If multiple miners find a valid block at the same time and broadcast it to the network, there can be a temporary split in the blockchain network. This is known as a "fork." The blockchain will eventually resolve the fork by accepting the longest chain, which is the chain that has the most computational work put into it.

This means that the miners who mined on the shorter chain will have their work invalidated, and they will not receive the mining rewards associated with that block. In short, only one of the competing blocks will ultimately be accepted by the network, and the miners who worked on the other block will have their work invalidated.