How to overhype a science press release

From the Sydney Morning Herald (here):

Melbourne researchers rewrite Big Bang theory

Melbourne researchers believe they may be on the brink of rewriting the history of the universe.

A paper being published in a US physics journal suggests it may be possible to view “cracks” in the universe that would support the theory of quantum graphity – considered to be the holy grail of physics.

The team of researchers from the University of Melbourne and RMIT say that, instead of thinking of the start of the universe as being a big bang, we should imagine it as a cooling of water into ice.

… Their research rests on a school of thought that has emerged recently to suggest space is made of indivisible building blocks, such as atoms, that can be thought of as similar to pixels that make up images on a computer screen.

Mr Quach said the standing model for the origins of the universe, the big bang, needed to be rewritten. He hoped experimentalists would be able to find evidence to support the theory put forward by the Melbourne team of researchers, that would replace it. ”The biggest problem with the big bang model is the bang itself,” Mr Quach said. …

Mr Quach and his fellow researchers theorise that if quantum graphity “cracks” do exist, they will bend or reflect light, which, if observed through a telescope would support their predictions.
“If they prove my predictions that’s really good evidence for the condensed matter model of quantum graphity in which case you can throw out all the other attempts.”

Here’s a few pointers for the layman trying to decipher this article.

• Note how the claim of the title changes. “They’ve rewritten the big bang theory” becomes “they believe they’re about to rewrite the big bang theory” becomes “it may be possible to observe the consequences of a theory that might provide a model for the big bang”.
• The name “quantum graphity” is a pun on the terms quantum gravity and graph theory [edit: 1/9/2012]. Quantum gravity is the “holy grail” of physics (to some). Quantum graphity is not. The journalist evidently didn’t get the pun.
• Note that the article quotes Mr Quach. Not Dr or Professor. I love grad students, but claims that they are about to rewrite everything we know about the fundamental laws of nature and the entire history of the universe should be taken with a grain of salt.
• The paper that the article refers to contains no cosmology. It doesn’t claim to. None of Mr Quach’s papers do. What the paper shows is that, if spacetime consists of these building blocks, and the blocks get put together imperfectly, then light will scatter of the imperfection. The paper concludes: “they produce intriguing scattering, double imaging, and gravitational lensing-like effects. Importantly this serves as a framework in which observable consequences of the QG model may allow it to be tested.”
• It is difficult to express just how astronomically huge the “if” is in the sentence “if observed through a telescope”.  What observational signature should we be looking for? There are an awful lot of things in the universe that bend and deflect light. How would we distinguish between the observation of a graphity imperfection and other gravitational lenses? What unique predictions does the model provide? How many imperfections should we expect in the universe?  What astronomical targets should we aim at?
• This idea isn’t new. The further we look in the universe, the more likely we are to see something funky along the way, so distant quasars have been used to test theories about interesting spacetime phenomena. So far: nothing. No evidence for quantum foam. No evidence for cosmic strings. No topological defects. Why would graphity defects be any different?

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The Traps of WAP and SAP

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:

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James Jeans and our finite universe(?)

“Leave only three wasps alive in the whole of Europe and the air of Europe will still be more crowded with wasps than space is with stars, at any rate in those parts of the universe with which we are acquainted.”

I love a good illustration.

For whatever reason, I’m drawn to old popular-level science books. I just finished reading “The Stars in Their Courses” by James Jeans, first published in 1931. Jeans is best known in my field for the “Jeans length”. Suppose a cloud of gas is trying to collapse under its own gravity, but is being held back by gas pressure. Jeans showed that there is a critical length scale, such that if the object is smaller than the Jeans length then pressure wins and the cloud is stable, but if it is larger then gravity wins and collapse ensues.

Jeans gives an overview of all of the astronomy of his day. It’s mostly familiar material, of course; the interesting bit is the glimpse inside the mind of the great scientist. Here’s a neat illustration:

“If we could take an ordinary shilling out of our pocket, and heat it up to the temperature of the sun’s centre [40 million kelvin], its heat would shrivel up every living thing within thousands of miles of it.”

Repeating this calculation, I think Jeans is reasoning as follows. A shilling is about 5 grams of copper (specific heat capacity 0.385 J/gram/kelvin), and so at 40,000,000 K we have about J of energy. This is ‘only’ 20 kg of TNT – most bombs are at least a tonne of TNT equivalent, and they don’t do miles of damage. That much energy could raise the temperature of the surrounding air to boiling point for about a 10 metre radius. Not too promising. However, the coin will be emitting thermal radiation at x-ray wavelengths. A lethal dose of x-rays is about 5 J/kg, so our coin has enough energy to kill about 100,000 people. One must factor in the fraction of energy emitted horizontally, the fraction absorbed by biological material, the cooling of the coin, etc, but certainly it’s a very dangerous coin.

Jeans’ views on cosmology are very revealing. He is writing within 5 years of the discovery of the expansion of the universe by Lemaitre (first!) and Hubble. Jeans says:

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Book Review: The Cosmic Landscape by Leonard Susskind (Part 1)

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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“If you don’t want to explain things, then you’re a moron”

I love David Mitchell. I love everything he’s done – Peep Show, Would I Lie to You, That Mitchell and Webb Look, Sound and Book, his work on QI, Mock the Week and any other panel show, Soapbox, and various articles. I was listening to a conversation with Mr Mitchell on CarPool with Robert Llewellyn of ‘Red Dwarf’ fame. He started talking about his time spent studying history at Cambridge, and why it interested him:

If you don’t want to explain things, then you’re a moron. As far as I’m concerned, trying to explain things through what the molecules people and things are made up of, or the chemicals and how they react to each other, is an incredibly roundabout way. You know, I don’t want to know that. I assume that will keep going whether or not I understand it. I want to know why we are in a country called Britain, why are these people in charge. That seems to me to be the direct way of generally explaining things. Obviously, I’ve got a lot of time for the scientific urge to explain. But for me, that’s always been a bit secondary to specifically explaining “what’s this stuff, and don’t tell me what it is at a subatomic level!”

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Dear Peter Coles …

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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Internet Finds of the “Week”

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 here: Plan 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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Lemaître Beats Hubble!

Today’s arxiv find is a historical fact that I really should have known by now. From “The linear redshift-distance relationship: Lemaître beats Hubble by two years“:

The facts are simple: Friedman (1922) was the first to publish non- static solutions to Einstein’s field equations. However, he did not extend that into a cosmological model built on astronomical observations. In 1927 Lemaître rediscovered these dynamical solutions. In the same publication he extracted (on theoretical grounds) the linear velocity–distance relationship v=Hr. Combining redshifts published by Stromberg (1925) (who relied mostly on redshifts from Slipher (e.g. Slipher 1917)) and Hubble’s distances via magnitudes (Hubble 1926), he calculated for the “Hubble constant” two values, 575 and 670 km/sec/Mpc depending on how the data is grouped. For Lemaître these results showed that the Universe was expanding. Two years later Hubble found the same velocity–distance relationship v=Hr on observational grounds from practically the same observations that Lemaître used in 1927. However, Hubble does not credit anyone for the redshifts, most of which again came from Slipher.

Why is this not more widely known? In 1931, Lemaître’s paper was translated into English with the help of Eddington, but  ”the two pages from the 1927 paper that contain Lemaître’s estimates of the Hubble Constant are not in the 1931 MNRAS paper”.

The standard story is that Friedman discovered the equations. Lemaître rediscovered the equations and promoted them. Hubble used Slipher’s observations to show that the expansion predicted by the equations was actually true. It seems that Lemaître did it all! And, according to Wikipedia, was one of the inventors of the Fast Fourier Transform.

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Of Nothing

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.

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Dark Matter Defended

A great post on Dark Matter over at Cosmic Variance by Sean Carroll. It’s also an interesting case study in science in the media, and the problem of the catchy headline.

The most interesting part for me was Sean’s case for MOND being ugly. To my mind, this is enough to rule out MOND even if it explained the data as well as dark matter. It’s more than just Ockham’s razor – nature has taught us to look not just for simplicity, but for elegance and beauty. General relativity, for example, perhaps isn’t particularly simple, but it is beautiful. Beauty in mathematics is one thing, but one of the great pleasures of physics is to bask in the thought: “I can’t believe that this actually describes the universe!”

Beauty in physical theories is such a difficult thing to define, especially to non-physicists. But in this case, MOND has clearly been dealt the wrong end of the ugly stick.

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