乐观主义可能起始于最卓绝的人类天份：精神的时间旅行——在头脑中沿时间和空间向前向后移动的能力。
Optimism starts with what may be the most extraordinary of human talents: mental time travel, the ability to move back and forth through time and space in one's mind.
随着时间，到达火星最乐观也需要五千亿美元。
An optimistic bill to get to Mars would come to half a trillion dollars over time.
不过，就是最乐观的观点也认为，该技术投入实用还至少需要八年的时间。
Even an optimistic view puts the technology eight years away from deployment, though.
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