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Tham khảo tài liệu 'anh ngữ sơ cấp - học tiếng anh bằng hình ành (phần 3) part 9', tài liệu phổ thông, tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Man s past is a very small part of all time but it is a very important part. How old are the stars How old are the Sun and the Earth and the Moon Nobody knows for certain. It is not possible at present to be certain about such great questions as these but two things seem probable. The universe is about five billion 5 000 000 000 years old. It has been becoming more and more complex from the start. certains two different meanings of certain 1. You are certain about something when there Is no question in your mlnd.lhat It is so. 2. Something Is certain is a foci If H Is well-supported by all the rest of knowledge. We are sometimes certain in sense 1 about things which are not certain in sense 2 . probable more than possible leu than certain. if there are seven block bolls and three white y w balls In a bag and you take one of them out without looking. It Is probable that you win get a black one. 488 However we tty to think of time it seems certain that the earth is older than our minds can take in. Things have been going on for a longer time than we can think of and they will go on and on through a longer time in the future than we can think of. Seventy years seems a long life-time if compared with the present minute. But if compared with the age of a stone it seems no time at all. There is a Chinese poem which says Quickly the years fly past forever Here forever is this spring morning. poem something said for the complete man his thoughts feelings desires hopes fears. in the best possible way. 489 We have to think of Time and Space together here and now there and then. We cannot see with our eyes how far off in Time and Space the stars are but asưonomers can measure their distances. Their unit of measure is the light-year the distance light ưavels through Space in a year. The greatest telescopes of today let us look two billion light-years out into Space. The stars we see there are two billion light-years away. We see them as they were two billion years ago. We are
