Invisibility: Theory & Practice - v3

http://timeandquantummechanics.comInvisibility: Theory & Practice - Capclave, Oct 12th, 2013
Invisibility:
Theory &
Practice
John Ashmead
Wednesday, October 9, 13
Our villain’s tapetum not in evidence! -- speciﬁcally mentioned in the novel. If you can see out, then they can see in.

http://timeandquantummechanics.comInvisibility: Theory & Practice - Capclave, Oct 12th, 2013
Invisibility:
Theory &
Practice
John Ashmead
A sufﬁciently
advanced science can be
even better than magic
Our villain’s tapetum not in evidence! -- speciﬁcally mentioned in the novel. If you can see out, then they can see in.

Invisibility: Theory & Practice - Capclave, Oct 12th, 2013 http://timeandquantummechanics.com
Transparent
Motives

Transparent
Motives
•Wicked cool

Transparent
Motives
•Wicked cool
•Very practical:
not just for war
anymore!

Transparent
Motives
•Wicked cool
•Very practical:
not just for war
anymore!
•And of great
scientiﬁc value

Outline
Image itself a nice illustration of how to show/see the invisible: we see the outlines of the invisible man, not the man himself
Note high levels of hype in this area
Has taken off since

Outline
•A brief history of
invisibility
Has taken off since

Outline
invisibility
•Reﬂections on
materials
Has taken off since

Outline
invisibility
•Reﬂections on
materials
•The future of
invisibility
Has taken off since

The Invisible
Man
“If a sheet of glass is smashed, Kemp, and
beaten into a powder, it becomes much more
visible while it is in the air; it becomes at last an
opaque white powder. … But if the white
powdered glass is put into water, it forthwith
vanishes. ” -- Griffin (the Invisible Man)
…
“Yes, yes,” said Kemp. “But a man's
not powdered glass!”
"Precisely," said Griffin. "But consider, visibility depends on the action of the visible bodies on light. Either a body absorbs light, or it reflects or refracts it, or does all these things. If it neither
reflects nor refracts nor absorbs light, it cannot of itself be visible. You see an opaque red box, for instance, because the colour absorbs some of the light and reflects the rest, all the red part
of the light, to you. If it did not absorb any particular part of the light, but reflected it all, then it would be a shining white box. Silver! A diamond box would neither absorb much of the light nor
reflect much from the general surface, but just here and there where the surfaces were favourable the light would be reflected and refracted, so that you would get a brilliant appearance of
flashing reflections and translucencies—a sort of skeleton of light. A glass box would not be so brilliant, nor so clearly visible, as a diamond box, because there would be less refraction and
reflection. See that? From certain points of view you would see quite clearly through it. Some kinds of glass would be more visible than others, a box of flint glass would be brighter than a
box of ordinary window glass. A box of very thin common glass would be hard to see in a bad light, because it would absorb hardly any light and refract and reflect very little. And if you put a
sheet of common white glass in water, still more if you put it in some denser liquid than water, it would vanish almost altogether, because light passing from water to glass is only slightly
refracted or reflected or indeed affected in any way. It is almost as invisible as a jet of coal gas or hydrogen is in air. And for precisely the same reason!"
"Yes," said Kemp, "that is pretty plain sailing."
"And here is another fact you will know to be true. If a sheet of glass is smashed, Kemp, and beaten into a powder, it becomes much more visible while it is in the air; it becomes at last an
opaque white powder. This is because the powdering multiplies the surfaces of the glass at which refraction and reflection occur. In the sheet of glass there are only two surfaces; in the
powder the light is reflected or refracted by each grain it passes through, and very little gets right through the powder. But if the white powdered glass is put into water, it forthwith vanishes.
The powdered glass and water have much the same refractive index; that is, the light undergoes very little refraction or reflection in passing from one to the other.
"You make the glass invisible by putting it into a liquid of nearly the same refractive index; a transparent thing becomes invisible if it is put in any medium of almost the same refractive index.
And if you will consider only a second, you will see also that the powder of glass might be made to vanish in air, if its refractive index could be made the same as that of air; for then there
would be no refraction or reflection as the light passed from glass to air."
"Yes, yes," said Kemp. "But a man's not powdered glass!"
"No," said Griffin. "He's more transparent!"
"Nonsense!"
"That from a doctor! How one forgets! Have you already forgotten your physics, in ten years? Just think of all the things that are transparent and seem not to be so. Paper, for instance, is
made up of transparent fibres, and it is white and opaque only for the same reason that a powder of glass is white and opaque. Oil white paper, fill up the interstices between the particles
with oil so that there is no longer refraction or reflection except at the surfaces, and it becomes as transparent as glass. And not only paper, but cotton fibre, linen fibre, wool fibre, woody
fibre, and bone, Kemp, flesh, Kemp, hair, Kemp, nails and nerves, Kemp, in fact the whole fabric of a man except the red of his blood and the black pigment of hair, are all made up of
transparent, colourless tissue. So little suffices to make us visible one to the other. For the most part the fibres of a living creature are no more opaque than water."

Sucker Bet
Octopus color blind! The separate chromatophores on the skin do the work. Massively parallel processing. Limits on processing a key factor in developing invisibility tech.

The last cry you hear
could be “Mimicry”
Or you can just run away when you see either. Which is what most sensible creatures do. The King Snake is a kind of parasite on the Coral snake.

The last cry you hear
could be “Mimicry”
Yellow
touches
red, you
be dead.
Red
touches
black, eat
Cracker
Jacks.
Or you can just run away when you see either. Which is what most sensible creatures do. The King Snake is a kind of parasite on the Coral snake.

Spicebush swallowtail
Larval mimicry [edit]
As larvae, Spicebush Swallowtails have two stages of mimicry. While the larvae are in the early stages, they are dark brown in color and thus appear to resemble bird droppings, which
encourages predators to leave them alone.[2] When the larvae have progressed to their fourth and last instar and are nearly ready to pupate, they turn a yellow-green color and are marked
by two large black dots with a white highlight. The placement of these dots on the swollen thorax creates the illusion that the caterpillars are common green snakes. Mimicking snakes help
the caterpillars to ward off predators, specifically birds. The caterpillar Spicebush Swallowtails enhance the physical resemblance behaviorally, as they have been observed to "rear up and
retract the actual caterpillar head."[18]
The osmeterium of the caterpillar also helps to enhance the resemblance to a snake. When attacked, the larvae will expose the osmeterium, a y-shaped organ typically folded up within the
caterpillar.[18] For many Spicebush Swallowtails, the osmeterium is red in color, thus creating the illusion of a snake tongue and even further enhancing the disguise.[20]
Larval mimicry, fourth instar.
Adult mimicry [edit]
Adult Spicebush Swallowtails practice another type of mimicry, as they resemble the Pipevine Swallowtail (Battus philenor), a foul-tasting butterfly.[9] Each of the sexes are able to exhibit
mimicry of B. philenor successfully, even though the brighter-blue color on female wings is a little more vibrant than the pipevine swallowtail’s coloring.[5] As they themselves are not
unapalatable and the pipevine are, this is an example of Batesian mimicry. If predators know that the Pipevine Swallowtail has a foul taste, they are unlikely to eat it and also unlikely to eat
the Spicebush Swallowtail.[1] There are other adult butterflies which mimic Battus philenor, including Papilio polyxenes, P. glaucus and L. astyanax, but the P. troilus most closely resembles
it. However, P. troilus has a greater physical resemblance to the other mimics than it does to B. philenor.[13]
Besides mimicry, another form of predator avoidance for Spicebush Swallowtails is the "club-like extensions from their hind-wings." The swallowtail will employ these during an attack from a
predator to attempt to convince the predator to leave them alone.[1]

Camouflage
“The soldiers
of France will
never
abandon
their
pantaloons
rouge!”

Camouflage
Modern camouﬂage began in
1915, when, after a crushing
defeat by the Germans, the
French army abandoned their
stylish white gloves and red
pantaloons and enlisted a cadre
of artists to develop stealthier
attire. The U.S. followed suit in
1917. In addition to hand-
painted uniforms, these
camouﬂeurs created false
bridges, decoy tanks, and, as
seen above, paper-mache horse
carcasses that snipers used as
blinds.

Dazzle
Not entirely clear how well dazzle painting worked.
A dazzle painted ship not harder to see, but much much harder to estimate its direction & speed. And if your torpedoes are only slightly faster than your target, even a small error can lead to
a miss.
And, they made the crews feel that at least something was being done.

Dazzle
•Ships in WWI &
WWII
a miss.

Dazzle
•Ships in WWI &
WWII
•Confusion to the
enemy
a miss.

Dazzle
•Ships in WWI &
WWII
•Confusion to the
enemy
•Morale boost at
least
a miss.

Stealth

Why so Boxy?
Also, ﬂat because that was all they could design (forward reference)

Why so Boxy?
•Reﬂections angle
away from source

Why so Boxy?
away from source
•Also, paint eats
radar waves

Why so Boxy?
away from source
•Also, paint eats
radar waves
•But, hard to ﬂy

Why so Boxy?
away from source
•Also, paint eats
radar waves
•And, crashes a lot

Why so Boxy?
away from source
•Also, paint eats
radar waves
•And, crashes a lot
•And, hard to build

Pretty crude frankly

Pay no attention…
Pretty crude frankly

Physics of
invisibility
Where to ﬁt cat’s eyes? Good examples! Cheshire cat, vanish till nothing but the eyes left. Good side reference to the invisible man, to the periscope in the Fighting man of mars; see also
the alcubierre warp drive

Physics of
invisibility
•Invisibility cloaks

Physics of
invisibility
•Negative refractive indexes

Physics of
invisibility
•Metamaterials

Physics of
invisibility
•Metamaterials
•Optical transformations

Physics of
invisibility
•Metamaterials
•Optical transformations
•General relativity helps make it simple?

Invisibility Cloaks
1968 Vassalage on negative refractive indices; only buildable as metamaterials
-- started to get references about year 2000
-- ﬁrst meta material devices 2004, 2005
-- ﬁrst invisibility cloak in wikipedia, 2006

Invisibility in Practice
“Invisibility is
theoretically possible
captain – the selective
bending of light – but
the power cost is
enormous.
They may have solved
that problem”
– Lt. Cmdr. Spock
“their invisibility screen may work both ways. With that kind of power consumption, they may
not be able to see us.” - Spock
Are some invisibility cloaks out there, but they have very deﬁnite limits.
One direction/all
One frequency/all
One polarization/all
Light, microwaves, radar, acoustics, water
There are some caveats, of course. You didn’t really think you’d soon be sneaking away with Ron or Hermione (delete as applicable) into the woods, did you? For now, the Duke invisibility
cloak only works with microwave radiation — and perhaps more importantly, the cloak is unidirectional (it only provides invisibility from one very speciﬁc direction). The big news here,
though, is that it is even possible to create an invisibility cloak of any description. It is now just a matter of time before visible-light, omnidirectional invisibility cloaks are created.
British Columbia company HyperStealth Biotechnology showed a functioning prototype of its new fabric to the U.S. and Canadian military this year. The material, called Quantum Stealth,
bends light waves around the wearer without the use of batteries, mirrors, or cameras. It blocks the subject from being seen by visual means but also keeps them hidden from thermal scans
and infrared.
Source: toxel.com

Lighten Up!
Redshift Rendezvous
Slow glass
EIT
Phase, group, & signal velocities

Lighten Up!
•Slow light
Redshift Rendezvous
Slow glass
EIT

Lighten Up!
•Slow light
•Light that goes faster than light
Redshift Rendezvous
Slow glass
EIT

Lighten Up!
•Slow light
•Stopped light - light that doesn’t go at
all
Redshift Rendezvous
Slow glass
EIT

Lighten Up!
•Slow light
•Stopped light - light that doesn’t go at
all
•Backwards light
Redshift Rendezvous
Slow glass
EIT

Cat’s eyes

Fermat’s
principle
Direct but slow
Faster

Fermat’s
principle
Direct but slow
Faster
Fastest!

Simple Lens

Lüneberg Lens
Lens with smoothly graded materials; more construction possibilities; more powerful effects.

Positive
Refraction
Energy conservation is key.
Note all of these bend away from the incoming beam; with negative refractive indexes, it will be reﬂected exactly back into the ongoing beam.

Negative Refraction
Dionne group at Standford
These are mathematical simulations of what the stick would look like if in liquid with a negative refractive index.

http://www.loa.espci.fr/cargese2009/Cargese2009_Pendry.pdfInvisibility: Theory & Practice - FOSSCON, Aug 10th 2013
Time Reversal
Time reversal is mathematical: equations look as if you ﬂipped the sign of the time variable. Not actually going backwards in time. That talk will be given last year.

Negative cancels
positive
But with negative refractive index, get very high levels of control of the incoming light.

Super lens

Regular materials, meta materials
Examples: physical. Give negative refractive index. Lots of more possibilities.
http://www.loa.espci.fr/cargese2009/Cargese2009_Pendry.pdf

Warping space

Like water
around a rock…

Hiding a lump
under the carpet
http://news.bbc.co.uk/2/hi/science/nature/8574923.stm

Invisible Tanks
New cloaking technologies could make a tank "disappear", "sweat" or even look like a cow
EVEN at a distance, a tank is hard to miss. Yet if it is a tank with adaptive camouflage you might barely realise you are looking straight at it. At least that's the aim of the "chameleon" system
being developed by BAE Systems in Sweden.
The system, which will be tested later this month, is part of a broad push to find ways of making tanks less conspicuous in the battlefield, says Hisham Awad at BAE Systems in Bristol, UK.
Given their large size and relatively slow speed, tanks are often sitting ducks for enemy fire. BAE Systems believes its system can not only make tanks harder to see, but also disguise them
thermally, by making the vehicles "sweat", or even look like cows.
At the moment, the visual camouflage system is the technology that is at the most advanced stage and is being developed to conceal the tank's sides, Awad says. A pair of "bug-eyed"
compound video cameras on each side capture the tank's surroundings. Each one contains nine small cameras, giving a wide field of vision. The images from these cameras are then fed to
displays built into the outer surface of the armour on the tank's opposite side. The displays use arrays of organic light-emitting diodes (OLEDs) to project the image onto a screen contained
within the armour, much like a rear-projection TV, says Awad. The screen will be built in to a layer of a transparent composite armour on the tank's side. How to hide the tank's tracks and roof
are challenges that the researchers have yet to overcome.
"There may be discontinuities at the edges," says Alan Johnston, head of the vision lab at University College London. But even so, provided the display refreshes fast enough it should work,
he says, adding that just matching the colours to the background could be enough.
BAE Systems would not reveal many of the details but claims that a working version of the system could be available within five years.
While this should make a tank more difficult to see, hiding its thermal appearance is much more challenging. "A lot of heat comes out of the vehicle at any one time," says Awad. This
produces a characteristic thermal signature, making tanks easy targets for heat-seeking missiles.
BAE researchers are modelling ways to capture the water component of the engine exhaust and channel it to composite armoured tiles along the tank's sides. The water could then
evaporate off, cooling the tank's surface just like sweating.
Rather than just hiding the vehicle's heat signature, though, the researchers want to be able to move water over the tank's body very quickly and create specific shapes. Individual composite
tiles could be switched on and off and used like pixels to depict simple shapes, the company claims. "You can make it look like a Ford Focus, or you can have the shape of a cow," says
Awad.

Foreseeable
Civilian
Uses …
"I live in Boston, and in Boston a lot of streets converge at very sharp angles, so when you look at the trafﬁc light, it's confusing whether you're seeing the trafﬁc light for you or the light that is
for the other street," he said.
With the current cloak, "you could hide certain lights from drivers so they do not get confused."
I think his tie may be on a bit crooked

•Trafﬁc light visibility
Foreseeable
Civilian
Uses …

•Earthquake &
tsunami avoidance
Foreseeable
Civilian
Uses …

•Earthquake &
tsunami avoidance
•Locating reactor core
with muons
Foreseeable
Civilian
Uses …

•Earthquake &
tsunami avoidance
•Locating reactor core
with muons
•Tourist revenue
enhancement…
Foreseeable
Civilian
Uses …

Black holes in
the laboratory
http://www.laserfocusworld.com/articles/print/volume-45/issue-10/features/photonic-frontiers-metamaterials-and-transformation-optics-newest-metamaterials-promise-customized-optical-
properties.html

Black holes as
lenses
Einstein Rings
English: What's large and blue and can wrap itself around an entire galaxy? A gravitational lens mirage. Pictured above, the gravity of a luminous red galaxy (LRG) has gravitationally
distorted the light from a much more distant blue galaxy. More typically, such light bending results in two discernible images of the distant galaxy, but here the lens alignment is so precise
that the background galaxy is distorted into a horseshoe -- a nearly complete ring. Since such a lensing effect was generally predicted in some detail by Albert Einstein over 70 years ago,
rings like this are now known as Einstein Rings. Although LRG 3-757 was discovered in 2007 in data from the Sloan Digital Sky Survey (SDSS), the image shown above is a follow-up
observation taken with the Hubble Space Telescope's Wide Field Camera 3. Strong gravitational lenses like LRG 3-757 are more than oddities -- their multiple properties allow astronomers
to determine the mass and dark matter content of the foreground galaxy lenses. (citation from

Time Cloak
http://phys.org/news/2012-01-pentagon-backed-cloak-clock.html
The researchers created what they call a time lens, which can manipulate and focus signals in time, analogous to the way a glass lens focuses light in space. They use a technique called
four-wave mixing, in which two beams of light, a "signal" and a "pump," are sent together through an optical fiber. The two beams interact and change the wavelength of the signal. To begin
creating a time gap, the researchers first bump the wavelength of the signal up, then by flipping the wavelength of the pump beam, bump it down.
The beam then passes through another, very long, stretch of optical fiber. Light passing through a transparent material is slowed down just a bit, and how much it is slowed varies with the
wavelength. So the lower wavelength pulls ahead of the higher, leaving a gap, like the hare pulling ahead of the tortoise. During the gap the experimenters introduced a brief flash of light at a
still higher wavelength that would cause a glitch in the beam coming out the other end.
Then the split beam passes through more optical fiber with a different composition, engineered to slow lower wavelengths more than higher. The higher wavelength signal now catches up
with the lower, closing the gap. The hare is plodding through mud, but the tortoise is good at that and catches up. Finally, another four-wave mixer brings both parts back to the original
wavelength, and the beam emerges with no trace that there ever was a gap, and no evidence of the intruding signal.
None of this will let you steal the crown jewels without anyone noticing. The gap created in the experiment was 15 picoseconds long, and might be increased up to 10 nanoseconds, Gaeta
said. But the technique could have applications in fiber-optic data transmission and data processing, he added. For example, it might allow inserting an emergency signal without interrupting
the main data stream, or multitasking operations in a photonic computer, where light beams on a chip replace wires.
Read more at: http://phys.org/news/2012-01-pentagon-backed-cloak-clock.html#jCp

How to Vanish a Cat
We are actually phasing out the cat; uses fact that human eye can’t see phase information to
help route

How to Vanish a Cat
The apparatus uses the fact that the
human eye can’t see phase information
to help route light around the “space
between”. With no need to preserve
the phase, the design is much simpler!
Only works from a few directions, alas.
http://arxiv.org/abs/1306.1780

Seeing the
invisible
New hope for tachyons, for warp drives, :)

Seeing the
invisible
•It’s all about the math
(really the information!)

Seeing the
invisible
•Brains at play

Seeing the
invisible
•Brains at play
•Any sufﬁciently
advanced science will
look like magic

Be Seeing You
Geometry and Light: The Science of Invisibility (Dover Books on Physics) Leonhardt, Ulf
Sold by: Amazon.com LLC
Slow Light: Invisibility, Teleportation, and Other Mysteries of Light Sidney Perkowitz
The Physics of Invisibility: A Story of Light and Deception Beech, Martin

Be Seeing You
•Forbes - Dazzled & Deceived - 2009 [Fun]

Be Seeing You
•Perkowitz - Slow Light: Invisibility,
Teleportation, & Other Mysteries of Light -
2011 [Solid]

Be Seeing You
2011 [Solid]
•Beech - Physics of Invisibility: A Story of Light
& Deception - 2011 [Lots of pictures]

Be Seeing You
2011 [Solid]
•Beech - Physics of Invisibility: A Story of Light
& Deception - 2011 [Lots of pictures]
•Leonhardt - Geometry & Light: Science of
Invisibility - 2010 [Technical]

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