The Grand Design

by Stephen Hawking

The notion that the laws of nature had to be intentionally obeyed reflects the ancients’ focus on why nature behaves as it does, rather than on how it behaves.

Though Aristotle’s theories often had little predictive value, his approach to science dominated Western thought for nearly two thousand years.

That effective theory is only moderately successful in predicting behavior because, as we all know, decisions are often not rational or are based on a defective analysis of the consequences of the choice. That is why the world is in such a mess.

simplicity is a matter of taste.

Despite its role in philosophical debates over the nature of our universe, the real advantage of the Copernican system is simply that the equations of motion are much simpler in the frame of reference in which the sun is at rest.

There is no picture- or theory-independent concept of reality. Instead we will adopt a view that we will call model-dependent realism: the idea that a physical theory or world picture is a model (generally of a mathematical nature) and a set of rules that connect the elements of the model to observations. This provides a framework with which to interpret modern science.

According to model-dependent realism, it is pointless to ask whether a model is real, only whether it agrees with observation. If there are two models that both agree with observation, like the goldfish’s picture and ours, then one cannot say that one is more real than another. One can use whichever model is more convenient in the situation under consideration.

Although physicists are indeed tenacious in their attempts to rescue theories they admire, the tendency to modify a theory fades to the degree that the alterations become artificial or cumbersome, and therefore “inelegant.” If the modifications needed to accommodate new observations become too baroque, it signals the need for a new model.

physicists are still working to figure out the details of how Newton’s laws emerge from the quantum domain.

Quantum physics tells us that no matter how thorough our observation of the present, the (unobserved) past, like the future, is indefinite and exists only as a spectrum of possibilities. The universe, according to quantum physics, has no single past, or history.

The fact that the past takes no definite form means that observations you make on a system in the present affect its past.

There is no model-independent test of reality. It follows that a well-constructed model creates a reality of its own.

The Game of Life is not really a game but a set of laws that govern a two-dimensional universe.