By Magis contributor Robert Kurland, PhD
As pointed out in a previous inxtallment, given the contracting size of the universe as one goes back to the origin, there will be a time such that quantum effects must come into play. However, there are some basic limitations to using quantum mechanics as a theory for the origin of the universe. As Ellis points out:
“The attempt to develop a fully adequate quantum gravity approach to cosmology is of course hampered by the lack of a fully adequate theory of quantum gravity, as well as by the problems at the foundation of quantum theory (the measurement problem, collapse of the wave function, etc.)”
The measurement problem is at the heart of difficulties in the interpretation of quantum mechanics. The quantum mechanical state function can be represented as a superposition of several possible states that could be measured—when the measurement is made and a particular state results, then the superposition “collapses” into the state that is measured (e.g. Schrodinger's dead and live cat paradox). An associated difficulty is the probability interpretation for measurement: the universe state function (wave function) gives probabilities that particular values of dynamical variables will be measured—what does probability mean in this context; are there an infinite number of possible universes (corresponding to various possible measurements) and who does the measurement? To quote Christopher Isham (referring to the measurement problem):
“This poses the obvious problems of (i) when is an interaction between two systems to count as a measurement by one system of a property of the other? and (ii) what happens if there is an attempt to restore a degree of unity by describing the measurement process in quantum mechanical terms rather than the language of classical physics which is normally used? There is no universally accepted answer to either of these questions.” (emphasis added).
That being said, the following quantum mechanical models have been proposed for the origin of the universe (the list is not exhaustive, and only general comments on each will be given; for more information please see the cited articles by Isham and Grib):
1) Quantum fluctuations in the vacuum (Tryon, 1979).
2) Tunneling from “superspace” into “real” space-time (Vilenkin, 1982)
3) The Hartle-Hawking Block Universe, replacement of t by ti(i=square root of -1) (Hartle, Hawking, 1981)
4) Chaotic Inflation (for a description of cosmological “inflation", see below; Linde, 1986)
5) The Participatory Universe (Wheeler, 1990)
6) Creation from non-Boolean logic to Boolean by an “observer” (Grib,1990)
Note that in none of these (except possibly 3 or 5) was the creation “ex nihilo”; for 1, the vacuum pre-existed; for 2 the “superspace” (a hypothetical space of multi-dimensions); for 4, previous universes from which a “bubble” universe emerged via inflation; for 6, a hypothetical space of quantum universe states.
For 3, the Hartle-Hawking model, the replacement of t by ti gives a term t^2 instead of -t^2 in the quantum mechanical equation, which enables the quantum mechanical equation to be solved without a singularity. The variable t becomes space-like, rather than time-like at very early values, and the space-like ti gradually becomes a time-like variable (goes back to t) as the value of t increases. An exact value for the time of origin becomes undefined (where does the earth start, at the South pole?). A diagram fromhttp://www.ipod.org.uk/reality/reality_cosmic_universe.asp illustrates the time-line involved (vertical axis is increasing “t”). Note that there is no experimental justification for the replacement of t by ti; the justification is “esthetic”, that is the substitution removes the singularity at t=0.
In order to understand the significance of models 5 (the Particpatory Universe of John Wheeler) and 6 (the quantum logic model of Andrej Grib), a comment on an interpretation of quantum mechanics that links qm to consciousness will be helpful. (A general discussion of the various interpretations of quantum mechanics is beyond the scope of this summary}.
The Participatory Universe and Quantum Logic models stem from the interpretation, first set forth by Von Neumann, London and Wigner, that since measurement is done by an observer, the final step in the measurement process must be awareness of the measurement result by the consciousness of the observer, which therefore must be an intrinsic part of quantum mechanics. Wheeler construes the basic relation to consciousness to imply a universe that is information (It from bits), and that by looking back in time, we create the past universe, as symbolized in the famous icon at this web site: http://www.upscale.utoronto.ca/PVB/Harrison/BellsTheorem/wheeleru.gif
Grib's quantum logic model invokes a reality of non-Boolean logic that we (as observers) convert to Boolean logic situations, which is the only type of logic that our minds can comprehend. Grib speculates that perhaps it was God who made the initial observation to create a “real” universe (one perceived according to Boolean logic). According to Grib, time is a framework (lattice) for arraying the non-Boolean events in a framework that can be scanned as Boolean, and quantum mechanics is the theory for converting the non-Boolean system to Boolean.
It should be clear that none of these models can be confirmed or denied by measurements, so in that respect they are outside the realm of science, but properly belong to the domain of mathematical metaphysics (my take).
One development of quantum cosmology that does have measurable consequences is the notion of inflation introduced by Guth (1981), here explained by Ellis:
“Particle physics processes dominated the very early eras, when exotic processes took place such as the condensation of a quark-gluon plasma to produce baryons. Quantum field theory effects were significant then, and this leads to an important possibility: scalar fields producing repulsive gravitational effects could have dominated the dynamics of the universe at those times. This leads to the theory of the inflationary universe, proposed by Alan Guth ...an extremely short period of accelerating expansion will precede the hot big bang era [11]. This produces a very cold and smooth vacuum-dominated state, and ends in ‘reheating’: conversion of the scalar field to radiation, initiating the hot big bang epoch. This inflationary process is claimed to explain the puzzles mentioned above (Sec.2.4.1): why the universe is so special (with spatially homogeneous and isotropic geometry and a very uniform distribution of matter), and also why the space sections are so close to being flat at present (we still do not know the sign of the spatial curvature), which requires very fine tuning of initial conditions at very early times. (emphasis added) Inflationary expansion explains these features because particle horizons in inflationary FL models will be much larger than in the standard models with ordinary matter, allowing causal connection of matter on scales larger than the visual horizon, and inflation also will sweep topological defects outside the visible domain.”
Inflation also explains the rarity (absence) of magnetic monopoles (predicted by the standard model of particle physics), the presence of stars/galaxies (from quantum fluctuations expanded by inflation) and several features of the observed CBR (Cosmic Background Radiation). The projected time scale for the inflationary period is from about 10^-36s after the origin to about 10^-32s, during which period the volume increased by a factor of at least 10^78. As pointed out above, the source of the inflationary increase is an assumed force, a scalar field or isotropic negative pressure, counteracting the force of gravity. Although the notion of inflation explains many puzzling features about our universe, not all physicists are satisfied with this explanation. Other explanations have been offered, and as Ellis says:
“The promise of inflationary theory in terms of relating cosmology to particle physics has not been realized. This will only be the case when the nature of the inflaton (the hypothetical particle corresponding to the scalar inflationary field). has been pinned down to a specific field that experiment confirms or particle physics requires to exist.outside the visible domain.” (emphasis in the original).
Roger Penrose also has misgivings about inflationary theory, primarily due to what he thinks is a misplaced motivation for applying the theory to explain flatness and homogeneity:
“In the standard model these issues (the flatness, horizon and smoothness problems) are handled by the 'fine-tuning' of the initial Big Bang state, and this is regarded by inflationists as “ugly”. The claim is that the need for such fine tuning is removed in the inflationary picture and this is regarded as a more aesthetically pleasing physical picture.” (<Road to Reality, p.754)
It should be understood that in this context, “aesthetically pleasing” corresponds to the absence of an intelligent designer to set the “fine-tuning”, that is to say the absence of a creative God, or, alternatively, the absence of an as yet unknown “theory of everything” that would set the fine-tuning by some universal physical law (my take).