Natural Science Forum / Physics / Relativity / April 2006

I just saw the passage in Lee Smolin "Three Roads to Quantum
Gravity" and just wondering what is people thought about it to
gain more insight. What you want instead is for us to spend 9
years taking up Ph.D. in physics to understand that part in
Smolin book.

Maybe you are the Grandfather of Pentchos zombies.

Next time you go to the diagnostic lab for checkup and
you visit a doctor. Hope the doctor would tell you to spend
10 years in medical school to understand what the blood
result means.

Grav

Dear Mr. Tucker,

Previously I have posted Smolin conceptual themes that
Gravityman has only mentioned in a small part.

The following is the complete context of it.

Pls. view this graphics first.

http://www.pbase.com/image/57927945/original

What I'd like to know is if Mr. Smolin has been biased in his
analysis due to his affiliation on Loop Quantum Gravity.
Your comments (and others) would be very valuable.

I'd first mention page 59 which is related to the graphics
above. Then mention page 119 which is related to
the passage concerned.

Page 59:

Many popular accounts of general relativity contain a lot
of talk about 'the geometry of spacetime'. But actually
most of that has to do with the causal structure.
[In our universe, specifying the paths of all the light
rays or, equivalently, drawing the light cones around
every event, is a way to describe the structure of
all possible causal relations. Together, these relations
comprise what we call the causal structure of the
univesre] Almost all of the information needed to
construct the geometry of spacetime consists of
the story of the causal structure. So not only do we
live in a causal universe, but most of the story of
our universe is the story of the causal relations
among its events. The metaphor in which space
and time have a geometry, call the spacetime
geometry, is not actually very helpful in understanding
the physical meaning of general relativity. That
metaphor is based on a mathematical coincidence
that is helpful only to those who know enough
mathematics to make use of it. The fundemental
idea in general relativity is that the causal structure
of events can itself be influenced by those events.
The causal structure is not fixed for all time. It is
dynamical: it evolves, subject to laws. The laws
that determine how the causal structure of the
universe grows in time are called the Einstein
equations. They are very complicated, but
when there are big, slow moving klutzes of matter
around, like stars and planets, they become much
simpler (see the Figure). Basically, what happens then
is that the light cones tilt towards the matter. (This is what
is often described as the curvature, or distortion
of the geometry of space and time) As a result,
matter tends to fall towards the massive object.
This is, of course, another way of talking about
the gravitational force.

Page 119:

What was wrong with my first paper was that Wilson's lattice was
an absolute, fixed structure and thus clashed with the relational
nature of Einstein's theory of gravity. So my theory did not
contain gravity and had nothing at all to do with relativity. To
fix this, the lattice itself would have to become a dynamical
structure which could evolve in time. The key lesson I learned
from this failed attempt was that one cannot fashion a successful
quantum theory of gravity out of objects moving against a fixed
background.

At about this time I met Julian Barbour, a physicist and
philosopher who lives in a little village near Oxford. Julian had
left the academic world after his Ph.D. in order to have the
freedom to think deeply about the nature of space and time. He
supported himself by translating Russian scientific journals into
English and, away from the usual pressures of academic life, he
used his considerable linguistic skills to read deeply into the
history of our understanding of space and time. He had understood
from his study the importance of the idea that space and time are
relational, and he had then applied this wisdom to modern
physics. He was I believe the first person to gain a deep
understanding of the role this idea plays in the mathematical
structure of Einstein's theory of relativity. In a series of
papers, first alone and then with an Italian friend, Bruno
Bertotti, he showed how to formulate mathematically a theory in
which space and time were nothing but aspects of relationships.
Had Leffiniz or anyo ne el se done this before the twentieth
century, it would have changed the course of science.

As it happened, general relativity already existed, but - and this
is a strange thing to say - it was widely misunderstood, even by
many of the physicists who specialized in its study.
Unfortunately, general relativity was commonly regarded as
a machine that produces spacetime geometries, which
are then to be treated as Newton treated his absolute
space and time: as fixed and absolute entities within which
things move. The question then to be answered was which
of these absolute spacetimes describes the universe? The
only differences between this and Newton's absolute space
and time is that there is no choice in Newton's theory,
while general relativity offers a selection of possible
spacetimes. This is how the theory is presented in some
textbooks, and there are even some philosophers, who
should know better, who seem to interpret it that way.

Julian Barbour's important contribution was to show
convincingly that this was not at all the right way to understand
the theory. Instead, the theory has to be understood as
describing a dynamically evolving network of relationships.
Julain was of course not the only person to learn to see
general relativity in this way. John Stachel also came
to this understanding, at least partly through his work
as the first head of the project to prepare Einstein's
collected papers for publication. But Julian came to
the study of general relativity equipped with a tool that no
one else had- the general mathematical formulation of a
theory in which space and time are nothing but dynamically
evolving relationships. Julian was then able to show how
Einstein's theory of general relativity could be understood
as an example of just such a theory. This demonstration
laid bare the relational nature of the description of space
and time in general relativity.

Since then, Julian Barbour has become known to most people
working in relativity, and recently he has become even more
widely known and appreciated as a result of the publication of
his radical theories on the nature of time. But in the early
1980s few people knew of his work, and I was very fortunate to
meet him shortly after I had realized that my lattice gravity
theory was in trouble. During this meeting he explained to me the
meaning of space and time in general relativity, and the role of
the relationa l concept in it. This gave me the conceptual
language to understand why my calculations were showing that
gravity was nowhere to be found in the theory I had constructed.
What I needed to do was invent something like Wilson's lattice
theory, but in which there was no fixed lattice, so that all the
structures were dynamical and relational. A set of points
connected by edges - in other words a graph - is a good example
of a system defined by relationships. But what I had done wrong
was to base t he theory on a fixed graph. Instead, the theory
should produce the graph, and it should not mirror any
pre-existing geometry or structure. It should rather evolve
according to rules as simple as those that Wilson had given for
the motion of loops on his lattice. It was to be ten years before
a way appeared which made this possible.

For more information. Grab this:

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02-8217717-6116959?%5Fencoding=UTF8

I only got it for $3.5 from the second hand marketplace which
is as good as new.

Mr. QG

Not even Einstein understood his own theory. Relativists have a funny
and rather annoying habit. As soon as someone points out a flaw in GR,
they immediately ripost that the theory is misunderstood. IMO, GR is
misunderstood because it really explains nothing. It is chicken sh.t
physics taken to its ultimate level.

The truth is that there can be no relationships in spacetime (or
between spacetimes) because relationships require the existence of
change whereas spacetime forbids change. This is the reason that Sir
Karl Popper called spacetime "Einstein's block universe in which
nothing ever happens".

Nasty Little Truth About Spacetime Physics:
http://www.rebelscience.org/Crackpots/notorious.htm

More Nasty Little Truth About Physics:
http://www.rebelscience.org/Crackpots/nasty.htm

But then again Smolin, like Brian "superstring" Greene of Columbia
University, is a notorious time travel believing crackpot. But we
already knew that. ahahaha... AHAHAHA... ahahaha...

Louis Savain

Why Software Is Bad and What We Can Do to Fix It:
http://www.rebelscience.org/Cosas/Reliability.htm