Quantum theory was first postulated early in Earth's space programme. The rudimentary theory held that electrons were actually waves of energy that lept from level to level ('orbitals', as they were called, although this is misleading as they didn't truly orbit anything) of distance from the nucleus, each jump causing some of the wave energy to be given off as an electromagnetic field. Through this theory, all kinds of electromagnetic radiation were explainable as the chain reaction of existing fields hitting electrons, causing them to switch orbitals and, in the process, forming new fields to perpetuate the reaction - in essence, each electron acting as a mini transmitter, passing information from one atom to the next. Thus the colours of the spectrum reach our eyes atom by atom, reducing over distance; radio waves are transmitted across large tracts of space with a slight time delay; and microwaves were harnessed to heat food or directed to excise cancer.
However, each specific element was only attunded, due to the configuration of its electrons, to certain frequencies on the electromagnetic spectrum. This was used to explain why objects had colour; an iron atom, with its valance of 2 electrons, was attuned to pick up and broadcast mostly grey colour waves, and all other waves could pass through it unimpeded.
This scientific principle was basic and rudimentary by todays standards, but it did set us on what turned out to be a very fruitful path. Quantum Theory inspired the Wave Harmonic theory, which suggested that, since electrons are actually waves, why shouldn't protons and neutrons be so too - and, by implication, all other forms of matter, meaning that the physical world is simply what our brains interpret from the shifting tides of electromagnetic energy? That in turn led to the Damin Oscilation Theory, which claimed that all matter could be fundamentally changed by circumventing the physical world and directly altering the waveform of the object in question. It was this research that lead to Cracker technology, which fires a waveform at a planet that 'cracks' all of the planet's water molecules into hyrdrogen and oxygen, then further 'cracks' its oxygen and hydrogen into carbon and lithium by redistributing the various protons, electrons and neutrons.
Not all results of the theory have been so calamitous, however. Ether was a project started by the rogue science group Klein Brittan. The group theorised that if a colour could be invented, by emiting a waveform of a frequency and wavelength that no existing atom was attuned to, then not only would that colour be invisible to the naked eye - as no atom would transmit it - but it would also be able to pass through solid matter. If an atom could then be created that was attuned to that and only that colour, that atom would have the same properties, and thus any item built from that mineral would be both invisible and capable of bypassing solid matter.
The members of Klein Brittan quickly seized upon an unoccupied wavelength, but immediately ran into difficulties. As they could not perceive what they were working on, they spent a lot of time uncertain as to whether their theories were actually correct, and whether their techniques were really effective. They later found that they were unable to modulate or work the new frequency, as no existing matter could interact with it. In solution to both of these problems, Klein Brittan adapted a large amount of iron ore to also react to the new frequency, allowing them to both percieve the wave by its passage through the iron, and work it with the iron itself.
The work was long and maddeningly difficult. Three members of the group went insane through the complications involved, while another commited suicide. However, the work was eventually finished, some twelve cycles before the events of the Orbital Wars began. The scientists had, in a modified iron box, a lump of a mineral that could be neither seen nor felt by any existing matter save the iron box it was held in.
The group trumpetted their success loudly, but were soon further perplexed by a further problem: what practical use did their invention have? A suit made of the stuff would be useless; while it would be able to walk through walls, it would be impossible for a person to actually wear it. It could be used for camoflage by modified-iron tanks and ships, although that seemed underambitious. Several years passed, and the mineral, which became known as Ether, was left in its box as a novelty.
Finally, one unnamed young scientist finally hit upon a solution that would change the course of the war. Legend has it that she borrowed a chunk of the mineral to experiment with, and ended up adding another frequency to the Ether she was working on. She noticed that it immediately gained form and colour based on the frequency she had given it. She quickly made a rod of the mineral and suspended it on two modified iron poles. Then, through the poles, she broadcast an electromagnetic pulse set at Ether frequency, and noticed that as long as that pulse was maintained the ether reverted to its invisible and intranscient form. As soon as the charge was cut, the ether regained corporeality.
It was initially used as shielding; with a generator, meshes or plates of ether could be used as either planetwide defence or military armour that added no weight or friction to the item it was defending. Later it obtained a more sinister use. The [New Unified Terrans]? bought the secret of the mineral from the Klein Brittan group - the one example of them ever working with terrorist factions, although they were the only ones who did. At the time their Gemini Wing was being constructed, which was quickly adapted to incorporate the new technology. All the ships in the group were fitted with Ether Coils, or enormously long lines of Ether rope which were kept in their etheral state. A common tactic was to attach two ships together by ether coil before a battle; then, positioning the ships either side of an enemy craft, allowing it to become corporeal, functionally drilling a hole straight through the ship from one side to the other. The Gemini Wing did experiment with using this tactic on planets and suns, but the heat of a planetary or solar core tended to melt the coils at the moment of corporeality.
It is rumoured that the Klein Brittan group have since succeeded in creating a suit that a human can wear, that will retain Ether's invisibility and incorporeality. The group have not commented, but it is clear that this is a new science; developments, even the most surprising kind, must certainly be expected.