The Universe is Fine Tuned

 In Space

The universe appears to be fine-tuned for life.  For example, seemingly infinitesimal adjustments to the dark-energy density or gravitational constant would render most conceivable forms of life impossible.  Adjusting the dark energy, for example, would result in either no planets or a collapsed universe. Clearly, cosmic fine-tuning is necessary (although not sufficient) for evolution to occur.

Fine-Tuning Arguments

How do you explain it?  As Jewish people, we shouldn’t find fine-tuning surprising.  “Hashem presumably would want there to be life, and indeed intelligent life with which (whom) to communicate and share love … and if he wanted to create human life in a universe at all like ours, he would have been obliged to fine-tune the constants.”

Conversely, I suspect that fine-tuning ought to be surprising to the atheist.  Accordingly, fine-tuning arguments (FTAs) tend to go something like this: “given theism, fine-tuning is not at all improbable; given atheism, it is; therefore theism is to be preferred to atheism.” Presentations of and objections to FTAs can be quite complex.  I’ll merely examine a couple interesting objections and one resolution we can simply propose.

Observer Selection

Often the skeptic will initially suggest that “were the universe not fine-tuned, we wouldn’t be here to talk about it.”  Call this the observer-selection principle. How exactly does this undermine FTAs?

All by itself, it doesn’t.  Fine-tuning is like a firing squad.  Suppose one is condemned to death.  A platoon of expert marksmen aim their weapons and fire.  Yet—miracle of miracles—one is not shot!  What a wonderful surprise!  But wait.  The skeptic reminds us that if one had been shot, one would be dead and therefore not surprised.  Surely this fact alone does not undermine one’s surprise to be alive against the odds. The same applies to fine-tuning.

Enter the Multiverse

Therefore, in order to reduce the surprise of fine-tuning (without Hashem) the skeptic must adjust the odds.  This is where the multiverse hypothesis may prove helpful.  The multiverse hypothesis “posits regions of spacetime outside our observable horizon, in which [physical] conditions are very different.” These many regions are the product of cosmic inflation; the variation of physical parameters is a result of superstring theory.

The multiverse hypothesis alone poses no problem to FTAs.  “The fact, if it is a fact, that there are enormously many universes has no bearing on the probability (on atheism) that this universe is fine-tuned for life; that remains very low.”  What is needed—in order to put the multiverse to work against FTAs—is the observer-selection principle described above.

The multiverse hypothesis tells us that some universe amongst many others will support life.  The observer-selection principle tells us that “we will inevitably find ourselves” in one such universe. Working together, the multiverse hypothesis and the observer-selection principle appear to remove the surprise of fine-tuning without a Creator.

Mere Observers versus Privileged Observers

In order to defend FTAs, one must respond to either the multiverse hypothesis or the observer selection principle.  We can do both.  On the one hand, we can argue that the multiverse hypothesis simply pushes “the problem of fine-tuning up one level to the laws required to generate the multiverse.”  On the other hand, we will argue that the observer selection principle fails upon closer consideration.  I’ll discuss this second approach.

Let us suggest that FTAs should not claim that the universe is fine-tuned for mere observers.  Rather, our universe is fine-tuned for embodied conscious agents “who can interact with each other for good or for ill.”  Additional fine-tuning ensures “that those observers can develop scientific technology and discover the universe.” So not only is our universe fine-tuned for mere observers, it is fine-tuned for privileged observers.

Suppose that the multiverse exists.  We can point out that most of the observers in the multiverse are not scientifically privileged like us.  For example, “consider a universe with a dark-energy density a million times the value in our universe.”  In that universe, the increased cosmic expansion rate would reduce the Hubble volume so that nothing beyond the galaxy would be visible.  This would seriously limit their ability to do cosmology.  Even greater expansion renders evolution impossible.

Alternatively, if the strength of gravity were slightly increased, “any kind of technology would become more difficult, for example, building a structure to live in or perform scientific experiments would become more difficult.”  At a certain point, conscious life could only evolve underwater since “a life form with a brain large enough to qualify as an [embodied conscious agent] would be crushed.”

Living underwater would “not allow them to develop scientific technology since they could not forge metals.” Further increases in gravity would rule out underwater life completely.  Just like with dark-matter, as gravity increases life first becomes less privileged scientifically and then becomes impossible.

However, some observers exist entirely independent of cosmic fine-tuning—Boltzmann brains.  Such observers come into being via random local quantum or thermal fluctuations.  They persist for a period long enough to make an observation and presumably vanish.  Given a sufficiently large individual universe, these fluctuating observers will likely exist, without cosmic fine-tuning.


The point is that very small changes in the cosmic fine-tuning parameters (dark energy and gravity) will rule out observers capable of science.  Further changes will rule out embodied life all together.  However, Boltzmann brains will still exist independently of cosmic-fine tuning.

All of this undercuts the observer selection principle.  It is simply not true, on the multiverse hypothesis, that we are likely to find ourselves in a world such as our own. Indeed, “it is vastly more likely for a generic observer to find itself in the smallest and least structured community required for it to be an observer than in a larger highly structured community of observers, such as the human race.”

So the question remains, why do we find ourselves in a universe fine-tuned for scientific civilization?  Why are we not instead unscientific life-forms or Boltzmann brains?  It would seem that the element of surprise remains, even given the multiverse.  FTAs remain on the table.

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