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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 symmetr
by bmitc 3y ago
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.
- extractionmech 3y ago> 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.
- hsuduebc2 3y agoAnd heating in that coming only from outside. Hah. I never realized that.
- jacquesm 3y agoHeating 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 3y agoNo. Put a cold thing into something hotter and the thing will heat up without cooling.
- geraldhh 3y agothe hot thing will get cooler. like to make something clean, you have to make something else dirty.
- VMG 3y agoIs 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.
- Etheryte 3y agoSorting something is not the same as cleaning it, just like sorting an array doesn't sanitize its contents.
- ben_w 3y agoIn 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 https://en.wikipedia.org/wiki/Maxwell%27s_demon
- jackhalford 3y agoThat’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 3y agoYou've just marginally warmed up everything else including yourself.
- alpaca128 3y ago
- taylorius 3y agoBut isn't that passing on of energy from one particle to the next, just conduction? Why wouldn't it apply in the same way when heating?
- sparrowInHand 3y agoParticles 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.
- taylorius 3y agoBut 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.
- bmitc 3y agoI'm not saying that it doesn't make sense. What I am getting at is that I thought this was already known.
- jvanderbot 3y agoWait 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.
- _a_a_a_ 3y agoI can't see any mention or implication of 'nuclear' - where do you see that?
- ivalm 3y agoHot molecules move faster, it’s just kinetic energy.
- jvanderbot 3y agoAnd heating/cooling is just transfer of kinetic energy? Seems strange if so.
- aeonik 3y agoIf 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?
- LeegleechN 3y agoThe molecules in a crystal still vibrate kinetically. A solid with no molecular motion would be at absolute zero temperature.
- aeonik 3y agoWouldn't a fair amount of the thermal energy be hanging out in the bonds themselves? The stress in the system has to count for something. I'm imagining a bunch of potential energy being stored in the fields at any given moment.
- PH95VuimJjqBqy 3y agoactive 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.
- pitherpather 3y ago> 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"?
- cmrx64 3y agoNo. 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.
- pitherpather 3y agoMy last sentence there, about a caveat, was silly of me, beyond mere HN affectation.
- m463 3y agoI 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.
- deleted 3y ago[deleted]
- akira2501 3y agoA 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.
- m463 3y agoI 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.
- akira2501 3y ago> which is disordered and not ordered. 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.
- farhanhubble 3y agoI'm confused too. Isn't this what entropy is about? Or is it a more fine grained version of macroscopic quantity that is entropy?
- Roark66 3y agoExactly, 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.
- mjevans 3y agoMy 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).
- Tyr42 3y agoThough 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.
- nyrikki 3y agoThe 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.
- shiandow 3y agoDepends 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).
- cyrillite 3y agoGiven that cooling is effectively just heating something else, I’m a little surprised.
- adrian_b 3y agoCooling is heating everything else. 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).
- ijhuygft776 3y agoI 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)...
- abcc8 3y agoWere your heater and cooler equally efficient?
- Projectiboga 3y agoAC 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.
- hulitu 3y ago> 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