DESPITE life on Earth appearing fairly stable and unchanging, the universe is a highly dynamic place.
Every day millions of stars are born or die, so nothing in our universe is eternal – or is it? That depends on how you define eternal.
Atoms exist in everything – they literally make our universe what it is. When we die our bodies are broken down into their constituent parts and recycled into the ecosystem, but our atoms go on long after we have departed.
Atoms go on after planets crumble and suns die and galaxies vaporise. But will atoms themselves eventually break down into nothingness?
Atoms contain a nucleus of protons and neutrons, surrounded by a “cloud” of electrons. The number of electrons in the cloud is equal to the number of protons, which helps keep the atom stable.
Generally, but not always, the number of neutrons in an atom is consistent. If an atom loses a neutron it becomes unstable and, in an attempt to become stable again, shoots off sub-atomic particles, mostly electrons, and in doing so starts to break down.
The ‘heavier’ the atom is – that is, the more particles it contains – the more likely it is to spontaneously break down into smaller particles. This is called radioactive decay.
Though we can’t predict when a subatomic particle will be shot off, we can analyse the pattern and determine how many atoms will decay over an average time. This is called an atom’s ‘half-life’, and is a very reliable estimate of an atom’s lifespan.
Since an atom has a finite number of protons and neutrons it will generally emit particles until it reaches a point where its half-life is so long that effectively it becomes stable.
For example, Bismuth-209 is believed to have the longest half-life of all atoms – more than a billion times longer than the age of the universe. So to all intents and purposes Bismuth-209 is eternal.
However, true eternal life depends whether or not protons can decay, and some scientists have suggested a hypothetical form of this, in which protons transition into a positron and a neutral pion, which then decays into two gamma ray photons (the Georgi-Glashow model).
Estimates put the half-life of protons at 1.29×10
34 years – a very large number indeed!