Prof. N. David Mermin from Cornell University published a new version of his elementary introduction to Special Relativity. "It's About Time: Understanding Einstein's Relativity".
I found two errors, one that is irrelevant, and another that is relevant.
In page 3 it says almost at the end of the page:
``I disgress to remark that the foot (plural ``feet") is a unit of distance (abbreviated ``f"), still used in backward nations, equal to 30.48 centimeters. In this book it will be highly convenient to redefine the ``foot" to be just a little shorter than the conventional English foot: about 30 centimeters (or, more precisely, 29.9798452 centimeters--98.36 percent of a conventional foot)."
Instead of 29.9798452 it should say, 29.9792458.
I am sure some of you must be thinking that this is completely irrelevant. Who cares about such a minor exchange of numbers. The last 8 was exchanged for the 2 in the fourth to the last position.
It is relevant because in 1983 the people in charge of defining physical units defined the speed of light as exactly:
299792458 m/s
The reason being that The Special Relativity theory of Einstein is based on the premise that all inertial observers measure the same speed of light in free space. This speed is denoted c, and appears in the most famous physics formula:
E = m c2
By the way you can memorize this number with its prime factors:
2x7x73x293339.
Posts
No comments:
Post a Comment