Re: a few simple questions (from a layman)


lamoore0777@xxxxxxxxxxxxx wrote:
> Under the old adage one is never too old to learn, I was wondering
> about 3 issues that I trust any number of thinkers here can either
> simply answer, or offer some direction to an answer.
>
> Ok, now before you laugh, I confess these are Physics 101 type
> questions. Not to be confused with learned ones. Akwardly phrased as a
> reflection of the mind posing them. Granted, some here might tell me to
> take a class on physics at the local college, however, I am appealing
> to the human doctrine of, well, helping educate the uneducated never
> hurt anyone (especially those of the later group). And not only that,
> but hearing educated people speak of what they understand, is a treat
> in itself. At least it always has been for me.
>
> Please feel free to correct the questions to accomodate an approriate
> answer.
>
> #1. What is the essential (or governing) principle of Gravity? In other
> words, if I drop a 10 lb 12" diameter bowling ball, and a 50 lb 12"
> diameter bowling ball from say, 100 feet, at the same time, why is it
> they both seem to fall at the same rate of speed? (or accelerate at the
> same speed, if that's the case). And, does this seemingly peculiar
> phenomena exists regardless of the planet I am dropping the balls from
> (or on)? And, well, why is that?

We call it the equivalence principle.

Although it has been greatly extended into ways that are harder to
explain, it basically means that under identical conditions, two
objects dropped will fall at the same rate. What I mean by identical
conditions is equal amounts of drag, or lack of. The famous style of
testing of the EP is called Eotvos, named after a Hungarian fellow.

If you are old enough, you might remember a video of one of the Apollo
astronaughts dropping a feather and something else, a golf ball I
believe, on the moon with them falling at the same rate. That doesn't
work on Earth due to drag from the air.

We have no reason to think that it wouldn't work on other planets.
Regarding that, we have a principle called the Copernican principle
which states that Earth doesn't have a special place in the universe.
What that means is that we don't assume physics is different
everywhere, or that things are unique just for us. Without that, we
would have a hard time justifying all the extrapolations that are done
to far, far away.

The equivalence principle has been tested to high precision without
fail to this point.

http://www.npl.washington.edu/eotwash/equiv.html

>
> #2. Does Light always travel? I mean, well, does it ever stand still?
> And if it does stand still, what makes it start traveling again
> (assuming it was traveling before it stopped for a rest)? I'm basically
> familiar with the accepted notion that light has a speed limit. Along
> the lines of 186,000 miles per second, I believe. But does some light,
> say for example, travel in the slow lane? Clipping along at a pace of
> say, 12.5 miles per hour? And if so, why so? And if not, why not?

Light always travels, as far as we can see. We still see the echo of
the big bang, which was about 14 billion years ago.

But light doesn't so much have a limit as it has one speed. The only
time light has a different speed is when it is traveling through
something. The speed of light in a medium can be really, really slow
though. Artificial conditions have been made such that light travels
around 30 miles per hour.

>
> #3. Ok, here's my biggy (which has stumped me for years): When someone
> speaks of our Universe, as a closed system, what exactly does that
> mean? I can't seem to shake the notion of reaching the edge of the
> universe and being met with a sign that says, stop, go back, you have
> reached the end of the Universe. Your are off limits. As a practical
> matter, as far as practicality and theoritical matters can converge, I
> seem to experience the mental equivilant of reaching a physical black
> hole when confronted with such thought.
>
> Restated, is there one universe or more than one universe (in physical
> terms)?. And if so, why? Ok, just kidding there. I've crossed the
> boundries of Science and Alice. In scientific terms, restating the
> question: is space regarded as being infinite, composed of a finite
> quantity of energy, in various stages of motion and rest, appearing in
> the form of matter and anti-matter?, which relationship Einstein
> clarified? Being, in laymans terms, the quantity of the total amount of
> energy (relative to the total mass) in the Universe is equal to the
> velocity of light squared?

I would say that we don't know. We can't say whether the universe is
open or closed yet, but that isn't to say people have not been looking.

Though I will say this: the anti-matter from the beginning of the
universe is gone. "Why" would be a great question, which I can't answer
satisfactorily.

E=mc^2 is a great soundbite but you have to be careful. It is *only*
true when the particle in question is not moving [there is a different
expression for massless particles], and *only* true in the context of
special relativity. Gravity permeates the universe, and there is a
seperate but related theory called general relativity that handles
gravitation. Unfortunately in GR, energy is less than well-defined in
the general sense. At least when compared to SR.

You should check this fellow's page out. Read near the bottom, he has a
fantastic series of pages that introduce folks to cosmology and
relativity.

http://www.astro.ucla.edu/~wright/intro.html

>
> Lastly, in an earlier post to this forum a gentlemen responded to an
> inquiry of mine by saying, in effect: all sincere questions are welcome
> here. With that in mind, my inquiries here are sincere (though
> admittedly tortured).

If someone replies to you and says anything about relativity being
false, they are full of ***. This newsgroup has a lot of folks who
don't understand highschool algebra but feel they can adequately
assault Einstein's theories.

>
> Thanks for your insights,
> Lar

.

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