A theoretically possible doomsday event.

I'm probably described well as a staunch sceptic. Certainly, you will not find me with a sandwich-board on the street corner toting the word's "Repent! The end of the world is nigh!"

Nor do I care a hoot about the Mayan calendar, planetary alignment, astrology, ghosts, religious apocalypse, hell, witchcraft, karma, reincarnation or voodoo.

But at least two things can't be dismissed.

The most likely, in fact with near certainty at some point a massive comet or asteroid will hit the Earth, as it has done in the past. The second is a little more interesting, very speculative, but also theoretically possible.

It is called a local minimum.

A local minimum is a stable configuration, but not necessarily the lowest-energy stable configuration. A true stable minimum requires external energy to move it out of stability, and hold it out of stability. A local minimum is a fool's minimum. It's the kind of stability that can be lost from an unfortunate nudge. A good example of this is a penny stood on-edge.

A penny stood on edge is stable until a little extra energy is added to the system that pushes it up over onto the corner after which it collapses to a true minimum, from which there is no return. You can easily imagine that a penny cannot spontaneously jump back to be on edge without a big shake and a boat-full of luck.

You will probably have heard the term 'quantum' this and 'quantum' that. It's the world of the very small. Unfortunately, doofus somewhere in business-land or Hollywood decided that 'quantum leap' was a very big step. That's a shame. It confuses people.

The quantum arena we are discussing now is at the scale of atoms and smaller. At this scale, very weird and unfamiliar things happen. It's not just theory either. For example, we have experiments that prove that an electron can be prepared in any orientation and yet only be measured in one of two states. The mathematical conclusions drawn from these experiments is like saying that the electron is in all states at the same time until measured. This is just one example of quantum weirdness.

Another example is how an electron is shown to be a particle that also behaves like a wave. This seems contradictory, and it certainly is on the scales that you and I operate. However, at the quantum scale, the position and momentum of an electron are mutually separated statistics. If you measure the position accurately, then its momentum is very inaccurate, and vice versa. The conclusion from the maths involved, and from experiments is that an electron is somehow spread out even though it acts like a particle.

Confused? Don't worry. No-one really understands it, but these are real facts.

There is a device available from the electronic shops called a tunnel-diode. You can buy one for a dollar or so. It is a special electronic part because it is a true practical exploitation of something called quantum tunnelling. So what is this? Because an electron is spread out, under the right conditions, there is a non-zero, and significant probability that it can be found on the other side of an energy barrier.

Although I hate classical analogies to quantum phenomena, the following seems acceptable just to bring-home the enormity of the possibility how the world just might end one day:

Imagine that penny, stood on end. Then, for no reason, and without a breath of externally applied force, it is suddenly found to be flat on the table. That's sort of what happens sometimes to an electron that is contained in a local minimum. Because of it's wave-like nature, and non-localised position, it can 'tunnel' through the barrier and carry on its merry way.

The tunnel-diode is a real device. Remember this...

Empty space is far from empty.

Let's take the electromagnetic force. (i.e. light) because it is familiar. The force-carrier for the electromagnetic force is called the photon. There should be no surprises there.

However, what many people will not know is that the photon has infinite range, and there are also things called virtual photons. These virtual photons have very short lifetimes, they permeate the vacuum of space, and they are very short-range. Virtual photons are accompanied by lots of other virtual particles, like virtual electrons and so on. Again, there are experiments that infer their existence and we consider this good scientific theory despite it's craziness.

This popping crackling quantum vacuum has a pressure, and an energy level. It is considered to be a minimum energy level, and therefore stable. For example, liquid helium does not freeze under atmospheric pressure at any temperature because of its zero-point energy. The zero-point energy and the quantum vacuum is a direct consequence of the wave-like nature of tiny particles, as is quantum tunnelling.

It's theoretically possible that the zero-point energy that we measure is a real minimum, but there is no particular reason to believe it cannot just be a local minimum - like the penny on edge.

Certain formulations of quantum theory permit there to be another lower-energy state but the universe is balanced currently at something a little higher in a local-minimum.

Nucleation happens to boiling water. If pure water is raised in a perfectly clean glass to above 100 ⁰C it will not boil. But if a single contaminating speck of dust lands in it, the whole lot will burst into a bubbling mixture. This is nucleation, and is another example of a local minimum. The clean water won't boil because there is nothing to start the process. The speck of dust provides a nucleation point out of which a chain-reaction is born.

What if...

Just what if, our universe is in a local minimum? What if the measured zero-point vacuum energy level is a local minimum? It's theoretically possible that a single quantum tunnelling event could nucleate a move to a new and true minimum. This would spread out at light speed without warning, and with it would come new physical constants. Chemistry as we know it would vanish, and there could be no way back and like a long row of dominoes, all of space would tumble to the new state, never to return.

Who knows - this may have already happened billions of light years from here, beyond the edge of the observable universe, inexorably heading towards us (in a few billion years). Or it could happen on the end of the sandwich-board man's nose tomorrow.

Eat that sandwich, apocalypse-board man!