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旁白：听一段科学史的课堂讲解。

Narrator: Listen to part of a lecture in a history of science class.

教授：好了，我们一直在讨论一个贯穿历史性的问题，那就是当人们坚信某个科学理论的时候，就很难再去放弃这种坚持，即便是错误的。

Professor: Ok, we've been talking about how throughout history, it was often difficult for people to give up ideas which have long been taken for granted as scientific truths, even if those ideas were false.

比如在天文学上来讲，人们对太阳系与宇宙的区别的认知直到现代才逐渐清晰起来。

In Astronomy, for example, the distinction between the solar system and the universe wasn't clear until modern times.

古希腊人认为我们所谓的太阳系就是整个宇宙，且相信地心说。

The ancient Greeks believed that what we called the solar system was in fact the entire universe, and that the universe was geocentric.

顾名思义，地心说就是指宇宙以地球为中心，地球是静止不动的，太阳、行星及恒星都围绕地球来转。

Geocentric means Earth-centered, so the geocentric view holds that the Sun, the planets, and the stars, all revolve around the Earth, which is stationary.

当然了，我们现在都知道所有的行星，包括地球，都是围绕太阳来转的，而且太阳系也仅仅是宇宙的一小部分而已。

Of course, we now know that the planets, including Earth, revolve around the Sun, and that the solar system is only a tiny part of the universe.

那么，古希腊人又为什么认为地球是宇宙的中心呢？

So, why did the ancient Greeks believe that the Earth was the center of the universe?

其实他们这种想法也不无道理。

当我们仰望天空的时候，给我们的视觉效果的确是太阳、月亮及星星都每天围绕地球来转的，而且地球是原地不动的。

Observations of the sky made it appear as if the Sun, the moon, and the stars all revolved around the Earth every day, while the Earth itself stayed in one place.

而且他们的哲学和宗教信仰也支撑着这种对宇宙的起源和构架的认知。

And this view is also supported by their philosophical and religious beliefs about the origin and structure of the universe.

这在公元前四世纪的希腊著名哲学家们的作品中都有体现，而地心说在西方国家也盛行到了17世纪，历经近2000年。

It was presented in the works of well-known Greek philosophers as early as the fourth century B.C.E., and the geocentric theory continue to prevail in Western thought for almost 2,000 years, until the 17th century.

极其有趣的是当天文观察的发现与地心说有所出入的时候，古希腊人却没有真正的去考虑过其它的理论。

Now, what's especially interesting is that when astronomical observations were made that seemed to be inconsistent with the geocentric view, the ancient Greeks did not really consider alternative theories.

天文学家们认为地球是宇宙的中心这种想法是那么的根深蒂固，以至于当他们发现与地心论不符的现象时，也会想办法找理由去解释。

It was so intuitive, so sensible that the Earth was the center of the universe that astronomers found ways to explain those seemingly inconsistent phenomena within the geocentric view.

比如说，希腊天学者对行星的移动能做出非常精准的观察，但是观察中却显示出了一个小问题。

For example, Greek astronomers made excellent, very accurate observations of the movements of the planets, but the observations revealed a bit of a problem.

地心说的理论是所有的行星都围绕地球朝着一个方向转动。

The geocentric theory said, that the planets would move around the Earth in one direction.

然而，天文学家却发现一些行星有时看上去停止朝一个方向转动，而是绕着地球沿着轨道朝相反的方向转动，这时他们就得出一个理论，就是这些行星在绕地球转动的同时也在沿着更小的圈——即本轮来转动。

However, astronomers noticed that at times, several planets seem to stop moving in one direction and start moving backward in their orbits around the Earth, and they came up with a theory that these planets themselves moved in smaller circles called epicycles as they travelled around the Earth.

这幅图就是他们想象中的画面。

你可以看到这个本轮理论表面上来讲就解释了行星倒行的这种现象了。

You see how this epicycle theory could account for the seeming backward motion of the planet.

当然了，现在我们知道这种倒行的现象其实是地球及其它行星在围绕太阳在自己轨道上公转时显现出来的，而行星间相对的运动也是非常复杂的。

Of course, today we know that this appearance of backward motion is caused by the fact that Earth, as well as other planets, all move in their own orbits around the Sun, and the relative movements of the planets with respect to each other can get quite complex.

然而，希腊及其它地区也有几位天文学家不相信地心说的，比如说公元前三世纪的一位希腊天文学家。

However, there were a few astronomers in Greece and other places who didn't agree with the geocentric view, for example, a Greek astronomer who lived in the third century B.C.E.

他提出了我们的行星系统的日心说，他就是阿利斯塔克斯。

He proposed the theory that our planetary system might be heliocentric, his name was Aristarchus.

日心说就是指太阳是中心，地球围绕太阳转。

Heliocentric means Sun-centered, that the Earth revolves around the Sun.

通过计算，阿利斯塔克斯认识到太阳比地球及其它行星都大很多。

Aristarchus recognized from his calculations that the Sun was much larger than the Earth and other planets.

可能正是这项发现让他得出日心说的结论。

It was probably this discovery that led him to conclude that the universe is heliocentric.

也就是说，小型的天体围绕大型的天体转动不是更说得通吗？反之，则不然。

I mean, isn't it more sensible to think that a smaller heavenly body would orbit a larger one, rather than the opposite?

然而，他的提议却在当时得到了极大的打击，即便当时的科学信仰并不正确，但是在某种意义上来讲也都说得通。

However, his proposition was rejected largely based on other scientific beliefs held at the time, which all made sense in a way even if they were incorrect.

让我来提一下当时对阿里斯塔克斯理论的两个反驳。

Let me mention two objections Greeks made to Aristarchus's theory.

首先，他们认为一切运动的物体都会产生风，这么说，每个人在跑的时候都有所体会吧。

First, they believe that everything that moves creates its own wind, so to speak, everyone has this experience when you are running, right?

因为，他们认为如果地球在运动的话，那么就会不停的刮风，将他们刮倒，当然了，并没有风。

So, they thought that if the Earth itself was moving, there would have to be a constant wind blowing, sweeping them off their feet, and of course there wasn't.

其次，地球运动的理论不符合古希腊人所理解的地球引力一说。

And second, the idea of an Earth that moved didn't fit in with the ancient Greeks' understanding of gravity.

他们认为地心力就是所有物体被宇宙的中心所吸引，也就是地球，或者说地球的中心，这也就解释了苹果或者其它掉落物体径直下落的原因。

They thought that gravity was basically a natural tendency of all things to move towards the center of the universe, which was the Earth, or the center of the Earth, so that explains why apples and other falling objects were falling straight down.

如果太阳是宇宙中心的话，那么一切物体都会朝着太阳方向掉落，而事实并非如此。

If the Sun was at the center of the universe, things would fall toward the Sun and away from the Earth, which of course they didn't.

所以这些就是他们反对日心说的原因。

So these were some of the reasons they rejected the heliocentric theory.

Why did the ancient Greeks hold the geocentric view of the universe?

Why does the professor point out that Greek astronomers tried to explain new astronomical discoveries within the geocentric concept?

Why does the professor discuss the epicycle theory?

In the professor's view, what might have caused Aristarchus to propose the heliocentric theory?

What were two arguments ancient Greeks used to reject the heliocentric model?

Narrator Listen to part of a lecture in a history of science class. Aristarchus-Heliocentric Theory Professor Ok, we have been talking about how throughout history, it was often difficult for people to give up ideas which have long been taken for granted as scientific truth, even if those ideas were false. In Astronomy, for example, the distinction between the solar system and the universe wasn’t clear until modern times. The ancient Greeks believed that what we called the solar system was in fact the entire universe, and that the universe was geocentric. Geocentric means Earth-centered, so the geocentric view holds that the Sun, the planets, and the stars, all revolve around the Earth, which is stationary. Of course, we now know that the planets, including Earth, revolve around the Sun, and that the solar system is only a tiny part of the universe. So, why did the ancient Greeks believe that the Earth was the center of the universe? Well, it made sense to them. Observations of the sky make it appear as if the Sun, the moon, and the stars all revolve around the Earth everyday, while the Earth itself stayed in one place. And this view is also supported by their philosophical and religious beliefs about the origin and structure of the universe. It was presented in the works of well-known Greek philosophers as early as the fourth century B.C.E., and the geocentric theory continue to prevail in Western thought for almost 2,000 years, until the 17th century. Now, what’s especially interesting is that when astronomical observations were made that seemed to be inconsistent with the geocentric view, the ancient Greeks did not really consider alternative theories. It was so intuitive, so sensible that the Earth was the center of the universe that astronomers found ways to explain those seemingly inconsistent phenomena within the geocentric view. For example, Greek astronomers made excellent, very accurate observations of the movements of the planets, but the observations revealed a bit of a problem. The geocentric theory said, that the planets would move around the Earth in one direction. However, astronomers noticed that at times, several planets seem to stop moving in one direction and start moving backward in their orbits around the Earth, and they came up with a theory that these planets themselves moved in smaller circles called epicycles as they travelled around the Earth. Here’s a picture of what they imagined. You see how this epicycle theory could account for the seemingly backward motion of the planet. Of course, today we know that this appearance of backward motion is caused by the fact that Earth, as well as other planets, all move in their own orbits around the Sun, and the relative movements of the planets with respect to each other can get quite complex. However, there were a few astronomers in Greece and other places who didn’t agree with the geocentric view, for example, a Greek astronomer who lived in the third century B.C.E. He proposed the theory that our planetary system might be heliocentric, his name was Aristarchus. Heliocentric means Sun-centered, that the Earth revolves around the Sun. Aristarchus recognized from his calculations that the Sun was much larger than the Earth and other planets. It was probably this discovery that led him to conclude that the universe is heliocentric. I mean, isn’t it more sensible to think that a smaller heavenly body would orbit a larger one, rather than the opposite? However, his proposition was rejected largely based on other scientific beliefs held at the time, which all made sense in a way even if they were incorrect. Let me mention two objections Greeks made to Aristarchus’s theory. First, they believe that everything that moves creates its own wind, so to speak, everyone has this experience when you are running, right? So, they thought that if the Earth itself was moving, there would have to be a constant wind blowing, sweeping them off their feet, and of course there wasn’t. And second, the idea of an Earth that moved didn’t fit in with the ancient Greeks’ understanding of gravity. They thought that gravity was basically a natural tendency of all things to move towards the center of the universe, which was the Earth, or the center of the Earth, so that explains why apples and other falling objects were falling straight down. If the Sun was at the center of the universe, things would fall toward the Sun and away from the Earth, which of course they didn’t. So these were some of the reasons they rejected the heliocentric theory.