8 ms·

First Demonstration Of Time Cloaking

143 points by NonEUCitizen 15y ago

_ikke_ 15y ago
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 15y ago
  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.
  - ph0rque 15y ago
    So basically, time cloaking enables the possibility of Cuil[0] realities over 2. [0] http://cuiltheory.wikidot.com/what-is-cuil-theory http://cuiltheory.wikidot.com/what-is-cuil-theory
  - Miky 15y ago
    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.
- dennyabraham 15y ago
  the abstract is clearer http://arxiv.org/abs/1107.2062 http://arxiv.org/abs/1107.2062. here's the relevant bit: Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking was proposed in which the dispersion of the material is manipulated in time to produce a "time hole" in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating and slowing down the front and rear parts, respectively, of the probe beam to create a well controlled temporal gap in which the event occurs so the probe beam is not modified in any way by the event.
- chalst 15y ago
  I found the MIT Tech Review's summary confusing. I didn't understand the article it was based on fully, but the idea seems to be covered in the following paragraph: Time-space duality represents the analogy between diffraction and dispersion that arises from the mathematical equivalence between the equations describing the diffraction of a beam of light and the one-dimensional temporal propagation of a pulse through a dispersive medium [17,18]. Similar to a spatial lens that imparts a quadratic phase in space, a time-lens can be implemented that produces a quadratic phase shift in time [19{21]. This time-lens can, for example, magnify [22] or compress [23] signals in time and has an equivalent of the lens law. Time-lenses can be created with an electro-optic modulator [18] or via a parametric nonlinear optical process such as four-wave mixing (FWM) with a chirped pump wave [19,20]. In the latter case the signal wave is converted to an idler wave with a linear frequency shift in time (i.e., a quadratic phase in time) [21,22]. I understand this to mean that the passage of time in observed space can be slowed down relative to an observer, rather as happens when observing a body falling into a black hole.
TeMPOraL 15y ago
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/ http://www.technologyreview.com/blog/arxiv/23519/ - illusion cloak - http://arxivblog.com/?p=698 http://arxivblog.com/?p=698 - cloaking at a distance
TeMPOraL 15y ago
http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.2062v1.pdf http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.2062v1.pdf - link to the original paper.
redthrowaway 15y ago
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 15y ago
  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.
  - RyanMcGreal 15y ago
    Related: http://www.useit.com/alertbox/20021209.html http://www.useit.com/alertbox/20021209.html
  - TeMPOraL 15y ago
    Our imagination expands as our possibilities become greater. Also, there is the 3rd Clarke's law, "Any sufficiently advanced technology is indistinguishable from magic". Sci-fi can easily get into the realm of fantasy (I've already seen a scientifically explained napalm-breathing dragons in 21st century Earth on TV) and vice versa (I've read a story about designing and building spaceships by stacking many layers of different magic onto a wooden ark). The really interesting thing that sci-fi can give us is this: assume that in described world, a selected type of "magic" is possible (handwaving it into a scientificly-sound concept for the sake of the reading experience) and extrapolate the consequences. What can be done with it, and - more important - how will people behave, how will it transform the society. Orson Scott Card did something like this with the Internet in "Ender's Game".
robinduckett 15y ago
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 15y ago
  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 15y ago
    This is actually a spatiotemporal cloak, not purely temporal. The probe is simply the laser (the green lines in the article picture).
- ignifero 15y ago
  no need for a box. You put a camera after the second lens, and, if "things happen" between the lenses, the camera will fail to record what happens while the cloak is on. Not because the light has moved around the events, but because it has been split in two parts, a fast-moving and a slow-moving, leaving a short gap in time in which neither the fast or slow parts can interact with the events. probable application: Magicians can make their tricks completely undetectable using a cloak while they do them (assuming they can do them in sub-microsecond time).
DanielBMarkham 15y ago
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 http://en.wikipedia.org/wiki/Schr%C3%B6dingers_cat
- retube 15y ago
  Schrodinger's cat is a flawed thought experiment. The cat is not in a super-position of live-dead just because the decay (or absence of a decay) hasn't been observed by a human. Observation just means "interaction". If one particle interacts with another, it has been "observed".
  - ced 15y ago
    Schrodinger's cat is a flawed thought experiment. Observation just means "interaction" The way I learned it, Bohr would say "the atom is in a superposition of states until it is observed". Schrödinger used the cat thought experiment to show the absurdity of Bohr's position: "... and then, when I look at the cat, it is forced to take a stand, poof it goes 'alive', or 'dead'" As far as I know, we still don't understand what, exactly, constitutes an "observation". Quoth Bell (the guy from Bell's experiment): ... current interest [in questions of foundations of quantum mechanics] is small. The typical physicist feels that they have long been answered, and that he will fully understand just how if he ever can spare twenty minutes to think about it. http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collected-philosophy/dp/0521368693 http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collec... Jaynes is also worth reading, in spite of his non-mainstream position: http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz
jamesrom 15y ago
Old. Shane Carruth showed me this back in 2004.
machrider 15y ago
Is this similar to the idea of the light cone? http://en.wikipedia.org/wiki/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 15y ago
  Not really, it's not a relativistic phenomenon.
ignifero 15y ago
There's a better article in the guardian http://www.guardian.co.uk/science/blog/2011/jul/13/harry-potter-invisibility-cloak http://www.guardian.co.uk/science/blog/2011/jul/13/harry-pot... . 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.
drieddust 15y ago
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.
sunpin 15y ago
It's a nice way to put people in prison.

143 points by NonEUCitizen 15y ago

_ikke_ 15y ago

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 15y ago
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.
- ph0rque 15y ago
  So basically, time cloaking enables the possibility of Cuil[0] realities over 2. [0] http://cuiltheory.wikidot.com/what-is-cuil-theory http://cuiltheory.wikidot.com/what-is-cuil-theory
- Miky 15y ago
  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.
dennyabraham 15y ago
the abstract is clearer http://arxiv.org/abs/1107.2062 http://arxiv.org/abs/1107.2062. here's the relevant bit: Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking was proposed in which the dispersion of the material is manipulated in time to produce a "time hole" in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating and slowing down the front and rear parts, respectively, of the probe beam to create a well controlled temporal gap in which the event occurs so the probe beam is not modified in any way by the event.
chalst 15y ago
I found the MIT Tech Review's summary confusing. I didn't understand the article it was based on fully, but the idea seems to be covered in the following paragraph: Time-space duality represents the analogy between diffraction and dispersion that arises from the mathematical equivalence between the equations describing the diffraction of a beam of light and the one-dimensional temporal propagation of a pulse through a dispersive medium [17,18]. Similar to a spatial lens that imparts a quadratic phase in space, a time-lens can be implemented that produces a quadratic phase shift in time [19{21]. This time-lens can, for example, magnify [22] or compress [23] signals in time and has an equivalent of the lens law. Time-lenses can be created with an electro-optic modulator [18] or via a parametric nonlinear optical process such as four-wave mixing (FWM) with a chirped pump wave [19,20]. In the latter case the signal wave is converted to an idler wave with a linear frequency shift in time (i.e., a quadratic phase in time) [21,22]. I understand this to mean that the passage of time in observed space can be slowed down relative to an observer, rather as happens when observing a body falling into a black hole.

TeMPOraL 15y ago

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/ http://www.technologyreview.com/blog/arxiv/23519/ - illusion cloak - http://arxivblog.com/?p=698 http://arxivblog.com/?p=698 - cloaking at a distance

TeMPOraL 15y ago

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

redthrowaway 15y ago

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 15y ago
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.
- RyanMcGreal 15y ago
  Related: http://www.useit.com/alertbox/20021209.html http://www.useit.com/alertbox/20021209.html
- TeMPOraL 15y ago
  Our imagination expands as our possibilities become greater. Also, there is the 3rd Clarke's law, "Any sufficiently advanced technology is indistinguishable from magic". Sci-fi can easily get into the realm of fantasy (I've already seen a scientifically explained napalm-breathing dragons in 21st century Earth on TV) and vice versa (I've read a story about designing and building spaceships by stacking many layers of different magic onto a wooden ark). The really interesting thing that sci-fi can give us is this: assume that in described world, a selected type of "magic" is possible (handwaving it into a scientificly-sound concept for the sake of the reading experience) and extrapolate the consequences. What can be done with it, and - more important - how will people behave, how will it transform the society. Orson Scott Card did something like this with the Internet in "Ender's Game".

robinduckett 15y ago

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 15y ago
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 15y ago
  This is actually a spatiotemporal cloak, not purely temporal. The probe is simply the laser (the green lines in the article picture).
ignifero 15y ago
no need for a box. You put a camera after the second lens, and, if "things happen" between the lenses, the camera will fail to record what happens while the cloak is on. Not because the light has moved around the events, but because it has been split in two parts, a fast-moving and a slow-moving, leaving a short gap in time in which neither the fast or slow parts can interact with the events. probable application: Magicians can make their tricks completely undetectable using a cloak while they do them (assuming they can do them in sub-microsecond time).

DanielBMarkham 15y ago

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 http://en.wikipedia.org/wiki/Schr%C3%B6dingers_cat

retube 15y ago
Schrodinger's cat is a flawed thought experiment. The cat is not in a super-position of live-dead just because the decay (or absence of a decay) hasn't been observed by a human. Observation just means "interaction". If one particle interacts with another, it has been "observed".
- ced 15y ago
  Schrodinger's cat is a flawed thought experiment. Observation just means "interaction" The way I learned it, Bohr would say "the atom is in a superposition of states until it is observed". Schrödinger used the cat thought experiment to show the absurdity of Bohr's position: "... and then, when I look at the cat, it is forced to take a stand, poof it goes 'alive', or 'dead'" As far as I know, we still don't understand what, exactly, constitutes an "observation". Quoth Bell (the guy from Bell's experiment): ... current interest [in questions of foundations of quantum mechanics] is small. The typical physicist feels that they have long been answered, and that he will fully understand just how if he ever can spare twenty minutes to think about it. http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collected-philosophy/dp/0521368693 http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collec... Jaynes is also worth reading, in spite of his non-mainstream position: http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz

jamesrom 15y ago

Old. Shane Carruth showed me this back in 2004.

machrider 15y ago

Is this similar to the idea of the light cone? http://en.wikipedia.org/wiki/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 15y ago
Not really, it's not a relativistic phenomenon.

ignifero 15y ago

There's a better article in the guardian http://www.guardian.co.uk/science/blog/2011/jul/13/harry-potter-invisibility-cloak http://www.guardian.co.uk/science/blog/2011/jul/13/harry-pot... . 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.

drieddust 15y ago

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.

sunpin 15y ago

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