4D Invisibility Cloak Bends Time as Well as Space

By Andrew Moseman | November 16, 2010 2:34 pm

Invisible ManFirst came the formulation of an invisibility cloak that could bend light around an object. Then, this spring, German scientists took that idea and made it three-dimensional. Is the invisibility cloak now ready to go 4D? For a study in the Journal of Optics, British researcher Martin McCall’s team adds the dimension of time to the invisibility cloak idea, creating a theoretical “space-time cloak.”

The key feature of the proposed space–time cloak is that its refractive index — the optical property that governs the speed of light within a material — is continually changed, pulling light rays apart in time. When the leading edge of a light wave hits the cloak, the material is manipulated to speed up the light, but when the trailing edge hits, the light is slowed down and delayed. “Between these two parts of the light, there will be a temporal void — a space in which there will be no illuminating light for a brief period of time,” explains McCall. [Nature]

Taking advantage of these differences, he says, it is theoretically possible to imagine a cloak that allows you—at least from my point of view—to transport instantaneously across space.

“By manipulating the way the light illuminating an event reaches the viewer, it is possible to hide the passage of time,” said [McCall]. “Not only can specific events be obscured, but it is possible for me to be watching you, and for you to suddenly disappear and reappear in a different location.” [AFP]

Like previous invisibility research, McCall’s relies on metamaterials: materials specifically designed to control electromagnetic waves (see a more in-depth description here). Unfortunately for people longing to disappear, he says, those materials today are efficient enough for only a nanoscale demonstration.

“Light travels at 100 million meters per second and in order to cloak it you’d need that many meters (of metamaterial), roughly speaking,” he said. But McCall said current optical-fibre technology could be used to construct a “poor man’s cloak” capable of demonstrating “proof of concept” by imperfectly hiding events taking place over a few nanoseconds. [CNN]

So McCall’s space-time cloaking requires some major breakthroughs to take it to the sci-fi kind of invisibility. But, that’s not his problem:

“We’ve provided a theoretical recipe and suggested how the experiment can be done. We believe the proof of principle experiment is available with current technology that experimentalist groups could achieve. It’s up to the experimentalists to rise to the challenge,” he said. [CNN]

Related Content:
DISCOVER: How to Build an Invisibility Cloak
DISCOVER: Invisibility Becomes More Than Just a Fantasy
80beats: The 3D Invisibity Cloak: It’s Real, But It’s Really Tiny
80beats: New Version of Invisibility Moves Closer to Visual Cloaking
80beats: Light-Bending Scientists Take a Step Closer to Invisibility

Image: iStockphoto

CATEGORIZED UNDER: Physics & Math, Technology
  • http://fantasyva.com Mitch

    Maybe they could just make a pocket for the cloak so you can store your stash in a pocket dimension…..

  • Torbjörn Larsson, OM

    So? They didn’t do anything that isn’t done on the nearest flash strobe disco.

    (Kidding. They may even have made a new type of “event horizon” black hole analog right after the first one reported some months ago – it temporarily soaks up (part of) illuminated light AFAIU.

    This may even be “the real deal” analog if it is using group velocity instead of phase velocity manipulation as the first construction.]

  • rabidmob

    Not sure if I really understand the implications.

    Changing the refractive index so that the light travels faster through the material than a vacuum or our atmosphere seems intrinsic to making a good invisibility cloak.

    However with an invisibility cloak isn’t it the point to disappear and reappear in another location, or just not appear at all?

    That said, having an item with an negative refractive index is quite amazing in and of itself.

  • krak

    I’m no physicist by any means, but how is this any different than a strobe effect?

    We seem to be talking about warping perspective, not time, or else don’t you run into a paradox in the space of a few meters?

    Take the thought experiment given, and imagine a cloak that would allow a person to “instaneously” move 10 meters according to observers w/ a stopwatch.

    Now change the cloak to a 3/4 cloak… so that directly behind the cloaked person, observers would have a continuous view of the subject and there would be no instantaneous travel.

    Are their clocks now 10 seconds ahead of those belonging to the observers who witnessed teleportation?

  • anthony

    i think the problem with the 4d theory is the fact that velocity was left out of the equation.

    your changing YOUR perception by watching someone dissappear and re-appear in another location.

    but that persons reality would be the sameas yours because they are not moving at higher velocities.

    their time passes the same as yours.

    the only way 4d can be manipulated would be for you to somehow reduce the distance the cloaked person had to travel, OR their velocity.

  • anthony

    if you really wanna mess with light… find a way to increase someones mass to something like… i dunno… 3000 solar masses. then reduce its size to about that of a pins head.

    im sure something will happen then. haha.

  • mikey

    GEE … I thought light traveled at exactly 299,792,458 metres per second (at least in empty space anyway – and the atmosphere only slows it by a very small fraction.) Why would this guy state 100 million meters per second? Even in water the speed of light is higher than that! What universe is he in?

  • Adam

    mikey some materials can significantly slow down the speed of light.

  • Jumblepudding

    I wish I wasn’t married yet so I could make my wife a wedding dress out of this stuff. Then I could peer beyond the VEIL OF TIME. (cue cheesy progressive rock music)

  • Brian Too

    This is so weird I still can’t wrap my head around it.

    If there was a temporal gap in the image, wouldn’t it appear that way to the viewer? As a gap?

    I’m thinking they wouldn’t see a person or an object jumping, because the image is combined foreground and background. I’m guessing the viewer would see the whole image ‘jump’, just like when an old-fashioned film reel had a small section cut out and spliced back together. Either that, or the whole image goes completely dark for a moment (the duration of the temporal gap), then reappears in the new configuration.

    But I have to admit, I’m mostly just guessing here. Also, I’m extrapolating from the OP’s demonstration image of the outline of a person jumping in the air.

  • http://Facebook Glenn D. Parham

    This physics has been around for some time now. It’s a cloak alright….a collection of mirrors and the cloak is very heavy. And as for as bending light, most likely so. Any time light slows down and then speeds back up, it effects time. Even total reflection bends time, but what good is it. All of this is a play on words to empress investors. I have seen this cloak. And it is no more than a shaggy coat of mirrors. And they have never been able to achieve total invisibility only a shadowy effect. Their success is no more than reflection . It takes more than mirrors to slow down time, like a black hole.

  • Decio

    Well in the end of the day, mirrors and bending light can slow down time, because time is a measurement of ligh travelling, so thus bending/slowing down light would be slowing down time. If there was no light there would be no time. So the idea that you could obsucre yourself from light essentually means time would not effect you. I think, but then again i’m not good at physics :)

  • Jason

    Indeed, I do not quite understand how this is effecting time itself. It appears you are simply preventing light from reaching a given object thus it appears never to exist, but just because you can not see it does not mean it is not there in that given time frame. Anyone elaborate on this to help me understand? Why does light effect time?

  • Jason

    Actually after re reading it, is what they are proposing to do, akin to someone standing in a room, someone turns off the light, said person then moves, light is turned on, person appears to have changed position instantaneously to the viewer. If this is the case you still are not manipulating time, you are altering the “refresh rate” if you will of our perception of the objects in the world around us?

    Edit: On even further thinking – the slight difference between my thought experiment above and the concept discussed in the article is that the cloak would be the thing that was going dark (not the room – they are effectively selectively turning off the light on specific objects), so the observer would just see them disappear instead of standing in darkness while this happened and the cloak wearer would in fact be the one in complete darkness – I hope they know their way around the room!
    But this still doesn’t allow me to explain any time bending… I can only seem to grasp the 3D nature of this – Thoughts? If you do have an answer let me know: @jason_mayes

  • Stuart

    Who needs this when we already have Fox News?

  • brannigan’slaw

    if the light is slowed so that it reaches you only when the person has already moved, they have appeared to move instantaneously.

  • Jo Dean

    Thats kinda crazy dude.


  • dg

    A better solution for stealth is an SEP (somebody else’s problem) field. An SEP is something we can’t see, or don’t see, or our brain doesn’t let us see, because we think that it’s somebody else’s problem…. The brain just edits it out, it’s like a blind spot. If you look at it directly you won’t see it unless you know precisely what it is. Your only hope is to catch it by surprise out of the corner of your eye.

    The technology involved in making something properly invisible is so mind-bogglingly complex that 999,999,999 times out of a billion it’s simpler just to take the thing away and hide it……. The “Somebody Else’s Problem field” is much simpler, more effective, and “can be run for over a hundred years on a 9Volt battery.”

    This is because it relies on people’s natural predisposition not to see anything they don’t want to, weren’t expecting, or can’t explain.

  • sandeep

    “it is possible for me to be watching you, and for you to suddenly disappear and reappear in a different location”

    This happens in computer games.Lag. Also doesn’t mean the actual object that you see has moved. Only looks like it moved.

  • makelle

    “Not only can specific events be obscured, but it is possible for me to be watching you, and for you to suddenly disappear and reappear in a different location.”

    Hey, I used to have this capability in school, however they insisted on calling it truancy; go figure!

  • makelle

    Sometimes when looking for an object the object seem hide itself, since if somebody else points out to me the position of the object it can be found exactly where I’ve been looking all the time. So, consequently some time soon, when searching for a lost item I’m going to close my eyes, reach out and just grab it. Imagine the time saved !

    A veces, cuando buscando un objeto el objeto parecen ocultar sí, ya que si alguien señala a mí la posición del objeto que se pueden encontrar exactamente donde he estado buscando todo el tiempo. Así, por lo tanto algún tiempo antes, cuando se busca un perdido tema voy a cerrar los ojos, llegar y sólo robársela. Imaginar el tiempo ahorrado !

  • JadeWolf

    This invention is nothing new, we’ve had a 4d cloak that changes time and space for ages – it’s the spin we refer to as history

  • lazyhound

    Ever seen one of those school group photos with the whole school spread out over 50 yards in front of the camera in several tiered rows? Look carefully and you’ll probably see a kid (almost always a boy for some reason) who is simultaneously at both ends of a row. It’s called bilocation, and some of the Christian saints were supposed to be able to do it – allegedly.

  • Snortual

    what sort of shadow would such a cloaked figure cast…collateral disturbance to viewed field wouldn’t be cloaked would it…

  • tim

    Isn’t this a stasis cloak? like the stasis fields in golden age Sci-fi used instead of hibernation for deep space trips?

  • http://www.electric-cigarette.biz electric cigarette reviews

    really valuable stuff, all in all I imagine this is worthy of a book mark, thanks

  • Samaffu

    Go into a new dimension, like say 4th dimension and you will be invisible. Since you are bounded in a 3D space, you cannot see the higher dimensions. And come back into the 3D, then you have made a teleportation. Simple, isn’t that?

  • http://mode=viewprofile&u=11437&sid=286ae137c03a75b34fdf5d71c9dbd99c Bruno Ganfield

    This is probably one of the best mentions of this subject I’ve seen within quite a while. It is apparent that the knowledge of the topic is actually heavy and this made for an extremely fascinating read.

  • http://www.pradaoutletbags.com Prada Outlet

    What you stated made a large amount of sense. But, think about this, imagine if you added somewhat articles? I mean, We dont want to tell you how you can run your website, yet what if a person extra something to be able to maybe get individuals interest? Just just like a movie or perhaps a image or even two to have people looking forward to exactly what you have to express. In my opinion, it might you could make your blog turn on a bit.

  • http://www.atimerncans.wordpress.com Raman

    I wish to discuss more on this topic. All the people here seem to have very easily migrated the idea which has been developed for a few picoseconds (or so) into a full human cloaking technique.

    Secondly, i fail to understand how disappearing from one location and appearing at another is anything but teleportation, and not limited to 3D. Where did the 4th dimension come in here.

    Also, personally, i have no idea on how time is related to light. I would be really appreciative of anyone who could enlighten me on this topic a little. Please find me on twitter as raman_alpha.


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