The seismologists are the first to notice that something bizarre is happening. A pattern of perplexing seismic activity begins, hundreds of metres beneath an existing rare earth mine in Chile. Chile is on the Pacific Rim, so a certain number of earthquakes is to be expected, but the pattern of the activity is odd from the outset and only becomes stranger. The mine itself briefly ceases production due to safety concerns, but, money being money, resumes. The strange thing about the readings is that they all originate from the same point in the crust. It's a repeating pulse, as if someone is hammering on the crust from below. The mining company becomes concerned that someone could be stealing the molybdenum ore which they have the rights to, and launches a search at ground level, and finds nothing. Finally, after encouragement from scientists, a new bore hole is made, so that sensors can be inserted down to the source of the pulse.
The sensors return balderdash, just pure nonsense. It's like whatever's down there isn't rock anymore. The behaviour of the drill bit doesn't make sense. The scientists pull the drill up and feed a camera down instead. What they see is what looks like a morphing spherical carapace of hard metal. It's a ball of metal, filthy and scratched from being buried for an uncertain period of time, but it isn't static. Its surface shifts, rotating, scratches appearing and disappearing.
The scientists examine the video recording and make two deductions. First, the metal exterior they're looking at is rotating through a fourth dimension. This is a hypersphere that they're looking at, or at least a hyperspherical shell surrounding something. Second, the shell is relatively new, and has forced its way into the rock somehow, producing the strange (if limited, and non-problematic) seismic activity, and, nearby, rock dust.
In fact, just as that second deduction is being made, the shell retracts completely, revealing a rapidly spinning blizzard of four-dimensional metal edges, perhaps two metres in diameter. The camera relays pictures of the cutting heads growing as they insert themselves into the camera's plane of reality, but the camera's capture framerate is sadly too poor to actually show the motion of the cutting head overall, or give a hint as to the cutting head's sophisticated four-dimensional structure. However, it is plainly obvious from what is visible, and from what can be heard through the ground, that the thing is expanding, drilling a four-dimensional hole in this reality's wulfenite ore field. The camera's lens is covered with rock dust in a few more seconds, and then destroyed.
Someone from a higher dimension is tunnelling into this one.
It's too dangerous to try to interfere when the other dimension is actively drilling, and when they're not drilling, the hard steel shroud closes around the hole, which is almost ten metres in diameter now. But eventually it looks like the shroud is just going to stay in place and no more drilling is occurring. At this point, following great controversy, the mining company takes over and launches an operation to drill through the shroud itself.
There is a loud implosion, a rapid movement of air, when the hole in the shroud is made. A lot of debris and drill lubricant (mud) falls into the drilled hole. Another camera is sent down, a drone on a long cable, and this time it makes its way through the crack in the shroud, and into the cavity inside. It swivels, shining a light on what seem to be plain old steel walls in every direction.
Then the drone swivels in a different direction. The picture warps, and the drone creaks under interdimensional pressure, and cable starts paying out, as the drone starts to fall further, not under the force of gravity, but pulled along by some lateral force. The shroud wall closes up completely — its power and data cables, as it looks "back", pinch out of existence somewhere in air behind it, while it is completely encased in metal.
At a first look it's impossible to make a guess as to how far through the four-dimensional steel hypercylinder the drone has travelled, but then someone bright at the surface realises that they can continue to measure the amount of cable which has been paid out, and subtract off the known depth of the borehole.
The drone continues for kilometres, dragged along by a kind of interdimensional suction. Finally the hypercylinder widens out, and the journey ends, and the drone drops, LEDs winking, onto the red- and white-painted floor of an underground laboratory. The person controlling its camera moves quickly, scanning the whole room, tracing the power and data cables back into a kind of luminous, hostile portal occupying the middle of the room, a multicoloured wormhole which flexes and screams with strange, Platonic harmonics. The wormhole is mounted inside a huge machine, behind which there is a four-dimensional tunnel boring head, in its stowed configuration, looking (at this angle) as if it shouldn't exist, or at least shouldn't have been constructed. The thing is all gleaming metal spirals. A person who fell into the top of it would be eviscerated by the time they fell out of the bottom, shredded by the drill bit edges, or at least gouged into a very ugly shape.
There is a control room. The drone's camera finds it. There are people, humans, behind the controls. There is no activity immediately, though a little discussion can just about be seen taking place. Then, after some minutes, the lighting in the laboratory changes a little, and a door opens off to one side of where the drone (which has no real motive force of its own) has landed, and someone comes through to take a curious look at it.
The man crouches for a long while, eyeing the drone up. He notices the primary camera immediately, and the secondary camera cluster within another few seconds. He appears to have some seniority: he wears a grey suit, not lab clothes, and his ID pass can be read to say "Director". Then, a lab assistant shows up, and he directs them to sever the power and data cables. The assistant dons heavy duty rubber gloves, and does the job with insulated bolt cutters, while the director holds the drone down.
The drone reappears a week later. The drone is mostly disabled, stripped of components, making only a shell. There is a message attached to it, an envelope containing a wodge of paper. The message says,
To the people of Earth 760v, greetings.
Regulations don't require us to keep you informed about our waste disposal operations, however, we are sending you this message as a courtesy. The borehole with which you have illegally interfered is a cross-dimensional pipeline linking Earth 1 with an uninhabited, sterile reality sixty-five kilometres beneath us in hyperspace, Earth 2985b. The purpose of the borehole is to allow us to dispose of byproducts of our Neutron Accretion Engine, a highly advanced, extremely clean, renewable energy resource which in the next three years will totally replace all other forms of energy generation on Earth.
Large-scale radioactive neutronium dumping begins thirty-six hours from the sending of this message. It is strongly encouraged that you to use the attached schematics to repair your section of the borehole before this. Radioactive quantum-density neutron waste products in transit through your reality will cause serious damage to local geology.
You may also consider this message a pre-emptive refusal of any appeal to divert waste disposal operations or suspend our timeline. We estimate our technology is approximately 140 to 160 years more advanced than yours, and legally speaking your Earth is as empty as Earth 2985b.
Put it this way. We consider ourselves a powerful culture, and this place is not a place of honour.
Dez (Director, Ξ Neutrona Conglomerated Fd.)
It's rapidly noted that the statement about "severe damage to local geology" is not qualified. That damage is apparently going to happen no matter what. In any case, efforts to send another drone up the transdimensional borehole meet with failure; the borehole, or rather waste pipe, is already flooded with an inexorable downward pressure. Sending the drone in the opposite direction is fruitless. There seems to be no bottom to the borehole, at least not as far as cables will reach or the drone can remain intact.
And, in the end, the schematics are useless. It appears that many vital pages of diagrams and data have been omitted, possibly intentionally, and what's left assumes the existence of numerous technologies not yet invented. It can't be done.
Dumping begins on schedule. It appears to start early, but it turns out that the message took more than four hours to arrive after being written. The loads of "quantum-density" waste emit harmful radiation like brilliant tiny suns, enough that the brief flicker of radiation making its way up the terrestrial borehole is enough to be dangerous to people standing at the surface. All equipment in the hole has to be abandoned and the hole itself hurriedly filled in. Even then, the seismologists are still screaming. Every time one of the ultradense loads passes through Earth 760v, it's like an earthquake. They must ricochet off the waste pipe interior. They must resonate as they fall, and they must weigh gigatonnes or teratonnes each. There are earthquakes, vastly damaging earthquakes on an unprecedented and repeating scale. Cracks spread, and two Andean mountains destabilise.
Within a year, more waste pipes are detected being excavated.
And the only idea anybody has, the profoundly stupid idea which would only compound the problem, is to try to develop the alluded-to Neutron Accretion technology for themselves.
After sixty years of increasing seismic horror during which most oceanic coastal cities come to be abandoned due to tsunamis, yet another new phenomon appears. A new borehole, with new characteristics. This one, apparently, is coming up, from the direction of the purported empty dimensions below, which Earth 760v still has not developed the technology to access.
It turns out not simply to be a drilling operation but a self-contained multidimensional tunnel boring machine, a vast one, as large as a battleship, oriented "vertically" between dimensions. A representative hops out, waving an unfamiliar flag, one which, the representative later explains, symbolically represents a clean Earth, with no illegal waste piped through it or dumped over it.
The representative is furious. He is from the very base layer of reality, reportedly the last Earth in that direction along the multiversal curve before there's nothing but dark space. His world has been ruined, made unlivable, and he now lives with a perpetual, frightening, cold fury, entirely directed upwards.
He says, "I'm taking the fight up to Earth 1. I've got eleven hundred Earths behind me already. Join us."