[QUOTE=ewmayer;364783]The t=0 point in the big bang model(s) you refer to are quite different in that regard.[/QUOTE]

Really? Why?

[QUOTE=chalsall;364784]Really? Why?[/QUOTE]

As Paul notes, t=0 in currently viable BB models is more than a mere coordinate singularity, i.e. one easily removable via change of coordinates, or traversible in a physically meaningful manner.

[QUOTE=ewmayer;364789]As Paul notes, t=0 in currently viable BB models is more than a mere coordinate singularity, i.e. one easily removable via change of coordinates, or traversible in a physically meaningful manner.[/QUOTE]

With all due respect, IMO you are talking out of your ass.

T=0 with regards to the Universe has about as much meaning as T-10 seconds during a NASA launch....

[QUOTE=chalsall;364792]With all due respect, [/QUOTE]

For readers unfamiliar with chalsall-speak, that is his standard lead-in meaning "I mistake your meaning or am way off-base myself, so now I shall make a typically inane trollish reply."

We forgive him, because his self-confessed fists of death[sup]tm[/sup] are so profoundly dangerous when unleashed, that any day we can keep him glued to his computer screens making troll-posts is a win for mankind. [Look for more such below.]

For our non-troll readership, what mean by "t=0" in the context of the BB is "the timepoint in the history of the finite-time-ago-created universe to which we assign the zero-time label."

[QUOTE=xilman;364734]Is the wrong answer for the right reason.

Once more, I was being too subtle for some readers. The north pole is not a physical singularity but a co-ordinate singularity. There is nothing north of the north pole because the very concept "north pole" depends on the choice of co-ordinates. However, there is nothing physically distinguished about the north pole --- the terrain there looks very much the same as it does in its neighbourhood and the rest of the planet is accessible along Ernst's (implied) geodesics. There is no physical singularity.

Now compare models of the big bang. All have a singularity at t=0 and there is nothing at t<0. The traditional models have a physical singularity at t=0. [B]This singularity perturbs some people because, almost by definition, it is difficult at least and arguably impossible to apply physical modelling there.[/B] Hawking's complex-time model argues that the singularity at t=0 is only a co-ordinate singularity analogous to the north pole on a sphere. The spacetime there looks very much the same as it does in its neighbourhood and the rest of the universe is accessible along Einstein's geodesics.

Anyway, amusement aside, I really would like to read davar55's response to my question about why the present universe is so far from thermal equilibrium.
[/QUOTE]

(( bolded above by me ))

The fact that the big bang's so-called initiating simgularity can not
be "modeled" should be the red flag - it didn't exist. Here's how
the monograph cosmo3.txt addressed this:

EPISTEMOLOGY

Is the Universe's infinite past and future certain or even possible?

Yes. The Universe has always existed, which means it has an infinite temporal
regress. This is not contradictory, because this regress doesn't represent
an actual infinity of measurable time, which would be impossible, but only
our potential ability to measure time arbitrarily far backwards. Only the
present or "now" can be said to actually exist, since "actual" means existent
in the now. The past no longer exists, except in its effect on the present.

To see that the Universe had no beginning in time and has always existed, imagine
trying to "push time" backwards to a first moment. Even the BBT and Creationism
require a process for the Universe to form, and a process or sequence of actions
takes time. Either there is no first moment and time can be tracked back
indefinitely, or there was a moment "before" which the concept "before" had no
meaning. But Time and Substance are co-existent; neither preceeds the other.
(( demonstrated earlier ))
So something would have to exist at that first moment. Then since "nothing
comes from nothing", there must have been a preceding moment which caused that
one and its existents. By repeating this argument over and over, every possible
first moment leads to an earlier "first" moment, so the infinite past is proved.

The fact that the Universe will always exist and will never have an ending in time
is not hard to demonstrate. Because of conservation of the mass-energy of
the Universe, and the finiteness and constancy of the total quantity of Space
(( discussed earlier ))
the overall density of the substance of the Universe remains fixed An end of time
could not be foreshadowed by universal loss of mass-energy (it doesn't change
quantity) or a shrinking of the Universe's size (it's constant) or by a universal
dispersion of matter and energy due to spatial expansion (it doesn't expand),
or some such other cataclysm that can't occur. With nothing universal changing,
time itself would have to just stop in the middle of "nothing happening". And this
couldn't happen, by the principle of cause and effect.

As to why the Universe isn't in thermal equilibrium after all this
(infinite) time: if this Universal thermal equilibrium means uniform
mass dispersion into the smallest sub-particles, with any residual
energy dispersed such that the whole Universe is maintaining a
constant temperature, then I give the steady-state principle as
the proximate cause, and the Galactic Cyclic Regeneration
Process (including star nucleosynthesis and black hole explosions)
as the method ((mentioned in the monograph)).

[QUOTE=davar55;364821]As to why the Universe isn't in thermal equilibrium after all this
(infinite) time: if this Universal thermal equilibrium means uniform
mass dispersion into the smallest sub-particles, with any residual
energy dispersed such that the whole Universe is maintaining a
constant temperature, then I give the steady-state principle as
the proximate cause, and the Galactic Cyclic Regeneration
Process (including star nucleosynthesis and black hole explosions)
as the method ((mentioned in the monograph)).[/QUOTE]I don't understand this, possibly because I'm being dim today, so please elaborate.

In particular, do you agree with the law of thermodynamics which states that the entropy in a [b]closed[/b] system never decreases with time? For present purposes, I will accept without question all of your cosmological modelling.

As I understand your model, the universe is a closed system. It is finite in extent and is neither expanding nor contracting. Indeed, not only is it a closed system, it is a system of constant hypervolume.

If the universe is both closed and of infinite age, it has for all that time either increasing its entropy or its entropy has at best remained the same.

At the moment, we can clearly see processes occurring which are increasing entropy. Every case in which local entropy is decreasing we can identify associated processes which increase entropy by a greater or equal amount.

Either the present moment is something remarkably special and for all but an infinitesimal fraction of the universe's history entropy remained constant, or entropy has been increasing for an infinite time. Any positive and non-infinitesimal increase of entropy occurring over an infinite timespan will give an infinite entropy at present. Given that, in your model, the universe is both closed and of infinite age, there are a finite number of states in which the universe can be. A state of maximal entropy, by the aforementioned law of thermodynamics, is one in which the system (here the system consists of the whole universe) is in thermal equilibrium.

I claim, and you appear to agree with me, that the universe is not presently in thermal equilibrium.

So what is the resolution of this conflict? The present moment is special, or the universe is not finite in space or the universe is finite in time, or you deny the validity of the third law of thermodynamics? If none of the above, please explain in greater detail. To avoid excess verbiosity, please assume that I have read your monograph --- which I have --- and make your explanation self-contained.

Paul


Remember that entropy is

In comparison with a topological ball, which, depending on the
topological space, may be open or closed or open-closed,
I think the Universe is an open-closed 4-ball with radius R
in the 3 dimensions and width S in the skin dimension.
The fact that there is no boundary to 3-space lets it be
called open, and the fact of finiteness lets it be called closed, too.

Is my understanding of the Universe at thermal equilibrium
as pictured above ^^ the one you meant?

I had to wrestle with entropy, and came up with
the Steady-State Principle (that since all the parameters
are constant, there must be a process keeping the Universe
from dissipating its mass and energy) and the
Galactic Cyclical Regeneration Process (which accomplishes this).
This last accomplishes a restoration of order that was lost as
objects (stars, etc.) exuded energy and paarticles.

Since entropy increases or remains constant in a closed system,
by considering the open Universe as covered by a spatial union
of many smaller open balls (systems) , and since the closed Universe
is spatially continuous and compact, I consider the total entropy
of the Universe (as a measure of disorder) to be a constant.
There are these processes that apparently reverse entropy in
regions of space (e.g.star and planet formation).

Then there's the Dark Entropy joke I made earlier.

[QUOTE=davar55;364859]I had to wrestle with entropy, and came up with
the Steady-State Principle (that since all the parameters
are constant, there must be a process keeping the Universe
from dissipating its mass and energy) and the
Galactic Cyclical Regeneration Process (which accomplishes this).
This last accomplishes a restoration of order that was lost as
objects (stars, etc.) exuded energy and paarticles.[/QUOTE]Ok, so you posit a process which violates the third law of thermodynamics. Yet another point of departure from the views of essentially all physicists.

It would be nice to see observational / experimental evidence of such a process.

[QUOTE=ewmayer;364789]As Paul notes, t=0 in currently viable BB models is more than a mere coordinate singularity, i.e. one easily removable via change of coordinates, or traversible in a physically meaningful manner.[/QUOTE]Actually, that's not quite true. "Classical" BB theories suggests that t=0 is a physical singularity, in that GR and most of its competitors do not attempt to explain what happens at that location in spacetime.

Hawking's "no boundary" proposal invokes the concept that time is a complex quantity and converts a physical singularity into a co-ordinate singularity. Some speculative models of quantum gravity hold that the granularity of spacetime avoids a physical singularity but, rather, that black holes and the BB have a spacetime 4-volume of size comparable to the (Planck length)^4.

Some cosmological models suggest a Big-Bounce for the universe as a whole. I'm not very keen on them myself for at least three reasons. FIrst, the the BB presumably resets the universal entropy to a fixed finite value (and one presumably close to zero) without any plausible (to my mind) proposal as to how this may occur. Secondly, I see no reason why a BH should not itself bounce into a white hole. Observational evidence for the latter is, at best, unconvincing and arguably none existent. Thirdly, observational evidence suggests that a positive cosmological constant is sufficient to keep (this) universe open and unable to contract prior to a big bounce. Admittedly, we may be inhabiting the very last universe in a series of bouncing predecessors but an emotional response of mine assigns a significant weight to the Copernicus principle.

One of the least unsatisfactory models of an eternal universe, in my personal view, is Penrose's picture of conformal similarity between the asymptotic end point of an exponential expansion of a λ>0 prior universe and the zero 4-volume BB of its successor. I don't pretend to understand all the ramifications of his hypothesis but at least it makes observationally verifiable predictions. One of the predictions, and not the only one, is that rest mass decreases with time and asymptotically becomes zero. Another is that evaporations of black holes late in the history of the previous universe will show up in the CBR of its predecessor.

[QUOTE=xilman;364883]Another is that evaporations of black holes late in the history of the previous universe will show up in the CBR of its predecessor.[/QUOTE]Erm, that doesn't really make sense to me. So you mean the CBR of its successor?

[QUOTE=retina;364891]Erm, that doesn't really make sense to me. So you mean the CBR of its successor?[/QUOTE]Yes, exactly.

Sorry about that.

Paul