Re: What's the difference between a rock, and an asteroid that's stopped?

Date: 23 Jul 2003 23:58:27 -0700
Newsgroups: sci.physics
Size: 3,661 bytes

Jim <email-address-deleted> wrote in message news:<email-address-deleted>...
> >
> >So now I'm looking at rock X, which appears to be zooming off away
> >from me, and rock Y which appears to be stationary. There is clearly
> >some difference between these two rocks.
>
> No there isn't.
> How can you prove that *you* are not observing any difference?
> Using your spaceship, catch up to the rock you kicked,
> Now you will observe that it is not moving. But the one you left
> behind is moving away from you, your spaceship, and the rock you
> kicked.
>
Indeed,
Okay,
I can see there is no difference between Rocks X and Y in that
relative to itself, each rock is motionless (Rock X is not moving
relative to itself, nor it Rock Y), and is physically identical. I
can appreciate this.
Furthermore, I would observe no difference in either Rock X or Rock Y,
provided I was moving along at the same speed as the rock I am
observing: The rock would have a certain physical makeup, and it
would also appear motionless in relation to myself. So I understand
your statement above: "No there isn't [any difference between X and
Y]". This makes sense to me, but does not answer my original question
to my satisfaction because...
...when my co-pilot comes out of the spaceship, he would be able to
tell me which rock I kicked (because he would see one of them zooming
off).
Isn't the fact that he is able to tell me which one was kicked proof
that there IS A DIFFERENCE BETWEEN THEM?
I mean, my co-pilot is able to distinguish between X and Y. He is
percieving INFORMATION about X which is different to that of Y. WHERE
IS THIS INFORMATION STORED??? If there was really absolutely no
difference between them, my co-pilot should not be able to tell me
which rock I kicked? No?
Also, any person who comes out of my spaceship and observes rocks X
and Y at ANY TIME FROM NOW UNTIL THE END OF TIME, will be able to
distinguish between X and Y, because X is moving away from them. So,
even though (as most people in this discussion have told me) there is
no difference between X and Y, the tiny act of me kicking it has been
indelibly associated with Rock X from here to eternity. Rock X now
"carries" this information. Where is it stored if there is no
physical difference between them?
So, according to the responses above:
1. There is no difference between X and Y.
2. An observer can tell the difference between X and Y.
Hmmm.
> You almost answered your own question. "Acted upon by a force".
> OK, you forced it to move. What is forcing it to stop? You aren't.
> I'm not, nothing is. Right? So why should it NOT, keep moving?
Good question -
Let me put a slightly different slant on what I'm trying to get at.
Rock X will keep moving until acted upon by another (opposing) force.
Great.
Presumably, the direction, speed and mass of my space-boot when I
kicked the rock will determine in which direction the rock zooms away,
and how fast.
Let's say I also now give Rock Y a kick (but not as hard). So now, X
and Y are moving off in the same direction, but X is travelling twice
as fast as Y. Fine.
After 1 second, rock X is 10M away from me, rock Y is 5M away from me.
At this time, I use my space-time-freeze-camera, to take a snapshot of
the physical composition of both rocks.
The snapshot of each rock looks identical (they're physically
identical). But *I* know that after another second, rock X will be 20M
away, and Rock Y will be 10M away. THIS IS A DIFFERENCE!! (20M vs
10M). So, where in my time-freeze photo of each rock is this
difference apparent? Where is an object's inertia "stored"???
Jon.