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.
The phys.org article and science paper text are both impenetrable for different reasons (though I don't blame the paper). Can anyone explain this result like I have a college degree but not in physics? I'm especially interested in what the actual difference in "microscopic" process is between heating and cooling.
They experimentally demonstrated that it takes significantly more energy to move a microparticle the same distance when cooled than the amount of energy it would take when heated.
If something is already bumping around randomly, all you need to do is constrain the bumping along some dimensions and it will move less randomly and more frequently toward the remaining free dimensions.
That's easier than having to provide all the energy to do the movement directly.
Constrained energy basically acts as mass right? So would an intuitive way to think of this be that the warm particle has more energy, but moving it confines where that energy can be so it behaves as if it has more mass?
>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 qualifies as "a device like a microwave oven for fast heating," and a blast chiller is just the reverse of that.
"Laser cooling relies on the change in momentum when an object, such as an atom, absorbs and re-emits a photon (a particle of light). For an ensemble of particles, their thermodynamic temperature is proportional to the variance in their velocity. That is, more homogeneous velocities among particles corresponds to a lower temperature. Laser cooling techniques combine atomic spectroscopy with the aforementioned mechanical effect of light to compress the velocity distribution of an ensemble of particles, thereby cooling the particles."
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.
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.
Microwaves penetrate the interior of objects (outside of metal) that are in their Faraday cages, leading the internal temperature of those objects to rise dramatically. Blast chillers work like reverse ovens, from the surface to the interior.
Microwaves target the resonant frequency of intermolecular hydrogen bonds and impart vibration. It's a very special mechanism that doesn't really lend itself to this sort of analogy.
Generally it is best to create an insulated box that stays warm when it is very cold and then cool it down when it is hot - because the reason it gets hot is due to increased energy outside (normally the big glowy thing in the sky) and that energy can be captured and used to power a house sized fridge.
Energy to warm things up tends to be the sort of energy we can't really use any more.
I'm not an expert at all, but from my understanding, the ideal building is one that has so much insulation that its interior is kept at a set temperature with very little cooling and heating needed.
> But in the Sweeden the opposite, optimize for heat.
Not that much. As you mentioned just above, shutters are a layer of insulation. In Sweden, they have big glass windows and no shutters. The purpose is clearly to get the tiny bit of daylight in winter for health sake, but in terms of insulation, it would be better to have shutters, and smaller windows.
The theorems of thermal kinematics derived apply to limited models with a quadratic energy potential, localized on a spatial manifold. is there any reason to believe the market is described by this sort of model?
This explanation is unrelated to anything considered. It trivializes what the paper actually studies, we certainly had no such theorem before this work.
My first thought upon reading the article was that absolute zero bounds coldness whereas there is no limit to how energetic a particle or bulk can be. Am I on the wrong track?
> While no immediate practical applications exist, the researchers envision enhanced efficiency in micromotors, microscale cargo transport, and materials that can self-assemble or self-repair.
Everyone who has ever written a grant application will recognise this wording.
> Everyone who has ever written a grant application will recognise this wording.
And then when they see the university publicity department article on the topic everyone will know that the wild claims on how it will revolutionize the future started out as a reluctant and hedged "practicality" sentence.
When a university pub office sends something out about a new theorem in pure math, the absurd "applications" claims are even funnier.
It’s the biggest stretch possible without it being technically dishonest. Everyone knows it: the researchers know it and gag a little as they write it, and the grant reviewers know it but pretty much require it without really ever saying that they require it (competitive landscape and all).
What else can you say when it gets to subject matter like this?
In experimental thermodynamic bench experiments, those who are familiar with boiling water in a common scientific vessel such as a tea kettle, are often familiar with how a system has its own characteristic rate of cooling, depending on the energy of the heated media to dissipate into whatever heat exchange facility is available at the time, usually ambient convection.
Under careful observation it can be seen that often it is possible to impart energy from an external source at a faster rate than the same amount of energy will later require to completely dissipate afterward.
People shouldn't be discouraged whether this is obvious or not.
Experimentation such as this can require quite a bit of dedication, especially among those who are not tea drinkers, but this is the workaround that would be required to arrive at such valid conclusions without the use of equations nor those pesky optical tweezers which are such a pain in the butt.
It’s code for: we are really interested in continuing to research this and we believe it’s important (for reasons that nobody will really understand apart from the other 5-6 world experts), so we are making this statement as much of a marketing stretch as possible without it being technically dishonest.
Getting research funding is just a brutally competitive game.
It's code for "this is important and useful to the world, but probably won't lead to any immediately practical applications from the perspective of the funders (economically, militarily, etc.). But we have to say it might or we won't get funded."
These applications specifically because anything that looks at anything on the micro scale includes these as “possible applications”. They sound cool and exciting, and the urge for making them has been around since before Feynman’s Room At The Bottom lecture.
But my comment is mainly surrounding the farce of making a cool discovery that progresses an area of understanding, and then being asked a question that is best posed to engineers: “but what can we do with it?” Wrong field, wrong people, wrong question.
Imagine if astrophysicists were asked these questions. “So you’ve discovered a new kind of star that is made entirely of sponge? What applications do you think will come out of this research?” “Well we hope it will help with Dyson Spheres, Astrology and sea navigation”
Meh, if self-assembling, self-repairing materials forming a swarm of nano bots was going to take over the world it would have already happened elsewhere in the universe and proliferated everywhere by now. instead we have biology. The actual dominate force in our dimension that did proliferate.
Do you have any evidence that us biologicals are not an outlier other than the anthropic principle? Maybe our solar system is in the machines’ nature preserve sector.
No tech would ever be developed or furthered without exploring possibilities. Huge swathes of process and tech is developed purely on just trying things.
HNs recent anti-science propaganda is getting pretty out of hand.
But the point is that it's a lie, they have no intention to actually try those things. They only say them because as a society we do not give material support to physics for the sake of physics, instead we demand that it has some kind of economic value. Therefore physicists are incentived (or, really, forced) to oversell the reach of their ideas, since governments believe knowledge is not good in itself, it's only really good if there's some whiff that it may give a political or economic edge. All scientists in the world are used to pandering to this, so that they can be left alone and actually work. Unfortunately it seems to be getting more and more intense as time goes on, and as economies contract.
