The Multiverse and Philosophy (June 16-18, 2025)
In recent decades, there has been tremendous growth in scientific theories which postulate the existence of universes beyond our own.
There are many fruitful connections between these multiverse theories and different subfields of philosophy, including the philosophy of science, the philosophy of physics, metaphysics, epistemology, and the philosophy of religion. But to date, these have not been explored systematically.
This conference will include presentations by philosophers working in these areas. Their presentations will be work-in-progress versions of chapters to be included in the Wiley-Blackwell Companion to the Multiverse and Philosophy, which will be co-edited by Daniel Rubio (external link) and Klaas Kraay.
To register to attend, please click the button below. (There is no fee to attend.)
All sessions will take place in (PDF file) POD-366.
The Podium Building (POD) is a four-storey building that connects Jorgenson Hall (JOR) to the north with the Library Building (LIB) to the south. You can enter POD directly, or enter JOR or LIB and then make your way to POD.
If you have trouble accessing the building, please contact Klaas Kraay or Daniel Rubio.
Schedule for Monday, June 16th.
8:30-9:00 |
Welcome / Coffee |
9:00-10:30 |
“How Real are Scientific Possibilities?” Abstract: Nobody today is a modal realist – at least, not in the sense of believing that other possible worlds are concrete entities just like the actual world. But many philosophers are realists about nomic possibility in a weaker sense: they think that nomically possible worlds are really and robustly possible, that there are facts about what is nomically possible, and that these facts are determined by the laws of nature in the actual world. In this paper, I’ll argue for a weak realism about nomically possible worlds. I’ll argue, against some ‘serious actualists’, that we need possible worlds to understand scientific or nomic possibility. I’ll also discuss how nomic possibility and necessity are connected to our reasoning about the future and distant parts of spacetime, and how well various views - both reductionist and non-reductionist - accommodate the features of nomic possibility that underlie scientific reasoning. |
10:30-11:00 |
Break |
11:00-12:30 |
“Can We Learn from Physics That We Live in a Multiverse?" Abstract: To answer this question, I distinguish three epistemological pathways: anthropic reasoning, empirical confirmation, and metaphysical arguments. Since anthropic reasoning has been widely discussed, I focus instead on the latter two. Regarding empirical confirmation, I argue that the situation is less bleak than critics suggest. Several plausible scenarios allow for indirect causal connections with other universes, and the current absence of a known causal mechanism does not rule them out. On the metaphysical side, I examine rationalist motivations often dismissed as unphysical, and argue that such principles can play a legitimate heuristic role in theory development—though they cannot serve as standalone evidence for multiverse hypotheses. This is important, as it shows that multiverse hypotheses can be fruitful guiding principles—and by this alone, are genuinely scientific. I conclude that while we do not yet know whether we live in a multiverse, it remains a serious and scientifically investigable possibility—one that future physics may well confirm. |
12:30-2:00 |
Lunch - Bangkok Garden (external link, opens in new window) (Thai Buffet), 18 Elm Street. |
2:00-3:30 |
“Fine-Tuning, Multiple Universes, and Self-Locating Beliefs.” Abstract: Does the evidence that our universe is fine-tuned life confirm the multiverse hypothesis? The answer depends on our approach to self-locating beliefs. In a recent paper, Isaacs, Hawthorne, and Russell (2022) offer two arguments for thinking that such evidence does confirm the multiverse hypothesis. First, they argue that the three leading approaches to self-locating beliefs all entail that such evidence confirms the multiverse hypothesis. Second, they present a pair of theorems showing that any approach to self-locating beliefs that satisfies certain “reasonable” constraints will entail that such evidence confirms the multiverse hypothesis. I argue that Isaacs, Hawthorne, and Russell’s two arguments are not compelling, the first because they fail to consider some natural approaches to self-locating beliefs, the second because their theorems rely on a suspect premise that we should reject. Contra Issacs, Hawthorne, and Russell, I argue that on a natural approach to self-locating beliefs the evidence that our universe contains fine-tuned life needn’t confirm the multiverse hypothesis. |
3:30-4:00 |
Break |
4:00-5:30 |
“Centering Cosmological Calculations.” Abstract: According to many cosmological theories, in extremely large universes - including, perhaps, ours - the probability of the observed data occurring somewhere or other is one. To address confirmation problems which this generates, cosmologists have developed what are called `first-person probabilities': roughly, probabilities of our seeing the observed data, rather than probabilities of the observed data occurring somewhere or other. This paper investigates the assumptions used to calculate first-person probabilities in cosmology. As I argue, certain justifications for those assumptions face problems stemming from exactly how first-person phenomena relate to third-person phenomena. The problems are not insurmountable: some assumptions can be justified in alternative ways; other assumptions can be qualified. But the problems highlight the importance of exploring the foundational underpinnings of first-person probabilities. And that, in turn, motivates continued investigation of first-person phenomena in cosmological theorizing. |
6:00- |
Dinner - The Host (external link, opens in new window) (Indian Buffet), 87 Elm Street |
Schedule for Tuesday, June 17th.
8:00-8:30 |
Welcome / Coffee |
8:30-10:00 |
“Essences of Universes" Abstract: Some philosophers and physicists think that, if the multiverse hypothesis were true, it would explain why the universe is fine-tuned for life. Some philosophers object that this view rests on a mistake they label “the inverse gambler’s fallacy.” Whether proponents of the multiverse explanation of fine-tuning indeed do make this mistake hinges, in turn, on whether or not the values of the free parameters in a universe are essential properties of it or are instead merely accidental. Yet physicists have said very little about the essences of universes – about what makes a universe within the multiverse be the universe that it is. In this paper I will survey the limited information we have from physicists about the inverse gambler’s fallacy and the essences of universes – specifically, responses to a multiple-choice survey I administered ten years ago. Then I will present for discussion a battery of prompts for written answers for a follow-up survey to be conducted later this year. |
10:00-10:15 |
Break |
10:15-11:45 |
"On Carroll's Multiverse Model" Abstract: Modern cosmology has been plagued by the specter of Boltzmann Brains. In what follows, I discuss the history of the notion of a random fluctuating observer in the development of statistical mechanics. I likewise discuss the historical development of the modern notion of a Boltzmann Brain in modern cosmology. Using cosmology, lessons from the historical discussion, the science and philosophy of mind together with some important modern epistemology, I show that given very modest assumptions, Boltzmann Brains cannot be justifiably used to motivate an abandonment of the multiverse explanation of the fine-tuning of our universe. In addition, I distinguish my argument for this conclusion from other arguments against Boltzmann Brains in the literature. |
11:45-1:00 |
Lunch - Catered in POD-366. |
1:00-2:30 |
“Cosmic Earliness and the Multiverse.” [via Zoom] Abstract: On some cosmological models, we’re cosmically early: whereas we arrived roughly 14 billion years after the Big Bang, our universe will remain habitable for trillions of years. Why are we so early? I’ll survey some candidate kinds of explanations and explore how they interact with multiverse hypotheses. In particular, I’ll discuss: (i) eternal (inflationary) youth explanations on universes are created at an accelerating rate, forever resulting in a preponderance of younger universes, (ii) impending doom explanations on which the universe will soon cease to be habitable, and (iii) growing block explanations on which the growing block theory of time holds an induces a bias toward earlier observations. I’ll then explore how each of these proposals distinctively interact with multiverse hypotheses. One takeaway will be that multiverse hypotheses are evidentially entangled with how our cosmic earliness is to be explained. |
2:30-2:45 |
Break |
2:45-4:15 |
“Self-Indication and the Multiverse.” [via Zoom] Abstract: The Self-Indication Assumption (SIA) is a controversial principle which says (roughly): observers should favor hypotheses on which there are more observers. SIA suggests a straightforward argument for multiverse hypotheses. The argument is of distinctive interest because it supports multiverse hypotheses using a mundane observation, not fine-tuning, quantum mechanics, or modal metaphysics. Building on some recent work on SIA, we defend this argument partly by showing that stock objections to SIA are misguided, and partly by showing how SIA can be understood as a species of inductive inference in a way that blocks these objections. Finally, we use this inductive understanding of SIA to shed light on the extent to which SIA supports different multiverse hypotheses. The upshot is that — properly understood — SIA lends significant support to some multiverse hypotheses, but not dramatic support of the sort that is often taken as a basis for rejecting SIA. |
| 4:15-4:30 | Break |
| 4:30-6:00 | "Against the Everettian Interpretation of Quantum Mechanics.” Abstract: TBA |
6:00- |
Dinner - 3 Brasseurs Pub (external link, opens in new window) (275 Yonge Street) |
Schedule for Wednesday, June 18th.
8:30-9:00 |
Welcome / Coffee |
9:00-10:30 |
“Who’s That Guy? Exploring Trans-Universe Identity.” Abstract: Various multiverse theories entail that there exist universes containing things that are near- duplicates of one another (or even duplicates). This paper argues that there are only two open options: such things are straightforwardly distinct (and, in no way, count as ‘being the same as’ the other things) or they stand in a relation analogous to that between the product of a fission process. The paper argues that which open option to opt for depends solely upon whether the multiverse is branched or not. The paper discusses alternatives (e.g. analogues of transworld identity/counterpart theory, treating people as trans-universal fusions à la perdurantism, treating people as multi-located entities etc.), and lays out the problems for such views. The paper also discusses how the two open options feed into the ways in which we might use multiverse theory, including: issues in quantum immortality; discussions about the problem of the best vs the problem of evil (with this paper arguing that the multiverse helps with the former but not the latter); and the fine-tuning argument. |
10:30-11:00 |
Break |
11:00-12:30 |
“On the Cosmological Argument for a Multiverse.” Abstract: Three distinct evidential arguments are commonly advanced in support of the multiverse hypothesis. The fine-tuning argument contends that support comes from the fact that nature's fundamental parameters are fine-tuned for life. The anthropic argument posits that our mere existence provides such evidence. Finally, the cosmological argument proposes that such evidence arises merely from the fact that the universe exists. The central claim of this chapter is that the success of both the fine-tuning and anthropic arguments hinges upon the success of the cosmological argument. After establishing this dependency thesis, I will explore several potential strategies for resisting the cosmological argument. My overall aim is twofold: first, to demonstrate the pivotal role of the cosmological argument in these related debates, and second, to sketch out some promising directions for future research regarding its viability. |
12:30-2:00 |
Lunch - Milestone's (external link, opens in new window) , 218 Yonge Street. |
2:00-3:30 |
“A Dispiriting Theistic Multiverse?” Abstract: Supposing that God exists, there is reason to think that God has created many universes. Creating a multiverse would allow God to produce a greater variety in the kinds of value exhibited in creation. And if God has created a multiverse, this fact could blunt the problem of evil by helping to explain why God might create some “mediocre” universes that, though good on the whole, are not sufficiently good to be choiceworthy in a hypothetical situation where God was limited to creating a single universe. I argue here that a theistic multiverse, especially one with numerous mediocre universes, may have a number of unpalatable implications. The prospect of such a multiverse may deplete theism of resources for countering philosophical pessimism, challenge the notion that creatures could be special to God, and undermine confidence in the adequacy of divine revelation. After explaining these concerns, I consider whether the theist has any plausible basis for rejecting multiverse theories which have these dispiriting implications. One promising position says that God would avoid creating merely mediocre universes since (i) their existence would compromise certain great goods that would otherwise be found in the best sorts of universes; and (ii) due to value incommensurability, the loss of these goods could not be compensated by goods in the mediocre universes. |
3:30-4:00 |
Break |
4:00-5:30 |
"God's Multiverse and the Inverse Gambler's Fallacy" Abstract: The multiverse objection to the fine-tuning argument holds that a multiverse explains fine-tuning just as well as, or better, than appeal to a designer. If an infinite collection of universes exist, all of which differ randomly in their fundamental constants and initial conditions, then by sheer chance, some universe or other within this collective will be life-permitting, and we could only observe one of those fortunate universes. So, it is no surprise, nor does it demand any further explanation, that we exist within a fine-tuned universe. In response, Michael Rota argues that even if our universe is part of a wider multiverse, fine-tuning is still evidence that a cosmic designer exists – because the fact that our universe is life-permitting is evidence that we exist as part of a theistic multiverse rather than a naturalistic one. After outlining Rota's argument, I draw out the parallels to philosophical discussion of the "this universe" objection to the multiverse: the charge that appealing to a multiverse to explain fine-tuning commits the inverse gambler's fallacy. I conclude that Rota's argument can only succeed if the "this universe" objection does so as well. Given that the latter does not succeed, neither does Rota's argument. |
6:00- |
Dinner |