[rif]

It's projecting onto a white screen, and you can't project "dark".

It's just been bugging me, like getting a song stuck in your head.

[Bob in St. Louis]

Not long ago, we friended some aliens that gave us dark matter they extracted from a black hole. 
At least, that's what I read on the internet once.

[rif]

Not long ago, we friended some aliens that gave us dark matter they extracted from a black hole. 
At least, that's what I read on the internet once.

I would have guessed dark energy, but if you read it on the information superhighway,  it must be true.

[Bob in St. Louis]

Black hole > Dark matter > Dark energy
I think they mine it using drained car batteries. The energy is attracted to the low state of charge and thereby captured. 

[rif]

But seriously, how does a projector show black on a white screen?

Anybody?

[Bob2]

This from How projectors work:
Black is “projected" by NOT projecting any light, mostly. The black you perceive on the darken screen surface is from the partial absence of illumination by the projector. In optical projectors the light from the projector's lamp is blocked by dark opaqueness of the film.

[rif]

I don't know ... "film"?  And that explanation requires a trick that the mind does when viewing an image.

How would it project white text on a black background, like a chalkboard?  Or black text on a white background like a piece of paper?

[rif]

No one?

[S Clark]

It's kind of an optical illusion.    https://www.wtamu.edu/~cbaird/sq/2015/06/16/how-do-projectors-project-the-color-black/