|
Fuzzballs are theorized by some superstring theory scientists to be the true quantum description of black holes. The theory resolves two intractable problems that classic black holes pose for modern physics: # The information paradox wherein the quantum information bound in infalling matter and energy entirely disappears into a singularity; that is, the black hole would undergo zero physical change in its composition regardless of the nature of what fell into it. # The singularity at the heart of the black hole, where conventional black hole theory says there is infinite spacetime curvature due to an infinitely intense gravitational field from a region of zero volume. Modern physics breaks down when such parameters are infinite and zero.〔The smallest linear dimension in physics that has any meaning in the measurement of spacetime is the Planck length, which is ((CODATA value )). Below the Planck length, the effects of quantum foam dominate and it is meaningless to conjecture about length at a finer scale—much like how meaningless it would be to measure ocean tides at a precision of one centimeter in storm-tossed seas. A singularity is thought to have a diameter that doesn’t amount to even one Planck length; which is to say, zero.〕 Fuzzball theory replaces the singularity at the heart of a black hole by positing that the entire region within the black hole’s event horizon is actually a ball of strings, which are advanced as the ultimate building blocks of matter and energy. Strings are thought to be bundles of energy vibrating in complex ways in both the three physical dimensions of space as well as in ''compact directions''—extra dimensions interwoven in the quantum foam (also known as ''spacetime foam)''. ==Physical characteristics== Samir D. Mathur of The Ohio State University, with postdoctoral researcher Oleg Lunin, proposed via two papers in 2002 that black holes are actually spheres of strings with a definite volume; they are not a singularity, which the classic view holds to be a zero-dimensional, zero-volume point into which a black hole’s entire mass is concentrated.〔Citation: ''AdS/CFT duality and the black hole information paradox'', SD Mathur and Oleg Lunin, Nuclear Physics B, 623, (2002), ((arxiv )); ''Statistical interpretation of Bekenstein entropy for systems with a stretched horizon'', SD Mathur and Oleg Lunin, Physical Review Letters, 88 (2002) ((arxiv )); and correspondence between Dr. Mathur and Wikipedia, as documented on this article’s talk page.〕 String theory holds that the fundamental constituents of subatomic particles, including the force carriers (e.g.leptons, photons, and gluons), are all composed of a one-dimensional string of energy that takes on its identity by vibrating in different modes and/or frequencies. Quite unlike the view of a black hole as a singularity, a small fuzzball can be thought of as an extra-dense neutron star where its neutrons have decomposed, or “melted,” liberating the quarks (strings in string theory) composing them. Accordingly, fuzzballs can be regarded as the most extreme form of degenerate matter. Whereas the event horizon of a classic black hole is thought to be very well defined and distinct, Mathur and Lunin further calculated that the event horizon of a fuzzball would, at an extremely small scale (likely on the order of a few Planck lengths),〔Three Planck lengths is five trillion trillion times smaller than the effective width (Van der Waals diameter) of the single proton comprising a hydrogen nucleus.〕 be very much like a mist: fuzzy, hence the name “fuzzball.” They also found that the physical surface of the fuzzball would have a radius equal to that of the event horizon of a classic black hole; for both, the Schwarzschild radius for a median-size stellar-mass black hole of 6.8 solar masses () is 20 kilometers. With classical black holes, objects passing through the event horizon on their way to the singularity are thought to enter a realm of curved spacetime where the escape velocity exceeds the speed of light. It is a realm that is devoid of all structure. Further, at the singularity—the heart of a classic black hole—spacetime is thought to have infinite curvature (that is, gravity is thought to have infinite intensity) since its mass is believed to have collapsed to zero (infinitely small) volume where it has infinite density. Such infinite conditions are problematic with known physics because key calculations utterly collapse. With a fuzzball, however, the strings comprising an object are believed to simply fall onto and absorb into the surface of the fuzzball, which corresponds to the event horizon—the threshold at which the escape velocity equals the speed of light. A fuzzball ''is'' a black hole; spacetime, photons, and all else that is not exquisitely close to the surface of a fuzzball are thought to be affected in precisely the same fashion as with a classic black hole featuring a singularity at its center. Classic black holes and fuzzballs differ only at the quantum level; that is, they differ only in their internal composition as well as how they affect virtual particles that form close to their event horizons (see ''Information paradox'', below). Fuzzball theory is thought by its proponents to be the true quantum description of black holes. Since the volume of fuzzballs is a function of the Schwarzschild radius (2,954 meters per ), fuzzballs have a variable density that decreases as the inverse square of their mass (twice the mass is twice the diameter, which is eight times the volume, resulting in one‑quarter the density). A typical fuzzball would have a mean density of .〔This is a mean, or average bulk density; as with neutron stars, the sun, and its planets, a fuzzball’s density varies from the surface where it is less dense, to its center where it is most dense.〕 A bit of such a fuzzball the size of a drop of water would have a mass of twenty million metric tons, which is the mass of a granite ball 240 meters in diameter.〔Smaller fuzzballs would be denser yet. The smallest black hole yet discovered, XTE J1650-500 is . Theoretical physicists believe that the transition point separating neutron stars and black holes is 1.7 to 2.7 (Goddard Space Flight Center: ''(NASA Scientists Identify Smallest Known Black Hole )).'' A very small, fuzzball would be over six times as dense as a median-size fuzzball of 6.8 , with a mean density of . A bit of such a fuzzball the size of a drop of water would have a mass of 126 million metric tons, which is the mass of a granite ball 449 meters in diameter.〕 Though such densities are almost unimaginably extreme, they are, mathematically speaking, infinitely far from infinite density. Although the densities of typical stellar-mass fuzzballs are quite great—about the same as neutron stars〔Neutron stars have a mean density thought to be in the range of which is equal to median-size fuzzballs ranging from 7.1 to 5.6 . However, the smallest fuzzballs are denser than neutron stars; a small, fuzzball would be four to seven times denser than a neutron star. On a “teaspoon” (≈4.929 mL) basis, which is a common measure for conveying density in the popular press to a general-interest readership, comparative mean densities are as follows: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fuzzball (string theory)」の詳細全文を読む スポンサード リンク
|