Science (from the Latin word scientia, meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
The earliest roots of science can be traced to Ancient Egypt and Mesopotamia in around 3500 to 3000 BCE. Their contributions to mathematics, astronomy, and medicine entered and shaped Greek natural philosophy of classical antiquity, whereby formal attempts were made to provide explanations of events in the physical world based on natural causes. After the fall of the Western Roman Empire, knowledge of Greek conceptions of the world deteriorated in Western Europe during the early centuries (400 to 1000 CE) of the Middle Ages but was preserved in the Muslim world during the Islamic Golden Age. The recovery and assimilation of Greek works and Islamic inquiries into Western Europe from the 10th to 13th century revived "natural philosophy", which was later transformed by the Scientific Revolution that began in the 16th century as new ideas and discoveries departed from previous Greek conceptions and traditions. The scientific method soon played a greater role in knowledge creation and it was not until the 19th century that many of the institutional and professional features of science began to take shape; along with the changing of "natural philosophy" to "natural science."
Modern science is typically divided into three major branches that consist of the natural sciences (e.g., biology, chemistry, and physics), which study nature in the broadest sense; the social sciences (e.g., economics, psychology, and sociology), which study individuals and societies; and the formal sciences (e.g., logic, mathematics, and theoretical computer science), which study abstract concepts. There is disagreement, however, on whether the formal sciences actually constitute a science as they do not rely on empirical evidence. Disciplines that use existing scientific knowledge for practical purposes, such as engineering and medicine, are described as applied sciences.
Science is based on research, which is commonly conducted in academic and research institutions as well as in government agencies and companies. The practical impact of scientific research has led to the emergence of science policies that seek to influence the scientific enterprise by prioritizing the development of commercial products, armaments, health care, and environmental protection.
A space elevator
is a hypothetical structure designed to transport material from a planet's surface into space. Many different types of space elevator structures have been proposed. They all share the goal of replacing rocket propulsion
with the traversal of a fixed structure via a mechanism not unlike an elevator
, hence its name, in order to move material into or beyond orbit
. Space elevators have also sometimes been referred to as space bridges
, space ladders
or space lifts
. The most common proposal is a tether (usually a cable or ribbon) that spans from the surface to a point beyond geosynchronous orbit
. As the planet rotates, the inertia at the end of the tether counteracts gravity and keeps the tether taut. Vehicles can then climb the tether and escape the planet's gravity without the use of rockets. Such a structure could eventually permit delivery of great quantities of cargo and people to orbit, and at costs only a fraction of those associated with current means.
(born February 9, 1963, New York
), is a physicist
at Columbia University
. His book The Elegant Universe: Superstrings, Dimensions, and the Quest for the Ultimate Theory
was a finalist for the Pulitzer Prize
in nonfiction, and winner of The Aventis Prizes for Science Books
. The Elegant Universe
was later made into a PBS
television special with Dr. Greene as the narrator. His second book, The Fabric of the Cosmos
(2004), is about space
, and the nature of the universe. Aspects covered in this book include non-local particle entanglement as he relates to special relativity
and basic explanations of string theory. It is an examination of the very nature of matter and reality, covering such topics as spacetime
, origins and unification, and including an exploration into reality and the imagination.
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