Maybe I’m misinformed about this. But I was always told matter cannot be destroyed or created. But I have been told space is constantly expanding. Is this expansion of space not made up of “matter”? Where does it come from?
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Space is not matter. The expansion of space need not entail any generation of additional matter in the universe.Furthermore, matter may in some cases be created or destroyed – at least in the sense of atoms. Nuclear fission reactions break large atoms into smaller ones, but some of the total mass is ‘lost’ by the atoms in the process, who emit subatomic particles that constitute nuclear radiation. The energy produced by this radiation is what powers atomic weaponry, and also nuclear fission power production. These reactions can therefore be sensibly described as transforming matter (ie atomic mass) into energy (ie radiation made up of subatomic particles). Nuclear fusion is a reverse process with a similar result: atoms combining to form larger ones and releasing large amounts of energy as radiation in the process. This is how stars emit light and generate elements more complex than Hydrogen: by squishing lots of atoms close together to combine them in fusion reactions.
Nevertheless, conservation of mass is a defining feature of processes that only involve *chemical* reactions, wherein atoms are not created, destroyed, or substantially altered, but are rather simply shuffled between different molecular configurations. This is essentially the difference between chemistry and nuclear physics.
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