Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 35 - Think and Explain - Page 684-685: 86


Yes, we agree.

Work Step by Step

You do see your hand "in the past." Light has a large but finite speed. When you look at your hand, you are receiving the light that left your hand a short time ago. Divide the distance between your hand and your eye by the speed of light to calculate how far back into the past you are seeing. Example: light travels a distance of 30 cm in a billionth of a second. One rule of thumb is that light travels about a foot per nanosecond (actually, about 1.02 ns). If the back of your hand is about 30 cm (a foot) from your eyes, you are seeing it as it was one-billionth of a second ago.
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