Can we zoom down with a microscope to a single transistor on a CPU?

Yes—but not with a normal light microscope. Modern CPU transistors are much smaller than the wavelength of visible light, so magnifying them more just gives you a blur.

Researchers can see individual transistors using an electron microscope. They usually cut and polish a tiny cross-section of the chip first, then image it with electrons. The result is a black-and-white image showing the transistor’s physical layers and connections.