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Dark Corners of Cosmology

Sam Vaknin, Ph.D. - 10/21/2010

When we look out to the Cosmos, we survey an inventory of all the objects – stars, galaxies, and, now, planets – that had ever existed. Owing to the limited speed of light, our telescopes peer not only out to space but back in time as well. There is no way of knowing whether what we see still exists. Example: light from the binary star Alpha-Centaury requires 4.4 years to reach us. Thus, at any given moment we can ascertain that it had existed 4.4 years ago. Had it exploded 1 year ago, we would still count it as among the living for the next 3.4 years. Thus, the disciplines of cosmology and astrophysics are knowingly based on outdated information. We cannot vouch for any important measurement: the distribution of matter in the Universe, for instance, or even the total mass and energy of the Cosmos.

This all-pervasive uncertainty led scientists to invent Dark Matter and Dark Energy to account for the behaviour of matter-clumps in the Universe and for the accelerating recession of the farthest galaxies, respectively. Yet, these postulated entities rely on observational data that may no longer be valid. Other explanations may account for the receding galaxies: (1) That the speed of light is constant only locally; or that (2) it is an observational effect owing to a particular gravitational lensing; or that (3) the topology of the Cosmos may be such that it makes far objects appear farther at an accelerating rate.

More traditionally, though, the recent “discovery” (rather, postulation) of dark energy seems to restore entropy on the scale of the entire Universe. Actually, the traits of dark energy (homogeneity, isotropy, a lack of interaction with other forms of energy and matter, infinitesimal density, negative pressure) suggest that dark energy, the Cosmological Constant (Lambda) and quintessence fields are merely other names for entropy and are not related to vacuum energy.

Thus, a Big Rip, or Big Chill as the outcome of cosmic acceleration would merely be the culmination of the Second Law of Thermodynamics. This is definitely true for our local supercluster. Dark energy also compensates for the entropy gap (between actual cosmic entropy and maximum potential cosmic entropy which grows as the Universe expands): it transforms the whole Universe into a single black hole with an infinite cosmic event horizon.

This thermodynamic slant also agrees with superstring theories:

As a universe tunnels through the landscape (of string theory), from (mathematically modelled) "hill" to "valley", it retains (conserves) the entire information regarding the volume of (mathematically modelled) "space" (or of the space-like volume) of the portion of the landscape that it has traversed. These data are holographically encoded and can be fully captured by specifying the information regarding the universe's (lightlike) boundary (e.g., its gravitational horizon).

As the universe's entropy grows (and energy density falls), it "decays" and its inflation stops. This event determines its nature (its physical constants and laws of Nature). Eternal inflation is, therefore, a feature of the entire landscape of string theory, not of any single "place" or space-time (universe) within it.

Note of caution:

What is interpreted to imply the existence of multiple universes may be merely an artefact, enumerating all the ways that a four-dimensional surface can be folded, using supersymmetric formalism.

But what about singularities, black holes, and other anomalies?

String theory, which is supposed to incorporate quantum gravity, should offer insights regarding black holes. String theories make use of the General Relativity Theory (GRT) formalism and add to it specific matter fields. Thus, many classical black hole solutions satisfy string equations of motion. In an effort to preserve some supersymmetry, superstring theory has devised its own black hole solutions (with D-branes, or "black branes", as the description of certain supersymmetric black holes). A match was even found between types of supersymmetric black holes and supergravity including greybody factors (frequency dependent corrections). String theorists have derived most of Hawking's (and Bekenstein's) work regarding the entropy of black holes from string theories.

This led to novel ways of thinking about strings. What if "open" strings were really closed ones with one part "hidden" behind a black brane? What if intersecting black branes wrapped around seven curled dimensions gave rise to black holes? The vanishing masses of black branes delineate a cosmological evolutionary tree: from a universe with one topology to another, with another topology. Our world may be the "default" universe on the path of least resistance and minimum energy from one universe to another.

It would appear that spacetime itself may be the anomaly!

The particles with half integer spins predicted by supersymmetry are nowhere to be found. Either supersymmetry is a wrong idea or the particles are too heavy (or too something) to be detected by us with our current equipment. The latter (particles too heavy) is possible only if supersymmetry has broken down (which is almost the same as saying that it is wrong). Had it existed, it would probably have encompassed gravity (as does the General Theory of Relativity) in the form of "supergravity". The non-supersymmetric equivalent of supergravity can be gravity as we know it. In terms of particles, supersymmetry in an 11-dimensional universe talks about a supersymmetric gravitino and a spin 2 graviton.

Supersymmetric supergravity was supplanted by 10-dimensional superstring theory because it could not account for handedness in nature (i.e., the preference of left or right in spin direction and in other physical phenomena) and for many quantum effects. From there it was a short - and inevitable - way to membrane theories. Branes with "p" dimensions moved in worldvolumes with p+1 dimensions and wrapped around curled dimensions to produce strings. Strings are, therefore, the equivalents of branes. To be more precise, strongly interacting (10-dimensional) strings are the dual equivalent of weakly interacting five-branes (solitons) (Duff, Scientific American, February 1998). Later, a duality between solitonic and fundamental strings in 6 dimensions (the other 4 curled and the five-brane wrapped around them) was established and then dualities between strings from the 5 string theories. Duff's "duality of dualities" states that the T-duality of a solitonic string is the S-duality of the fundamental string and vice versa. In other words, what appears as the charge of one object can also be construed as the inversion of the length of another (and, hence, the size of the dimension). All these insights - pulled together by Witten - led to M Theory in 11 dimensions. Later on, matrix theories replaced traditional coordinates in space time with non-commutable matrices. In other words, in an effort to rigorously define M Theory (that is, merge quantum physics with gravity), space time itself has been "sacrificed" or "quantum theorized".