The Grand Design

by Stephen Hawking

Quantum theories can be formulated in many different ways, but what is probably the most intuitive description was given by Richard (Dick) Feynman, a colourful character who worked at the California Institute of Technology and played the bongo drums at a strip joint down the road.

But common sense is based upon everyday experience, not upon the universe as it is revealed through the marvels of technologies such as those that allow us to gaze deep into the atom or back to the early universe.

model-dependent realism. It is based on the idea that our brains interpret the input from our sensory organs by making a model of the world.

just as there is no flat map that is a good representation of the earth’s entire surface, there is no single theory that is a good representation of observations in all situations.

According to M-theory, ours is not the only universe. Instead, M-theory predicts that a great many universes were created out of nothing. Their creation does not require the intervention of some supernatural being or god. Rather, these multiple universes arise naturally from physical law.

To understand the universe at the deepest level, we need to know not only how the universe behaves, but why. Why is there something rather than nothing? Why do we exist? Why this particular set of laws and not some other?

The human capacity for guilt is such that people can always find ways to blame themselves.

Anaximander (c. 610 BC–c. 546 BC), a friend and possibly a student of Thales, argued that since human infants are helpless at birth, if the first human had somehow appeared on earth as an infant, it would not have survived. In what may have been humanity’s first inkling of evolution, people, Anaximander reasoned, must therefore have evolved from other animals whose young are hardier.

Democritus believed that every material phenomenon is a product of the collision of atoms. In his view, dubbed atomism, all atoms move around in space, and, unless disturbed, move forward indefinitely. Today that idea is called the law of inertia.

This distinction matters because it illustrates that not all generalizations we observe can be thought of as laws of nature, and that most laws of nature exist as part of a larger, interconnected system of laws.

we now know that Newton’s laws must be modified if objects are moving at velocities near the speed of light. Yet we still consider Newton’s laws to be laws because they hold, at least to a very good approximation, for the conditions of the everyday world, in which the speeds we encounter are far below the speed of light.

So if we involve God in the answer to the first question, the real crunch comes with the second question: Are there miracles, exceptions to the laws?

A scientific law is not a scientific law if it holds only when some supernatural being decides not to intervene. Recognizing this, Napoleon is said to have asked Laplace how God fit into this picture. Laplace replied: “Sire, I have not needed that hypothesis.”

Do people have free will? If we have free will, where in the evolutionary tree did it develop? Do blue-green algae or bacteria have free will, or is their behaviour automatic and within the realm of scientific law? Is it only multicelled organisms that have free will, or only mammals? We might think that a chimpanzee is exercising free will when it chooses to chomp on a banana, or a cat when it rips up your sofa, but what about the roundworm called Caenorhabditis elegans—a simple creature made of only 959 cells? It probably never thinks, “That was damn tasty bacteria I got to dine on back there,” yet it too has a definite preference in food and will either settle for an unattractive meal or go foraging for something better, depending on recent experience. Is that the exercise of free will?

It is hard to imagine how free will can operate if our behaviour is determined by physical law, so it seems that we are no more than biological machines and that free will is just an illusion.

Because it is so impractical to use the underlying physical laws to predict human behaviour, we adopt what is called an effective theory. In physics, an effective theory is a framework created to model certain observed phenomena without describing in detail all of the underlying processes.

That effective theory is only moderately successful in predicting behaviour 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.

The goldfish’s picture of reality is different from ours, but can we be sure it is less real?

Classical science is based on the belief that there exists a real external world whose properties are definite and independent of the observer who perceives them.

Anti-realists suppose a distinction between empirical knowledge and theoretical knowledge. They typically argue that observation and experiment are meaningful but that theories are no more than useful instruments that do not embody any deeper truths underlying the observed phenomena.

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David Hume (1711–1776), who wrote that although we have no rational grounds for believing in an objective reality, we also have no choice but to act as if it is true.

To paraphrase Einstein, a theory should be as simple as possible, but not simpler.

In our quest to find the laws that govern the universe we have formulated a number of theories or models, such as the four-element theory, the Ptolemaic model, the phlogiston theory, the big bang theory, and so on. With each theory or model, our concepts of reality and of the fundamental constituents of the universe have changed.

Richard Feynman wrote that the double-slit experiment like the one we described above “contains all the mystery of quantum mechanics”.

Scientists hope to replicate the buckyball experiment someday using a virus, which is not only far bigger but also considered by some to be a living thing.

According to quantum physics, no matter how much information we obtain or how powerful our computing abilities, the outcomes of physical processes cannot be predicted with certainty because they are not determined with certainty. Instead, given the initial state of a system, nature determines its future state through a process that is fundamentally uncertain.

It is, to paraphrase Einstein, as if God throws the dice before deciding the result of every physical process.

According to the quantum model, however, the particle is said to have no definite position during the time it is between the starting point and the endpoint. Feynman realized one does not have to interpret that to mean that particles take no path as they travel between source and screen. It could mean instead that particles take every possible path connecting those points. This, Feynman asserted, is what makes quantum physics different from Newtonian physics.

When both slits are open, the paths in which the particle travels through one slit can interfere with the paths in which it travels through the other, causing the interference.

Can’t we, as we do when our supervisor has a spot of mustard on her chin, discreetly watch but not interfere? No. According to quantum physics, you cannot “just” observe something. That is, quantum physics recognizes that to make an observation, you must interact with the object you are observing.

But a quantum buckyball cannot be said to have taken a definite path from source to screen. We might pin down a buckyball’s location by observing it, but in between our observations, it takes all paths. 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 choice whether to take one or both paths in this case would have been made billions of years ago, before the earth or perhaps even our sun was formed, and yet with our observation in the laboratory we will be affecting that choice.

The most incomprehensible thing about the universe is that it is comprehensible. —ALBERT EINSTEIN

Faraday had little formal education. He had been born into a poor blacksmith’s family near London and left school at age thirteen to work as an errand boy and bookbinder in a bookshop. There, over the years, he learned science by reading the books he was supposed to care for, and by performing simple and cheap experiments in his spare time. Eventually he obtained work as an assistant in the laboratory of the great chemist Sir Humphry Davy. Faraday would stay on for the remaining forty-five years of his life and, after Davy’s death, succeed him. Faraday had trouble with mathematics and never learned much of it, so it was a struggle for him to conceive a theoretical picture of the odd electromagnetic phenomena he observed in his laboratory. Nevertheless, he did.

Our sun radiates at all wavelengths, but its radiation is most intense in the wavelengths that are visible to us. It’s probably no accident that the wavelengths we are able to see with the naked eye are those in which the sun radiates most strongly: it’s likely that our eyes evolved with the ability to detect electromagnetic radiation in that range precisely because that is the range of radiation most available to them.

So aliens who evolved in the presence of X-rays might have a nice career in airport security.

lol

In light of such disagreements, when Maxwell claimed to have discovered the “speed of light” popping out of his equations, the natural question was, what is the speed of light in Maxwell’s equations measured relative to?

Maxwell suggested an experiment. If there is an ether, the earth must be moving through it as it orbits the sun. And since the earth is travelling in a different direction in January than, say, in April or July, one ought to be able to observe a tiny difference in the speed of light at different times of the year—see the figure.

Einstein didn’t attempt to construct an artificial explanation for this. He drew the logical, if startling, conclusion that the measurement of the time taken, like the measurement of the distance covered, depends on the observer doing the measuring. That effect is one of the keys to the theory in Einstein’s 1905 paper, which has come to be called special relativity.

Electromagnetic forces are responsible for all of chemistry and biology.

According to string theory, particles are not points, but patterns of vibration that have length but no height or width—like infinitely thin pieces of string.

why is there a universe, and why is the universe the way it is?

It was as if a coin 1 centimetre in diameter suddenly blew up to ten million times the width of the Milky Way. That may seem to violate relativity, which dictates that nothing can move faster than light, but that speed limit does not apply to the expansion of space itself.

Feynman showed that this arises because a particle does not have a unique history. That is, as it moves from its starting point A to some endpoint B, it doesn’t take one definite path, but rather simultaneously takes every possible path connecting the two points.

So look carefully at the map of the microwave sky. It is the blueprint for all the structure in the universe. We are the product of quantum fluctuations in the very early universe. If one were religious, one could say that God really does play dice.

But there will be different histories for different possible states of the universe at the present time. This leads to a radically different view of cosmology, and the relation between cause and effect. The histories that contribute to the Feynman sum don’t have an independent existence, but depend on what is being measured. We create history by our observation, rather than history creating us.

the earth’s orbit has an eccentricity of only about 2 percent, which means it is nearly circular.

Large orbital eccentricities are not conducive to life, so we are fortunate to have a planet for which orbital eccentricity is near zero.