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Hamara Forums -> Amazing, Intriguing Light...

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 | Category: Physics
entry Jul 5 2005, 06:02 PM
Ever stopped to wonder at the most obviously overlooked thing?

What exactly is this thing called light?

Light travels only in a straight line. Is made up of 'packets'. Has a speed of almost 3,00,000 km/sec !!

Why is it that we can never see the speeding up or slowing down of a light ray? From the time it leaves it's source to the time it reaches us, there is no visible speeding up of a ray!!

Since it is made up of packets, if I were to hold my hand in the way of a beam, shouldn't the 'packets' drop down near my feet?

When light passes through a jar of water, shouldn't it slow down?

When I put my hand in the path of a beam, millions of 'packets' travelling at a terrifying pace of 3,00,000 km/sec should hurt me at least some. They don't. Why?? Because they don't have a 'body' that can stick?

Then how do clothes left in bright light fade eventually? Isn't the light that's falling on them taking away the colour bit by bit? (Of course it is)

If a beam of white light from a torch can light up an object on the table in a dark room, is it possible to 'vanish' an object on the table in a brightly lit room by using a torch that emits 'black light' so to say? (Here I am not referring to the 'black light' that is used commonly)

I have many more questions on light. Does anybody want to discuss?

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Mandrake
post Jul 12 2005, 09:49 AM
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It seems this topic is a bit 'heavy' for discussion blab.gif

But let me just add two interesting bits of information:
1) Scientists have succeeded in slowing down a ray of light
2) They have also succeeded in speeding up a light ray by 300 times by passing it through a chamber containing Cesium vapours.

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shivani
post Aug 2 2005, 02:21 PM
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Umm.. My physics is as rustic as can be... btu then what has ever stopped me from pondering and talking about things I have absolutely no idea about..
Light as I remember is another form of energy, and can be transformed easily. When an object obstructs the path of light the light particles would collide with it and would result in trnasformation of a differnt form. Keep your hand for long time in a strong beam, and you would feel the transformation to heat energy, due to those constant collisions. So figuraively those packets fall at your hands rahter than feet biggrin.gif.
Same is exhibited but fading clothes.

though I would have to read more about the experiments mentioned. Do you have the link??
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shivani
post Aug 2 2005, 03:56 PM
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Also, about "vanishing" an object by throwing a beam of light on it... isnt it that whether an object is transparent or opaque is quality of the object rather than the light.
Are you suggesting that same light or different light can change the physical properties of an object?
umm..
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Mandrake
post Aug 5 2005, 05:10 PM
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Stop light

18:49 18 January 2001
From New Scientist Print Edition.
Eugenie Samuel, Boston
Scientists have stopped light in its tracks in two landmark experiments. In doing so they have overcome a fundamental obstacle to the development of quantum computers.

Light normally travels at 300,000 km per second but both groups of researchers slowed a laser beam to a complete standstill by passing it through a specially prepared cell of gas atoms. Later the researchers restarted the light beam and sent it speeding off again.

Ron Walsworth from the Harvard Smithsonian Centre for Astrophysics led one of the groups and says the demonstration shows how information could be transported in a quantum computer. "The light could take information from node to node as required," he told New Scientist.

"Everybody thought it was pretty wild," says Seth Lloyd, a quantum computing engineer from MIT who attended the Physics Optics and Electronics conference in Utah where the Smithsonian group presented their idea. "We thought it would be what's needed in quantum computing."

Steady state
In conventional quantum computing, researchers aim to store quantum states in individual atoms. However the states are very delicate and liable to be destroyed by background noise.

In contrast, in the light stopping experiment, the information is contained in the electromagnetic fields of the light beam and is transferred to the state of the gas atoms. "We have over 1012 atoms which makes the state very robust," says David Phillips, who worked on the experimental set-up at Harvard-Smithsonian.

Both Phillip's group and Lene Hau's at Harvard University and the Rowland Institute in Cambridge, Massachusetts, prepared their gas atoms in the same way. They used a control laser beam tuned at just the right frequency to put the atoms into a so-called dark state. In this state the atoms cannot absorb light as usual.

When a second pulse beam is passed into the cell, rather than being absorbed it interacts with the atoms by flipping their spins. Doing this slows the beam by an amount that depends on the intensity of the control beam.

So to slow the beam to a standstill, the researchers fade out the control beam completely. But they have to do it smoothly or the dark state is destroyed. "Showing that could be done was the clever theory," says Phillips.

This theoretical breakthrough was achieved in 2000 by Misha Lukin and Suzanne Yellin at Harvard-Smithsonian and Michael Fleischhauer at the University of Kaiserslautern, Germany.

The Walsworth-Lukin work will be published in Physical Review Letters and Lene Hau's experiment will be reported in Nature.



Shivani you can find this article at www.newscientist.com

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Mandrake
post Aug 5 2005, 05:17 PM
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I guess it is simpler to give you a link to the article, as the article is rather big, and not so interest-evoking wink2.gif

You can read about the speeding up of light here:
http://partners.nytimes.com/library/nation...sics-light.html

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Poppy
post Aug 11 2005, 02:16 PM
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If a beam of white light from a torch can light up an object on the table in a dark room, is it possible to 'vanish' an object on the table in a brightly lit room by using a torch that emits 'black light' so to say? (Here I am not referring to the 'black light' that is used commonly)


.... madrake bandhu ... I need a detailed explanation on these... plz forward me some material or direct link :-)

Thanks in advance

SAchin
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Mandrake
post Aug 12 2005, 06:51 PM
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Sorry Sachin, I did not understand your request. My point was simple. If we are in a dark room, and switch on a pencil torch. The beam falls on a vase on the table. Now we can see only the vase. Since the light is not very powerful, the remaining room is still dark. So effectively we are only seeing the vase.
The beam of light showed us only the vase and nothing else.

I reverse the scenario. The entire room is brightly lit. Now if I know something which can change the properties of light (just some words to explain), can I use a pencil torch that emits a beam of 'black light' or 'anti-light' or whatever, which if directed at that vase, will render it invisible?

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