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Study: galactic habitable zone depends on fine-tuning of cosmological constant

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The galactic habitable zone (GHZ) is shown in green against a spiral galaxy
The galactic habitable zone (GHZ) is shown in green superimposed on a spiral galaxy

This is going to be old news to readers of this blog who are familiar with the Michael Strauss, Walter Bradley and Guillermo Gonzalez lectures on habitability and fine-tuning. But, it’s nice to see these ideas show up in one of the most prestigious peer-reviewed science journals in the world (if not the most prestigious).

Here’s the article from Science.

It says:

Scientists have known for several years now that stars, galaxies, and almost everything in the universe is moving away from us (and from everything else) at a faster and faster pace. Now, it turns out that the unknown forces behind the rate of this accelerating expansion—a mathematical value called the cosmological constant—may play a previously unexplored role in creating the right conditions for life.

That’s the conclusion of a group of physicists who studied the effects of massive cosmic explosions, called gamma ray bursts, on planets. They found that when it comes to growing life, it’s better to be far away from your neighbors—and the cosmological constant helps thin out the neighborhood.

“In dense environments, you have many explosions, and you’re too close to them,” says cosmologist and theoretical physicist Raul Jimenez of the University of Barcelona in Spain and an author on the new study. “It’s best to be in the outskirts, or in regions that have not been highly populated by small galaxies—and that’s exactly where the Milky Way is.”

Jimenez and his team had previously shown that gamma ray bursts could cause mass extinctions or make planets inhospitable to life by zapping them with radiation and destroying their ozone layer. The bursts channel the radiation into tight beams so powerful that one of them sweeping through a star system could wipe out planets in another galaxy. For their latest work, published this month in Physical Review Letters, they wanted to apply those findings on a broader scale and determine what type of universe would be most likely to support life.

The research is the latest investigation to touch on the so-called anthropic principle: the idea that in some sense the universe is tuned for the emergence of intelligent life. If the forces of nature were much stronger or weaker than physicists observe, proponents note, crucial building blocks of life—such fundamental particles, atoms, or the long-chain molecules needed for the chemistry of life—might not have formed, resulting in a sterile or even completely chaotic universe.

Basically, the best place for a galaxy that permits complex, embodied life to exist is one where you can pick up enough heavy elements from dying stars nearby, but not be in an area that is so crowded by stars that you will be murdered by intense gamma radiation when they die.

The cosmological constant has to be set just right that we spread out enough to make space between spiral arms for life-permitting solar systems, but no so spread out that we cannot pick up the heavy elements we need for a metal-rich star, a moon, and the bodies of the intelligent agents themselves.

More:

As it turns out, our universe seems to get it just about right. The existing cosmological constant means the rate of expansion is large enough that it minimizes planets’ exposure to gamma ray bursts, but small enough to form lots of hydrogen-burning stars around which life can exist. (A faster expansion rate would make it hard for gas clouds to collapse into stars.)

Jimenez says the expansion of the universe played a bigger role in creating habitable worlds than he expected. “It was surprising to me that you do need the cosmological constant to clear out the region and make it more suburbanlike,” he says.

Remember, this is only one of many characteristics that must obtain in order for a have a location in the universe that can support complex, embodied life of any conceivable kind.

Let’s review the big picture

Time for me to list out some of the things that are required for a galaxy, solar system and planet to support complex embodied life. Not just life as we know it, but life of any conceivable kind given these laws of physics.

  • a solar system with a single massive Sun than can serve as a long-lived, stable source of energy
  • a terrestrial planet (non-gaseous)
  • the planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation
  • the solar system must be placed at the right place in the galaxy – not too near dangerous radiation, but close enough to other stars to be able to absorb heavy elements after neighboring stars die
  • a moon of sufficient mass to stabilize the tilt of the planet’s rotation
  • plate tectonics
  • an oxygen-rich atmosphere
  • a sweeper planet to deflect comets, etc.
  • planetary neighbors must have non-eccentric orbits

It’s not easy to make a planet that supports life. For those who are interested in reaching out to God, he has left us an abundance of evidence for his existence – and his attention to detail.

Oh, and there’s also a circumstellar habitable zone:

Circumstellar Habitable Zone
Circumstellar Habitable Zone

And remember, these requirements for a habitable planet are downstream from the cosmic fine-tuning of constants and quantities that occurs at the Big Bang. No point in talking about the need for plate tectonics if you only have hydrogen in your universe. The habitability requirements are a further problem that comes after the fine-tuning problem.

Resources

The best book to read on this topic is “The Privileged Planet“, by Guillermo Gonzalez and Jay W. Richards. The latter is one of my absolute favorite Christian scholars, a real renaissance man. If the book is too much, there is a DVD by the same name that covers everything you need to know at a high level. Just FYI, Gonzalez made the cover of Scientific American in 2001, for his research on habitable zones. This is real evidence you can discuss with anyone, anywhere.

You can also watch the DVD for FREE on YouTube. Not sure how long that will be there. If you like it, buy the DVD, so you can show your friends.

Related posts

News

Cosmologist Luke Barnes answers 11 objections to the fine-tuning argument

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This is from the blog Common Sense Atheism.

Atheist Luke Muehlhauser interviews well-respect cosmologist Luke Barnes about the fine-tuning argument, and the naturalistic response to it.

Luke M. did a good job explaining the outline of the podcast.

Details:

In one of my funniest and most useful episodes yet, I interview astronomer Luke Barnes about the plausibility of 11 responses to the fine-tuning of the universe. Frankly, once you listen to this episode you will be better equipped to discuss fine-tuning than 90% of the people who discuss it on the internet. This episode will help clarify the thinking of anyone – including and perhaps especially professional philosophers – about the fine-tuning of the universe.

The 11 responses to fine-tuning we discuss are:

  1. “It’s just a coincidence.”
  2. “We’ve only observed one universe, and it’s got life. So as far as we know, the probability that a universe will support life is one out of one!”
  3. “However the universe was configured, evolution would have eventually found a way.”
  4. “There could be other forms of life.”
  5. “It’s impossible for life to observe a universe not fine-tuned for life.”
  6. “Maybe there are deeper laws; the universe must be this way, even though it looks like it could be other ways.”
  7. “Maybe there are bajillions of universes, and we happen to be in one of the few that supports life.”
  8. “Maybe a physics student in another universe created our universe in an attempt to design a universe that would evolve intelligent life.”
  9. “This universe with intelligent life is just as unlikely as any other universe, so what’s the big deal?”
  10. “The universe doesn’t look like it was designed for life, but rather for empty space or maybe black holes.”
  11. “Fine-tuning shows there must be an intelligent designer beyond physical reality that tuned the universe so it would produce intelligent life.”

Download CPBD episode 040 with Luke Barnes. Total time is 1:16:31.

There is a very good explanation of some of the cases of fine-tuning that I talk about most on this blog – the force of gravity, the strong force, etc. as well as many other examples. Dr. Barnes is an expert, but he is also very very easy to listen to even when talking about difficult issues. Luke M. is very likeable as the interviewer.

Polemics

Is the definition of atheism “a lack of belief in God”?

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First, let’s see check with the Stanford University Encyclopedia of Philosophy:

‘Atheism’ means the negation of theism, the denial of the existence of God.

Stanford University is one of the top 5 universities in the United States, so that’s a solid definition. To be an atheist is to be a person who makes the claim that, as a matter of FACT, there is no intelligent agent who created the universe. Atheists think that there is no God, and theists think that there is a God. Both claims are objective claims about the way the world is out there, and so both sides must furnish forth arguments and evidence as to how they are able to know what they are each claiming.

Philosopher William Lane Craig has some thoughts on atheism, atheists and lacking belief in God in this reply to a questioner.

Question:

In my discussions with atheists, they  are using the term that they “lack belief in God”. They claim that this is different from not believing in God or from saying that God does not exist. I’m not sure how to respond to this. It seems to me that its a silly word-play and is logically the same as saying that you do not believe in God.
What would be a good response to this?
Thank you for your time,

Steven

And here is Dr. Craig’s full response:

Your atheist friends are right that there is an important logical difference between believing that there is no God and not believing that there is a God.  Compare my saying, “I believe that there is no gold on Mars” with my saying “I do not believe that there is gold on Mars.”   If I have no opinion on the matter, then I do not believe that there is gold on Mars, and I do not believe that there is no gold on Mars.  There’s a difference between saying, “I do not believe (p)” and “I believe (not-p).”   Logically where you place the negation makes a world of difference.

But where your atheist friends err is in claiming that atheism involves only not believing that there is a God rather than believing that there is no God.

There’s a history behind this.  Certain atheists in the mid-twentieth century were promoting the so-called “presumption of atheism.” At face value, this would appear to be the claim that in the absence of evidence for the existence of God, we should presume that God does not exist.  Atheism is a sort of default position, and the theist bears a special burden of proof with regard to his belief that God exists.

So understood, such an alleged presumption is clearly mistaken.  For the assertion that “There is no God” is just as much a claim to knowledge as is the assertion that “There is a God.”  Therefore, the former assertion requires justification just as the latter does.  It is the agnostic who makes no knowledge claim at all with respect to God’s existence.  He confesses that he doesn’t know whether there is a God or whether there is no God.

But when you look more closely at how protagonists of the presumption of atheism used the term “atheist,” you discover that they were defining the word in a non-standard way, synonymous with “non-theist.”  So understood the term would encompass agnostics and traditional atheists, along with those who think the question meaningless (verificationists).  As Antony Flew confesses,

the word ‘atheist’ has in the present context to be construed in an unusual way.  Nowadays it is normally taken to mean someone who explicitly denies the existence . . . of God . . . But here it has to be understood not positively but negatively, with the originally Greek prefix ‘a-’ being read in this same way in ‘atheist’ as it customarily is in . . . words as ‘amoral’ . . . . In this interpretation an atheist becomes not someone who positively asserts the non-existence of God, but someone who is simply not a theist. (A Companion to Philosophy of Religion, ed. Philip Quinn and Charles Taliaferro [Oxford:  Blackwell, 1997], s.v. “The Presumption of Atheism,” by Antony Flew)

Such a re-definition of the word “atheist” trivializes the claim of the presumption of atheism, for on this definition, atheism ceases to be a view.  It is merely a psychological state which is shared by people who hold various views or no view at all.  On this re-definition, even babies, who hold no opinion at all on the matter, count as atheists!  In fact, our cat Muff counts as an atheist on this definition, since she has (to my knowledge) no belief in God.

One would still require justification in order to know either that God exists or that He does not exist, which is the question we’re really interested in.

So why, you might wonder, would atheists be anxious to so trivialize their position?  Here I agree with you that a deceptive game is being played by many atheists.  If atheism is taken to be a view, namely the view that there is no God, then atheists must shoulder their share of the burden of proof to support this view.  But many atheists admit freely that they cannot sustain such a burden of proof.  So they try to shirk their epistemic responsibility by re-defining atheism so that it is no longer a view but just a psychological condition which as such makes no assertions.  They are really closet agnostics who want to claim the mantle of atheism without shouldering its responsibilities.

This is disingenuous and still leaves us asking, “So is there a God or not?”

So there you have it. We are interested in what both sides know and what reasons and evidence they have to justify their claim to know. We are interested in talking to people who make claims about objective reality, not about themselves, and who then go on to give reasons and evidence to support their claims about objective reality. There are atheists out there that do make an objective claim that God does not exist, and then support that claim with arguments and evidence. Those are good atheists, and we should engage in rational conversations with them. But clearly there are some atheists who are not like that. How should we deal with these “subjective atheists”?

Dealing with subjective atheists

How should theists respond to people who just want to talk about their psychological state? Well, my advice is to avoid them. They are approaching religion irrationally and non-cognitively – like the person who enters a physics class and says “I lack a belief in the gravitational force!”.  When you engage in serious discussions with people about God’s existence, you only care about what people know and what they can show to be true. We don’t care about a person’s psychology.