Charles,
That's a very good description of the situation.
The real dilemma has to do with why some people require absolutes,
as perfect, complete, or pure, when nature doesn't offer any. The
need originates in the brain, where perceptions are adjusted to
find absolutes.
Absolute zero is merely the theoretical bottom of the temperature
scale, where atoms and molecules no longer collide with each other.
Ah, "acceleration" isn't a force. It's a measure of the relative
change in velocity per unit of time. Velocity is a measure of the
relative change in distance per unit of time. F=MA, and all that.
Bill Hawkins
-----Original Message-----
From: Charles P. Steinmetz
Sent: Sunday, December 13, 2009 12:52 PM
Nigel wrote:
> I use "absolute" in the sense that is commonly implied in the term
> "absolute quantity", where an absolute quantity is the measure of
> the absolute occurence of a variable, as in "so many volts, yards, kilos,
etc.
Volts and yards, at least, are also not absolute measurements in the
same sense that measurements of time are not absolute. Volts express
the difference in electrical potential, and yards the physical
separation, between two spatial points. But two points in space just
define a spatial interval, precisely analogously to two points in
time specifying a temporal interval (more below).
>Whether or not one accepts that everything in the universe was
>initially collapsed into a singularity, even if we still haven't
>observed large parts of that "everything", it would seem that
>everything physical in that universe, including "space", fits my
>definition of "absolute". No matter how large or small, in one way
>or another, and in theory at least, it can be measured and quantified.
>
>The properties of what we call "time", however, are unique and lie
>outside of that categorisation. Time as such, unlike everything
>else, is not a physical entity that would have been collapsed into
>that singularity but can only have come about as a consequence of
>the ongoing expansion of material out of it that followed the
>Big-Bang. I know I've laboured to death the point about measuring
>time intervals but that's because it's really all we have.
But that is no different than the other three dimensions of spacetime
-- measuring intervals is all we have there, too. "One kilometer" is
no different from "one second" in this regard -- in both cases, it is
one unit *between* two places (we usually call places in time
"events," but it's the same thing). If general relativity ("GR") is
correct (and we have every reason to believe that it is), time is no
different than space, although we perceive it quite differently. For
example, in order to move about in the space dimensions we think we
need to "do something," while we need to do nothing to move about in
the usual way in the time dimension (and, indeed, have not figured
out how to move differently in time or to stay in one place). But
note that we are really hurtling through space at a good clip,
without it being apparent to our natural senses -- and in comparison
to this, we really haven't much power to move about in space,
either. So, we could say that we have an initial velocity through
both space and time when we are born, and our initial velocity
through time is more apparent to our natural senses than our initial
velocity through space -- but in reality, there is no difference
between them.
> When considering whether or not time exists, perhaps we should
> first ask exactly what we mean when we refer to "time", do events
> occur "within" time, for example, or is time merely a consequence
> of events occuring? If the latter then does time have any real
> existence other than as a convenience to describe sequentiality, is
> spacetime really an entity or just a mathematical convenience, etc etc?
In my view, these are all questions, not about time, but rather about
our perception of time. At the end of the day, we have every reason
to believe that GR is correct and, consequently, that spacetime is
the fabric of the universe. Space and time are both altered, in
complementary ways, by the great forces of the universe (gravity and
acceleration -- time will tell whether the nuclear forces do so, as
well, and there is some evidence to date that they may), implying
that there is a conservation relationship that applies to the four
dimensions collectively. But there is no difference in terms of the
spatial dimensions being "absolute" and the temporal dimension not
being "absolute" -- all of our measurements of the four spacetime
dimensions are relative and "not absolute" in the sense you mean
(although, as I've pointed out, by refering both back to the origin
of this universe, which we have good reason to believe was a
mathematical and physical point where this universe began, we could
in principle at least have a master datum for all four dimensions,
providing a form of absolutism).
The puzzle is why we perceive the spatial dimensions so differently
from the temporal dimension. It is a fascinating question, but may
not be fundamentally a question of the physics of spacetime.
Best regards,
Charles
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