# Mathematician designs event cloaking device without using metamaterials

(Phys.org) —Miguel A. Lerma a mathematician at Northwestern University has uploaded a paper to the preprint server arXiv, in which he describes the design of an event cloaking device that doesn't require the use of metamaterials. In his design, events are cloaked using mirrors.

An event cloaking device, also known as a time cloak or an that hides time is a mechanism that causes what appears to an observer, to be a lapse in time during which events have occurred but have not been observed. The idea is based on first slowing down light, then speeding it up again. Doing so causes a lag or gap during which events cannot be observed. Researchers have built such devices using that are able to speed up light or slow it down. But those devices have proven to be complicated and expensive. In contrast, in this new method introduced by Lerma, can be manipulated with mirrors by causing it to travel longer or shorter distances before striking an object.

The basic idea involves using multiple mirrors, half of which can be manipulated on-demand to either allow light to pass through or to reflect. The mirrors are arranged in such a way as to first cause light to "slow" by sending it to another mirror instead of directly to an object, which then reflects it to the object. Following that, the light is caused to take a direct route to the source, effectively causing it to speed up again. Doing so creates a "lag" in time, which to an observer would appear as a lapse. If the object were a regular wall clock for example, the observer might see the clock jump from 12:05 to 12:07, if the lag were two minutes. The duration of the lag is dependent on the distance of the mirrors from the , thus lags of minutes, hours or days could be caused by placing mirrors on distant planets or .

Lerma hasn't actually created an event cloaking device, but now that he's discovered a way for doing it cheaply, it's likely others will very soon set to work developing such devices as well as for ways to use it. At this time, it's not really clear if such devices could be used to deceive people, such as jewelry thieves as the device would only cloak objects in a direct line of sight.

More information: A Mirror Based Event Cloaking Device, arXiv:1308.2606 [physics.optics] arxiv.org/abs/1308.2606

Abstract
We propose a way of implementing an event cloaking device without the use of metamaterials. Rather than slowing down and speeding up light, we manipulate an obscurity gap by diverting the light through paths of appropriate length with an arrangement of switchable transreflective mirrors.

via Arxiv Blog

Journal information: arXiv

Feedback to editors

Aug 15, 2013
I wouldn't call this an event cloaking device, I'd call it an illusion. A magic trick. Smoke and mirrors without the smoke. Not really anything I didn't invent when I was 10 years old. no seriously. I'm serious.

Aug 15, 2013
No you didn't - because when you were 10 you didn't know that there were mirrors that could switch that fast.

Aug 15, 2013
My God this is stupid easy.

I thought of shit like this ages ago....I thought this stuff was obvious...

Aug 15, 2013
No you didn't - because when you were 10 you didn't know that there were mirrors that could switch that fast.

antialias, I don't think you understand the theoretical device. It doesn't even require fast mirrors. Only long distances. You could be operating the mirrors by hand, and it would still work you moron. Learn to read.

Aug 15, 2013
You probably thought of a mirror arrangement around an object as a kid, but that is not what this is (Hint: look at the image).

The thing this solves is that just redirecting the signal would mean that at some point you'd get either a gap or double the photons fom the light source - which would be noticeable. The double (more precise: alternate) redirect to compensate for the runtime of light is the trick here.

It doesn't even require fast mirrors.

You need to switch the first set of mirrors PRECICESLY when you switch the second set. No. You can't do this by hand.

No. You didn't think of this as a 10 year old. And even as an adult you didn't understand the article.

you moron

Right back at ya.

Aug 15, 2013
I think he might be pulling your leg.

Aug 15, 2013
You need to switch the first set of mirrors PRECICESLY when you switch the second set. No. You can't do this by hand..

If light takes X minutes to traverse the "short route", it may take X+2 minutes to traverse the "long route" (in the example given in the article). Switching the mirrors fast is not the issue, unless you claim you meant switching mirrors "fast enough" simply to fool the eye, in some sort of actual magic trick or something. But that would be a practical matter involving how skilled the magician is, and has nothing to do with HOW this experiment WORKS. Any 10 year old should be able to understand this thought experiment. I think that "research paper" may actually be a hoax, btw.

Aug 15, 2013
If light takes X minutes to traverse the "short route"

There is no short route in this setup. The length of the route is always the same (when you take the lomng path in the first set you take the short path in the second set of mirrors and vice versa) When you switch from the long way in the first part you have to switch to the short way in the second path. Otherwise you'd get gaps in your observation (e.g. times when no photons arrive at all).

Just found the link to the paper. It describes exactly what I've been saying all along (down to noting the precise timing needed for the mirror switching.)
http://arxiv.org/...2606.pdf

Any 10 year old should be able to understand this thought experiment

Obviously not.
Q.E.D.

Aug 15, 2013
There is no short route in this setup.

Search for the word "transparent" in the paper. Light is taking a shorter path when it passes directly thru, rather than being reflected. duh?

Since we are talking about minutes of light travel, not milliseconds, you could have the mirrors controlled by motors that took a full second to rotate, and every aspect of this experiment would still work. You would only need fast mirrors to conduct this experiment at very short distances.

Aug 15, 2013
I'm not sure the mirrors between the light source and the object is useful. Unless the light source itself is time-dependent and thus contains information, there is no need to delay it, since it always provide the same light.

Aug 16, 2013
I'm not sure the mirrors between the light source and the object is useful.

You need it, because when you switch to the long path after the object then you need the light travelling already in that long path before the object to fill in, what would otherwise be a visible gap of the timelength it takes the light to travel the long path after the object.

If you were to switch the mirrors only to semi transparent you'd register a drop in brightness.
You could, conceivably, alleviate this by playing with the brightness of the light source - but since the temperature/brightness curve of a light source isn't linear that would be noticeable as well.

But the real point is to mask something that is happening at the object for a time. If you don't have those mirrors before the object you can't do that.

Aug 16, 2013
I'm not sure the mirrors between the light source and the object is useful. Unless the light source itself is time-dependent and thus contains information, there is no need to delay it, since it always provide the same light.

If you think about it, this is a classical "ray tracing" scenario where you follow a beam of light as it bounces off an object and onto a camera. Interestingly with the mirrors space-time itself is used to create a sort of 'video buffer' (FIFO frame queue), of fixed time-length. There are two "caches" of image data: 1) ABCD is a "cache", and 2) EFGH, is a "cache". Transparent AD or EH essentially controls whether each cache is active or inactive at any given time.

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