https://physicsworld.com/a/light-is-seen-to-scatter-off-ligh...

Link to paper from 1997: Positron Production in Multiphoton Light-by-Light Scattering

(published in Phys. Rev. Lett., Vol. 79, p. 1626 (1997).) http://www.slac.stanford.edu/exp/e144/ps/positron_slacpub.ps

"Light-by-light scattering is a very rare phenomenon in which two photons – particles of light – interact, producing again a pair of photons."

This is the process that they observe (for the first time) whereas E144 observed the Breit-Wheeler process.

You can argue that this is too narrow a definition of light-by-light scattering but they have at least tried to make it self consistent...

[0]: http://adsabs.harvard.edu/full/1996ApJ...456..124M

Would have been nice if that info was featured somewhere in the article. I don't like to say it but this am I correct in saying that this article gives off the impression that this is an experimental first in terms of directly observing this photonic interaction?

making real Jedi saber

Projecting in the air without a screen could be a potential use.

On the other hand, it's true that a purely text-based medium like a comment doesn't have room for a lot of nuance. So for the sake of clarity, I will say that it was a good question. We should always look for ways to use new discoveries to our advantage. Let's just stick to things which are possible, like Dyson spheres, and leave the impossible for science fiction.

See also https://what-if.xkcd.com/1/.

My favorite part of this is looking at all the toasted skin on the fingertips in the video.

If of photon energy, then the device is clearly impossible -- you would need to use invisible (and harmful) gamma-rays for scattering.

If of energy density, it still may not be theoretically feasible. For instance, you cannot make monochromatic pulses arbitrarily short -- eventually they will become spread in frequency (more and more energy in higher and potentially harmful frequencies), such that the total dosage necessary to get the desired visible flux is too large. (some calculations would need to be made...)

Making them imperceptible, if that is even so important, has some challenges but not impossible (e.g. increasing resolution, lowering weight, or even adding devices to compensate its weight if the former is infeasible).

“Better dead than rouge?” Hm.

But a similar limit happens to protons (the GZK limit at 50 EeV, where protons and CMB photons can make a Delta+). For heavier nuclei, photodisintegration will happen at even higher energies.

https://en.wikipedia.org/wiki/Oh-My-God_particle

The main problem is that photons only can interact with charged particles, but photons have no charge, so the photons don't interact (directly) with photons.

The gluons that are the bosons of the strong force can interact between them, so it's not a problem of bosons vs fermions. In particular, gluons have color that is the equivalent of charge for the strong force.

The idea is that the photons can sometimes create a virtual electron-positron pair that is very short lived [1], and the other photon can colide with the electron or positron before they annihilate. This is very rare, and you can ignore it unless you have a really huge amount of photons flying around.

[1] Insert here a technical remark about "virtual" and "very short lived". It's more complicated. Take this as a metaphor to hide a lot of math.

Could anyone point me to some good starting material? Thanks :)

In which frame of reference?

Which frame of reference the resulting particles might "inherit", well, that's a very interesting question that I've never thought about!