Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Transparent ceramics made with aluminum

hackaday.com

Post reply on HN
Print view View original

71–80 of 84 posts

Re: Transparent ceramics made with aluminum

#71

Post by mcguire »

didgeoridoo wrote: post #58
saiya-jin wrote: post #41

Earlier quoted context omitted.

that doesn't make sense - if that would be the case, the back-emitted photon would have a random vector, not pertaining the same one as original one (thus preserving the picture beyond the sheet of metal). you are stating somehow the direction of photon is preserved when absorbed by electron - absurd idea even for layman physics (not claiming I know how this works, but this can't be the way)

I barely understand even layman-level physics, but it would seem to me that this “absurd” idea is just a natural implication of the conservation of momentum? edit: to all the downvoters of saiya-jin — let the one who has never defended their incorrect intuitions in physics cast the first downvote!

I've had that same question before.

Re: Transparent ceramics made with aluminum

#73

Post by calibas »

talltimtom wrote: post #24

The deal is that it isn’t aluminium. Seriusly, what’s with the clickbate headline? If you consider everything that contains aluminium atoms in the structure to be actual aluminium, then Saffire is also transparent aluminium. The authors are diliberatly misleading their readers in order to cincrease interest. That’s a shitty thing to do in science even if do have a cool materiale on It’s own merits.

To add to this, the "transparent aluminum" is really aluminum oxynitride crystals.

Re: Transparent ceramics made with aluminum

#74

Post by CompelTechnic »

nerfhammer wrote: post #68
tim333 wrote: post #12

Earlier quoted context omitted.

Roughly light is electromagnetic radiation and puts force on electrons it comes in contact with. If the electrons are fixed in a non conductor they don't move much and so don't absorb the energy. If they can move as in most metals the force accelerates them and they absorb energy from the radiation, stoping of reducing it.

huh, is this why sometimes metal gets unbelievably hot if left in the sun? but that should be true of any opaque material

For a given temperature rise, metals feel hotter than many other materials because they have a high thermal conductivity and enough heat capacity to deliver a lot of heat quickly.

As another though experiment, consider that you dread walking barefoot across cold tile floors but can bear to walk across carpeted floors in the same house. These two materials are at the same temperature.

Also consider aluminum foil you just pulled out of the oven. It's thinness runs contrary to the large thermal capacity of a solid chunk of metal- you can touch it immediately because you are such a large heat sink compared to it that it can't burn you even while it has only just started (rapidly) cooling from 350°F.

Re: Transparent ceramics made with aluminum

#75

Post by Izkata »

delecti wrote: post #61
emaginniss wrote: post #55

Earlier quoted context omitted.

Wouldn't that mean that nobody ever invented it?

No humans maybe. And if humans were in fact the source of Starfleet's knowledge of transparent aluminum then it'd be an instance of a causal loop, of which there are many examples in fiction.

> of which there are many examples in fiction.

Hell, there's several examples just in Star Trek.

Re: Transparent ceramics made with aluminum

#76

Post by nonbel »

jacquesm wrote: post #35
dvh wrote: post #3

Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.

If the film is thin enough metal is transparent. See for instance 50/50 mirrors and gold plated windows. Of course you can now argue that if the photons hit the metal they will not pass through, but that's not how it works: the photons will excite an electron to a higher orbit and it may drop back to a lower orbit on the other side of the film making the metal appear transparent or it may reflect. edit: saiya-jin I c…

This is the only relevant part:

>"In a quantum-mechanical picture, light consists of photons, or packages of optical energy. The photons of the light reflected from a metal (or a dielectric mirror) are identical to the incident ones, apart from the changed propagation direction."

This doesn't explain anything about how it works quantum mechanically.

Re: Transparent ceramics made with aluminum

#78

Post by jacquesm »

nonbel wrote: post #76
jacquesm wrote: post #35

Earlier quoted context omitted.

If the film is thin enough metal is transparent. See for instance 50/50 mirrors and gold plated windows. Of course you can now argue that if the photons hit the metal they will not pass through, but that's not how it works: the photons will excite an electron to a higher orbit and it may drop back to a lower orbit on the other side of the film making the metal appear transparent or it may reflect. edit: saiya-jin I c…

This is the only relevant part: > "In a quantum-mechanical picture, light consists of photons, or packages of optical energy. The photons of the light reflected from a metal (or a dielectric mirror) are identical to the incident ones, apart from the changed propagation direction. " This doesn't explain anything about how it works quantum mechanically.

A minute current is induced which then results in the creation of a new photon identical to the original.

They are identical in terms of their quantum mechanical properties.

Post reply on HN