It seems that with every year that passes, some technology pundit or journalist predicts that Moore's Law will come to an end. The components on today's microprocessors are now on the nanoscale -- a scale so tiny that you can't even see individual elements using a powerful light microscope. Physics behave differently at this size and quantum mechanics begin to take over for classical physics. Things get pretty weird.
For example, there's quantum tunneling. Imagine an electron isn't a particle with a defined position. Instead, it's a particle that behaves like a wave. The probability of the electron's position varies within the wave. In a way, the wave looks like a bell curve -- the narrow ends represent areas where it's possible -- but not probable -- for the electron to be. The wide middle section represents the area where the electron would most likely be found.
As this wave comes close to a barrier, such as a gap between two conductors, one end of the wave might overlap the barrier and touch the other conductor. That means the electron has the potential to be on the other side of the gap. If the potential is there, that means sometimes the electron is on the other side. It's as if the electron tunneled right through the barrier.
In a microprocessor, this is what we would call a bad thing. You can think of a microprocessor as a complex road system for electrons to travel through. Transistors in the microprocessors are gates -- they govern traffic flow. A closed gate shouldn't allow electrons to pass through. But if you get the gates thin enough -- shrinking those elements down further to keep up with Moore's Law -- you start to encounter quantum problems like electron tunneling. Electron leakage will cause computer errors as the microprocessor gets the wrong results in its calculations.
Over the years, engineers have found new ways to build transistors on the nanoscale while minimizing effects like quantum tunneling. Sometimes this involves using a different type of material within the transistor gates. Sometimes, it means creating a three-dimensional gate to increase the efficiency of the microprocessor. These have helped companies keep pace with the predictions of Moore's Law. But another reason Moore's Law hasn't gone away is because we keep fiddling with the definition.