A good starting point for our brief discussion of consciousness is quantum cosmology, the theory that tries to unify cosmology and quantum mechanics.
If quantum mechanics is universally correct, then one may try to apply it to the universe in order to find its wave function. This would allow us find out which events are probable and which are not. However, it often leads to paradoxes. For example, the essence of the Wheeler-DeWitt equation (DeWitt, 1967), which is the Schrödinger equation for the wave function of the universe, is that this wave function does not depend on time, since the total Hamiltonian of the universe, including the Hamiltonian of the gravitational field, vanishes identically. This result was obtained in 1967 by Bryce DeWitt. Therefore if one would wish to describe the evolution of the universe with the help of its wave function, one would be in trouble: The universe as a whole does not change in time.
The resolution of this paradox suggested by Bryce DeWitt is rather instructive (DeWitt, 1967). The notion of evolution is not applicable to the universe as a whole since there is no external observer with respect to the universe, and there is no external clock that does not belong to the universe. However, we do not actually ask why the universe as a whole is evolving. We are just trying to understand our own experimental data. Thus, a more precisely formulated question is why do we see the universe evolving in time in a given way. In order to answer this question one should first divide the universe into two main pieces: i) an observer with his clock and other measuring devices and ii) the rest of the universe. Then it can be shown that the wave function of the rest of the universe does depend on the state of the clock of the observer, i.e. on his ‘time’. This time dependence in some sense is ‘objective’: the results obtained by different (macroscopic) observers living in the same quantum state of the universe and using sufficiently good (macroscopic) measuring apparatus agree with each other.
Thus we see that without introducing an observer, we have a dead universe, which does not evolve in time. This example demonstrates an unusually important role played by the concept of an observer in quantum cosmology. John Wheeler underscored the complexity of the situation, replacing the word observer by the word participant, and introducing such terms as a ‘self-observing universe’.
Most of the time, when discussing quantum cosmology, one can remain entirely within the bounds set by purely physical categories, regarding an observer simply as an automaton, and not dealing with questions of whether he/she/it has consciousness or feels anything during the process of observation. This limitation is harmless for many practical purposes. But we cannot rule out the possibility that carefully avoiding the concept of consciousness in quantum cosmology may lead to an artificial narrowing of our outlook.
Let us remember an example from the history of science that may be rather instructive in this respect. Prior to the invention of the general theory of relativity, space, time, and matter seemed to be three fundamentally different entities. Space was thought to be a kind of three-dimensional coordinate grid which, when supplemented by clocks, could be used to describe the motion of matter. Space-time possessed no intrinsic degrees of freedom, it played secondary role as a tool for the description of the truly substantial material world.
The general theory of relativity brought with it a decisive change in this point of view. Space-time and matter were found to be interdependent, and there was no longer any question which one of the two is more fundamental. Space-time was also found to have its own inherent degrees of freedom, associated with perturbations of the metric – gravitational waves. Thus, space can exist and change with time in the absence of electrons, protons, photons, etc.; in other words, in the absence of anything that had previously (i.e., prior to general relativity) been called matter.
Of course, one can simply extend the notion of matter, because, after all, gravitons (the quanta of the gravitational field) are real particles living in our universe. On the other hand, the introduction of the gravitons provides us, at best, with a tool for an approximate (perturbative) description of the fluctuating geometry of spacetime.This is completely opposite to the previous idea that space-time is only a tool for the description of matter.
A more recent trend, finally, has been toward a unified geometric theory of all fundamental interactions, including gravitation. Prior to the end of the 1970’s, such a program seemed unrealizable; rigorous theorems were proven on the impossibility of unifying spatial symmetries with the internal symmetries of elementary particle theory. Fortunately, these theorems were sidestepped after the discovery of supersymmetry and supergravity. In these theories, matter fields and space-time became unified within the general concept of superspace.
Now let us turn to consciousness. The standard assumption is that consciousness, just like space-time before the invention of general relativity, plays a secondary, subservient role, being just a function of matter and a tool for the description of the truly existing material world. But let us remember that our knowledge of the world begins not with matter but with perceptions. I know for sure that my pain exists, my ‘green’ exists, and my ‘sweet’ exists. I do not need any proof of their existence, because these events are a part of me; everything else is a theory. Later we find out that our perceptions obey some laws, which can be most conveniently formulated if we assume that there is some underlying reality beyond our perceptions.
This model of material world obeying laws of physics is so successful that soon we forget about our starting point and say that matter is the only reality, and perceptions are nothing but a useful tool for the description of matter. This assumption is almost as natural (and maybe as false) as our previous assumption that space is only a mathematical tool for the description of matter. We are substituting reality of our feelings by the successfully working theory of an independently existing material world. And the theory is so successful that we almost never think about its possible limitations. Guided by the analogy with the gradual change of the concept of space-time, we would like to take a certain risk and formulate several questions to which we do not yet have the answers (Linde, 1990a; Page, 2002):
Is it possible that consciousness, like space-time, has its own intrinsic degrees of freedom, and that neglecting these will lead to a description of the universe that is fundamentally incomplete? What if our perceptions are as real (or maybe, in a certain sense, are even more real) than material objects? What if my red, my blue, my pain, are really existing objects, not merely reflections of the really existing material world? Is it possible to introduce a ‘space of elements of consciousness,’ and investigate a possibility that consciousness may exist by itself, even in the absence of matter, just like gravitational waves, excitations of space, may exist in the absence of protons and electrons?
Note, that the gravitational waves usually are so small and interact with matter so weakly that we did not find any of them as yet. However, their existence is absolutely crucial for the consistency of our theory, as well as for our understanding of certain astronomical data. Could it be that consciousness is an equally important part of the consistent picture of our world, despite the fact that so far one could safely ignore it in the description of the well studied physical processes? Will it not turn out, with the further development of science, that the study of the universe and the study of consciousness are inseparably linked, and that ultimate progress in the one will be impossible without progress in the other?
Instead of discussing these issues here any further, we will return back to a more solid ground and concentrate on the consequences of eternal inflation and the multiverse theory that do not depend on the details of their interpretation. As an example, we will discuss here two questions that for a long time were considered too complicated and metaphysical. We will see that the concept of the multiverse will allow us to propose possible answers to these questions.
Inflation, Quantum Cosmology and the Anthropic Principle
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Anthropic principle can help us to understand many properties of our world. However, for a long time this principle seemed too metaphysical and many scientists were ashamed to use it in their research. I describe here a justification of the weak anthropic principle in the context of inflationary cosmology and suggest a possible way to justify the strong anthropic principle using the concept of the multiverse.
Department of Physics, Stanford University, Stanford, CA 94305, USA