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Scientists report asymmetry between heating and cooling

phys.org

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Re: Scientists report asymmetry between heating and cooling

#121

Post by PH95VuimJjqBqy »

extractionmech wrote: post #7
bmitc wrote: post #3

I always feel a little stupid or strange reading a lot of these science headlines and introductions. I wasn't aware that people considered there to be a symmetry between heating and cooling. I thought that the entire point of thermodynamics is that they are asymmetric. Even the article mentions that it's been known that heating is more efficient than cooling.

> On the other hand, cooling at the microscopic level involves the release of energy from individual particles, resulting in a dampening of their motion. This process corresponds to the system losing energy, leading to a decrease in the intensity of particle movement. It actually makes sense, doesn’t it? Heating the object adds energy constructively. In cooling, energy removed from one particle may in fact be absorbe…

active vs passive, it makes sense to me that they would only be symmetric if the active side (heating) was done at a lower threshold than the upper threshold for cooling.

But it makes sense as to why heating would potentially be faster than cooling.

Re: Scientists report asymmetry between heating and cooling

#122

Post by nyrikki »

Ma8ee wrote: post #110
darkerside wrote: post #83

Earlier quoted context omitted.

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.

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

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.

Re: Scientists report asymmetry between heating and cooling

#123

Post by nyrikki »

jvanderbot wrote: post #106
extractionmech wrote: post #7

Earlier quoted context omitted.

> On the other hand, cooling at the microscopic level involves the release of energy from individual particles, resulting in a dampening of their motion. This process corresponds to the system losing energy, leading to a decrease in the intensity of particle movement. It actually makes sense, doesn’t it? Heating the object adds energy constructively. In cooling, energy removed from one particle may in fact be absorbe…

Wait so hot objects have molecules with greater nuclear energy? This seems wrong. Are they emitting energy like radiation? I suppose that makes some sense, and would in fact support the asymmetry. Without thinking about it I thought heat was kinetic energy. And I don't see how collisions would transfer kinetic energy in positive direction any better than negative direction.

Black body radiation, the emission of photons or EM radiation is one area to dig into for more information.

But also note the all mater you interact with is almost entirely comprised of empty space, despite the illusion of solidness at our scale.

Re: Scientists report asymmetry between heating and cooling

#124

Post by nyrikki »

Roark66 wrote: post #53
bmitc wrote: post #3

I always feel a little stupid or strange reading a lot of these science headlines and introductions. I wasn't aware that people considered there to be a symmetry between heating and cooling. I thought that the entire point of thermodynamics is that they are asymmetric. Even the article mentions that it's been known that heating is more efficient than cooling.

Exactly, I always thought heating raises the entropy of a system and cooling puts it back in the "more orderly" state. So of course it can't be symmetric. Just like breaking a wine glass, reversing that process takes a lot more effort. Of course I have no idea if the above makes any sense, it's just an "intuitive understanding" I somehow got.

The disorder analogy used to explain entropy in school is flawed and it is best to disregard it entirely.

Thinking of entropy as a measurement of how had it is to describe a system is a safer analogy.

Gibbs free energy, or the energy in a system available for work is

∆Enthalpy - ∆Entropy * Temperature

Temperature and Entropy are independent properties of a system.

Re: Scientists report asymmetry between heating and cooling

#125

Post by nyrikki »

jmilloy wrote: post #11
schiffern wrote: post #5

>And have questions like: 'Why don't we have a device like a microwave oven for fast cooling?'" Isn't that... just a blast chiller? (AKA a convection oven in reverse) It's not commonly found in households, but that's different from saying "we don't have a device" that does this. EDIT: Yes folks, I do understand how the principles of operation differ. Point being that the humble countertop convection oven definitely q…

No, because I think microwaves heat in a very different way from radiant heat gain (or loss) such as in an oven or this chiller you're talking about. The internal water is heated directly.

Same mechanism, different frequency.

Microwaves and radiant heat are both primarily EM radiation at different frequencies.

The frequency of microwaves was chosen due to the resonant frequency of water and thus is absorbed in the area near the surface of most food items, with radiant and kinetic heating spreading to the interior.

There is some minor differences with convection but a conventional stove heating element doesn't care if it is the air or the food that absorbs the photons it is releasing.

I guess the near surface of the food being directly heated vs nichrome wire producing infrared radiation can be considered 'very different'

But the need to preheat a conventional oven for even cooking is because it is mostly radiant heat transfer of infrared radiation.

Re: Scientists report asymmetry between heating and cooling

#126

Post by Ma8ee »

nyrikki wrote: post #122
Ma8ee wrote: post #110

Earlier quoted context omitted.

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

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.

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.

Re: Scientists report asymmetry between heating and cooling

#127

Post by hulitu »

bmitc wrote: post #3

I always feel a little stupid or strange reading a lot of these science headlines and introductions. I wasn't aware that people considered there to be a symmetry between heating and cooling. I thought that the entire point of thermodynamics is that they are asymmetric. Even the article mentions that it's been known that heating is more efficient than cooling.

> I thought that the entire point of thermodynamics is that they are asymmetric.

Those people are journalists. For them, thermodynamics is something they never heard about. That's why they became creative. /s

Re: Scientists report asymmetry between heating and cooling

#128

Post by m463 »

akira2501 wrote: post #49
m463 wrote: post #34

Earlier quoted context omitted.

I think the human mind tries to impose order or symmetry on things. Like, "if time can move forward, it should be able to move backwards" I kind of think of explosions and entropy. I just don't see there being an equivalent reverse phenomenon. Even shooting a bullet into icewater or something colder seems like it would cool off many orders of magnitude slower. maybe I'm wrong.

A lot of our experiences are with symmetrical physical phenomenon. So, we're modeled that way. Time does not "move." Yet we need to conceptualize it. So our language here gets sloppy. You can recognize this by using the modified "if time can move forward, it should be able to be stopped." The obvious incongruity of this defies the idea that we're attempting to impose ourselves. In terms of Entropy, the universe does…

I guess it depends on the second law of thermodynamics if you believe it. I thought the universe wants to be maximum entropy, which is disordered and not ordered.

I'm not saying that that the universe doesn't want to cool off, just that it seems ok to think it would be faster to warm up than cool off.

Re: Scientists report asymmetry between heating and cooling

#129

Post by Kerb_ »

NoZebra120vClip wrote: post #72
leoqa wrote: post #32

Earlier quoted context omitted.

name an impossible thing and a grant writer will propose a solution

Could God write a grant proposal so ambitious that He couldn't fund it?

Looking at how churches collect tithes, I wonder if He already has

Re: Scientists report asymmetry between heating and cooling

#130

Post by angiosperm »

cmrx64 wrote: post #74
angiosperm wrote: post #39

We knew about this: some kinds of heating can affect all the molecules, but cooling generally only those colliding with the walls.

This explanation is unrelated to anything considered. It trivializes what the paper actually studies, we certainly had no such theorem before this work.

Acknowledged, good point.
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