history - What is the origin of the use of the letter/symbol $c$ for the speed of light?

A cow-orker recently "informed" me that the reason we call the speed of light $c$ is that c stands for "causality.I would guess that can't be the case, because I think the symbol $c$ was used to represent the speed of light as early as the days of Faraday and certainly in Maxwell's papers, while the idea that light propagation and causality are related came into being decades later, with relativity.But I'm not absolutely certain that Maxwell used the symbol $c$. At any rate, does anyone know when using the symbol $c$ to represent the speed of ...Read more

speed of light - Do/Would Gravitational Waves have these properties?

I haven't done a ton of research on Gravitational Waves, but I have done some theorizing. Are these properties confirmed (by theory or observation) characteristics of GW?Gravitational Waves travel at the speed of lightReasoning: The observation of GW coordinated with the observation of the two black holes colliding. The observations of the collision were Electromagnetic, and inherently traveled at the speed of light (or pretty darn close). If the two sets of waves originated from the same point, and arrived at another point at the same time...Read more

vacuum - How is it possible the speed of light is not constant?

I was reading this article recently, which summarizes a couple of new studies into the speed of light. In one paper, Marcel Urban from the University of Paris-Sud, located in Orsay, France and his colleagues identified a quantum level mechanism for interpreting vacuum as being filled with pairs of virtual particles with fluctuating energy values. As a result, the inherent characteristics of vacuum, like the speed of light, may not be a constant after all, but fluctuate. Meanwhile, in another study, Gerd Leuchs and Luis L. Sánchez-Soto, f...Read more

speed of light - Was the direction, from where the gravitational wave in the LIGO experiment came from, identified?

The time difference of the arrival of the gravitational wave in the two Ligo detectors had a certain value. This difference would have been zero if the source of the wave had an equal distance to both detectors. In that case, the source of the wave had to lie on a plane perpendicular to the line connecting the detectors. It would have been maximal if the source lied on the extended line connecting the two detectors. But because the speed of gravity is unknown, only in the case of equal arrival time the source could have been said to lie on the ...Read more

speed of light - Microsecond trading with neutrinos

The Spread Networks corporation recently laid down 825 miles of fiberoptic cable between New York and Chicago, stretching across Pennsylvania, for the sole purpose of reducing the latency of microsecond trades to less than 13.33 milliseconds (http://www.spreadnetworks.com/spread-networks/spread-solutions/dark-fiber-networks/overview). The lesson I would draw from this is that, in the near future, oil and natural gas extraction won't be the only lucrative use of ocean platforms. So here's my question - since trades are occurring on the scale...Read more

Why can't we use this method to achieve extreme speeds?

Turn an axle with diameter 1 inch at 1 mile per hour, and an attached wheel with diameter 5 inches will spin at 5 miles per hour.Why can't we apply this principle on a much bigger scale? Say you put an axle 1 foot in diameter at the peak of a mountain, and attached a cable to it 1 mile long (with another cable for counterweight), and then spun the axle 1000 miles per hour. The cable could have a satellite attached to it set to launch when top speed is reached.That's already about 5,000,000 miles per hour (1 mile/1 foot =~ 5000, times 1000mph). ...Read more

conductors - Speed of Signals in a Wire vs Fiber Optic Cable

How much faster is the transmission of a signal in a fiber optic cable than in a copper wire? I would assume fiber optic cables transmit signals at the speed of light (this begs the question, are fiber optic cables vacuum sealed or is the light moving through air, but that wouldn't make much of a difference) but how does that compare with the speed of a signal moving through a conductor? I've seen online that signals travel at about the speed of light as well. If that is the case though, why are fiber optic cables preferable?...Read more

velocity - Is there a case (besides light speed in any given medium) where speed is experimentally measured rather than theoretically calculated?

I studied physics throughout college, but I cannot recall a single time where I directly measured the velocity of an object or force. Every time I measured the components of velocity (distance and time) rather than the actual velocity instead. This got me thinking as to whether or not there is some instance where I would have a known velocity, but not components by which to calculate it. Light, being constant within any given medium, is the only velocity I can measure. Knowing the velocity of an object could be useful for measuring distance, bu...Read more

faster than light - speed of freezing vs. moving

An idea came to my mind and like to discuss it.We know that out there in the space the absolute zero (aka. -273 C) is almost reached where all the particles and atoms would freeze up and stop giving the matter its resilience and shape.We know as well that for instance if water is to be thrown or poured in some freezing parts of the globe (e.g. Atartica or Nordic countries) where temperture is really really low it would freeze on its way or that might take few seconds no more. (even streams get to be frozen!)So the questions is:if superman to be...Read more

Is our physics and system of units based on time (second) or the speed of light?

The speed of light in vacuum is stated in our physics as a universal physical constant, c, when measured locally, in vacuum. The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associa...Read more

speed of light - Will laser scanning system miss photons when the mirror scans too fast?

So in many applications like Optical Coherence Tomography, LIDAR, a mechanical scanning mirror is often used to reflect the laser to outside and also reflect the back scattered light to detector.Since light has a constant speed, when the light hits the mirror at scan angle A and goes out side, then gets back scattered by an object and goes back to the mirror, the mirror already moved to another angle. My understanding is that if the mirror scans extremely fast, or if the object is far far away, then the mirror will not be able to reflect the li...Read more

speed of light - Undoing problems caused by setting $c = 1$ { or "Undoing $c = 1$" }

In the mathematical derivation of equations for physics, and involving wave propagation in particular, the propagation speed at the start of the derivation is often set to one (c = 1). I am working with long derivations where the resulting final equations assume c = 1 and would like to convert them to have propagation speeds that are represented by a variable, say v, and do this without going through the complete derivation from the start to the finish. It is not at all obvious where the c's would reappear if they were not set to 1.My questio...Read more