The no boundary theory of the universe likens the universe to the Earth, in that is impossible to find any boundaries traveling around the Earth or to fall off it. This is possible as a result of theorizing that prior to the Big Bang, the generally accepted laws of physics did not apply and that the concept of time as we know it did not exist.Know More
The no boundary theory of the universe was advanced by the physicists Stephen Hawking and James Hartle. It is called the no boundary theory because it posits that the universe has no boundaries.
The theory says the quantum singularity that gave birth to the universe via the Big Bang was of infinite density. In that strange state of flux, particles appear and disappear spontaneously, and space and time become separated. It is therefore at the moment that the Big Bang takes place that time starts to exist; before the Big Bang, it is nonsensical to talk about time.
Hawking uses the Earth once again to illustrate this point. While on Earth it is always possible to travel south, that is, until you reach the South Pole. Once on the South Pole, "south" doesn't exist. The same concept applies to time before the Big Bang — once you reach t=0, time ceases to exist.Learn more about Universe
Ptolemy's model of the universe was geocentric, containing the Earth at the center with a series of circles, called deferents, moving outward from the Earth, containing the moon, Mercury, Venus, the sun, Mars, Jupiter and Saturn. Ptolemy placed fixed stars and the Primum Mobile in the spheres after Saturn.Full Answer >
The belief of early astronomers that the Earth was the center of the universe stemmed from limited astronomical tools and geocentric attitudes. The Ptolemaic Model, developed around 100 A.D., presented the Earth-centered solar system in which most early Roman astronomers believed.Full Answer >
Greek philosopher Claudius Ptolemy believed that the sun, planets and stars all revolved around the Earth. This belief gave way to the ancient Greek theory of a geocentric or Ptolemaic model of the universe. "Geocentric" refers to the belief that the Earth is the center of the universe.Full Answer >
The geocentric theory, or the Ptolemaic system, was one of the earliest theories regarding the origins of the universe, and it posited that the sun, stars and even the other planets revolve around the Earth. Ptolemy was not the first to suggest this theory, though, as documents indicate that Aristotle and Plato discussed this paradigm.Full Answer >