
First Demonstration Of Time Cloaking - NonEUCitizen
http://www.technologyreview.com/blog/arxiv/26992/
======
redthrowaway
These articles always remind me of how prescient Star Trek was when it came to
technology, and how we really don't have anything like that these days. The
last big SciFi show, Battlestar Galactica, seemed to go out of its way to
avoid making any bold tech predictions, and the Star Trek franchise seems to
have fizzled out (that movie doesn't count). ST:TOS predicted cloaks just _six
years_ after the first _laser_ was ever fired, and 3 years before development
began on UNIX. Holograms took until TNG, but they were still a good 20 years
early.

I feel like we're getting ripped off. I want radical predictions that I can
watch daytime specials on Discovery about in 50 years.

~~~
DrCatbox
Do you have any ideas or predictions yourself?

Maybe I have a weak imagination, but Star Trek and other sci-fi have probably
done anything that can be done with any kind of technology we can come up
with. Beyond sci-fi is fantasy land, and sci-fi as a genre has reached that
border, beyond that its where Harry Potter and Lord of the Rings take over.

~~~
wladimir
+1 technology has advanced much since then, but nothing spectacular enough to
change SF. What we have is basically faster and smaller computers, and network
effects due to global connectivity.

There's nothing really new in travel methods (nope, still no flying cars),
cities are the same, VR never took off, human-level AI is still far away,
we're still fighting for resources (with bullets) and space programs are being
dismantled as we speak.

So it makes sense that our current sci-fi is still the same as that of the
80-90's.

~~~
egor83
_space programs are being dismantled as we speak._

US is not the whole world.

<http://news.ycombinator.com/item?id=2758221>

China is going to launch its first mini-space station soon. Yes, they are a
few decades behind US/Russia, but they are moving.

~~~
wladimir
Yes, I sincerely hope they are for real and not just posturing, and that this
will start a new space race.

~~~
egor83
I sincerely hope one day humans will be able to explore space for reasons
other than just outrunning the other guy.

------
DanielBMarkham
I'm still trying to get my head around this. To the layman, it sounds almost
like something trivial (properties of metamaterials) extrapolated into a bit
of a sensationalist headline.

So I go grab my good friend Schrödinger. We take his cat, subject of numerous
cruel and unusual experiments, and stick it in a box. We tie the health of the
cat to a quantum state which could condense either way. If it goes one way,
the cat lives. If it goes the other way, the cat dies. Then we wrap the
quantum state in these time-cloaking lenses.

We look at the cat, and what? Does the lack of ability to observe the quantum
state mean that the condensation of probabilities never happened? Perhaps the
cat disappears?

EDIT: Link for those who don't get the reference.
<http://en.wikipedia.org/wiki/Schr%C3%B6dingers_cat>

~~~
mechanical_fish
I haven't read the paper, just the abstract. But the literal answer to your
question is: You don't observe the cat. Ergo, it's like the "box" was never
even opened.

Now that I've answered that, let's caution you about your deployment of Mr.
Cat. First of all, I don't believe you'll need an uncertain quantum object to
observe in this particular thought experiment. Life is complicated enough
without bringing in more quantum mechanics than you need. Just imagine a
brick. It's red. Light is shining on the brick and it looks red. Now, I
install my time-bending lenses around the brick, and then at one particular
instant the brick changes to be yellow, and then goes back to being red. But
you don't see that, you just see a continuously red brick, _even though the
light was "shining on" the brick the whole time_ , because our lenses made a
"time hole" in the stream of light and the color change happened during the
hole.

I should also warn you that our friend Mr. Cat is a bad metaphor in many ways.
(He was originally an in-joke, after all, used by people who were debating the
apparent absurdity of a new theory.) The problem with the cat is that he's a
completely unrealistic creature, and he primes your intuition in all sorts of
incorrect ways. In real life you will never stumble across a coherent
superposition of two quantum states as dramatically large (trillions of
cells!) and dramatically different (alive vs dead!) as this imaginary cat.
Real cats interact with their surroundings. A lot. They breathe and meow, they
emit organic molecules that smell like cat, they charge up with static
electricity (electric fields) and then run around in circles (magnetic
fields), and above all they gravitate (which is difficult to cloak). So to
make the thought experiment work the cat's imaginary box has to _be_ a
cloaking device, a box that permits no interaction with the outside world
until it is "opened". And that doesn't exist in real life.

And, therefore, importing the cat into _this_ thought experiment is a
_particularly_ bad move, because it's redundant. If you have Shroedinger's
imaginary box you don't need an additional set of imaginary time-cloaking
lenses. The box is already cloaking the cat, for a fairly long period of time.

Always be careful: Thinking about completely impossible things is fun for a
while, but don't make a habit of it, or you'll become the sort of insufferable
spaced-out quantum-mechanics groupie who says things like _gosh, maybe when I
turn around and stop believing in this tree it will cease to exist_. Of course
not. Tree-sized objects do not physically disappear from your universe, not
without the sound of a chainsaw.

~~~
Shenglong
_Real cats interact with their surroundings. A lot. They breathe and meow,
they emit organic molecules that smell like cat, they charge up with static
electricity (electric fields) and then run around in circles (magnetic
fields)_

I actually laughed out loud; thank you for this lucid description. Fantastic
way to start my morning.

------
TeMPOraL
Just got my mind blown for the rest of the day...

Anyway, I'm reading it over and over again, and I'm still not sure if I
understand this well. Can someone confirm that, and elaborate on that a little
bit?

And I also didn't realize that we've gone so far with "traditional" cloaking
devices. I thought we're still at microwave and near-infrared level.

EDIT. Abstract of the original paper makes this a little bit easier to
understand for me.

EDIT 2. And here we have:

\- <http://www.technologyreview.com/blog/arxiv/23519/> \- illusion cloak

\- <http://arxivblog.com/?p=698> \- cloaking at a distance

------
robinduckett
Could someone tell me a practical application of this?

If someone made a box, with time lenses around it, and someone went inside the
box, what would happen?

~~~
chrisrogers
This is essentially a concept for a device that interrupts the observation of
the space it protects by probes meant to glean temporal information. My
understanding is that nothing spectacular would happen to the contents of the
device, but to a probe aimed at the contents. That probe would be manipulated
around the space, preventing it from making inferences about what would be
occurring in the space.

As for what exactly constitute a temporal probe, I am not certain. Some form
of laser meant to be manipulated by the occurrence of an event perhaps.

~~~
ignifero
This is actually a spatiotemporal cloak, not purely temporal. The probe is
simply the laser (the green lines in the article picture).

------
_ikke_
What I miss in this article is what it implies that time is cloaked. What does
is it mean and where can it be used for?

~~~
geuis
I'll hope that other brighter members of our community correct me if I'm
wrong, but here's a stab at it.

We all learn about causality. Things don't just happen without being there
being some kind of reversible action. If an ice cube melts, that's a time
reversible aspect of physics. Basically if you could run time backwards like a
video in reverse, you would see the ice unmelt.

In another instance, imagine a block of ice in the middle of a star. There's
no way that a chunk of ice can just appear in a star. Now, that's not to say
its impossible for such a chunk to be there. But you can trace back a line of
actions that led to it being there, ranging from the debris of the spacecraft
that contained it to the launch pad on a planet orbiting nearby, to all of the
patterns of matter and information encompassing the civilization that built
and launched it in the first place.

So if I'm understanding this correctly, the temporal cloak effectively allows
stuff to happen inside it that isn't detectable from the outside. To stretch
my last analogy a bit, imagine you put such a temporal cloak around the entire
civilization leading up to where the ice ends up in the star. To an outside
observer, say some aliens doing a research study on our star, all of a sudden
they would detect the block of ice in the star but not have any idea where it
came from.

~~~
Miky
Nice Anathem reference :)

The problem with your analogy is that the debris from the spaceship, etc.
would still be visible to an observer after the fact. A better analogy would
be this:

The aliens point a camera at our entire civilization. Ignoring the fact that
this cloak works on the order of monumentally smaller scales than
civilizations and the time it takes to put an ice chunk in a star, we use the
cloak while we put an ice chunk in a star. The aliens would see our
civilization jump from a state with no ice chunk in a star to one with an ice
chunk in a star. Assuming that their measuring devices are up to the task,
they would still be able to find all the spaceship debris, etc.

------
machrider
Is this similar to the idea of the light cone?
<http://en.wikipedia.org/wiki/Light_cone>

That is, it's impossible for information from this "cloaked" time to reach us,
because it's outside of our light cone?

~~~
ignifero
Not really, it's not a relativistic phenomenon.

------
TeMPOraL
<http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.2062v1.pdf> \- link to the
original paper.

------
drieddust
Fantastic its like that movie I saw in which a guy can freeze time whenever he
likes and then gets the reality going by cracking his knuckles.

------
jamesrom
Old. Shane Carruth showed me this back in 2004.

------
sunpin
It's a nice way to put people in prison.

------
ignifero
There's a better article in the guardian
[http://www.guardian.co.uk/science/blog/2011/jul/13/harry-
pot...](http://www.guardian.co.uk/science/blog/2011/jul/13/harry-potter-
invisibility-cloak) . They have an interesting intuitive description:

 _He used one set of lenses to prise open a gap in a beam of light, by slowing
down long wavelengths, such as red, and speeding up short wavelengths, such as
blue. With a second set of lenses, he then closed the gap, so at the end of
the experiment, the light beam looked exactly as it did at the start._

I'm not sure that i understand it correctly, the "cloak" occurs because there
_is no light_ during the event as it has either moved on or is lagging behind.
It's the recombination at the second lens that does the trick, giving a false
sense of continuity to the observer after the lens.

