首页
登录
职称英语
It is hardly surprising that something called dark energy is hard to study.
It is hardly surprising that something called dark energy is hard to study.
游客
2023-09-09
34
管理
问题
It is hardly surprising that something called dark energy is hard to study. It is important, though. If it exists at all, it makes up about three-quarters of the stuff in the universe. And if it does not exist, then existing theories of physics will have to be useless.
The latest evidence that dark energy really does exist was produced on December 16th by Alexey Vikhlinin, of the Smithsonian Observatory in Cambridge, Massachusetts, and his colleagues. They used an orbiting X-ray telescope called Chandra to study the way that groups of galaxies grow. They discovered that this growth is restrained in exactly the way that dark-energy theory predicts.
The idea of dark energy was dreamed up ten years ago, to explain why the expansion of the universe that began with the Big Bang seems to be accelerating, rather than slowing down. That unexpected finding was the result of studies of supernovas (超新星) whose apparent brightness (and therefore distance) did not match the previous theory. Dark energy causes the acceleration by pushing space itself apart, altering the distances to the supernovas as it does so.
Dark energy is also a convenient explanation for another curiosity. Geometrically, space is flat. For it to be held that way, rather than getting more and more curved over time, the amount of matter and energy it contains must be at a particular, critical density. Without the dark energy needed to explain the acceleration, the universe would have only a quarter of the necessary density. It is therefore a relief that Dr Vikhlinin’s results agree with the theory: the pushing apart of space that dark energy causes makes it harder than it otherwise would be for galactic clusters(银河星团) to grow.
This result does not bring physicists much closer to understanding what dark energy actually is. The favored explanation is the so-called universal constant -- an as-yet-unobserved consequence of the general theory of relativity. But that theory predicts a force far more powerful than the one actually seen. So the truth is that physicists are still in the dark. [br] In order to maintain the flatness of space, its substance and energy should be kept at a ______.
选项
答案
From the result of studies of supernovas
解析
由定位句可知,空间从几何学来说是平的,为了维持这种平坦的状态,其间所含的物质和能量必须保持一个特殊的临界密度(particular,critical density),故本题答案是particular,critical density。
转载请注明原文地址:https://tihaiku.com/zcyy/2997746.html
相关试题推荐
[originaltext]W:Let’sdosomething!Whydon’twegooutfordinnerorgodanci
[originaltext]W:Let’sdosomething!Whydon’twegooutfordinnerorgodanci
Atsometimeinyourlife,youmayhaveastrongdesiretodosomethingstran
Atsometimeinyourlife,youmayhaveastrongdesiretodosomethingstran
Atsometimeinyourlife,youmayhaveastrongdesiretodosomethingstran
Itissurprisingthatmychoice______(证明是个可怕的错误).turnedouttobeahorrible
[originaltext]M:Ijustcalledthetravelagency,it’sallset.OnJunefirst,
[originaltext]M:Ijustcalledthetravelagency,it’sallset.OnJunefirst,
[originaltext]Todaywhenamanstepsontothemoon,orsomethingnewandi
[originaltext]Todaywhenamanstepsontothemoon,orsomethingnewandi
随机试题
IntheUnitedStatesthefirstdaynurserywasopenedin1854.Nurserieswe
Ifyouhadcomeyesterday,I(finish)______thetask.wouldhavefinished
WhenIfirstentereduniversity,myaunt,whoisanEnglishprofessor,gave
设线性方程组(I)与(II)有公共的非零解,其中(I)为,(II)有基础解系,求
从营养学的角度考虑,“老年”的年龄范围是( )。A.65岁以上 B.70岁以
公积金个人住房贷款的还款方式不包括()。A.一次还本付息法 B.等额本金还
共用题干 Fewmenhaveinfluencedthedevelo
下面植物中属于国家一级保护植物的是( )。A.木棉 B.红椿 C.水杉
根据《环境影响评价技术导则—声环境》,户外声源传播过程中,与声屏障引起的衰减值无
以人年为单位计算的率为A.发病率 B.发病密度 C.病死率 D.现患率
最新回复
(
0
)