broken glass

[michel123456]

There is a very common example in litterature about entropy and the arrow of time. You keep a glass in your hand, you let it fall down, the glass breaks. You never observe the reverse situation where the broken pieces jump together in your hand: the example shows the one-way direction of the arrow of time. (except in a movie played backward)

 

On the other hand, living organisms use overall physical entropy to organize, sometimes compared as a spark of negative entropy in the general frame of the second law of thermodynamics.

 

So I was wondering if the example with the glass is applicable, because glass is a product we humans have made, a product of a living organism. One can not extract safe conclusions about physical systems on the basis of observation of living organisms.

 

The same goes about the example of milk getting dissipated in your coffe, because milk is a product of a living organism and coffee too (from the coffee bean, since plants are living).

 

If one takes another example, like the clear water of the river mixing into the ocean, one will not observe the salted water from the ocean climbing up the river and becoming clear fresh water, but one will eventually observe the water from the oceans evaporate, then fall as rain on a continent and form a river of fresh water. In this sense, one would observe the salted water getting into the river again.

 

Just some thoughts.

Edited August 16, 2011 by michel123456

[J.C.MacSwell]

There is a very common example in litterature about entropy and the arrow of time. You keep a glass in your hand, you let it fall down, the glass breaks. You never observe the reverse situation where the broken pieces jump together in your hand: the example shows the one-way direction of the arrow of time. (except in a movie played backward)

 

On the other hand, living organisms use overall physical entropy to organize, sometimes compared as a spark of negative entropy in the general frame of the second law of thermodynamics.

 

So I was wondering if the example with the glass is applicable, because glass is a product we humans have made, a product of a living organism. One can not extract safe conclusions about physical systems on the basis of observation of living organisms.

 

The same goes about the example of milk getting dissipated in your coffe, because milk is a product of a living organism and coffee too (from the coffee bean, since plants are living).

 

If one takes another example, like the clear water of the river mixing into the ocean, one will not observe the salted water from the ocean climbing up the river and becoming clear fresh water, but one will eventually observe the water from the oceans evaporate, then fall as rain on a continent and form a river of fresh water. In this sense, one would observe the salted water getting into the river again.

 

Just some thoughts.

 

All these examples are applicable. Entropy of each system increases in every case. The broken glass is a more isolated and obvious one. If you pick up the pieces and reheat them, then reform them into glass the entropy of a larger system has increased even more.

 

Organisms are stuck with the same Law. If you don't eat, and keep your system isolated, you die.

Edited August 16, 2011 by J.C.MacSwell

[michel123456]

All these examples are applicable. Entropy of each system increases in every case. The broken glass is a more isolated and obvious one. If you pick up the pieces and reheat them, then reform them into glass the entropy of a larger system has increased even more.

 

Organisms are stuck with the same Law. If you don't eat, and keep your system isolated, you die.

 

Yes, but entropy is a law we have learned from observation, not something that arises from some maths. The same goes for the arrow of time.

 

My thoughts continued:

 

In a river, the salmons swim counter the flow. The river represents the flow of time, the salmons are the living organisms. Life fights against the arrow of time. Life goes in one direction, time flows in the other. The past of the salmon is the future of the river, and the future of the salmon is the past of the river.

 

If you use this analogy, one can imagine that what we call the future could be the past of the universe.

The immediate problem in this concept is that reversing the arrow of time for the universe reverses also the law of entropy.

So I wondered if a universe with reversed entropy would be logical (and without living components for the sake of simplification). And in order to do that, I was asking myself some example of entropy of a physical system not engaged by any means with living components, no milk, no glass, no hand, no laboratory, only dead physical phenomenon, and then look at the same phenomenon reversed to see if it makes sense or not.

[Bignose]

Actually, there are several good mathematical definitions of entropy, all of which strictly increase with time. There is the definition from thermodynamics, and the definition from the kinetic theory of gases.

[mississippichem]

So I wondered if a universe with reversed entropy would be logical (and without living components for the sake of simplification). And in order to do that, I was asking myself some example of entropy of a physical system not engaged by any means with living components, no milk, no glass, no hand, no laboratory, only dead physical phenomenon, and then look at the same phenomenon reversed to see if it makes sense or not.

 

Don't know about a universe with reversed entropy. But if you're looking for an example of a process that makes sense in reverse, we have something in chemistry called the principle of microscopic reversibility. It basically states that the chemical mechanism for a forward reaction [imath] A \rightarrow B [/imath] is the reverse of the mechanism for the reverse reaction, [imath] B \rightarrow A [/imath]. It can be easily shown mathematically that if this doesn't hold, perpetual motion machines are a thermodynamic possibility.

 

Remember that it's totally possible to totally violate entropy locally but you must "pay the entropy tax", as a professor of mine put it, and satisfy the Clausius inequality for the entire universe, similar to what J.C. MacSwell stated in post #2.

Edited August 17, 2011 by mississippichem

[pantheory]

There is a very common example in litterature about entropy and the arrow of time. You keep a glass in your hand, you let it fall down, the glass breaks. You never observe the reverse situation where the broken pieces jump together in your hand: the example shows the one-way direction of the arrow of time. (except in a movie played backward)

 

On the other hand, living organisms use overall physical entropy to organize, sometimes compared as a spark of negative entropy in the general frame of the second law of thermodynamics.

 

So I was wondering if the example with the glass is applicable, because glass is a product we humans have made, a product of a living organism. One can not extract safe conclusions about physical systems on the basis of observation of living organisms.

 

The same goes about the example of milk getting dissipated in your coffee, because milk is a product of a living organism and coffee too (from the coffee bean, since plants are living).

 

If one takes another example, like the clear water of the river mixing into the ocean, one will not observe the salted water from the ocean climbing up the river and becoming clear fresh water, but one will eventually observe the water from the oceans evaporate, then fall as rain on a continent and form a river of fresh water. In this sense, one would observe the salted water getting into the river again.

 

Just some thoughts.

I think the two simple examples to a type of negative entropy would be life and gravity. In both the motion of time is from molecular and temperature dissipation, to a condition of high organization and isolated complexity.

 

I think the broken glass idea might not be a bad analogy concerning the arrow of time, the meaning being one cannot change what has already happened -- such as going backward in time.

[michel123456]

I was looking for some example.

 

The Sun. It radiates and produces a lot of entropy. But the reverse mechanism, an object eating radiation, is the same logical: I don't see any aberration or maybe I miss something.

[pantheory]

I was looking for some example.

 

The Sun. It radiates and produces a lot of entropy. But the reverse mechanism, an object eating radiation, is the same logical: I don't see any aberration or maybe I miss something.

The only object that eats more radiation than it produces is a black hole, you might consider one an example of reverse entropy.

//

Edited August 17, 2011 by pantheory

[Bignose]

The only object that eats more radiation than it produces is a black hole, you might consider one an example of reverse entropy.

//

 

black holes emit Hawking radiation, and thus the entropy of the universe increases even as mass or energy falls into a black hole.

[Realitycheck]

Everything. The universe coalesced into a huge mass of primordial particles, eventually organizing into hydrogen and helium, and through the formation, explosion, and rebirth of stars, larger and evermore complicated elements and chemicals, continuing on to life, ever-more complicated organisms of increasingly complicated assortments of chemicals and defense systems - both innate and sentient - all designed to preserve the lineal progression of organization. Peace and utopia is like the only logical conclusion, but we need to take off the blinders and see our place, become aware in its entirety.

Edited August 18, 2011 by Realitycheck

[michel123456]

This seems an interesting article. I will not subscribe though...

 

http://www.newscientist.com/article/mg20126882.800-did-gravity-point-time-in-the-right-direction.html