Science

IceBone

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Basically (and with a lot of liberties taken), it goes something like this:



Normal glass, due to the difference in refraction coefficients between it and air, has only about 92% transparency (8% is reflected). An anti reflex coating is made in such a way that the refraction coefficient between air and it and it and glass is exactly the same, meaning half of those 8% being reflected happens when light hits the coating, the other half when it passes from the coating into the glass. The thickness of the coating is set to around 1/4 of the mean of visible light, meaning that most of the light that reflects then comes into phase with the second reflection and cancels itself out. But since there are laws about preservation of energy, that light has to go somewhere. So it just... passes through without reflecting in the first place and you get about 99% transparency (there's still a slight green or purple reflection, but that's due to the varying wavelengths of light and not being able to cover the whole spectrum)...

:blowup:
 
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IceBone

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Universe May Have Been Around Since Forever, According to Rainbow Gravity Theory

When did the clock of the universe start ticking? For decades we?ve believed that 13.8 billion years ago the Big Bang set the universe?s clock in motion. While that?s still the prevailing viewpoint, researchers are now exploring a theory called ?rainbow gravity? that, if correct, does away with the Big Bang. In a ?rainbow? universe, the clock has been ticking forever.

Behind the scenes of the Big Bang is Einstein?s theory of general relativity. But there?s a problem. Einstein?s theory is at odds with quantum mechanics, the theory of tiny particles. Rainbow gravity was proposed to reconcile the two, and if it were correct, the universe would have no beginning?there is no big treasure at the foot of this ?rainbow? because the ?rainbow? universe goes back forever.

Why is it called rainbow gravity? Because according to the theory, gravity becomes a cosmological prism that can separate different colors of light. Our eyes can?t see that?when we gaze longingly into the night sky, the stars? white light appears to have streamed smoothly to our eyes. If rainbow gravity is right though, light?s path through outer-space may be more like the famous Pink Floyd poster, where the different colors become spread apart.

So, why don?t we see rainbow stars? Clara Moskowitz, writing for Scientific American, tells us more:

The effects would usually be tiny, so that we wouldn?t notice the difference in most observations of stars, galaxies and other cosmic phenomena. But with extreme energies, in the case of particles emitted by stellar explosions called gamma-ray bursts, for instance, the change might be detectable. In such situations photons of different wavelengths released by the same gamma-ray burst would reach Earth at slightly different times, after traveling somewhat altered courses through billions of light-years of time and space. ?So far we have no conclusive evidence that this is going on,? says Giovanni Amelino-Camelia, a physicist at the Sapienza University of Rome who has researched the possibility of such signals. Modern observatories, however, are just now gaining the sensitivity needed to measure these effects, and should improve in coming years.
Rainbow gravity may just be an illusion, a pretty idea that makes science a bit more colorful. But soon we may find out if we?re living in an infinitely old rainbow universe.
http://www.pbs.org/wgbh/nova/next/physics/universe-may-have-been-around-since-forever-according-to-rainbow-gravity-theory/
 

MXM

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Maybe someone less of a dilettante in the quantum physics could shed a light on this: are "particles" still relevant these days? If all matter and all forces are of quanta of underlying fields, why are we still talking about field-particle duality? This (among many, many other things) confuses me.
 

maxtortheone

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Can anyone here explain how compound bows work? Maybe something that shows the forces going on there? Me an my Dad have some trouble wrapping our heads around this. Have an awesome pic of one as a reward

 

narf

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The main force magic happens in the wheels at either end. The bow itself works like any other bow, you bend it and it wants to bend back.

Here's a German-labelled series of pictures showing what happens in the wheels with differently coloured parts, your black-on-black bow makes it hard to tell them apart.



The red string is attached to the other side of the bow, in yours you can see one looped around the right-hand wheel and fixed on the left-hand side. The yellow string is the one you draw and hold, in your example it's already drawn.
Observe the brass centre of rotation, and the length of the levers for each string relative to this point.
At first, the red string has a huge lever, giving it a large force on the yellow string (and hence the arrow). However, fully drawn you can see the red string "collapse" close to the brass centre, taking most of the force away - as a result, you don't have to hold the peak force of the bow, despite being fully drawn. After you release, a bit of rotation on the wheels gives the lever back to the red string to allow full force on the arrow.

All the complex-looking bow does is apply increasing force on the two "red" ropes.
 

jibduh

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However, fully drawn you can see the red string "collapse" close to the brass centre, taking most of the force away - as a result, you don't have to hold the peak force of the bow, despite being fully drawn. After you release, a bit of rotation on the wheels gives the lever back to the red string to allow full force on the arrow.

All the complex-looking bow does is apply increasing force on the two "red" ropes.
And this is the apparent magic. It allows you to hold and strain against far lower force than the full power of the bow while you're training on your target. Of course, it doesn't help if you aren't able to overcome that peak to begin with... :lol:
 

Cellos88GT

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Maybe someone less of a dilettante in the quantum physics could shed a light on this: are "particles" still relevant these days? If all matter and all forces are of quanta of underlying fields, why are we still talking about field-particle duality? This (among many, many other things) confuses me.
I'm not sure I understand your question, are you asking why there is still a focus on particles at all? Or why people still care about particle-field duality?

The reality is, theories involving particles need to be tried and tested until they're metaphorically "blue in the face".
 

MXM

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I'm not sure I understand your question, are you asking why there is still a focus on particles at all? Or why people still care about particle-field duality?

The reality is, theories involving particles need to be tried and tested until they're metaphorically "blue in the face".
It's hard to even organize my thoughts to form a question :p
Basically, I wanted to know what is the state of the art in quantum physics regarding the notion of "particles". Because popular media can be very confusing in its attempts to simplify explanations.

Of course I understand why people care about matter behaviour. What I don't quite understand is what points towards idea of matter being made of particles? It has been shown numerous of times that all matter (even whole molecules) behaves like a wave and exhibits interference. So in my view that makes the smallest portion of matter a wave quantum, not a particle.

If we are to take on the idea that quantum mechanics is inherently probabilistic, then I can intuitively understand (strong word ;), let's say believe) how a single wave quantum can interfere with itself. And how with some manipulation of the experiment the interference can be destroyed when scientists are "forcing" it to chose a path with elaborate detection schemes. But I can't understand how a particle - a lump of mass - can interfere at all. If it does, how can it be called a particle?

Or am I just stuck in the semantics?
 

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http://phys.org/news/2014-01-energy-dense-sugar-battery.html
A Virginia Tech research team has developed a battery that runs on sugar and has an unmatched energy density, a development that could replace conventional batteries with ones that are cheaper, refillable, and biodegradable.


https://www.simonsfoundation.org/quanta/20140122-a-new-physics-theory-of-life/
Why does life exist?

Popular hypotheses credit a primordial soup, a bolt of lightning and a colossal stroke of luck. But if a provocative new theory is correct, luck may have little to do with it. Instead, according to the physicist proposing the idea, the origin and subsequent evolution of life follow from the fundamental laws of nature and ?should be as unsurprising as rocks rolling downhill.?

From the standpoint of physics, there is one essential difference between living things and inanimate clumps of carbon atoms: The former tend to be much better at capturing energy from their environment and dissipating that energy as heat. Jeremy England, a 31-year-old assistant professor at the Massachusetts Institute of Technology, has derived a mathematical formula that he believes explains this capacity. The formula, based on established physics, indicates that when a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy. This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life.
 

awdrifter

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'Hand of God' Spotted by NASA Space Telescope (Photo)

Religion and astronomy may not overlap often, but a new NASA X-ray image captures a celestial object that resembles the "Hand of God."

The cosmic "hand of God" photo was produced when a star exploded and ejected an enormous cloud of material, which NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, glimpsed in high-energy X-rays, shown in blue in the photo. NASA's Chandra X-ray Observatory had imaged the green and red parts previously, using lower-energy X-rays.

"NuSTAR's unique viewpoint, in seeing the highest-energy X-rays, is showing us well-studied objects and regions in a whole new light," NuSTAR telescope principal investigator Fiona Harrison, of the California Institute of Technology in Pasadena, said in a statement.

The new image depicts a pulsar wind nebula, produced by the dense remnant of a star that exploded in a supernova. What's left behind is a pulsar, called PSR B1509-58 (B1509 for short), which spins around 7 times per second blowing a wind of particles into material ejected during the star's death throes.

As these particles interact with nearby magnetic fields, they produce an X-ray glow in the shape of a hand. (The pulsar is located near the bright white spot in the image but cannot be seen itself, NASA officials said.)

Scientists aren't sure whether the ejected material actually assumes the shape of a hand, or whether its interaction with the pulsar's particles is just making it appear that way.

"We don't know if the hand shape is an optical illusion," Hongjun An, of McGill University in Montreal, said in a statement. "With NuSTAR, the hand looks more like a fist, which is giving us some clues."

The red cloud appearing at the fingertips is a separate structure called RCW 89. The pulsar's wind may be heating the cloud to produce the low-energy X-ray glow, astronomers believe.

The X-ray energies seen by NuSTAR range from 7 to 25 kiloelectron volts, or keV, whereas the energies seen by Chandra range from 0.5 to 2 keV.

The Hand of God is an example of pareidolia, the psychological phenomenon of perceiving familiar shapes in random or vague images. Other common forms of pareidolia include seeing animals or faces in clouds, or the man in the moon. Despite its supernatural appearance, the Hand of God was produced by natural astrophysical phenomena.
http://www.space.com/24225-hand-of-god-photo-nasa-telescope.html

That's pretty cool.
 
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