[LEAPSECS] BBC radio Crowd Science

[michael.deckers]

    On 2017-01-30 21:39, Tom Van Baak wrote:


> 2017-01-01T00:00:35.5 TAI = 2016-12-31T23:59:59.5 UTC

    I do have problems with your notation.

    You apparently want to say that
       "whenever TAI assumes the value 2017-01-01T00:00:35.5,
        then UTC assumes the value 2016-12-31T23:59:59.5"
    but I do not see which two things are denoted by the two
    members of your equation, and are supposed to be equal.

    If the value of the left member is the set
         { X : TAI( X ) = 2017-01-01T00:00:35.5 }
    of all points X in spacetime where TAI assumes the value
    2017-01-01T00:00:35.5, and similarly for the right member,
    then in fact you would have a correct equation.

    But the notation
       2017-01-01T00:00:35.5 TAI
    normally is not taken to mean a set of points in
    spacetime, but the epoch 2017-01-01T00:00:35.5
    with the additional information that it is a value of
    the TAI time scale.

> 2017-01-01T00:00:35.5 TAI - 36 s = 2016-12-31T23:59:59.5 UTC

    I am completely lost here. If your first equation was
    A = B, then you are now saying  A - 36 s = B. I cannot
    make sense out of it.

    If you mean
       2017-01-01T00:00:35.5 - 36 s = 2016-12-31T23:59:59.5
    then why not say it?

    My original point was that your arithmetic on datetimes
    was confused. If the additive group of time values operates
    on datetimes in the usual manner, then
       2017-01-01T00:00:00.5
           =  2017-01-01T00:00:00.5 +      0 s
           =  2017-01-01T00:00:00.5 + (36 s  - 36 s)
           = (2017-01-01T00:00:00.5 +  36 s) - 36 s
           =  2017-01-01T00:00:36.5          - 36 s
           = "2016-12-31T23:59:60.5" in your notation
    as I claimed. But possibly you do not want to use
    the usual operation of the group of time values on
    datetimes. I cannot reasonably comment on your posts
    it unless you specify rigorously which operations
    you mean.

    Michael Deckers.




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