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### Course: HS biology (archived)>Unit 8

Lesson 3: Laws of thermodynamics

# Second Law of Thermodynamics and entropy

Entropy is a measure of disorder or randomness in a system. It represents the number of possible states or configurations that a system can take on. According to the Second Law of Thermodynamics, entropy tends to increase over time, meaning that systems naturally progress towards a more disordered or random state.

## Want to join the conversation?

• If we could understand all of the bare fundamentals of how all molecules behave and interact, and we could also take a "snapshot" of every molecule and it's state in the universe,

Then from that, would we be able to technically predict everything that will ever happen, inside of our universe?
• in quantum world things behave weirdly . "NO SNAPSHOTS"
• If entropy only increases in the universe, and that is meaning that there is more and more heat, how does that relate to the notion that energy can be neither created nor destroyed? This definition of entropy is making it seem like energy is being created and that there is more and more of it.
• No energy is being created. Energy is being converted ultimately into heat, which is dispersed in the expanding universe. Eventually, entropy increases to a point that heat energy is no longer useful for doing any work.
• The first video on your list is the one that thoroughly explains the Second Law.
• Okie dokie, entropy is irreversible in terms of being observable - you could watch the same container of gas your entire life and never see the molecules resume their original positions/orientations simultaneously; however, is there not any probability that throughout the rest of time, there would be an instance in which this happened? Being in a theoretically, entirely closed system, wouldn't the molecules eventually achieve that, since all probable positions of the molecules and combinations will eventually occur/reoccur at some point?
Not that this is really helpful in any sense, but it's fun to think about!
• When you look at a finite closed system from a quantum perspective there are only a finite number of possible states that a system can be in. So with random fluctuations the system will eventually occur.

There is a good book by Sean Carroll called "From Eternity to Here" about Entropy and the Arrow of time.
• love the increasingly impassioned speech at the end

and thank you very helpful for review
• How do we know that the universe is a closed system if it's deemed to be infinite?
• Well, what is a closed system? One that doesn't exchange matter with its surroundings. If the universe was infinite, then there wouldn't be any surroundings, so there wouldn't be an exchange of matter, or anything for that matter because the surroundings don't exist. It wouldn't matter if the universe was infinite or finite for it to be a closed system, assuming that there is nothing beyond the universe for it to exchange mass with.
• Doesn't this disprove evolution? if something is left to itself, wouldn't it just get worse, instead of getting more complicated, as evolution says?
(1 vote)
• Nope. There is source of low entropy energy that comes from the sun. The process of life and evolution is converts this low entropy energy into higher entropy waste energy.

If you look into the way complex systems that are not in equilibrium change over time their complexity will increase to a point and then degrade into low complexity as the lower entropy system transitions into a higher entropy system at equilibrium.

If you look at a starting system where you have a layer of cold cream on top of a layer of hot coffee which has low entropy and low complexity. Over time these two fluids will start to merge and mix as they transition to equilibrium. As they mix there will be complex patterns of streaks of cream and coffee but when it comes to equilibrium you have a homogenous mixture of cream and coffee with low complexity.
• If we cannot create/destroy energy, shouldn't the number of states remain the same?
• No, because it does not rely on energy but on the space.

Since molecules take up greater space, the number of possible states increases.
• If energy cannot be created or destroyed and only converted, then why does entropy of the universe only increase? Shouldn't entropy be conserved as well?