Am decis sa amin ce aveam de gind sa scriu saptamina aceasta in favoarea unor simple citate relevante pentru o discutie recenta. Sint astfel de cel putin doua ori nedrept. In primul rind pentru ca respectiva discutie nu intereseaza probabil prea multa lume. Si, in al doilea, pentru ca am preluat fragmentele in originalul englezesc. Nadajduiesc ca-mi veti trece cu vederea eventuala vexatiune.
Autorul rindurilor de mai jos este J. Craig Wheeler, astrofizician american. Cartea se numeste Cosmic Catastrophes. Si-a avut prima editie in 2000. A doua editie, din care citez, e din 2007, din timpul mandatului autorului ca presedinte al American Astronomical Society.
„The singularity of Einstein’s theory cannot exist. Something else must happen to space and time ‘‘there.’’ In the absence of the full development of quantum gravity, physicists are left to grope. When physicists grope, startling ideas emerge.
We know the scale on which Einstein’s theory must break down, even if we do not fully understand what must replace it. This scale can be estimated from the simple idea of asking about the conditions where quantum uncertainty must be as important as the
space–time curvature of gravity. The fundamental constants of quantum gravity are the strength of gravity as measured by Newton’s constant from the world of the large, the degree of quantum uncertainty as measured by Planck’s constant from the world of the small, and Nature’s speed limit, the speed of light from the world of the very fast. With values for these constants of Nature in some set of units, English or metric, it does not matter, one can estimate the scale where Einstein’s theory, and ordinary quantum theory, fail. This scale, of length, time, density, is called the Planck scale. Newton’s constant has units of length cubed, time squared, and the inverse of mass. Planck’s constant has units of mass, length squared, and the inverse of time. The speed of light has units of length over time. There is only one way we can combine these three fundamental constants with their individual units to produce a quantity of only length, only one other way to produce a time, and only a single third way to produce a mass. This exercise is a simple one of sorting out units, but it has profound implications because the building blocks are the fundamental constants that tell us how space curves, the degree of quantum uncertainty, and how fast things can move. Their combination implicitly tells us where space gets so curved that a quantum wave cannot exist and simultaneously where quantum uncertainty is so large that speaking of a given curvature makes no sense. We learn the conditions where the two great theories of twentieth-century physics butt heads and contradict one another, the conditions that call for a new theory of physics.
The resulting value of the length, the Planck length, is about 10^(-33) centimeters. This is an incredibly small value, much smaller than the size of a proton, but it is not zero! This is roughly how large the singularity must be. At this level, space and time break down into something else, and Einstein’s prediction of a singularity goes awry. The corresponding Planck time is about 10^(-43) seconds. This is again an incredibly short time, but not zero. Time as we know it probably does not exist at shorter intervals, so that asking what happened when the Universe was younger than 10^(-43) seconds or before the big bang may not make sense, at least not in the traditional way. The Planck mass is about 10^(-5) grams. This is a small number, but not incredibly small. It is vastly bigger than any elementary particle we know. One can also work out the Planck density, the Planck mass divided by the cube of the Planck length. The answer is about 10^93 grams per cubic centimeter. This is a gigantic density, but it is not infinite. In some average way, this must be the density of a singularity, the density from which our Universe expanded in the big bang, the density to which all is compressed in the centers of black holes.”
Nu ezitati sa cititi cartea profesorului Wheeler in intregime. Poate va vor contraria fraze precum: „When a black hole forms, all the matter is crushed into the singularity. The mass of the star is no longer represented by an area but by a point.” Sau: „The singularity is a region of mystery, where our present laws of physics break down.” Si, din nou: „For a black hole, all the mass that creates the gravity is literally at this point in the center, at the singularity.” Nu-i nimic.
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