Tag Archives: Multiverse

MIT physicist Alan Lightman on fine-tuning and the multiverse

Christianity and the progress of science
Christianity and the progress of science

Here’s the article from Harper’s magazine.

The MIT physicist says that the fine-tuning is real, and is best explained by positing the existence of an infinite number of universes that are not fine-tuned – the so-called multiverse.

Excerpt:

While challenging the Platonic dream of theoretical physicists, the multiverse idea does explain one aspect of our universe that has unsettled some scientists for years: according to various calculations, if the values of some of the fundamental parameters of our universe were a little larger or a little smaller, life could not have arisen. For example, if the nuclear force were a few percentage points stronger than it actually is, then all the hydrogen atoms in the infant universe would have fused with other hydrogen atoms to make helium, and there would be no hydrogen left. No hydrogen means no water. Although we are far from certain about what conditions are necessary for life, most biologists believe that water is necessary. On the other hand, if the nuclear force were substantially weaker than what it actually is, then the complex atoms needed for biology could not hold together. As another example, if the relationship between the strengths of the gravitational force and the electromagnetic force were not close to what it is, then the cosmos would not harbor any stars that explode and spew out life-supporting chemical elements into space or any other stars that form planets. Both kinds of stars are required for the emergence of life. The strengths of the basic forces and certain other fundamental parameters in our universe appear to be “fine-tuned” to allow the existence of life. The recognition of this fine-­tuning led British physicist Brandon Carter to articulate what he called the anthropic principle, which states that the universe must have the parameters it does because we are here to observe it. Actually, the word anthropic, from the Greek for “man,” is a misnomer: if these fundamental parameters were much different from what they are, it is not only human beings who would not exist. No life of any kind would exist.

If such conclusions are correct, the great question, of course, is why these fundamental parameters happen to lie within the range needed for life. Does the universe care about life? Intelligent design is one answer. Indeed, a fair number of theologians, philosophers, and even some scientists have used fine-tuning and the anthropic principle as evidence of the existence of God. For example, at the 2011 Christian Scholars’ Conference at Pepperdine University, Francis Collins, a leading geneticist and director of the National Institutes of Health, said, “To get our universe, with all of its potential for complexities or any kind of potential for any kind of life-form, everything has to be precisely defined on this knife edge of improbability…. [Y]ou have to see the hands of a creator who set the parameters to be just so because the creator was interested in something a little more complicated than random particles.”

Intelligent design, however, is an answer to fine-tuning that does not appeal to most scientists. The multiverse offers another explanation. If there are countless different universes with different properties—for example, some with nuclear forces much stronger than in our universe and some with nuclear forces much weaker—then some of those universes will allow the emergence of life and some will not. Some of those universes will be dead, lifeless hulks of matter and energy, and others will permit the emergence of cells, plants and animals, minds. From the huge range of possible universes predicted by the theories, the fraction of universes with life is undoubtedly small. But that doesn’t matter. We live in one of the universes that permits life because otherwise we wouldn’t be here to ask the question.

I thought I was going to have to go outside this article to refute the multiverse, but Lightman is honest enough to refute it himself:

The… conjecture that there are many other worlds… [T]here is no way they can prove this conjecture. That same uncertainty disturbs many physicists who are adjusting to the idea of the multiverse. Not only must we accept that basic properties of our universe are accidental and uncalculable. In addition, we must believe in the existence of many other universes. But we have no conceivable way of observing these other universes and cannot prove their existence. Thus, to explain what we see in the world and in our mental deductions, we must believe in what we cannot prove.

Sound familiar? Theologians are accustomed to taking some beliefs on faith. Scientists are not. All we can do is hope that the same theories that predict the multiverse also produce many other predictions that we can test here in our own universe. But the other universes themselves will almost certainly remain a conjecture.

The multiverse is not pure nonsense, it is theoretically possible. The problem is that the multiverse generator itself would require fine-tuning, so the multiverse doesn’t get rid of the problem. And, as Lightman indicates, we have no independent experimental evidence for the existence of the multiverse in any case. Atheists just have to take it on faith, and hope that their speculations will be proved right. Meanwhile, the fine-tuning is just as easily explained by postulating God, and we have independent evidence for God’s existence, like the the origin of biological information, the sudden appearance of animal body plans, the argument from consciousness, and so on. Even if the naturalists could explain the fine-tuning, they would still have a lot of explaining to do. Theism (intelligent causation) is the simplest explanation for all of the things we learn from the progress of science.

We need to be frank about atheists and their objections to the progress of science. Within the last 100 years, we have discovered that the physical universe came into being out of nothing 15 billion years ago, and we have discovered that this one universe is fine-tuned for intelligent life. I don’t think it’s like that the last 100 years of scientific progress on the origins question are going to be overturned so that science once again affirms what atheists believe about the universe. Things are going the wrong way for atheists – at least with respect to science.

See it in action

To see these arguments examined in a debate with a famous atheist, simply watch the debate between William Lane Craig and Christopher Hitchens, and judge which debater is willing to form his beliefs on scientific progress, and which debater is forming his beliefs against the science we have today, and hoping that the good science we have today based on experiments will be overturned by speculative theories at some point in the future. When you watch that debate, it becomes very clear that Christian theists are interested in conforming their beliefs to science, and atheists are very interested in speculating against what science has shown in order to maintain their current pre-scientific view. That’s not what rational people ought to do when confronted with evidence.

Positive arguments for Christian theism

Lawrence Krauss debates “A Universe From Nothing” with an astrophysicist

Two horses fight it out, may the best horse win!
Two horses fight it out, may the best horse win!

Dina sent me news of a cracking good episode of Unbelievable, which features Lawrence Krauss, who debated William Lane Craig. Krauss’ book was also reviewed in the New York Times.

The MP3 file is here.

Details:

Lawrence Krauss is a Cosmologist at Arizona State University who describes himself as an “anti-theist”. His latest book “A Universe From Nothing” has received both acclaim and criticism for its attempt to answer the question “Why is there something rather than nothing?” Debating the issue with Krauss is Rodney Holder, Course director at the Faraday Institute, Cambridge. An astrophysicist and priest by background. In a lively exchange they debate whether Krauss’ “nothing” is “nothing”, fine tuning and multiverses, scientific knowledge, miracles and the usefulness of theology and philosophy.

This debate is quite entertaining, and do not be intimidated if your don’t understand science. You can understand pretty easily who is arguing based on facts and who is speculating about unobservable, untestable entities. At one point, Krauss actually denies that there is any fine-tuning in the universe, so please see this link to refute that claim as well as this podcast which explains some examples of fine-tuning. Krauss gets a bit angry at the beginning, but calms down.

Quotation marks are for direct quotes, italics is for made-up snark. See below the summary for more posts that are related to this one.

Summary of the discussion: (picked up at 9:30 when they start talking about the book)

Brierley:

  • explain your theory of how the universe can come into being from nothing

Krauss:

  • the nothing that preceded the universe is “no space, no time, no universe”
  • theists say that God is responsible for creating the universe out of this nothing
  • but the laws of nature can create the universe uncaused out of nothing

Holder:

  • Krauss sometimes writes that the nothing is really a quantum vacuum, but that is not nothing
  • He even acknowledges in his book that a quantum vacuum is not nothing
  • He thinks that the nothing has properties, even though it has no being
  • It has the property of being unstable
  • It has the property of being acted on by quantum fields
  • It has the property of being acted on by gravity

Krauss:

  • But nothing can have the potential to do things inside it
  • For example suppose you have an electron, which is not nothing
  • If it jumps from one level to another, it emits light
  • There was no potential for the light in the electron, but it was there as part of atomic structure

Holder:

  • But in cases like that, there is something physical that has the potential
Krauss:
  • Well, how did God makes the universe then if it had no potential?

Holder:

  • God existed, and the potential for creating the universe in himself

Brierley:

Krauss:
  • It was written by a philosopher, so I dismissed it

Brierley:

Krauss:
  • These book reviewers have not even read my book!

Krauss:

  • Science will be able to figure out how to make something from nothing in the future
  • We are even now speculating about interesting questions, like is there a multiverse?

Brierley:

  • Consider the critical review of your book in the New York Times
  • The author of the review claims that you equivocate on the term “nothing”
  • In order to get things to pop into being, you have to make “nothing” mean “something”
  • Reviewer: none of Krauss’ theories explain how something can come from actual nothingness

Krauss:

  • In physics, something and nothing are not that different
  • The reviewer doesn’t understand the physics
  • He doesn’t understand quantum field theory
  • You could call a quantum vacuum “nothing”, (this is the vacuum fluctuation model, refuted by William Lane Craig in a peer-reviewed publication in an astrophysics journal – get the full text of the article here)
  • Maybe there is an eternally existing multiverse that we can’t observe or test scientifically
  • Maybe it has laws that we don’t know about which allow our universe to pop into being
  • Maybe this popping into being is uncaused
  • (alarmed) Who made God? Who made God?

Holder:

  • God is eternal and necessary

Krauss:

  • (interrupting, angry) What does it mean for something to be necessary?

Holder:

  • Basically, you have to decide whether there is more evidence that the necessary being God or a multiverse

Brierley:

  • So Dr. Krauss are you willing to say that the universe is a brute fact, in some sense, and requires no explanation

Krauss:

  • (angry) Religious people are stupid because they just assume brute facts, not like me and my unobservable, untestable multiverse
  • (angry) Religious people are against the progress of science, they don’t want to figure out how things work

Brierley:

  • But isn’t it possible that naturalists can be opposed to the progress of science?
  • What about the way the Fred Hoyle opposed the Big Bang because he wanted an eternal universe

Krauss:

  • (angry) But naturalists like me let the facts determine our beliefs, like the facts about the eternal unobservable, untestable multiverse
  • (angry, shouting) Philosophers are stupid, they know nothing!

=== Break ===

Brierley:

  • Do you see any evidence of purpose in the universe?

Krauss:

  • Well maybe I would believe if the stars lined up to spell out a message from God

Brierley:

  • Actually no, that wouldn’t be evidence for God on your multiverse view
  • if there an infinite number of universes existing for an infinite amount of time, then anything can happen no matter how unlikely it is
  • therefore, no evidence could convince you that God exists, since the unobservable, untestable, eternal multiverse can make anything it wants

Krauss:

  • That’s a true statement, and very convenient for atheists who don’t want to be accountable to God, don’t you think?
Brierley:
  • Back to the multiverse, how does it solve the fine-tuning?

Krauss:

  • “We have no idea if the universe is fine-tuned for life”, even though the atheist Martin Rees who endorsed Krauss’ book wrote his own book about the fine-tuning of the universe called “Just Six Numbers”
  • Inflationary theory does suggest a way to create multiple universes, (this is the chaotic inflationary model, refuted by William Lane Craig in a peer-reviewed publication in an astrophysics journal – get the full text of the article here)

Brierley:

  • But this theory is still very much a hypothesis, isn’t it? We can’t observe or test this hypothesis can we?

Krauss:

  • “No, and that is really important to state”
  • “I’m an empiricist, so if you can’t falsify it and if you can’t test it then it’s not science”
  • In my book, I speculate about a way that we could test the multiverse theory

Holder:

  • Yes, in principle, the multiverse would be scientific if you could test it through other theories like inflationary theory
  • There are a lot of speculations about multiverse theory, but no evidence from predictions that were validated in the lab

Krauss:

  • “I agree completely with everything you just said”

Brierley:

  • Roger Penrose agrees with Holder that the multiverse theory is too speculative
  • (To Holder) Isn’t the multiverse theory better than positing a completely different kind of being, which is God?

Holder:

  • The multiverse theory is extremely speculative
  • Even if the multiverse were true, you would still need to explain the multiverse

Krauss:

  • People don’t oppose my book because it’s full of self-contradictory speculations
  • People oppose my book because they are stupid and ignorant

Holder:

  • There are things that exist that science cannot measure, like objective morality
  • It’s possible to give explanations for moral behavior by appealing to evolution
  • But that does not ground self-sacrificial morality, such as what occurs in the Christian life

Brierley:

  • Dawkins says there is no purpose or morality in in the universe, do you agree?

Krauss:

  • “There is certainly no evidence of any of that”

Brierley:

  • In the book, you talk about how we live in a special time in the universe’s history to be able to do science, (i.e. – The Privileged Planet hypothesis)
  • You also write about how all the discoveries were are making will not be communicated to anyone in other places in the universe
  • So what is the meaning of doing science on your view? And why are you sad at the knowledge that will not be available to people in the future?
  • Are you longing for some kind of purpose?

Krauss:

  • No, I just get enjoyment from studying the universe with science to gain understanding

Holder:

  • What do you make of Einstein’s statement about the unexpected comprehensibility of the universe
  • Theists would say that this is because God wanted us to study and understand and gain knowledge

Krauss:

  • “It is remarkable that the universe is comprehensible”

Brierley:

  • Why is the universe comprehensible?

Krauss:

  • Well, maybe the universe just has to be that way

Brierley:

  • What do you make of the heat death of the universe, when all life in the universe will die out?

Krauss:

  • That’s the way the universe is
=== BREAK ===

Krauss:

  • I wouldn’t want to live in a universe where there was a God
  • God is a cosmic Saddam Hussein
  • “Religious people turn their minds off” and believe in God for consolation

Holder:

  • First, Jesus is the revelation of God and he is no Saddam Hussein
  • Second, the Christian life is anything but easy, we are facing some persecution already in the UK
  • Third, there is also the problem of being accountable to God when we die
  • It’s very much like science – Christianity is the way it is, not the way we want it to be

Krauss:

  • “If you don’t believe in him, you don’t get any of the benefits, so you have to believe”
  • “And then if you’ve done something wrong, you’re going to be judged for it”
  • “So I don’t want to be judged by God, I want to be… that’s the bottom line”

Holder:

  • Well, Jesus has died to pay the price for those things we’ve done wrong
  • Although we will have to face the charges for what we’ve done, believers will ultimately be forgiven

Finally, Peter Sean Bradley note that Krauss is now walking back his rhetoric in response to criticisms from people like atheist John Horgan.

Related posts

William Lane Craig and atheist Daniel Dennett discuss cosmology and fine-tuning

British Spitfire and German Messerschmitt Me 109 locked in a dogfight
British Spitfire and German Messerschmitt Bf 109 locked in a dogfight

A friend of mine mentioned that she met a girl who was raised Christian, who is now an atheist, and who thought that atheist Daniel Dennett was the bee’s knees when it came to philosophy of religion. So I thought I would re-post something related to Dennett for my friend.

Here is audio of a very interesting exchange between William Lane Craig and leading atheist Daniel Dennett.

This audio records a part of the Greer-Heard debate in 2007, between prominent atheist Daniel Dennett and lame theistic evolutionist Alister McGrath. Craig was one of the respondents, and this was the best part of the event. It is a little bit advanced, but I have found that if you listen to things like this over and over with your friends and family, and then try to explain it to non-Christians, you’ll get it.

By the way, this is mostly original material from Craig, dated 2007, and he delivers the speech perfectly, so it’s entertaining to listen to.

Craig presents three arguments for a Creator and Designer of the universe:

  • the contingency argument
  • the kalam cosmological argument
  • the teleological argument

He also discusses Dennett’s published responses to these arguments, and that’s what I want to focus on, since most of you are already familiar with Craig’s philosophical arguments for the existence of God.

Dennett’s response to Craig’s paper

Here is my snarky paraphrase of Dennett’s reponse: (this is very snarky, because Dennett was just awful)

  • Craig’s three arguments are bulletproof, the premises are plausible, and grounded by the best cutting edge science we know today.
  • I cannot find anything wrong with his arguments right now, but maybe later when I go home it will come to me what’s wrong with them.
  • But atheism is true even if all the evidence is against it today. I know it’s true by my blind faith.
  • The world is so mysterious, and all the science of today will be overturned tomorrow so that atheism will be rational again. I have blind faith that this new evidence will be discovered any minute.
  • Just because the cause of the beginning of time is eternal and the cause of the beginning of space is non-physical, the cause doesn’t have to be God.
  • “Maybe the cause of the universe is the idea of an apple, or the square root of 7”. (HE LITERALLY SAID THAT!)
  • The principle of triangulation might have brought the entire physical universe into being out of nothing.
  • I don’t understand anything about non-physical causation, even though I cannot even speak meaningful sentences unless I have a non-physical mind that is causing my body to emit the meaningful sentences in a non-determined manner.
  • Alexander Vilenkin is much smarter than Craig and if he were here he would beat him up good with phantom arguments.
  • Alan Guth is much smarter than Craig and if he were here he would beat him up good with phantom arguments.
  • This science stuff is so complicated to me – so Craig can’t be right about it even though he’s published about it and debated it all with the best atheists on the planet.
  • If God is outside of time, then this is just deism, not theism. (This part is correct, but Craig believes that God enters into time at the moment of creation – so that it is not a deistic God)
  • If deism is true, then I can still be an atheist, because a Creator and Designer of the universe is compatible with atheism.
  • I’m pretty sure that Craig doesn’t have any good arguments that can argue for Christianity – certainly not an historical argument for the resurrection of Jesus based on minimal facts, that he’s defended against the most prominent historians on the planet in public debates and in prestigous books and research journals.

This is a very careful treatment of the arguments that Dr. Craig goes over briefly during his debates. Recommended.

Positive arguments for Christian theism

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

Christianity and the progress of science
Christianity and the progress of science

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 what was in the podcast. (I wish more people who put out podcasts would do that).

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.

What are Boltzmann brains, and what challenge do they pose to the multiverse hypothesis?

Christianity and the progress of science
Christianity and the progress of science

I thought I would turn to the atheist theoretical physicist Sean Carroll, who has previously debated William Lane Craig, to explain to us what a Boltzmann brain is, and what threat it posts to the multiverse hypothesis.

Here is Sean Caroll, quoted by About.com:

Ludwig Boltzmann was one of the founders of the field of thermodynamics in the nineteenth century.

One of the key concepts was the second law of thermodynamics, which says that the entropy of a closed system always increases. Since the universe is a closed system, we would expect the entropy to increase over time. This means that, given enough time, the most likely state of the universe is one where everything is the in thermodynamic equilibrium … but we clearly don’t exist in a universe of this type since, after all, there is order all around us in various forms, not the least of which is the fact that we exist.

With this in mind, we can apply the anthropic principle to inform our reasoning by taking into account that we do, in fact, exist.

Here the logic gets a little confusing, so I’m going to borrow the words from a couple of more detailed looks at the situation. As described by cosmologist Sean Carroll in From Eternity to Here:

Boltzmann invoked the anthropic principle (although he didn’t call it that) to explain why we wouldn’t find ourselves in one of the very common equilibrium phases: In equilibrium, life cannot exist. Clearly, what we want to do is find the most common conditions within such a universe that are hospitable to life. Or, if we want to be more careful, perhaps we should look for conditions that are not only hospitable to life, but hospitable to the particular kind of intelligent and self-aware life that we like to think we are….

We can take this logic to its ultimate conclusion. If what we want is a single planet, we certainly don’t need a hundred billion galaxies with a hundred billion stars each. And if what we want is a single person, we certainly don’t need an entire planet. But if in fact what we want is a single intelligence, able to think about the world, we don’t even need an entire person–we just need his or her brain.

So the reductio ad absurdum of this scenario is that the overwhelming majority of intelligences in this multiverse will be lonely, disembodied brains, who fluctuate gradually out of the surrounding chaos and then gradually dissolve back into it. Such sad creatures have been dubbed “Boltzmann brains” by Andreas Albrecht and Lorenzo Sorbo….

In a 2004 paper, Albrecht and Sorbo discussed “Boltzmann brains” in their essay:

A century ago Boltzmann considered a “cosmology” where the observed universe should be regarded as a rare fluctuation out of some equilibrium state. The prediction of this point of view, quite generically, is that we live in a universe which maximizes the total entropy of the system consistent with existing observations. Other universes simply occur as much more rare fluctuations. This means as much as possible of the system should be found in equilibrium as often as possible.

From this point of view, it is very surprising that we find the universe around us in such a low entropy state. In fact, the logical conclusion of this line of reasoning is utterly solipsistic. The most likely fluctuation consistent with everything you know is simply your brain (complete with “memories” of the Hubble Deep fields, WMAP data, etc) fluctuating briefly out of chaos and then immediately equilibrating back into chaos again. This is sometimes called the “Boltzmann’s Brain” paradox.

[…]Now that you understand Boltzmann brains as a concept, though, you have to proceed a bit to understanding the “Boltzmann brain paradox” that is caused by applying this thinking to this absurd degree. Again, as formulated by Carroll:

Why do we find ourselves in a universe evolving gradually from a state of incredibly low entropy, rather than being isolated creatures that recently fluctuated from the surrounding chaos?

Unfortunately, there is no clear explanation to resolve this … thus why it’s still classified as a paradox.

Naturalists like to propose the multiverse as a way of explaining away the fine-tuning that we see, and explaining why complex, embodied intelligent beings like ourselves exist. But even if the multiverse hypothesis were true, we still would not expect to observe stars, planets, and conscious embodied intelligent beings. It is far more likely on a multiverse scenario that any observers we had would be “Boltzmann” brains in an empty universe. The multiverse hypothesis doesn’t explain the universe we have, which contains “a hundred billion galaxies with a hundred billion stars each” – not to mention our bodies which are composed of heavy elements, all of which require fine-tuning piled on fine-tuning piled on fine-tuning.

William Lane Craig answered a question about Boltzmann brains a while back, so let’s look at his answer since we saw what his debate opponent said above.

He writes:

Incredible as it may sound, today the principal–almost the only–alternative to a Cosmic Designer to explain the incomprehensibly precise fine tuning of nature’s constants and fundamental quantities is the postulate of a World Ensemble of (a preferably infinite number of) randomly ordered universes. By thus multiplying one’s probabilistic resources, one ensures that by chance alone somewhere in this infinite ensemble finely tuned universes like ours will appear.

Now comes the key move: since observers can exist only in worlds fine-tuned for their existence, OF COURSE we observe our world to be fine-tuned! The worlds which aren’t finely tuned have no observers in them and so cannot be observed! Hence, our observing the universe to be fine-tuned for our existence is no surprise: if it weren’t, we wouldn’t be here to be surprised. So this explanation of fine tuning relies on (i) the hypothesis of a World Ensemble and (ii) an observer self-selection effect.

Now apart from objections to (i) of a direct sort, this alternative faces a very formidable objection to (ii), namely, if we were just a random member of a World Ensemble, then we ought to be observing a very different universe. Roger Penrose has calculated that the odds of our solar system’s forming instantaneously through the random collision of particles is incomprehensibly more probable that the universe’s being fine-tuned, as it is. So if we were a random member of a World Ensemble, we should be observing a patch of order no larger than our solar system in a sea of chaos. Worlds like that are simply incomprehensibly more plentiful in the World Ensemble than worlds like ours and so ought to be observed by us if we were but a random member of such an ensemble.

Here’s where the Boltzmann Brains come into the picture. In order to be observable the patch of order needn’t be even as large as the solar system. The most probable observable world would be one in which a single brain fluctuates into existence out of the quantum vacuum and observes its otherwise empty world. The idea isn’t that the brain is the whole universe, but just a patch of order in the midst of disorder. Don’t worry that the brain couldn’t persist long: it just has to exist long enough to have an observation, and the improbability of the quantum fluctuations necessary for it to exist that long will be trivial in comparison to the improbability of fine tuning.

In other words, the observer self-selection effect is explanatorily vacuous. It does not suffice to show that only finely tuned worlds are observable. As Robin Collins has noted, what needs to be explained is not just intelligent life, but embodied, interactive, intelligent agents like ourselves. Appeal to an observer self-selection effect accomplishes nothing because there is no reason whatever to think that most observable worlds are worlds in which that kind of observer exists. Indeed, the opposite appears to be true: most observable worlds will be Boltzmann Brain worlds.

Allen Hainline explained some of the OTHER problems with the multiverse in a post on Cross Examined’s blog. I recommend taking a look at those as well, because I feel funny even talking about Boltzmann brains. I would rather just say that there is no experimental evidence for the multiverse hypothesis, as I blogged before, and leave it at that. But if the person you are talking to fights you on it, you can disprove the multiverse with the Boltzmann brains.