I searched a lot here and on the Internet to figure how how randomness selection of validators in PoS works? I understand it is a random selection based on fraction of stake a validator has, similar to PoW.
In PoW, we can model block arrival as a possion process. E.g., if block interval is 10 seconds,, we expect on average a block to be created each 10 seconds. You can get two blocks where the time between them less than a second (hence memoryless process). The chance each miner has for each block depends on its hash power fraction, but random in terms of assigning miners to blocks.
Now, how block arrival and assignment differs in PoS? from what i think is the same as in PoW. From other sources, i read time is divided into slots, where each slot is assigned to a validator (say deterministic). But not really understand how this differs from PoW. Any plain English explannation is appreciated (without too much technical details).