It’s much worse than that, though, because the slow glass is basically a hologram–you can look at it from different angles and it behaves the way a window would. A hologram of a scene contains vastly more data than a 2D image from one angle. Naively stored, it goes with resolution to the fourth power, instead of just squared (a medium-res 2D image has 1000^2 pixels; a hologram needs 1000^4 pixels). Although hologram-specific compression would help, my guess is that you’d need at least 1000x the storage, and more likely 10,000x on up for decent quality.
You can look at it only from one angle – straight on. Any other angle, it appears as a mirror. This would, of course, be equally impossible - you wouldn’t even be able to triangulate bifocal vision properly, and your pupils are probably too big for the allowable angle. And also since the capture angle is so small, the available light at exit is probably too low to be visible, even in a dark room.
Looking at it from a dark room would be like looking at a wall with a very very very narrow slit. In normal light, like an old-fashioned one-way mirror (the one with reflective strips, not the one with the reflective film), but where the transmission slits are almost infinitely narrow.
Since the angle of capture is so narrow, I don’t expect a problem with the slow-glass overheating. On the other hand, if you did pump it with enough light to be visible at exit, yes you would have momentum effects (“mass”) and compression effects (“volume”) which normally can only be demonstrated with very high power lasers.
It looks quite a lot like a mirror straight on, too, R = [(1 - n)/(1 + n)]^2 goes to 1 as n goes to infinity.
Are you sure that transmission falls off faster vs. angle than with lower indices of refraction? I’m too lazy to do the algebra, but I plotted a few curves, and they seem to just get scaled vertically as n changes.
I meant in terms of the story. I was going from memory, but it turns out that the story describes it as being like a hologram as well.
There are various techniques for reducing Fresnel reflection, and I don’t see any reason why believing in a “perfect” anti-reflection coating is less believable than slow glass is in the first place. You want your index of refraction to scale continuously from ~0 (air) to the desired level.
To me the difficulty would be in the fantastic precision you’d need in the manufacture. Suppose we’re talking about 6 year slow glass. Assuming a quarter inch thickness, that’s more than 210,000 hours per inch. A variation of 0.0000001 inches between one spot on the pane and another puts that spot 13 minutes out of phase. A 0.2mm variation, which is given as the tolerance of normal float glass thickness here, would result in over two months difference between two spots that may mere inches apart.
How is this functionally different from watching a video you recorded with a cell phone last year?
For one thing, a cellphone video is not holographic - even if it’s been recorded in stereoscopic 3D, you can’t peer at an angle through the frame and see things that are off to the side a little.
Yeah, it would really have to be a perfect crystal lattice of some sort. Even with fine engineering tolerances, the amorphous nature of glass would make the phase difficult to maintain even if the thickness was uniform.
Another problem with precision is that this isn’t happening in an isolated lab, it’s happening in a house with all kinds of ambient noise. How well is the slow glass going to keep it’s very precisely tuned properties when a train goes by or a workman starts demoing an interior wall?
No one’s mentioned yet that the slow glass of the story is two-way. It was placed in the windows of the house to capture the scenery outside, but the old man spends his days outside of the house, watching his late wife and son who were inside.
I don’t think we should take the word “glass” to literally mean “amorphous pseudocrystal”, here. It’s clearly not very closely related to any material substance we know of-- “glass” probably just means “clear stuff you can make a window out of”, in this context.
Checking back, at first I went half/half that’s okay. Then … oh. Oops. Yeah. So wavelength goes the other way. Frequency goes up, etc. Much better situation as far as resolution.
So, what are the effects of gamma rays on … this substance? Are slow moving, gamma ray frequency photons still gamma rays? Regular gamma rays would do hellacious damage to the material, moving atoms around, etc. But these have visible light energies.
At some point the wavelength gets so short that interactions with the material like photon-absorbtion-re-emission in glass should stop. Traveling longer distances before being absorbed, giving the opposite effect of time delay. Right?
Actually in the context of the stories, it really is just glass, if I recall correctly. It was originally created accidentally, while trying to manufacture ordinary glass for car windshields. It was noticed that a lot of accidents happened in cars with this type of glass, and investigation revealed that drivers were seeing events outside their car some milliseconds after they actually happened.
–Mark
Imagining that the slow glass is really just a huge chunk of flash memory with imaging devices on both sides…
10 years of glass is described as being 1/4 inch thick. Let’s suppose that we want resolution equivalent to a large HDTV, so I’ll assume pixels 0.5 mm on a side. That gives us 1.5 mm[sup]3[/sup] of volume for each pixel.
Since it’s holographic, each pixel actually stores an image that is projected out to its hemisphere view. Since we aren’t going for perfect resolution, I’ll just assume it needs 1000x1000 pixels (at 60 fps).
Modern flash memory has a cell size of perhaps 40x40x40 nm. It’s already stackable, though not quite to the extent of supporting giant slabs of the stuff, but I’ll assume we can get to that point. If each cell can hold 3 bits, our 1.5 mm[sup]3[/sup] pixel chunk should store around 7e13 bits of data.
10 years of video then needs 1.9e10 frames, or 4.5e17 bits uncompressed. So we need 6400x compression, which sounds like a lot, but really isn’t so bad–h.265 does a reasonable job at 2000x compression. And this isn’t taking into account the benefits from adjacent cells. Not to mention that unlike a movie, the average scene doesn’t have much going on most of the time. Nearly static scenes compress very well.
So the technology isn’t totally nuts, at least in a somewhat primitive form. And I’m making pretty conservative assumptions here; there’s no physical reason why storage can’t increase by a factor of 1000x, or even (optimistically) by 1000000x.
The wavelength changes, but the frequency (and hence energy) does not. The light inside the glass might have the same wavelength as ultra-high-energy gamma rays, but it is not gamma rays.
On the other hand, having such ludicrously small wavelengths might present problems of its own. It’s very difficult to make a material which acts optically (reflection, refraction, whatever) on light of a wavelength shorter than the interatomic spacing in the material, and there’s no way this slow glass could have an interatomic spacing that short.