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 explain events of 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.
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 utilize 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 quantum dot
is a semiconducting crystal
in nanotechnology. Quantum dots confine electrons
, electron-hole pairs
, or excitons
to zero dimensions in a region of the order of the electrons' Compton wavelength
. This confinement leads to discrete quantized
energy levels and to the quantization of charge in units of the elementary electric charge e
. Quantum dots are particularly significant for optical applications due to their theoretically high quantum yield
. Quantum dots have also been suggested as implementations of a qubit
for quantum information processing
Because the quantum dot has discrete energy levels, much like an atom, they are sometimes called artificial atoms. The energy levels can be controlled by changing the size and shape of the quantum dot, and the depth of the potential. Like in atoms, the energy levels of small quantum dots can be probed by optical spectroscopy techniques. In contrast to atoms it is relatively easy to connect quantum dots by tunnel barriers to conducting leads, which allows the application of the techniques of tunneling spectroscopy for their investigation.
Michio Kaku (Kanji: 加来 道雄) (born January 24, 1947 in the United States) is a Japanese American theoretical physicist, tenured professor, and co-creator of string field theory, a branch of string theory.
Dr. Kaku is the author of several scholarly, Ph.D.-level textbooks and has had more than 70 articles published in physics journals covering topics such as superstring theory, supergravity, supersymmetry, and hadronic physics. He is also known as an author of popular science books, including the best-sellers Beyond Einstein, Visions, Hyperspace, and Parallel Worlds, and the host of several radio shows, as well as being a popular figure in science television shows due to his accessible approach to the layman on explaining complex physics.
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