Question: how many atoms are there

Bernard Ennis answered on 9 Nov 2015:

There are so many atoms (just on earth, never mind the whole universe) that it would take you your whole life just to write down the number. That’s the clever answer, the real answer is: no-one knows for sure, we can only make a good guess based on what we know about what the universe is made up of. To give you a better idea of just how many atoms there might be, there are around 50 quintillion (that’s a 5 with 19 zeros after it) in one grain of sand.