Posts Tagged ‘cosmology’

Front Cover of Australian PhysicsMy article “Cosmology Q & A” has been published! It appeared in the magazine Australian Physics, 51 (2014) 42-6 and is reproduced here with permission. After a brief overview of modern cosmology, it (tries to) answer the following questions:

  1. Is space expanding, or are galaxies just moving away from us?
  2. Is everything getting bigger?
  3. Ordinary matter and radiation cause the expansion of the universe to decelerate. But our universe is accelerating! How? What is the universe made of?
  4. Dark Energy? Is that like Dark Matter?
  5. How big is the universe?
  6. How big is the universe really?
  7. If the universe were finite, could I see the back of my own head?
  8. Is space expanding faster than the speed of light?
  9. Are there galaxies moving away from us at more than the speed of light?
  10. Light from distant galaxies is observed to be redshifted. Is this because the expansion of space stretches the wavelength, or because is it a Doppler shift due to the recession of the galaxy?
  11. Does the universe have zero total energy?
  12. Energy is not conserved!? Shouldn’t that send shivers up the spine of any physicist?
  13. The very universe, we are told, began in thermal equilibrium. How did equilibrium establish itself so quickly?
  14. How does the initially smooth universe we see in the CMB become today’s universe of stars and galaxies?

As before, further questions in the comments are always welcome.


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I’ve invited cosmology questions before, but I wanted to renew the call. I’ve got a Q&A article on cosmology coming out soon, so ask away!

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On February 21-22 (2014), Sean Carroll and William Lane Craig will debate at the Greer-Heard Forum, at the New Orleans Baptist Theological Seminary. The topic is “God and Cosmology: The Existence of God in Light of Contemporary Cosmology”. For a number of reasons, I have high hopes for this one. Here’s why.

I (mostly) like the format

We start with a dialogue between the two parties, for 1.5 hours. As a spectator, I prefer the debate format. While a dialogue sounds like a friendly chat rather than a confrontation, in practice it unfairly unfavors the rude and the loud. We are at the mercy of the disciplinary skill of the moderator. However, this one shouldn’t be too bad. Craig will let his opponent talk, and I get the same impression from Carroll.

Given the list of things I’d like them to discuss, as I’ll discuss in future posts, I’m hoping that each party gets an opening statement of at least 20 minutes. They both have a lot to say about this topic, and need the time to present their case thoroughly.

The next day we’re back with 4 speakers, each with an hour that includes responses from Carroll and Craig. That’s a very interesting arrangement and I’m keen to see how it works in practice. The day rounds out with concluding comments from the two debaters.

Good choice of debaters

I’ve listened to a number of William Lane Craig’s debates and the best ones are usually against other philosophers, for this reason. The topic is God, or at least something closely related to the almighty. In any argument for or against the existence of God, at least one of the premises must be metaphysical. So against, say, a scientist, Craig can absorb a lot of the scientific expertise of his opponent and focus on the (often unstated) philosophical assumptions behind their remarks. The debate moves to matters philosophical, which gives Craig the home advantage. Some of Craig’s opponents know less than nothing about philosophy; what they think they know about philosophy is wrong. On the other hand, Craig knows enough of the science that is relevant to his arguments to be able to defend the scientific premises against a philosopher.

Carroll has an undergraduate philosophy minor and as a grad student in astrophysics at Harvard, sat in on courses with John Rawls and Robert Nozick. His blog posts and articles show a familiarity with and respect for philosophical issues. Carroll is close to the ideal opponent for this debate, as he should be able to hold his own on matters philosophical, whilst holding a substantial advantage on matters cosmological.

Good Choice of Respondents

I’m guessing that Craig will defend three of his usual five arguments – the Kalam cosmological argument from the beginning of the universe, the contingency argument, and the design argument from the fine-tuning of the universe for intelligent life. The contingency argument doesn’t rely on any particular scientific theories, so Craig doesn’t need any particular backup on that front. For the Kalam cosmological argument, his scientific case for the premise “the universe has a beginning” has been provided in recent times by James Sinclair. In particular, Craig’s most sophisticated defence of the argument in recent times is in the The Blackwell Companion to Natural Theology, which was co-written with Sinclair. Sinclair is a Warfare Analyst with a masters in cosmology, so his credentials are slightly unorthodox.

Also writing in the The Blackwell Companion to Natural Theology is Robin Collins, a philosopher with a background in physics. He has specialised in the argument from the fine-tuning of the universe for intelligent life. So that gives Craig his backup for his third argument.

Carroll has two philosophers in tow. Alex Rosenberg is a philosopher at Duke University who Craig has debated before, and whose book “The Atheist’s Guide to Reality” was praised by both sides of the debate as seeing rather clearly the consequences of atheism. Tim Maudlin is a philosopher of science at New York University. His book “Philosophy of Physics: Space and Time” is marvellous. He also seems to have taken an interest in the fine-tuning of the universe for intelligent life. (I have a few reservations about his opinions on that topic.)

That’s an interesting line up. I’d gladly hear any of them speak on the topic at hand; all four of them in a row with responses from Carroll and Craig is very promising.

My advice

I think this debate could be uniquely insightful on this important topic. Craig has said an awful lot about cosmology in recent years, and no one has really pressed him on the details. They’ve mostly (though not unreasonably) appealed to cosmological authorities. (For the love of Pete, nobody read out an email from Alex Vilenkin. More on that soon.) Carroll has said a lot about the implications of cosmology for theism, and there are some philosophical niceties to be examined there as well. Stay tuned for parts two, three, and four.

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I’m going to jump back on one of my favourite high horses. I’ve previously blogged about Lawrence Krauss and his views on the question “why is there something rather than nothing?”. I’ve just finished his book, and he appeared last night on an Australian TV show called Q&A. It was a good panel discussion, but as usual the show invites too many people and tries to discuss too much so there is always too little time. Krauss’ discussions with John Dickson were quite interesting.

I’ll be discussing the book in more detail in future, but listening to Krauss crystallised in my mind why I believe that science in principle cannot explain why anything exists.

Let me clear about one thing before I start. I say all of this as a professional scientist, as a cosmologist. I am in the same field as Krauss. This is not an antiscience rant. I am commenting on my own field.

Firstly, the question “why is there something rather than nothing?” is equivalent to the question “why does anything at all exist?”. However, Krauss et al have decided to creatively redefine nothing (with no mandate from science – more on that in a later post) so that the question becomes more like “why is there a universe rather than a quantum space time foam?”. So I’ll focus on the second formulation, since it is immune to such equivocations.

Here is my argument.
A: The state of physics at any time can be (roughly) summarised by three things.

1. A statement about what the fundamental constituents of physical reality are and what their properties are.
2. A set of mathematical equations describing how these entities change, move, interact and rearrange.
3. A compilation of experimental and observational data.

In short, the stuff, the laws and the data.

B: None of these, and no combination of these, can answer the question “why does anything at all exist?”.

C: Thus physics cannot answer the question “why does anything at all exist?”.

Let’s have a closer look at the premises. I’m echoing here the argument of David Albert in his review of Krauss’ book, which I thoroughly recommend. Albert says,

[W]hat the fundamental laws of nature are about, and all the fundamental laws of nature are about, and all there is for the fundamental laws of nature to be about, insofar as physics has ever been able to imagine, is how that elementary stuff is arranged. (more…)

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“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 8 \times 10^7 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: (more…)

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I’m back enjoying the Cambridge life for a fortnight, and already have some cricket lined up. Some comments from a previous post got me thinking …

Cosmic Variance recently polled its readers on what got them interested in science. The most common answer was popular science books, and this was certainly true for me. I discovered the nerdy pleasures of a good book on physics as I finished high school, and still enjoy such books today. Below is a list of some of my favourite cosmology and physics books for the interested layperson, organised alphabetically by author. I obviously don’t agree with everything written in these books, but they all presented the science accurately (to the best of my knowledge) and were thoroughly entertaining.

John Barrow: I’ve read and greatly enjoyed many of Barrow’s writings – New Theories of Everything, Between Inner and Outer Space, Impossibility, Pi in the Sky, The Book of Nothing, The Infinite Book, The Anthropic Principle. He combines mathematics and science seamlessly, loves a good historical anecdote or illustration, and isn’t afraid to wander into regions metaphysical. I think that my personal favourite was “Pi in the Sky”, which was my first introduction to the mind-blowing legacy of Kurt Godel. “New theories of everything” is a great introduction to modern physics and cosmology.

Paul Davies: As with Barrow, I haven’t met a Davies book I haven’t enjoyed – God and the New Physics, The Matter Myth, The Mind of God, The Last Three Minutes, The Goldilocks Enigma. A Davies book will always be wide ranging, from pure mathematics to cosmology to physics to biology. His forays into philosophy are thoughtful, even if I don’t always agree. I’d start with “The Goldilocks enigma” – it’s nominally about the fine-tuning of the universe for intelligent life but gives a very good introduction to modern cosmology and physics along the way. (more…)

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[Edit, 4/2/2012: I’ve written a more complete critique of Stenger’s book The Fallacy of Fine-Tuning: Why the Universe Is Not Designed for Us. It’s posted on Arxiv. In particular, the program MonkeyGod is critiqued in Appendix B; most of the points raised below remain valid.]

This post is the second critiquing Victor Stenger’s take on the fine-tuning of the universe for intelligent life. Here are some more of Stenger’s claims. (The quotes below are an amalgam of the articles on this page.)

I think it is safe to conclude that the conditions for the appearance of a universe with life are not so improbable as the those authors, enamored by the anthropic principle, would have you think … [T]here could be many ways to produce a universe old enough to have some form of life.

How does Stenger reach this conclusion?

I have written a program, MonkeyGod … I have studied how the minimum lifetime of a typical star depends on three parameters: the masses of the proton and electron and the strength of the electromagnetic force. (The strong interaction strength does not enter into this calculation.) Varying these parameters by ten orders of magnitude around their present values, I find that over half of the stars will have lifetimes exceeding a billion years, allowing sufficient time for some kind of life to evolve. Long stellar lifetime is not the only requirement for life, but it certainly is not an unusual property of universes. (more…)

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Today I’ll be looking at a paper on the fine-tuning of the universe by Professor Fred Adams. He is professor of physics at the University of Michigan, where his main field of research is astrophysical theory focusing on star formation, background radiation fields, and the early universe.

Fred Adams published a paper in 2008 entitled “Stars In Other Universes: Stellar structure with different fundamental constants”. The paper garnered some interest from the science blogosphere and popular science magazines. Here are the relevant parts of the abstract:

Motivated by the possible existence of other universes, with possible variations in the laws of physics, this paper explores the parameter space of fundamental constants that allows for the existence of stars. To make this problem tractable, we develop a semi-analytical stellar structure model. [We vary] the gravitational constant G, the fine structure constant $\latex alpha$, and a composite parameter C that determines nuclear reaction rates. Our main finding is that a sizable fraction of the parameter space (roughly one fourth) provides the values necessary for stellar objects to operate through sustained nuclear fusion. As a result, the set of parameters necessary to support stars are not particularly rare.


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I’ve elsewhere described my views on the so-called fine-tuning of the universe for intelligent life. In the course of preparing that talk, I read some internet articles that were rather woeful. It’s time to quote John Leslie again: “The ways in which ‘anthropic’ reasoning can be misunderstood form a long and dreary list”.

My first target is Dr Hugh Ross. Ross was a postdoctoral research fellow in astronomy at Caltech before founding Reasons to Believe, a Christian ministry that aims to “show that science and faith are, and always will be, allies, not enemies”. (more…)

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We can’t let the official “switch-on” of the Large Hadron Collider (LHC) pass without comment. The goal of the LHC is to find the Higgs Boson, the last particle of the standard model of particle physics (“the standard model”) that has yet to appear in the debris of a collision in a particle accelerator. The standard model is a phenomenally successful theory – the existence and properties of the menagerie of particles that emerge from particle accelerators can be predicted with astonishing accuracy, using mathematical equations.

If the Higgs Boson is found, it will join the other successful predictions of modern physics. The fact that successful predictions are commonplace makes it easy to overlook the astonishing fact that mathematical equations and physical reality are somehow intertwined. Paul Davies, in his book “The Goldilocks Enigma” remembers sitting in his school library, using Newton’s laws to predict how far away a ball thrown on sloping ground will land. A girl he had taken a fancy to asked what he was doing. He explained. She was skeptical: “how can you possibly know what a ball will do by writing things on a sheet of paper?”


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