Chaisson is an astrophysicist who sees the entire history of the Universe from the Big Bang 14 billion years ago to the present as showing an evolution from simplicity to complexity that passes through eight epochs: the Particle Epoch, the Galactic Epoch, the Stellar Epoch, the Planetary Epoch, the Chemical Epoch, the Biological Epoch, the Cultural Epoch, and the Future Epoch. Chaisson has a website that sketches his account of this cosmic evolution, which is elaborated in his Epic of Evolution: Seven Ages of the Cosmos (Columbia University Press, 2006) and in his Astronomy Today (8th edition, Pearson, 2014).
Ever since the emergence of human self-conscious awareness, human beings have wondered about how the world came to be, how humans came to be, and how the human place in the world illuminates the meaning of human life. To answer their questions, human beings have told themselves myths about cosmic history, and generally these myths have appealed to religious beliefs about the powers of supernatural beings.
Chaisson says that his story of cosmic evolution is also a "cultural myth" (Epic, 426). But it's a scientific myth that does not rely on beliefs about supernatural beings or philosophical speculation, because modern science as it began in the Renaissance can achieve true knowledge through the scientific method of gathering relevant data, formulating theories, and then testing those theories through rigorous observation and experimental testing and rejecting those theories that fail to be empirically confirmed. Without mentioning Karl Popper, Chaisson assumes Popper's standard of falsifiability for science: a theory is not truly scientific if it is not in principle empirically testable, and a theory is falsified when it's empirical predictions fail.
I wonder whether this is true, or whether any science of cosmic evolution must confront the ultimate limits to science in facing fundamental mysteries of nature that are not open to observational or experimental study. Herbert Spencer set forth a scientific account of cosmic evolution that is very similar to Chaisson's. Like Chaisson, Spencer saw a cosmic evolution from simplicity to complexity, from homogeneity to heterogeneity, which could be explained through natural laws. But unlike Chaisson, Spencer thought that increasing scientific knowledge reveals "the ultimate mystery of things," and thus provides "a firmer basis to all true Religion" ("Progress: Its Law and Cause," 484). Modern science shows the power of the human intellect in explaining everything that comes within the range of human experience. But it also shows the weakness of the human intellect in dealing with all that transcends human experience.
In studying the origin of the external world, Spencer observed, we can hypothesize that all matter originally existed in a diffused form, but we cannot prove this, and we cannot conceive how this came to be, because we can have no experience of the distant origin of all things. Likewise in studying the internal world of our human mind, we cannot conceive of how consciousness is possible, of how mind emerges from matter. And thus we see that "absolute knowledge is impossible," because "under all things there lies an impenetrable mystery" (485). If science is limited to thinking about nature that is empirically testable and falsifiable, Spencer would seem to say, then there can be no scientific understanding of those realms of nature that are beyond human observation.
That this might be true has recently become a hotly contested issue among some scientists and philosophers of science. About a year ago, two physicists--George Ellis and Joe Silk--wrote an article for Nature complaining that some physicists were threatening the intellectual integrity of science by asserting that if speculative theories of the Universe were sufficiently elegant and explanatory, they should be accepted as true, even if they could never be empirically tested. This would deny the traditional understanding of science as empirical knowledge based on observational evidence and experimental testing, which might make it impossible to distinguish scientific knowledge from philosophical speculation or religious belief (Ellis and Silk, "Defend the Integrity of Physics," Nature 516 : 321-23).
According to Ellis and Silk, string theory and the theory of the multiverse are prime examples of theories accepted by many physicists that are not testable. According to string theory, elementary particles should be understood as infinitesimally thin vibrating one-dimensional strings in multidimensional space that are too small to be seen through microscopes or detected through collisions in any particle collider. According to the idea of the multiverse, our universe is just one of many universes with different cosmic and physical properties. Scanning over all possible universes, everything that can physically happen does happen an infinite number of times. But it's impossible for us in our universe to observe these other universes. Since these theories cannot be tested by observational or experimental evidence, Ellis and Silk argue that they are not scientific theories at all, because science should be limited to theories that are testable.
In December, a meeting of scientists and philosophers of science was convened in Munich to debate the issues raised by Ellis and Silk. A report on the meeting can be found at the website for Quanta Magazine.
David Gross, a proponent of string theory, opened the meeting by arguing that the problem identified by Ellis and Silk is simply a "fact of nature"--the fundamental constituents of nature are either too small, too far away, or too far in the past to be observed directly by us or indirectly through our instruments, and thus nature's secrets are buried so deep or so far away that we have no way to test our theoretical speculations about them.
Here is a sketch of what Gross sees as the limits on the scale of human observational experience of nature. At the small scale, microscopes have extended our experience beyond our visual reach, and the Large Hadron Collider (LHC) has extended our reach even deeper. We have gone from scales of centimeters to millionths of a millionth of a millionth of a centimeter. But we have reasons to believe that the fundamental constituents of nature that string theory attempts to describe lie at a distance scale 10 million billion times smaller than the resolving power of the LHC. At the cosmic scale, telescopes have extended our experience of the astronomical universe; but no telescope will ever look beyond our universe's cosmic horizon and see the other universes assumed by the multiverse hypothesis. The white area is the range of scales within human experience. The grey area is outside that range. You can click on the image to enlarge it.
Philosophers of science like David Dawid (String Theory and the Scientific Method) have argued that this shows the need for Popperian falsificationism to be replaced with Bayesian confirmation theory, which allows for a non-empirical science in which we rate the confidence we have in a theory from zero to 100 percent. We can be confident in a theory even when it makes claims about phenomena that we cannot directly observe. No one has ever directly seen an atom or subatomic particles, but we can be confident in atomic theory based on indirect inferences using instruments. We might even have good reasons for accepting string theory, even though we might never have either direct or indirect empirical evidence for it.
At the Munich conference, some defenders of Popperian falsificationism pointed out that Popper recognized the importance of speculative theories that lack testable predictions. He identified such theories as "metaphysics," and he saw that such metaphysical thinking could be taken seriously, with the thought that eventually it might become possible to devise empirical tests for a metaphysical theory.
Chaisson adopts the Popperian position when he describes the scientific method that was first formulated by scientists in the Renaissance:
"They realized that thinking about Nature was no longer sufficient. Looking at it was also necessary. Experiments became a central part of the process of inquiry. To be effective, ideas had to be tested experimentally, either to refine them if data favored them or to reject them if they did not. The 'scientific method' was born--probably the most powerful technique ever conceived for the advancement of factual information. Modern science had arrived" (Epic, x).With this standard in mind, Chaisson rejects string theory and the multiverse as unscientific theories: "I see no evidence for cosmic strings, eleven dimensions, or multiple universes" (xvi). Such thinking "borders on science fiction (or even religion)" (75). Such ideas cannot be truly scientific, because they depend on thinking without looking, speculative thought without empirical observation.
An alternative position would be to say that while our knowledge of the world is most reliable when it is based on both thinking and looking, we must ultimately come up against the limits of human observational experience, and then we must settle for thinking without looking, even as we hope to someday push the boundaries of our experience deeper into nature, so that we can empirically test our theories. Here we must fall back onto what Chaisson calls "informed speculation" (67).
Consider, for example, what might be the most difficult metaphysical question of all: Why is there something rather than nothing, and why are things as they are an not different? The modern theory of the Big Bang as the beginning of the Universe forces us to ask this question. What was there before the Big Bang? Why did it occur? What or who caused it?
In a previous post, I have argued that Why is there something rather than nothing? is a meaningless question, because it rests on two false assumptions. First, it falsely assumes the possibility of absolute nothingness. Since human beings have no experience of absolute nothingness, whereas all of our experience confirms the being of things, there is no empirical evidence for absolute nothingness. Even the very idea of nothingness as a product of the theological imagination pondering the doctrine of creation ex nihilo is dubious, because in the absence of any empirical evidence, I doubt that people even understand what they are saying when they ask why the world arose out of nothingness.
Chaisson comes close to agreeing with me when he says that questions about the origins of the Big Bang cannot be addressed by modern science, because there are no ways to experimentally test our thinking about such questions (Epic, 33). Asking what came before the Big Bang might be a "meaningless puzzle" (57). And yet he thinks it is reasonable for scientists to speculate about such questions by formulating various models of the Universe.
One is the steady-state model that stipulates that the average density of the Universe is eternally constant. Although the Universe is expanding, the average density of matter remains the same. For this to be true, however, new matter must be constantly created out of nothing, and thus the steady-state theorists still face the problem of explaining how something arises from nothing, which seems to contradict the scientific principle of the conservation of mass and energy.
A second model of the Universe is that of the "open Universe," in which the Universe expands eternally from the Big Bang. A third model is that of the "closed Universe," in which the Universe expands from the Big Bang until the gravitational pull of matter pulls everything back, and matter collapses back onto itself in a "big crunch." Both of these models face the problem of explaining the initial Big Bang.
A fourth model is that of the "cyclic Universe," in which the Universe expands from a big bang, collapses back onto itself, and then expands again from another big bang; so that the Universe oscillates eternally. In this view, there is no single, unique beginning that has to be explained, because the oscillation of the Universe is eternal. For that reason, Chaisson observes, "subjectively, in our guts, many researchers prefer it," because this model avoids the philosophical problem of what preceded the Big Bang (32). But notice that Chaisson appeals here to some subjective "gut feeling" for which there is no objective empirical test. Isn't this thinking without looking?
Repeatedly, Chaisson first affirms the truth of some mysterious idea in science and then admits that it might be purely imaginary. So, for example, he says that black holes "apparently really do exist" (95), but then says that they might be "a whim of human fantasy," because there can be no evidence, either direct or indirect, for their existence (106). There are no experimental tests for explaining what happens deep inside black holes, and so this might be "the ultimate in the unknowable" (101).
Sometimes, Chaisson insists that scientific cosmology can supplant religious myth (418). At other times, however, he says that we might need "a merger of science and religion" (76).
Was Spencer right in seeing "the ultimate mystery of things" as providing "a firmer basis to all true Religion"?
Other posts on cosmic evolution can be found here, here, here, here, here., here, here, here, and here.