Space & Beyond

CosmologySpace & Beyond

The science of the origin and development of the universe. Modern cosmology is dominated by the Big Bang theory, which brings together observational astronomy and particle physics.Cosmology

What is Cosmology?Cosmology is one of the most exciting disciplines in all of physical science. It is concerned not so much with individual stars or galaxies in their own right, but rather with the properties of the Universe as a whole: its origin, evolution and eventual fate.

Cosmologists work to understand how the Universe came into being, why it looks as it does now, and what the future holds. They make astronomical observations that probe billions of years into the past, to the edge of the knowable Universe. They seek the bases of scientific understanding, using the tools of modern physics, and fashion theories that provide unified and testable models of the evolution of the Universe from its creation to the present, and into the future.

Observable UniverseThe observable universe, also known as the Hubble volume, is the region of space that it is theoretically possible for us to observe, small enough that light from the furthest regions has had sufficient time to reach Earth since the Big Bang. This region of space has a diameter of approximately 92.94 billion light-years, centred on the planet Earth. Each different portion of space has its own visible universe, some overlapping, some not.

There are a number of misconceptions about the concept of the observable universe. The first is that its size is equal to its age in years times the speed light travels in a year, about 15 billion light years. This figure would be true if it was flat, but thanks to Einstein, we know that the universe is highly curved on cosmological distances by virtue of its expansion.

Origin of the UniverseThe Big Bang is the origin of the universe, occurring approximately 13.7 billion years ago. It began as a point of nearly zero volume and tremendous density. Then this point started stretching outward in all directions, not expanding within space but causing the expansion of space itself.

The Big BangOnce it was understood that the Universe had a beginning, scientists began to ask how did it come into existence, and what existed before it?

Most scientists now believe that the answer to the first part of the question is that the Universe sprang into existence from a singularity -- a term physicists use to describe regions of space that defy the laws of physics. We know very little about singularities, but we believe that others probably exist in the cores of black holes.The second part of the question, as to what existed before the Big Bang, has scientists baffled. By definition, nothing existed prior to the beginning, but that fact creates more questions than answers. For instance, if nothing existed prior to the Big Bang, what caused the singularity to be created in the first place?

The Big BangOnce the singularity was created, it began to expand through a process called inflation. The Universe went from very small, very dense, and very hot to the cool expanse that we see today. This theory is now referred to as the Big Bang, a term first coined by Sir Fred Hoyle during a British Broadcasting Corporation (BBC) radio broadcast in 1950.Interestingly, there really wasnt any sort of explosion as the name suggests, but rather the rapid expansion of space and time. It is like blowing up a balloon, as you blow air in, the exterior of the balloon expands outward.

Evidence for the Big BangThe CMB signal detected by Penzias and Wilson, a discovery for which they later won a Nobel Prize, is often described as the echo of the Big Bang. Because if the Universe had an origin, it would leave behind a signature of the event. The Big Bang left behind a heat signature throughout all of space.Another prediction of the Big Bang theory is that any direction we look out into space, we should see objects moving away from us with a velocity proportional to their distance away from us, a phenomenon known as the red shift.

Evidence for the Big Bang

Edwin Hubble, in 1929, was able to correlate the distance to objects in the universe with their velocities -- a relation known as Hubble's Law. Big Bang theorists later used this information to approximate the age of the Universe at about 15 billion years old, which is consistent with other measurements of the age of the Universe.

Space is the boundless three-dimensional extent in which objects and events have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime.Space

Will Space expand forever?The fate of the universe is determined by a struggle between the momentum of expansion and the pull of gravity. The rate of expansion is expressed by the Hubble Constant, Ho, while the strength of gravity depends on the density and pressure of the matter in the universe.If the pressure of the matter is low, as is the case with most forms of matter of which we know, then the fate of the universe is governed by the density. If the density of the universe is less than the critical density, which is proportional to the Ho2, then the universe will expand forever. If the density of the universe is greater than the critical density, then gravity will eventually win and the universe will collapse back on itself, the so called Big Crunch.

Will Space expand forever?

However, the results of the WMAP mission and observations of distant supernova have suggested that the expansion of the universe is actually accelerating, which implies the existence of a form of matter with a strong negative pressure, such as the cosmological constant. This strange form of matter is also sometimes referred to as dark energy.

If dark energy in fact plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.

Shape of the spaceThe density of the universe also determines its geometry.If the density of the universe exceeds the critical density, then the geometry of space is closed and positively curved like the surface of a sphere.If the density of the universe is less than the critical density, then the geometry of space is open (infinite), and negatively curved like the surface of a saddle.If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper, and infinite in extent.The simplest version of the inflationary theory, an extension of the Big Bang theory, predicts that the density of the universe is very close to the critical density, and that the geometry of the universe is flat, like a sheet of paper.

Space-timeThe concepts of time and space are very important for understanding the function of phenomena in the natural world. The measurement of time is not absolute. Time is perceived by humans in a relative fashion by using human created units of measurement i.e. seconds, minutes, hours, and days.

In physics, spacetime (spacetime continuum) is any mathematical model that combines space and time into a single interwoven continuum.

Relativity and the Space-time ContinuumIn order to sidestep the issue of Newton's Third Law of Motion and the impossibility of matter traveling faster than the speed of light, we can look to Einstein and the relationship between space and time. Taken together, space, consisting of three dimensions and time are all part of what's called the space-time continuum.In his Special Theory of Relativity, Einstein states two postulates:The speed of light (~300,000,000 m/s) is the same for all observers, whether or not they're moving.Anyone moving at a constant speed should observe the same physical laws.

Relativity and the Space-time ContinuumPutting these two ideas together, Einstein realized that space and time are relative -- an object in motion actually experiences time at a slower rate than one at rest. Although this may seem absurd to us, we travel incredibly slow when compared to the speed of light, so we don't notice the hands on our watches ticking slower when we're running or traveling on an airplane.Scientists have actually proved this phenomenon by sending atomic clocks up with high-speed rocket ships. They returned to Earth slightly behind the clocks on the ground.

Relativity and the Space-time ContinuumThe closer an object gets to the speed of light, that object actually experiences time at a significantly slower rate.

Speed of LightThe speed of light in a vacuum is 299,792 km/s, and in theory nothing can travel faster than light. If you could travel at the speed of light, you could go around the Earth 7.5 times in one second.Early scientists thought it must travel instantaneously. Over time, however, measurements of the motion of these wave-like particles became more and more precise. Thanks to the work of Albert Einstein and others, we now understand light speed to be a theoretical limit: light speed a constant called c is thought to be not achievable by anything with mass.

Faster than Light?Faster-than-light (also superluminal or FTL) communication and travel refer to the propagation of information or matter faster than the speed of light. Under the special theory of relativity, a particle (that has rest mass) with subluminal velocity needs infinite energy to accelerate to the speed of light, although special relativity does not forbid the existence of particles that travel faster than light at all times

In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it.

In modern physics, space and time are unified in a four-dimensional continuum called spacetime.Dimension

3D SpaceThree-dimensional space is a geometric three-parameter model of the physical universe in which all known matter exists. These three dimensions can be labelled by a combination of three chosen from the terms length, width, height, depth, and breadth. Any three directions can be chosen, provided that they do not all lie in the same plane.

4th Dimension?In mathematics, four-dimensional space is a geometric space with four dimensions. It has been studied by mathematicians and philosophers for over two centuries, both for its own interest and for the insights it offered into mathematics and related fields.

In modern physics, space and time are unified in a four-dimensional Minkowski continuum called spacetime, whose metric treats the time dimension differently from the three spatial dimensions. Spacetime is not a Euclidean space.

Hypercube or The TesseractHypercube is a multidimensional analogue of a 3-dimensional cube in that each coordinate of a point in a hypercube is restricted to the same 1-dimensional (line) segment. Tesseract is a 4-dimensional hypercube.This hence verifies that a 4th dimensional world is possible with 4 dimensional objects.

Time travel has been a popular topic for science fiction for decades, Often jumping on special vehicles and arriving at a different point in time.The reality, however, is more muddled.Not all scientists believe that time travel is possible.

To understand time travel, we have to understand time.Time Travel

Understanding timeWhile most people think of time as a constant, physicist Albert Einstein showed that time is an illusion; it is relative it can vary for different observers depending on your speed through space. To Einstein, time is the fourth dimension. Space is described as a three-dimensional arena, which provides a traveller with coordinates such as length, width and height showing location. Time provides another coordinate direction although conventionally, it only moves forward.

Understanding timeEinstein's theory of special relativity says that time slows down or speeds up depending on how fast you move relative to something else. Approaching the speed of light, a person inside a spaceship would age much slower than his twin at home. Also, under Einstein's theory of general relativity, gravity can bend time.Picture a four-dimensional fabric called space-time. When anything that has mass sits on that piece of fabric, it causes a dimple or a bending of space-time. The bending of space-time causes objects to move on a curved path and that curvature of space is what we know as gravity.

Understanding timeBoth the general and special relativity theories have been proven with GPS satellite technology that has very accurate timepieces on board. The effects of gravity, as well as the satellites' increased speed above the Earth relative to observers on the ground, make the unadjusted clocks gain 38 microseconds a day. (Engineers make calibrations to account for the difference.)In a sense, this effect, called time dilation, means astronauts are time travellers, as they return to Earth very, very slightly younger than their identical twins that remain on the planet.

A wormhole is a hypothetical topological feature of spacetime that would fundamentally be a shortcut through spacetime. A wormhole is much like a tunnel with two ends.Wormholes

Through the wormholeGeneral relativity also provides scenarios that could allow travellers to go back in time, according to NASA. The equations, however, might be difficult to physically achieve.One possibility could be to go faster than light, which travels at 299,792 km/s in a vacuum. Einstein's equations, though, show that an object at the speed of light would have both infinite mass and a length of 0. This appears to be physically impossible, although some scientists have extended his equations and said it might be done.A linked possibility would be to create wormholes between points in space-time. While Einstein's equations provide for them, they would collapse very quickly. Also, scientists haven't actually observed wormholes yet. The technology needed to create a wormhole is far beyond anything we have today.

Black holesAnother possibility would be to move a ship rapidly around a black hole, or to artificially create that condition with a huge, rotating structure."Around and around they'd go, experiencing just half the time of everyone far away from the black hole. The ship and its crew would be traveling through time, physicist Stephen Hawking wrote in the Daily Mail in 2010.Imagine they circled the black hole for five of their years. Ten years would pass elsewhere. When they got home, everyone on Earth would have aged five years more than they had."However, he added, the crew would need to travel around the speed of light for this to work. Physicist Amos Iron at the Technion-Israel Institute of Technology in Haifa, Israel pointed out another limitation if one used a machine: it might fall apart before being able to rotate that quickly.

Cosmic StringsAnother theory for potential time travellers involves something called cosmic strings narrow tubes of energy stretched across the entire length of the ever-expanding universe. These thin regions, left over from the early cosmos, are predicted to contain huge amounts of mass and therefore could warp the space-time around them.Cosmic strings are either infinite or theyre in loops, with no ends, scientists say. The approach of two such strings parallel to each other would bend space-time so vigorously and in such a particular configuration that might make time travel possible, in theory.

Grandfather ParadoxBesides the physics problems, time travel may also come with some unique situations. A classic example is the grandfather paradox, in which a time traveller goes back and kills his parents or his grandfather the major plot line in the Terminator movies or otherwise interferes in their relationship think Back to the Future so that he is never born or his life is forever altered.If that were to happen, some physicists say, you would be not be born in one parallel universe but still born in another. Others say that the photons that make up light prefer self-consistency in timelines, which would interfere with your evil, suicidal plan.

So.. Is it possible?While time travel does not appear possible at least, possible in the sense that the humans would survive it with the physics that we use today, the field is constantly changing. Advances in quantum theories could perhaps provide some understanding of how to overcome time travel paradoxes.

One possibility, although it would not necessarily lead to time travel, is solving the mystery of how certain particles can communicate instantaneously with each other faster than the speed of light.

A black hole is a mathematically defined region of spacetime exhibiting such a strong gravitational pull that no imminent particle or electromagnetic radiation can escape from it.Black Holes

When a super-massive star dies, it's corpse collapses into a knot so tight not even light can escape. And this drain on the fabric of the Universe can alter the shape of space and shift the flow of time.Black Holes

Formation of Black HolesBlack holes are the cold remnants of former stars, so dense that no matternot even lightis able to escape their powerful gravitational pull.When giant stars reach the final stages of their lives they often detonate in cataclysms known as supernovae. Such an explosion scatters most of a star into the void of space but leaves behind a large cold remnant on which fusion no longer takes place.In younger stars, nuclear fusion creates energy and a constant outward pressure that exists in balance with the inward pull of gravity caused by the star's own mass. But in the dead remnants of a massive supernova, no force opposes gravityso the star begins to collapse in upon itself.With no force to check gravity, a budding black hole shrinks to zero volumeat which point it is infinitely dense. The star's own light becomes trapped in orbit, and the dark star becomes known as a black hole.

Effect of Black HolesBlack holes pull matter and even energy into themselvesbut no more so than other stars or cosmic objects of similar mass. That means that a black hole with the mass of our own sun would not "suck" objects into it any more than our own sun does with its own gravitational pull.

Planets, light, and other matter must pass close to a black hole in order to be pulled into its grasp. When they reach a point of no return they are said to have entered the event horizonthe point from which any escape is impossible because it requires moving faster than the speed of light.

Power of Black HolesBlack holes are small in size. A million-solar-mass hole, like that believed to be at the centre of some galaxies, would have a radius of just about three million kilometresonly about four times the size of the sun. A black hole with a mass equal to that of the sun would have a three-kilometre radius.

Because they are so small, distant, and dark, black holes cannot be directly observed. Yet scientists have confirmed their long-held suspicions that they exist. This is typically done by measuring mass in a region of the sky and looking for areas of large, dark mass.

What lies inside a black hole?We cannot glimpse what lies inside the event horizon of a black hole because light or material from there can never reach us. Even if we could send an explorer into the black hole, she could never communicate back to us.Current theories predict that all the matter in a black hole is piled up in a single point at the centre, but we do not understand how this central singularity works.To properly understand the black hole centre requires a fusion of the theory of gravity with the theory that describes the behaviour of matter on the smallest scales, called quantum mechanics. This unifying theory has already been given a name, quantum gravity, but how it works is still unknown. This is one of the most important unsolved problems in physics. Studies of black holes may one day provide the key to unlock this mystery.

What lies inside a black hole?Einstein's theory of general relativity allows unusual characteristics for black holes. For example, the central singularity might form a bridge to another Universe. This is similar to a so-called wormhole (a mysterious solution of Einstein's equations that has no event horizon). Bridges and wormholes might allow travel to other Universes or even time travel. But without observational and experimental data, this is mostly speculation. We do not know whether bridges or wormholes exist in the Universe, or could even have formed in principle. By contrast, black holes have been observed to exist and we understand how they form.

Gravity: Not what it seemsWhen Einstein wrote his general theory of relativity in 1915, he found a new way to describe gravity. It was not a force, as Sir Isaac Newton had supposed, but a consequence of the distortion of space and time, conceived together in his theory as space-time. Any object distorts the fabric of space-time and the bigger it is, the greater the effect.Just as a bowling ball placed on a trampoline stretches the fabric and causes it to sag, so planets and stars warp space-time - a phenomenon known as the geodetic effect. A marble moving along the trampoline will be drawn inexorably towards the ball.

Gravity: Not what it seemsThus the planets orbiting the Sun are not being pulled by the Sun; they are following the curved space-time deformation caused by the Sun. The reason the planets never fall into the Sun is because of the speed at which they are travelling.According to the theory, matter and energy distort space-time, curving it around themselves. Frame dragging theoretically occurs when the rotation of a large body twists nearby space and time. It is this second part of Einstein's theory that the NASA mission has yet to corroborate.

Einsteins RelativityEinstein's Theory of Relativity is mostly known for its assertion that time travel is possible, but in reality this theory encompasses much more.

The theory itself is actually split into Special Relativity and General Relativity.

Special RelativitySpecial Relativity is based upon two postulates:

The laws of physics are the same for all observers in uniform motion relative to one another.The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

General RelativityGeneral Relativity is the geometric theory of gravitation put out to argue against Newtons Law of Universal Gravitation. Newtons law was based on the idea that gravity could move faster than the speed of light, which Einstein obviously found to be false.

Consequently, Einstein stated that gravity is instead a property of the geometry of space and time, also called spacetime.

ConclusionWe know little about the world we live in. The amount of questions we havent been able to answer is far more than we have.We are an infinitesimally small part of a universe bigger than we can imagine. There are many phenomenon's that are beyond our capability to understand, but well never stop trying. Our journey may be long and hard, but our curiosity will drive us to the truth.

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