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 that
From the beginning, the idea of a finite universe ran into its own obstacle, the apparent need for an edge, a problem that
admin
2009-05-19
52
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
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.
选项
A、searching for an accurate method of determining whether the universe is finite or infinite
B、discussing problems and possibilities involved in providing a definite picture of the shape of the universe
C、declaring opposition to the notion that spherical geometry is a possible model for the shape of the universe
D、criticizing discredited theories about the possible topologies of the universe
E、refuting the idea that there is no way to tell whether the universe is finite and if so what shape it has
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/JOkO777K
本试题收录于:
GRE VERBAL题库GRE分类
0
GRE VERBAL
GRE
相关试题推荐
Advertisementcanbethoughtof"asthemeansofmakingknowninordertobuyorsellgoodsorservices".Advertisementaimst
Itiseasiertonegotiateinitialsalaryrequirementbecauseonceyouareinside,theorganizationalconstraints(约束)influencew
Left-handedpersonssuffermorefrequentlythandoright-handedpersonsfromcertainimmunedisorders,suchasallergies.Left-h
DISINGENUOUS:MISLEAD::
BANALITY:
CARDINAL:
REDUNDANT:SUPERFLUITY:
Thevireo’scomebackmayprovethathabitatalongstreamsinSouthernCaliforniaisrecoveringfromtheeffectsofpollution,__
TAINTED:
随机试题
换热器出现管子本身泄漏时,可以用圆锥金属头将管子的两端堵塞,用此方法消除泄漏时,堵管数不得超过总管数的()。
张力性气胸急救的首先措施是()。
充填过程中引起咬合增高的原因是
属于抑菌作用的抗结核药物是
根据《建设工程质量管理条例》的规定,()必须按照工程设计图纸和施工技术标准施工,不得擅自修改工程设计,不得偷工减料。
《发票管理办法》规定,取得发票时,不得要求变更()。
法定代理是法律规定依国家主管机关的行政命令或人民法院的指定而产生的代理。()
阴阳合同是指合同当事人就同一事项订立两份以上内容不相同的合同,一份对内,一份对外,其中对外的一份并不是双方真实意思表示,而是以逃避国家税收为目的;对内的一份则是双方真实意思表示,可以是书面或口头的。“阴阳合同”是一种违规行为,在给当事人带来“利益”的同时,
习近平总书记强调:“对马克思主义的信仰,对社会主义和共产主义的信念,是共产党人的政治灵魂,是共产党人经受住各种考验的精神支柱:”我们之所以要信仰马克思主义,是因为马克思主义()
我国专利申请的原则之一是(7)。
最新回复
(
0
)