Scientists report asymmetry between heating and cooling
phys.org
phys.org
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.
like to make something clean, you have to make something else dirty.
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.
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.
An individual molecule in an open system can freely exchange energy with its surroundings and can/does have a temperature.
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.
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.
But also note the all mater you interact with is almost entirely comprised of empty space, despite the illusion of solidness at our scale.
I'm imagining a bunch of potential energy being stored in the fields at any given moment.
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 it makes sense as to why heating would potentially be faster than cooling.
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.
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).
The intuition is that the heat pump is moving heat, as opposed to just generating it.
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.
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"?
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).
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.
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'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.
Those people are journalists. For them, thermodynamics is something they never heard about. That's why they became creative. /s
That's easier than having to provide all the energy to do the movement directly.
>And have questions like: 'Why don't we have a device like a microwave oven for fast cooling?'"
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.
https://en.wikipedia.org/wiki/Laser_cooling
"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."
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.
"While the actual occurrence of the Mpemba effect is disputed"
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.
Houses built in southern Italy are like that (white paint, shutters on windows, ...)
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.
1. https://www.smithsonianmag.com/smart-news/new-experiment-sho...
It's like if you have sand and water, it's really quick to mix the two together, but waiting for them to settle requires minutes to hours.
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.
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.
The incentive structures you hint at don’t make sense either.
Is it actually code for "very dangerous military applications, DARPA please pay attention to me!"
Getting research funding is just a brutally competitive game.
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=more...
A sentence like that or a variation thereof is part of the 'dance' around funding.
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”
Our “dimension” the one unique to our perception and interpretation on Earth is dominated by biology.
I don’t see an artificial system being able to sustain a supply chain long enough to defeat that. The supply chain of biology is inherit.
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.