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>heat death of the universe Off topic here, but there is no such thing as the heat death of the Universe. The second princile of thermodynamics (entropy cannot
by credit_guy 10y ago
>heat death of the universe
Off topic here, but there is no such thing as the heat death of the Universe. The second princile of thermodynamics (entropy cannot decrease in a closed system) does not hold at cosmic scales. That's because that principle assumes the gravity is negligible compared to the other forces that move the molecules around, which is a perfectly valid approximation for all human-scale systems (such as engines). At cosmic scales gravity becomes dominant and the entropy of closed systems can and does spontaneously decrease. For example a giant gas cloud evolves to become a spinning disc and then a planetary system.
- erikpukinskis 10y agoDoesn't that break down if the cloud of gas is expanding at such a rate that the particles have enough momentum to escape the gravity well?
- credit_guy 10y agoFor sure there are cases (plenty of them) where the second principle continues to hold (entropy goes up). I was just pointing out that there are very natural example where that principle breaks down at cosmic scales. Such an example is exactly how our planetary system was born. People know vaguely that in a few billion years our Sun will collapse and it will either become a supernova or become a star where the fusion reaction is a higher one (instead of hydrogen+hydrogen->hellium, something like hellium+hellium->carbon). At some point possibly after trillions of years, all the nuclear reaction converge to produce only iron, and from that point on there's no more fusion and fission, and later on the heat death of the universe occurs. Well, even if there are no more nuclear reactions, the universe will not die from reaching a maximum state of entropy (heat death), but may continue to evolve forever, going periodically through states of higher and lower entropy.