With virtual memory, every process runs inside a sandbox, which is the extent of its VAS. The key rule: it cannot look outside the box.
So, think about it, it's impossible for a process to peek or poke the memory of any other process's VAS. This helps in making the system secure and stable.
Example: we have two processes, A and B. Process A wants to write to the 0x10ea virtual address in process B. It cannot, even if it attempts to write to that address, all it's really doing is writing to its own virtual address, 0x10ea! The same goes for reading.
So we get process-isolation – each process is completely isolated from every other process. Virtual address X for process A is not the same as virtual address X for process B; ...
