The Universe Explained

The Universe is all of space and time and their contents, including planets, stars, galaxies, and .. An explanation for why the expansion of the Universe is accelerating remains elusive. It is often attributed to "dark energy", an unknown form of.
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This relic of the Big Bang pervades the universe and is visible to microwave detectors, which allows scientists to piece together clues of the early universe. Among other discoveries, WMAP was able to determine the age of the universe — about Slide 3 of The Universe's First Growth Spurt. The Universe's First Growth Spurt When the universe was very young — something like a hundredth of a billionth of a trillionth of a trillionth of a second whew! During this burst of expansion, which is known as inflation, the universe grew exponentially and doubled in size at least 90 times. As space expanded, the universe cooled and matter formed.

Slide 5 of Too Hot to Shine. The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time.

The Universe

Before the birth of the Universe, time, space and matter did not exist. The Universe contains billions of galaxies, each containing millions or billions of stars. The space between the stars and galaxies is largely empty. However, even places far from stars and planets contain scattered particles of dust or a few hydrogen atoms per cubic centimeter. Space is also filled with radiation e. Ordinary matter is composed of two types of elementary particles: An atom consists of an atomic nucleus , made up of protons and neutrons, and electrons that orbit the nucleus. Because most of the mass of an atom is concentrated in its nucleus, which is made up of baryons , astronomers often use the term baryonic matter to describe ordinary matter, although a small fraction of this "baryonic matter" is electrons.

Soon after the Big Bang , primordial protons and neutrons formed from the quark—gluon plasma of the early Universe as it cooled below two trillion degrees. A few minutes later, in a process known as Big Bang nucleosynthesis , nuclei formed from the primordial protons and neutrons. This nucleosynthesis formed lighter elements, those with small atomic numbers up to lithium and beryllium , but the abundance of heavier elements dropped off sharply with increasing atomic number.

Some boron may have been formed at this time, but the next heavier element, carbon , was not formed in significant amounts. Big Bang nucleosynthesis shut down after about 20 minutes due to the rapid drop in temperature and density of the expanding Universe. Subsequent formation of heavier elements resulted from stellar nucleosynthesis and supernova nucleosynthesis. Ordinary matter and the forces that act on matter can be described in terms of elementary particles.

A true force-particle "theory of everything" has not been attained. A hadron is a composite particle made of quarks held together by the strong force. Hadrons are categorized into two families: Of the hadrons, protons are stable, and neutrons bound within atomic nuclei are stable. Other hadrons are unstable under ordinary conditions and are thus insignificant constituents of the modern Universe. Most of the hadrons and anti-hadrons were then eliminated in particle-antiparticle annihilation reactions, leaving a small residual of hadrons by the time the Universe was about one second old.

A lepton is an elementary , half-integer spin particle that does not undergo strong interactions but is subject to the Pauli exclusion principle ; no two leptons of the same species can be in exactly the same state at the same time. Electrons are stable and the most common charged lepton in the Universe, whereas muons and taus are unstable particle that quickly decay after being produced in high energy collisions, such as those involving cosmic rays or carried out in particle accelerators.

The electron governs nearly all of chemistry , as it is found in atoms and is directly tied to all chemical properties. Neutrinos rarely interact with anything, and are consequently rarely observed. Neutrinos stream throughout the Universe but rarely interact with normal matter. The lepton epoch was the period in the evolution of the early Universe in which the leptons dominated the mass of the Universe.

It started roughly 1 second after the Big Bang , after the majority of hadrons and anti-hadrons annihilated each other at the end of the hadron epoch. The mass of the Universe was then dominated by photons as it entered the following photon epoch. A photon is the quantum of light and all other forms of electromagnetic radiation.

It is the force carrier for the electromagnetic force , even when static via virtual photons. The effects of this force are easily observable at the microscopic and at the macroscopic level because the photon has zero rest mass ; this allows long distance interactions. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave—particle duality , exhibiting properties of waves and of particles. The photon epoch started after most leptons and anti-leptons were annihilated at the end of the lepton epoch, about 10 seconds after the Big Bang.

Atomic nuclei were created in the process of nucleosynthesis which occurred during the first few minutes of the photon epoch. For the remainder of the photon epoch the Universe contained a hot dense plasma of nuclei, electrons and photons.

About , years after the Big Bang, the temperature of the Universe fell to the point where nuclei could combine with electrons to create neutral atoms. As a result, photons no longer interacted frequently with matter and the Universe became transparent. The highly redshifted photons from this period form the cosmic microwave background.

Tiny variations in temperature and density detectable in the CMB were the early "seeds" from which all subsequent structure formation took place. General relativity is the geometric theory of gravitation published by Albert Einstein in and the current description of gravitation in modern physics. It is the basis of current cosmological models of the Universe. General relativity generalizes special relativity and Newton's law of universal gravitation , providing a unified description of gravity as a geometric property of space and time , or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present.

The relation is specified by the Einstein field equations , a system of partial differential equations. In general relativity, the distribution of matter and energy determines the geometry of spacetime, which in turn describes the acceleration of matter. Therefore, solutions of the Einstein field equations describe the evolution of the Universe. Combined with measurements of the amount, type, and distribution of matter in the Universe, the equations of general relativity describe the evolution of the Universe over time.

The Beginning of Everything -- The Big Bang

This metric has only two undetermined parameters. An overall dimensionless length scale factor R describes the size scale of the Universe as a function of time; an increase in R is the expansion of the Universe. The index k is defined so that it can take only one of three values: When R changes, all the spatial distances in the Universe change in tandem; there is an overall expansion or contraction of space itself. This accounts for the observation that galaxies appear to be flying apart; the space between them is stretching. The stretching of space also accounts for the apparent paradox that two galaxies can be 40 billion light years apart, although they started from the same point Second, all solutions suggest that there was a gravitational singularity in the past, when R went to zero and matter and energy were infinitely dense.

It may seem that this conclusion is uncertain because it is based on the questionable assumptions of perfect homogeneity and isotropy the cosmological principle and that only the gravitational interaction is significant. However, the Penrose—Hawking singularity theorems show that a singularity should exist for very general conditions. Hence, according to Einstein's field equations, R grew rapidly from an unimaginably hot, dense state that existed immediately following this singularity when R had a small, finite value ; this is the essence of the Big Bang model of the Universe. Understanding the singularity of the Big Bang likely requires a quantum theory of gravity , which has not yet been formulated.

Third, the curvature index k determines the sign of the mean spatial curvature of spacetime [] averaged over sufficiently large length scales greater than about a billion light years. Conversely, if k is zero or negative, the Universe has an infinite volume. By analogy, an infinite plane has zero curvature but infinite area, whereas an infinite cylinder is finite in one direction and a torus is finite in both.

A toroidal Universe could behave like a normal Universe with periodic boundary conditions. Some speculative theories have proposed that our Universe is but one of a set of disconnected universes, collectively denoted as the multiverse , challenging or enhancing more limited definitions of the Universe.

Max Tegmark developed a four-part classification scheme for the different types of multiverses that scientists have suggested in response to various Physics problems. An example of such multiverses is the one resulting from the chaotic inflation model of the early universe. In this interpretation, parallel worlds are generated in a manner similar to quantum superposition and decoherence , with all states of the wave functions being realized in separate worlds.

Effectively, in the many-worlds interpretation the multiverse evolves as a universal wavefunction. If the Big Bang that created our multiverse created an ensemble of multiverses, the wave function of the ensemble would be entangled in this sense. The least controversial category of multiverse in Tegmark's scheme is Level I. The multiverses of this level are composed by distant spacetime events "in our own universe".

If space is infinite, or sufficiently large and uniform, identical instances of the history of Earth's entire Hubble volume occur every so often, simply by chance. However, this existence does follow as a fairly straightforward consequence from otherwise unrelated scientific observations and theories. It is possible to conceive of disconnected spacetimes, each existing but unable to interact with one another. The entire collection of these separate spacetimes is denoted as the multiverse. Historically, there have been many ideas of the cosmos cosmologies and its origin cosmogonies. Theories of an impersonal Universe governed by physical laws were first proposed by the Greeks and Indians.

The modern era of cosmology began with Albert Einstein 's general theory of relativity , which made it possible to quantitatively predict the origin, evolution, and conclusion of the Universe as a whole. Most modern, accepted theories of cosmology are based on general relativity and, more specifically, the predicted Big Bang. Many cultures have stories describing the origin of the world and universe. Cultures generally regard these stories as having some truth. There are however many differing beliefs in how these stories apply amongst those believing in a supernatural origin, ranging from a god directly creating the Universe as it is now to a god just setting the "wheels in motion" for example via mechanisms such as the big bang and evolution.

Ethnologists and anthropologists who study myths have developed various classification schemes for the various themes that appear in creation stories. In related stories, the Universe is created by a single entity emanating or producing something by him- or herself, as in the Tibetan Buddhism concept of Adi-Buddha , the ancient Greek story of Gaia Mother Earth , the Aztec goddess Coatlicue myth, the ancient Egyptian god Atum story, and the Judeo-Christian Genesis creation narrative in which the Abrahamic God created the Universe. In another type of story, the Universe is created from the union of male and female deities, as in the Maori story of Rangi and Papa.

In other stories, the Universe emanates from fundamental principles, such as Brahman and Prakrti , the creation myth of the Serers , [] or the yin and yang of the Tao. The pre-Socratic Greek philosophers and Indian philosophers developed some of the earliest philosophical concepts of the Universe.

In particular, they noted the ability of matter to change forms e. The first to do so was Thales , who proposed this material to be water. Thales' student, Anaximander , proposed that everything came from the limitless apeiron. Anaximenes proposed the primordial material to be air on account of its perceived attractive and repulsive qualities that cause the arche to condense or dissociate into different forms.

Anaxagoras proposed the principle of Nous Mind , while Heraclitus proposed fire and spoke of logos. Empedocles proposed the elements to be earth, water, air and fire. His four-element model became very popular. Like Pythagoras , Plato believed that all things were composed of number , with Empedocles' elements taking the form of the Platonic solids.

Democritus , and later philosophers—most notably Leucippus —proposed that the Universe is composed of indivisible atoms moving through a void vacuum , although Aristotle did not believe that to be feasible because air, like water, offers resistance to motion. Air will immediately rush in to fill a void, and moreover, without resistance, it would do so indefinitely fast. Although Heraclitus argued for eternal change, his contemporary Parmenides made the radical suggestion that all change is an illusion, that the true underlying reality is eternally unchanging and of a single nature.

Parmenides' idea seemed implausible to many Greeks, but his student Zeno of Elea challenged them with several famous paradoxes. Aristotle responded to these paradoxes by developing the notion of a potential countable infinity, as well as the infinitely divisible continuum. Unlike the eternal and unchanging cycles of time, he believed that the world is bounded by the celestial spheres and that cumulative stellar magnitude is only finitely multiplicative.

The Indian philosopher Kanada , founder of the Vaisheshika school, developed a notion of atomism and proposed that light and heat were varieties of the same substance. They denied the existence of substantial matter and proposed that movement consisted of momentary flashes of a stream of energy. The notion of temporal finitism was inspired by the doctrine of creation shared by the three Abrahamic religions: Judaism , Christianity and Islam.

The Christian philosopher , John Philoponus , presented the philosophical arguments against the ancient Greek notion of an infinite past and future. Astronomical models of the Universe were proposed soon after astronomy began with the Babylonian astronomers , who viewed the Universe as a flat disk floating in the ocean, and this forms the premise for early Greek maps like those of Anaximander and Hecataeus of Miletus. Later Greek philosophers, observing the motions of the heavenly bodies, were concerned with developing models of the Universe-based more profoundly on empirical evidence.

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The first coherent model was proposed by Eudoxus of Cnidos. According to Aristotle's physical interpretation of the model, celestial spheres eternally rotate with uniform motion around a stationary Earth. Normal matter is entirely contained within the terrestrial sphere. De Mundo composed before BC or between and BC , stated, "Five elements, situated in spheres in five regions, the less being in each case surrounded by the greater—namely, earth surrounded by water, water by air, air by fire, and fire by ether—make up the whole Universe".

This model was also refined by Callippus and after concentric spheres were abandoned, it was brought into nearly perfect agreement with astronomical observations by Ptolemy. The success of such a model is largely due to the mathematical fact that any function such as the position of a planet can be decomposed into a set of circular functions the Fourier modes. Other Greek scientists, such as the Pythagorean philosopher Philolaus , postulated according to Stobaeus account that at the center of the Universe was a "central fire" around which the Earth , Sun , Moon and Planets revolved in uniform circular motion.

The Greek astronomer Aristarchus of Samos was the first known individual to propose a heliocentric model of the Universe. Though the original text has been lost, a reference in Archimedes ' book The Sand Reckoner describes Aristarchus's heliocentric model. You, King Gelon, are aware the Universe is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth.

This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the Universe is many times greater than the Universe just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.

Aristarchus thus believed the stars to be very far away, and saw this as the reason why stellar parallax had not been observed, that is, the stars had not been observed to move relative each other as the Earth moved around the Sun. The stars are in fact much farther away than the distance that was generally assumed in ancient times, which is why stellar parallax is only detectable with precision instruments.

The geocentric model, consistent with planetary parallax, was assumed to be an explanation for the unobservability of the parallel phenomenon, stellar parallax. The rejection of the heliocentric view was apparently quite strong, as the following passage from Plutarch suggests On the Apparent Face in the Orb of the Moon:. Cleanthes [a contemporary of Aristarchus and head of the Stoics ] thought it was the duty of the Greeks to indict Aristarchus of Samos on the charge of impiety for putting in motion the Hearth of the Universe [i.

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The only other astronomer from antiquity known by name who supported Aristarchus's heliocentric model was Seleucus of Seleucia , a Hellenistic astronomer who lived a century after Aristarchus. Seleucus' arguments for a heliocentric cosmology were probably related to the phenomenon of tides. The Aristotelian model was accepted in the Western world for roughly two millennia, until Copernicus revived Aristarchus's perspective that the astronomical data could be explained more plausibly if the Earth rotated on its axis and if the Sun were placed at the center of the Universe.

In the center rests the Sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time? As noted by Copernicus himself, the notion that the Earth rotates is very old, dating at least to Philolaus c. Roughly a century before Copernicus, the Christian scholar Nicholas of Cusa also proposed that the Earth rotates on its axis in his book, On Learned Ignorance Empirical evidence for the Earth's rotation on its axis, using the phenomenon of comets , was given by Tusi — and Ali Qushji — This cosmology was accepted by Isaac Newton , Christiaan Huygens and later scientists.

In , when Hooker Telescope was completed, the prevailing view still was that the Universe consisted entirely of the Milky Way Galaxy.

Explained at last: life, the universe and everything

Using the Hooker Telescope, Edwin Hubble identified Cepheid variables in several spiral nebulae and in — proved conclusively that Andromeda Nebula and Triangulum among others, were entire galaxies outside our own, thus proving that Universe consists of multitude of galaxies. The modern era of physical cosmology began in , when Albert Einstein first applied his general theory of relativity to model the structure and dynamics of the Universe. Kanada, founder of the Vaisheshika philosophy, held that the world is composed of atoms as many in kind as the various elements.

The Jains more nearly approximated to Democritus by teaching that all atoms were of the same kind, producing different effects by diverse modes of combinations. Kanada believed light and heat to be varieties of the same substance; Udayana taught that all heat comes from the Sun; and Vachaspati , like Newton , interpreted light as composed of minute particles emitted by substances and striking the eye. Movement consists for them of moments, it is a staccato movement, momentary flashes of a stream of energy They are called "qualities" guna-dharma in both systems in the sense of absolute qualities, a kind of atomic, or intra-atomic, energies of which the empirical things are composed.

Both systems, therefore, agree in denying the objective reality of the categories of Substance and Quality, What we call quality is but a particular manifestation of a subtle entity.

Step 1: How It All Started

To every new unit of quality corresponds a subtle quantum of matter which is called guna , "quality", but represents a subtle substantive entity. The same applies to early Buddhism where all qualities are substantive From Wikipedia, the free encyclopedia. For other uses, see Universe disambiguation.