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Archive for the ‘cosmology’ Category

Last time, I started a review of the Carroll vs. Craig debate with a (mostly historical) overview of the back-and-forth about the beginning of the universe for the last 90 years of modern cosmology. Here, I’ll have a look at fine-tuning. I should start by saying how much I enjoyed the debate. They should do it again some time.

In his speeches, Sean Carroll raised five points (transcript) against the fine-tuning of the universe for intelligent life as an argument for the existence of God. I want to have a look at those five. Carroll (here) and Craig (here, here and here) had a few points to make post-debate, too.

Here is fine-tuning reply number one:

First, I am by no means convinced that there is a fine-tuning problem and, again, Dr. Craig offered no evidence for it. It is certainly true that if you change the parameters of nature our local conditions that we observe around us would change by a lot. I grant that quickly. I do not grant therefore life could not exist. I will start granting that once someone tells me the conditions under which life can exist. What is the definition of life, for example? If it’s just information processing, thinking or something like that, there’s a huge panoply of possibilities. They sound very “science fiction-y” but then again you’re the one who is changing the parameters of the universe. The results are going to sound like they come from a science fiction novel. Sadly, we just don’t know whether life could exist if the conditions of our universe were very different because we only see the universe that we see.

“Interesting” Games

Is the debate over the definition of life a problem for fine-tuning? Sean and I had a brief discussion on this point during my talk at the UCSC Summer School on Philosophy of Cosmology. My response was (roughly) as follows.

Consider chess. In particular, I’m wondering whether minor changes to the laws of chess would result in a similarly interesting game. Wait a minute, you say, you haven’t defined “interesting”. In fact, different people are going to come up with different definitions of interesting. So how can we know whether a game is interesting or not?

It’s a good point, but instead of considering this question in abstract, consider this particular example. Change one word in the rules of chess: instead of “Knights may jump over other pieces”, we propose that “Bishops may jump over other pieces”. If we were to rewrite the 530 page “Silman’s Complete Endgame Course“, we would need just one page, one paragraph, two sentences: “White bishop moves from f1 to b5. Checkmate.”

Chess2

My claim is that this particular case is so clear that by any definition of interesting, this is not an interesting game. The game is no more interesting than tossing a coin to see who goes first. It is too simple, too easy. (more…)

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It’s been a while, but I’ve finally gotten around to jotting down a few thoughts about the Sean Carroll vs. William Lane Craig debate. I previewed the debate here (part one, two, three, four). I thoroughly enjoyed the debate. Future posts will discuss a few of the philosophical questions raised by the debate, but I’ll briefly discuss some of the science in this point. (I didn’t manage to record my talk a few weeks ago, but this post summarises it.)

Firstly, I want to refer you to the much greater expertise of Aron Wall of UC Santa Barbara. I’ll list them all because they’re great.

(I’m on the “astrophysics” end of cosmology. The beginning of the universe probes the “particle and plasma and quantum gravity and beyond” end of cosmology. I know the field, but not as well as someone like Wall or Carroll.)

No one expects the beginning of the universe!

Regarding the scientific question of the beginning of the universe, here is how I see the state of play. Cosmologist don’t try to put a beginning into their models. For the longest time, even theists who believed that the universe had a beginning acknowledged that the universe shows no sign of such a beginning. We see cycles in nature – the stars go round, the sun goes round, the planets go round, the seasons go around, generations come and go. “There is nothing new under the sun”, says the Teacher in Ecclesiastes. Aristotle argued that the universe is eternal. Aquinas argued that we cannot know that the world had a beginning from the appearance of the universe, but only by revelation.

So when a cosmic beginning first raised its head in cosmology, it was a shock to the system. Interestingly, theists didn’t immediately jump on the beginning as an argument for God. Lemaître, one of the fathers of the Big Bang theory and a priest, said:

“As far as I can see, such a theory [big bang] remains entirely outside any metaphysical or religious question.”

In 1951, Pope Pius XII declared that Lemaître’s theory provided a scientific validation for existence of God and Catholicism. However, Lemaître resented the Pope’s proclamation. He persuaded the Pope to stop making proclamations about cosmology.

The philosophical defence of the argument from the beginning of the universe to God (the Kalam cosmological argument) starts essentially with Craig himself in 1979, half a century after the Big Bang theory is born.

In fact, the more immediate response came from atheist cosmologists, who were keen to remove the beginning. Fred Hoyle devised the steady state theory to try to remove the beginning from cosmology, noting that:

“… big bang theory requires a recent origin of the Universe that openly invites the concept of creation”. His steady-state theory was attacked “because we were touching on issues that threatened the theological culture on which western civilisation was founded.” (quoted in Holder).

Tipping the Scales

But what of the beginning in the Big Bang model? Singularities in general relativity weren’t taken seriously at first. Einstein never believed in the singularities in black holes. Singularities were believed to be the result of an unphysical assumption of perfect spherical symmetry. In Newtonian gravity, a perfectly spherical, pressure-free static sphere will collapse to a singularity of infinite density. However, this is avoided by the slightest perturbation of the sphere, or by the presence of pressure. A realistic Newtonian ball of gas won’t form a singularity, and the same was assumed of Einstein’s theory of gravity (General Relativity).

The next 80 years of cosmology sees the scales tipping back and forth, for and against the beginning. (more…)

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I’ve been a bit quiet around here, lately. Travel is my excuse. I’m currently in Cambridge, collaborating with a few colleagues on a project. I’ll be back in Sydney next week, so if you’re near Epping on Friday 4th July 2014, why not come along to hear me speak at the Astronomical Society of NSW:

“What Happened at the Big Bang?”

Friday 4th July 2014 – 8:00pm
Topic: What happened at the Big Bang?
Speaker: Dr Luke Barnes, University of Sydney
Venue: Epping Creative Centre – 26 Stanley Road, Epping

Abstract:
Was the big bang the beginning of the universe? Does the big bang represent the beginning of time itself? This is an age-old question, and has been remarkably informed by modern cosmology.

I will answer this question once and for all.

I will follow the theorems, evidence and hints that lead us back in time. In particular, I will discuss the expansion of the space, the physics of the very early universe, the recent BICEP2 results and cosmic inflation, the effect of quantum physics, and the reason (or one of them) why Stephen Hawking is famous.

Biography:
Dr Luke A. Barnes is a postdoctoral researcher at the Sydney Institute for Astronomy. After undergraduate studies at the University of Sydney, Dr. Barnes earned a scholarship to complete a PhD at the University of Cambridge. He worked as a researcher at the Swiss Federal Institute of Technology (ETH), before returning to Sydney in 2011. He has published papers on galaxy formation and cosmology, and recently has taken an interest in the fine-tuning of the universe for intelligent life. He blogs at letterstonature.wordpress.com.

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The Conversation has published an article of mine, co-authored with Geraint Lewis, titled “Have cosmologists lost their minds in the multiverse?“. It’s a quick introduction to the multiverse in light of the recent BICEP2 results. Comments welcome!

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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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More on the upcoming Carroll vs. Craig dialogue (previously, one, two, three). I have some leftover business from my previous post on the contingency argument for the existence of God. It concerns the question why is there something something rather than nothing?, a question I’ve discussed on a few previous occasions.

The Question

The question “why is there something something rather than nothing?” is not an argument, obviously. It’s a question. It’s relationship to the cosmological argument for the existence for God is as an entree, a taster. It’s supposed to get you thinking about existence.

Imagine two parties. At one is everything that actually exists (or has existed) – the “actual” party. At the other, everything that could exist – the “possible” party. Horses are at both parties, unicorns only the possible party. Why? Because of something at the actual party, in this case the evolutionary ancestors of the horse. When something moves from possible to actual, it’s because of an invitation from the actual party. Those in the possible party can’t crash the actual party. They don’t exist, and so don’t have any causal powers, so can’t make anything actually happen.

So this actual party – did everyone get their invitation off someone else? Is there an infinite regress of inviters? It can’t form a loop – I invite you and you invite me – because that’s just crashing the party. Could there be a party where everyone must be invited by someone who’s already there? Why is anyone at the party? Why does anything exist?

Not the Question

Aside: The question is not: “something came from nothing. How could that happen?”, to which the answer is supposedly: because God can make something out of nothing. That confuses the contingency argument with the Kalam argument. The question is “Why is there something rather than nothing?”. The answer is: God is a necessary being, so it is not possible for there to be nothing. God must exist.

Nothing, Naturally

Carroll discusses the question “why is there something rather than nothing?” in this blog post. Amongst other things, he discusses the claim that “nothingness is uniquely natural”, so that we need some special reason why something exists. He argues that we have no basis for such a conclusion, as our intuitions for naturalness and simplicity are based on our experience in this world, and so don’t automatically apply to the universe itself.

However, most versions of the cosmological argument don’t explicitly appeal to the naturalness of nothing. Carroll, following Grunbaum, discusses Swinburne. In Grunbaum’s paper “Why is There a World AT ALL, Rather Than Just Nothing?”, he quotes Swinburne: “It remains to me, as to so many who have thought about the matter, a source of extreme puzzlement that there should exist anything at all” (pg. 336). I think, however, they’ve missed the point of what Swinburne is saying. (I say this with some trepidation. Grunbaum is a professional philosopher, and something of a legend. Fools rush in …) (more…)

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I don’t know who Rob Sheldon is, but he doesn’t know much about cosmology. He recently was quoted in this post at uncommondescent.com regarding the geometry of the universe. If I lecture cosmology this year, I’ll set this passage as an assignment: find all the mistakes. It gets more wrong than right. I have an article for “Australian Physics” on common questions about cosmology that I’ll post here once it’s out (a fortnight, maybe). In the meantime, I’ll try to clear up a few things.

The discussion of the mathematics of curvature (flat, positive, negative) is about right. It’s when he discusses the universe that things go wrong.

It takes a lot of effort to find any curvature at all, and certainly it is difficult to get good agreement between different types of measurement.

Nope. That’s why it’s called the “concordance model of cosmology” – because the different measurements converge on the same set of cosmological parameters. For example, this plot.

… a “closed” universe that collapses back down to itself …

A common error. In a matter and radiation-only universe, closed implies collapsing. A cosmological constant and/or dark energy changes this: closed vs. open no longer divides collapse vs. expand forever. Here is the plot you’ll need, from John Peacock’s marvellous Cosmological Physics.

… one would like it to have positive curvature to avoid infinities …

Flat and negatively curved universes can be finite. A flat 3-torus, for example, is finite, unbounded and has a flat geometry. Einstein’s general relativity constrains the geometry of the universe but not its topology. (more…)

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