(PhysOrg.com) -- By suggesting that mass, time, and length can be converted into one another as the universe evolves, Wun-Yi Shu has proposed a new class of cosmological models that may fit observations of the universe better ...
(Phys.org)—Stanford engineers have designed and built a prism-like device that can split a beam of light into different colors and bend the light at right angles, a development that could eventually lead to computers that ...
Optics & Photonics
Dec 3, 2014
10
1
Cosmic rays are really sub-atomic particles, being mainly protons (hydrogen nuclei) and occasionally helium or heavier atomic nuclei and very occasionally electrons. Cosmic ray particles are very energetic as a result of ...
Astronomy
Jun 13, 2011
11
0
Could the famed "Big Bang" theory need a revision? A group of theoretical physicists suppose the birth of the universe could have happened after a four-dimensional star collapsed into a black hole and ejected debris.
Astronomy
Sep 19, 2013
229
19
(PhysOrg.com) -- The phenomenon of time dilation is a strange yet experimentally confirmed effect of relativity theory. One of its implications is that events occurring in distant parts of the universe should appear to occur ...
Believe it or not, time travel is possible.
General Physics
May 14, 2020
27
2076
University of Central Florida researchers have developed a way to control the speed of light. Not only can they speed up a pulse of light and slow it down, they can also make it travel backward.
Optics & Photonics
Apr 4, 2019
25
23818
A research collaboration between Queen Mary University of London, the University of Cambridge and the Institute for High Pressure Physics in Troitsk has discovered the fastest possible speed of sound.
General Physics
Oct 9, 2020
14
9891
(Phys.org) —Physicist James Franson of the University of Maryland, Baltimore County has captured the attention of the physics community by posting an article to the peer-reviewed New Journal of Physics in which he claims ...
Scientists at the world's biggest atom smasher on Tuesday started colliding particles at record energy levels, opening a new era in the quest for the universe's deepest secrets.
General Physics
Mar 30, 2010
72
0
The term speed of light generally refers to a fundamental physical constant of spacetime that limits the rate of transfer of matter or information. The speed of light is the speed of not just visible light, but of all electromagnetic radiation in vacuum (also called free space), and usually is denoted by the symbol c. Speeds faster than that of light are encountered in physics but, in all such cases, no matter or information is transmitted faster than c. The speed of light also plays a role in general relativity, and is believed to be the speed of gravitational waves.
In SI units, the magnitude of the speed of light in vacuum is exactly 299,792,458 metres per second (m/s) because of the way the metre is defined. More about this topic is found below in Speed of light set by definition.
For many practical purposes, the speed of light is so great that it can be regarded to travel instantaneously. An exception is where long distances or precise time measurements are involved. For example, in the Global Positioning System (GPS), a GPS receiver measures its distance to satellites based on how long it takes for a radio signal to arrive from the satellite. In astronomy, distances are often measured in light-years, the distance light travels in a year.
The speed of light when it passes through a transparent or translucent material medium, like glass or air, is less than its speed in vacuum. The speed is inversely proportional to the refractive index of the medium. In specially-prepared media, the speed can be tiny, or even zero.
For many years the speed of light was the subject of speculation, some believing it to be infinite. The first effective measurements of the speed of light were made in the seventeenth century, and these were progressively refined until, in 1983, the speed of light in vacuum was fixed by definition.
This text uses material from Wikipedia, licensed under CC BY-SA
