Demonstration of temporal cloaking
I was originally going to call out AP for bad science reporting when I read the initial news about this paper, but it’s the paper’s authors who are being slightly hyperbolic in their statements. You can’t make a ‘time hole’ - you can however fool perceptions and instruments by manipulating the index of refraction which is what the paper is really about: masking events from perception.
When you poke a stick below the surface of a sunny lake, it appears to be slightly bent or to have a jag in it, when in reality you haven’t changed the physical properties of the stick other than getting it wet. The stick is still straight, it just appears bent due to the different index of refraction between water and air.
What’s really happening is that the light traveling to the rods and cones in your eye reflected back by the portion of the stick from beneath the surface is moving slightly slower while beneath the water than the light reflected from the part of the stick above water and traveling only through air. The different speeds of the light create that optical illusion, but what interests scientists are what happens to the light in that thin layer of meniscus where water meets air and the stick appears to magically bend among other things.
What they are exploring here has some application in real world, I can think of a few in fiber optics, movie making, digital imaging, and other things.
Recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking1, 2. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a ‘hole’ in space is created, and the object remains hidden3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking has been proposed in which the dispersion of the material is manipulated in time, producing a ‘time hole’ in the probe beam to hide the occurrence of the event from the observer15. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap—inside which an event occurs—such that the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking in an optical fibre-based system by applying concepts from the space-time duality between diffraction and dispersive broadening16. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on. These results are a significant step towards the development of full spatio-temporal cloaking.
More on this type of research at Cornell here.
The speed of light varies by the media it passes through, but time doesn’t ever stop that I’ve seen demonstrated — so to me the speed of light shouldn’t be the constant, but time should be…