首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
From the beginning, the idea of a finite universe ran into its own obstacle, the apparent need for an edge, a problem tha
From the beginning, the idea of a finite universe ran into its own obstacle, the apparent need for an edge, a problem tha
admin
2011-01-17
44
问题
From the beginning, the idea of a finite universe ran into its own obstacle,
the apparent need for an edge, a problem that has only recently been grappled
with. Aristotle’s argument, that the universe is finite, and that a boundary was
Line necessary to fix an absolute reference frame, held only until scientists wondered
(5) what happened at the far side of the edge. In other words, why do we not
redefine the "universe" to include that other side?
Riemann ingeniously replied by proposing the hypersphere, the three-
dimensional surface of a four-dimensional ball. Previously it was supposed that
the ultimate physical reality must be a Euclidean space of some dimension, and
(10) thus if space were a hypersphere, it would need to sit in a four-dimensional
Euclidean space that allows us to view it from the outside. But according to
Riemann, it would be perfectly acceptable for the universe to be a hypersphere
and not embedded in any higher-dimensional space; nature need not therefore
cling to the ancient notion. According to Einstein’s powerful but limited theory
(15) of relativity, space is a dynamic medium that can curve in one of three ways,
depending on the distribution of matter and energy within it, but because we are
embedded in space, we cannot see the flexure directly but rather perceive it as
gravitational attraction and geometric distortion of images. Thus, to determine
which of the three geometries our universe has, astronomers are forced to
(20) measure the density of matter and energy in the cosmos, whose amounts appear
at present to be insufficient to force space to arch back on itself in "spherical"
geometry. Space may also have the familiar Euclidean geometry, like that of a
plane, or a "hyperbolic" geometry, like that of a saddle. Furthermore, the
universe could be spherical, yet so large that the observable part seems
(25) Euclidean, just as a small patch of the earth’s surface looks flat.
We must recall that relativity is a purely local theory: it predicts the
curvature of each small volume of space-its geometry-based on the matter
and energy it contains, and the three plausible cosmic geometries are consistent
with many different topologies: relativity would describe both a torus and a
(30) plane with the same equations, even though the torus is finite and the plane is
infinite. Determining the topology therefore requires some physical
understanding beyond relativity, in order to answer the question, for instance,
of whether the universe is, like a plane, "simply connected", meaning there is
only one direct path for light to travel from a source to an observer. A simply
(35) connected Euclidean or hyperbolic universe would indeed be infinite-and seems
self-evident to the layman-but unfortunately the universe might instead be
"multiply-connected", like a torus, in which case there are many different such
paths. An observer could see multiple images of each galaxy and easily interpret
them as distinct galaxies in an endless space, much as a visitor to a mirrored
(40) room has the illusion of seeing a huge crowd, and for this reason physicists have
yet to conclusively determine the shape of the universe.
The author refers to the illusion of seeing crowds primarily in order to
选项
A、illustrate that relativity theory remains a useful tool in determining the topology of the universe
B、indicate a descriptive advantage that toruses might have over Euclidean or hyperbolic universes
C、argue that empirical methods of determining the shape of the universe are invariably doomed to failure
D、suggest that the common sense behind the notion that the universe is simply- connected may be misguided
E、assert that two models of the geometry of the universe may vary in terms of observable predictions but be mathematically equivalent
答案
D
解析
转载请注明原文地址:https://kaotiyun.com/show/BFjO777K
本试题收录于:
GRE VERBAL题库GRE分类
0
GRE VERBAL
GRE
相关试题推荐
Ifherefusesto______myplan,Icanprobablyfindsomeonemorecooperative.
Ifyoudon’tputthemilkintherefrigerator,itmay______.
Guest:Oh,it’steno’clock.I’dbettergonow.Host:______
—Youcouldn’thavechosenanygiftbetterforme.—______.
Jeandidnothavetimetogototheconcertlastnightbecauseshewasbusy______forherhistoryexamination.
He______themathsexaminationifhehadworkedhardenough,buthedidn’t
Youhavefailedtwotests.You’dbetterstartworkingharder,______youwon’tpassthecourse.
Itisnoteasy()theanswertothedifficultmathproblem.
Thestudentsdidn’tmanagetoworkouttheproblem______theirteacherhadexplainedhow.
Adividebetweenaestheticandtechnicalconsiderationshasplayedacrucialroleinmapmakingandcartographicscholarship.Sin
随机试题
对隐孢子虫病作病原学检查时检出率最高的方法是
鞍区肿瘤、垂体瘤患者应首选的摄影位置是
滤线栅使用原则中,X线管的管电压须超过
60岁甲亢病人,甲状腺Ⅲ度肿大,高代谢症状严重,心、肺、肝、肾功能均正常,首选的治疗措施是
环境保护法的基本原则包括( )。
关于金融市场基本要素的说法,正确的有()。
一百年来,党外靠发展人民民主、接受人民监督,内靠(),勇于坚持真理、修正错误,勇于刀刃向内、刮骨疗毒,保证了党长盛不衰、不断发展壮大。
Thisrulemayhavepreservedthesharkfrombeingeatenaswellasotheranimals_______.
TheancientEgyptians_____________(被假定已发射过火箭)tothemoon.
Haveyoueverusedemailtoapologizetoacolleague?Delivereda【C1】______toasubordinate(下属)withavoice-mailmessage?Flow
最新回复
(
0
)