why is particle decay happenning and why can’t matter just exist forever?
In: Physics
If matter is so stable then it will also not interact. If it doesn’t interact then lots of other interesting things like life cannot develop. You won’t have things like stars/sun etc. Chemical reactions are harder to take place or don’t take place at all. So nothing happens and the universe is pretty boring undifferentiated soup of very stable stuff. (ELI5).
For things to happen, there is a need for some instability. Instability gives a “direction” for things to happen.
The somewhat unsatisfying answer to “why does particle decay happen? is”because it can”. On a quantum level, everything that isn’t literally impossible has some probability of happening. If you wait long enough, it will happen.
There’s a huge range of how long “long enough” is, depending on the energies of the system and what types of decay or interaction are physically possible. Some are very stable and decay with low probability. Some are barely keeping it together and decay rapidly. But if it’s possible, it will happen.
Back in the day, someone solved the equation for a particle in a box and found that there’s a little bit of the wave function outside the box. That means if you wait long enough, the particle will somehow be outside the box even though it doesn’t have enough energy to go over the side. Turns out this is quantum tunneling and it happens. Basically any time you have a barrier that isn’t infinite, something that can’t get over the barrier will eventually go *through* it. So you can’t keep things together forever if there’s any way they could decay.
One way of thinking of stuff in the universe is that everything is trending towards lower energy levels. Particles have a certain amount of energy, and when they bind with other particles, they lock up some extra energy in those connections, but in the long run that energy ‘wants’ to get out and the whole configuration wants to end up in a lower energy state.
As humans, we’re much more familiar with seeing this happen at a chemical level. When something burns in a fire, molecules in it are serving as a fuel and combining with oxygen molecules in the air. The resulting chemicals that are created from that reaction have less energy bound up in them than the original chemicals, and that excess energy is released as heat and light. And combustion / oxidizing isn’t the only chemical reaction, there’s tons of them that can potentially occur. Now some reactions actually reverse that flow and cause more energy to be bound up inside of molecules given the right conditions, but overall there’s far more reactions releasing energy than capturing it.
And then there are some similar processes at the atomic / subatomic level. There’s actually far more energy bound up in connections between subatomic particles than there are in chemical bonds, which is why nuclear weapons are so much more destructive than conventional explosives.
All that being said, it’s not entirely clear if matter itself is entirely unstable. Electrons seem to be a fundamental particle, meaning they’re not made up of any smaller particles that would represent a lower energy state, so there’s nothing for them to decay into. Protons we’re a little more hazy about. We’ve never observed proton decay, but there are some theoretical reasons why it seems like it could be a thing, although through testing we’ve bounded protons’ half-life to be a ridiculously long time, on the order of at least 10^34 years.
Anyways, this whole concept of matter stability and decay is really complicated and not entirely understood, but I’d go back to my starting suggestion and summarize it as Long term all of the stuff in the universe trends towards its lowest possible energy state, and at the particle level, we call this transition process ‘decay’.
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