Weak Anthropic Principle Research Articles

Contemporary Philosophical Perspectives on the Cosmological Constant

The (re)introduction of Λ into cosmology has spurred debates that touch on central questions in philosophy of science, as well as the foundations of general relativity and particle physics. We provide a systematic assessment of the often implicit philosophical assumptions guiding the methodology of precision cosmology in relation to dark energy. We start by briefly introducing a recent account of scientific progress in terms of risky and constrained lines of inquiry. This allows us to contrast aspects of Λ that make it relevantly different from other theoretical entities in science, such as its remoteness from direct observation or manipulability. We lay out a classification for possible ways to explain apparent accelerated expansion but conclude that these conceptually clear distinctions may blur heavily in practice. Finally, we consider the important role played in cosmology by critical tests of background assumptions, approximation techniques, and core principles, arguing that the weak anthropic principle fits into this category. We argue that some core typicality assumptions—such as the Copernican principle and the cosmological principle—are necessary though not provable, while others—such as the strong anthropic principle and appeals to naturalness or probability in the multiverse—are not similarly justifiable.

Sometimes Size Does Not Matter

Recently Díaz, Hössjer and Marks (DHM) presented a Bayesian framework to measure cosmological tuning (either fine or coarse) that uses maximum entropy (maxent) distributions on unbounded sample spaces as priors for the parameters of the physical models ( https://doi.org/10.1088/1475-7516/2021/07/020 ). The DHM framework stands in contrast to previous attempts to measure tuning that rely on a uniform prior assumption. However, since the parameters of the models often take values in spaces of infinite size, the uniformity assumption is unwarranted. This is known as the normalization problem. In this paper we explain why and how the DHM framework not only evades the normalization problem but also circumvents other objections to the tuning measurement like the so called weak anthropic principle, the selection of a single maxent distribution and, importantly, the lack of invariance of maxent distributions with respect to data transformations. We also propose to treat fine-tuning as an emergence problem to avoid infinite loops in the prior distribution of hyperparameters (common to all Bayesian analysis), and explain that previous attempts to measure tuning using uniform priors are particular cases of the DHM framework. Finally, we prove a theorem, explaining when tuning is fine or coarse for different families of distributions. The theorem is summarized in a table for ease of reference, and the tuning of three physical parameters is analyzed using the conclusions of the theorem.

Olympism and himalaism

As the title makes it clear, this article concerns the anthropological issue involving the figures of an Olympic athlete and a Himalayan climber. On a broader, philosophical level, I consider and explain the differences between Olympism and Himalaism, as well as the predecessor of Himalaism, Alpinism. The study aims to explain the reason for the origin of Olympism as a social movement independent of Himalaism. To understand why Olympism and Himalaism should be considered separately, one must go back to the dawn of the two modern events: “visiting the mountains” and “populating the stadiums”. The philosophical method was used in the consideration .The two events never became a unity of being in the anthroposphere, nor a unity of meaning in the axiosphere. The distinctness of each is explained by the metaphysical anthropic principle. Olympism is governed by the strong anthropic principle of the “zone of life”, while Himalaism is governed by the weak anthropic principle of the “zone of death”. The anthropic principle of the Himalayas states that the mountains have those exact properties that enable a person to get to know themselves as an antagonist – a warrior and ultimately a conqueror. For people the initial and boundary conditions of the Himalayas, which are marked by the “zone of death”, are the verge of the anthroposphere in their expansive transgression. Olympism with its anthropically strong 'zone of life' is something different. Only “at” the foot of the mountain can one set up a stadium, engage in an agonistic relationship and get to know oneself as the winner of a good competition or even, if historically necessary, the redeemer of the moral evil in the antagonism of war. In this sense, Olympism becomes a philosophy of moral consolation. The result of the study shows that the Himalayan climber does not participate in the universe of the humanistic culture of the Olympics. Sport climbing to be introduced into the Games of the XXXII Olympics, in 2021 will remind us of this self-referencial existence at the edges of the anthroposphere, as well as the predecessor, of Himalaism, Alpinism.

Is cosmological tuning fine or coarse?

The fine-tuning of the universe for life, the idea that the constants of nature (or ratios between them) must belong to very small intervals in order for life to exist, has been debated by scientists for several decades. Several criticisms have emerged concerning probabilistic measurement of life-permitting intervals. Herein, a Bayesian statistical approach is used to assign an upper bound for the probability of tuning, which is invariant with respect to change of physical units, and under certain assumptions it is small whenever the life-permitting interval is small on a relative scale. The computation of the upper bound of the tuning probability is achieved by first assuming that the prior is chosen by the principle of maximum entropy (MaxEnt). The unknown parameters of this MaxEnt distribution are then handled in such a way that the weak anthropic principle is not violated. The MaxEnt assumption is “maximally noncommittal with regard to missing information.” This approach is sufficiently general to be applied to constants of current cosmological models, or to other constants possibly under different models. Application of the MaxEnt model reveals, for example, that the ratio of the universal gravitational constant to the square of the Hubble constant is finely tuned in some cases, whereas the amplitude of primordial fluctuations is not.

Alternative mechanisms for Gaia

A long-standing objection to the Gaia hypothesis has been a perceived lack of plausible mechanisms by which life on Earth could come to regulate its abiotic environment. A null hypothesis is survival by pure chance, by which any appearance of regulation on Earth is illusory and the persistence of life simply reflects the weak anthropic principle - it must have occurred for intelligent observers to ask the question. Recent work has proposed that persistence alone increases the chance that a biosphere will acquire further persistence-enhancing properties. Here we use a simple quantitative model to show that such ‘selection by survival alone’ can indeed increase the probability that a biosphere will persist in the future, relative to a baseline of pure chance. Adding environmental feedback to this model shows either an increased or decreased survival probability depending on the initial conditions. Feedback can hinder early life becoming established if initial conditions are poor, but feedback can also prevent systems from diverging too far from optimum environmental conditions and thus increase survival rates. The outstanding question remains the relative importance of each mechanism for the historical and continued persistence of life on Earth.

Prediction and typicality in multiverse cosmology

In the absence of a fundamental theory that precisely predicts values for observable parameters, anthropic reasoning attempts to constrain probability distributions over those parameters in order to facilitate the extraction of testable predictions. The utility of this approach has been vigorously debated of late, particularly in light of theories that claim we live in a multiverse, where parameters may take differing values in regions lying outside our observable horizon. Within this cosmological framework, we investigate the efficacy of top-down anthropic reasoning based on the weak anthropic principle. We argue contrary to recent claims that it is not clear one can either dispense with notions of typicality altogether or presume typicality, in comparing resulting probability distributions with observations. We show in a concrete, top-down setting related to dark matter, that assumptions about typicality can dramatically affect predictions, thereby providing a guide to how errors in reasoning regarding typicality translate to errors in the assessment of predictive power. We conjecture that this dependence on typicality is an integral feature of anthropic reasoning in broader cosmological contexts, and argue in favour of the explicit inclusion of measures of typicality in schemes invoking anthropic reasoning, with a view to extracting predictions from multiverse scenarios.

Big bang nucleosynthesis: The strong nuclear force meets the weak anthropic principle

Contrary to a common argument that a small increase in the strength of the strong force would lead to destruction of all hydrogen in the big bang due to binding of the diproton and the dineutron with a catastrophic impact on life as we know it, we show that provided the increase in strong force coupling constant is less than about 50% substantial amounts of hydrogen remain. The reason is that an increase in strong force strength leads to tighter binding of the deuteron, permitting nucleosynthesis to occur earlier in the big bang at higher temperature than in the standard big bang. Photodestruction of the less tightly bound diproton and dineutron delays their production to after the bulk of nucleosynthesis is complete. The decay of the diproton can, however, lead to relatively large abundances of deuterium.

IS COSMOLOGICAL ACCELERATION DRIVEN BY CLASSICAL SPACE–TIME GEOMETRY?

The homogeneous expansion history H(z) of our universe (Hubble diagram) measures only kinematic variables, it cannot fix the underlying dynamics driving the recent acceleration: cosmographic measurements of the homogeneous universe are consistent with either a static fine-tuned cosmological constant or a dynamic "dark energy" mechanism, which itself may be either material dark energy or low-curvature modifications of Einstein gravity (dark gravity). This dark energy/dark gravity degeneracy in the homogeneous expansion observations can only be resolved by observing the growth of the cosmological fluctuations. However, because the "dark energy" evolution is now quasi-static at most, any dynamical effects on the fluctuation growth function g(z) will be minimal. Projected observations may potentially distinguish static from dynamic "dark energy", but distinguishing dynamic dark energy from dark gravity will require a weak lensing shear survey more ambitious than any now projected. Dark gravity is also, in principle, observable in the solar system or in isolated galaxy clusters. The cosmological constant problem — that quantum material vacuum fluctuations apparently do not gravitate — suggests identifying gravitational "vacuum energy" with classical intrinsic space–time curvature, divorcing it from any quantum material property. This empty space–time curvature appears cosmologically and about isolated sources and can only be fine-tuned, at present. The cosmological coincidence problem — that we live when the ordinary matter density approximates the "gravitational vacuum energy" — on the other hand, is a material problem, calling for an understanding of the observers' role in cosmology. A particularly restrictive weak anthropic principle, that dark energy and dark gravity be indistinguishable, selects static "dark energy" (ΛCDM) and rejects any dynamical effects in the growth of fluctuations.

The Non-trivial character of the Weak Anthropic Principle

In contemporary debates on the status of the Anthropic Principle, the Weak Anthropic Principle (WAP) appears noncontroversial from the standpoint of the natural sciences. It states that the observed values of physical parameters belong to the small set of values required for genesis of carbon-based life [1, p. 15], WAP is evidently free of the strong metaphysical assumptions underlying either the Participatory or the Final variant of the Anthropic Principle. Its critics, however, when trying to question its philosophical significance, argue that WAP is trivial; the very fact of our existence implies that these parameters assume the values necessary for the emergence of carbon-based life. In this approach, stronger versions of the Anthropic Principle could by philosophically significant, but they are physically unfounded; WAP is physically justified but philosophically trivial.

Anthropic reasoning and typicality in multiverse cosmology and string theory**Thanks to Yuri Balashov, Gordon Belot, Rob Caldwell, Marcelo Gleiser, Brad Monton, Ken Olum, Jim Peebles, Lee Smolin and Alex Vilenkin for helpful discussions and comments on an earlier draft.

Anthropic arguments in multiverse cosmology and string theory rely on the weak anthropic principle (WAP). We show that the principle is fundamentally ambiguous. It can be formulated in one of two ways, which we refer to as WAP1 and WAP2. We show that WAP2, the version most commonly used in anthropic reasoning, makes no physical predictions unless supplemented by a further assumption of ‘typicality’, and we argue that this assumption is both misguided and unjustified. WAP1, however, requires no such supplementation; it directly implies that any theory that assigns a non-zero probability to our universe predicts that we will observe our universe with probability one. We argue, therefore, that WAP1 is preferable, and note that it has the benefit of avoiding the inductive overreach characteristic of much anthropic reasoning.

Anthropic Interpretation of Quantum Theory

The problem of interpreting quantum theory on a large (e.g. cosmological) scale has been commonly conceived as a search for objective reality in a framework that is fundamentally probabilistic. The Everett programme attempts to evade the issue by the reintroduction of determinism at the global level of a “state vector of the universe.” The present approach is based on the recognition that, like determinism, objective reality is an unrealistic objective. It is shown how an objective theory of an essentially subjective reality can be set up using an appropriately weighted probability measure on the relevant set of Hilbert subspaces. It is suggested that an entropy principle (superseding the weak anthropic principle) should be used to provide the weighting that is needed. The application of this ansatz to a toy gedanken example (involving Schroedinger's legendary cat) is described in an appendix.

ON THE COSMOLOGICAL CONSTANT AND THE COSMIC COINCIDENCE PROBLEM

According to a recently proposed idea the indirectly observed negative pressure of our present universe might be explained by the trace anomaly of quantum chromo-dynamics (QCD) as a non-perturbative effect of quantum fields in curved space-times. Examining some of the consequences of the proposed mechanism for the cosmic evolution yields no apparent contradiction with our present picture of the universe. In conjunction with the weak anthropic principle a natural explanation of the cosmic coincidence can be provided. Further aspects such as the late-time behavior are also addressed.

Copernicus, Kant, and the anthropic cosmological principles

In the last three decades several cosmological principles and styles of reasoning termed ‘anthropic’ have been introduced into physics research and popular accounts of the universe and human beings’ place in it. I discuss the circumstances of ‘fine tuning’ that have motivated this development, and what is common among the principles. I examine the two primary principles, and find a sharp difference between these ‘Weak’ and ‘Strong’ varieties: contrary to the view of the progenitors that all anthropic principles represent a departure from Copernicanism in cosmology, the Weak Anthropic Principle is an instance of Copernicanism. It has close affinities with the step of Copernicus that Immanuel Kant took himself to be imitating in the ‘critical’ turn that gave rise to the Critique of Pure Reason. I conclude that the fact that a way of going about natural science mentions human beings is not sufficient reason to think that it is a subjective approach; in fact, it may need to mention human beings in order to be objective.

Anthropic Fluctuations vs. Weak Anthropic Principle

A modern assessment of the classical Boltzmann-Schuetz argument for large-scale entropy fluctuations as the origin of our observable cosmological domain is given.The emphasis is put on the central implication of this picture which flatly contradicts the weak anthropic principle as an epistemological statement about the universe. Therefore, to associate this picture with the anthropic principle as it is usually done is unwarranted. In particular, Feynman's criticism of theanthropic principle based on the entropy-fluctuation picture is a product of this semantic confusion.

Observer-Relative Chances In Anthropic Reasoning?

John Leslie presents a thought experiment to show that chances are sometimes observer-relative in a paradoxical way. The pivotal assumption in his argument – a version of the weak anthropic principle – is the same as the one used to get the disturbing Doomsday argument off the ground. I show that Leslie's thought experiment trades on the sense/reference ambiguity and is fallacious. I then describe a related case where chances are observer-relative in an interesting way. But not in a paradoxical way. The result can be generalized: At least for a very wide range of cases, the weak anthropic principle does not giverise to paradoxical observer-relative chances. This finding could be taken to give new indirect support to the doomsday argument.

The Universe and Life: Deductions from The Weak Anthropic Principle

The existence of life in the Universe is interpreted in terms of the `Weak Anthropic Principle'. It is shown that cosmological models are constrained to a class that involves an open timescale and access to infinite quantities of carbonaceous material.

THE WEAK ANTHROPIC PRINCIPLE AND THE DESIGN ARGUMENT

Abstract. The design argument for God's existence was critically assessed when in the growth of modern science the cognitive value of ideological categories was called into question. In recent discussions dealing with anthropic principles there has appeared a new version of the design argument, in which cosmic design is described without the use of ideological terms. The weak anthropic principle (WAP), a most critical version of all these principles, describes the fine‐tuning of physical parameters necessary lo the genesis of carbon‐based life. It defines no physical mechanisms of the observed coordination between physical parameters. If in a future unified physical theory such mechanisms are discovered, the weak anthropic principle should be replaced by the strong anthropic principle, which asserts the physical necessity of fine‐tuning. Neither of the versions can be regarded as physically trivial unless one accepts strong assumptions of the existence of parallel universes. Consequently, a new version of the philosophical design argument can be developed on the basis of the weak anthropic principle.

Indifference principle and anthropic principle in cosmology

The successes scored by the big bang model of cosmic evolution in the 1960’s led to an intensive application of quantum theory to the problem of how the expansion might have begun and what its likely first stages were. It seemed as though an incredibly precise setting of the initial conditions would have been needed in order that a long-lived galactic universe containing heavy elements might develop. One response was to suppose that the fine-tuning could somehow be explained by the presence of humans in the universe. This ran quite counter to the traditional supposition, according to which an initial chaos was sufficient. This essay outlines the history of the two principles, argues that the so-called weak anthropic principle is banal, distinguishes between two sorts of anthropic explanation, and assesses the prospects of the anthropic turn in cosmology.

Origin of time asymmetry.

It is argued that the observed thermodynamic arrow of time must arise from the boundary conditions of the Universe. We analyze the consequences of the no-boundary proposal, the only reasonably complete set of boundary conditions that has been put forward. We study perturbations of a Friedmann model containing a massive scalar field, but our results should be independent of the details of the matter content. We find that gravitational wave perturbations have an amplitude that remains in the linear regime at all times and is roughly time symmetric about the time of maximum expansion. Thus gravitational wave perturbations do not give rise to an arrow of time. However, density perturbations behave very differently. They are small at one end of the Universe's history, but grow larger and become nonlinear as the Universe gets larger. Contrary to an earlier claim, the density perturbations do not get small again at the other end of the Universe's history. They therefore give rise to a thermodynamic arrow of time that points in a constant direction while the Universe expands and contracts again. The arrow of time does not reverse at the point of maximum expansion. One has to appeal to the weak anthropic principle to explain why we observe the thermodynamic arrow to agree with the cosmological arrow, the direction of time in which the Universe is expanding.

A many-universe theory of the cosmological constant or warm universe in the googolplexus

We reexamine the discouraging conclusion of Fischler, Klebanov, Polchinski and Susskind that second quantization of the Wheeler-DeWitt equation leads to the production of only cold and empty universes with vanishing cosmological constant Λ. We argue that if gravity is coupled to a scalar field with a suitable inflationary potential, the number of created universes which have at least one warm, inhabitable region by late times is exponentially peaked at Λ = 0. This appears to be a viable solution to the cosmological constant problem, invoking the weak anthropic principle in a natural way.