user60718: I am studying the algorithm of Bitcoin and I don't understand one thing. If all miners are mining the next block at the same time, and there are thousands of nodes, how could it be that there are no collisions (two blocks found at the same time)? I wonder how effective this process is? As I understood the algorithm, the mining must be sequential (with order), and this can only be done if all miners mine the next block at the same time, because hash of the previous block must go within the next block. But if they mine it at the same time, there must be a lot of collisions. However I can't find anything about collisions or low effectiveness of this blockchain algorithm. 

user11253: Every miner tries to mine a different block. One reason is that the reward payment address (which pays the miner for their work) is naturally different for each miner. Therefore, no two miners are competing to mine the same block.
Similarly, each individual miner changes other things in blocks to make sure that each of their mining rigs is not duplicating work too.

user12983: 
how could it be that there are no collisions ?

There are.

I wonder how effective this process is ?

Very ineffective. ~$10 natural cost for securing one transaction :)

60718: <p>I am studying the algorithm of Bitcoin and I don't understand one thing. If all miners are mining the next block at the same time, and there are thousands of nodes, how could it be that there are no collisions (two blocks found at the same time)? I wonder how effective this process is? As I understood the algorithm, the mining must be sequential (with order), and this can only be done if all miners mine the next block at the same time, because hash of the previous block must go within the next block. But if they mine it at the same time, there must be a lot of collisions. However I can't find anything about collisions or low effectiveness of this blockchain algorithm. </p>
 11253: <p>Every miner tries to mine a <em>different</em> block. One reason is that the reward payment address (which pays the miner for their work) is naturally different for each miner. Therefore, no two miners are competing to mine the same block.</p>

<p>Similarly, each individual miner changes other things in blocks to make sure that each of their mining rigs is not duplicating work too.</p>
 12983: <blockquote>
  <p>how could it be that there are no collisions ?</p>
</blockquote>

<p>There are.</p>

<blockquote>
  <p>I wonder how effective this process is ?</p>
</blockquote>

<p>Very ineffective. ~$10 natural cost for securing one transaction :)</p>
