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Course 14 · Lesson 5.5

The multiverse and other replies

9 minute read

Lessons in this course

Course 14 outline

Module 1: Arguments, Existence and Necessity

  1. What natural theology attempts and what it does not
  2. Necessary and contingent existence
  3. How to read and test an argument for God
  4. Philosophy of religion today: a map of the field

Module 2: The Ontological Argument

  1. Anselm and the argument of the Proslogion
  2. Gaunilo and the perfect island objection
  3. Kant: existence is not a real predicate
  4. What the ontological argument would show if it worked

Module 3: Cosmological Arguments

  1. Aquinas: the first three ways
  2. Infinite regress: what is the problem?
  3. Leibniz, the principle of sufficient reason and the argument from contingency
  4. Objections: the brute fact reply and the fallacy of composition

Module 4: The Kalam Cosmological Argument

  1. The kalam tradition: Philoponus, al-Ghazali and Bonaventure
  2. The modern argument: whatever begins to exist has a cause
  3. Did the universe begin? Philosophy and cosmology
  4. Objections and replies, and what follows about the cause

Module 5: Teleological and Fine-Tuning Arguments

  1. From Aquinas’s fifth way to Paley’s watch
  2. Hume and the Dialogues Concerning Natural Religion
  3. Darwin and the change in the design argument
  4. The fine-tuning argument: what is claimed and what is debated
  5. The multiverse and other replies

Module 6: The Moral Argument and Divine Hiddenness

  1. The moral argument: Kant, Lewis and contemporary forms
  2. The Euthyphro question and moral realism without God
  3. Evolution and moral knowledge
  4. The argument from divine hiddenness and Christian replies

Module 7: Contemporary Modal Arguments and Evaluation

  1. Possible worlds and modal logic in plain language
  2. Plantinga’s modal ontological argument
  3. Assessing the modal argument: what it needs and what it shows
  4. Weighing the arguments together, and what none of them prove

All courses

Program / Course 14: Arguments for the Existence of God / Lesson 5.5

What you will learn

  • Describe the multiverse hypothesis and the physical theories that suggest it.
  • State the inverse gambler’s fallacy objection and the reply to it.
  • List other replies to fine-tuning, including the claim that life is robust and that deeper laws fix the constants.
  • Evaluate what each reply costs.

The big idea

The most discussed reply to fine-tuning is the multiverse: if there are very many universes with different constants, it is no surprise that at least one permits life, and observers find themselves in such a one. Critics of the reply say that the multiverse is not observable, that the mechanism generating universes would itself need fine-tuning, and that the reasoning may commit the inverse gambler’s fallacy. Defenders reply that some physical theories predict many universes. Other replies are that the physics is overstated, or that deeper laws will explain the constants.

Key terms

Multiverse
A hypothetical collection of many universes, with perhaps different constants or laws.
Eternal inflation
A cosmological theory in which regions of space keep inflating and producing new universe-like bubbles.
String theory landscape
The idea in some versions of string theory that there are an enormous number of possible vacuum states, each with different constants.
Inverse gambler’s fallacy
The mistake of reasoning that, because a rare result occurred, many trials must have occurred. A gambler who sees a double six at a table cannot infer that many throws happened before.
Many-worlds interpretation
A reading of quantum mechanics in which every outcome occurs in a branching reality. It is not the same as the cosmological multiverse.
Occam’s razor
The principle that one should not multiply entities without need.
Falsifiable
Capable of being shown false by some possible observation.

Background

Several physical theories have been taken to suggest many universes. Eternal inflation, developed by Andrei Linde, Alan Guth, Alexander Vilenkin and others, predicts bubble universes that form in an ever-expanding background. String theory has been argued to allow a vast landscape of states. Leonard Susskind and Steven Weinberg have used the multiverse to explain the small value of the cosmological constant. Other physicists, such as Paul Steinhardt, one of the founders of inflation theory, have become critical of the multiverse and argue that it makes inflation untestable.

Philosophers distinguish the use of the multiverse as a physical hypothesis from its use as a reply to a philosophical argument. The two uses stand or fall on different considerations.

Step-by-step explanation

Step 1: The multiverse reply

If there are enormous numbers of universes with differing constants, then some will permit life, and observers will find themselves in those. Fine-tuning then needs no designer. The reply keeps the physics claim and rejects the inference.

Step 2: Problems with the multiverse

First, it is hard to test. Other universes are, by definition, beyond observation. Critics say a hypothesis that cannot be tested is not science. Defenders say that a theory is tested when its predictions about observable matters are confirmed, even if some of its consequences are unobservable.

Second, the mechanism that generates universes, such as inflation or string theory, seems to have its own special features. Defenders of design say that a universe-generator must itself be well-tuned to produce life-permitting universes, so the problem is moved back. Multiverse supporters reply that such generators are simple and need less tuning.

Step 3: The inverse gambler’s fallacy

Ian Hacking argued that reasoning from a single life-permitting universe to many universes is like inferring from a double six that the dice have been thrown many times. The throw that produced the double six was independent of earlier throws. Applied to this case, the fact that this universe permits life is not evidence for many others. Defenders of the multiverse reply that the analogy fails if the question is why any life-permitting universe exists at all, and that selection effects matter. Philosophers disagree on whether Hacking’s point is sound.

Step 4: Other replies

Some argue that the physics is exaggerated, and that life might exist in other forms across a wider range of constants. Some hope that a final theory will show that the constants are determined. Some say that the apparent improbability rests on a flawed probability measure. Some accept that fine-tuning calls for explanation but think that the conclusion drawn from it should be limited.

Each reply has a cost: speculation about unobservable realities, hope for a future theory, or a denial that the physics is as it seems.

Step 5: Can both be true?

A theist may accept a multiverse. A God who creates could create many universes, and some theists see the multiverse as a sign of divine abundance. In that case, the multiverse does not remove God, but changes the argument. The question becomes whether the world-generating mechanism itself points to a creator. Atheist philosophers hold that this question is open and that there is no good reason to answer yes.

  1. Is an untestable hypothesis a good explanation?
  2. Does the multiverse explain fine-tuning or only move it?
  3. Is the inverse gambler’s fallacy a fair charge here?
  4. Why might a believer welcome the multiverse?
  5. Would you accept a final theory that fixes the constants as an answer?
  6. What costs does each reply carry?

Examples

The lottery

If millions of people buy tickets, someone will win, and the winner will not be surprised that a winner exists. But the winner of a single-ticket lottery would have reason to suspect the draw was rigged. Multiverse supporters say the human situation is like the first case. Critics say there is no evidence of many tickets.

Dice at a table

A visitor enters a room and sees two dice showing sixes. Should he conclude that the dice have been thrown many times that evening? Hacking said no. The throw that he saw could have been the first. The example is used to challenge the move from a single life-permitting universe to many.

Weinberg’s prediction

In 1987 Steven Weinberg used anthropic reasoning to predict that the cosmological constant would be small but not zero. Supporters of the multiverse cite the later discovery of dark energy as a success. Critics say the prediction was loose and could have been reached otherwise.

Different perspectives

Catholic

Catholic thinkers have no fixed view of the multiverse as a physical theory. Most hold that it would not remove the need for a Creator, since it too would be a created and contingent reality. Aquinas argued in the Summa that the world is one, and the Church has not defined a position on other universes.

Orthodox

Orthodox theologians usually hold that the existence of other universes would not change the doctrine of creation, and that the uniqueness of the incarnation concerns this world. They are cautious about using speculative cosmology in theology.

Protestant

Craig and Collins reply that the multiverse has its own difficulties. Others, such as John Polkinghorne, an Anglican priest and physicist, say that a multiverse is a metaphysical speculation as much as design is, and a theist might equally accept it.

Scientific views

Physicists divide. Susskind and Sean Carroll take the multiverse seriously. Steinhardt, George Ellis and Roger Penrose argue that it is untestable or unnecessary. The community has no agreed view.

Skeptical views

Skeptical philosophers argue that the multiverse, or a final theory, or observer selection, each removes the force of fine-tuning, and that any one suffices. They also say it is wrong to treat a theory that explains less as a better alternative to one that explains more.

Why it matters

The multiverse debate shows how arguments for God interact with frontier science. It teaches a student to ask what a reply costs, not just whether it is possible, and to see that rival explanations also have to be weighed.

Common misunderstandings

Misunderstanding: The multiverse has been established by science.

Correction: It is a hypothesis suggested by some theories. No direct evidence exists, and physicists disagree about whether it is testable.

Misunderstanding: The multiverse is an atheist idea.

Correction: It is a physical hypothesis. Atheists use it against fine-tuning, but some theists accept it as part of creation.

Misunderstanding: Science fiction ideas of parallel worlds are the same as the cosmological multiverse.

Correction: Different theories use the word. The many-worlds reading of quantum mechanics and the inflationary multiverse are distinct proposals.

Misunderstanding: If there is a multiverse, God is unnecessary.

Correction: A multiverse generator would also need explanation. Whether God is needed for that is the same question one level up.

Knowledge check

How does the multiverse answer fine-tuning?

If there are enormous numbers of universes with varying constants, some will permit life, and observers will necessarily find themselves in one of those. So a life-permitting universe is not improbable overall and needs no designer. The reply accepts the physics but rejects the inference to a creator.

What is the inverse gambler’s fallacy objection?

Hacking argued that inferring many universes from the one observed is like inferring many earlier throws from seeing a double six. Each throw is independent, so the result does not show earlier throws. Multiverse defenders reply that the analogy fails if one asks why any life-permitting universe exists, and philosophers disagree.

Why is the multiverse said to be hard to test?

Other universes are by definition not observable from this one. Critics say a theory that cannot be tested is not science. Defenders say that a theory is tested through its observable predictions, even if some consequences cannot be observed. Some physicists, like Steinhardt, think the multiverse makes inflation theory untestable.

Can a theist accept the multiverse?

Yes. A Creator could make many universes, and some theists see this as a sign of abundance. The multiverse and the mechanism that produces it would still be contingent and need explanation. The argument then shifts from the fine-tuning of one universe to the nature of the generating mechanism.

Think it through

  1. What would you accept as evidence for another universe?
  2. Does the multiverse seem to you simpler or more complex than a Creator?
  3. Is it fair to count unobservable entities against a theory?
  4. What do you make of a theist welcoming the multiverse?

Independent assignment

Weighing the replies

In your own notebook, write 350 to 500 words. List the replies to fine-tuning in this lesson, and for each write what it asserts, what it costs, and the best objection to it. Then write which reply seems strongest and why. Do not send this to anyone.

Further study