Strictly speaking, human beings have been contemplating and studying the nature of the Universe since prehistoric times. As such, the earliest accounts of how the Universe came to be were mythological in nature and passed down orally from one generation to the next.
In these stories, the world, space, time, and all life began with a creation event, where a God or Gods were responsible for creating everything. Astronomy also began to emerge as a field of study by the time of the Ancient Babylonians. Systems of constellations and astrological calendars prepared by Babylonian scholars as early as the 2nd millennium BCE would go on to inform the cosmological and astrological traditions of cultures for thousands of years to come.
By Classical Antiquity, the notion of a Universe that was dictated by physical laws began to emerge. Between Greek and Indian scholars, explanations for creation began to become philosophical in nature, emphasizing cause and effect rather than divine agency. The earliest examples include Thales and Anaximander, two pre-Socratic Greek scholars who argued that everything was born of a primordial form of matter. By the 5th century BCE, pre-Socratic philosopher Empedocles became the first western scholar to propose a Universe composed of four elements — earth, air, water and fire.
This philosophy became very popular in western circles, and was similar to the Chinese system of five elements — metal, wood, water, fire, and earth — that emerged around the same time. The Indian philosopher Kanada who lived in the 6th or 2nd century BCE took this philosophy further by proposing that light and heat were the same substance in different form. The 5th century CE Buddhist philosopher Dignana took this even further, proposing that all matter was made up of energy.
The notion of finite time was also a key feature of the Abrahamic religions — Judaism, Christianity and Islam. Perhaps inspired by the Zoroastrian concept of the Day of Judgement, the belief that the Universe had a beginning and end would go on to inform western concepts of cosmology even to the present day. Between the 2nd millennium BCE and the 2nd century CE, astronomy and astrology continued to develop and evolve.
In addition to monitoring the proper motions of the planets and the movement of the constellations through the Zodiac, Greek astronomers also articulated the geocentric model of the Universe, where the Sun, planets and stars revolve around the Earth. This treatise and the cosmological model it espoused would be considered canon by medieval European and Islamic scholars for over a thousand years to come. However, even before the Scientific Revolution ca.
These included Greek astronomer Aristarchus of Samos ca. During the Middle Ages, Indian, Persian and Arabic philosophers and scholars maintained and expanded on Classical astronomy. In addition to keeping Ptolemaic and non-Aristotelian ideas alive, they also proposed revolutionary ideas like the rotation of the Earth. Some scholars — such as Indian astronomer Aryabhata and Persian astronomers Albumasar and Al-Sijzi — even advanced versions of a heliocentric Universe.
By the 16th century, Nicolaus Copernicus proposed the most complete concept of a heliocentric Universe by resolving lingering mathematical problems with the theory. These seven principles stated that:. A more comprehensive treatment of his ideas was released inwhen Copernicus completed his magnum opus — De revolutionibus orbium coelestium On the Revolutions of the Heavenly Spheres. In it, he advanced his seven major arguments, but in more detailed form and with detailed computations to back them up.
Due to fears of persecution and backlash, this volume was not released until his death in Using a telescope of his own creation, Galileo would make recorded observations of the Moon, the Sun, and Jupiter which demonstrated flaws in the geocentric model of the Universe while also showcasing the internal consistency of the Copernican model.
His observations were published in several different volumes throughout the early 17th century. His observations of the cratered surface of the Moon and his observations of Jupiter and its largest moons were detailed in with his Sidereus Nuncius The Starry Messenger while his observations were sunspots were described in On the Spots Observed in the Sun Galileo also recorded his observations about the Milky Way in the Starry Messengerwhich was previously believed to be nebulous.
Instead, Galileo found that it was a multitude of stars packed so densely together that it appeared from a distance to look like clouds, but which were actually stars that Universe much farther away than previously thought. Johannes Kepler advanced the model further with his theory of the elliptical orbits of the planets. Combined with accurate tables that predicted the positions of the planets, the Copernican model was effectively proven.
From the middle of the seventeenth century onward, there were few astronomers who were not Copernicans. These laws stated that:, Universe. Together, these laws described the relationship between any object, the Universe acting upon it, and the resulting motion, thus laying the foundation for classical mechanics. This volume would have a profound effect on the sciences, with its principles remaining canon for the following years.
Another major discovery took place inwhen Immanuel Kant proposed that the Milky Way was a large collection of stars held together by mutual gravity. Just like the Solar System, this collection of stars would be rotating and flattened out as a disk, with the Solar System embedded within it. Universe, this theory stated that the speed of light is the same in all inertial reference frames.
This broke with the previously-held consensus that light traveling through a moving medium would be dragged along by that medium, which meant that the speed of the light is the sum of its speed through a medium plus the speed of that medium.
It also made the existence of a medium entirely superfluous, accorded with the directly observed speed of light, and accounted for the observed aberrations. Between andEinstein began considering how Special Relativity could be applied to gravity fields — what would come to be known as the Theory of General Relativity.
He also advanced what is known as the Equivalence Principlewhich states that gravitational mass is identical to inertial mass. Einstein also predicted the phenomenon of gravitational time dilation — where two observers situated at varying distances from a gravitating mass perceive a difference in the amount of time between two events.
Another major outgrowth of his theories were the existence of Black Holes and an expanding Universe. Ina few months after Einstein had published his Theory of General Relativity, German physicist and astronomer Karl Schwarzschild found a solution to the Einstein field equations that described the gravitational field of a point and spherical mass.
This solution, now called the Schwarzschild radiusdescribes a point where the mass of a sphere is so compressed that the escape velocity from the surface would equal the speed of light.
InIndian-American astrophysicist Subrahmanyan Chandrasekhar calculated, using Special Relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass would collapse in Universe itself. Another consequence of General Relativity was the prediction that the Universe was either in a state of expansion or contraction.
InEdwin Hubble confirmed that the former was the case. After confirming independently that the Universe was in a state of expansion, he suggested that the current expansion of the Universe meant that the father back in time one went, the smaller the Universe would be. In other words, at some point in the past, the entire mass of the Universe would have been concentrated on a single point.
These discoveries triggered a debate between physicists throughout the s and 30s, with the Universe advocating that the Universe was in a steady state i. In this model, new matter is continuously created as the Universe expands, thus preserving the uniformity and density of matter over time.
Eventually, the observational evidence began to favor the Big Bang over the Steady State, which included the discovery and confirmation of the CMB in Since that time, astronomers and cosmologists have sought to resolve theoretical problems arising from this model. In addition, papers submitted by Stephen Hawking and other physicists showed that singularities were an inevitable initial condition of general relativity and a Big Bang model of cosmology. Inphysicist Alan Guth theorized a period of rapid cosmic expansion aka.
The s also saw the rise of Dark Energy as an attempt to resolve outstanding issues in cosmology. Significant progress has been made in our study of the Universe thanks to advances in telescopes, satellites, and computer simulations.
These have allowed astronomers and cosmologists to see farther into the Universe and hence, farther back in time. This has in turn helped them to gain a better understanding of its true age, and make more precise calculations of its matter-energy density. These have not only allowed for deeper views of the cosmos, but allowed astronomers to test theoretical models to observations.
For example, in June ofNASA announced findings that indicate that the Universe is expanding even faster than previously thought. Without a doubt, the Universe is beyond the reckoning of our minds. Our best estimates say hat it is unfathomably vast, but for all we know, it could very well extend to infinity. In the end, our understanding of it is nothing less than the result of thousands of years of constant and progressive study.
Perhaps some day we will be able to see to the edge of it assuming it has one and be able to resolve the most fundamental questions about how all things in the Universe interact. To speed you on your way, here is a list of topics we hope you will enjoy and that will answer your questions. Good luck with your exploration! When you talk about the CMB appearing equidistant around us, at a distance which is a function of the expansion of space over time, you are describing what may well be an absolute limit to our perception.
It does not follow that the universe is being perceived in full here. It seems pretty well established that the universe is It also seems well established that the CMB started as photons of visible light million years after the Big Bang.
Therefore, the universe has been expanding for a finite period of time. Ergo, space-time must also be finite. Indeed, it is estimated that our universe is some 48 billion light years across. Unlike matter stars and galaxies which cannot move faster than light, space-time has no such speed limit.
As space-time expands, it carries the galaxies along with it and once that expansion exceeds light speed, then we can never observe those galaxies in our telescopes. Many aspects of the Big Bang theory puzzle me, but there is one that is especially puzzling.
The theory states that the universe began from a single point of infinite density and that at the instant time began, space-time began expanding and has been expanding ever since.
Within the singularity in the beginning, the theory says that gravity was the the dominant force. The only analogy we have for the singularity is a black hole. If gravity was the dominant force, I fail to understand how it was possible for the Big Bang to occur. One possible speculation concerns dark energy. Dark energy has been proposed as an explanation for the acceleration in the expansion of the universe, such acceleration dating from some 5 billion years ago as I understand it. I would not think that dark energy would only be in existence for the past 5 billion years.
Rather, I should think it has existed since the very beginning. If that is so, then might not dark energy have been the strongest force in the singularity, stronger than gravity, and that dark energy drove the Big Bang?
There is a difference from the black hole analogy, which is that a black hole is a singularity of infinite density, from which nothing can escape into the surrounding space, while the primordial atom was not surrounded by any space. All space emerged from it with all the matter. Quintessentially, a vacuum energy filled universe in balance, changing but always steady, eternal but ever-reborn, is exactly what we observe.
Excellent article! I first heard about the Big Bang and Steady State in from a middle school teacher who was a creationist. He put aside in personal bias and give an excellent intro. He gave both equal weight to both theory and refuse to discussed a religious view of point, saving that for his Sunday School class. The hardest thing the class had was understanding that the expansion of the Big Bang was something into to nothing.
No air, no stuff, nothing, not even vacuum exists until the Universe expanding. He has an inspiration. At first, I preferred the Steady State. It really has shaken my faith in science. Alan Watts you have to learn Chinese to really understand Zen and I believe you have to learn the higher maths to understand astrophysics. In my dreams, I gain the superpowers to do the scary math to truly understand this weirdness. Or correct it. The most obvious and indisputable experimental evidence, which everybody with basic knowledge of special relativity should immediately understand: is the existence of the absolute time shown by the universally synchronized clocks on the GPS satellites which move at high velocities relative to each other while special relativity claims that time is relative i.
Many physicists claim that clocks on the GPS satellites are corrected according to both special relativity and general relativity.
This is not true. The corrections of the atomic clocks on the GPS satellites are nothing to do with relativistic effects because the corrections are absolute changes of the clocks, none of which is relative as claimed by special relativity. After all corrections, the clocks are synchronized not only relative to the ground clocks but also relative to each other. Some people may argue that the clocks are only synchronized in the earth centered inertial reference frame, and are not synchronized in the reference frames of the GPS satellites.
If it were true, then the time difference between a clock on a GPS satellite and a clock on the ground observed in the satellite reference frame would grow while the same clocks observed on the earth centered reference frame were keeping synchronized. If you corrected the clock on the satellite when the difference became significant, the correction would break the synchronization of the clocks observed in the earth centered frame.
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