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

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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 wiped out by intense gamma radiation when they die. So, you want to be between the “arms” of a spiral galaxy, close enough to the areas with a lot of stars, and not too far away. But you can only get that pattern of stars if the universe is expanding at the right rate.

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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.

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

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

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.

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The author of the books of Luke and Acts was an eyewitness to the life of Paul

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I was listening to a friend give a talk on the book of Acts on the weekend. He had a number of interesting points, but the most interesting was from chapter 16. His point will help everyone who likes to answer questions about the historical basis for Christian faith. It has to do with the author of Acts, and why historians think that he was in contact with eyewitnesses to the life of Jesus.

Let’s take a look at the passage from Acts 16:1-10 (NASB), and notice how Luke is talking about what Paul and his helper Timothy are doing:

1 Now Paul also came to Derbe and to Lystra. And a disciple was there, named Timothy, the son of a Jewish woman who was a believer, but his father was a Greek,

2 and he was well spoken of by the brothers and sisters who were in Lystra and Iconium.

3 Paul wanted this man to leave with him; and he took him and circumcised him because of the Jews who were in those parts, for they all knew that his father was a Greek.

4 Now while they were passing through the cities, they were delivering the ordinances for them to follow which had been determined by the apostles and elders in Jerusalem.

5 So the churches were being strengthened in the faith, and were increasing in number daily.

6 They passed through the Phrygian and Galatian region, after being forbidden by the Holy Spirit to speak the word in Asia;

7 and after they came to Mysia, they were trying to go into Bithynia, and the Spirit of Jesus did not allow them;

8 and passing by Mysia, they went down to Troas.

9 And a vision appeared to Paul in the night: a man of Macedonia was standing and pleading with him, and saying, “Come over to Macedonia and help us.”

10 When he had seen the vision, we immediately sought to leave for Macedonia, concluding that God had called us to preach the gospel to them.

Now something interesting happens in the next few verses. Read them closely and see if you catch it:

11 So after setting sail from Troas, we ran a straight course to Samothrace, and on the following day to Neapolis;

12 and from there to Philippi, which is a leading city of the district of Macedonia, a Roman colony; and we were spending some days in this city.

13 And on the Sabbath day we went outside the gate to a riverside, where we were thinking that there was a place of prayer; and we sat down and began speaking to the women who had assembled.

Did you catch it? The narrator switches from the third-person (“they”) to the first-person (“we”). And there are several more “we” passages in the book:

  • Acts 16:10-17: The first “we passage” occurs during Paul’s second missionary journey, starting with the departure for Macedonia and ending after the events in Philippi.
  • Acts 20:5-15: The “we” perspective resumes during Paul’s journey from Philippi to Miletus.
  • Acts 21:1-18: The “we” narrative continues as Paul travels to Jerusalem.
  • Acts 27:1-28:16: The final “we passage” covers Paul’s sea voyage to Rome.

Now, for the apologetic significance of this, let’s turn to William Lane Craig:

The most obvious explanation is that the author had joined Paul on his evangelistic tour of the Mediterranean cities. In chapter 21 he accompanies Paul back to Palestine and finally to Jerusalem. What this means is that the author of Luke-Acts was in fact in first hand contact with the eyewitnesses of Jesus’s life and ministry in Jerusalem.

[…]There is no avoiding the conclusion that Luke-Acts was written by a traveling companion of Paul who had the opportunity to interview eyewitnesses to Jesus’s life while in Jerusalem. Who were some of these eyewitnesses? Perhaps we can get some clue by subtracting from the Gospel of Luke everything found in the other gospels and seeing what is peculiar to Luke. What you discover is that many of Luke’s peculiar narratives are connected to women who followed Jesus: people like Joanna and Susanna, and significantly, Mary, Jesus’s mother.

So, the author of Acts was an eyewitness to the life of Paul, and he was able to interview eyewitnesses to the life of Jesus.

But the best part of all is testability. My friend who gave the talk on Acts mentioned that many details that Luke recorded can be tested by archaeologists. And what do the archaeologists find?

Dr. Craig says:

Was the author reliable in getting the facts straight? The book of Acts enables us to answer that question decisively. The book of Acts overlaps significantly with secular history of the ancient world, and the historical accuracy of Acts is indisputable. This has recently been demonstrated anew by Colin Hemer, a classical scholar who turned to New Testament studies, in his book The Book of Acts in the Setting of Hellenistic History. Hemer goes through the book of Acts with a fine-toothed comb, pulling out a wealth of historical knowledge, ranging from what would have been common knowledge down to details which only a local person would know. Again and again Luke’s accuracy is demonstrated: from the sailings of the Alexandrian corn fleet to the coastal terrain of the Mediterranean islands to the peculiar titles of local officials, Luke gets it right.

According to Professor Sherwin-White, “For Acts the confirmation of historicity is overwhelming. Any attempt to reject its basic historicity even in matters of detail must now appear absurd.” The judgement of Sir William Ramsay, the world-famous archaeologist, still stands: “Luke is a historian of the first rank. This author should be placed along with the very greatest of historians.” Given Luke’s care and demonstrated reliability as well as his contact with eyewitnesses within the first generation after the events, this author is trustworthy.

I asked Grok about the accuracy of Luke, and Grok listed out the confirmed details, and concluded:

While archaeology cannot confirm every detail in Luke and Acts, numerous findings—such as inscriptions, structures, and artifacts—corroborate the historical, geographical, and cultural settings described in these texts. The accuracy of Luke’s references to officials, places, and events lends credibility to his accounts, though some specifics remain debated.

It’s important to understand that the gospels are not trying to make people feel good and have community. They’re trying to tell you who God is and what God really did in history. It’s a bit scary to think “oh my, all this really happened”, but it really did, and we have to come to terms with it and adjust our goals and priorities.

News

How does church appear to someone raised in a non-Christian home?

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My friend Wes posted an article about how communication is set up in the church, and why it’s not effective at equipping Christians to defend their worldview in hostile environments. The article describes what I encountered in church, after I was raised in a non-Christian home and become a Christian on my own by reading the New Testament. The view presented in the essay is how I viewed the church, and is probably how most outsiders view church. I think it explains why young people leave the church in droves once they move out of their parents’ houses.

The author writes:

On the Internet, one soon discovers that many respected church leaders are quite unable to deal directly with opposing viewpoints. In fact, many of them can’t even manage meaningful engagement with other voices. Their tweets may be entirely one-way conversations. They talk at their audiences. They can talk about other voices, but fail to talk to them, let alone with them. Their representations of opposing viewpoints reveal little direct exposure to the viewpoints in question.

[…]Around this point, it can start to dawn on one that many church leaders have only been trained in forms of discourse such as the sermon and, to a much lesser extent, the essay. Both forms privilege a single voice—their voice—and don’t provide a natural space for response, questioning, and challenge. Their opinions have been assumed to be superior to opposing viewpoints, but have never been demonstrated to be so. While they may have spoken or written about opposing voices, they are quite unaccustomed to speaking or writing to them (not to mention listening to or being cross-examined by them). There are benefits to the fact that the sermon is a form of discourse that doesn’t invite interruption or talking back, but not when this is the only form of discourse its practitioners are adept in.

Many church leaders have been raised and trained in ideologically homogenous cultures or contexts that discouraged oppositional discourse. Many have been protected from hostile perspectives that might unsettle their faith. Throughout, their theological opinions and voices have been given a privileged status, immune from challenge. Nominal challenges could be brushed off by a reassertion of the monologue. They were safe to speak about and habitually misrepresent other voices to their hearers and readers, without needing to worry about those voices ever enjoying the power to answer them back. Many of the more widely read members of their congregations may have had an inkling of the weakness of their positions in the past: the Internet just makes it more apparent.

One of my friends who comments here as “Wintery’s Friend” actually did his M. Div, and I think it was he who told me that his seminary had dropped the lone course in apologetics that had been part of the curriculum. Now seminary grads don’t learn any opposing views. They just pre-suppose that the Bible is true in the same way that Mormons pre-suppose their Bible is true, or Muslims pre-suppose their Bible is true, etc.

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If one’s opinion has never been subjected to and tried by rigorous cross-examination, it probably isn’t worth much. If one lacks the capacity to keep a level head when one’s views are challenged, one’s voice will be of limited use in most real world situations, where dialogue and dispute is the norm and where we have to think in conversation with people who disagree with us.

The teachers of the Church provide the members of the Church with a model for their own thinking. The teacher of the Church does not just teach others what to believe, but also how to believe, and the process by which one arrives at a theological position. This is one reason why it is crucial that teachers ‘show their working’ on a regular basis. When teaching from a biblical text, for instance, the teacher isn’t just teaching the meaning of that particular text, but how Scripture should be approached and interpreted more generally. An essential part of the teaching that the members of any church need is that of dealing with opposing viewpoints. One way or another, every church provides such teaching. However, the lesson conveyed in all too many churches is that opposing voices are to be dismissed, ignored, or ‘answered’ with a reactive reassertion of the dogmatic line, rather than a reasoned response.

You can imagine that the first questions that you’ll be asked by a non-Christian co-worker would be things like “why think God exists?” and “why think the Bible is history rather than legend?”. In order to answer those questions, you would have to know how to counter what a non-Christian believes. You would have to show them the reasons for your view.

Unfortunately, many of the conservative Christian leaders we trust think that the best way to be convincing is not to show your work, but just to speak Bible verses at people who don’t accept the Bible as an authority. Some people attend church for 20 years, and they never meet a single person who didn’t just assume that the Bible is trustworthy without doing an investigation first.

What’s most surprising is that this fideistic view of Christianity is not even Biblical. The Biblical view of faith is that faith is trust in God, based on evidence. This is why Jesus offered his own resurrection as evidence to a generation of unbelievers. His miracles were also evidence offered to unbelievers. And the Old Testament is filled with examples of people like Isaiah presenting evidence to unbelievers. The fideist view sounds more like the Mormon “burning of the bosom” view. We can do better than that!

Look:

That debate has over 6 million views on YouTube. That’s a debate with Christopher Hitchens, one of the most famous atheists of the last 100 years. In the post-debate comments, the atheist admitted he lost. Watch it. You won’t find it in most churches, so you’re going to have to learn it on your own. Without anyone’s help. Don’t be a spectator. Don’t settle for youth pastor Christianity.