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In physics, gravity (from Latin gravitas ' weight ' [1]) is a fundamental interaction primarily observed as a mutual attraction between all things that have mass.Gravity is, by far, the weakest of the four fundamental interactions, approximately 10 38 times weaker than the strong interaction, 10 36 times weaker than the electromagnetic force, and 10 29 times weaker than the weak interaction.
The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.
Isaac Newton applied his theory of mechanics to the tides and the precession of the equinox; and instruments were developed to measure the Earth's shape, density and gravity field, as well as the components of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and the ocean, and ...
A stellar mass black hole can pull in a substantial inflow of surrounding matter, but only if the star from which it formed was already doing so. [ 10 ] The Earth's equator does not line up with the plane of the Earth's orbit , so for half of the year the Northern Hemisphere is tilted more towards the Sun and for the other half the Northern ...
Taken together, in general relativity it is mass, energy, momentum, pressure and tension that serve as sources of gravity: they are how matter tells spacetime how to curve. In the theory's mathematical formulation, all these quantities are but aspects of a more general physical quantity called the energy–momentum tensor. [21]
Dark matter can refer to any substance which interacts predominantly via gravity with visible matter (e.g., stars and planets). Hence in principle it need not be composed of a new type of fundamental particle but could, at least in part, be made up of standard baryonic matter, such as protons or neutrons. Most of the ordinary matter familiar to ...
Early universe processes, such as inflation or a phase transition. [44] Cosmic strings could also emit gravitational radiation if they do exist. [45] Discovery of these gravitational waves would confirm the existence of cosmic strings. Gravitational waves interact only weakly with matter. This is what makes them difficult to detect.
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. [ 83 ] [ 84 ] Physicists generally are interested in the root or ultimate causes of phenomena , and usually frame their understanding in mathematical terms.