The third law does not say that "if the entropy of a system approaches a minimum, it's temperature approaches absolut zero." It says that if the temperature approaches absolute zero, the entropy does. These are logical converses.
The second law of thermodynamics says that entropy can only increase, so if the early universe had been in a state of maximum entropy, then the cosmos would have experienced its heat death immediately after being born. This contradicts the observation that the present universe contains burning stars, heat engines, and life. These observations imply that the early universe was in a very low-entropy state, which shows that its initial conditions were extremely finely tuned. The reasons for this fine-tuning are not explained by general relativity or the standard model. Adding inflation to the model does not cure this fine-tuning problem.[Penrose 2005]
These ideas are strongly counterintuitive to most people, since we picture the early universe as an undifferentiated soup of hot gas, very much like what we might imagine a heat-dead universe to be like. In what way is the early universe not equilibrated?
We observe that the cosmic microwave background radiation's spectrum is a blackbody curve, which would normally be interpreted as evidence of thermal equilibrium. However, this observation only really tells us that the matter degrees of freedom were in thermal equilibrium. The gravitational degrees of freedom were not. In standard cosmological models, which are constructed to be as simple as possible, there are no gravitational waves. Although the real universe presumably does have gravitational waves in it, they are apparently very weak. In a maximum-entropy universe, the gravitational modes would be equilibrated with the matter degrees of freedom, and they would be very strong, as in models like Misner's mixmaster universe.[Misner 1969]
Even in Newtonian mechanics, gravitating systems violate most people's intuition about entropy. If we psssssht a bunch of helium atoms into a box through an inlet valve, they will quickly reach a maximum-entropy state in which their density is nearly constant everywhere. But in an imaginary Newtonian "box" full of gravitating particles, the maximum-entropy state is one in which the particles have all glommed onto each other in a single blob. This is because of the attractive nature of the gravitational force.
Charles W. Misner, "Mixmaster Universe", Physical Review Letters 22(1969)1071. http://astrophysics.fic.uni.lodz.pl/100yrs/pdf/07/036.pdf
Roger Penrose, 2005 talk at the Isaac Newton Institute, http://www.newton.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/
Carlos,
I’m going to answer your question from a completely different perspective than current physics.
I have been working on a New Way of looking at physics from Inner Space through Outer Space for the past 7 years.
Your question relates to Outer Space.
I believe the COSMOS is a closed system and cycles along a Cosmological Entropy Wave.
All Matter – Energy – aNd Dynamics: MEND was contained in a singular super huge Origin Particle 120 Billion light years in diameter before NATURE’S TRUE BIG BANG.
External Entropy 0, Dark Energy 0, Dark Matter 0, Pressure 0, Temperature 0.
Everything was contained inside HER Origin Particle.
After HER TRUE BIG BANG there were Universe Size Chunks, Galactic Sized Chunks, Solar Sized Chunks, Planet Sized Chunks, and Plasma and dust flying out into the newly formed Outer Space. Thus there is an Entropy level greater than 0. Dark Energy Spiking.
At the Core of this TRUE BIG BANG is a Super Vacuum Dark Hole. Literally a hole in space with a great vacuum energy.
As these Chunks fly out into Outer Space they have secondary, tertiary, and on and on various levels of little Big Bangs that increase the entropy and form universes, galaxies, stars, solar systems, planets, and more plasma and dust and increase the entropy. Dark Energy reaches a maximum and begins to decrease.
We even have tiny little Big Bangs going off in Outer Space today increasing the entropy.
And we have many more Dark Holes formed.
As the COSMOS is expanding from our view point which is increasing entropy it has already started collapsing at the CORE which is actually decreasing entropy. Thus one needs to consider total system entropy and not just conditions at individual points. The COSMOS after all is a very dynamic place.
When Dark Energy again reaches zero in the maximum expanse of the COSMOS, total system entropy maximum, the Vacuum Core Dark Hole will complete the collapse and recycle it all over again. And Again and Again. Thus the total system entropy will decrease in the collapse and thus a wave function develops.
A new singular super huge origin particle develops and external entropy is zero. Everything is internal to the Origin Particle once again.
Now to answer your question.
If you want to distinguish between the COSMIC beginning point of entropy, the peak point of entropy (prior to collapse), and the end point of entropy, you need to look at the rate of change of the entropy at each point. There would be a very high rate of entropy change in the beginning and a very low rate of entropy change just before the collapse, near zero change, and a very high rate of entropy change at the end.
Dark Energy can be a tracer for this, for Dark Energy at zero will mark the beginning of the collapse. It appears Dark Energy would increase again for a time during the collapse while entropy would be decreasing.
The catch is that the COSMIC Plane-Plain could be 120 Trillion light years in diameter and we can only see 20 billion light years of our local universe within the COSMIC Plane-Plain. I used Plane-Plain because the COSMOS appears to be a flying flat discuss shape, much like the Milky Way Galaxy.
Hope this helps.
You can see an introduction to my work and ask more questions at:
http://expeditiongranted.nationalgeographic.com/project/sharing-natures-mend-for-the-universe/
Sincerely & Respectfully,
klo
Best Answer
This is somewhat controversial issue. But let me present the reasons, as far as I understood, why people like Sir Penrose thinks so.
Their arguments are roughly as follows:
The basic microscopic laws of physics are perfectly time symmetric. They are not biased in any time direction past or future.
Second law follows from the fact that that given an initial condition of a system which is not in the most probable state will tend to go towards the most probable state by the same microscopic laws. Since number of disordered states are much higher the system will become more and more disordered with time. Accordingly its entropy will increase until a maximum value when the system comes to the thermal equilibrium.
Since the microscopic laws are time symmetric the same argument can be made towards the past time direction as well. Given an an initial condition of a system which is not in the most probable state should go towards more disordered (high entropy) states towards past as well. That's what the mathematics of the laws tells us.
This is against our experience. Either all the parts of the universe we are observing (including our memories of past) has just undergone a HUGE fluctuation right now to give the impression that there was a more ordered past (which is crazy) OR the system was already even more ordered (low entropy) and more special in the past. But that means even more huge a fluctuation. This reasoning will lead us to conclude that at the moment of big bang the universe was extra ordinarily ordered and most special. It should be so special that it requires explanation.
Critics often point out that prediction and retrodiction is not the same thing forgetting that when one talks about the very "arrow of time" no one can say with justification which is prediction and which is retrodiction. Other than that it is also questionable whether second law can be applied this way to the whole universe or not.