>https://www.youtube.com/watch?v=8Y kfEft4p-w What is pr

The physical impossibility of blocking light in mid-air with projections.

>>7671648
With a "screen"/tank/etc or without?

With, it's expensive and there's no good way to get occlusion, so it's pretty confusing. Net result: Just not worth it.

Without, same problems as above, except with the additional complication that there's no real way to generate that kind of light field without having light be emitted from points floating in empty space, which limits all your options to "shitty" and "shitty and doesn't work,"

I mean like if you have a box with a cloud of dust, and you send manipulated light at specific wavelengths and intensities so that the waves cancel each other out where the hologram is "hollow" and so that the correct specks of dust get lit with high intensity. Since with a Fourier transform of the original image you can calculate exactly what waves you need to reconstruct the image.

>>7671648
Nothing, holograms are real. If you mean images floating in mid-air, that is not a hologram, please see the definition of hologram.

To get images floating in midair you have to modify the properties of air. This can be done by putting particles that reflect light in it, IE smoke and fog. This has been used to make floating 2d projector screens. 3d is virtually impossible, just try making shapes out of fog.

You can make air glow by getting it really hot, which can be done with a laser. The problem with this is that the laser required to do this can blind you and that getting air hot enough to glow creates air pollution.

Another way to make floating displays is to have actively propelled stuff with lights on them. This has been in low resolution using quadcopters with LEDs. Barring advanced nanotechnology, resolution will stay low

Not much, I think.
Japan expects to have it by 2022.

http://gizmodo.com/5543595/japan-promises-3d-holographic-broadcasts-for-2022-world-cup

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>>7671683
What if you do it like this?

>>7671687
If there is zero oscillation in the electromagnetic field, at all points between the emitter and the light point, how do you expect anything to change at the light point?

>>7671691
You have oscillations at the parts that are glowing

>>7671666
>> only the correct specs of dust get lit
Light does not work that way.

Volumetric displays are a thing though.

>>7671648

It looks to me (a novice) that holograms are real already and pretty much doable, the problem might be scaling it up and making it affordable.

You can even touch and feel some holograms
https://www.youtube.com/watch?v=AoWi10YVmfE

https://www.youtube.com/watch?v=r18Gi8lSkfM

Like if you add up a bunch of waves on one "side" and then on the other "side" you have a different bunch of waves that happen to cancel out the first waves at each point between the emitter and the light point but then at the light point they don't cancel each other out any more because they're different.

>>7671698
It uses a laser that can blind you and it creates air polllution.

>>7671704
>It uses a laser that can blind you
Just by looking at the image being created or by putting your eye on it?
Just don't get too close?

>air pollution
Meh.

>>7671698
Very neat but I agree with >>7671704, generating a plasma doesn't seem optimal.

>>7671687
Won't work. The light will just scatter off of the dust particles getting rid of whatever wave structure you had.

>>7671730
IT'S OVER; OP IS FINISHED AND BANKRUPT

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>>7671734
There is this though: http://www.nature.com/nnano/journal/v10/n3/full/nnano.2014.317.html

You use special nanoparticles that upconvert IR to visible light. In order to go from a higher wavelength from a lower one you have to have an amplitude above a certain value, so to get 3d shapes you focus a laser to different points in space. The researchers also made the particles respond to different pulse lengths to get different colors.

This would even work in air, and probably would not require laser capable of blind you. Of course this would require that the air be filled with toxic/expensive nanoparticles.

>>7671789
This has actually been done, in color, with a big block of glass doped with flourescent dyes.

It's expensive, you have to move the lasers way faster in order to raster a volume instead of a plane, and again, there's no way to get occlusion so it's unambiguously worse than a regular display.