Category: thermodynamics

No, Thermodynamics Does Not Explain Our Perceived Arrow Of Time

“As far as we can tell, the second law of thermodynamics is true: entropy never decreases for any closed system in the Universe, including for the entirety of the observable Universe itself. It’s also true that time always runs in one direction only, forward, for all observers. What many don’t appreciate is that these two types of arrows — the thermodynamic arrow of entropy and the perceptive arrow of time — are not interchangeable.

During inflation, where the entropy remains low and constant, time still runs forward. When the last star has burned out and the last black hole has decayed and the Universe is dominated by dark energy, time will still run forward. And everywhere in between, regardless of what’s happening in the Universe or with its entropy, time still runs forward at exactly that same, universal rate for all observers.

If you want to know why yesterday is in the immutable past, tomorrow will arrive in a day, and the present is what you’re experiencing right now, you’re in good company. But thermodynamics, interesting though it may be, won’t give you the answer. As of 2019, it’s still an unsolved mystery.”

No matter who you are, where you are, or what you’re doing, you’ll always perceive time running forward, from your frame of reference, at exactly the same rate: one second-per-second. The fact that this is true has led many to speculate as to what the cause of time’s arrow might be, and many, having noticed that entropy never decreases in our Universe, place the blame squarely on thermodynamics as the root of our arrow of time.

But that’s almost certainly not the case, and we can demonstrate that fact in a number of ways, including by decreasing entropy in a region and noting that time still moves forwards. The perceived arrow of time is still a mystery.

Physics, Not Genetics, Explains Why Flamingos Stand On One Leg

“Compared to a flamingo in the water that stands on one leg, an identical flamingo with two legs in the water will lose somewhere between 140-170% the total body heat that the flamingo on one leg loses. That means the flamingo that does learn the preferred behavior — standing on one leg — is free to spend more time in the water: more time feeding, grooming itself, scouting the waters, etc.

In short, a flamingo that learns to stand on one leg will have more chances for evolutionary success and survival than one that stands on two legs. The flamingos may not be smart enough to know that it’s important to stand on one leg in the water but not so much in the air; instead, it appears to be a behavior that flamingos engage in regardless of their environment. And, as far as scientists can tell, there’s no gene for standing on one leg; rather, it’s a behavior that gets passed down from a mother flamingo to her offspring as she raises them.”

Flamingos are pretty weird birds. They have unusually long and skinny legs and necks; their beaks are inverted from most birds; their mating dances only occur in enormous groups; and they range in color from a pale white to a deep pink, orange, or even red. But the defining property of a flamingo, at least to most humans, is that they stand on one leg.

Why would it benefit a flamingo to stand on one unstable leg, rather than two stable ones? Physics, not genetics, explains this flamingo behavior. Come understand the reason today.


The bottom line of every thermodynamics conference.

The bottom line of every thermodynamics conference.

Sunday 5.5.19, 9:00 am. The best moment of the day when you’re arriving at the library for doing some thermodynamics and you’re still alone.

Ask Ethan: Why Is The Black Hole Information Loss Paradox A Problem?

“Why do physicists all seem to agree that the information loss paradox is a real problem? It seems to depend on determinism, which seems incompatible with QM.”

There are a few puzzles in the Universe that we don’t yet know the answer to, and they almost certainly are the harbingers of the next great advances. Solving the mysteries of why there’s more matter than antimatter, what dark matter and dark energy are, or why the fundamental particles have the masses they do will surely bring physics to the next level when we figure them out. One much less obvious puzzle, though, is the black hole information loss paradox. It’s true that we don’t yet have a theory of quantum gravity, but we don’t need one to see why this is a problem. When matter falls into a black hole, something ought to happen to keep it from simply losing its information; entropy must not go down. Similarly, when black holes evaporate, a la Hawking radiation, that information can’t just disappear, either.

So where does it go? Are we poised to violate the second law of thermodynamics? Come find out what the black hole information paradox is all about, and why it compels us to find a solution!

We Still Don’t Understand Why Time Only Flows Forward

“It’s true that entropy does explain the arrow of time for a number of phenomena, including why coffee and milk mix but don’t unmix, why ice melts into a warm drink but never spontaneously arises along with a warm beverage from a cool drink, and why a cooked scrambled egg never resolves back into an uncooked, separated albumen and yolk. In all of these cases, an initially lower-entropy state (with more available, capable-of-doing-work energy) has moved into a higher-entropy (and lower available energy) state as time has moved forwards. There are plenty of examples of this in nature, including of a room filled with molecules: one side full of cold, slow-moving molecules and the other full of hot, fast-moving ones. Simply give it time, and the room will be fully mixed with intermediate-energy particles, representing a large increase in entropy and an irreversible reaction.”

Why does time flow forwards and not backwards, in 100% of cases, if the laws of physics are completely time-symmetric? From Newton’s laws to Einstein’s relativity, from Maxwell’s equations to the Schrödinger equation, the laws of physics don’t have a preferred direction. Except, that is, for one: the second law of thermodynamics. Any closed system that we look at sees its entropy only increase, never decrease.

Could this thermodynamic arrow of time be responsible for what we perceive as the forward motion of time? Interestingly enough, there’s an experiment we can perform: isolate a system and perform enough external work on it to force the entropy inside to *decrease*, an “unnatural” progression of entropy. What happens to time, then? Does it still run forward?

Find out the answer, and learn whether thermodynamics has anything to do with the passage of time or not!

Heat sinks

If you have explored the interior of your CPU then you might have noticed that there are these horizontal metal plates (called fins) many a times with a fan on top of the central or graphic processors.

They are called heat sinks/heat exchangers and are used to dissipate the heat generated by the processor to the surrounding.


The reason why they work is that according to the Fourier’s law, the
heat dissipated is directly proportional to the cross sectional area.


And adding protrusions to the surface increases the net cross section area for exchanging the heat with the surrounding.

Cooking with a computer

In order to demonstrate the extent to which the processor would heat up, let’s remove the heat sink and place a piece of meat on it.


At such high temperatures where cooking a piece of meat becomes possible on a processor, you can be damn sure that the probability of the survival of a computer running without a heat sink is just  0. **

Have a great day!

Stegosaurus and its huge ‘fins’

** for all practical intents and purposes, not merely for testing

If you’ve ever popped open a chilled bottle of champagne, you’ve probably witnessed the gray-white cloud of mist that forms as the cork flies. Opening the bottle releases a spurt of high-pressure carbon dioxide gas, although that’s not what you see in the cloud. The cloud consists of water droplets from the ambient air, driven to condense by a sudden drop in temperature caused by the expansion of the escaping carbon dioxide. Scientifically speaking, this is known as adiabatic expansion; when a gas expands in volume, it drops in temperature. This is why cans of compressed air feel cold after you’ve released a few bursts of air. 

If your champagne bottle is cold (a) or cool (b), the gray-white water droplet cloud is what you see. But if your champagne is near room temperature ( c ), something very different happens: a blue fog forms inside the bottle and shoots out behind the cork. To understand why, we have to consider what’s going on in the bottle before and after the cork pops. 

A room temperature bottle of champagne is at substantially higher pressure than one that’s chilled. That means that opening the bottle makes the gas inside undergo a bigger drop in pressure, which, in turn, means stronger adiabatic expansion. Counterintuitively, the gas escaping the warm champagne actually gets colder than the gas escaping the chilled champagne because there’s a bigger pressure drop driving it. That whoosh of carbon dioxide is cold enough, in fact, for some of the gas to freeze in that rushed escape. The blue fog is the result of tiny dry ice crystals scattering light inside the bottleneck. 

That flash of blue is only momentary, though, and the extra drop in temperature won’t cool your champagne at all. Liquids retain heat better than gases do. For more, on champagne physics check out these previous posts. (Image and research credit: G. Liger-Belair et al.; submitted by David H.)