Entry
What causes gravity? I know how it works, the equations, etc. But why are two distant bodies attracted to one another? Is there any current research?
Nov 11th, 2006 09:07
Knud van Eeden, Mike Ogilvie,
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--- Knud van Eeden - 10 November 2001 - 06:18 am ---------------------
What causes gravity? I know how it works, the equations, etc. But why
are two distant bodies attracted to one another? Is there any current
research?
---
The Einstein model to explain gravity:
Mass can change the shape of space.
The more mass the more it changes this shape.
Imagine yourself shooting a ball, while it touches the surface, over a
flat soccer field.
That ball will go in a rather straight line.
Now imagine that there are a lot of (shallow) holes in
this soccer field.
If you shoot this ball its path will be deviated from this straight
line
when it passes over such a (shallow) hole.
E.g. the planets play the role of the holes in the otherwise flat
field.
They are like laying in the bottom of the holes, and the more mass they
contain, the steeper the border of that hole will be and the deeper
that
hole.
The path of any object (e.g. the ball in the example) which now moves
over that otherwise flat field will be influenced by the holes.
Its path will be deviated, and if the hole is steep enough it will go
down
in the hole and go to its lowest point. Otherwise its path will be
deflected,
but it will otherwise continue.
---
The cause of the acceleration of the motion of falling bodies is not a
necessary part of the investigation
[book: author: Galilei, Galileo - title: Two New Sciences -
http://www.amazon.com/exec/obidos/tg/detail/-
/0879757078/qid=1075059501/sr=1-2/ref=sr_1_2/002-7249826-0710429?
v=glance&s=books]
===
It is important to understand that while Newton was able to formulate
his law of gravity in his monumental work, he was not comfortable with
it because he never, in his words, "assigned the cause of this power."
In all other cases, he used the phenomenon of motion to explain the
origin of various forces acting on bodies, but in the case of gravity,
he was unable to experimentally identify the motion that produces the
force of gravity. Moreover, he refused to even offer a hypothesis as to
the cause of this force on grounds that to do so was contrary to sound
science.
---
[Internet: source: http://www.google.com search for 'newton gravity
cause': http://en.wikipedia.org/wiki/Gravity]
---
A similar approach regarding quantum theory:
"Do not take the lecture too seriously . . . just relax and enjoy it. I
am going to tell you what nature behaves like. If you will simply admit
that maybe she does behave like this, you will find her a delightful,
entrancing thing. Do not keep saying to yourself "But how can it be
like that?" because you will get...into a blind alley from which nobody
has yet escaped. Nobody knows how it can be like that."
This was Richard Feynman, speaking about quantum theory. It pays to
take his warning seriously. By the time you finish this section of the
site, you will understand the most extraordinary implications of a
truly extraordinary theory. But if you try to picture it in familiar
ways you will come hopelessly unstuck. The quantum world really is
different, and the only way to come to grips with it is to suspend
disbelief. So open your mind and become a genius in your own lunchtime.
[Internet: source: http://www.newscientist.com/hottopics/quantum/]
===
Working backwards towards the beginning of any chain of explanations
there are some basic faqts, which you have to accept as is, because it
is. If you change that faqts, you change the basic rules of our
universe (basically creating another universe).
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So in the end you explain phenomena by referring to hypotheses or laws.
These facts you do not explain anymore, you just accept them, e.g.
based on statistical evidence suggesting this law.
So I would tend to say that in the end you are describing, less
explaining.
===
Possible 'explanations' for gravity might be:
-gravity waves
-gravity particles
-specific types of motion
-curving of space
===
A central property for gravity is for example motion.
One of the properties of the laws of gravity shows itself e.g. via the
law, postulated by Einstein, that light always travels in a straight
line.
Suppose you move in a box through space, with one window, and while you
are accelerating faster and faster, a light beam enters this window.
The faster you accelerate, the more this beam will appear bend to your
eyes, as the room moves up from the moment this beam enters your room.
But this law of Einstein says no that is not possible, that beam of
light can not bend, it will alway travel in a completely straight line.
But what if it is not this beam that bends, what is it that does bend?
Something has to change, in order to explain the phenomenon, but it can
not be that straight line beam of light.
Well here the hypothesis is that the surrounding space bends instead.
So if that is true then acceleration causes appearent bending of light
rays, or thus bending of space. In other words, acceleration influences
the path of the light beam.
Also any mass influences the path of light rays in a similar way (as
shown by Arthur Eddington during the sun eclipse early in the 20th
century, when rays of light coming from a distant star where shown in a
different position on a photographic plate, before and after. The
deviation was supposed caused by the gravity of the sun. The prediction
following Einstein's calculations matched fine the facts), causing
light rays to bend, that is, follow a curved space route, in the
presence of large bodies (e.g. the sun).
So basically acceleration and gravity have an equivalent influence on
the path of straight light rays. Consequently, you might use both to
explain the effects of gravity, leading to different models both
explaining the same phenomena in their own specific way.
The implications of this idea led to the general theory of relativity.
===
PS Similarly, another law, postulated by Einstein, says that the
velocity of light must always be constant. Velocity is defined by
distance divided by time, so in order to keep it constant, both time
and distance may vary, e.g. when analysing the relative velocity of
fast moving objects. So the distance might also bend, that is shrink
smaller or grow larger. Similar the time might flow slower or faster.
The implications of this idea led to the special theory of relativity.
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Attraction, which manifests itself e.g. in a deviation (e.g. towards
each other), or thus a different path in space, could be explained or
better described, by saying that this bodies follow the contours of a
bent surface. The heights and throughs are then by caused the gravity
of the present bodies. The heavier, the higher the peaks or the lower
the throughs.
===
Internet: see also:
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What causes gravity?
http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/GR/gravity.html
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[Internet: source: http://www.google.com search for 'newton gravity
cause': http://www.autodynamicsuk.org/NewtonianGravity.htm]
---
Math: Calculus: Differential equation: Partial: Laplace: Can you tell
more about Laplace equation?
http://www.faqts.com/knowledge_base/view.phtml/aid/35610/fid/813
---
Physics: Nature: Law: Overview: Can you give an overview of the laws
of nature?
http://www.faqts.com/knowledge_base/view.phtml/aid/35527/fid/677
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