The Entropy Paradox
Mainstream cosmology tries to avoid this puzzling pitfall. The topic is rather embarrassing. The truth of the matter is that both the open and the flat BB universes (these are the versions that have the universe expanding forever) are based on a paradox —actually a double paradox. And what is so embarrassing is that it is the worst kind of paradox one could have in any theory —thermodynamic law violation.
It is useful to understand the basic fact that heat energy is disordered energy and is therefore the highest entropy form of energy. And we all know that at the primordial big-bang-moment things were hot —really, really hot! In theory, the temperature was at its maximum. Naturally we should be able to assert that entropy was also highest at that moment at the birth of the BB universe. Now if entropy is maximum in the early big bang, then how can entropy increase as it is supposed to during the subsequent evolution of the universe? Entropy is already at maximum! How can it increase further? And yet thermodynamic law says it must increase! ... A paradox.
Recall that the primordial fireball was a thermal state—a hot gas in expanding thermal equilibrium. Recall, also, that the term ‘thermal equilibrium’ refers to a state of maximum entropy. However, the second law demands that in its initial state, the entropy of [the BB] universe was at some sort of minimum, not a maximum!
What has gone wrong? –Roger Penrose [Penrose 1990, p328]
What is more, the open/flat universe (this includes the currently popular accelerating version), by definition, expands forever. As it expands its regional average temperature becomes colder and colder. In time, stars die, galaxies collapse, black holes evaporate. Left-over radiation is relentlessly redshifted (a consequence of universal space expansion). The temperature —the measure of the weakening radiation— drops. The temperature in all regions of the universe approaches the ultimate low of absolute zero. And in tandem, entropy approaches its ultimate low value. By definition a system at absolute zero has zero entropy. So the universe ends up having an ultimately low entropy when it is supposed to end up (according to proven physical law) in a maximum state of disorder (i.e., high entropy).
And we are left wondering: How can it be that entropy decrease in this supposedly natural and closed system —the BB-expanding-universe system? The second law is clear, entropy must only increase or remain constant! Again, a paradox.
Mainstream cosmology tries to avoid this puzzling pitfall. The topic is rather embarrassing. The truth of the matter is that both the open and the flat BB universes (these are the versions that have the universe expanding forever) are based on a paradox —actually a double paradox. And what is so embarrassing is that it is the worst kind of paradox one could have in any theory —thermodynamic law violation.
It is useful to understand the basic fact that heat energy is disordered energy and is therefore the highest entropy form of energy. And we all know that at the primordial big-bang-moment things were hot —really, really hot! In theory, the temperature was at its maximum. Naturally we should be able to assert that entropy was also highest at that moment at the birth of the BB universe. Now if entropy is maximum in the early big bang, then how can entropy increase as it is supposed to during the subsequent evolution of the universe? Entropy is already at maximum! How can it increase further? And yet thermodynamic law says it must increase! ... A paradox.
Recall that the primordial fireball was a thermal state—a hot gas in expanding thermal equilibrium. Recall, also, that the term ‘thermal equilibrium’ refers to a state of maximum entropy. However, the second law demands that in its initial state, the entropy of [the BB] universe was at some sort of minimum, not a maximum!
What has gone wrong? –Roger Penrose [Penrose 1990, p328]
What is more, the open/flat universe (this includes the currently popular accelerating version), by definition, expands forever. As it expands its regional average temperature becomes colder and colder. In time, stars die, galaxies collapse, black holes evaporate. Left-over radiation is relentlessly redshifted (a consequence of universal space expansion). The temperature —the measure of the weakening radiation— drops. The temperature in all regions of the universe approaches the ultimate low of absolute zero. And in tandem, entropy approaches its ultimate low value. By definition a system at absolute zero has zero entropy. So the universe ends up having an ultimately low entropy when it is supposed to end up (according to proven physical law) in a maximum state of disorder (i.e., high entropy).
And we are left wondering: How can it be that entropy decrease in this supposedly natural and closed system —the BB-expanding-universe system? The second law is clear, entropy must only increase or remain constant! Again, a paradox.
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