Hawking's The Grand Design: A Summary of Sorts
I recently happened to read Stephen Hawking's The Grand Design. It is a fascinating book, and I like how it makes the difficult ideas and theories of modern physics accessible to the general public. Even though the book claims right in the start that 'philosophy is dead', a lot of philosophical reasoning has been employed through out the book (at times, in a sloppy manner). I would be charitable and assume that the remark does not imply a wholesale condemnation of philosophy on Hawking's part, but rather that it expresses his perception that modern philosophers are not taking the advancements of modern physics into account, which to a certain extent is true.
The book highlights several important ideas, some of which I'd point out here, using excerpts from the book.
* 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 observation.'
'there is no picture- or theory-independent concept of reality'
'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..., then one cannot say that one is more real than another. One can use whichever model is more convenient in the situation under consideration.'
'[There is one possible model that the world was created not too far in the past,] favoured by those who maintain that the account given in Genesis is literally true even though the world contains fossil and other evidence that makes it look much older.... One can also have a different model, in which time continues back 13.7 billion years to the big bang.... The second model can explain the fossil and radioactive records and the fact that we receive light from galaxies millions of light-years from us, and so this model - the big bang theory - is more useful than the first one. Still, neither model can be said to be more real than the other.' [my underlining]
* Scientific Determinism: 'given the state of the universe at one time, a complete set of laws fully determines both the future and the past.'
'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.... Quantum physics might seem to undermine the idea that nature is governed by laws, but that is not the case. Instead it leads us to accept a new form of determinism: given the state of a system at some time, the laws of nature determine the probabilities of various features and pasts rather than determining the future and past with certainty.'
* Effective Theory of Free Will: 'While conceding that human behavior is indeed determined by the laws of nature, it also seems reasonable to conclude that the outcome is determined in such a complicated way and with so many variables as to make it impossible in practice to predict.... Because it is so impractical to use the underlying physical laws to predict human behavior,... we use the effective theory that people have free will.'
* Fundamental Randomness in Nature: 'Our use of probabilistic terms to describe the outcomes of events in everyday life is ... a reflection not of the intrinsic nature of the process but only of our ignorance of certain aspects of it. Probabilities in quantum theories are different. They reflect a fundamental randomness in nature.'
* Alternative Histories: 'the universe does not just have a single existence or history, but rather every possible version of the universe exists simultaneously in what is called a quantum superposition.'
'... rather than following a single path, particles take every path, and they take them all simultaneously! That sounds like science fiction, but it isn't. Feynman formulated a mathematical expression - the Feynman sum over histories - that reflects this idea and reproduces all the laws of quantum physics.'
'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.'
* Empty Space Does Not Exist: 'It is not obvious, but it turns out that with regards to that principle [Heisenberg uncertainty principle], the value of a field and its rate of change play the same role as the position and velocity of a particle. That is, the more accurately one is determined, the less accurately the other can be. An important consequence of that is that there is no such thing as empty space. That is because empty space means that both the value of a field and its rate of change are exactly zero.... Since the uncertainty principle does not allow the values of both the field and the rate of change to be exact, space is never empty. It can have a state of minimum energy, called the vacuum, but that state is subject to what are called quantum jitters, or vacuum fluctuations - particles and fields, quivering in and out of existence.'
* No-Boundary Condition: [Once we add the effects of quantum theory to the theory of relativity, it is predicted that in certain extreme situations, time can behavior like another dimension of space.] 'In the early universe - when the universe was small enough to be governed by both general relativity and quantum theory - there were effectively four dimensions of space and none of time.... Suppose the beginning of the universe was like the South Pole of the earth... To ask what happened before the beginning of the universe would become a meaningless question, because there is nothing south of South Pole. In this picture, space-time has no boundary... This idea that histories should be closed surfaces without boundary is called the no-boundary condition.
* Multiple Universes: 'M-theory has eleven space-time dimensions.... the extra dimensions are curled up into what is called the internal space.... In M-theory those extra spaces cannot be curled up in just any way. The mathematics of the theory restricts the manner in which the dimensions of the internal space can be curled. The exact shape of the internal space determines both the values of the physical constants... In other words, it determines the apparent laws of nature.'
'The laws of M-theory therefore allow for different universes with different apparent laws, depending on how the internal space is curled. M-theory has solutions that allow for many different internal spaces, perhaps as many as 10^500, which means it allows for 10^500 different universes, each with its own laws.'
* Spontaneous Creation: '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.'
'Quantum fluctuations lead to the creation of tiny universes out of nothing. A few of these reach a critical size, then expand in an inflationary manner, forming galaxies, stars and, in at least one case, beings like us.'
'On the scale of the entire universe, the positive energy of the matter can be balanced by the negative gravitational energy, and so there is no restriction on the creation of whole universes.'
'Spontaneous creation is the reason why there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going.'
I will post my thoughts about these ideas separately in another blogpost.