Boffins preparing to fire up the most powerful particle-smasher ever built have released another reassuring report which says that their machine will definitely not destroy the universe - nor even the planet Earth.

The Large Hadron Collider (LHC), a titanic 27-kilometre doughnut made of ultra-chilly superconductor magnet pipe, is situated in hollowed-out caverns deep beneath the Franco-Swiss border. The machine functions essentially as a kind of enormous, outrageously powerful subatomic billiard cue, the idea being that it will smash protons into swarms of other protons at large fractions of the speed of light. Even though hadrons are much more strongly put together than ordinary billiard balls, banging them together at warp speed will blow them violently to bits.

Quite apart from this being beezer fun in itself, the exploding hadrons should scatter outrageously bizarre sub-subatomic debris in all directions. It's planned that teams of top-bracket boffins, operating extremely complicated machines situated as it were at the pockets of the relativistic proton billiard table, will be able to snare - or at least snap a few pics of - the hurtling hadro-chunk weirdness.

It's particularly hoped that Higgs Bosons, dark matter and other sundry theoretical gubbins - which may or may not be in fact the basic building blocks of life, the universe and everything - will appear or conclusively fail to. This will permit the whole of physics and perhaps therefore all knowledge to be rendered invalid, and allow many shouty, arm-waving, incomprehensible arguments to take place in front of blackboards.

That's all good clean fun. But others worry that in fact the mighty atom-smasher may do damage to other things than applecarts in physics faculties.

Some people worry, for instance, that an overly aggressive hadron rim-shot manoeuvre at the LHC might create a teeny, microscopic black hole. This might then expand to gobble up the entire Earth, packing the human race down inside its swelling event horizon and possibly cramming us through an interdimensional portal into a hostile universe where life as we know it couldn't exist. (There might not be any hops, for instance; or low gravity might mean that ice cubes wouldn't reliably stay in one's glass.)

The new report from the independent LHC Safety Assessment Group is having none of that, however. According to the proton-cannon safety boffins:

Any microscopic black holes produced at the LHC are expected to decay by Hawking radiation before they reach the detector walls. If some microscopic black holes were stable, those produced by cosmic rays would be stopped inside the Earth or other astronomical bodies. The stability of astronomical bodies constrains strongly the possible rate of accretion by any such microscopic black holes, so that they present no conceivable danger.

The argument is that cosmic rays are always smacking into the upper atmosphere at the same sort of speeds as protons shot from the LHC's magno-doughnut cannons. If that kind of thing led to planet-gobbling black holes, the boffins argue, the Earth ought to have vanished already; and other planets and stars should be winking out of existence all the time as well. As it hasn't, and they aren't, it's clearly OK to fire the thing up.

Other worries include the possibility that LHC boffins might absent-mindedly convert the Earth - and indeed, if they weren't careful perhaps the entire universe - into "strangelet soup", monopole custard or some other kind of fearful hypothetical-particulate semolina, Angel Delight, squirty cheez™ etc. Again, the Safety Assessment Group gives these notions short shrift.

In the case of strangelets, the good agreement of measurements of particle production at RHIC* with simple thermodynamic models constrains severely the production of strangelets in heavy-ion collisions at the LHC, which also present no danger.

According to the official LHC reassurance webpage, "It is difficult for strange matter to stick together in the high temperatures produced by such colliders, rather as ice does not form in hot water". Although soup can be made in hot water, it seems that strangelet soup can't, or anyway not this kind of hot water. It ought to be called strangelet gazpacho, really; that would avoid confusion. (Perhaps not, as the LHC is actually kept very cold in order to maintain its superconductor magnets in top shape. When the boffins say "high temperature", they seem to be speaking about the immediate vicinity of an exploding proton.)

The LHC chaps say people have also been bugging them about a mysterious catastrophic phenomenon called a "vacuum bubble" - not, apparently, anything as simple as an actual bubble of vacuum - which might be called into existence by meddling subterranean boffinry chiefs. That's cobblers too, the safety-assessment team reckon.

There have been speculations that the Universe is not in its most stable configuration, and that perturbations caused by the LHC could tip it into a more stable state, called a vacuum bubble, in which we could not exist... Since such vacuum bubbles have not been produced anywhere in the visible Universe, they will not be made by the LHC.

Although presumably you couldn't observe a vacuum bubble if it ever happened, as you would cease to exist? Or maybe the wavefront of nonexistence would spread out only at light speed, so allowing you millennia to see your doom bearing down? It's all jolly difficult. Anyway, no need to worry - again, if the LHC was going to flip the universe into a more stable state and incidentally wipe out humanity, cosmic rays would be bound to have done it already.

The Safety Assessment Group concludes that they have checked "all the proposed speculative scenarios for new particles and states of matter that currently raise safety issues", and the LHC is All Right. And don't be coming to them with some new wackjob notion, either:

Since our methodology is based on empirical reasoning based on experimental observations, it would be applicable to other exotic phenomena that might raise concerns in the future.

All in all, we here on the Reg crazy-science desk feel much better following the LHC release. Its message is basically this: Be reassured. Very reassured.

The waiting will be over soon, anyway. The magno-tunnel doughnut was chilled down to hadron-headbang operating temperatures last month, and will generate its first circulating beam next Wednesday. Shortly thereafter an opposing stream will be fired up. Then it'll be time to start loosing off the twin proton cannons into each others' muzzles on full auto and watch the chunks of weird-o-frag fly.

A pre-print abstract of the new safety report can be read here, by the way. The paper is published online today, ref: "Review of the Safety of LHC Collisions" (J. Ellis et al, 2008 J. Phys. G: Nucl. Part. Phys. 35 1150004). ®

*The Relativistic Heavy Ion Collider, an earlier and less muscular particle-punisher in the US. It too was thought likely to turn everything into some kind of particulate blancmange.