Time orientation and the big bang
(This page is still a draft, gathering 2 separately written versions
of the same topic, which will be cleaned up later)
On the metaphysical source of time orientation
While there is no time asymmetry in the fundamental evolution laws
for the states of physical systems, the time asymmetry that appears
in the entropy creation "process", can be understood as introduced
into physics by the a priori condition that consciousness puts in
the choice of which states the physical systems are in. Namely, the
present (probabilistic) state of physical systems must be assumed as
fixed in a unique way by the past history (only). If the previous
state of the universe (at any fixed past time) was not in some sense
"completely known", then there would be "no reason" able to specify
the probability for being now something than something else
compatible with the observations that happened since, just as (with
the inverse time orientation) there is still "no reason" why the
future state of the universe will be that where this or that
perceptions happened, that are given nonzero probabilities.
The entropy creation process can be roughly described as a process
of evolution from a system with a number N of possible states, into
a system with a much larger number N' of possible states, where the
N states evolve into the space of N' states with near certainty, and
are "dissolved" in it (distinctions with the other states there are
no more accessible to observation in practice).
The very fact of assuming the initial state as given, while the
final state is not determined yet, is an assumption that treats time
asymmetrically. This assumption can be understood as based on the
metaphysics of time, and more precisely the time of consciousness.
This would mean that consciousness was already there and observed
the universe since its beginning (the big bang).
However, this reasoning is not very rigorous (as it is quite
metaphysical...), so its status as a "proof" remains subject
to personal opinion.
For more details, see: The Mind makes
collapse interpretation - A
mind/mathematics dualistic foundation of physical reality
An alternative candidate explanation, is to consider the state of
the big bang. Let us discuss this in more details.
Some figures on entropy creation
To help making an informed opinion, the following scientific clues
on the subject can be mentioned:
- The flow of entropy creation from a human body (or any
animal), is very much bigger than the flow of sensorial
perceptions in the same body, making it much too unlikely for
entropy to be reduced, or even to not be created "as it should",
at the macroscopic scale.
- With the expansion of the universe, we can consider that the
increase of available space for every quantity of matter,
provides it manier possible states for its evolution, thus more
opportunities for entropy creation. Thus we have 3 growing
quantities, from the biggest to the smallest (in each big volume
of the universe):
- the "possible entropy" (log of the total number of states
into which matter might potentially evolve);
- the entropy as it is (the "measure of our ignorance" on
the state of the universe);
- the total information that has been received from
concious perceptions of matter (the "measure of our
knowledge" on the universe, even if we forgot most of it).
What if we compute backwards ?
But what we take the final observable system of N' states and
compute the inverse evolution ? Then, for a reason of numbers, the
probability to get back among the initial N states is extremely
small. A still larger set of more than N' possibilities is needed,
including the N first ones.
But then, how can we know from the present state in the N' set, that
the past state of the system was more probably among the first N
than among the others that the theory "retro-predicts" from the
present observed state ?
We could say: because if it was others, then it would probably not
have evolved into what it is now.
But this argument requires to assume that, inside this larger set,
the previous state of the system was only possibly oriented towards
"previously observable" directions, and did not have a "hidden
purity" precisely designed to make it much more probably evolve
towards what it is now.
These considerations seem to confirm that the reasoning which
explains the thermodynamic time orientation (irreversible entropy
creation), requires the assumption that the probability laws of the
present state of the universe is precisely what is given by the
formulas of the theory as determined by past observations.
If we decide (unrealistically) to "compute backwards" the evolution
of the universe from its present state (or from any other
"unrealistic" state in the set of possible states of some objects)
into the past (the big bang) while keeping (and thus necessarily
increasing) its current entropy rather than accepting its previously
lower values, so as to include the same number of possible
states as there are now in the smaller universe of the time near the
big bang, then the possible pasts of these unrealistic states differ
from the "normal big bang" by the following differences:
- The universe there is quite more irregular, with diverse parts
collapsing (to the past) in separate black holes rather than
converging to a single origin; as opposed to the remarkable
homogeneity of the real big bang where distances between future
galaxies are arbitrarily small near the birth of the universe.
- At many places, there is more energy for every material
particle at every time defined by a specified density, which
explains the higher number of available states (we said that the
number of possible states of a system depends both on the
available space and available energy, so more states with
the same space, takes its room by involving higher energies)
A naive objection to the idea that the backwards evolution from a
state of higher entropy (but the same energy) would correspond to a
warmer big bang, is the law of energy conservation.
Let us explain something well-known by cosmologists that naively
looks very paradoxical : in usual life, states of uniform perfect
mixtures are usually those of maximal entropy, while the structured,
non-uniform states (with low density at some places and high density
at other places) have lower entropy. But with the Big Bang, things
go the other way round. Why ? Because in usual life, states of
equilibrium that maximize the entropy come in a context of a limited
amount of energy that is conserved, so the maximal entropy is
achieved by uniformly distributing the energy.
But this law only appears as a "constant energy" in the case of an
isolated systems with a fixed volume, which is not the case of the
expanding universe: in the big bang it does not work like this
because the energy is not
conserved during the universal expansion. Here in the present
universe, matter emits radiation (above the temperature of the
cosmic microwave background) from nuclear energy coming from
the fact that the energy of the Big Bang had largely separated
protons and neutrons, putting them in the form of hydrogen and
helium that can make nuclear reactions in stars. A reversed
evolution from this would emit light that would increase its energy
by blueshift (inverse of the cosmological redshift), giving the
involved supplementary energy.
The result is that, when taking other "possible states of the
universe" slightly different than what the big bang predicts (and
thus with higher entropy), and computing their backwards evolution
into "alternative versions of the big bang", we no more get a clean
uniform big bang but a chaotic one with higher entropy, as a big
crunch would look like with time reversed : a big crunch is made of
- Some cold regions but also some hot regions with quite higher
temperature for a given density of matter (i.e. density of
nucleons), which explains the higher entropy ;
- Separate collapses of diverse regions into black holes that
only merge later.
Between the very first time of the big bang supposedly with "very
low entropy" which we cannot yet describe by our theories, a lot
of things could happen to create the relative lot of entropy there
is later in the rather uniform soup that we can describe (such as
the time of big bang nucleosynthesis).
See also:
Notes on decoherence and
interpretations of quantum physics