The Grand Design

by Stephen Hawking

Quantum physics provides a framework for understanding how nature operates on atomic and subatomic scales, but as we’ll see in more detail later, it dictates a completely different conceptual schema, one in which an object’s position, path, and even its past and future are not precisely determined. Quantum theories of forces such as gravity or the electromagnetic force are built within that framework.

Quantum physics is a new model of reality that gives us a picture of the universe. It is a picture in which many concepts fundamental to our intuitive understanding of reality no longer have meaning.

Our use of probabilistic terms to describe the outcome of events in everyday life is therefore a reflection not of the intrinsic nature of the process but only of our ignorance of certain aspects of it.

The universe, according to quantum physics, has no single past, or history.

The laws of nature tell us how the universe behaves, but they don’t answer the why? questions that we posed at the start of this book: Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some other? Some would claim the answer to these questions is that there is a God who chose to create the universe that way. It is reasonable to ask who or what created the universe, but if the answer is God, then the question has merely been deflected to that of who created God.

How can one tell if a being has free will?

We would therefore have to say that any complex being has free will—not as a fundamental feature, but as an effective theory, an admission of our inability to do the calculations that would enable us to predict its actions.

the laws of our universe determine the evolution of the system, given the state at any one time.

Alternative histories • a formulation of quantum theory in which the probability of any observation is constructed from all the possible histories that could have led to that observation. Anthropic principle • the idea that we can draw conclusions about the apparent laws of physics based on the fact that we exist. Antimatter • each particle of matter has a corresponding anti-particle. If they meet, they annihilate each other, leaving pure energy. Apparent laws • the laws of nature that we observe in our universe—the laws of the four forces, and the parameters such as mass and charge that characterize the elementary particles—in contrast to the more fundamental laws of M-theory that allow for different universes with different laws. Asymptotic freedom • a property of the strong force that causes it to become weaker at short distances. Hence, although quarks are bound in nuclei by the strong force, they can move within nuclei almost as if they felt no force at all. Atom • the basic unit of ordinary matter, consisting of a nucleus with protons and neutrons, surrounded by orbiting electrons. Baryon • a type of elementary particle, such as the proton or neutron, that is made of three quarks. Big bang • the dense, hot beginning of the universe. The big bang theory postulates that about 13.7 billion years ago the part of the universe we can see today was only a few millimeters across. Today the universe is vastly larger and cooler, but we can observe the remnants of that early pe...