Secondly, you're not going to need the Large Hadron Collider. Let's make it clear from the outset: the LHC simply isn't up to the job, and by many, many orders of magnitude. Using the LHC to do what I'm going to suggest is like trying to set off a nuclear explosion with a small lump of Uranium ore and a toffee hammer, it simply isn't going to happen.
So with the obvious warnings out of the way, how are we going to destroy the entire Universe? Simply blowing up a star or two isn't going to do it. In fact, blowing up all the stars isn't going to do it, despite Steven Moffat's best effort in the last season of Doctor Who. Even if you could make every star go supernova at once, the Universe would still be there...OK, it would be a Universe full of dust and ashes rather that stars, but it would still be there. We're going to need a much bigger bang.
The bang we're looking for is something called 'vacuum decay', and it has nothing to do with household appliances. A vacuum, to a physicist, is a rather complicated thing. It's exactly what you're thinking of - an absence of matter, a space that contains no atoms, no molecules. In the middle of the last century, however, it became apparent that a vacuum is never really empty, quite the opposite in fact. A vacuum, even the most perfect one you can imagine, is a bit busy. There's space and time for starters, and a plethora of 'virtual particles' popping in and out of existence the whole time...on the smallest scales a vacuum is a seething mass of weirdness.
All of this weirdness requires energy - even in particle physics, there's no such thing as a free lunch. This energy is called, with remarkable clarity and lack of imagination, vacuum energy. Depending on the theory you use to calculate it, the vacuum energy in a cubic centimetre of space is somewhere between 0.00000000000000000001 Joules and 1x10^107 Joules (a 1 with 107 zeros after it), so it's fairly safe to say there's a certain amount of uncertainty.
(As a point of reference it takes about 35,000 Joules to bring a litre of water to the boil)
Whatever the actual value is, the point is that empty space has energy. There's no particularly good reason why our Universe has the amount of vacuum energy it does, in fact it could have values far outside our (already uncertain) estimates, and therein lies our method for destroying everything.
Now, not content with throwing some big numbers around, I'm going to drop a graph into the mix as well. Don't Panic. If it helps you can think of it as a picture of a rollercoaster. In fact it will probably help if you do, because I'm going to stick with the analogy. Here it comes, hold tight....
What this shows is a completely made up graph of the possible amount of vacuum energy in the Universe. We're the little red dot. Now, imagine pushing the little red dot to one side or the other...it'll just roll back down to where it started. Push it a bit harder though, and it'll roll over the peak to the right and settle in a new position in the second, lower dip to the right, and a lot of energy will be released in the process (equal to the difference in height between the two dips). That's potentially a lot of energy. If you can push one tiny bit of the Universe, a sphere of just a few hundred metres in diameter, over the peak then it gives off enough energy to push the space around it over the edge, which pushes the space around that over the edge, and you have a bit of a chain reaction on the go.
The bubble expands at nearly the speed of light, and inside it everything changes. The very laws of physics, and by association those of chemistry and biology, alter, and not in a good way.
...one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy. This possibility has now been eliminated.
Coleman & de Luccia
Voila, we've destroyed the Universe, at least as far as we currently understand it. So how do we do it in practice? Well, we need a very high energy density, something like a very, very big bomb to push it over the edge. This was one of the "risks" associated with the LHC by people who didn't quite get the numbers (or "twats" as Brian Cox refers to them) - the energy densities created by the LHC are indeed very high, but they're nowhere close to high enough. How do we know when there's such uncertainty over how much vacuum energy the Universe has? Well several times a day cosmic rays slam into the Earth's atmosphere with very much the same energy density as the LHC's experiments. Once a month or so we get hit by a cosmic ray with far higher densities even than that, and every decade or so there's a truly exceptional event which surpasses the LHC by hundreds of times. None of these events seems to have triggered vacuum decay, after all, we're still here. (So why have we spent so much on the LHC when nature regularly beats the pants off it? Well the whole point is, in effect, to take a photo of the event with a very big digital camera, and we never know where and when the natural events will happen.)
Supernova, black holes merging, even gamma ray bursters, the most violent explosions ever observed, have so far failed to tip us over the peak and destroy the Universe, so we're going to have to dream up something else, an even bigger bang.
Which brings us to a curious little post-script, one best illustrated by a quote from Douglas Adams:
There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.What if we're in a Universe where vacuum decay has already happened? From the inside of the bubble it would look very much like a Big Bang....