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So bitcoin could go down if no one host the nodes, if this happens, can someone just download the node and host it on his computer? Or a computer can't handle that?
If in a scenario, no one host a node, you would not be able to get the data of the new blocks from your peers. If you are the only person on earth to have a node, with no latest blockchain data, any data after your last Bitcoin block would be forgotten. Of course, you can mine the blocks and continue the blockchain but it is not plausible with the high difficulty.
If I run the bitcoin core wallet it says 6 peers, so only 6 people host the blockchain at that moment?