CWL

Speed of light

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time.

In imperial units this speed is approximately 186,282 miles per second. According to special relativity, c is the maximum speed at which all energy, matter, and information in the universe can travel. It is the speed at which all massless particles and associated fields (including electromagnetic radiation such as light) travel in vacuum.

It is also the speed of gravity (i.e. of gravitational waves) predicted by current theories. Such particles and waves travel at c regardless of the motion of the source or the inertial frame of reference of the observer. In the theory of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.

archiemcphee:

This surprisingly lovely little orange is being illuminated from the inside by a lightbulb powered by the orange itself. That’s right, it’s an orange battery:

“The electricity powering the lightbulb inside the orange is generated through a chemical reaction between citric acid and the zinc nails inserted into each wedge.”

The beautiful orange battery was built by photographer Caleb Charland (previously posted here) as part of an ongoing project using pieces of produce and other objects as light sources for his long-exposure photography. Pretty awesome stuff. 

“…but before you start work on a bunch of orange lights to keep on the nightstand, the light generated was so dim this particular photograph required a 14 hour exposure.”

Visit Caleb Charland’s website to view of his wonderful photographic work.

[via Colossal]

scinerds:

Is light made of waves, or particles?

This fundamental question has dogged scientists for decades, because light seems to be both. However, until now, experiments have revealed light to act either like a particle, or a wave, but never the two at once.

Now, for the first time, a new type of experiment has shown light behaving like both a particle and a wave simultaneously, providing a new dimension to the quandary that could help reveal the true nature of light, and of the whole quantum world.

The debate goes back at least as far as Isaac Newton, who advocated that light was made of particles, and James Clerk Maxwell, whose successful theory of electromagnetism, unifying the forces of electricity and magnetism into one, relied on a model of light as a wave. Then in 1905, Albert Einstein explained a phenomenon called the photoelectric effect using the idea that light was made of particles called photons (this discovery won him the Nobel Prize in physics).

Ultimately, there’s good reason to think that light is both a particle and a wave. In fact, the same seems to be true of all subatomic particles, including electrons and quarks and even the recently discovered Higgs boson-like particle. The idea is called wave-particle duality, and is a fundamental tenet of the theory of quantum mechanics.

Depending on which type of experiment is used, light, or any other type of particle, will behave like a particle or like a wave. So far, both aspects of light’s nature haven’t been observed at the same time.

Now, for the first time, researchers have devised a new type of measurement apparatus that can detect both particle and wave-like behavior at the same time. The device relies on a strange quantum effect called quantum nonlocality, a counter-intuitive notion that boils down to the idea that the same particle can exist in two locations at once.

“The measurement apparatus detected strong nonlocality, which certified that the photon behaved simultaneously as a wave and a particle in our experiment,” physicist Alberto Peruzzo of England’s University of Bristol said in a statement. “This represents a strong refutation of models in which the photon is either a wave or a particle.”

Peruzzo is lead author of a paper describing the experiment published in the Nov. 2 issue of the journal Science.

Constellation Lampshade Projects the Starry Sky Across Your Ceiling

The Mileage of Light

Composite Image Credit & Copyright: Dennis L. Mammana

If you’re driving down a dark road on a starry night, you might want to check the odometer. Earlier this month, when traveling astronomer Dennis Mammana did he was greeted with the significant mileage reading of 186,282 miles.

That’s the number of miles light travels in one second. Or, if you prefer kilometers, the number you are looking for is 299,792. Mammana muses that in driving to countless observatories, star parties, and night sky photo shoots it has taken his 1998 vintage sport utility vehicle over 13 years to cover that distance. Of course, he considers his next important mileage milestone to be the distance to the Moon.

scinerds:

Physicists Discover Quantum Speed Limit

The speed of light is the cosmic speed limit, according to physicists’ best understanding: No information can be carried at a greater rate, no matter what method is used. But an analogous speed limit seems to exist within materials, where the interactions between particles are typically very short-range and motion is far slower than light-speed. A new set of experiments and simulations by Marc Cheneau and colleagues have identified this maximum velocity, which has implications for quantum entanglement and quantum computations.

coursekit:

This lamp supposedly “mimics and reproduces the cosmic light that fills the Universe.” How?

 They claim the the lights twinkle in various colors and sequences that visualize how stars’ light has changed over billions of years. This works via an algorithm that expresses the 14-billion-year history of the cosmos in a 14-second loop. 

Woah.

via Fast Co Design

Citizen Science: GLOBE at Night

For starters, what is GLOBE at Night?

The GLOBE at Night program is an international citizen-science campaign designed to raise public awareness of the impact of light pollution on our night skies. GLOBE at Night aims to raise awareness by inviting citizen-scientists to measure their night sky brightness and submit their observations to a website from a computer or smart phone.

Light pollution not only threatens our “right to starlight”, but also affects energy consumption, wildlife and health. For the past six years, the GLOBE at Night campaign has been involving people in 115 countries.

Participating in GLOBE at Night requires only five easy steps:

1) Find your latitude and longitude.

2) Find Orion, Leo or Crux by going outside more than an hour after sunset (about 8-10pm local time).

3) Match your nighttime sky to one of the provided magnitude charts.

4) Report your observation.

5) Compare your observation to thousands around the world.

You can also use the new web application data submission process. The GLOBE at Night website is easy to use, comprehensive and holds an abundance of background information. The database is usable for comparisons with a variety of other databases, like how light pollution affects the foraging habits of bats.

jtotheizzoe:

Time Cloak Hides (Very Small) Events in Time

You’ve probably seen this on your dashboard today, as a few of my science buds have covered it: “Time Cloak Can Make Time Disappear!” That’s very cool stuff, but what does it mean? 

You might remember a few months ago when I posted about an “invisibility cloak” technology, where beams of light are bent around an object preventing it from reflecting (becoming invisible). There’s a video here. This new “time cloak” uses a special way of slowing down certain of wavelengths of light to do the same thing. Sort of. From SciAm:

The cloak, described in the January 5 issue of Nature, relies on the fact that light of different colors moves at different speeds through certain media. (Scientific American is part of Nature Publishing Group.) Using a device that they call a “time lens,” the researchers split a single-color laser beam into a spread of wavelengths, then slowed half of those wavelengths while speeding up the others. That created a very brief time gap that could be closed again before the beam reached the detector by reversing the lensing process, restoring the beam to a single, seemingly undisturbed wavelength.

Very cool, with implications for computing (good and bad). But you know what’s better? ANIMATIONS!

Click above for a great video explanation of the time cloak, put together by Rose Eveleth. Make much more sense now.

Zodiacal Light above Himalayan Hills

Site: Uttarakhand - India

Copyright: Babak A. Tafreshi