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On 10/29/2006 07:46 AM, carmelo@pacific.net.sg wrote:
In a sense, we can't tell whether we are feeling the gravity or the effect of acceleration, or a
mixture of both. We could not even feel the effect of acceleration due to the rapid expansion of
the universe, if there is any.
Does that mean to say gravity, or uniform gravity?
There's a big difference between uniform acceleration and
acceleration in general.
We can only deduce the feeling if we can look out of the so-called
"window"...
That depends. We don't need a window in the wall if the
wall is already far-enough away.
Whether we can feel gravity depends on three things
-- the degree of inhomogeneity
-- the size-scale of our measurements
-- the sensitivity of our measurements
It's like a term in a Fourier series: f' delta(x).
Without the f', this term is zero.
Without the delta(x), this term is zero.
If this term is nonzero, we must ask whether it is big enough
to be significant as determined by the sensitivity of our
measurements.
f' goes to zero in the /limit/ of a uniform field, but this
limit is never really achieved in practice.
delta(x) goes to zero in the /limit/ of a very very local
measurement, but this limit is never really achieved in
practice.
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