Physics & Physical Sciences playlist:
Points out some of the amazing consequences of Albert Einstein’s Theory of Relativity. Silent.
Originally a public domain film, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
Wikipedia license:
The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity. Special relativity applies to elementary particles and their interactions, describing all their physical phenomena except gravity. General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.
The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton. It introduced concepts including spacetime as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. In the field of physics, relativity improved the science of elementary particles and their fundamental interactions, along with ushering in the nuclear age. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves…
Special relativity
Special relativity is a theory of the structure of spacetime. It was introduced in Einstein’s 1905 paper “On the Electrodynamics of Moving Bodies” (for the contributions of many other physicists see History of special relativity). Special relativity is based on two postulates which are contradictory in classical mechanics:
– The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity).
– The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the light source.
…the theory has many surprising and counterintuitive consequences. Some of these are:
– Relativity of simultaneity: Two events, simultaneous for one observer, may not be simultaneous for another observer if the observers are in relative motion.
– Time dilation: Moving clocks are measured to tick more slowly than an observer’s “stationary” clock.
– Length contraction: Objects are measured to be shortened in the direction that they are moving with respect to the observer.
– Maximum speed is finite: No physical object, message or field line can travel faster than the speed of light in a vacuum…
– Mass–energy equivalence: E = mc2, energy and mass are equivalent and transmutable…
The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations. (See Maxwell’s equations of electromagnetism).
General relativity
General relativity is a theory of gravitation developed by Einstein in the years 1907–1915. The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example, when standing on the surface of the Earth) are physically identical. The upshot of this is that free fall is inertial motion: an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics. This is incompatible with classical mechanics and special relativity because in those theories inertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To resolve this difficulty Einstein first proposed that spacetime is curved. In 1915, he devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and any momentum within it.
Some of the consequences of general relativity are:
– Clocks run slower in deeper gravitational wells. This is called gravitational time dilation…
– Rays of light bend in the presence of a gravitational field.
– Rotating masses “drag along” the spacetime around them; a phenomenon termed “frame-dragging”.
– The universe is expanding, and the far parts of it are moving away from us faster than the speed of light…
