Scientists gained profound understanding when they discovered that the laws and constants of physics themselves impose theoretical limits on how much cosmic history astronomers can view. Astronomers now recognize that only one relatively brief epoch in cosmic history allows for direct observation and measurement of its entire sweep. For example, it takes time for light to travel from distant galaxies to an observer’s telescope. Up to a certain limit, the older the universe, the greater the distance at which astronomers can make observations, or the farther back in time they can see. The
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Fascinating but should be common knowledge and taught in grade school.
