If you find all of this a bit fuzzy and unsatisfactory, you are in good company: Albert Einstein positively disliked some of the perceived implications of quantum mechanics and the Copenhagen school in particular, especially the idea that the universe is fundamentally governed by random events (he famously quipped that "God doesn't play dice," to which Bohr allegedly replied that he wished Einstein would stop telling God what to do). Indeed, Einstein spent much of the time during the last part of his career trying to come up with a more solid interpretation of quantum mechanics, one that would recover some sense of physical reality beyond randomness and probabilities (he failed). Other physicists eventually produced one such attempt, the so-called many-worlds interpretation endorsed by Tegmark at the discussion I enjoyed at NYU. The many-worlds theory basically maintains that the reason quantum mechanics seems so strange is because we have access to only one of an infinite number of worlds. From our narrow perspective, the output of certain measurements (like that of the double-slit experiment) seems random and probabilistic, but that is an artifact of the fact that, literally, we don't have the full picture. In fact, proponents of the many-worlds hypothesis say, reality is such that there are infinite universes, all differing to a greater or lesser extent from each other. Because of this infinity of possibilities, everything that can happen does in fact happen, just not in our little corner of the "multiverse," the only one to which we have access. This may sound preposterously Star Trek-like, but bear in mind that it is a mainstream view among fundamental physicists.
Not so mainstream, and yet increasingly popular, is the third idea we will consider briefly: string theory, supported by Brian Greene at the NYU event and beautifully explained in his book The Elegant Universe. This is where things have the potential to get even further remote from science proper, despite the fact that people working on string theory are unquestionably legitimate scientists doing some of the most cutting-edge work in their discipline. In fact, it is so cutting edge that some consider it to be beyond the line that separates science from nonscience. First we need to understand why people are attempting to construct a new theory of the physical sciences at the same time that everyone acknowledges the spectacular successes of the two currently dominant theories in physics, quantum mechanics and general relativity. The problem is that these two theories work very well when applied to their proper domains, respectively, the very microscopic and the very macroscopic worlds. That is, quantum mechanics does a beautiful job at predicting how matter behaves at the scale of quarks, electrons, photons, and the like. Relativity, on the other hand, works very nicely when it is a question of describing the behavior of systems like planets, galaxies, and so forth. However, when one tries to apply quantum mechanics to typically relativistic problems -- such as developing a quantum theory of gravity -- the two theories behave very differently and their predictions diverge. The same happens if one attempts to apply relativity to the subnuclear world. The logical conclusion is that either one of the two theories is seriously flawed, or that they both are, or at the very least that they are incomplete. In any case, it seems clear to physicists today that there is something amiss, hence the search for a so-called final theory of everything, a rather boastful name for a framework that would unify our understanding of the basic forces of the universe and describe all the particles of which matter is made.
Enter string theory. It is based on the idea that the known subatomic particles are not the most fundamental constituents of matter. Rather, the stuff of which everything is made are even stranger objects termed "strings," which take the properties of various particles/waves depending on the frequency at which the strings vibrate. This notion has a variety of strange consequences, including that the universe actually possesses eleven, not just four dimensions (the three familiar spatial dimensions plus time). Another consequence is that if string theory (which is actually a family of related theories differing in some of their details) is correct, then physicists would find themselves with a mathematically internally coherent quantum theory of gravity, something they have been after now for several decades.
String theory, if you think about it, is a beautiful idea: it means that everything in the universe is made of just one kind of thing and that this fundamental aspect of matter takes a variety (not an infinite variety, mind you) of forms, depending on a simple property such as its vibration frequency. It is so elegant an idea that it deserves to be true. But is it? Therein lies the problem: at the moment, at least, string theory does not seem to make any empirically testable predictions that both differ from those of other competing theories and that can conceivably be evaluated in actual experiments. If one defines science as a type of inquiry into nature characterized by the availability of empirically testable hypotheses, then string theory is, strictly speaking, not science.
Perhaps, then, we should think of string theory, the multiverse interpretation of quantum mechanics, and similar intellectual pursuits as more akin to philosophical investigations, albeit mathematically rigorous and informed by the empirical science. Of course, if one begins with the common assumption that physics is not only the queen of the sciences, but that science is in turn the sovereign of all intellectual disciplines, then it is an insufferable insult for string theory to be "downgraded" to mere philosophy (or even to purely mathematical work).
Obviously, this is not to argue that all areas of logical and philosophical analysis will eventually transform themselves into science, regardless of how much time or technological advance one allows. For example, despite the fact that biology provides some insights into human concepts of morality and aesthetics, it is hard to imagine simply turning the latter two disciplines over to science departments, because they involve human values, not just matters of fact. Moreover, it may simply well be the case that we will never find a way to test the idea that there are multiple universes out there. Just because we are curious animals, there is no assurance that nature behaves in a way that allows us to get answers to every mystery that happens to intrigue us.
SETI: How Do We Find Out If Anybody Is Out There?
Arguably, people have been wondering about life in the cosmos outside Earth ever since the human species has been able to wonder about anything at all. Even worshiping stars and planets as gods can be seen as a way to project agency, and therefore intelligence, outside of the narrow confines of our own home among the stars. Until the twentieth century, however, the question of extraterrestrial intelligence was a matter of philosophical debate and speculation. SETI, as the quest is now so often referred to, entered the scientific discourse in 1959, when Giuseppe Cocconi and Philip Morrison, two physicists at Cornell University, published a paper in Nature arguing that human technology was now advanced enough to actively search for radio signals emitted by other civilizations in the galaxy. The following year, radio astronomer Frank Drake started the short-lived but historically important project OzMa, during which he used the radiotelescope at Green Bank in West Virginia to actually listen and ascertain whether anyone was trying to communicate.
Project OzMa did not discover any sign of extraterrestrial intelligence, and neither have any of its successors so far, including extensive searches conducted in the Soviet Union during the cold war, NASA's Project Cyclops, NASA's Project Phoenix, and University of California, Berkeley's Project SERENDIP, among others. There are currently several efforts along similar lines, the most ambitious of which is the search undertaken using the newly constructed (in fact, still under construction at the time of this writing) Allan Telescope Array, the first group of radiotelescopes expressly dedicated to a SETI project. Moreover, millions of people are now contributing to SETI by virtue of the ingenious "SETI at Home" project, which distributes software that anyone can acquire for free7 and run on any personal computer. The software periodically downloads data from the SETI project on your machine, works in the background (or as a screensaver) to analyze it, and then sends it back to the team at Berkeley, where processed data from all over the world are compared, searching for a radio signal that cannot be attributed to natural phenomena. Hundreds of millions of dollars, decades of active research by several teams of scientists, and millions of hours of computer time have been spent. So far, however, nothing has turned up. Is this science?
SETI certainly does meet the minimum criteria for science that we have identified so far: it is based on the ability to conduct systematic observations, often of particularly promising star systems and at radio frequencies deemed more likely to be used for interstellar communication; and it allows for the possibility of empirical confirmation of its central hypothesis (namely, that there is intelligent life out there). The fact that such a hypothesis has so far failed to be supported, however, puts SETI in a different category from ordinary science, because there is no reasonable way to disprove the hypothesis either, given that the search is more akin to looking for a needle in a proverbial (and huge!) haystack. We have seen at the beginning of this book that falsification, the ability of a hypothesis to be rejected, at least potentially, is not necessarily the all-encompassing solution to the demarcation problem that Popper thought it was, because confirmation also plays an important role in science. As a result, hypotheses are usually given a fair chance to succeed despite initially negative results. But in the case of SETI, negative results are what are expected most of the time, perhaps even forever, regardless of the truth of the central hypothesis. This raises the question: when will SETI researchers think that enough negatives have been accumulated to reject the hypothesis of existence of other technological civilizations? If the answer is that such hypothesis can never be rejected, regardless of the empirical results, that pushes SETI uncomfortably close to the status of pseudoscience.
Let us step back for a moment and reexamine each of the terms in the Drake equation, not from the point of view of what might be the best current estimate, but of whether they are estimable at all; if they are not, then the whole idea of using the Drake equation as a theoretical underpinning for SETI runs into serious trouble. R*, the rate of star formation in the galaxy, is something astronomers have methods to estimate, at least approximately. Although one has to make assumptions about how constant (or not) the rate is over the lifespan of the galaxy, this is no different from estimating any uncertain parameter in other branches of science (say, for instance, the rate of production of new species in biology).
There are various reasons why we have not transmitted repeatedly and toward a variety of targets, beginning with a dearth of political will (or even downright paranoia at revealing our position in the sky!), and therefore lack of funding. But also the obvious absence of a tangible reward: should we ever succeed in capturing an extraterrestrial signal, the payoff would be enormous regardless of what the message said: it would be confirmation that there is indeed other intelligent life out there, which would have tremendous psychological, philosophical, and even theological consequences. But what's in it for a team of scientists who send, rather than listen to, messages? They are certainly not going to be around if and when an answer comes back, making the whole thing much, much worse than the proverbial message in a bottle. If that sort of rather selfish, or at least self-absorbed, human psychology permeates the galaxy (again, following the principle of mediocrity), then we are not very likely to get a hello any time soon.