亚洲免费av电影一区二区三区,日韩爱爱视频,51精品视频一区二区三区,91视频爱爱,日韩欧美在线播放视频,中文字幕少妇AV,亚洲电影中文字幕,久久久久亚洲av成人网址,久久综合视频网站,国产在线不卡免费播放

        ?

        宇宙的起源

        2021-04-01 09:05:44左連凱
        英語世界 2021年1期
        關(guān)鍵詞:測量

        左連凱

        One of the dominating astronomical discoveries of the 20th century was that the galaxies of the universe all seem to be moving away from Earth. Doppler redshifts were observed for spiral nebulae around 1920 even though they were not yet known to be galaxies. By the early 1930s, Edwin Hubble and M. L. Humason had established that the more distant a galaxy, the faster it was receding. It turned out that they were moving away not just from the Earth but from one another—that is, the universe is expanding. Scientists conclude that the universe must once, very long ago, have been extremely compact and dense, and a rapid expansion caused the energy and matter to rapidly expand. The beginning of this expansion is referred to as the Big Bang.

        On the subatomic level, according to this theory, there were vast changes of energy and matter and the way physical laws operated during the first few minutes after the Big Bang. After those early minutes the percentages of the basic matter of the universe—hydrogen, helium, and lithium—were set. Everything was so compact and hot that radiation dominated the early universe and there were no stable, un-ionized atoms. The universe was opaque, in the sense that any energy emitted was quickly absorbed and then re-emitted. As the universe expanded, density and temperature continued to drop. A few hundred thousand years after the Big Bang, the temperature dropped far enough that electrons and nuclei could combine to form stable atoms as the universe became transparent. Once that occurred, the radiation that had been trapped was free to escape.

        In the 1940s, George Gamow and others predicted that remnants of this escaped radiation should be observable. They had started to search for this background radiation when physicists Arno Penzias and Robert Wilson, using a radio telescope, inadvertently found it.

        In 2003, NASAs Wilkinson Microwave Anisotropy Probe made measurements of the temperature of this cosmic microwave background radiation to within millionths of a degree. From these measurements, scientists were able to deduce that our universe is 13.7 billion years old and that first-generation stars began to form a mere 200 million years after the Big Bang.

        In 2014, scientists operating a telescope in Antarctica claimed to have found direct evidence for cosmic inflation, the rapid expansion of the universe during the first 10-32 seconds after the Big Bang that helps explain why variations of the cosmic background radiation are so small. Follow-up observations have cast doubt on this result, and higher precision measurements are planned.

        A related mystery is evidence suggesting hidden matter and hidden energy that cannot be directly observed. The presence of dark matter is indicated by the rotation curves of galaxies and the dynamics of clusters of galaxies. Dark matter may be composed of gas; large numbers of cool, compact objects like dead stars; or even subatomic particles. Evidence for dark energy is derived from studies of distant Type Ia supernovae indicating that the expansion of the universe is accelerating rather than slowing. Dark energy seems to work on the very fabric of the universe, acting as a force that increases the rate at which space expands. Visible matter seems to constitute only about 4%1 of the total mass of the universe while the rest of the universes mass is in the form of dark matter (27%) and dark energy (68%).

        20世紀(jì)天文學(xué)的一個重大發(fā)現(xiàn)表明,宇宙中的所有星系似乎都在退離地球。1920年前后,盡管人們尚未認(rèn)識到螺旋星云就是星系,但觀察到了它們的多普勒紅移。1930年代初,埃德溫·哈勃和M. L.赫馬森證實,星系越遠(yuǎn),退離得越快。原來它們不僅離地球而去,而且離彼此也越來越遠(yuǎn),也就是說,宇宙在膨脹??茖W(xué)家推斷,宇宙很久以前一定十分緊湊密集,由于它快速膨脹,能量和物質(zhì)也迅速膨脹。這種膨脹的開始叫作宇宙大爆炸。

        根據(jù)該理論,大爆炸后的最初幾分鐘里,能量、物質(zhì)和物理定律的作用方式在亞原子層面發(fā)生了巨大變化。這最初的幾分鐘過后,宇宙的基礎(chǔ)物質(zhì)如氫、氦、鋰的比例就確定了。一切都高密、高溫,所以輻射主導(dǎo)著早期宇宙,不存在穩(wěn)定的非離子化原子。宇宙是不透明的,意味著釋放的能量很快被吸收,然后重新釋放。隨著宇宙的膨脹,密度和溫度持續(xù)下降。大爆炸發(fā)生幾十萬年后,宇宙變得透明,溫度下降到足以使電子和原子核結(jié)合形成穩(wěn)定的原子。這時,被束縛的輻射自由逸出。

        1940年代,喬治·伽莫夫等人預(yù)測,應(yīng)該能觀測到這種逸出輻射的殘余。他們開始尋找這種背景輻射,這時物理學(xué)家阿諾·彭齊亞斯和羅伯特·威爾遜用射電望遠(yuǎn)鏡不經(jīng)意間發(fā)現(xiàn)了它。

        2003年,美國國家航空航天局的威爾金森微波各向異性探測器對這種宇宙微波背景輻射的溫度進(jìn)行了測量,精確至百萬分之一度以內(nèi)。根據(jù)這些測量結(jié)果,科學(xué)家推斷宇宙有137億年的歷史,第一代恒星在大爆炸僅僅2億年后開始形成。

        2014年,在南極洲用望遠(yuǎn)鏡觀測的科學(xué)家聲稱他們發(fā)現(xiàn)了宇宙膨脹(大爆炸后的10-32秒內(nèi),宇宙迅速膨脹)的直接證據(jù),這有助于解釋宇宙背景輻射變化非常小的原因。后續(xù)觀察質(zhì)疑這一結(jié)果,更精密的測量便納入計劃之中。

        一個與此有關(guān)的謎團是,證據(jù)顯示暗物質(zhì)和暗能量無法直接觀測到。星系的旋轉(zhuǎn)曲線和星系團的力學(xué)特性揭示了暗物質(zhì)的存在。暗物質(zhì)可能由氣體、大量冷而致密的物體(如死星)甚或亞原子粒子組成。對遙遠(yuǎn)的Ia型超新星的研究證明了暗能量的存在,表明宇宙膨脹在加速而不是放緩。暗能量似乎影響了宇宙的結(jié)構(gòu),使空間膨脹速度越來越快。可見物質(zhì)似乎只占宇宙總質(zhì)量的4%左右,宇宙中的其他物質(zhì)以暗物質(zhì)(27%)和暗能量(68%)的形式存在。

        猜你喜歡
        測量
        測量重量,測量長度……
        把握四個“三” 測量變簡單
        滑動摩擦力的測量和計算
        滑動摩擦力的測量與計算
        測量的樂趣
        二十四節(jié)氣簡易測量
        日出日落的觀察與測量
        滑動摩擦力的測量與計算
        測量
        測量水的多少……
        久久亚洲中文字幕精品熟| 亚洲中文字幕免费精品| 国产啪精品视频网给免丝袜| 欧美在线资源| 激情 一区二区| av网站影片在线观看| 一区二区三区四区午夜视频在线| 国产一区二区三区成人| 国产精品熟女视频一区二区三区| 一本色道久久综合狠狠躁篇| 区二区三区玖玖玖| 色婷婷久久一区二区三区麻豆| 久久久精品久久波多野结衣av| 亚洲AV无码精品色午夜超碰| 国产三级国产精品三级在专区| 亚洲香蕉久久一区二区| 国产女人精品视频国产灰线| 正在播放强揉爆乳女教师| 国产无人区码一码二码三mba| 亚洲中文字幕无码久久2020| 国产成人拍精品免费视频| 成人一区二区三区蜜桃| 美女免费观看一区二区三区| 人妻仑乱a级毛片免费看| 亚洲国产av导航第一福利网| 午夜国产精品久久久久| 成人免费播放视频影院| 日韩乱码人妻无码系列中文字幕| 成l人在线观看线路1| āV第三区亚洲狠狠婷婷综合久久| 国产av一区二区凹凸精品| 亚洲av资源网站手机在线| 爆操丝袜美女在线观看| 精品国产免费一区二区三区 | 激情另类小说区图片区视频区| 日本少妇按摩高潮玩弄| 国产区高清在线一区二区三区| 精品人妻一区二区三区狼人| 成人日韩熟女高清视频一区| 国产专区国产av| 素人激情福利视频|