在技术演讲中，为什么你不能在32位操作系统上运行64位应用程序？

I need some help to describe, in technical words, why a 64-bit application prompts a "Not a valid Win32 application" in Windows 32-bit on a 32-bit machine? Any MSDN reference is greatly appreciate it (I couldn't google a reliable source). I know it shouldn't run, but I have no good explanation for this.I need some help to describe, in technical word