Well, my first beginning of this post was lost in the aether, so here we go
again. Before directly addressing Trevor's ideas, let me start with a brief
discussion of the nature of science. The purpose of science is to model,
predict, and allow us to manipulate phenomenon. It does not address the
validity of our senses and does not directly answer any ontological or
epistemological questions. (It can however, provide help in answering these
questions by providing an organized understanding of those observations.) My
favorite quotation on the nature of science is from the sci.physics
newsgroup where Patrick Van Esch stated "the most important step in the
history of science was when it was decided that it wasn't about the truth.
>If you read on, do so with an open mind ...
>
>My thoughts came from the idea that gravity is a real natural FORCE which I
>have seen in action (things fall to the ground, tides go up and down).
>This led me to think about gravity beyond earth -- meaning the sun, the
>moon, and the other planets of the solar system -- all of which have
>gravity of various degrees. We know the gravity of other massive bodies
>such as planets influence events on earth.
Well, not really. The earth's orbit is subtly affected by the orbit of the
other planets, but the gravitational attraction of the planets on you and me
is very small. A good way to remember this is that, when you are reading a
newspaper, the gravitational attraction of the newspaper has a greater
influence on your body than the gravitational attraction of Jupiter.
>The moon is credited with the power to move entire oceans hundreds of feet
>up and hundreds of feet down every day in the form of shifting tides.
Again, not really. I believe you are thinking of that Bay (Fundi?) where a
funnel effect causes 40 foot tides. 2 feet is much more common.
It naturally follows, then, that these same gravitational forces would have
an influence on our bodies, which are made of 96% water.
The type of matter is not important. It is, indeed, universal gravitation.
But, the influence of the moon on us is extremely small. For example, the
force of the moon on your brain, which weighs about 3 pounds, is about
0.00001 pounds. It cannot have much effect.
>The fabric of space-time is influence profoundly by gravity. Black holes
>are said to contain the strongest gravity known, gravity stronger than
>light. Einstein taught us that light is directly related to time.
Ah, no not really. I really don't think that a special relativity course
would fit here, even if I expanded this to GLL-VM (Gord like length, verbose
mode). But, let me say that SR should be thought of as describing
spacetime. The speed of light is important in the deriving and the
understanding of spacetime, but its not as though photons are needed to
describe spacetime. It would be better to say that there is a natural upper
velocity: c, and that an object will travel this velocity if and only if it
has no rest mass. Photons are the only known particles with zero rest mass.
>Therefore, gravity is stronger than time.
That's not really a good way to look at it. Remember, gravity is the
weakest of the four forces: in order they are
Strong
Electromagnetic
Weak
Gravitational
>If you can imagine the solar system and beyond in relation to gravity, you
>will see that all bodies of motion are guided by the ebb and flow of
>gravity in an intricate, profoundly complex exchange of energy.
Actually, there is typically very little exchange of energy. Discounting,
for the moment, the effects of the other planets, the energy of a planet
orbiting the sun is constant. As the planet goes to apogee, it loose
kinetic and gains potential energy. As it goes to perigee, it gains kinetic
and loses potential energy.
This is because gains and losses of energy do not occur in a two body
gravitational system. It takes the interactions of a three body system for
there to be the potential for gains and losses of energy. An example of
this is the slingshot effect used by some satellites. A satellite enters
the gravity well of a planet in the opposite direction of its orbit around
the sun. It can be seen, for the moment, to be in a parabolic orbit of the
planet. As it goes from the front side to the back side of the planet, it
has constant energy in terms of the two-bodied satellite/planet system.
With respect to the planet, its entrance velocity is equal to its exit
velocity. But, since it goes from traveling against the orbit of the planet
to traveling with the orbit of the planet, it gains energy with respect to
the solar system.
To some extent, of course, this does happen between planets. But, the
effect is so small, it can practically be ignored.
>It is the merging and tearing apart of mass on a huge, cosmic scale. On
>earth, these forces are invisible to us, yet are acting on us every moment
>we are alive. Gravity is very real and very much and active part of
>existence for all of humanity -- and all of the Universe, for that matter.
>
>All of this is acting on a subatomic level as well. As forces of gravity
>bombard me from all directions (from distant stars as well as asteroids and
>planets), the "mass" of my matter -- my blood, bones, and tissues are
>tugged, pushed, and pulled in minuscule ways I cannot consciously
>recognize. The atoms that make up the sum total of my body (and perhaps
>even my consciousness) are as subject to the influence of gravity as a
>planet or a moon. The quantum state is, in simple terms, a microcosm for
>what is happening on the largest scale conceivable.
>
A couple of points worth noting here. First of all, a theory of quantum
gravity has yet to be developed. Thus, there is a certain lack of clarity
when one discusses gravity at the quantum level. We do know that, say,
beams of protons or electrons are affected by gravity, but we do not have
precise measurements of the effects of gravity on different elementary
particles. For example, AFAIK, we have yet to run experiments to see if
matter and anti-matter are affected by gravity in the same way. We
certainly expect that to be the case, but I have not heard of any
measurement showing that gravity affects anti-matter exactly as it affects
matter.
Finally, I think it would be worthwhile to briefly discuss general
relativity. I'll have to admit, that I did not take a formal course in GR.
Few experimentalists do, they only offered the course once every couple of
years at Wisconsin. With that caveat, let me give a brief overview of GR.
In GR, matter affects the curvature of space, and the curvature of space
dictates the motion of objects. In Newtonian mechanics, in the absence of
external forces, an object will continue moving in a straight line. In
Newtonian mechanics, gravity is a force, and causes objects to deviate from
a straight line.
In GR, gravity is not a force. Matter curves space, and objects that travel
in space follow the geodesics if they are not subjected to outside forces.
So, a planet in orbit is not subjected to a force, but is just following a
geodesic.
Well, that�s it for the physics. Next post, I�ll tackle the metaphysics.
Dan'm Traeki Ring of Crystallized Knowledge.
Known for calculating, but not known for shutting up
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