Can We Make

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Can We Make Harry Potter Invisible??
Harry Invisible Man
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Is invisibility possible?
?Invisibility?
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How it works
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Is this any use?

• Good points
• Results that work
• Possible improvements
• Inexpensive

• Bad points
• Only works in 2D
• Shows some reflection
• Not very dynamic!

• Bit of a cheat really!!

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What is Light?
An electromagnetic wave, made up of different
wavelengths.
See for yourselves!!
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How does light interact with objects?
Natural form of invisibility is an object which
neither reflects nor absorbs light (it allows
light to pass through it).
Absorption - Occurs when electrons absorb light
energy
Reflection - Occurs strongly in smooth,
conducting metals with free electrons
Transmission - Occurs strongly when there are
large enough gaps between atoms for the light to
pass.
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Does invisibility exist in nature?
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Secret of the sky practical

• Pour water into tank

• Shine the flashlight beam through the tank as
  shown in the diagram.
• Hold white paper in the two places shown on the
  diagram and record what light you see.
• Add a pinch of powdered milk and then stir.
  Repeat the previous step.

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So why is the sky red/orange at sunset?
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Are there any invisible materials?
Man made transparent solids
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How do we make glass transparent?
Glass is made from sand!
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Can we use this to make Harry invisible?
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A different approach
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Can we bend light?
Yes - Refraction!!
When light passes through a material it slows as
it has to pass trillions of atoms. The denser
the material the slower it goes.
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How does this work?
Disappearing bottle
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Why do the stars twinkle?
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Everyday examples of Refraction!!
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Do we need any special materials?
Yes! Metamaterials!
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Cylindrical Cloak
1 mm
2006 a metamaterial made at Durham, North
Carolina and Imperial College made an object
invisible to microwave radiation.
Fiberglass rings patterned with copper elements.
The internal structures embedded in the
metamaterial must be smaller than the wavelength
of the radiation. This device works in the
microwave spectrum.
http//Duke University cloak
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Funded by the Pentagons Defence Advanced
Research Projects Agency DARPA.
The material properties vary from point to point
and in a very specific way. This gives a subtle
gradient in the electromagnetic properties of the
cloak.
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Problem
The internal structures embedded in the
metamaterial must be smaller than the wavelength
of the radiation.
Wavelength of visible light 380nm (purple) to
780nm (red) We need structures 10s of nms in size
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How big is a nanometer?
1 m 1 meter 0.01 m 1 centimeter 0.001 m
1 millimeter 0.000001 m 1 micrometer
. 0.000000001 m 1 nanometer . There are
approximately five atoms to 1 nanometer!
20,000 per 1 mm!!!
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Is this possible?
American news
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Is this any use?
Claims to work for red light (780 nm)

• Bad points
• Only works in 2D
• Only works for one wavelength (the easiest one
  too!)

• Good points
• The practical data agrees with the theory
• Large step towards an invisible cloak

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David Smith Duke University
A true invisibility cloak IS possible within the
laws of physics. With good research it should be
a matter of time
Steps to success
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Differences compared with Harrys cloak
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What are the uses for an invisibility cloak?
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Philosophical View on Invisibility
Plato Greek philosopher Born 424 BC, Athens
Morality is a social construct . The use of
invisibility removes this construct and the
temptation to steal and kill at will becomes
irresistible.