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What Alfred Russel Wallace Really Thought About Darwin 79

Calopteryx writes "The correspondence of Alfred Russel Wallace has gone online for the first time. New Scientist has opened a wormhole between the 21st and 19th centuries and has 'interviewed' the great man."
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What Alfred Russel Wallace Really Thought About Darwin

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  • by __aaltlg1547 ( 2541114 ) on Sunday January 27, 2013 @05:00PM (#42709725)

    No. No digital representation of a date can represent values before 1900, nor is it even mathematically possible.

    Really? Are you sure about that? Not mathmatically possible? I guess negative numbers don't exist in your realm.

    <david_attenborough_voice>A spectacular example of a Whoosh in the wild! Let's be careful not to disturb it</david_attenborough_voice>

    The original comment was tongue-in-cheek. But most computer date representation systems are prospective from modern zero date.

    For example, Unix time was originally coded as elapsed whole seconds since midnight January 01, 1970 and represented time as an UNSIGNED 32-bit integer. Such systems still exist and will roll over on 2038. More modern timekeeping systems use 64-bit integers to represent time and date. I'm not sure whether they interpret them as unsigned or signed. If they interpret them as signed, there is certainly an opportunity to represent dates before 1970 and I can think of no reason not to do so since a 63-bit second count will not have a rollover problem in the next 292 billion years. I'm personally comfortable with putting the problem off that long if it also gets me a nice representation of the day on which I was born, which is before the Unix epoch.

    NTP uses the same epoch date as Unix but uses the top 32 bits as seconds and the lower 32 bits as fractional seconds. It thus cannot uniquely represent dates before 1970 or after 2038.

    Windows uses some different time representation systems but they suffer from similar deficiencies.

    And with all that, supposing you do use a system that can represent negative numbers, you don't have to go that far back before you run into other problems. The first is what to do about leap-seconds. I'd say that once you go back before the adoption of atomic time standards, you should count days as being 86400 seconds long by definition of the ante-atomic second. That gets you back to the next problem date, which is adoption time zones synchronized to Greenwich Time or local adoption of the Gregorian Calendar. Depending on where you are, either may have happened before the other. Greenwich synchronization adds an error of up to several hours depending on location. Gregorian calendar adoption caused a slip of several days to the calendar; the later the adoption, the more days of slip. And that gets you back, at best, to 1582 A.D. Computer representation of the date is thus a very messy business back to 1582, subject to the vagaries and religion of the country under consideration. (Protestant and Orthodox countries tended to hold out against the tide of popery and non-Christian countries weren't interested in any kind of Roman dates.)

    And that gets us on the Julian Calendar, which is usable back to it its introduction in 45 BC. But it was only used in the Roman Empire and its historical descendants including Christendom. That's as far as the West goes. You can then switch locally to the Jewish calendar, which represents dates back to 3670 or so BCE. But it has lot of slop in it. It's a lunisolar calendar so precise date synchronization with any modern system depends on precise knowledge of historic (and prehistoric) lunar phase with respect to the Earth's prehistoric rate of rotation. Also, the cycles were determined by observation in ancient times and we don't know whether they were always observed on the right day with respect to the lunar phase because some months would have started on a cloudy day, preventing official observation. And though that calendar can represent dates back 5773 years from today, it may not have been in use that long.

    In the East, e.g. China, they had their own calendar system and the first opportunity to align it to a Western system was fairly recent. The Chinese system is lunisolar, similar to the Hebrew system, so it has the same kind of imprecision. What's worse, people recorded regnal years of the Emperors (or worse, some local potentate) and you have to know when each monarch took the throne to figure when things happened. And that only gets you back to 862 or so. Before that, people generally didn't write down what year things happened at all.

Stinginess with privileges is kindness in disguise. -- Guide to VAX/VMS Security, Sep. 1984