Re: Curved space

"Dick" <remdickhm@xxxxxxxxxxxxx> wrote in message
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On Mon, 14 Aug 2006 22:05:46 GMT, "Sam" <sam@xxxxxxxxxx> wrote:

"Dick" <remdickhm@xxxxxxxxxxxxx> wrote in message
news:otk1e2hp1qc4enoe2mf8k8o193sljre714@xxxxxxxxxx
I am trying to imagine how space curves as a planet passes through. I
have seen the graph like grids curving away from the object/planet,
but nothing in 3D.

Is space rigid enough that it creates a "bow wave and wake?" If so how
far away from the local passage does the wave go? Does it extend into
space indefinitely setting up interference patterns as the curve
passes other curves?

Or, is space compressible like jello? Is the curve only local due to
space viscousness?

dick


The universe is esstially two things, matter/energy and space-time.

Matter/energy is two forms. The cold, barionic, stuff we can see like
stars, planets, people... is only about 4% of the total matter. The
other
96% is dark matter/energy that we can't see, but seems to be there based
on
it's effects on the matter we can see.

As you point out later, I am still accepting "gravity" as meaningful.
The "lens" effect of starlight bending around a large body due to the
attraction between the large body and the photon is understandable to
me, but if I am to rely on space (can't bring myself to say
"space-time") doing the bending, I just can't make the leap. It
requires adding abstraction upon abstraction. Why should the universe
be so complicated?

As Sir Arthur Eddington said, "not only is the universe stranger than we
imagine, it is stranger than we can imagine."

All we can do is strive to achieve an understanding based on observation and
experiment. With Newton things seemed to be pretty well worked out, that
was until Einstein had to go and start thinking about the nature of light.

You've actually almost got the whole curved space idea with your photo idea,
you just have to flip it around like Einstein did. When the photon passes
by the star on it's journey from it's source to your eye, the deflection is
not caused by gravity in the same sense of scale from Newtonian models.
From the photo's point of view it IS traveling in a straight line. It has
nothing to do with the classical F=Gm1m2/r2, by which you can determine the
force by knowing the mass of the star and the mass of the photon and the
distance. In fact if you did that you would in no way come close to
describing the observed deflection, gravity is just to weak. The deflection
occurs not because of gravitational attraction between the sun and the
photon, but because the photon is traveling a path along curved space.

Space-time appears to be litterally the "space" between different chunks
of
matter. As this matter moves further apart, "space" is created.

How is "dark matter" different from the earlier "ether"? Dark matter
has mass, so why not gravity? (I still find mass attracting mass
simpler)

They are similar from the standpoint that they are both theoretical
abstracts that fit the existing framework until something better comes along
and they are better understood.

Ether is really a dead concept, at least in the form it was originally
concieved. The ether was an "invention" of Einstein as the "fabic" of
space-time over which electromagnetic waves propagated. The idea was that
there was no such thing as a true vacuum, all space contained Ether.

Dark Matter came about from the discovery that stars at the edges of spiral
galaxies appeared to be rotating faster than they should. By adding more
mass the problem was solved, so the idea was based on the observation that
they were in fact rotating faster than they should, so the missing matter
must be there, but doesn't emit any sort of detectable radiation. Also in
this sense Dark Matter does has the same gravitional effect as normal matter
by having the same effect on space-time.

Also Dark Energy may or may not be related to Dark Energy in the same since
that "cold" matter/energy are by E=mc2. Dark Energy is another theoretical
abstraction that is used to account for the apparent acceleration of the
rate of expansion of the universe. Big Bang theory says everything is
expanding, but in the last 10 years it's been found that not only is it
expanding, the rate of expansion is increasing. This is attributed to Dark
Energy as exhibiting a "negative pressure" on "normal space" driving the
expansion itself.

Brief summary:
http://en.wikipedia.org/wiki/Lambda-CDM_model



Rather than think of space as "bent", imagine it as a "density". The
effect
of matter/energy on space-time is to "increase" it's density in an
r-squared
sort of way. Where there isn't significant matter, space is not very
dense
or "spread out/stretched thin". Where you have a large object like a
star
or planet, space gradualy get's more dense the closer you get. In a
sense
it's "warped" inward toward the center of mass.

I would say it is density as dark matter is real stuff with mass. As
I would speak of the density of air on earth, why not density of dark
matter in space? Still following the "gravity" field, I have read
that earth does not have enough mass to hold its position around the
sun, that its mass is supplemented by the cumulative vectors of the
mass of the whole universe. (I am really freewheeling in this
statement, but it is what my memory makes of it.)

Bear in mind when I was making the metaphor with density I meant density of
space, not density of matter. I find it easier to relate a model of curved
space in my head by attaching a property of density to it that is altered by
the presense of mass. But as far as Dark Matter is concerned the assumption
is that is does have some sort of mass and thus gravity.

As far as the orbit of the Earth around the Sun I havn't seen anything to
indicate anything special beyond normal orbital physics so I can't comment.


The result is an object passing by would appear to travel a curved path
to
an observer. The appearance is that the original object "pulled" it out
of
it's original trajectory. Where actually the object in motion's path was
altered as it incountered the "change in density"/"warpedness" of space
around the original objects.

If a "change in density" like viscosity, imposes a force why shouldn't
that density be dark matter and allow the continued use of gravity?
Why must we accept the unimaginable, curved space?

The changes in the behavior of the different densities of space are
what's
described by relativity. A yard stick in dense space would be shorter
than
one in less dense space. A clock in dense space runs slower than in more
dense space. Of course if you yourself were to travel with a clock and a
yard stick from one point to another you wouldn't notice the difference
because you yourself, as in your physical dimensions in space and
biological
clock are also subject to the changes along with everything else. So the
relativeness kicks in and you won't be able to tell the difference. You
can
only measure from the standpoint of a neutral observer at a different
location.
As I have questions about the reality of "time" why shouldn't the
clock run slower as its energy value changes in more density?

If you're trying to imagine in 3D, picture spacial-density/"bentness" as
a
color. Let blue represent normal space, so picture a empty cube filled
with
blue representing a region of space. Now stick a planet in the middle.
The
density of space at the survace of the planet is greater than the normal
blue space. Let red represent the higher density. Now just imagine a
transition through colors from red to blue, emminating from the surface
out
and you have it. Not a perfect picture, but better than trying to
convert a
bowling ball on a trampoline grid to 3D.

I believe dark matter density could be changed due to gravity creating
the same condition, couldn't it?

Now if you were paying attention, you may have picked up on something
stated
from relativity that doesn't click with most folks. There is no such
thing
as gravity. The "force of gravity" as we call it, is just the observed
illusion of one object "pulling" another. Where in fact the "pulling" as
in
the thing that is affecting another object, is not really a force, but
just
the behaviour of the objects as their motions are affected as a result of
the different density of space around them. The term "gravity well"
lends
some clarity, but really it's a "spacial well".

There is a fundamental question, "curved space or gravity?"


You can even picture this as how gravity appears to work on the surface
of
earth, keeping in mind that objects will move or be "pulled" from areas
of
less dense space to areas of higher density. (Stuff flows downhill.)
Imagine yourself standing up and surround your body with an upright
rectangular box. Now to add in the effect of bent space just imagine the
square at the bottom of the box is smaller than the square over your head
at
the top of the box. What you have is a box that's not all right-angles.
The space at your feet is more dense than the space at your head thanks
to
the Earth. (It's the 3D equilivent to a bowling ball on a 2D trampoline
thing again.) Objects are "pulled" "down" not because of "gravity", but
because of matter's tendency to move in the direction of more dense
space.

How is the tendency of matter to move toward "dense space" any
different from mass attracting mass as in gravity?

In response to the last three, probably the best way to answer is with the
mathematics. To go back to the basics, it comes down to the fact that it
had gotten to the point where Newtonian gravity didn't sufficiently explain
nature. Now that's probably a hard statement to support in 1905, because
much of Einsteins ideas were verified after the fact, which says volumes for
the leaps of logic he took. Nonetheless, the result was a different
mathematical model that has shown to be more in line with observation than
classical Newtonain. So from that standpoint what you have then is
Einsteins mathematicaly curved space, or invent something else to explain
the discrepencies between Newton and nature.

It's still a mathmatical construct, but so is all of physics. Math itself
as evolved since the time of Galileo partly out of the need for a better way
to represent observations. Newton himself essentially invented calculus out
of the need for a mathematical language of nature.

If you consider then what happens the more you bend space. Add more
mass,
space bends more, keep going and you have a black hole. Black holes
appear
then to be the storm drains of the universe. Matter (cold energy)
bounces
around, interacts, forms stars, galaxies, etc... but ends up if it gets
too
clumped together "vanishing" down a black hole. But now we know actually
that black holes aren't entirely black. They actually give off "Hawking
Radiation" in the form of elementry particles. They eventually evaporate
after having converted all the matter that fell into it. So rather than
storm drains, they're more like recycling centers.

I thought black holes started by the collapsing of a star thus forming
a dense enough mass to attract matter passing close by. I never
thought to see it in a curved space fashion. Since radiation has
mass, if it is too close to the black hole it wouldn't escape to be
detected. I can imagine mass moving toward the black hole gaining
energy and some strong enough to escape back into space until the mass
reached the horizon of no escape.

As tricky as trying to imagine curved 4 dimensional space-time, if you
look
into the latest varients of string theory that resulted when it and
super-gravity theories were combined, which now appears to be the most
promising attempt to merge the world of the big (relativity/gravity) to
the
world of the small (quantum mechanics), it shows how the universe is
actually made up of 11 dimensions and not 4. Try to imagine that! Also
the
latest thing is now "M-Theory", which is the first theory that seems to
have
a chance at explaining what the big bang was.


As I understand String theory, the dimensions beyond the first 3 or 4
are folded much as DNA proteins fold, thus having limited effects.

I think that comes across in the language of the way it's attempted to be
explained to us lay people. I also think that notion has evolved some into
an almost "phase" type idea. Not quite the same from science-fiction, but
that they are somehow "displaced" from the ones we observe. I'm not
extremely familiar with the details however.

Fun stuff.


I too find these mind exercises fun. Weird.

"Origins" cannot begin with "life", for me it must be part of a
continuum starting with THE origin, what ever it is. I refer to the
"Singularity" as concentrated virgin energy. Was it at minimum or
maximum entropy? If it was not already formed, then what influences
created quarks, electrons and neutrons? How did these elementary
force/particles come to become atoms/molecules? What separates matter
and life. and so on. So much material to play with.

The problem I have with those sorts of ideas is that many discoveries in the
past have shown how far our current understanding was at the time from being
able to describe new discoveries. That new languages have to be invented at
the same time. That's not to say that such questions are completely without
merit, just that my instinct is that whatever new discovery comes about will
once again fall just outside the current abilty to describe it.

I like to think of a "Young God" getting his first "energy kit."
Being young he is careless and the energy gets away from him, like in
the Sorcerer's Apprentice. He must summon all of his training to
collar the escaping energy. and so on.

dick



.

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