Actually it doesn't, which is the really cool thing about these cloaks. The cloaks are made of a metamaterial for which the refractive index is less than 1, so light travels faster than c in that medium. That's what makes them tricky (but not impossible) to build! The reduced refractive index with respect to the surrounds exactly makes up for the extra distance travelled. It's neat stuff.

How would it show movement? AFAIK the cloak should be able to move around and this movement shouldn't be visible to you.

Or do you mean they won't be able to make a flexible cloaking ninja suit that keeps cloaking the ninja as they walk, despite the suit bending? The solution to that, of course, is to roll around inside a giant hamster ball/zorb cloaking device! Watch out... i'll sneak up on you and ROLL YOU TO DEATH.

Yep, and even if you got a broadband cloak that worked at all those frequencies, you could still pick it up by a number of ways not mentioned in TFA. You could pick it up with sonar (I guess in principle it could also be an acoustic cloak to beat that too), but you could also change the refractive index of the room. The cloak is designed so that no matter what's in the cloaked region, it appears to have a refractive index of 1 (or whatever the cloak's surrounds are supposed to be). If you change the refractive index of the surrounds slightly (change temperature, spray an aerosol, fill the room with water (!)) then the cloak should be relatively easy to spot.

The other downside of these cloaks, of course, is that you can't see out of them since no light interacts with your eyes.

Yes! It got fixed in Jaunty a month or two ago - and it looked like they were sitting on the bugfix for about a month. Pretty unprofessional stuff, since many people's computers were rendered unusable, but now it's fixed and Karmic sings on my EEE. It does tell me that my battery's broken and that the SMART status of my SSD indicates that it's on its way out, but let's not shoot the messenger.

Which is exactly what the Commonwealth Bank of Australia does.

Whenever you try to do anything 'serious', e.g. transfer money to someone new, change your details etc, you have to enter a code they'll send you by SMS. This SMS will briefly say what you're trying to do, e.g. a part of the account number you're sending money to. It's fast and doesn't get in your way unless you're doing something potentially dangerous

The libs and greens are voting against the filter, so yes the dentist-filter plan is dead in the water. But I wouldn't be surprised if the libs supported this copyright bill, which would be more than enough to get it through.

I never thought I'd say this, but I think I preferred Richard Alston, who had the international reputation of "Worlds Biggest Luddite", as IT minister. At least he was too incompetent to do much damage.

Oops, I neglected to mention the 'shrink' part. It's a lot easier to shrink (and warp) a submarine than make it disappear entirely. Proper cloaks have a singularity on the inner surface of the cloak, as the entire inner surface has to seem like a single point. If you build the outer part of the cloaking device properly, but just give up when you get to a certain radius, then your cloaking device more or less makes the cloaked region appear much smaller than it really is, e.g. turning your submarine-sized object into a shark-sized object. Tweak the cloak a bit and you can shape the visible object like a shark.

This kind of cloak should even be possible to build without resonant structures, since it doesn't need the presence of a medium in which the speed of sound is infinite (the singularity), it just needs a medium in which the speed of sound is greater than in water.

Actually it's the other way around - because this uses resonant cavities, it only works on a very small range of frequencies. But the 'super' thing about a superlens is that it can focus sound/light to a region smaller than any other kind of lens, 'beating the diffraction limit'.

Nup, time of flight will be exactly the same. If this is like the optics ones, then this cloak is designed so that sound is indeed bent around the object, and it's made out of a fancy resonant metamaterial that's cleverly designed so that sound travels faster through it than through the surrounding water.

You could intentionally let a little bit of light/sound in and out at your favourite frequency. Or you could choose not to be entirely invisible, designing the cloaking device to warp your submarine into, say, the shape of a shark. All the sound that would have hit the shark will be spread across your submarine's surface (or if you design the cloak REALLY cleverly it could be focussed on your receiver). So with this kind of cloak, the enemy COULD see your submarine and receiver, but it would just be disguised like a shark. Since they can see you, you can see them. And you know your cloak's design, so you can use clever computer stuff to unwarp the pictures you get of the outside world.