Fact and Fiction

Thoughts about a funny old world, and what is real, and what is not. Comments are welcome, but please keep them on topic.

Thursday, January 26, 2006

A war on science

The latest Horizon programme on BBC2 was entitled A war on science, and it covered the debate between evolution and intelligent design.

As usual, Horizon did an excellent job, leading the audience deep behind the intelligent design frontier, before destroying them from within by using the all-powerful biological weapon known as Richard Dawkins, backed up by David Attenborough.

I relished this Horizon programme. There was a beautiful statement by Richard Dawkins, which was something like (quoting from memory) "The only people who are convinced by the proponents of intelligent design are people who know nothing". Go for it, Richard!

Both Richard Dawkins and David Attenborough pointed out that intelligent design explains precisely nothing, because the "explanation" is as complicated as what it purports to explain, and it isn't even verifiable, so it isn't science despite its claims to be science.

Monday, January 23, 2006

The cosmic landscape: chapter 1

This is my interpretation of chapter 1 of Leonard Susskind's book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design.

He introduces evolution as the origin of modern cosmological ideas, which prepares the intellectual ground for the arguments that I suspect he will use later on in the book. He then goes on to say that cosmology must use universal rules that have nothing to do with our existence, citing by analogy Richard Dawkins' "blind watchmaker".

Up until now the science of cosmology has assumed that the same laws of nature hold everywhere in the universe, but the new cosmology has the universe embedded in a landscape of alternative universes (which Susskind calls a megaverse), where the "constants" of nature depend on which universe you inhabit in the megaverse.

He then notes the "coincidence" that the laws of nature are consistent with our existence, which is called the anthropic principle. At this point he does not mention the important distinction between the weak and strong versions of the anthropic principle.

I found this rather disconcerting, because it could mislead some readers into thinking that he is about to embark on an "intelligent design" argument for our existence, which would be the strong anthropic principle in which the laws of nature are selected a priori to be hospitable for our existence. Fortunately, he actually uses the weak anthropic principle, in which the laws of nature are selected a posteriori conditioned on our existence, as is detailed below.

He points out that the theory of inflation implies a megaverse, and that there is experimental evidence to support the theory of inflation. He also points out that string theory implies a landscape of alternative universes; this is where the "frontier" of string theory is currently to be found. He notes that the extremely small observed value of the cosmological constant is not predicted by theory, but this value could be "explained away" by the anthropic principle, where we inhabit a part of the megaverse in which the cosmological constant happens to have the observed value, whose smallness is a prerequisite for our existence.

He then gives a fairly detailed and conventional summary of particle physics:

  1. Clockwork Newtonian physics is replaced by intrinsically uncertain quantum physics, giving the uncertainty principle, where measuring something with greater precision causes the sytem to be disturbed more.
  2. The smaller the wavelength of a photon the larger its energy, so big accelerators are needed to probe small objects. Use this to discover that protons and neutrons are made of quarks.
  3. Quantum mechanics implies zero point energy, where confining particles causes them to have "quantum jitters". Conjugate quantities which are subject to the uncertainty principle are position and velocity, energy and time, and electric and magnetic fields; this last example is what gives rise to the vacuum energy all around us.
  4. QM implies discreteness, where energy comes in packets.
  5. QM implies interference, as famously exemplified by the two slit experiment, where very low light intensity still gives rise to interference effects, even though there is only one photon at a time passing through the apparatus. Therefore photons must be both particles and waves at the same time. There is no point trying to understand this using everyday intuition; it is a property of the universe that lies outside our everyday common sense.
  6. Nature seems to be organised hierarchically, in which you break large objects down into smaller pieces, and so on. This is called "reductionism". Thus far in experiments we have followed down the hierarchy as far as elementary particles, which are described by quantum field theory, and intuitively visualised using Feynman diagrams to describe interactions between the particles.
  7. He then summarises quantum electrodynamics (QED), the nucleus, Feynman diagrams (propagators, vertices, coupling constants), antimatter, fine structure constant, quantum chromodynamics (QCD), weak interactions, and that all of physics is derived from simple underlying particle creation and annihilation events.
  8. The use of reductionism in physics has truly been a success story. Note that neither I nor Susskind assert that the reductionist approach should a priori be assumed to work in all cases.

He then goes on to make observations and ask questions that prepare the ground for later on:

  1. He notes that there are 3 generations of elementary particles, and that the extra generations of particles appear to be unnecessary. Thus he says that elementary particle physics is not simple and elegant, despite what particle physicists would try to tell you; it is messy and it is more like zoology or botany. To be fair, particle physics is in much better shape now than it ever was before, but Susskind makes a valid point about the "spin" that particle physicists put on the elegance of their subject.
  2. He points out that the "standard model" describes properties with incredible precision, but it needs around 30 experimentally measured constants of nature to achieve these results; this is too many constants for a fundamental theory. We have no theory that says why the standard model is right and not some other model.
  3. Are there deeper laws that govern the standard model?

That final question is the focus of Susskind's book.

Tuesday, January 17, 2006

Wi-fi network

I have finally bought a wireless router for home use, plus a wireless network card for my rather old laptop PC (a Pentium 3 - remember those?). This wi-fi network has transformed the way that I use my laptop PC (I used to use a rickety and unreliable Bluetooth link). Yes, I know that this upgrade is rather belated, but I have a policy of following the "trailing edge" of technology, because it saves me from wasting a lot of money on the hectic race to always have the latest and the best kit.

What I really want to do is to banish the large computer-related boxes with their whirring fans away from the living area of my house, and to use a wi-fi network to link them to my laptop PC. I can't do that yet, at least not as a cheap upgrade from where I am at the moment, but technology does seem to be moving in the right direction.

Now all I need to do is to wait for that brief moment known as British Summertime, so I can use my new wi-fi network to work outside in my garden.

The cosmic landscape: preface

This is my interpretation of the preface to Leonard Susskind's book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design.

How is it that the universe appears to be so well designed for our existence? Here are two possibilities:

  1. The laws-of-nature are unique, so that a priori it is a lucky accident that the universe is hospitable for our existence.
  2. There is an ensemble of many possible laws-of-nature, within which one can find laws-of-nature that happen to be hospitable for our existence.

Historically, physicists have assumed that (1) is the case, even though it would appear to be a stroke of luck that this could lead to our existence. It is an open research question whether (1) is how the universe works, but it may eventually turn out that (1) is indeed true. However, in the meantime, recent results (i.e. an ensemble or landscape of alternative laws-of-nature) from research into string theory open up the possibility that (2) might be the case.

The fact that (2) is now being considered as a realistic possibility has annoyed many physicists who have assumed (1) all along. However, this book describes an interesting type of science (i.e. (2)) that needs to be understood more widely, so that more people can enter into informed discussion about it.

If (2) is true then the ultimate "theory of everything" will have far less predictive power than if (1) is true. There is a sliding scale of possibilities ranging all the way from (1) to (2), and we should not make strong prior judgements about where the universe lies on this scale.

The laws-of-nature appear to be fine-tuned in such a way that they are consistent with the fact of our own existence. This is called the "anthropic principle".

The direction in which one chooses to use the anthropic principle is very important:

  1. The laws-of-nature are fine-tuned a priori so that we can exist. This is the strong anthropic principle, which is also known as "intelligent design".
  2. The universe is such that there is an ensemble of many possible laws-of-nature, amongst which we find one that happens to be fine-tuned a posteriori by the fact of our existence. This is the weak anthropic principle.

Susskind's book uses the weak version of the anthropic principle, as (potentially) applied to the rich landscape of laws-of-nature that emerges from string theory. His aim is to show that there is no need for the strong version of the anthropic principle, so "intelligent design" in superfluous.

In fact Susskind makes his intentions clear with this quotation from Laplace at the front of the book:

Your Highness, I have no need of this hypothesis.

Laplace said this to Napolean in response to being asked why he didn't mention God in his book on the System of the World.

Friday, January 13, 2006

The cosmic landscape: string theory and the illusion of intelligent design

Finally, my copy of Leonard Susskind's new book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design has arrived.

I posted some comments earlier (see here) about the weak form (i.e. not driven by an external goal-seeking agency) of the anthropic principle and its relationship to Bayes theorem, and made some generally disparaging remarks about the hostile attitude of some physicists to the weak anthropic principle. There was some misplaced criticism of Bayesian methods posted here, but I don't know whether this was related in any way to my earlier comments on Bayes theorem and the anthropic principle. However, I do know that it prompted me to reinforce my statement about Bayesian methods here, which led to this spectacular response, and my own response to that here. I will not comment further on that exchange; I leave it for you to read for yourselves.

Anyway, now I actually have Susskind's book, I can focus more on the particular details of his arguments, rather than my own favourite argument based on Bayes theorem. What I plan to do is to work through the book in stages, and to report back here at each stage to explain the material that I have read, and to interpret it in my own particular way.

For the record, I have no prior prejudice about whether the cosmic landscape (i.e. the possibility of choosing between multiple alternative laws of physics) exists or not, but I do care about following up all credible avenues of enquiry, until they can be shown to be wrong because they are inconsistent theoretically or experimentally. In a nutshell, that is the scientific method. So we have to view the cosmic landscape as a valid possibility for now.

Friday, January 06, 2006

Bayesian probability (update)

Blimey! Look ye here! The lady doth protest too much, methinks. I will try to respond succinctly.

I will continue to write in a fairly informal style in this blog, and to point to the relevant literature for the more discerning readers. I made this decision to embrace a wider readership at the cost of annoying a few readers. I can see why one might uncharitably compare this style of writing to that of postmodern literature criticism, but I will just have to live with that. I have a more "scholarly" (in places) blog here, but the blog is currently dormant because of problems with uploading images.

My main interest here is how we do inference about complicated systems consisting of many interacting parts. Note that there are two levels here: the system's behaviour itself (e.g. physics) and the reasoning about the system (e.g. inference). I am mainly talking about the second of these two levels. Note that this second level is where we all operate when we reason about "the world", because all we are doing is manipulating knowledge about things, rather than manipulating the things themselves.

The above paragraph must sound rather postmodern, but it's not! See the next paragraph.

Let's start by citing the literature yet again: Cox R T, "Probability, frequency and reasonable expectation", Am. J. Phys., 1946, 14(1), 1-13. This paper gives a neat derivation of the Bayesian approach to inference, by deriving everything from some elementary axioms which demand that the inference process must be internally consistent. Loosely speaking, if x is the state of a system, and Pr(x) is the joint probability of the components of x, then all inferences can be done by Bayesian manipulations of Pr(x) not x.

Bayesian inference is about manipulating joint probabilities (i.e. inference) rather than about defining joint probabilities in the first place (i.e. prior probabilities). These prior probabilities can be constructed in any way that you please, as long as they satisfy the usual properties (i.e. non-negativity, summing to unity), and then the Bayesian inference machinery can make use of them.

The freedom to choose a prior probability is an advantage, not a disadvantage, because it allows you freedom in your choice of model (or ensemble of alternative models). Bayesian inference then uses any relevant data to convert this prior probability into a posterior probability, which effectively updates the model (or ensemble of alternative models) in the light of the data.

Here is my original posting on the anthropic principle and Bayesian inference, so you can see for yourself how it has been selectively quoted here. In particular, check out the penultimate paragraph (the one starting "If the properties of the universe are correctly described by string theory (this may indeed be the case)...") for what I say about science, philosophy, and string theorists.

One can aspire to relate one's conjectured scientific theory to the real world, but the longer you are unable to demonstrate a strong connection between the two, the more your activity can be credibly labelled as "philosophy" rather than "science". I too would like to see the laws of physics derived from first principles, but I would not go so far as to assert that the laws of physics had to be derivable in this way. Whether we like it or not, the landscape is still a logical possibility, and we should at least be aware of what science would look like in that type of universe.

I also live dangerously in my own research activities, where I follow up some fairly wild ideas for long periods of time, but I always have "bread and butter" threads of research running alongside, where I dive for cover when the going gets tough. I never put all of my eggs in one basket no matter how elegant (or even how promising) it looks.

Thursday, January 05, 2006

Why bother playing guitar?

My local musical instrument shop (see www.music47.co.uk) has changed over the past ten years or so, from one that used to be mainly classical instruments and sheet music, to one that is now mainly electric guitars and sheet music. The shop now has a specialist guitar section (see www.onlineguitars.uk.com) that seems to dominate the floor of the high street shop.

OK, so electric guitars have become more popular in the British popular music scene, and now it seems that every teenager (and 20-something) wants to play electric guitar. This is not quite as bad as everyone wanting to be a sound engineer, because at least there are quite a few young bands around each of which could absorb two (and a bit) electric guitar players, but there are very few sound engineering jobs.

I would have thought that (other things being equal) if you wanted to enhance your value as a musician you should learn to play something other than a guitar. Maybe you should forget the electric guitar altogether, and learn the electric violin instead.

I know this would tax the musical talent of most would-be guitarists, because there are no frets on a violin, so you would have to actually listen to what you are playing in order to get the intonation as you want it. Also that damn violin bow thingy can be so difficult to control if you have no muscular discipline.

However, the up-side is that if you can play electric violin even half decently, using a bit of reverb to fill in the holes in the music, then you are almost guaranteed a high-profile position in a band, and you can compete on equal terms with an electric guitar because the violin bow gives you a fantastic sustain.

Bayesian probability

I recently blogged about The cosmic landscape, where I made some remarks about the relationship between Bayes theorem, the anthropic principle, and the cosmic landscape. I pointed out that the anthropic principle is a consequence of Bayes theorem applied to systems of interacting parts (e.g. observers and the observed). Thus our existence as observers is always part of the overall set of experimental observations that should be taken into account when constructing candidates for the "laws of physics". I would have thought that this much was obvious!

Not so, apparently. Such is the strength of conviction by some people that the anthropic principle is pseudo-scientific (e.g. many postings here!) that they choose to criticise the Bayesian approach, presumably because it is a rigorous approach to drawing inferences, which is thus justifiably perceived as a credible threat to their anti-anthropic stance. To assert that the Bayesian approach or the anthropic principle is pseudo-scientific (or a "dangerous idea", or whatever) won't make them go away, because they are more rigorous than some people appear to realise.

A particularly "fine" example of such misplaced criticism is by Luboš Motl here, because it appears to be based on an undergraduate level of understanding of the Bayesian approach, including all of the philosophical mumbo-jumbo that gets taught about the frequentist versus the Bayesian versions of probability. I too went through a frequentist versus Bayesian stage of my learning, mostly due to the influence of the otherwise excellent MaxEnt series of workshops . A good paper to read that uses an "axiomatic" approach to understanding all of this is: Cox R T, "Probability, frequency and reasonable expectation", Am. J. Phys., 1946, 14(1), 1-13.

It is such a pity when an intelligent scientist (e.g. Luboš Motl) chooses to criticise something by making apparently sage pronouncements too far outside their own area of expertise. Yes, you might read a text book one evening and then pass an exam the next day, but this limits you to what is in the text book, doesn't it? Experienced researchers know that the real expertise is not recorded as simple bite-sized entries in text books, but is accumulated over years of careful reflection about a subject.

Or maybe I have fallen for a troll, where Luboš Motl tricks me into mentioning his name (more than once!) in my blog, thus helping him on towards world domination.