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宇宙中96%的物质由什么组成?——天文学家也不知道的事(图)

via:老外怎么说?老外这么说     time:2011/5/16 9:10:04     readed:2374

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来源Missing: 96 Percent of the Universe

译者元一

What’s 96 Percent of the Universe Made Of? Astronomers Don’t Know

Clara Moskowitz, SPACE.com senior writer

Date: 12 May 2011 Time: 06:00 AM ET

宇宙中96%的物质是什么?——天文学家也不知道的事

克拉拉·莫斯科维茨 ,SPACE.com资深作者

This Hubble Space Telescope image shows NGC 1275, the galaxy located in the center of the Perseus Galaxy Cluster. The red threadlike filaments are composed of cool gas suspended by a magnetic field.

这幅哈伯天文望远镜拍摄的图片显示的是新总表1275,该星系位于英仙座星系团的中部。红色细长的丝状体是由冷却下来的气体组成,气体处于磁场中。

NEW YORK — All the stars, planets and galaxies that can be seen today make up just 4 percent of the universe. The other 96 percent is made of stuff astronomers can’t see, detect or even comprehend.

全部现今可观测的恒星、行星和星系只占宇宙的4%。剩下的96%则由天文学家也不知道的物质组成,它们甚至无法被探测或理解。

These mysterious substances are called dark energy and dark matter. Astronomers infer their existence based on their gravitational influence on what little bits of the universe can be seen, but dark matter and energy themselves continue to elude all detection.

这些神秘物质称为暗物质与暗能量。基于宇宙中观测到的微小万有引力作用,天文学家推断出它们的存在,但暗物质与暗能量本身仍在可直接探测的盲点区。

“The overwhelming majority of the universe is: who knows?” explains science writer Richard Panek, who spoke about these oddities of our universe on Monday (May 9) at the Graduate Center of the City University of New York (CUNY) here in Manhattan. “It’s unknown for now, and possibly forever.”

“宇宙中占绝对优势的多数物质是什么:又有谁知道呢?”科学作家理查德·潘尼克解释道,这是周一(5月9号)他在曼哈顿纽约城市大学的毕业中心,提及宇宙中奇异物质时所说。“这属于未知,现在,甚至永远。”

In Panek’s new book, “The 4 Percent Universe” (Houghton Mifflin Harcourt, 2011), Panek recounts the story of how dark matter and dark energy were discovered. It’s a history filled with mind-boggling scientific surprises and fierce competition between the researchers racing to find answers. [Strangest Things in Space]

在潘尼克的新书《4%的宇宙》(哈考特出版社,2011)中,潘尼克详述了暗物质与暗能量怎样发现的经过。这是一段交织着思维泥沼的科学新发现,与那些求索真知的研究者间激烈竞争的历史。

Dark matter

暗物质

Some of the first inklings astronomers had that there might be more mass in the universe than just the stuff we can see came in the 1960s and 1970s. Vera Rubin, a young astronomer at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, observed the speeds of stars at various locations in galaxies.

Simple Newtonian physics predicted that stars on the outskirts of a galaxy would orbit more slowly than stars at the center. Yet Rubin’s observations found no drop-off at all in the stars’ velocities further out in a galaxy. Instead, she found that all stars in a galaxy seem to circle the center at roughly the same speed.

“It means that galaxies should be flying apart, should be completely unstable,” Panek said. “Something’s missing here.”

我们能观测到的物质以外也许还有其他更多物质,这一观念在天文学家头脑中萌芽于上世纪60年代到70年代。维拉·鲁宾,华盛顿卡内基研究机构地磁项目中一名年轻的天文学家,观测了同一星系中各个位置下星体的运动速度。

单纯用牛顿经典物理预测,星系边缘的星体将以慢于中心星体的速度沿轨道运动。然而鲁宾的观测结果则表明,远离星系中心的全部星体的速率都没有降低。反而,她发现所有同一星系的星体似乎都是以近似于相同的速率作圆周运动。

“这表明星系自身正在飞散开来,应该非常地不稳定,”潘尼克说,“这里有什么物质被遗漏了”。

But research by other astronomers confirmed the odd finding. Ultimately, based on observations and computer models, scientists concluded that there must be much more matter in galaxies than what’s obvious to us. If the stars and gas that we can see inside galaxies are only a small portion of their total mass, then the velocities make sense.

但另有一些天文学家的研究证实了这一奇怪发现。最后,基于观测结果和计算模型,科学家得出结论,星系中存在的东西肯定要比我们明显已知的物质多得多。假设我们在星系中看到的星球和气体只占了星系总体积的一小部分,那么像这样的速率就说得通了。Astronomers nicknamed this unseen mass dark matter.

天文学家将这种不可见物质通俗地称为暗物质。

Where is it?

它在哪儿呢?

Yet, in the nearly 40 years that followed, researchers still haven’t been able to figure out what dark matter is made of.

然而,在后来的近40年里,研究人员仍然每能弄清暗物质的组成。

A popular hypothesis is that dark matter is formed by exotic particles that don’t interact with regular matter, or even light, and so are invisible. Yet their mass exerts a gravitational pull, just like normal matter, which is why they affect the velocities of stars and other phenomena in the universe. [Video: Dark Matter in 3D]

有种普遍的假说:暗物质是由极不稳定的粒子组成,它们不能与普通物质相互作用,甚至连光也不能,因此人们无法看到它们。而它们的质量却能产生引力,正如一般物质那样,这就是它们能够影响星体速度及产生其他宇宙现象的原因。

However, try as hard as they might, scientists have yet to detect any of these particles, even with tests designed specifically to target their predicted properties.

可是,不管科学家如何努力,甚至用专门设计出的,检测其预期性质的实验,也没能探测出任何此类粒子。

“I think on the dark matter side there is some discouragement among the people who are kind of mid-career,” Panek said. “They went into this field thinking, ‘OK, we’re going to solve this problem and then we’ll build from there.’ But 15, 20 years later, they’re saying, ‘I’ve invested my career in this and I don’t know if I’m going to find anything in my lifetime.’”

Still, many hold out hope that we’re getting close and that experiments such as the newly built Large Hadron Collider particle accelerator in Geneva may finally solve the puzzle.

“我认为,在暗物质方面,步入职业生涯中期的人们有些倦怠,”潘尼斯说,“最初进入这一领域时他们想着,‘好吧,我们要先解决掉这个问题,然后就从这儿开始建立发展(出理论体系)’但是,15、20年过去了,他们开始说‘我已经把我的生涯投进去了,可是我不确信还能否在有生之年发现什么。’”

同时,仍有很多人对此抱有希望,他们认为我们正在接近答案,或者寄希望于新出现的装置,如日内瓦的大型强子碰撞型加速器,来进行实验。也许最后能够解决这个谜团。

Dark energy

暗能量

Dark energy is possibly even more baffling than dark matter. It’s a relatively more recent discovery, and it’s one that scientists have even less of a chance of understanding anytime soon.

暗能量大概要比暗物质更让人无头绪。它的发现相对晚些,但它对科学家而言甚至更难理解——不管过去了多长时间。

It all started in the mid-1990s, when two teams of researchers were trying to figure out how fast the universe was expanding, in order to predict whether it would keep spreading out forever, or if it would eventually crumple back in on itself in a “Big Crunch.”

这全部始于20世纪90年代中期,其时两个研究团体正试着测算宇宙膨胀有多快,目的是预测出宇宙是要永远扩散下去呢,还是最终自身缩皱回“大坍塌”。

To do this, scientists used special tricks to determine the distances of many exploded stars, called supernovas, throughout the universe. They then measured their velocities to determine how fast they were moving away from us.

为进行研究,科学家用了一种特殊技巧来确定许多爆炸星体——超新星,在宇宙间的距离。他们随后测量了星体的速度,以便确知它们在以多快的速度远离我们。

When we view very distant stars, we are viewing an earlier time in the history of the universe, because those stars’ light has taken millions and billions of light-years to travel to us. Thus, looking at the speeds of stars at various distances tells us how fast the universe was expanding at various points in its lifetime.

当我们观看极其遥远的恒星时,我们看到的其实是历史上的早期宇宙,因为这些恒星发出的光历经了百万乃至亿万光年的行程才抵达我们的眼睛。所以说,看各个距离下星体的速度可以告诉我们,宇宙扩张处于其生命周期的哪个阶段。

Astronomers predicted two possibilities: either the universe has been expanding at roughly the same rate throughout time, or that the universe has been slowing in its expansion as it gets older.

天文学家预想了两种可能性:一定时间内,宇宙不是以严格一致的速率膨胀,就是随着它的不断老化而减慢膨胀。

Shockingly, the researchers observed neither possibility. Instead, the universe appeared to be accelerating in its expansion.That fact could not be explained based on what we knew of the universe at that time.

All the gravity of all the mass in the cosmos should have been pulling the universe back inward, just as gravity pulls a ball back down to Earth after it's been thrown into the air.

出乎意料的是,研究人员两种可能都没观测到。相反,宇宙表现出了加速膨胀现象。在对当时宇宙有所了解的基础上,能够解释这一事实。

宇宙中每一物体的每个引力都会对宇宙产生一个指向物体本身的拉力,就像在重力作用下,抛向空中的球会被拉回地面。

“There’s some other force out there or something on a cosmic scale that is counteracting the force of gravity,” Panek explained. “People didn’t believe this at first because it’s such a weird result.”

“一定有其他力同时作用,或是有什么力在全宇宙范围与万有引力相互抵消,”潘尼克解释道。“人们最初不相信这个结论,因为它太诡异了。”

Fierce competition

激烈竞争

Scientists named this mysterious force dark energy. Though no one has a good idea of what dark energy is, or why it exists, it is the force that appears to be counteracting gravity and causing the universe to accelerate in its expansion.

科学家将这种神秘外力命名为暗能量。尽管没有人能较好说明什么是暗能量,或它为什么存在,但它就是那个表现出抵消引力、引起宇宙加速膨胀现象的力。

The lack of a good explanation for dark energy hasn’t seemed to dampen scientists’ enthusiasm for it.

缺乏对暗能量的完善解释似乎并未浇熄科学家的热情。

“What I hear again and again is how excited people are to be working in this field right now, when this revolution is going on,” Panek told SPACE.com. “The problems are so great and profound, they’re actually rather thrilled with it.”

“在这场变革持续之时,我再三听到的都是当前正从事这一领域的人们有多么兴奋,”潘尼克告诉 SPACE.com,“问题如此巨大深刻,他们都为此热血沸腾。”

Overall, dark energy is thought to contribute 73 percent of all the mass and energy in the universe. Another 23 percent is dark matter, which leaves only 4 percent of the universe composed of regular matter, such as stars, planets and people.

总的来说,一般认为暗物质占据了宇宙中73%的质量和能量。另外的23%是暗物质,最后留下4%的宇宙是由一般物质构成的,比如恒星、行星,还有人类。

This bizarre, but apparently true, conclusion was reached at about the same time by the two groups working to measure the expansion of the universe. The competition between the groups became very contentious, Panek said, and they grew to dislike each other quite a lot.

这个怪异但明显正确的结论,几乎同时被这两个研究宇宙膨胀的团体得出。两个团体间的竞争不可调和,潘尼克说,然后他们变得彼此反感。

Ultimately, though, members of both teams should reap the rewards of finding one of the biggest surprises in the history of science.

尽管,最终两个团队的成员都应该因发现了科学史上最神奇之物而获奖。

“I think that it’s kind of assumed the dark energy will win the discoverers the Nobel,” Panek said. “There certainly is that assumption that it’s just a matter of years.”

“我觉得,这个假设事关暗物质能否获诺贝尔奖,”潘尼克说,“而它无疑会实现,只不过是时间问题罢了。”

译者注:NGC 星表是由丹麦天文学家德雷尔于 1887 年所编集的星云、星团与星系总目录。

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