As with most technological devices, the Rustie step-through drive is not an isolated development but rather springs from a more general ability to control the energy level of the vacuum (empty space). This technology allows the Rusties to control how space curves under the influence of matter or energy fields and gives them their gravitic drives and in-ship gravity, as well as more mundane applications such as medical and military scanning equipment, hyper toasters and so on.

The step-through drive is the most advanced application of this type of technology, and makes use of some convenient short cuts provided by nature to do in a specific case what would normally be totally beyond the range of the technology. This is similar to the case of the atomic bomb. The chain reaction in uranium or plutonium allows a quite spectacular application of nuclear technology to be created by races which do not have an overall mastery of the nuclear realm (controlled fusion power, cheap transmutation and so on).

The requirements to make a traversable wormhole through space may be directly deduced from Einstein’s General Theory of Relativity. Quantum mechanics indicates that empty space should be filled with wormholes of extremely small sizes (much, much, smaller than known elementary particles). In theory, if you could tease such a wormhole out of the vacuum, open it out to a larger size and keep it stable then a permanent gateway would be made open to a different part of space and time. The problem is that as you go to smaller and smaller scales, the energies required to do anything get larger and larger. The energy needed to single out a wormhole from the vacuum would be astronomical. At the energy levels available to the Rusties, any jump field they could set up would encompass billions of wormholes which would all try and expand at once, draining the field’s energy. Even if a single hole were to be opened, the energy needed to widen and stabilise it would also be astronomical.

Fortunately, Roving science predicted that under some unique circumstances, a single wormhole would expand much more than all the others. These wormholes always linked two points with the same gravitational potential and were always operated along a line directly linking the centres of two masses creating the gravity fields (or at right angles to the gravity fields, if you prefer). Even better, if you used exactly the right kind of jump field, the hole would “borrow” the energy to expand for long enough to allow a ship to pass through (if it were quick about it), before collapsing and returning the energy to the vacuum. Since the hole just opens and closes, there is no need to stabilise it.

So it seems that nature gave the Rusties a helping hand. To use step-through you have to:

1. Orbit around your sun until you are approaching a point which is directly on the line between your sun and the destination star. Note that getting to this point will usually take you out of the plane of the planets.
2. You now activate your jump field. This starts to expand all the wormholes in a tiny volume of space in front of your ship, which still contains countless billions of wormholes. However, wormholes which lie along the line of sight and link the two systems will expand more rapidly than the rest. Since all of these holes link neighboring parts of space, the line of slightly larger wormholes quickly coalesces into a single large wormhole which absorbs more and more of the field’s energies and starts to expand very rapidly, changing from a linear to a spherical shape as it does.
3. A change soon occurs in the wormhole and it starts to borrow the energy for its own expansion (rather like the early universe in its inflationary phase)
4. You will now see the wormhole as a rapidly expanding sphere in front of you. A ship that dives into the sphere from any direction will exit a similar sphere which has opened at the destination star. If you dive into the top of the origin sphere you will come out of the top of the destination sphere; into the base and you exit from the base; and so on. A ship in the destination system could pass through to the origin system but it would have to be in exactly the right place at the right time to catch the wormhole opening.
5. Entering the sphere is harder than it sounds since it is stationary and you are in orbit moving at high speed. You may need to blast back along your orbital path to enter the gateway if you don’t plough into it directly (for instance if you are not in the ship that opened the gate and can’t get a direct approach line)
6. After a short time the gateway spheres will collapse (whether anyone has gone through them or not). The collapse releases a tiny fraction of the tremendous energy of the wormhole in the form of gravity waves and some exotic high-energy particles.
7. You should now be in orbit about your destination star.

Any inconsistencies between this draft of a technical paper and the actual description of step-through in His Majesty’s Starship can be attributed to Gilmore’s imperfect understanding of the science.

From the Author on Step-Through:

I am indebted to my friends David Angier and Tim Bellerby for the step-through process. They know more physics and maths and other clever stuff than I do, so I explained my dilemma:

• I wanted a faster-than-light process for the novel.
• It had to be convincing and plausible-sounding, based on our present scientific knowledge and extrapolating suitably (no magic “he pressed the hyperdrive button and the ship shot away …”).
• It had to have limitations.

Let me explain that last point. A ship that can just turn on the warp drive (Star Trek) or leap into hyperspace (Star Wars) has it too easy, and whenever dramatic tension is required, the warp drive or the jump generator fails with monotonous regularity. Far more fun from the writer’s point of view is to have the technology invariably work under the right circumstances, but to make those circumstances hard to attain. For instance, in Babylon 5, the ability to get into hyperspace is never in doubt for anyone for can reach a jumpgate, and never once in the five-year run of the series did a jumpgate malfunction. But, if you are in a small craft like a Starfury, you still have to get there, and anything can happen on the way. Larger ships, which can open their own jump points, have it easier but still are constrained: doing it too near a planet is problematic, and the jump generators always need to recharge (at a consistent rate) before they can be used again.

And my friends came up with step-through.

The basics really are based on what we know of quantum theory and wormholes: but as it stood to reason that the inventors of the process, not being human, wouldn’t have called them wormholes, nor do my characters. More contentious, but dramatically interesting, is the contrivance that step-through only works between points of the same gravitational potential, and are easily detectable if you have the right equipment. Again, this introduces limitations that the characters might have to get around in a hurry.

Well, you wouldn’t want it too easy, would you?