时差N小时 地心引力为何有益于人类?(下)（在线收听）

This gravitational state of affairs might seem rather limiting: wouldn’t it be fun to be able to float around like astronauts?

引力状态似乎会让人更加受限：像宇航员一样漂浮起来难道不是一件很有意思的事情吗？

Perhaps, but anyone who spends an extended period of time in space faces serious medical problems due to the near total absence of gravity.

或许吧，不过因长期缺乏引力，生活在太空的人会面临严重的医疗问题。

For instance, the small bones and fluid of the inner ear that allow us to keep our balance and know which way is up depend on gravity.

例如，耳朵内的小骨与液态流质对保持身体平衡意义重大，而引力是人体判断向上的决定因素。

In weightlessness, astronauts often initially experience intense dizziness, and are sometimes unable to orient themselves to their hands and feet.

在失重状态下，宇航员首先会感到强烈眩晕，有时甚至无法控制手脚活动。

What’s worse, our bones, ligaments and muscles all maintain strength by working against the weight caused by gravity.

更糟糕的是，人体的骨骼，韧带以及肌肉需要与引力产生的重量抗衡方能保持强健。

Without weight, bones weaken, ligaments deteriorate, and muscles atrophy.

在失重的情况下，骨头变得脆弱，韧带情况恶化，肌肉出现萎缩。

That’s why astronauts who have been in space for many months have trouble walking when they return to earth.

这就是宇航员经过数月的太空旅行返回地球后无法正常行走的原因。