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A favourite XKCD:

Made out of Meat

Here’s a few idle, Friday afternoon thoughts. I study distant galaxies. I use mathematical models of the laws of nature (and a supercomputer) to try to predict the properties of light emitted by and scattered through swirling vortices of matter, each containing a thousand trillion trillion trillion tons of stars, gas and dark matter, almost a trillion trillion kilometers away. My discipline – cosmology – has taken as its object of study the universe as a whole. And we’re doing pretty well, thanks for asking. I’d like to think that I am an evidence collecting, theory discovering, model investigating, equation solving (with a little help from my computer) machine.

And then I hear a talk from a biologist. I am reminded that I’m a fighting, fleeing, feeding, and reproducing machine. The lump of stuff in my head was produced by causes that “see” survival and reproduction. My brain is the control centre of a biological organism, and there seems to be precious little overlap between survival, reproduction and astrophysical ability. (Unless my astrophysical brain has made me so attractive to the ladies that it significantly increases my chances of reproduction. I’ll ask my wife.) An accurate mental picture of the world, formed using mostly reliable senses and the ability to reason logically, creatively and flexibly, seems useful to survival. But to use a brain to do cosmology? Really? (If you haven’t read Terry Bisson’s wonderful short essay “They’re made out of meat“, then do it now: “Thinking meat! You’re asking me to believe in thinking meat!”.)

A parable. Suppose I call Toyota customer services.

Me: Hi there. I own a 1993 Toyota Camry. I have a question.

Toyota: Certainly, sir. Is the car running well, getting you from A to B in comfort?

Me: Sure. It’s doing all that nicely. I was thinking about using it to drive to the moon.

Toyota: … Right … Wouldn’t recommend that, Mr Barnes. No … uh … not really in the user manual, I’m afraid. Not what it’s made for.

Suppose I find a customer support label on the back of my brain.

Me: Hi there. I own and operate one of your brains. I have a question.

Support: Certainly, sir. Is it operating your body, correctly? Are you getting enough food? Have you found a mate?

Me: Sure. It’s doing all that nicely. I was thinking about using it to do theoretical physics, discover the fundamental laws of the universe and use them to understand the structure and evolution of the universe and all its contents.

Support: … Right … Wouldn’t recommend that, Mr Barnes. No … uh … not really in the user manual, I’m afraid. Not what it’s made for.

Let’s be clear about the point I’m making here. I don’t doubt that physicists in general and cosmologists in particular have discovered true facts about the universe. It’s just a tad amazing that we can do that sort of things with our brains. (We use computers and telescopes as well, of course, but they too are the products of human brains). To extend the analogy, it’s as if I find myself standing on the moon, wondering how I got there. And as I look around, all I can see is a 1993 Toyota Camry. It’s not that I doubt where I am; I’m wondering how I got here in that! I’m not asking: how do I know that our investigation of the universe is successful? I’m asking: why is our investigation of the universe successful? How does fighting/fleeing/feeding/reproducing machine manage to do theoretical physics?

Perhaps the boring answer is the right one: we do it bit by bit. If we view science as extended and refined common sense, then maybe we can understand how a brain “made for” understanding local terrestrial environments is able to understand the universe. We don’t directly grasp the universe, of course. We rely on mental pictures and analogies. Mathematical models of the universe are perhaps analogies with equations. Having a mental picture of the world is useful. Just add curiosity and get practicing.

It seems like the same problem arises for mathematics – how does a brain manage to investigate such abstract ideas as those of pure mathematics? The same answer suggests itself: abstract thinking is useful. Just add curiosity and get practicing.

The universe is easy

We seem to need another ingredient in this explanation. That a brain can do theoretical physics and cosmology suggests not only that it is a remarkably adaptable, programmable thing, but also that the universe is an easier problem than we might have expected. A great example of this is the so-called cosmological principle. (I discuss this in more detail in my Australian Physics article here.)

That the universe is rationally analysable at all, that there is order and reason waiting for us in the mathematical structure of the universe, is a remarkable fact. The intellectual problem we are presented with in nature is, in a very real and precise sense, solvable.  It is one thing that the universe exemplifies such beautiful mathematics as Lagrangian dynamics; it is another, a fortiori, that the Lagrangians that describe our universe display numerous and deep symmetries. The universe is a complicated place, and the mathematics that describes it must be complicated at some level. The remarkable thing is that the complication is on top; there is simplicity underneath. To be more precise, the laws of nature are simple, their solutions can be complicated. Newton’s law of gravitation is simple, but for even three bodies, its solution cannot be written down analytically.

In physics’s search for the ultimate laws of nature, many physicists wouldn’t accept a proposed fundamental theory unless it were simple, elegant, and beautiful. Paul Dirac went so far as to say that “it is more important to have beauty in one’s equations than to have them fit experiment”. It follows that physics cannot explain why the laws of nature are simple, elegant, and beautiful. Now there’s a thought for the weekend.

Next month, I’ll be in Minnesota at the St. Thomas Summer Seminars in Philosophy of Religion and Philosophical Theology, presenting the science of fine-tuning to a bunch of philosophers. I presented similar lectures back in 2011 – they’re on YouTube. I’ve got a new section this time on Bayesian approaches to the multiverse and naturalism. I found a few guinea pigs to test it out on, so if you’re in Sydney on Saturday then come along. Here’s the details:

Title: Fine-tuning and Naturalism

Abstract: Christopher Hitchens stated that “At some point, we [the New Atheists] are all asked which is the best argument you come up against from the other side. I think every one of us picks the fine-tuning one as the most intriguing.” After introducing the fine-tuning of the universe for intelligent life, I will consider what it means for naturalism, the multiverse, and science’s quest for the ultimate laws of nature.

Time: Saturday 30th of May 2015, 4pm.

Address: St Philips Anglican Church, 402 Port Hacking Rd Sth Caringbah

If you’re in Sydney on Monday (18th May, 2015), then come along to The Royal pub in Darlington to see A Pint of Science! It’s an international science festival, with similar events in 9 countries. I’ll be speaking on:

Universes, one after the other)
Cosmologists are considering the idea that our universe is just one of a vast ensemble. I’ll give two reasons to take that incredulous look off your face, and two reasons to put that incredulous look right back again.

You’ll also hear “Quantum origin of galaxies, stars and life”, by Archil Kobakhidze (theoretical particle physicist), and Quantum Technologies of the Future by David Reilly (quantum physicist).

And, naturally, beer. All welcome!

Research question: Do telepathic powers exist? Such powers would be highly in demand, so highly in fact that telepaths might become paranoid and keep their abilities secret. Here, I propose a method to identify hidden telepaths. Continue Reading »

Another video of one of my talks. The goal is to take Bayesian probability theory as it is used in the physical sciences and see if it can make sense of postulating and testing a multiverse theory.

As part of a project called Establishing the Philosophy of Cosmology, I attended a conference in Tenerife, Spain in September last year. The line-up of fellow attendees was, frankly, intimidating. Nevertheless, I had a wonderful time, learned a lot and presented some of my own ideas towards the end of the conference.

The videos are now available on YouTube here; talk slides are here. Just about all the talks are worth a listen – I’ve been enjoying listening to them again. Here are a few highlights.

Joel Primack – Cosmological Structure Formation. A nice introduction to how the universe made its galaxies.

Barry Loewer – Metaphysics of Laws & Time in Cosmology. A very helpful talk on how to think about the laws of nature, and the place of probabilities therein.

George Ellis – Observability and Testability in cosmology and Cosmology: what are the Limits of Science. Made an important distinction between “big-C” Cosmology, whose purview is all of reality, and “little-c” cosmology, which is a branch of science about what physics and physical observations can say about the universe as a whole.

Sean Carroll – What Happens Inside the Wave Function? (I’ll let Sean explain here.)

The talks by Don Page, Bob Wald, Jim Hartle, Joe Silk, David Wallace, David Albert, Chris Smeenk, Brian Pitts, Tom Banks, and Jean-Philippe Uzan were very interesting, as were the discussion panels of Dean Zimmerman, Jennan Ismael & Tim Maudlin, and Janna Levin, Priya Natarajan, Claus Beisbart & Pedro Ferreira.

Here’s mine.  Enjoy.

(My sister is a TV journalist. I’m going to have to get some tips about not fidgeting, what to do with my hands, and not flubbing my words. I say “quantise” instead of “quantify” at one point. *cringe* My good wife has seen me give public lectures, and has commented that I appear to be on speed.)

I’ve started a new project at the University of Sydney. I’m still at the same desk, but I’ll be doing something a bit different. More details soon, but basically I’ll be using cosmological simulations of galaxy formation to try to make precise the connection between the fundamental parameters of cosmology – like the density of matter, the lumpiness of the early universe and the cosmological constant – and the conditions required by stars, and hence anything that requires stars.

For a brief overview of why anyone would do this, he’s a short presentation I gave at the Australian Academy of Science’s “Australian Frontiers of Science – The edges of astronomy” meeting in December 2014. My talk starts at 25:09. I think it’s queued up below. The other talks are also well worth your time:

The edge of the Universe—a fundamental limit how much we can know? – Associate Professor Tamara Davis
The small-scale spatial limits to the Universe – Dr Alessandro Fedrizzi
The edges of knowledge —the ‘physics is done’ syndrome – Associate Professor Michael Murphy

Gabriel Popkin has written a nice overview of some recent work on the fine-tuning of the universe for intelligent life at insidescience.org, titled “A More Finely Tuned Universe“. It’s well worth a read, and features a few quotes from yours truly.

It details the work of Ulf Meissner and colleagues on the dependence of the Hoyle resonance in Carbon on the masses of the up and down quarks. The quark masses are fundamental parameters of the standard model, meaning that we can measure them, but the model itself can’t predict them. They are just arbitrary constants, so far as the equations are concerned. Their work shows that a change in the quark masses of ~3 percent with respect to their values in this universe will not result in the universe producing substantially less carbon or oxygen, so this is something of a safe zone. As the article quotes me as saying, I hope that they continue to push things further, to see if and where the universe really starts to change.

I have a problem, however, with the following quote:

David Kaplan, a particle physicist at Johns Hopkins University in Baltimore, said two to three percent gives the quark mass a lot of wiggle room compared to other much more finely tuned parameters within physics, including the cosmological constant.

(Just to note: I was quoted accurately in the article, so probably the other scientists were too. This isn’t always the case in science journalism, so I’m responding here to the quote, not necessarily to the scientist.)

The three percent change in the quark masses is with respect to their values in this universe. This is a useful way to describe the carbon-based-life-permitting range, but gives a misleading impression of its size. For fine-tuning, we need to compare this range to the set of possible values of the quark masses. This set of possible values – before you ask again, Jeff Shallit – is with defined by the mathematical model. It is part of our ideas about how the universe works. If you’ve got a better idea, a natural, simple idea for why constants like the quark masses must have the values they do, then write it down, derive the constants, and collect your Nobel Prize. The standard model of particle physics has no idea why the constants take any value over their possible range, that is, the range in which the model is well-defined and we can calculate its predictions. Moreover, in testing our ideas in a Bayesian framework, we cannot cheat by arbitrarily confining our free parameters to the neighbourhood of their known value. The prior is broad. Fine-tuned free parameters make their theories improbable.

The smallest possible mass is zero; the photon, for example, is massless. The largest mass that a particle can have in the standard model is the Planck mass. Larger particles are predicted to become their own black hole, so we would need a quantum theory of gravity to describe them. Alas, we’re still working on that.

3% of the quark masses value in our universe is one part in $ latex10^{23}$ (one followed by 23 zeros) of the Planck mass. Technically, the down quark mass is (roughly) the product of the “Higgs vev” and a dimensionless parameter called the Yukawa parameter. The possible range of the Higgs vev extends to the Planck mass; why it is so much smaller than the Planck mass is known as the Hierarchy problem. The quark Yukawa parameters are about 3 \times 10^{-5}, which leads Leonard Susskind to comment (in The Cosmic Landscape),

.. the up- and down-quarks … are absurdly light. The fact that they are roughly twenty thousand times lighter than particles like the Z-boson and the W-boson is what needs an explanation. The Standard Model has not provided one.

In my paper on fine-tuning, I discuss the “cheap binoculars fallacy”: you can make anything look big, if you just zoom in enough. Actually, the fine-tuning of the cosmological constant is a good example of avoiding this fallacy. Relative to its value in our universe, the cosmological constant doesn’t seem very fine-tuned at all. Forget 3%; it can increase by a factor of ten, or take on similar but negative value, and the universe would still contain galaxies and stars. No one thinks that this is the answer to the cosmological constant problem, because comparing the life-permitting range with the value in our universe is irrelevant. When we compare to the range the constant could take in our models, we see fine-tuning on the order of one part in 10^{120}.

Later in the article, Kaplan states:

“Maybe if you change the quark masses not by three percent but by 50 percent you could end up with a situation where life as we know it couldn’t exist, but life as we don’t know it could exist,”

I agree with that sentence, so long as it starts with “Maybe”. But the state of understanding of our models is such that the burden of proof is now firmly on the “life as we don’t know it” claim. There is zero evidence for it, and piles against it. For example, one doesn’t have to change the quark masses by very much to obliterate nuclear binding. No nuclei. No atoms. No chemistry. No periodic table. No stars. No planets. Just hydrogen gas. These calculations have been done, for example “Constraints on the variability of quark masses from nuclear binding” by Damour and Donoghue. If they are wrong, then write a paper about it and send it to Physical Review D. Possibilities are cheap.

Of course, when Geraint Lewis and I publish our fine-tuning book, all this will be sorted out once and for all, bringing fame and fortune and a movie deal. Editing continues, so stay tuned.

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