How Does Multiverse Proposal Affect the Design Argument?

Abstract

Recent observations suggest that many fundamental physical constants and conditions in our universe are fine-tuned for life to exist. This provides an important piece of evidence to support the Design Argument and the existence of God in the philosophy of religion. However, the proposal of multiverse provides a naturalistic account of the fine-tuning phenomena which apparently challenges the Design Argument. In general, most of the multiverse models have specific features and they have to satisfy empirical and logical constraints. Therefore, they may be intrinsically dependent on theistic proposal under the probabilistic Bayesian framework. In this article, I present a Bayesian framework to show how multiverse proposal affects the Design Argument. I show that there exist two specific scenarios in which the inclusion of multiverse proposal can indirectly increase the credence of the Design Argument.

1. Introduction

In the past few decades, observations suggested that many fundamental physical constants and conditions are fine-tuned for life to exist in our universe (McGrath 2009; Barnes 2012). For example, Martin Rees summarizes six important fine-tuned numbers in our universe (Rees 1999, pp. 2–3). If any of them has changed slightly in value, the existence of life would not be possible. In particular, the formation of stars and galaxies in our universe depends sensitively on the matter content of our universe. If the matter content has differed by one part in 10¹⁵ at one second after the Big Bang, formation of stars and life would not be possible (Rees 1999, p. 88). Moreover, the values of some constants controlling the fundamental forces in our universe lie within the extremely small life-permitting parameter of space (McGrath 2009, pp. 119–20; Lewis and Barnes 2016, pp. 65–94). The chance for these values to be inside the Goldilocks zone is, naturally, extremely small.

The precision of the fundamental constants and conditions apparently reveals that our universe is teleological and designed by a supernatural power (i.e., God). Therefore, the fine-tuning phenomena have provided an important piece of evidence to support the Design Argument (DA). The DA suggests that God has designed our universe and fine-tuned the fundamental constants and conditions for life to exist (Jantzen 2014, pp. 272–90). It can be shown that the universe having been designed by God is more likely than the chance that it arose randomly (Swinburne 2010, p. 80). Generally speaking, the DA is one of the most important arguments in the philosophy of religion to support the existence of God (Collins 2002).

Moreover, the string theory in theoretical physics has suggested another possible picture to describe our reality. The string theory landscape allows a large number of possible values of fundamental physical constants (Hawking and Mlodinow 2010; Read and Le Bihan 2021). If the multiverse exists and our universe is just one of the universes in reality, every universe may have a unique set of fundamental constants and initial conditions. It would be more probable to have one universe like our universe which has a correct set of fundamental constants and conditions for life to exist (Siegfried 2019, pp. 208–28). This idea of a multiverse is often modelled like the bubble universes (Hawking and Mlodinow 2010, pp. 136–37), or pocket universes (Carroll 2012, p. 191). When bubble universes pop up and each bubble universe can generate a unique set of fundamental constants and initial conditions, it would eventually hit one in the Goldilocks zone after a huge number of attempts. Therefore, the chance of getting a fine-tuned universe is not that small. The life appearance can be regarded as a result of the “cosmological natural selection” (Smolin 2007, pp. 351–52). It seems that the proposal of a multiverse can provide a naturalistic account of the fine-tuning phenomena which challenges and undermines the DA. Roughly speaking, the ideas of multiverse can be classified into two major types: inflationary multiverse (Linde 2007) and Many World Interpretation (MWI) (Everett 1957). In the following, our discussions do not depend on the type of multiverse in general.

There is a general impression and a standard contention that the multiverse proposal would undermine the fine-tuning version of the DA (Saward 2013). Nevertheless, when we discuss whether the multiverse can explain the fine-tuning phenomena, we should not treat the multiverse proposal as an arbitrary or ad hoc proposal. This means that the multiverse proposal that can address the fine-tuning universe should have some specific features to satisfy empirical and logical constraints. Otherwise, the multiverse proposal can explain everything, which explains nothing (Flew 2007, p. 118). For example, the multiverse proposal cannot suggest a very general multiverse which contains contradictory mathematical structures (Page 2007, p. 424). Therefore, the multiverse proposal we considered must have some intrinsic properties. It is logically possible that these intrinsic properties would have some relations with the theistic proposal. These potential relations would give influence to the DA.

In fact, the idea of multiverse and the existence of God are not completely incompatible. Some theistic scientists support the idea of theistic multiverse. For example, Collins (2007, pp. 459–80) believes that creation through multiverse by God is more elegant and ingenious than creating a single universe. However, the theistic multiverse proposals are usually regarded as a defence of the DA and a prevention of the multiverse proposal to explain away completely the fine-tuning phenomena for the DA. In fact, only a few philosophical discussions have investigated how the multiverse proposal affects the DA. For example, Glass (2012) has shown that there are reasons to believe that there is a significant residual confirmation of the DA even if we include the consideration of the multiverse proposal. Additionally, Swinburne (2012) has demonstrated that both confirmation and disconfirmation of the multiverse can affect the DA. However, the effects might not be very significant (Swinburne 2012, p. 120). In this article, based on the Bayesian framework demonstrated in Glass (2012), I explicitly show that there are two specific scenarios which can increase the credence of the DA with the inclusion of multiverse theory: 1. a theistic multiverse is more probable than a naturalistic multiverse; 2. God has reasons not to create the multiverse. We will briefly discuss the implications of the results in the final section.

2. Results

Consider two theories, T1 and T2, which can explain the evidence E of the fine-tuning phenomena. Let T1 and T2 be the DA (or God hypothesis) and the multiverse proposal, respectively. In Bayesian framework, if both T1 and T2 can give satisfactory explanations for the fine-tuning phenomena E, then we have P(T1|E) > P(T1) and P(T2|E) > P(T2). However, since T1 and T2 are not mutually exclusive in general, they can affect one another in principle. The effect can be characterised by the residual confirmation (RC), which is defined as follows (Glass 2012, p. 84):

$$\mathrm{RC}=\log \frac{\mathrm{P}(\mathrm{T}1|\mathrm{E},\mathrm{T}2)}{\mathrm{P}\left(\mathrm{T}1\right)}.$$

The above expression examines how T2 affects the credence of P(T1|E). If P(T1|E,T2) > P(T1), then we will have RC > 0. In this case, we can conclude that T1 still has some residual confirmation even if T2 exists. Otherwise, if RC < 0, the theory T2 would explain away the evidence E for T1.

In fact, theoretically evaluating the actual value of RC or the prior probability P(T1) would be very difficult. Therefore, we are not going to show whether RC is positive or negative. In the following, we will discuss if there are any special relations between T1 and T2 such that the value of RC would be increased (i.e., the credence of the DA is increased). If T1 and T2 are not independent, then we have P(T2|T1) ≠ P(T2). This means that T1 would affect the prior probability of T2. If T1 and T2 are independent of each other, then P(T2|T1) = P(T2) and the RC can be expanded as (Glass 2012, p. 85):

$$\mathrm{RC}\left(\mathrm{independent}\right)=\log {\left[\mathrm{P}\left(\mathrm{T}1\right)+\frac{\mathrm{P}\left(\mathrm{E}|~\mathrm{T}1,\mathrm{T}2\right)}{\mathrm{P}\left(\mathrm{E}|\mathrm{T}1,\mathrm{T}2\right)}\mathrm{P}\left(~\mathrm{T}1\right)\right]}^{-1}.$$

In the naturalistic framework, there should be no relation between T1 and T2 (or even refute T1). Therefore, the case of the independency between T1 and T2 would serve as a benchmark scenario for comparison.

2.1. Scenario 1

If T1 and T2 are not independent, starting from the definition of RC, we can expand the expression as (Glass 2012, p. 85):

$$\mathrm{RC}\left(\mathrm{dependent}\right)=\log {\left[\mathrm{P}\left(\mathrm{T}1\right)+\frac{\mathrm{P}\left(\mathrm{E}|~\mathrm{T}1,\mathrm{T}2\right)\mathrm{P}(\mathrm{T}2|~\mathrm{T}1)}{\mathrm{P}\left(\mathrm{E}|\mathrm{T}1,\mathrm{T}2\right)\mathrm{P}(\mathrm{T}2|\mathrm{T}1)}\mathrm{P}\left(~\mathrm{T}1\right)\right]}^{-1}.$$

If we have P(T2|T1) > P(T2|~T1), then we have:

$$\mathrm{RC}\left(\mathrm{dependent}\right)>\log {\left[\mathrm{P}\left(\mathrm{T}1\right)+\frac{\mathrm{P}\left(\mathrm{E}|~\mathrm{T}1,\mathrm{T}2\right)}{\mathrm{P}\left(\mathrm{E}|\mathrm{T}1,\mathrm{T}2\right)}\mathrm{P}\left(~\mathrm{T}1\right)\right]}^{-1}=\mathrm{RC}\left(\mathrm{independent}\right).$$

RC (dependent) > RC (independent) implies that the value of RC would increase if P(T2|T1) > P(T2|~T1). In other words, the credence of DA would increase if it were more probable to have a theistic multiverse than a naturalistic multiverse.

This scenario depends on the intrinsic properties or constrained properties of the multiverse theory. For example, some studies have pointed out that the probability of all the necessary conditions sufficient for life to exist is extremely small: log P < −10¹²³ (Penrose 1990, pp. 343–44). However, the number of universes in current string landscape multiverse theory (~10⁵⁰⁰) (Hawking and Mlodinow 2010, p. 118) is not enough to explain the fine-tuning phenomena. Additionally, computer simulations show that the multiverse would imply time-dependent natural laws in our universe (Gil and Alfonseca 2013). However, this is not the observed case. Therefore, the multiverse theory required has to be fine-tuned in order to match the current observations and the necessary conditions for life to exist. The existence of God can increase the prior probability of the required multiverse theory. If this is the case, we would have P(T2|T1) > P(T2|~T1). Moreover, some studies have shown that inflationary multiverse requires a beginning in a larger set of time (Chan 2019). Otherwise, it would have actualized the impossible actual infinity. In view of this, the existence of God can provide the possible origin of the multiverse, which may also support P(T2|T1) > P(T2|~T1). Therefore, these arguments can indirectly increase the credence of DA even if we accept the theory of multiverse.

In other words, the multiverse proposal does not necessarily eliminate the place of a Designer or Creator. The intrinsic properties required for the multiverse proposal to address the empirical data or logical consistency may point to the need of a Designer as well. The potential relation between multiverse and the Designer can be merely implicit. We may have a rough idea that the multiverse proposal contains nearly infinitely many universes which can increase the probability of hitting the Goldilocks zone. However, even if we assume that there are infinitely many universes, it does not entail that we must have the right universe for life to evolve. For instance, there are infinitely many odd numbers in the number system. However, it is impossible to get an even number from a pool of infinitely many odd numbers. Putting this idea in the context of our physical world, if there is a constraint on the charge of an electron that keeps it always ten times greater than its present value, we can have an infinity of different universes, but none will have the electron charge in the Goldilocks zone. Therefore, infinity does not imply all options. Logical gaps might still exist in the infinitely many universes if there is any implicit constraint on the fundamental constants. In other words, the number of universes may not be the most important issue. Rather, whether the fundamental constants allowed in the multiverse proposal can hit the Goldilocks zone is also important. In view of this, some multiverse models (e.g., the string landscape) suggest that the fundamental constants are related to the Calabi-Yau manifolds in string theory (Yau and Nadis 2012). The shapes of the manifolds depend on the intrinsic geometry. Therefore, specific manifolds are required to match the right fundamental constants. This means that we still need to ask why these manifolds exist to produce the right fundamental constants. This may move the problem of fine-tuning up one level to the higher-level fine-tuning (Murray and Rea 2008, p. 154), which further supports the DA. It is possible for the DA to be more likely given the premises inherent in the multiverse objection.

2.2. Scenario 2

Starting from the definition of RC and replacing T2 by ~T2, we can rewrite the expression as:

$$\mathrm{RC}\left(\mathrm{dependent}\right)=\log {\left[\mathrm{P}\left(\mathrm{T}1\right)+\frac{\mathrm{P}\left(\mathrm{E}|~\mathrm{T}1,~\mathrm{T}2\right)\mathrm{P}(~\mathrm{T}2|~\mathrm{T}1)}{\mathrm{P}\left(\mathrm{E}|\mathrm{T}1,~\mathrm{T}2\right)\mathrm{P}(~\mathrm{T}2|\mathrm{T}1)}\mathrm{P}\left(~\mathrm{T}1\right)\right]}^{-1}.$$

If we have P(~T2|T1) > P(~T2|~T1), then we have

$$\mathrm{RC}\left(\mathrm{dependent}\right)>\log {\left[\mathrm{P}\left(\mathrm{T}1\right)+\frac{\mathrm{P}\left(\mathrm{E}|~\mathrm{T}1,~\mathrm{T}2\right)}{\mathrm{P}\left(\mathrm{E}|\mathrm{T}1,~\mathrm{T}2\right)}\mathrm{P}\left(~\mathrm{T}1\right)\right]}^{-1}=\mathrm{RC}\left(\mathrm{independent}\right).$$

Therefore, the value of RC would increase if P(~T2|T1) > P(~T2|~T1). In other words, the credence of the DA would increase if God had some reasons not to create a multiverse. This result is not trivial. If there is any theological model which suggests that God would not create a multiverse, the probability of actualizing a multiverse would decrease because a multiverse can only originate naturally. Therefore, the probability of the single universe scenario would be relatively larger, which indirectly increases the credence of the DA.

This scenario is theologically model-dependent. For example, Chan (2015) has pointed out that based on the principle of simplicity, ontological economy, and minimum disadvantages, God would create a single universe rather than a multiverse if God is perfectly good. Chan (2015) argues that God can create our fine-tuned universe through either a multiverse proposal or single-universe proposal, if God is omnipotent. However, creating a single universe is much simpler than creating many universes. There is no strong reason why God would follow a complicated way (i.e., a multiverse) to create our fine-tuned universe. Secondly, creating a multiverse would generate a lot of unwanted or wasted universes. These universes have no relation with us so therefore creating a multiverse is not ontologically economical. A wise God should choose an economical way to manifest His creation (Chan 2015). Thirdly, one can imagine that allowing useless universes in the multiverse proposal might generate bad universes, which are purposeless and totally dead (Chan 2015). Creating these useless universes is not consistent with the good creation from a perfectly good God. Nevertheless, Collins (2007) believes that God might create a multiverse if God is infinitely creative. He believes that God behaves like a great artist rather than a great engineer. He would express creativity and ingenuity in creation rather than considering the smallest amount of material used in the creation (Collins 2007). Therefore, the theological views on multiverse are quite diverse. In fact, the ideas of a multiverse in theology have been discussed for a very long time (Rubenstein 2014). There are various theological multiverse proposals to fit with the required scenarios.

Here, we are not going to discuss which theological model is correct. The scope of this study is to point out that the credence of DA could be increased for specific scenarios. Further studies following this direction can possibly formulate new arguments to support the DA.

3. Discussion

Intuitively, the proposal of the multiverse would challenge the credence of the DA. However, in this article, I show that there exists two scenarios in which including the consideration of multiverse proposal would indirectly increase the credence of the DA. If one can theoretically show that a theistic multiverse is more probable than a naturalistic multiverse or God has reasons not to create multiverse, then these arguments could indirectly raise the credence of the DA. I have briefly outlined a certain possible models and proposals (e.g., fine-tuned multiverse) which can satisfy these scenarios. Our results imply that more in-depth investigations of the related theological models or multiverse models could be able to provide new arguments to support the DA indirectly. Moreover, our results also point out that the multiverse objection does not necessarily undermine the DA. The multiverse proposal should not be an arbitrary idea or ad hoc model to account for the fine-tuning phenomena. The multiverse proposal must contain intrinsic features which can satisfy the required empirical and logical constraints. These intrinsic features might be related to the theistic proposal implicitly, which would indirectly affect the credence of the DA. Therefore, the multiverse objection of the DA is not a knock-down argument by default. It depends on what multiverse proposal we are considering and the details of the multiverse proposal.

Note that the above discussion does not depend on whether multiverse theory can be verified or falsified. Some recent defence of the DA focuses on the falsifiability of the multiverse theory (Ellis 2011). Some studies attack the proposal of multiverse by arguing its complexity (Swinburne 1998, p. 178; Lewis and Barnes 2016, p. 306). In fact, whether multiverse theory is falsifiable or it is complicated is controversial (Carroll 2019). Here, I show that the DA could gain credence even if multiverse theory could be considered, or even verified. The inclusion of multiverse theory does not necessarily challenge the DA in general. Therefore, it can provide a new direction of study for the theistic version of multiverse or the relation between God and multiverse.