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On Mon, Dec 20, 2010 at 10:49 AM, Laurence Cuffe <cuffe@xxxxxxx> wrote:
>
>
> On Dec 19, 2010, at 10:07 PM, Don Williams <dwilli10@xxxxxxx> wrote:
>
>
> Today, the fundamental unit of time suggested by the International System of
> Units is the second, since 1967 defined as the second of International
> Atomic Time, based on the radiation emitted by a Caesium-133 atom in the
> ground state. Its definition is still so calibrated that 86,400 seconds
> correspond to a solar day. 31,557,600 (86,400 × 365.25) seconds are a Julian
> year, exceeding the true length of a solar year by about 21 ppm.
>
> At 06:58 AM 12/17/2010, Carlos wrote:
>
> Don:
> I could copy definitions, every viewpoints, etcetera from
> different sources, but I think it would be more easy to read this
> Wikipedia article:
>
http://en.wikipedia.org/wiki/Time
>
> Carlos
>
> Yes, I have read that entry and in the first paragraph it says: "Time has
> been a major subject of religion, philosophy, and science, but defining it
> in a non-controversial manner applicable to all fields of study has
> consistently eluded the greatest scholars."
> ________________________________
> I just noticed the above incomplete response on the subject. I had been
> holding this message in order to find a statement by Einstein, that he
> couldn't define time, but it's buried somewhere in a 400 page bio I have
> been reading and I can't easily find that sentence Just trust me that he
> did say that.
>
> Einstein even used time as a fourth dimension, and also attempted to prove
> that the universe is curved back on itself. Current evidence now points to
> a flat universe. He even won a Nobel Prize in Physics, but not for his work
> on relativity.
>
> Interesting situation, Hawking wrote a Brief History of Time, but even there
> he didn't define the term.
>
> It's clear that even though there seems to be no scientific definition of
> time, we all use it, mutually understand what the word means, and are not
> hampered in our daily lives by the lack of such definition.
>
> DAW
>
>
> Scientific definition of a unit of time. Wikipedia, Units of Time.
> Today, the fundamental unit of time suggested by the International System of
> Units is the second, since 1967 defined as the second of International
> Atomic Time, based on the radiation emitted by a Caesium-133 atom in the
> ground state. Its definition is still so calibrated that 86,400 seconds
> correspond to a solar day. 31,557,600 (86,400 × 365.25) seconds are a Julian
> year, exceeding the true length of a solar year by about 21 ppm.
> We can, as scientists, define time with about the same level of certainty
> with which we can define distance, and mass. All of these entities when we
> look closely become quite slippy as concepts. For instance, the length of a
> meter stick, which seems a very concrete thing, turns out to depend in a
> very real way on which way and how fast you are traveling when you measure
> it.
> Similarly duration depends on the relative velocities of the observers
> discussing it, and also depends on how deep into a gravity well you have
> descended, This effect is real, a height difference of 12 meters can put two
> Iron atoms out of sinc with each other so that they can no longer have the
> same energy levels. (
http://en.wikipedia.org/wiki/Pound-Rebka_experiment)
> Even before and after is up for grabs. So long as two events are too far
> apart for a light beam to get from one event to the other before the other
> event happens in some rest frame, than its possible to find another rest
> frame, where the second event will happen before the first.
> This is all fascinating stuff, and although I touched on it in college, I
> find MIT open courseware, and even ITunes U (both free!) a great source of
> world class lectures on this material.
> All the best
> Larry Cuffe
>
---
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