Snowflake Engineering, Quantum Mirages and Matter-Replicators

One of the most impressive things about snowflakes is that we still don't really understand how they work.

We understand how conventional crystals grow – normal crystals assemble into large, faceted, regular-looking forms because the flat facets attract new atoms more weakly than the rougher, "uncompleted" parts of the structure, which provide more friendly neighbours for a new atom to bond with. So if you have an "incomplete" conventional crystal, it'll preferentially attract atoms to the sites needed to fill in the gaps, to produce a nice large-faceted shape that tries to maximise the size of its facets, as far as it can bearing in mind the original random initial distribution of seed crystals.

But snowflakes do something different. Their range of forms makes their growth appears pretty chaotic, but they also manage to be deeply symmetrical. It'd seem that the point of greatest attraction on a region of snowflake doesn't just depend on the atoms that are nearby, but also on the arrangement of atoms on a completely different part of the crystal, which might be some way away, and facing in a different direction, on a different spur. The sixfold symmetry of a snowflake suggests that when you add an atom to the point of one of the six spurs, the other five points become more attractive ... add an atom to the side of a spur, and we're dealing with twelve separate sites (twenty-four if the atom is off the plane). Add an atom to a side-branch, and a copy of the electrical-field image of that single atom is transmitted and reflected and multiplied and refocused at potentially tens of corresponding sites on the crystal surface. And that's for every atom in the crystal.

This would be beyond fibre-optics, and beyond conventional holography. It'd be multi-focus holography, and the holographically-controlled assembly of matter at atomic scales to match a source pattern – making multiple copies without destroying the original. It'd be using holographic projection to assemble multiple macroscopic structures that are atom-perfect copies of an original. And that idea should make the hairs on the back of your neck start to stand up.

The closest thing I've seen in print to this is the quantum mirage effect described in Nature, 3 Feb 2000. Researchers assembled an elliptical quantum corral of atoms on a substrate, and placed another atom at one of the ellipse's two focal points. They then examined the second focal point, and found that the atom's external field properties seemed to be projected and refocused at the second point, to give a partial "ghost" of the source atom [*][*][*]. You could interact with the ghost even though it wasn't there. Presumably your actions on the "ghost particle" copy would be transmitted back to the source, which'd be recreating the ghost behaviour by a process of electrical ventriloquism, using the elliptical reflecting wall to "throw" its voice to the ghost location.

Something similar may be happening in a perfectly-symmetrical monocrystalline snowflake as it grows. Maybe the crystal's regular structure just happens to not just split the image of the atom into multiples, but refocus them with phase coherence at all the key symmetry points. Maybe we could try adding a few metal atoms to one part of a snowflake crystal and seeing if matching atoms are preferentially attracted to the other corresponding sites.

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A possible clue is the phenomenon of triangular-symmetry snowflakes.
It's been suggested that these form in nature when an asymmetrical snowflake falls corner-first, with the airflow disrupting regular hexagonal crystal formation (see also Wired). But since the remaining triangular symmetry is still so strong, this hints that perhaps the strongest linkage between crystal sites is in triples, with a secondary slightly weaker triplet attraction producing the hex.

Okay, so I suppose there might be problems in attempting to use giant snowflake crystals as matter-photocopiers ... for snowflake formation, every copied pattern forms an extension of the crystal, if you use the crystal to try to copy other things, then the "irregular" matter being copied is liable to disrupt of the focusing. You might only be able to copy layers an atom or two thick (at least, to start with).

But a giant atom-perfect monocrystalline snowflake would be an awfully fun thing to play with if you had a chip-fabrication lab with goodies like force-sensing tunnelling microscopes.

And to me, that was the one thing that could have justified building the International Space Station. The ability to build a giant, heavy-duty zero-gravity snowflake, hopefully one big and chunky enough to withstand eventually being brought back to Earth immersed in liquid helium for further study (what does Bose-Einstein condensate do when it's in in contact with a hex crystal?). That had to be worth a few billion in research money, and would have given the public something pretty to look at when it came time to tell them what the money had bought. We haven't done it yet, but maybe ...

Holograms at Halloween

I don't suppose that there's any reason why holograms have to be created on a flat sheet.
It's traditional to do it that way, and it probably makes the optics easier, but there doesn't seem to be an especial reason why all of the sheet has to be at the same angle. If you created a hologram on a curved sheet that surrounded an object, then as long as the sheet kept the same shape, it should presumably look as if the object is inside the volume (rather than appearing to be in front of or behind a flat "window"). There's also no obvious reason why you can't produce cheap printed lenticular holograms on curved sheets either, other than that it'd make the initial processing more difficult.

So, Halloween. Once we're set up for manufacturing curved holograms, the obvious application (at this time of year) is the creation of the world's most scary Halloween masks.

Put a hologram of a human skull onto a curved transparent sheet, use the sheet as a visor, fitted inside the cowl of a black cloak, and make the inside smoked or semi-mirrored, and you have a "Death" Halloween costume, where, if anyone gets too close and peers under the cowl though the sheet to try to see who's face is behind the visor, they get a rather nasty shock!

Okay, on reflection, maybe not such a great idea after all. :(
You don't want people dropping dead of heart attacks when they realise that "the death guy" appears to be wandering about with what seems to be a real, genuine, gaping skull on the top of his neck. I mean, realism is all very well, but to be striding around town leaving a trail of traffic accidents and screaming people and dead bodies in your wake would probably be taking authenticity a bit too far. Oh well.

Holographic Diamonds

Back in January 2000, the Millennium Dome exhibition opened to what was supposed to be a display of the best of British achievement. Unfortunately the people in charge of setting it up didn't seem to have a clue how to run this sort of exhibition or what to put inside the dome, and it ended up as a bit of a national embarrassment.

One of the last-minute additions to the show was the Millennium Star diamond.

To see the diamond, you had to walk though an angled passageway that was completely pitch black apart from some slightly odd (monochromatic?) blue light, and there, in the middle, you'd see a case walled with bulletproof glass, containing the blue-lit diamond. You walk past it, perhaps pause, and then make your way out. No loitering, no photography.

Something struck me when I was in there. The thickness of the cabinet's glass meant that the diamond appeared be in different places, depending on which pane you viewed it through - that's completely normal, you usually see a similar effect with fishtanks. But the blue light confused me, because normally you only see blue-lit rooms when someone's trying to hide something. Okay, so it was a blue diamond, but still ...
The human eye is pretty bad at seeing sharp details in blue light, which is why Windows has traditionally had a blue-themed startup screen - the old splash screen used crude dithering to recreate the effect of a smooth variation in tone using the default 16-colour VGA pallette, and by doing this in blue, the eye was fooled into not noticing the effect too much. If Windows 3.1 had tried that trick in red or green or yellow, the result would have been bitty and grainy and would have looked awful. In blue, you can't see the fine detail that gives the trick away.

Now, the glass.
Bulletproof glass uses a "sandwich" of alternating toughened glass and shock-absorbing plastic sheets, so that even if you shatter every layer of glass, the shatter-patterns are different, and the pieces stay stuck together by the plastic. If someone had simply added an additional sheet of plastic film with a with a hologram of a diamond ... then how would you be able to tell? You couldn't look for alignment errors between the sheets on different panes, because the diamond woudl appear at differtent positions when viewed through the different panes anyway, due the the thickness of the glass.
Does a holographic diamond appear to refract light in the same way as a real diamond? I don't know, but if someone wanted to look for an "anomalous" spectrum effect that didn't correspond to real diamond, the use of monochromatic blue light might be a good way to stop them. And with single-colour light source, we'd also find it difficult to see any interference fringes due to misregistration of the holographic films. Optical theory says that to see those coloured fringes, the colours already have to be present in the original lightsource, andf in our "blue room", that light wouldn't be there.

Of course, for all this to work, de Beers would have to have their own in-house holography R&D department aligned with their security people, which sounds pretty unlikely. But in fact, deBeers do have very strong links to holographic reseach: They have laser systems for checking diamonds, and for laser-etching holographic security marks onto them, and slightly more peripherally, Lucent have been researching diamond as a potential holographic storage medium. DeBeers also have a holographic diamond passport scheme. So diamonds and security and holography research and lasers and de Beers all have a pretty strong overlap. There probably aren't that many companies that know more about certain sorts of holography than de Beers do.


So here's a fun, harmless little conspiracy theory to ponder that's worthy of Sherlock Holmes or Jonathan Creek: What if this diamond, which thieves tried to steal from the Dome in November 2000 in a ram-raid using a mechanical digger, nailguns and a getaway speedboat, was protected by the ultimate "stage magic-based" security system? What if the diamond, that perhaps many thousands of people would swear on oath to having seen in person ...
... was never actually there?