# Entropy vs life

• brajesh
brajesh
I understand entropy as a movement from order to less order and that the universe's entropy is increasing.

So I was wondering, life takes molecules and organizes them into organisms, so isn't life a reversal of entropy?

Mentor
Summary:: Is life reversing entropy?

isn't life a reversal of entropy?
Yes. Do you think that is a problem? If so, why?

256bits and russ_watters
brajesh
Yes. Do you think that is a problem? If so, why?

I thought/read that entropy could only increase?

Mentor
I thought/read that entropy could only increase?
The entropy of an isolated system can only increase. But there's nothing wrong with the entropy in one place decreasing as long as it increases more somewhere else.

Last edited:
PhDeezNutz, BillTre, 256bits and 2 others
Mentor
I thought/read that entropy could only increase?
It is important to pay attention to the details. That is only true for isolated systems. Living systems that are isolated immediately cease to decrease their entropy and soon die.

Last edited:
brajesh
brajesh
Interesting.

So my big question is this.

The mass or amount of lifeforms has been increasing since life first formed.
Assume we start colonizing and terraforming other planets.
And then other solar systems.
And then other galaxies.
Until life is everywhere.
Wouldn't the entropy of the universe now have decreased?

Mentor
Until life is everywhere.
Wouldn't the entropy of the universe now have decreased?
No. If the universe was filled with nothing but life, what would it eat?

Living things are not closed systems. They decrease their own entropy, but by doing the things living things do they increase the entropy of the universe.

PhDeezNutz, BillTre, alan123hk and 1 other person
brajesh
No. If the universe was filled with nothing but life, what would it eat?

Living things are not closed systems. They decrease their own entropy, but by doing the things living things do they increase the entropy of the universe.

So how about at the point where 1/2 the universe is alive and 1/2 dead...the entropy would still be a lot less than today, right? So it would have decreased at least to that point in time.

Motore
Mentor
So how about at the point where 1/2 the universe is alive and 1/2 dead...the entropy would still be a lot less than today, right? So it would have decreased at least to that point in time.
No. In order for the life to grow, it has to eat!

...and/or breathe, poop, photosynthesize.

I think you're just confusing yourself by creating a nonsensical scenario to try to support your preconceived incorrect understanding. Forget that -- start simple. Consider the lifecycle of a single tree. Then you can multiplex it.

The mass or amount of lifeforms has been increasing since life first formed.
Assume we start colonizing and terraforming other planets.
And then other solar systems.
And then other galaxies.
Until life is everywhere.
Life being "everywhere", doesn't imply that everything is alive. Colonizing a solar system doesn't make its star alive.

Dale and 256bits
DrStupid
So how about at the point where 1/2 the universe is alive and 1/2 dead...the entropy would still be a lot less than today, right?

That sounds like you are thinking about matter only and forget the waste heat. Even if you turn all existing matter into life, the total entropy would still be increased.

Mentor
Wouldn't the entropy of the universe now have decreased?
No. The decrease in entropy provided by life is minuscule compared to the entropy increase from the sun.

Let me be super clear: life as we know it in no way whatsoever comes anywhere near violating the second law of thermodynamics. In fact, it is many many orders of magnitude away from it.

BillTre
Homework Helper
One data point is the pig. At some points in their life cycle, the feed to gain ratio for a pig is three to one. That is, it takes three pounds of feed (plus some water and air) to allow the pig to gain one pound of weight.

So, naively, you start with three pounds of corn over here and end with one pound of pig and two pounds of manure over there. Entropy has increased. The entropy in one pound of pig plus two pounds of manure is more than was in the three pounds of corn.

You can never turn half of the universe into pig because you'll inevitably have two thirds of it end up as manure.

BillTre, artis, Nugatory and 5 others
brajesh
So from reading everyone's responses ---> @russ_watters @Dale @jbriggs444 @DrStupid @Nugatory , it seems the mistake I'm making is that I am thinking that entropy stays constant while life increases.

What's really happening is that for "life to live" it actually creates more entropy to live, than it reduces by living?

Have I finally got this right?

russ_watters
Mentor
What's really happening is that for "life to live" it actually creates more entropy to live, than it reduces by living?

Have I finally got this right?
Yep!

Something else to make sure you understand is closed vs open systems. If @jbriggs444's pig lived in a bubble, the entropy in that bubble would be dropping as it grew. That's not a violation because it is not a closed system; food/water and air have to be continuously fed into the bubble and waste materials (and their associated entropy) removed from the bubble.

BillTre and brajesh
Mentor
What's really happening is that for "life to live" it actually creates more entropy to live, than it reduces by living?
Yes. Substantially more

brajesh
brajesh
thank you all, sorry for my stubbornness in not understanding initially

BillTre and berkeman
BWV
I do not think its that simple, but am above my pay grade here, so any help / corrections appreciated. Chemical reactions can either increase or decrease entropy. H20 is lower entropy than separate H and O atoms, and generally the entropy declines as you go from gas to liquid to solid. Complex organic molecules reduce entropy as they are lower energy states than their respective components. Cant find a great reference, but it appears that the basic photosynthesis reactions result in a decline in entropy. So don't plants use the sun's energy to accomplish a reduction of entropy? Has the overall entropy of the Earth increased or decreased since life began 4 billion years ago?

Also Gibbs free energy equations states

So a marginal joule of energy coming in from the sun (G) could result in an overall decline in entropy in the Biosphere if the change in enthalpy is small enough?

Homework Helper
So don't plants use the sun's energy to accomplish a reduction of entropy?
Plants are manifestly not closed systems. They use the sun's energy. Also, less obviously, they radiate waste heat into space. The sun provides the energy. The difference in temperature between sun and space provides a dump for the entropy.

You cannot grow plants without the sun. You can also not grow them if there is sun on all sides. They bake instead.

Dale
Mentor
So don't plants use the sun's energy to accomplish a reduction of entropy?
Yes. And an enormous amount of entropy is generated from absorbing sunlight at several thousand K and re-radiating it at a few hundred K. Life's small decrease in entropy is utterly negligible in comparison.

BWV
Plants are manifestly not closed systems. They use the sun's energy. Also, less obviously, they radiate waste heat into space. The sun provides the energy. The difference in temperature between sun and space provides a dump for the entropy.

You cannot grow plants without the sun. You can also not grow them if there is sun on all sides. They bake instead.

Right, never argued that it is a closed system, question is whether plants use the energy coming in from the sun to reduce the overall entropy on the planet

Yes. And an enormous amount of entropy is generated from absorbing sunlight at several thousand K and re-radiating it at a few hundred K. Life's small decrease in entropy is utterly negligible in comparison.

Isn't the absorption of sunlight into the heat of organisms an increase in enthalpy? so per Gibbs, if the marginal increase in enthalpy is lower than the marginal energy input from the sun, entropy will decrease?

Mentor
H20 is lower entropy than separate H and O atoms
Careful... that’s not the right way of thinking about it. We start with a flask containing a stoichiometric mixture of 8 parts (by weight) oxygen to 1 part of hydrogen. They react and we end up with hot water vapor, shards of flask flying every which way, and a bunch of heat energy spread around the surroundings. Entropy has increased in this process.

brajesh and BWV
Homework Helper
Right, never argued that it is a closed system, question is whether plants use the energy coming in from the sun to reduce the overall entropy on the planet
The Earth as a whole is not a closed system either. For the same reason. It is not clear to me whether the entropy of the planet is increasing or decreasing.

But yes, one can grow coal deposits over eons, thereby decreasing the entropy of the planet. No second law violation because no closed system.

BWV