As we discover more about how nature works,

the line dividing the possible and the impossible will have to be redrawn, over and over, in ways we cannot yet imagine. Yet some enduring insights are possible. Certain principles have survived serious challenges and even whole revolutions in physics. Logical connections can be forged between apparently different concepts connections that persist whether the concepts are possible or impossible. Unless we arrive at a ﬁnal theory of physics if such a theory can even exist the study of the impossible is our best way of thinking about the shape of the undiscovered deep laws of nature.

Our exploration of the impossible has led us to some quite deep insights into the laws of nature.

We have examined the central ideas of symmetry, information, and probability. Our discussion has been based on the best present understanding of the laws of physics, but that understanding is subject to change. Given the possibility of change, is there anything that we can confidently call impossible?

In Impossible Science Part 2, we heard some wise words from Sir Arthur C. Clarke, the British science fiction writer.

Here, we want to discuss his third law: “Any sufficiently advanced technology is indistinguishable from magic.” Is Clarke wrong? Can we distinguish between super-advanced technology, which is based on the fundamental laws of nature, and magic, which is supernatural?

In the 18th century, finding the longitude of a ship at sea was a vital puzzle in the science of navigation.

Finding latitude, or north-south location, was comparatively easy, based on the angle of the pole star. Finding longitude had no such simple solution. The essential problem was accurately measuring time. Being one minute off could put a ship up to 15 nautical miles out of reckoning. Ships roll and pitch as they travel. Any simple pendulum clock of the day would be knocked off its time.

John Harrison was a great English clock maker.

He worked on the problem for several decades and ﬁnally developed a large pocket watch that could keep time to within a few seconds in a sailing voyage across an ocean. As amazing and awe-inspiring as this watch was, it was still obviously a machine, a piece of engineering. Imagine you are John Harrison or one of his contemporaries and someone presents you with a 21st-century GPS unit. The principles of electricity, of radio communication, and so forth would be totally unfamiliar. The lack of moving parts would be baffling. However, after some experiments, you would realize that the GPS follows explicable laws of physics.

There were some magical ideas for solving the longitude problem.

Even in those days, scientists and engineers understood causality and knew they would not work. New discoveries in physics will lead to unexpected things, but not to things that seem, on examination, like magic. New scientific theories do not really change everything they always leave a lot of our previous understanding in place.

Remember our classification system for the impossible from Impossible Science Part 1.

An absolute impossibility involves a logical or mathematical inconsistency.
A physical impossibility, or derived impossibility, violates a law of physics.
A statistical impossibility is not impossible but is extremely improbable.

Of the 3, a physical impossibility is the weakest, because it depends on the details of the laws, but new discoveries can change the details all the time. Which of the things we have discussed in this series do you think will always remain impossible, even if we discover new laws of physics?

We have examined the impossible as a means to an end.

Our real goal has been to understand the unity of physical law and the way the laws of nature work together. Time and again we have found deep and surprising relationships between apparently disparate branches of physics. Time and again we have seen how the central themes of symmetry, information, and probability shape many different branches of physics. As we said at the outset, if our goal is understanding, then there is no tool more practical than the impossible.