime interval
s along a curve is defined by ds2 = c2dt - dx2 - dy2 - dz2 where
c is the speed of light (some people flip the signs of the equation).
A basic assumption of relativity is that coordinate transformations
have to leave intervals invariant. Intervals are invariant under
Lorentz transformations.
A light-year
, abbreviation ly, is the
distance light travels in one year: roughly 9.41 trillion kilometers
(or about 5.85 trillion miles). More specifically, a light-year
is defined as the distance that a photon would travel, in free space
and infinitely far away from any gravitational or magnetic fields,
in one Julian year (365.25 days of 86400 seconds each). Since the
speed of light in vacuum is 299,792,458 m/s, one light year is approximately
equal to 9.46 × 1015 m = 9.46 petameter. The light-year is
used to measure large distances, like the distance from the solar
system to a nearby star. A light-year is not a unit of time. In
astronomy, the parsec is nowadays the preferred unit for large distances;
one parsec equals 3.26 light-years.
Gravitational singularity
A gravitational singularity occurs when
an astrophysical model, typically based on general relativity, predicts
a point of infinite curvature. The term is closely related to the
mathematical meaning of "singularity":
a gravitational singularity occurs
when the equations produce a
mathematical singularity. The Big Bang cosmological model of
the universe contains a gravitational singularity at the start of
time (t=0)
. At the "Big Bang Singularity," the model predicts that the density
of
the universe and the curvature of space-time are infinite. However,
the basic Big Bang model does not
include quantum effects, so its predictions
are valid only shortly after the projected singularity. A singularity
also exists within a
black hole, where general relativity predicts a region of infinite
curvature.
In a non-rotating black hole, the singularity occurs at a single
point in the model coordinates,
and is called a "point singularity". In a rotating
black hole, the singularity occurs on a ring, and is called a "ring
singularity".
Rotating black holes are sometimes referred to as Kerr black holes.
Until the early 1990s, it was widely
believed that general relativity hides every singularity behind an
event
horizon, making naked singularities impossible. This is referred to
as
the cosmic censorship principle. However, in 1991 Shapiro and Teukolsky
performed
computer simulations of a rotating plane of dust which indicated that
general relativity allows for naked singularities. What these objects
would
actually look like is unknown. Nor it is known if singularities would
still arise if the simplifying assumptions used to make the
simulation tractable were removed. Many physicists believe that
gravitational singularities are
" unphysical", meaning that general relativity
ultimately ceases to be an accurate description of gravity somewhere
in the vincinity of what would
otherwise be a singularity. It is generally
assumed that a theory of quantum
gravity - a theory that unifies general
relativity with quantum mechanics
- will provide a better description of what
actually occurs where general relativity predicts a singularity. However,
no theory of quantum gravity has been experimentally confirmed to
date.
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