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  • 爱因斯坦的重力理论

    Silhouettes of children jumping on a trampoline against a blue sky.

    Why is jumping on a trampoline so much fun? Its springy surface helps you jump higher than you ever could on the hard ground. But even on a trampoline, you can’t keep jumping higher and higher. Gravity always pulls you back down. You’ve probably known about gravity since you were in elementary school. It’s the force that pulls all objects on Earth down toward the ground. Is that all there is to gravity? Absolutely not!
    ::为何跳到蹦床上如此有趣? 它的弹簧表面帮助你跳得比在硬地上高得多。 但即使是在蹦床上,你也不能继续跳得越高越高。 重力总能把你拉倒。 你可能从上小学时就已经知道重力。 将地球上所有物体拖向地面的正是这种力量。 是否只有重力? 绝对不是!

    It Started with Newton
    ::它从牛顿开始

    In the late 1600s, Isaac Newton introduced his law of gravity, which identifies gravity as a force of attraction between all objects with mass in the universe. The law also states that the strength of gravity between two objects depends on their mass and apart. Newton’s law of gravity was accepted for more than two centuries. It can predict the motion of most objects and was even used by NASA to land astronauts on the moon. It’s still used for most practical purposes. However, Newton’s law doesn’t explain why gravity occurs. It only describes how gravity seems to affect objects. There are also some cases in which Newton’s law doesn’t even describe what happens.
    ::1600年代末期,Isaac Newton引入了他的重力定律,该定律将重力确定为宇宙中所有质量物体之间的吸引力。该定律还规定,两个物体之间的重力强度取决于质量和分离。牛顿的重力定律被接受两个多世纪了。它可以预测大多数物体的动向,甚至被NASA用于在月球上着陆宇航员。它仍然用于大多数实际目的。然而,牛顿的法律并没有解释重力为何会发生。它只描述了重力对物体的影响。在有些案例中,牛顿的法律甚至没有描述发生的情况。

    Q : Newton expressed his ideas about gravity as a law. A law in science is a description of what always occurs in nature. For example, according to Newton’s law, objects on Earth always fall down, not up. What is needed to explain gravity?
    ::问题:牛顿以法律的形式表达了他对重力的看法。 科学法是描述自然界中总是发生的事情。 例如,根据牛顿法则,地球上的物体总是倒塌,而不是上升。 需要解释什么来解释重力呢?

    A : A theory is needed to explain gravity. In science, a theory is a broad explanation that is supported by a great deal of evidence.
    ::A:解释重力需要一个理论。在科学中,理论是一个广义的解释,有大量证据支持。

    Einstein Explained It All
    ::爱因斯坦解释这一切

    In the early 1900s, Albert Einstein came up with a theory of gravity that actually explains gravity rather than simply describing its effects. Einstein showed mathematically that gravity is not really a force that of attraction between all objects with mass, as Newton thought. Instead, Einstein showed that gravity is a result of the warping, or curving, of space and time, which made up the same space-time “fabric.” These ideas about space-time and gravity became known as Einstein’s theory of general relativity . 
    ::19世纪初,艾伯特·爱因斯坦提出了一个引力理论,该理论实际上解释了引力,而不是简单地描述其影响。 爱因斯坦从数学上表明,引力并不是像牛顿所想的那样在所有质量物体之间真正吸引的力量。 相反,爱因斯坦表明,引力是空间和时间扭曲或弯曲的结果,而空间和时间构成同样的时空“构件 ” 。 这些关于时空和重力的想法被称为爱因斯坦的一般相对论。

    Visualizing Einstein’s Ideas
    ::将爱因斯坦的思想理念可视化

    Einstein derived his theory using mathematics. However, you can get a good grasp of it with the help of a simple visual analogy. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve downward instead of being flat. Now imagine placing a lighter ball at the edge of the trampoline. What will happen? It will roll down toward the bowling ball. This apparent attraction to the bowling ball occurs because the trampoline curves downward, not because the two balls are actually attracted to one another by an invisible force called gravity.
    ::爱因斯坦用数学来推理他的理论。 但是, 您可以借助一个简单的视觉类比来很好地理解它。 想象一个保龄球在蹦床上被压下来。 蹦床的表面会向下倾斜而不是平滑。 现在设想在蹦床边缘放置一个较轻的球。 会发生什么? 它会向保龄球倾斜。 这种对保龄球的明显吸引力之所以发生,是因为蹦床曲线向下倾斜, 不是因为两个球实际上被一个叫作引力的无形力量吸引到对方。

    Einstein theorized that the sun and other very massive bodies affect space and time around them in a way that is similar to the effect of the bowling ball on the trampoline. The more massive a body is, the more it causes space-time to curve. This idea is represented by the Figure . According to Einstein, objects move toward one another because of the curves in space-time, not because they are pulling on each other with a force of attraction. Einstein’s theory is supported by evidence and widely accepted today, although Newton’s law is still used for many calculations. 
    ::爱因斯坦认为太阳和其他非常庞大的物体对周围空间和时间的影响方式类似于保龄球对蹦床的影响。 体积越大,越是造成时空曲线。 这一想法由图来代表。 爱因斯坦认为,物体相互向上是因时空曲线而起的,不是因为它们相互拉动的吸引力。 爱因斯坦的理论得到了证据的支持,今天得到了广泛接受,尽管牛顿的法律仍然用于许多计算。

    Visual analogy of Earth's mass curving space-time, affecting nearby objects like satellites.

    This diagram shows how Earth’s mass bends the “fabric” of space and time around it, causing smaller objects such as satellites to move toward Earth.
    ::这个图表显示了地球质量如何弯曲周围空间和时间的“结构”,导致卫星等小型物体向地球移动。

    Could we ever get close enough to black hole to observe its effect on space and time? Well,we really don’t know what black holes look like up close but we can use our understanding of physics to make accurate predictions and simulate what might happen. Try placing the space probe or clock near the event horizon of the black hole in the simulation below to learn more:
    ::我们能否靠近黑洞,观察黑洞对时空的影响?我们真的不知道黑洞的近似是什么,但是我们可以利用对物理的理解做出准确的预测,模拟可能发生的事情。尝试在下面的模拟中将空间探测器或时钟放在黑洞事件地平线附近,以学到更多东西:

    Summary
    ::摘要

    • Newton’s law of gravity can predict the motion of most but not all objects. It also doesn’t explain gravity. It only describes its effects on the motion of objects.
      ::牛顿的重力定律可以预测大多数但并非全部物体的动作。 它也不能解释引力。 它只描述其对物体运动的影响。
    • Einstein showed mathematically that gravity is not really a force of attraction between all objects with mass, as Newton thought. Instead, gravity is a result of the warping of space-time.
      ::爱因斯坦从数学上表明,引力并不是像牛顿想象的那样在所有质量物体之间真正吸引力。相反,引力是空间时间扭曲的结果。
    • Einstein’s ideas have been supported by evidence and are widely accepted today.
      ::爱因斯坦的想法得到了证据的支持,今天被广泛接受。

    Review
    ::回顾

    1. How did Newton describe gravity?
      ::牛顿如何描述重力?
    2. How did Einstein explain gravity?
      ::爱因斯坦如何解释重力?
    3. Why is Einstein’s theory of gravity widely accepted today?
      ::为什么爱因斯坦的引力理论今天被广泛接受?