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The Problem of the Primitive Universe.
...Consider a particle at time t = 0, or at a time "close to t = 0." Suppose it emits any kind of signal, for example electromagnetic radiation. This signal will propagate at speed c. After time t, the spherical wavefront will have a radius ct, known as the horizon. However, the law of expansion—the separation between two particles assumed to be tied to the "cosmic substrate" (so-called comoving particles)—follows a parabolic pattern (this distance grows as t²/³). Going backward in time, we will always find an epoch t < th where particles were physically incapable of communicating with each other, since they were receding "faster than the electromagnetic wave emitted at a time close to zero."
...The following image evokes the autistic state of the universe: the white spheres, linked to each particle, represent the volumes within which a neighboring particle would have to be located for communication to be possible. Unfortunately, these spheres do not overlap, and will not do so for a very long time.
...Thus, it becomes difficult to justify the remarkable homogeneity of the primitive universe, whose fossil trace is the cosmic microwave background radiation at 2.7 K.
...The currently favored theory is Linde's: inflation—and that is its sole justification. Without going into detail, this theory consists in endowing the primitive universe with a super-cosmological constant (time-dependent!), reflecting a "repulsive power of the vacuum" beyond all imagination. This then triggers an expansion by a factor of ten to the power of who knows how many...
The Problem of the Origin.
What, in fact, is this time t = 0? Does it even make sense?
...As we go back in time, the temperature of the "cosmic fluid" increases. The thermal agitation velocity of particles with non-zero mass also increases. Eventually, this velocity becomes relativistic. In fact, as t approaches zero and temperature T approaches infinity, the individual energy of particles tends toward infinity, and their velocity tends toward c. Proper time follows the law:
...As v approaches c, proper time "freezes in clocks." Defining a clock becomes problematic, even conceptually.
...Thus, we see that the standard model is far from perfect. The list of problems mentioned is by no means exhaustive. Fundamental physics faces similar issues. String theory involves extending the dimensional framework (ten dimensions, for many). Yet, ten-dimensional geometry remains a dark jungle. While two-dimensional surfaces have lost their mystery, the classification of three- and four-dimensional hypersurfaces remains to be done.
...Moreover, when extra dimensions are added to the cosmos, characteristic lengths emerge, associated with each dimension. And these are invariably... the Planck length. Now, length implies wavelength, which is linked to energy via the relation:
...Planck energy is enormous. To harness it using classical techniques, one would need an accelerator with the diameter of a galaxy. Experimental physicists raise their hands in despair.
...The Japanese-born theoretical physicist Michio Kaku ("Hyperspace: A Scientific Odyssey Through the Tenth Dimension," Oxford University Press, 1995) offers a delicious personal interpretation: in his view, string theory is simply centuries ahead of its time. At the current stage of technology, it is therefore merely a way to entertain oneself among friends.
The Aspen Conference.
...In 1996, the renowned magazine Scientific American published a report on a recent conference on string theory held in Aspen, Colorado, written by staff writer Madhusree Mukerjee. The text reads like a sketch from the Marx Brothers:
...As the article's author recalls, in 1986 they had asked Jeffrey A. Harvey, of the University of Chicago, to define string theory in seven words. His response had been:
- Oh, Lord, why have you forsaken me? (God, why have you forsaken me?)
But the paper notes that God seems to have answered, through the discovery of a new symmetry: duality.
...Witten, the most optimistic of the string theorists, believes this duality will not only lead to the TOE (Theory of Everything) but also explain "why the universe is the way it is." He thinks we are converging toward an explanation of the deep nature of quantum mechanics.
...Few people actually tackle string theory, which is indeed so complex on every level—including mathematically—that physicists and mathematicians shy away from it.
...The article states that this "duality" would make elementary particles and composite objects interchangeable. Specialists then refer to clumps (massive, bunches, tufts) which they attempt to visualize as "hedgehogs." To curl like a hedgehog: to ball up tightly. Other images include "spheres studded with vectors," dubbed "solitons."
...But, the authors of this concept emphasize, if such duality existed, it would remain impossible to demonstrate (by duality, one must understand "double nature": English dictionary). The article clarifies, therefore, that composite structures could be equivalent when "tangled up" (entangled, interwoven) and thus become "elementary objects."
The concept of "mirror symmetry" is then raised, without much success.
...In 1986, Duff from Imperial College London had considered the vibrations of a new entity, "a bubble" (a bubble). While strings wriggled (wiggle) in ten dimensions, these bubbles would float in an eleven-dimensional space. Then Duff considered five-dimensional membranes—alternative descriptions relative to strings. He later imagined these membranes could themselves wrap around like "the skin of a sausage." And he evoked a "string-string duality."
...In 1995, Witten delivered a lecture at Berkeley, conjecturing that Duff's bubbles could be solitons of a particular string corresponding to ten dimensions.
And Schwarz from Caltech (one of the pioneers of the theory) added:
- I should have been a truck driver!
In any case, currently, ten new papers on string theory appear every day.
A soliton "resembles a hairy caterpillar," bristling with vectors—thus, "the dual object of the string."
Duff then proposed a duality of duality between spaces. And Susskind commented:
The size and internal dimension of an object would "switch places" from one location to another.
Townsend:
- Membranes transforming into string solitons could have the same status as strings. Unfortunately, calculations using membranes make no sense.
...A marriage between strings and black holes is then discussed. Hawking had indicated that black holes, being capable of emitting particles, would thus lose mass and shrink. If they were initially made of strings ("stringy black holes"), their evolution would transform them into objects of zero size: "an extremal black hole looking in fact rather like a particle." A debate arises between Susskind and Strominger on this point:
- Strominger's work is "great," but calling these things black holes is still pushing it a bit.
For reference, the title of the...