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From Cecil's Mailbag by the Straight Dope Science Advisory Board
Dear Straight Dope:
Do you care to elaborate how 2+2=5 for very large values of 2? I
thought 2
was a constant and had only one value, or can I toss 12 years of
math out
the window? --Adam
SDSTAFF Dex replies:
The statement is, "2 + 2 = 5 for very large values of 2." It's a
joke about rounding and estimating. For instance, suppose you have
your calculator set to round all numbers to integers (no decimal
places) and the problem you're actually computing is 2.48 + 2.47.
The calculator will automatically round, so when you punch 2.48 and
ENTER, it will show up on the screen as 2. When you punch in the
2.47 and ENTER, it will also show up on the screen as
2. Then when you add, the sum 4.95 will be rounded to 5. Hence,
2 + 2 = 5 if the value of 2 is large enough.
It's a joke ... but a joke with a somewhat serious point. All
measurements in the real world (as opposed to the esoteric whirled
of mathematics) are estimates; they're always rounded to something.
There's no such thing as absolute precision. So rounding must come
into play sometime or other, and the joke about 2 + 2 = 5 if 2 is
large enough, is a reminder about the way that estimation errors
compound.
--SDSTAFF Dex
Straight Dope Science Advisory Board
Cecil's Mailbag is researched and written by members of the Straight Dope Science Advisory Board, Cecil's online auxiliary. Although the SDSAB does its best, these articles are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.
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