The cosmological multiverse and falsifiability in science

The cosmological “multiverse” model talks about regions far beyond the observable portion of our universe (set by the finite light-travel distance given the finite time since the Big Bang). Critics thus complain that it is “unfalsifiable”, and so not science. Indeed, philosopher Massimo Pigliucci states that instead: “… the notion of a multiverse should be classed as scientifically-informed metaphysics”.

Sean Carroll has recently posted an article defending the multiverse as scientific (arXiv paper; blog post). We’re discussing here the cosmological multiverse — the term “multiverse” is also used for concepts arising from string theory and from the many-worlds interpretation of quantum mechanics, but the arguments for and against those are rather different.

How not to defend humanistic reasoning

Sometimes the attitudes of philosophers towards science baffle me. A good example is the article Defending Humanistic Reasoning by Paul Giladi, Alexis Papazoglou and Giuseppina D’Oro, recently in Philosophy Now.

Why did Caesar cross the Rubicon? Because of his leg movements? Or because he wanted to assert his authority in Rome over his rivals? When we seek to interpret the actions of Caesar and Socrates, and ask what reasons they had for acting so, we do not usually want their actions to be explained as we might explain the rise of the tides or the motion of the planets; that is, as physical events dictated by natural laws. […]

The two varieties of explanation appear to compete, because both give rival explanations of the same action. But there is a way in which scientific explanations such as bodily movements and humanistic explanations such as motives and goals need not compete.

This treats “science” as though it stops where humans start. Science can deal with the world as it was before humans evolved, but at some point humans came along and — for unstated reasons — humans are outside the scope of science. This might be how some philosophers see things but the notion is totally alien to science. Humans are natural products of a natural world, and are just as much a part of what science can study as anything else.

Yes of course we want explanations of Caesar’s acts in terms of “motivations and goals” rather than physiology alone — is there even one person anywhere who would deny that? But nothing about human motivations and goals is outside the proper domain of science.

Science is a product of science!

The latest issue of Free Enquiry magazine contains several articles about philosophy and science, including an article by Susan Haack, a philosopher of science who “defends scientific inquiry from the moderate viewpoint”, rejecting cynical views that dismiss science as a mere social construction, but also rejecting “scientism”.

While Susan Haack talks quite a bit of sense about science, she promotes a view that is common among philosophers of science but which I see as fundamentally wrong. That is the idea that science and the scientific method depend on philosophical principles that cannot be justified by science, but instead need to be justified by philosophy.

Reductionism and Unity in Science

One problem encountered when physicists talk to philosophers of science is that we are, to quote George Bernard Shaw out of context, divided by a common language. A prime example concerns the word “reductionism”, which means different things to the two communities.

In the 20th Century the Logical Positivist philosophers were engaged in a highly normative program of specifying how they thought academic enquiry and science should be conducted. In 1961, Ernest Nagel published “The Structure of Science”, in which he discussed how high-level explanatory concepts (those applying to complex ensembles, and thus as used in biology or the social sciences) should be related to lower-level concepts (as used in physics). He proposed that theories at the different levels should be closely related and linked by explicit and tightly specified “bridge laws”. This idea is what philosophers call “inter-theoretic reductionism”, or just “reductionism”. It is a rather strong thesis about linkages between different levels of explanation in science.

To cut a long story short, Nagel’s conception does not work; nature is not like that. Amongst philosophers, Jerry Fodor has been influential in refuting Nagel’s reductionism as applied to many sciences. He called the sciences that cannot be Nagel-style reduced to lower-level descriptions the “special sciences”. This is a rather weird term to use since all sciences turn out to be “special sciences” (Nagel-style bridge-law reductionism does not always work even within fundamental particle physics, for which see below), but the term is a relic of the original presumption that a failure of Nagel-style reductionism would be the exception rather than the rule.

For the above reasons, philosophers of science generally maintain that “reductionism” (by which they mean the Nagel’s strong thesis) does not work, and on that they are right. They thus hold that physicists (who generally do espouse and defend a doctrine of reductionism) are naive in not realising that.

“The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble.”     — Paul Dirac, 1929 [1]

The problem is, the physicists’ conception of reductionism is very different. Physicists are, for the most part, blithely unaware of the above debate within philosophy, since the ethos of Nagel-style reductionism did not come from physics and was never a live issue within physics. Physicists have always been pragmatic and have adopted whatever works, whatever nature leads them to. Thus, where nature leads them to Nagel-style bridge laws physicists will readily adopt them, but on the whole nature is not like that.

The physicists’ conception of “reductionism” is instead what philosophers would call “supervenience physicalism”. This is a vastly weaker thesis than Nagel-style inter-theoretic reduction. The physicists’ thesis is ontological (about how the world is) in contrast to Nagel’s thesis which is epistemological (about how our ideas about the world should be).

Contra theologian Roger Trigg on the nature of science

Roger Trigg is a senior theologian and philosopher. His new book, “Beyond Matter”, is soon to be published by the Templeton Press, part of the wealthy Templeton Foundation whose aim is to produce a religion-friendly version of science.

An excert from the book promotes a view of science that is common among philosophers. Those of us with a scientistic perspective see it as erroneous, and yet, since Trigg’s account of science is widely accepted, it is instructive to rebut it.

Trigg argues that science rests on metaphysical assumptions:

What then has to be the case for genuine science as such to be possible? This is a question from outside science and is, by definition, a philosophical — even a metaphysical — question. Those who say that science can answer all questions are themselves standing outside science to make that claim. That is why naturalism — the modern version of materialism, seeing reality as defined by what is within reach of the sciences — becomes a metaphysical theory when it strays beyond methodology to talk of what can exist. Denying metaphysics and upholding materialism must itself be a move within metaphysics. It involves standing outside the practice of science and talking of its scope. The assertion that science can explain everything can never come from within science. It is always a statement about science.

This view can be summarised by the “linear” schematic:

One can see why theologians like this account of science. If it were really true that science rested on metaphysical assumptions then science would be in big trouble, since no-one has ever proposed a good way of validating metaphysical assumptions.

A scientific response to the Brain in a Vat

Scientia Salon is an enjoyable webzine discussing philosophical matters, which recently addressed an old conundrum: how do we know we are not a brain in a vat? As I see it, this question is straightforwardly answered by the usual scientific method, so here I’ll summarise the argument that I advanced in the Scientia Salon discussion.

The Matrix-style scenario, which dates back to the skepticism of Descartes, supposes that we are a brain kept alive in a vat, being fed with a stream of inputs generated by an Evil Genius. Everything that we experience as sense data is not real, but is artificially simulated and fed to us. Since, ex hypothesi, our stream of experiences is identical to that in the “real world” explanation, we cannot know for sure whether or not we are such a brain in a vat.

How to respond? First, the whole point of science is to make sense of our “stream of experiences”. We do that by looking for regularities and patterns in those experiences, and we develop those into descriptions and explanations of the world (I’ll use the term “world” here for the sum of those experiences, regardless of whether they derive from our contact with a real world, or from a simulated world being fed to us).

Applying falsifiability in science

Falsifiability. as famously espoused by Karl Popper, is accepted as a key aspect of science. When a theory is being developed, however, it can be unclear how the theory might be tested, and theoretical science must be given license to pursue ideas that cannot be tested within our current technological capabilities. String theory is an example of this, though ultimately it cannot be accepted as a physical explanation without experimental support.

Further, experimental science is fallible, and thus we do not immediately reject a theory when contradicted by one experimental result, rather the process involves the interplay between experiment and theory. As Arthur Eddington quipped: “No experiment should be believed until it has been confirmed by theory”.

Sean Carroll recently called for the concept of falsifiability to be “retired”, saying that:

The falsifiability criterion gestures toward something true and important about science, but it is a blunt instrument in a situation that calls for subtlety and precision.

Meanwhile, Leonard Susskind has remarked that:

Throughout my long experience as a scientist I have heard un-falsifiability hurled at so many important ideas that I am inclined to think that no idea can have great merit unless it has drawn this criticism.

Jon Snow, climate change, and the nature of science

Channel 4 News tonight gave extensive coverage to the widespread flooding in England, the wettest spell for two hundred years we’re told. The senior news anchor, Jon Snow, was interviewing Andrew McKenzie, a hydrogeologist with the British Geological Survey:

Snow: Answer me the question that everyone keeps asking. Is this caused by climate change?

McKenzie: Well … quite probably.

Snow: I like that answer, but of course it’s not a scientific answer is it?

Aaargh! Obviously we’re getting nowhere in educating the public about science if a leading journalist such as Jon Snow thinks that being uncertain is “unscientific”, when in reality being uncertain is exactly the scientific response to partial and unclear evidence.

Tools of science: Induction and Occam’s razor

As philosophers are fond of pointing out, induction is logically unsound: no track record, however lengthy, of observing that swans are white can validate the conclusion that all swans are certainly white and that no-one will ever encounter a black swan. Yet science uses induction every day, and it works. Our sampling of information is always partial, and yet that partial information tells us enough about the world around us to generate highly successful predictions and to produce engineering and technology that works. One can thus ask on what basis science uses the principle of induction.

Some would argue that induction is an example of a basic assumption of science that cannot be further justified. They might claim that all “ways of knowing” depend on such unverified assumptions, that science is just one example of such a system, and that other assumptions can lead to equally valid domains of understanding, such as theology.

A scientist, though, would argue that tools of science such as induction are not arbitrary, but are themselves justified by science. The scientific method is itself the product of science, deriving from a long historical process of working out what works. Thus, by bootstrapping, science arrives at methods that produce good predictions about the world, and produce engineering and technology that works.

A scientism defence of Logical Positivism

Like everyone else I read Ayer’s Language, Truth and Logic as a teenager and, like many people of a scientific bent, I loved it. The Logical Positivism that it espoused can be summarised as the claim that knowledge is of two types: (1) logical reasoning from axioms, such as used by mathematics; and (2) claims about the universe that can (in principle) be verified empirically. Anything else — such as metaphysics — is literally meaningless.

Logical Positivism is generally held to have been refuted (following criticisms from notables such as Quine, Popper and others), and as stated in its original form that is a fair assessment. However, its general thrust can be defended as sound. Indeed, Logical Positivism was a forerunner of what today gets called scientism, and interpreting it as scientism it is very much alive.

First, a defender of scientism would subsume the first type of knowledge, the “logical reasoning from axioms”, into the knowledge that derives from empiricism and can be empirically verified. Afterall, the reason that we adopt our basic axioms of logic and mathematics is because they work — they give results that apply to our universe. Where else would we have got them from?