[jacquesm]

Heating and cooling are rarely nicely split up in time. While you're heating something it is also cooling and while you're cooling something it is also warming up. This usually limits your ability to heat something up or to cool it because at some point these two are in balance.

[Ma8ee]

No. Put a cold thing into something hotter and the thing will heat up without cooling.

[tsimionescu]

No. The outer layer of the hot thing will quickly heat up to the temperature of the hot medium, then it will cool down as is stays in contact with the middle layer, which will heat up itself. The same thing repeats in layers all over the object.

[JonChesterfield]

Your idea is inconsistent with the heat equation and with basic materials science. What do you derive this model from?

[Ma8ee]

No, why do you think the outer layer will cool down? There will be heat transfer between the outer layer and the layer within, but at no point in time will the temperature of the outer layer be cooler than it was at an earlier point in time, so it will never cool down.

[jacquesm]

Other than the outer surface of the object there are no layers.

[geraldhh]

the hot thing will get cooler.

like to make something clean, you have to make something else dirty.

[VMG]

Is that true though? If I have say a box with mixed red and blue bricks and I sort them by color, both sides are "clean" now.

[ben_w]

In a sense that misses the metaphor, sure.

But the thing which is "dirtier" is the wider universe, where the energy you used to do that sorting has higher entropy.

At the scale of atoms and molecules in a gas, you can also sort them into high-energy particles on one side of a barrier and low-energy particles on the other side, and now there's a heat difference you can run a heat engine. This is totally a thing you can do with the right devices — but those devices will necessarily consume more energy than you get from a heat engine running on that heat difference.

https://en.wikipedia.org/wiki/Maxwell%27s_demon

[alpaca128]

Red bricks won't magically disappear by sorting, just like dirt won't disappear when you wipe it off a surface.

[arkey]

Cleaning is usually relocating dirt.

If either red or blue were dirt, one of the sides is dirty, and the other is clean.

If neither red or blue were dirt, then nothing was dirty, it was just mixed up.

[jackhalford]

That’s because the box isn’t a closed system, you’ve interacted with in and you have spent energy sorting the bricks. It’s the same story with humans on earth, things get sorted because of the energy inout from the Sun.

[jacquesm]

You've just marginally warmed up everything else including yourself.

[x86_64Ubuntu]

You've left out the entropy you've added to the universe by ordering the system. That entropy is in the form of wasted heat.

[Etheryte]

Sorting something is not the same as cleaning it, just like sorting an array doesn't sanitize its contents.

[darkerside]

At the boundary between water and air, molecules are constantly snapping back and forth between being liquid and vapor. It's just that an equilibrium has been reached that makes the system appear static.

[Ma8ee]

A molecule isn’t liquid or vapour. A molecule doesn’t have a temperature.

[darkerside]

Molecules don't have innate solid or liquid properties, but they do operate as a solid or liquid, correct? It has nothing to do with them having a temperature of their own, and everything to do with how they are currently acting with their peers. IIUC.

[nyrikki]

You are using a didactic oversimplification as an absolute truth while it is more nuanced.

An individual molecule in an open system can freely exchange energy with its surroundings and can/does have a temperature.

[Ma8ee]

You can call the limitations of your knowledge about the exact state of a molecule a temperature, but that doesn't mean that any single molecule has an actual physical temperature in the same way as a collection of particles. You can say that a passing car had a speed between 60 mph and 70 mph because you couldn't measure it more exact, but the car has at any given moment an exact speed independent of your knowledge of it, not a distribution of speeds.

[darkerside]

You may be right about the molecule, but the car absolutely has a distribution of speeds depending on what you are measuring in relation to.

[wybiral]

You mean putting cold ice cubes into a warmer drink doesn't cool it down?

[Ma8ee]

The ice cubes will only get warmer and will never get cooler.

[wybiral]

I don't think you understood me. I meant the drink gets cooler.

[Ma8ee]

I told you what I meant. Of course the drink gets colder, but that is not what we discuss.