The Universe Around Us: An Integrative View of Science & Cosmology

Chapter 7: The Congenial Environment


Section 7.1: The Anthropic question

Section 7.2: The Weak Anthropic Principle

Section 7.3: The Strong Anthropic Principle

Section 7.4: Issues of ultimate causation

References for Chapter 7

This chapter looks at the issue of why the Universe has the very special nature required in order that life can exist. The various fundamental ways to explain this fact are explored.


Section 7.1: The anthropic question

The previous discussion has made it clear that initial conditions in the Universe are such as to provides a suitable the environment for the Earth, and for life on the Earth. One of the most profound fundamental issues arising is the Anthropic question, see [91,95,105-108].

·        Why have conditions in the Universe been so ordered that intelligent life can exist ?

The point is that a great deal of "fine tuning" has taken place in order that life be possible; in particular various fundamental constants are highly constrained in their values if life as we know it is to exist. There are many relationships imbedded in physical laws that are not explained by physics, but are required for life to be possible. How has it come about that the Universe permits the evolution and existence of intelligent beings at any time or place?

As discussed above, the laws of physics and chemistry are such as to allow the functioning of living cells, individuals, and ecosystems of incredible complexity and variety, and it is this that has made evolution possible. What requires explanation, is why the laws of physics are such as to allow this complex functionality to work, without which no evolution whatever would occur. We must take into account here the perilous nature of the evolutionary procedure: many false starts can occur, with entire species repeatedly being wiped out [67]; even once life has started [68], it is far from certain it will reach the heights it has done on Earth. Nevertheless if the laws and boundary conditions are right, evolution of intelligent life is possible.

7.1.1 The issue of fine tuning

We can easily consider universes where life would not be possible. There could be universe that expanded and then recollapsed with a total lifetime of only 100 thousand years; evolution could not take place on that timescale. The background radiation might never drop below 3000 K, so that matter was always ionised (electrons and nuclei always remaining separate from each other); the molecules of life could then never form. Black holes might be so common that they rapidly attracted all the matter in the universe, and there never was a stable environment in which life could develop. Cosmic rays could always be so abundant that any tentative organic structures are destroyed before they can replicate.

Thus there are many ways that the boundary conditions in a universe could prevent life occurring. But additionally, we can conceive of universes where the laws of physics (and so of chemistry) were different than in ours. Almost any change in these laws will prevent life as know it from functioning. If the neutron mass were just a little less than it is, proton decay could have taken place so that no atoms were left at all. The production of carbon and oxygen in stars requires the careful setting of two different nuclear energy levels; if they were just a little different, the elements we need for life would not exist [91]. Perhaps most important of all, the chemistry on which the human body depends [24] involves intricate folding and bonding patterns that would be destroyed if the fine structure constant (which controls the nature of chemical binding) were a little bit different. If the dimensions of space and time were wrong, life would not be possible, see Max Tegmark's paper on this: [webpage]. He also gives a diagram showing how life would be impossible if the strong coupling constant or the electromagnetic coupling constant were to have the wrong values: [webpage]. Weinberg has emphasized that if the cosmological constant is too large then galaxies will not form.

The series of such issues have been summarised usefully by Al Schroeder, as follows:

Anthropic Issues

size of the universe


emptiness of universe


the weak force and helium production


stellar balance


electron excitation and stellar types


beryllium bottleneck in the making of heavy elements  


neutrinos the weak interaction and supernovae  


electron to proton mass ratio


electron-neutron mass ratio


neutron-proton mass differential


electron-proton charge equality


di-protons and nuclear force


asymptotic freedom and the number of quark flavours




the number of spatial dimensions


the size of the cosmological constant

  no web page  

Table 7.1 Anthropic issues arising in cosmology, astrophysics, and physical laws.

To understand the import of this, one must appreciate the complexity of what has been achieved [49-53]. The structure and function of a single living cell is immensely complex. However a human grows to an interconnected set of 10 thousand billion cells, all working together as a single purposive and conscious organism in a hierarchically controlled way (the organisation issue), put together according to instructions in the DNA molecules that are read out and executed in an order that depends both on time and position (the issue of development), able to function continuously all the time as the number of cells increases coherently from 1 to 10 thousand billion in a highly organised fashion, passing through different stages of maturity (the issue of growth), all of this happening in an interacting set of organisms of a similar levels of complexity within a hospitable environment (the ecosystem issue), this system itself developing from a single cell to the level of complexity we see around us today (the evolution issue), all the while remaining functional. And all of this is possible because of the nature of quantum mechanics (essentially the Schrödinger equation and the Pauli exclusion principle) and of the forces and particles described by physics (essentially the electromagnetic force acting on the proton and the electron, together with the strong force binding the protons and neutrons in the atomic nuclei), which together control the nature of chemistry and hence of biological activity. They all fit together as required because of the precise values taken by the fundamental constants that control the strengths of physical interactions, which happen also to allow the functioning of stars as required to produce the needed elements, and allow development of the solar system (which is made possible through the force of gravity), with a hospitable surface for life on the Earth [91,95,107] (one of the key elements here being the remarkable properties of water [49,95], which again would be different if the fundamental constants were different). They are based on the properties of biochemical molecules, in turn based on the chemistry of the periodic table. The following version shows the elements that are essential to life as we know it:

1H                                 4 He
3 Li 4 Be                       5B   6 C 7 N 8 O 9 F 10 Ne
11 Na 12 Mg                     13 Al  14Si   15 P 16 S 17 Cl 18 Ar
19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga  32Ge  33As  34 Se 35 Br 36 Kr
37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51Sb   52Te  53 I 54 Xe
55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi   84Po  85 At 86 Rn
87Fr 88 Ra 89 Ac 104 Unq 105 Unp 106 Unh                        

Table 7.2: The Periodic Table of the Elements. Those in red are essential to all biological species. Those in purple are essential to human beings.

If we have altered physics that results in altered chemistry, we must somehow attain elements that will replace the functioning of all those shown in red above. That may be possible but to demonstrate it is possible is a tall order.

The nature of this achievement is truly awesome. And the modern moves towards determining a unified fundamental theory of all forces could make this even more amazing, because if physics ever achieved its aim of determining a single theory with essentially no free constants [37,38], then these extraordinarily complex structures would be the result of the action of that unified theory: in effect, the nature of the unified fundamental force would be pre-ordained to allow, or even encourage, the existence of life.

In summary, to allow life to occur, we require the existence of heavy elements; sufficient time for evolution of advanced life forms to take place; regions that are neither too hot nor too cold; restricted values of fundamental constants that control chemistry and local physics; and so on. Thus only particular laws of physics, and particular initial conditions in the Universe, allow the existence of intelligent life. No evolution whatever is possible if these laws and conditions do not have a restricted form.

7.1.2 Necessary general features

Apart from all the specific features of the laws of nature that allow complex functioning, there are four general features that are of importance.

Firstly, as emphasized by P C W Davies [6], the concept of locality is fundamental, allowing local systems to function effectively independently of the detailed structure of the rest of the Universe. The complex of interacting systems in a human body could not possibly work if this were not so.

Secondly, the existence of an arrow of time, and hence of laws like the second law of thermodynamics are probably necessary for evolution and for consciousness. This depends on boundary conditions at the beginning and end of the Universe (cf. the discussion in the previous chapter) (Thus local systems do depend critically on the large-scale properties of very distant matter; but not on its detailed properties, so allowing locality. The large-scale structure provides a stable local environment within which forces can act to provide locally deterministic behaviour..

Thirdly, physical conditions must be in a quasi-equilibrium state, or the delicate balances that allow our existence and evolution will not be fulfilled.

Finally, presumably the emergence of a classical era is required (the very early universe would be a domain where quantum physics would dominate, leading to complete uncertainty and an inability to predict the consequence of any initial situation; we need this evolve to a state where classical physics leads to the properties of regularity and predictability that allow order to emerge).

All of these will only occur if the boundary conditions of the Universe are chosen in a particular way. They will not be true in a generic universe. Thus the Universe provides a hospitable environment for humanity. Why is this so? Because of the deep connections just discussed, this is not an issue related to only one aspect of the structure of the Universe; it refers to the total inter-related organisation of the laws of nature and the boundary conditions for those laws, that fashions the Universe as we know it.


Section 7.2: The Weak Anthropic Principle

There are two purely scientific approaches to the Anthropic issue (I omit the so-called Final Anthropic Principle (FAP for short [95]), which maintains that intelligent life must necessarily evolve and then remain in existence until the end of the universe, for I do not believe merits serious discussion as a scientific proposal; indeed it led to a famous book review referring to the Completely Ridiculous Anthropic Principle (CRAP for short).). The first is the weak anthropic principle (WAP), based on the comment: it is not surprising the observed Universe admits the existence of life, for the Universe cannot be observed unless there are observers in it [95,106,107]. This seemingly empty statement gains content when we turn it round and ask, at what times and places in the Universe can life exist, and what are the inter-connections that are critical for its existence? It could not for example exist too early in the present expansion phase, for the night sky would then have been too hot. Indeed from this viewpoint the reason the observed night sky is dark at night is that if it were not dark, there would be no observers to see it.

Furthermore one can deduce various necessary relations between fundamental quantities in order that the observers should exist (e.g. those mentioned above), so that if for example the fundamental constants vary with time or place in the Universe, life will only be possible in restricted regions where they take appropriate anthropic values.

Hence this view basically interprets the anthropic principle as a selection principle:

  • the necessary conditions for observers to exist restricts the times and places from which the Universe can be observed.

This is an interesting and often illuminating viewpoint (for example, neither the Chaotic Inflationary Universe idea nor the Many-World interpretation of Quantum Cosmology (discussed below) work unless we add such an Anthropic component into their interpretation to explain why we observe the Universe from a viewpoint where it appears homogeneous and isotropic). It is now used by senior physicists to explain the low value of the cosmological constant (which quantum field theory predicts shoul have a very much larger value then observed). Its successful use may be claimed to depend on use of Bayesian statistics to underpin inductive inference [108]. However it is also a conservative approach, avoiding the main issue under discussion in this section.


Section 7.3: The Strong Anthropic Principle

By contrast, the Strong Anthropic Principle (SAP) tackles the issue head on [95,106,107], claiming that it is necessary that intelligent life exist in the Universe; the presence of life is required in order that a universe model make sense.

This is clearly a very controversial claim, for it is hard to provide scientific reasons to support this view. The most solid justification attempted is through the claim that existence of an observer is necessary in order that quantum theory can make sense. However this is based on one of a number of different interpretations of quantum theory; the nature of these quantum foundations is controversial [19], and probably falls within the untestable category of issues discussed above. Furthermore if we were to suppose this argument correct, then the next step is to ask, Why does the Universe need quantum mechanics anyway? The argument would be complete only if we could prove that quantum mechanics was absolutely necessary for every self-consistent Universe; but that line of reasoning cannot be completed at present, not least because quantum mechanics itself is not a fully self-consistent theory (apart from the logical issues at its foundation, it suffers from divergences that so far have proved irremediable in the sense that we can work our way round them to calculate what we need, but cannot remove them).

Neither argument by itself gives a convincing answer to the anthropic question. To make progress, we have to seriously consider the nature of ultimate causation.


Section 7.4: Issues of ultimate causation

The question posed is, what is the foundational cause for the surface phenomena we see? That is, if we pursue the chain of physical cause and effect as far as we can follow it, we still are left with the question: Why did this all occur? [1,7,8]. Whatever the reason is, that is the ultimate cause we are seeking when we follow the chain of causation to its conclusion.

Note that we are here leaving the terrain of science itself, and starting to probe the domain of metaphysics - the foundations of science and indeed of existence. Those who are interested purely in scientific issues should skip the rest of this section.

There appear to be basically six approaches to the issue of ultimate causation [10]: namely Random Chance, High Probability, Necessity, Universality, Cosmological Natural Selection, and Design. We briefly consider these in turn.

7.4.1 Option 1: Random Chance, signifying nothing

Conditions in the Universe just happened initially, and led to things being the way they are now, by pure chance. Probability does not apply. There is no further level of explanation that applies; searching for `ultimate causes' has no meaning.

This is certainly logically possible, but not satisfying as an explanation, particularly because we obtain no unification of ideas or predictive power from this approach). Nevertheless some scientists implicitly or explicitly hold this view.

7.4.2 Option 2: High probability

Although the structure of the Universe appears very improbable, for various physical reasons it is in fact highly probable (the chaotic cosmology idea). These arguments are only partial successful even in their own terms, for they run into problems if we consider the full set of possibilities (many discussions implicitly or explicitly restrict the considered possibilities a priori, for otherwise it is not very likely the Universe will be as we see it); and we do not have a proper measure to apply to the set of initial conditions, enabling us to assess these probabilities. Furthermore, application of probability arguments to the Universe itself is dubious, because the Universe is unique.

Despite these problems, this approach has considerable support in the scientific community, for example they underlie the inflationary proposal for cosmology discussed above.

7.4.3 Option 3: Necessity

Things have to be the way they are; there is no option. This can be taken in a strong form or a weak one. The strong form is the claim that the features we see and the laws underlying them are demanded by the unity of the Universe (coherence and consistency require that things must be the way they are; the apparent alternatives are illusory). Thus it is the claim that only one kind of physics is self-consistent: all logically possible universes must obey the same physics. The weak form is that only one kind of physics is consistent with the sort of world we actually see around us.

To really prove either would be a powerful argument, potentially leading to a self-consistent and complete scientific view; but we can imagine alternative universes! - why are they excluded?

Bondi has emphasized that insofar as the view that there is a major unity underlying the Universe is valid, sufficient study of any part of Universe will reveal its whole structure, because of bonds of necessity. However a partial counter-argument is provided by considering the locality of physics, mentioned above: we are able to predict what will happen in a laboratory without knowing the total state of distant regions of the Universe. Furthermore we run here into he problem that we have not succeeded in devising a fully self- consistent view of physics: neither the foundations of quantum physics nor of mathematics are on a solid, consistent basis. Until these issues are resolved, this line cannot be pursued to a successful conclusion.

In this and the last case, life exists essentially as an accidental by-product of a probable or a necessary situation; in effect, as far as the existence of life is concerned, we have a more sophisticated version of the "chance" argument. Indeed if one could make the "necessity" argument stick, or even determine a ``theory of everything" that explained the relations between the fundamental constants, then (as mentioned above) the issue would become even more mysterious: for why would this unique theory have precisely the qualities required to allow life? It would be a most extraordinary kind of coincidence linking the foundation of physics to emergent layers of meaning in the macroscopic world.

7.4.4 Option 4: Universality

This is the stand that ``All that is possible, happens": an ensemble of universes is realised in reality. In its full version, the Anthropic principle is realised in both its strong form (if all that is possible happens, then life must happen) and its weak form (life will only occur in some of the possibilities that are realised; these are picked out from the others by the WAP, viewed as a selection principle). There are four ways this has been pursued.

1: The view may be that this happens in space through random initial conditions, as in chaotic inflation. While this provides a legitimate framework for application of probability, from the viewpoint of ultimate explanation it does not really succeed, for there is still then one unique Universe whose (random) initial conditions need explanation. Initial conditions might be globally statistically homogeneous, but also there could be global gradients in some physical quantities so that the Universe is not statistically homogeneous; and these conditions might be restricted to some domain that does not allow life. It is a partial implementation of the ensemble idea; insofar as it works, it is really a variant of the "high probability" idea mentioned above.

2: It could happen in time, in a universe that has many expansion phases (a Phoenix universe, cf. the previous chapter), whether this occurs globally or locally. Much the same comments apply as in the previous case.

3: Alternatively, it could occur through the existence of the Everett-Wheeler ``many worlds" of quantum cosmology, where all possibilities occur through quantum branching (This is one of the few real alternatives proposed to the Copenhagen interpretation of quantum mechanics, which leads to the necessity of an Observer, and so to the controversial Strong Anthropic interpretation considered above..

This view is controversial; it is accepted by some but not all quantum theorists [19,34]. If we hold to it, we then have to explain the properties of the particular history we observe (why does our macroscopic Universe develop to have high symmetries when almost all these branchings will not?).

4: Finally they could occur as completely disconnected universes: there really is an ensemble of universes in which all possibilities occur, without any connection with each other (cf. [109] and see [webpage]). A problem that arises then is, what determines what is possible? (for example, what about the laws of logic themselves? Are they inviolable in considering all possibilities?) We cannot answer, for we have no access to this multitude of postulated worlds.

In all these approaches, on the one hand, major problems arise in relating this view to testability and so we have to query the meaningfulness of the proposals as scientific explanations (particularly in the last case, where it is not even claimed that there is some causal connection to "our" Universe); on the other hand, in each case in order to explain our actual observations one has of necessity to introduce an (anthropic) selection element (cf. the previous section), for most of the universe(s) will not look like a isotropic model; why do we live in a region that does ?

Furthermore they all contradict the Ockham's razor approach to physics: they are very uneconomical in the mode of explanation. Why does this ensemble of Universes exist? (we "solve" one issue at the expense of envisaging an enormously more complex existential reality; ultimate explanation of this reality is even more problematic than in the case of single Universe). Nevertheless this approach has an internal logic of its own some find compelling.

7.4.5 Option 5: Cosmological Natural Selection

This has been described above - Smolin's idea that the universe will evolve through a Darwinian-like process to wards a state that will maximise black hole production and re-expansion to new expanding universe regions. The problem here is that it is not clear - assuming this proposed process can be explicated in detail - that the physics which maximises black hole production is necessarily also the physics that favours the existence of life. If this argument could be made water-tight, this would become probably the most powerful of the multi-verse proposals.

7.4.6 Option 6: Design

The symmetries and delicate balances we observe require an extraordinary coherence of conditions and cooperation of laws and effects, suggesting that in some sense they have been purposefully designed, i.e. they give evidence of intention, realised both in the setting of the laws of physics and in the choice of boundary conditions for the Universe.

This is the basic theological view. Unlike all the others, it introduces an element of meaning, of signifying something (in all the other cases, life exists by accident; as a chance by-product of processes blindly at work [65]). The prime disadvantage of this view, from the scientific viewpoint, is its lack of testable scientific consequences ("Because God exists, I predict that the density of matter in the Universe should be x and the fine structure constant should be y"); this is one of the reasons scientists generally try to avoid this approach. There will be some who will reject this possibility out of hand, as meaningless or as unworthy of consideration. However it is certainly logically possible.

One should note here that the modern version of the Design argument is different from the old one. Originally one might have envisaged God specifically designing human beings. The more modern version, consistent with all the scientific discussion preceding, would see God designing the Laws of Nature and the Boundary conditions for the Universe, in such a way that life (and eventually humanity) would then come into existence through the operation of those laws, leading to the development of specific classes of animals through the process of evolution as evidenced in the historical record [65,67]. The issue we are concerned with, in terms of ultimate causation, is the nature of matter and fundamental forces, and why they not only admit the existence of life but even prefer it. Given the acceptance of evolutionary development, it is precisely in the choice and institution of particular physical laws and initial conditions, allowing such development, that the profound creative activity takes place, and is where one might conceive of design taking place. However from the viewpoint of physical sciences per se, there is no reason to accept this argument. Indeed from this viewpoint there is really no difference between design and chance, for they have not been shown to lead to different physical predictions.

It must be emphasized that particular models of the nature of the physical Universe (a `big-bang' origin, a steady state Universe without temporal origin, chaotic inflation, a Universe starting according to the Hartle-Hawking `no-boundary' ideas) do not seriously affect the issue of fundamental causation, despite claims to the contrary; a priori, either existence or non-existence of a Designer could be compatible with any of these modes of realisation of a physical Universe. Indeed a Designer could choose to work through any of the other proposed "fundamental" approaches, should he or she wish to do so. However the ultimate issue of existence of Designer and any associated higher reality remains unanswered (as does the ultimate issue of existence in all approaches).

7.4.7 The essential choice

The major point is that

  • In considering the Anthropic issue, in the end we are faced with a choice between one of the options above as to the nature of ultimate causation of the Universe.

If we look at the Anthropic Issue from a purely scientific basis, we end up without any resolution, basically because science attains reasonable certainty by limiting its considerations to restricted aspects of reality; even if it occasionally strays into that area, it is not designed to deal with ultimate causation. By itself, it cannot make choice between these options.

Thus a broader viewpoint is required to make progress, taking into account both the scientific and broader viewpoints. The issue is of philosophical rather than scientific nature. One important issue that then arises is what kind of data is relevant to these philosophical choices, in addition to that which can be characterised as purely scientific data. That issue will not be pursued further here.


References for Chapter 7: The congenial environment

The Anthropic Principle is discussed in [91], [95] and

[105] P C W Davies: The cosmic Blueprint (London: Heinemann, 1987)

[106] J Leslie: Universes (Routledge, 1989)

with a masterly survey of the literature of the subject given in

[107] Y V Balashov: Resource Letter Ap-1 The Anthropic Principle Amer Journ Phys 54:1069-1076 (1991),

and its relation to statistical testing discussed in

[108] A J M Garrett and P Coles: Bayesian Inductive Inference and the Anthropic Cosmological Principle. Preprint (Queen Mary College, London, 1992)*.

The issue of multiples universes is presented in an intriguing novel:

[109] O Stapledon: Starmaker. (Dover, 1968) 

and is discussed in various recent books by Martin Rees, for example

[110] M Rees: Just Six Numbers (2000).