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 absorbed again by neighboring particles, so it is not ‘efficient’. So I’d venture a guess at saying the object cools from outside until it is entirely cooled.
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.
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.
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.
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.
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.
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.
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.
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.
That is exactly GPS point: a car doesn't have a distribution of speeds unless you measure it relative to something else whereas a liquid or a solid does have a temperature, regardless of anything else. Depending on what the something else is that you measure your car's speed by you may decide it goes forward, backward or is motionless.
When you start talking about individual molecules, atoms or particles the whole concept of temperature becomes very counterintuitive. Think of it as a substitute for motion or vibration if you wish and even that is grossly inaccurate (but less so...).
Maybe this will help: a gas in a container has a pressure and a density as well as a temperature, all of which are properties of the gas and not of the individual gas molecules. A single molecule that the gas is made up from does not have a density, it doesn't have a temperature and it doesn't have a pressure. What it may have though is a speed relative to something else, and when it hits the something else it may impart some energy relative to that speed difference.
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.
If this were the case, then how can a solid have a temperature at all? Especially crystalline solids, where all the molecules/elements are bound in a lattice?
Absolutely, but that’s not heat. Things like heat produced from burning wood is an example of potential energy of binds getting released as kinetic energy + photons.
Particles in heat are more active, as in brownian motion puts them allover the place, the cooler things get, the smaller the ripples, the less likely to interact with another particle, by transfering that ripple.
Now in solid materials, that neighbour is always there to distribute any energy to everyone equally. But from solid to gas, there is only the surface and a gases density is lower, so the transfer propability shrinks again.
But that's hot vs cold. As I understood it, this article is talking about difference in rate of heating vs. cooling, from the same starting temperature.
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.
My source of the same intuitive understanding; electric bills.
Power to heat, waste is more heat (just not where desired?).
Power to cool is used to move the state of one side of the system to another, ideally open, side.
Though this does raise the question of if it's possible to cancel energy out. I think that's likely stopped by Heisenberg's uncertainty of measurements (and exactly matching them even when measured).
Though if you compared the efficiency of a heap pump for cooling and a resistive heater for heating, you might be surprised that cooling is more efficient.
The intuition is that the heat pump is moving heat, as opposed to just generating it.
> I wasn't aware that people considered there to be a symmetry between heating and cooling
Same here. By analogy, while any chemical reaction is in principle reversible, the kinetics "forward" and "backward" are unlikely to be equally favorable.
Likewise, with atomic nuclei, fission and fusion tend to be favored under distinctly different conditions.
The article does mention "far from equilibrium." Could this be a caveat similar to "in mice"?
No. This research is all about far from equilibrium systems, which also happens to be the realm of life. There IS symmetry near equilibrium, and I think a high school level of thermodynamics would expect it to be symmetric. In comparison with the high school chemistry which already considers enough phenomena to get meaningful asymmetry easily. I’m surprised at the level of surprise here, it seems motivated by some kind of certainty that I can’t tell the origin of.
The symmetry between cooling and heating is only a linearization approximation, like also the symmetry between compression and expansion.
There is no surprise that there are scenarios when the approximations deviate too much from the actual behavior and cooling and heating are asymmetric (and also compression and expansion).
Depends how you look at it, the Carnot engine is in principle reversible. You can either let heat move from hot to cold and get work as an output at efficiency (T_hot - T_cold)/T_hot, or input work and move heat from cold to hot at efficiency T_hot/(T_hot - T_cold).
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 not _want_ to be hot, it _wants_ to be cold and empty. So, the finding is genuinely counterintuitive.
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.
Which would like a bunch of randomized almost undetectable energy near absolute zero. So, I'm out on a limb past my comfort zone here, but my working model is:
Higher temperatures mean higher velocities mean the particles are less likely to interact with other particles and so their amount of entropy decreases, they become more predictable, have fewer possible future states, than they had before.
The second law just implies that work energy will always escape the system as heat because heat always moves from space with higher temperatures to space with lower temperatures. In a sense the universe is trying to move the hot things away from each other because it wants to be cold.
I used to live in Florida and it costs me a lot more to heat the house than cooling it even though the outside temperature rarely went below 32F (and I kept the home at 74F in the winter and 78F in the summer)...
AC is way more energy efficient, heat pumps too. They both move heat, rather than heat it with electric resistance heating. ACs move +-4 degrees of heat per watt of electricity used.
