Archive for the ‘fine tuning’ Category

Let’s begin by quoting from Radford Neal:

There is a large literature on the Anthropic Principle, much of it too confused to address.

I’ve previously quoted John Leslie:

The ways in which ‘anthropic’ reasoning can be misunderstood form a long and dreary list.

My goal in this post is to go back to the original sources to try to understand the anthropic principle.

Carter’s WAP

Let’s start with the definitions given by Brandon Carter in the original anthropic principle paper:

Weak Anthropic Principle (WAP): We must be prepared to take account of the fact that our location in the universe is necessarily privileged to the extent of being compatible with our existence as observers.

Carter’s illustration of WAP is the key to understanding what he means. Carter considers the following coincidence: (more…)

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I recently posted on Arxiv a paper titled “The Fine-Tuning of the Universe for Intelligent Life”. A slightly shortened version has been accepted for publication in Publications of the Astronomical Society of Australia. The paper is primarily a review of the scientific literature, but uses as a foil Victor Stenger’s recent book “The Fallacy of Fine-Tuning: Why the Universe Is Not Designed for Us” (FoFT). Stenger has since replied to my criticisms. The following is my reply to his reply to my article criticising his book which criticises fine-tuning. Everybody got that?

A few points before I get into details:

  • There isn’t much in this post that wasn’t in my original article. I write this to summarise the important bits.
  • “Barnes does not challenge my basic conclusions.” Not even close. Re-read.
  • “Barnes seems to want me to reduce this to maybe 1-5 percent.” Nope. I didn’t say or imply such a figure anywhere in my article. On the contrary, the cosmological constant alone gives 10^{-120}. The Higgs vev is fine-tuned to 10^{-17}. The triple alpha process plausibly puts constraints of order 10^{-5} on the fine-structure constant. The “famous fine-tuning problem” of inflation is 10^{-11} (Turok, 2002). The fine-tuning implied by entropy is 1 in 10^{10^{123}} according to Penrose. For more examples, see my article. Or just pull a number out of nowhere and attribute it to me.
  • “He fails to explain why my simplifications are inadequate for my purposes.” Red herring. My issue is not oversimplification. I do not criticise the level of sophistication of Stenger’s arguments (with one exception – see my discussion of entropy in cosmology below). Stenger’s arguments do not fail for a lack of technical precision. Neither does the technical level of my arguments render them “irrelevant”.

Point of View Invariance (PoVI)

A major claim of my response (Section 4.1) to FoFT is that Stenger equivocates on the terms symmetry and PoVI. They are not synonymous. For example, in Lagrangian dynamics, PoVI is a feature of the entire Lagrangian formalism and holds for any Lagrangian and any (sufficiently smooth) coordinate transformation. A symmetry is a property of a particular Lagrangian, and is associated with a particular (family of) coordinate transformation. All Lagrangians are POVI, but only certain, special Lagrangians – and thus only certain, special physical systems – are symmetric. Stenger replies:

“PoVI is a necessary principle, but it does not by itself determine all the laws of physics. There are choices of what transformations are considered and any models developed must be tested against the data. However, it is well established, and certainly not my creation, that conservation principles and much more follow from symmetry principles.”

Note how a discussion of PoVI segues into a discussion of symmetry with no attempt to justify treating the two as synonymous, or giving an argument for why one follows from the other.

Of course conservation principles follow from symmetry principles – that’s Noether’s theorem. It’s perfectly true that “if [physicists] are to maintain the notion that there is no special point in space, then they can’t suggest a model that violates momentum conservation”. The issue is not the truth of the conditional, but the necessary truth of the antecedent. Physicists are not free to propose a model which is time-translation invariant and fails to conserve energy1. But we are free to propose a model that isn’t time-translation invariant without fear of subjectivity.

And we have! Stenger says: “But no physicist is going to propose a model that depends on his location and his point of view.” This is precisely what cosmologists have been doing since 1922. The Lagrangian that best describes the observable universe as a whole is not time-translation invariant. It’s right there in the Robertson-Walker metric: a(t). The predictions of the model depend on the time at which the universe is observed, and thus the universe does not conserve energy. Neither does it wallow in subjectivity.

Watch closely as Stenger gives the whole game away: (more…)

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I’m a great fan a popular science books, particularly when the topic is cosmology or fundamental physics. Susskind’s “The Cosmic Landscape” was particularly enjoyable, though I will take issue with a few things in later posts. For now, here are a few highlights:

I love a good illustration:

A rocket-propelled lemon moving away from you might have the color of an orange or even a tomato if it were going fast enough. While its moving toward you, you might mistake it for a lime.

This is simply the Doppler effect, which we’ve all observed for sound as an ambulance drives past. It works for light as well, but you have to be going close to the speed of light. Using the right formula from Einstein’s special relativity, we find that you must fire a lemon at a tenth of the speed of light to make it look red. About the same speed, but moving toward you, will make it look green.

Susskind gives an excellent account of the fine-tuning of the universe for intelligent life.

[T]he Laws of Physics may not only be variable but are almost always deadly. In a sense the laws of nature are like East Coast weather: tremendously variable, almost always awful, but on rare occasions, perfectly lovely. … One theme has threaded its way through our long and winding tour from Feynman diagrams to bubbling universes: our own universe is an extraordinary place that appears to be fantastically well designed for our own existence. This specialness is not something that we can attribute to lucky accidents, which is far too unlikely. The apparent coincidences cry out for an explanation.

In particular, he takes the discussion to the cutting edge of particle physics, discussing the gauge hierarchy problem:

Physicists puzzled for some time about why the top-quark is so heavy, but recently we have come to understand that it’s not the top-quark that is abnormal: it’s the up- and down-quarks that 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. Thus, we can ask what the world would be like is the up- and down-quarks were much heavier than they are. Once again – disaster!

… the cosmological constant problem:

Throughout the years many people, including some of the illustrious names in physics, have tried to explain why the cosmological constant is small or zero. The overwhelming consensus is that these attempts have not been successful.

… fine-tuning of cosmic inflation needed to give the universe the right amount of lumpiness:

A lumpiness of about 10^-5 is essential for life to get a start. But is it easy to arrange this amount of density contrast? The answer is most decidedly no! The various parameters governing the inflating universe must be chosen with great care in order to get the desired result.

… and even supersymmetry:

The biggest threat to life in an exactly supersymmetric universe [has to do] with chemistry. In a supersymmetric universe every fermion has a boson partner with exactly the same mass, and therein lies the trouble. The culprits are the supersymmetric partners of the electron and the photon. These two particles, called the selectron (ugh!) and the photino, conspire to destroy all ordinary atoms. … in a supersymmetric world, an outer electron can emit a photino and turn into a selectron. … That’s a big problem: the selectron, being a boson, is not blocked (by the Pauli exclusion principle) from dropping down to lower energy orbits near the nucleus. … Goodbye to the chemical properties of carbon – and every other molecule needed by life.

Susskind is also clear to distinguish between the landscape of string theory and a multiverse (or megaverse):

The two concepts – Landscape and megaverse [a.k.a. multiverse] – should not be confused. The Landscape is not a real place. Think of it as a list of all the possible designs of hypothetical universes. Each valley represents one such design. … The megaverse, by contrast, is quite real. The pocket universes that fill it are actual existing places, not hypothetical possibilities.

All in all, the Susskind’s book is highly recommended.

Part 2 of my review is here.

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I was just re-reading this post over at Cosmic Variance about a paper by Sean Carroll, which he summarises as:

Our observed universe is highly non-generic, and in the past it was even more non-generic, or “finely tuned.” One way of describing this state of affairs is to say that the early universe had a very low entropy. … The basic argument is an old one, going back to Roger Penrose in the late 1970′s. The advent of inflation in the early 1980′s seemed to change things — it showed how to get a universe just like ours starting from a tiny region of space dominated by “false vacuum energy.” But a more careful analysis shows that inflation doesn’t really change the underlying problem — sure, you can get our universe if you start in the right state, but that state is even more finely-tuned than the conventional Big Bang beginning. We find that inflation is very unlikely, in the sense that a negligibly small fraction of possible universes experience a period of inflation. On the other hand, our universe is unlikely, by exactly the same criterion. So the observable universe didn’t “just happen”; it is either picked out by some general principle, perhaps something to do with the wave function of the universe, or it’s generated dynamically by some process within a larger multiverse. And inflation might end up playing a crucial role in the story. We don’t know yet, but it’s important to lay out the options to help us find our way.

It’s a very nice paper and Sean’s post is also worth a read. What I didn’t notice before was this comment from Peter Coles:

I remember having a lot of discussions with George Ellis way back in the 90s about this issue. I strongly agree that what inflation does is merely to push the fine-tuning problems back to an earlier epoch where they are effectively under the carpet (or beyond the horizon, if you prefer a different metaphor). In fact we were planning to write a sort of spoof of Galileo’s “Dialogue concerning the Two Chief World Systems” featuring characters with names like “Inflatio” and “Anthropicus” …. but never got around to it.

Dear Peter Coles, Please write that paper!!! I’ve been looking through the inflation literature lately and there seems to be an uncomfortably large portion of it devoted to propaganda, arguing that inflation is inevitable and the only possible solution to the problems of the standard hot big bang. A good example is this exchange of papers (one, two and three), where Hollands and Wald face off against Kofman, Linde, and Mukhanov on the issue of whether inflation can explain the low entropy of our universe. The question of whether inflation can be the last word in cosmology (and initial conditions) is in need of clarification.

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A few quick things from around the internet.

1. Our favourite Welsh astrophysicist and supervisor, Geraint Lewis, has been keeping himself busy. He’s appeared on Wikipedia, and even has his own blog: Cosmic Horizons. And he’s presented a lecture titled “The Life of Galaxies on ABC Radio National as part of their Music and the Cosmos event, which manages the most depressing end to a public lecture ever:

They have fuel in their cores which is slowly being used up, and eventually stars will start to turn off. Once they’ve used up all their fuel, they can’t burn any more, they will turn off, they will become black, they will emit no light. At some point in the very dim and distant future there will be one remaining star in our Milky Way galaxy, and at some point that too will run out of fuel and it will become dark and the Milky Way will enter into a night and the night will go on forever.

Well worth a listen.

2. A set of three excellent lectures on gravitational waves from Kip Thorne were delivered as the Pauli Lectures at ETH. Video and audio are available here. The first lecture was for the general public and shows some wonderful recent simulations of colliding black holes. Later lectures were more technical but no less fascinating. I’d almost forgotten how much I like General Relativity.

3. I was recently sent this and I loved it. From herePlan of the City is a new animated film, conceived and directed by Joshua Frankel, about the architecture of New York City blasting off into outer space and resettling on Mars. The film’s visuals are an animated collage combining live action footage, animated elements, illustrations and treated photographs, including photos taken by the Mars rovers Spirit and Opportunity made available to the public domain by the NASA Jet Propulsion Laboratory. Plan of the City was created in collaboration with composer Judd Greensteinand NOW Ensemble, an acclaimed “indie classical” chamber ensemble; the ensemble, including Greenstein, feature prominently in the film as live actors set inside the animated framework.

4. If you’re a sucker for punishment … I was recently invited to give four lectures on the fine-tuning of the universe for intelligent life at the St. Thomas Summer Seminar in Philosophy of Religion in Minnesota. The first and second lectures attempt to cover all of modern physics, astrophysics and cosmology in 2 hours, from the structure of atoms and molecules to planet, star and galaxy formation. The third lecture considers what would happen if we changed the laws of nature. In particular, we find that in many cases, the universe would not be able to evolve and sustain complex, intelligent life. The fourth lecture discusses the multiverse – the idea that the universe that we observe is just one of many, each different. I discuss the most popular multiverse today – the inflationary multiverse – and the challenges that the multiverse faces. The talks are on youtube.

5. Aesop himself couldn’t have invented a fable as obvious as this.

6. If you can get a hold of it, Andy Fabian has written an excellent article titled The Impact of Astronomy, which “assesses the variety and scope of the impact astronomy has on science, technology and society – and why it is so hard to measure”. It describes a number of cases in which astronomy has lead to important advances in other areas, including the development of WiFi and digital cameras.

7. Look at this! And also, a wonderful bit of Fry & Laurie.





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I’ve just finished listening to a debate between philosopher William Lane Craig and cosmologist Lawrence Krauss on the debate topic “Is there evidence for God?”. I have a load of these on my iPod – some are very good (Craig vs Austin Dacey is probably the best), while some represent 2 hours of my life that I’ll never get back. They get a bit repetitive after a while. The debate with Krauss was somewhere in the middle. Craig was polished and concise, presenting the same 5 arguments (contingency, Kalam, fine-tuning, moral, resurrection of Jesus) he’s presented for decades. Krauss was less organised and much less focussed. I’ve responded to some of Craig’s claims elsewhere. I’ll focus on some of what Krauss said.

First and foremost, I’m getting really rather sick of cosmologists talking about universes being created out of nothing. Krauss repeatedly talked about universes coming out of nothing, particles coming out of nothing, different types of nothing, nothing being unstable. This is nonsense. The word nothing is often used loosely – I have nothing in my hand, there’s nothing in the fridge etc. But the proper definition of nothing is “not anything”. Nothing is not a type of something, not a kind of thing. It is the absence of anything.

Some of the best examples of the fallacy of equivocation involve treating the word nothing as if it were a type of something:

  • Margarine is better than nothing.
  • Nothing is better than butter.
  • Thus, margarine is better than butter.

We can uncover the fallacy by simply rephrasing the premises, avoiding the word nothing:

  • It is better to have margarine than to not have anything.
  • There does not exist anything that is better than butter.

The conclusion (margarine is better than butter) does not follow from these premises.

Now let’s look at Krauss’ claims again. Does it make sense to say that there are different types of not anything? That not anything is not stable? This is bollocks. What Krauss is really talking about is the quantum vacuum. The quantum vacuum is a type of something. It has properties. It has energy, it fluctuates, it can cause the expansion of the universe to accelerate, it obeys the (highly non-trivial) equations of quantum field theory. We can describe it. We can calculate, predict and falsify its properties. The quantum vacuum is not nothing. (more…)

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This is my second critique of the work of Ikeda and Jefferys (IJ) on the fine-tuning of the universe for intelligent life. IJ insist that we must always condition on everything that we know is true. Here, I’ll raise a few case studies in need of clarification. I should warn that I’m somewhat less certain about this part than the previous one. The fog is probably in my own head.

A. Magneto saves the day

This is a variation on John Leslie’s firing squad parable. You are sitting with your grandpa on his porch. Grandpa says, “I have a confession. I’m Magneto.” You: “What? You’re one of the Xmen? You can manipulate metals at will?” Grandpa: “Yes. That’s right”. You: “Right. Sure. Prove it.”

Grandpa pulls a set of keys from his pocket and makes them levitate two inches above his hand. “Yeah, nice magic trick, Grandpa”, you say. But then, up on the hill overlooking the porch, a freight train derails! Its carriages tumble toward the house. And, just your luck, this train happened to be loaded with TNT and samurai swords. The ensuing explosion sends several tonnes of rather pointy metal hurtling towards the porch. You instinctively flinch. A few seconds later … you’re alive! You turn in shock to see that every inch of your Grandpa’s house has shards of metal sticking out of it, except for two perfect silhouettes of you and your Grandpa. He looks at you, and smiles. “Not bad, huh?”

Now, like the nerd you are (you’re reading a science-themed blog, so there’s no point denying it), you want to formalise your conclusion. (more…)

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