"Australopithecus Afarensis"
Message-id: lWiQa.12225$zy.2594@fed1read06

Lorentz Transform is here to stay. However, can anybody explain time
dilation caused by gravity or acceleration? All explanations boil down
to speed change. Other than going through the math of general
relativity, there is no intuitive explanation.

Could you explain why you have to go through math of
GR to see time dilation during acceleration? It puzzles
me because if you accelerate toward a clock (together
with this clock to avoid Doppler effects) your intuition
should tell you that this clock will run faster (as it does),
otherwise what kind of intuition is it?

Opposite in other direction where you have "time dilation"
as a very simple intuitive thing. Since what your intuition
should tell you is just what is observed, you apply the
principle of equivalence to tie gravity to time dilation and
so there is nothing else left to understand.

Also, one success of general relativity is to explain the
bending of light around the sun and gravitational lens. That
is nice, but light also bends going from one material to
another with different index of refraction. Bending of light
can be explained with slower speed of light around the sun
without introducing time dilation.

Not if except of treating it only qualitatively you start
calculating things and start worrying about conservation
of energy. Then you will see that bending of light has to
be tied to time dilation, and that exact amount of bending
(increased by curvature of space) is determined by
inability of nature to create energy from nothing. This way
you gain intuitive understanding of reasons for curvature
of space. Everything without any "math of GR" yet.

A good exercise to understand (intuitively) those things
is to drop a stone and observe its kinetic energy growing
while it is falling down. When you already see that its
kinetic energy changed from zero to something, try to
guess where this kinetic energy came from, knowing that
there is no "attractive gravitational force" in the nature
(as Einstein discovered) and so it couldn't create this
energy. And yet this energy is a fact. Isn't it strange?
It turns out that you know already everything to solve
this puzzle (all you need is in my text before this
paragraph since the rest is only elementary physics
which I assume you've learnt in high school). What's
the solution (where the kinetic energy of this falling
object is coming from)? (Qualitative solution suffices :-).

-- Jim