Holograms are a staple in science fiction, but creating ones detailed enough to have serious applications in the real world has proved
difficult. While scientists have been slowly pushing the field of holographic projection forward, they haven't been able to overcome a problem called cross-talk. However, in
a recent paper published in
Nature, they have been able to manipulate the shape of light to overcome this, thus allowing them to produce 3D holograms that are orders of magnitude clearer, larger, and more detailed.What Are Holograms?

© Photo by DrBob at the English language Wikipedia / CC BY-SA 3.0
Simple holograms are 2D surfaces that produce the illusion of a 3D object when light is shined through it.
These are created by splitting a laser into two beams, bouncing one off an object, bouncing the other off a mirror, and recombining them on a specialized photographic plate.
Lasers are coherent light, meaning they're composed of one specific frequency, in that all light waves are moving in unison. When two coherent light waves are combined, a process known as interference, an orderly and predictable pattern is produced. The peaks amplify other peaks, the troughs amplify other troughs, and peaks and troughs cancel each other out, thus producing alternating bands of light and dark.
However, when the light is reflected off of an object, it's no longer coherent, and when it's recombined with the coherent light of the laser beam, an interference pattern is created that is specific to the object.
The photographic plate is placed exactly where the light is recombined, thus capturing the unique interference pattern, which holds all the information needed to reproduce a 3D image of the object, including the depth cues of perspective and parallax (the difference in the apparent position of an object viewed along two different lines of sight). To reproduce the image of the object, the reference beam needs to be shined through the back of the plate, thus hitting the interference pattern and producing the object beam, as if it has just come off the object.
Put another way, (the reference beam) + (the object beam) = (the interference pattern on the plate), and shining the reference beam in from the other direction is like rearranging this equation so that (the interference pattern on the plate) - (the reference beam) = (the object beam), making the image appear.
Comment: The following video from BraveTheWorld does a good (partial) summary of a some of the science on the differences between male and female brains:
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