Relativistic Illumination

[Jim Leff]

In RJN’s posting today seeking a grad student assistant, he mentions that one of his research interests is “relativistic illumination”, and I’m not familiar with the term (and Google and Wikipedia offer scant help).

Can anyone fill me in?

[Chris Peterson]

In RJN’s posting today seeking a grad student assistant, he mentions that one of his research interests is “relativistic illumination”, and I’m not familiar with the term (and Google and Wikipedia offer scant help).

Can anyone fill me in?

Just an educated guess... but I'd speculate it has to do with the peculiar way that we see things under relativistic conditions. For instance, the distorted view when we're traveling at relativistic speeds (where light from behind us appears in front), the geometric distortion that is created in external objects, possibly gravitational distortions, as well (such as seeing much of the backside of very dense bodies).

[Jim Leff]

Yeah, makes sense. Certainly fits well with (if not entirely subsumes) the gravitational lensing he also mentioned.

[geckzilla]

When I read that, I thought it meant light echoes. I went ahead and posted a reply to try and get RJN to clarify for us here.

[RJN]

Thanks for the question! By "relativistic illumination fronts" I mean the dividing lines between light and dark areas that move with speeds close to the speed of light. Shadows, laser pointers, and supernovae reflections can all create relativistic illumination fronts. This has been a focus (OK, obsession) of mine in recent years and I now have a few papers published on the topic. For example: 

Nemiroff, Robert J., Superluminal Spot Pair Events in Astronomical Settings: Sweeping Beams, Publications of the Astronomical Society of Australia, Volume 32, id.e001 12 pp. (2015)Link: https://arxiv.org/abs/1412.7581

Nemiroff, Robert J.; Zhong, Qi; Lilleskov, Elias, Lights illuminate surfaces superluminally, Physics Education, Volume 51, Issue 4, pp. 043005 (2016).Link: https://arxiv.org/abs/1506.02643

Nemiroff, Robert J.,Pair Events in Superluminal Optics, Physik, Annalen der Physik, vol. 530, issue 2, p. 1700333 (2018) Link: https://arxiv.org/abs/1705.05873

Last, a graduate student and I have just had a paper accepted to the Astrophysical Journal titled Toward the Detection of Relativistic Image Doubling in Imaging Atmospheric Cerenkov Telescopes, which deals with relevant topics!

What's really cool is that illumination fronts carry no mass and so can actually move faster than light without violating Einstein's special relativity. Relativistic illumination fronts (RIFs)  occur all around us -- and all around astronomy -- but since they happen so fast people don't know to look for them. Shadows are an example of an illumination front (sort of a reverse illumination front) that, when seen, typically move much slower than light. Light echoes from flashes are also an example of RIFs, although many don't realize they are inherently relativistic and so can appear to do counter-intuitive things (like image doubling). 

A cool thing is that RIFs can code important information, which makes them more than oddities -- even potentially valuable tools.  Exactly how valuable is unclear (at least to me) and so a reason for this line of research. 

- RJN

[Jim Leff]

Thanks for the reply, Prof. Nemiroff. I hope at some point there’s a way to make this a bit more accessible to non-astrophysicists. Until then, I don’t understand well enough to even intelligently ask the questions that arise.

The information coding possibility sounds (if I understand correctly, which I probably don’t) absolutely transformative.

Dumb question: is this as basic as noting that, by creating a shadow by blocking a light close enough and moving the block fast enough, the resulting shadow, as it fans out over great distances, can move >light speed? If so, it’s literally child’s play, no?

Hmm, but wait, you don’t need that complexity; the light source itself, eg a laser beam, can similarly create that result if you swing it around fast enough....

[RJN]

Dumb question: is this as basic as noting that, by creating a shadow by blocking a light close enough and moving the block fast enough, the resulting shadow, as it fans out over great distances, can move >light speed? If so, it’s literally child’s play, no?

Hmm, but wait, you don’t need that complexity; the light source itself, eg a laser beam, can similarly create that result if you swing it around fast enough....

Yes, it starts that simple -- child's play. But actually it can become pretty complicated and include effects like image doubling -- effects that are not initially obvious -- beyond child's play.

And yes, swinging a laser beam fast enough will work too. I gave a few lectures on this elsewhere on this Asterisk board. Please see:
http://asterisk.apod.com/viewtopic.php?f=39&t=21004 .

- RJN

[Jim Leff]

Wow, what a treasure trove of ideas. I hope there's more interest here than is indicated by the thin response. This is way more interesting than orbital trajectories and cooling rates!

Maybe you could find a diagram/illustration to publish as an APOD to disseminate this stuff (especially that great lecture) more widely.

[RJN]

Actually, now that you mention it, I am writing a book on some of this. I sure hope I can find a publisher who is as enthusiastic as you!