For relativity experts who are familiar with GR master
Lee Smolin and especially the following concept of
his, pls. expand on it:

Lee Smolin declares:

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. 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 gravitional force.

Comments?

QG

For relativity experts who are familiar with GR master
Lee Smolin and especially the following concept of
his, pls. expand on it:

Lee Smolin declares:

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. 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 gravitional force.

Comments?

QG