page_title: Natural science
section_title: Physics
hierarchical_section_title: Natural science / Branches of natural science / Physics
caption_attribution_description: English: First few hydrogen atom orbitals; cross section showing color-coded probability density for different n=1,2,3 and l="s","p","d"; note: m=0 The picture shows the first few hydrogen atom orbitals (energy eigenfunctions). These are cross-sections of the probability density that are color-coded (black=zero density, white=highest density). The angular momentum quantum number l is denoted in each column, using the usual spectroscopic letter code ("s" means l=0; "p": l=1; "d": l=2). The main quantum number n (=1,2,3,...) is marked to the right of each row. For all pictures the magnetic quantum number m has been set to 0, and the cross-sectional plane is the x-z plane (z is the vertical axis). The probability density in three-dimensional space is obtained by rotating the one shown here around the z-axis. Note the striking similarity of this picture to the diagrams of the normal modes of displacement of a soap film membrane oscillating on a disk bound by a wire frame. See, e.g., Vibrations and Waves, A.P. French, M.I.T. Introductory Physics Series, 1971, ISBN&#160;0393099369, page 186, Fig. 6-13. See also Normal vibration modes of a circular membrane. Slovenščina: Valovne funkcije elektrona v vodikovem atomu imajo določeno energijo (naraščajoče od zgoraj: n=1,2,3 ...) in vrtilno količino (naraščajoče prek: s, p, d ...). Svetlejša področja odgovarjajo višji verjetnostni gostoti za merjenje lege. Vrtilna količina in energija sta kvantizirani in zavzemata le nezvezdne vrednosti, kot jih kažejo slike.
context_page_description: Natural science is a branch of science concerned with the description, prediction, and understanding of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer review and repeatability of findings are used to try to ensure the validity of scientific advances.
  Natural science can be divided into two main branches: life science and physical science. Life science is alternatively known as biology, and physical science is subdivided into branches: physics, chemistry, astronomy and Earth science. These branches of natural science may be further divided into more specialized branches. As empirical sciences, natural sciences use tools from the formal sciences, such as mathematics and logic, converting information about nature into measurements which can be explained as clear statements of the "laws of nature".
  Modern natural science succeeded more classical approaches to natural philosophy, usually traced to Taoists traditions in Asia and in the Occident to ancient Greece. Galileo, Descartes, Bacon, and Newton debated the benefits of using approaches which were more mathematical and more experimental in a methodical way.
context_section_description: Physics embodies the study of the fundamental constituents of the universe, the forces and interactions they exert on one another, and the results produced by these interactions. In general, physics is regarded as the fundamental science, because all other natural sciences use and obey the principles and laws set down by the field. Physics relies heavily on mathematics as the logical framework for formulation and quantification of principles.
  The study of the principles of the universe has a long history and largely derives from direct observation and experimentation. The formulation of theories about the governing laws of the universe has been central to the study of physics from very early on, with philosophy gradually yielding to systematic, quantitative experimental testing and observation as the source of verification. Key historical developments in physics include Isaac Newton's theory of universal gravitation and classical mechanics, an understanding of electricity and its relation to magnetism, Einstein's theories of special and general relativity, the development of thermodynamics, and the quantum mechanical model of atomic and subatomic physics.
  The field of physics is extremely broad, and can include such diverse studies as quantum mechanics and theoretical physics, applied physics and optics. Modern physics is becoming increasingly specialized, where researchers tend to focus on a particular area rather than being "universalists" like Isaac Newton, Albert Einstein and Lev Landau, who worked in multiple areas.
caption: The orbitals of the hydrogen atom are descriptions of the probability distributions of an electron bound to a proton. Their mathematical descriptions are standard problems in quantum mechanics, an important branch of physics.
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