"cannot" isn't accurate. "cannot easily" would be accurate. For example, FPGAs themselves can be emulated in software with precise timing accuracy, so anythin

"cannot" isn't accurate. "cannot easily" would be accurate. For example, FPGAs themselves can be emulated in software with precise timing accuracy, so anything you can run on an FPGA can be emulated in software without the FPGA. It's difficult and sometimes infeasible with current CPUs to get up to the same speed though. This depends a lot on the FPGA circuit being emulated. Source: I used to work on an FPGA-targetting hardware compiler and accelerated FPGA circuit simulators.