[LEAPSECS] BBC radio Crowd Science

[Warner Losh]

On Sat, Feb 4, 2017 at 10:32 AM, Steve Summit <scs+ls at eskimo.com> wrote:
> Warner wrote:
>> I think this is the crux of my problem with Tom's answer to my first
>> leap second question. We have two times, that are obviously different
>> that when subtracted produce 0 as the answer. x-y = 0 should only be
>> true when x and y are the same. But we get that answer when they are
>> different.
>
> So what about x = 100 degrees Celsius, y = 212 degrees Fahrenheit?
> Two obviously different numbers.  What should the difference be?

That's a bad analogy, because there's a 1:1, onto mapping between the
two. There's also a unit shift involved. And no "leap degrees." And
also, it turns out, universal agreement as to what the right answer
is.

A better analogy would be between Julian and Gregorian calendars. Does
the offset for those increase on Feb 29, 2100 (Gregorian) or on March
1, 2100 (Gregorian)? I suspect we'd have a similar debate about that.

> This is a suggestion, not a proof.  The analogy between
> Celsius-versus-Fahrenheit and TAI-versus-UTC is not at all
> perfect.  And we're dancing around between proofs from first
> principles, versus demonstrations based on what makes the math
> easier.  But I'm afraid the "the numbers are different, so the
> difference can't be zero" argument is not as compelling as you'd
> like.

I guess we're at logger heads then. Any "proof" that involves a lossy
mapping is suspect, imho.

Warner