[bbq]

The author goes from

Every careful person equipped with a reliable thermometer will make the same reading of temperature. There are alternative scales, Fahrenheit and Celsius, but both record the same thing...

to

Economics is genuinely harder. National income is a more complicated concept than temperature, and there are plausible alternative sets of rules for calculating it. Serious minded statisticians have spent many years discussing these issues, and there is now a UN-sponsored standardised system of national accounts.

But it is easy to write a mathematical symbol without giving thought to what observable fact in the real world corresponds to that symbol, or whether there is such an observable fact at all.

But isn't that exactly how we settled on the truth of temperature? Years of debate about what the right constructs for defining temperature mathematically are?

[Mattasher]

Yes and no. There's no single god-given way to measure temperature (though the 0-point seems clear), but once you have a scale, comparing the temperatures of two liquids is straightforward. On the other hand, a symbol like GDP is really a mix of thousands of inputs sampled using a variety of techniques and adjusted according to dozens of criteria like inflation and hedonics. Comparing GPD over time in a single country is crude, modeling GDP across countries is nothing at all like calculating how quickly water heats up compared to mercury.

[hugh4]

It should be noted that a "temperature scale" is a pretty non-obvious thing. The idea that the temperature we call "ten degrees" is as much colder than "twenty degrees" as that is colder than "thirty degrees" is something you'd never figure out without getting as far as the 18th century.

Even the concept of "temperature" is not obvious. Give someone a hot piece of bread and a hot piece of metal and the metal seems hotter even if they're at the same temperature.

[yomritoyj]

Statistical mechanics is a subject for which it is very hard to pin down the conceptual foundations. To read a thermometer I need to be sure it has reached "thermal equilibrium" with the object being measured. But how do you define thermal equilibrium in terms of underlying mechanical ideas? How do we identify the mechanical systems to which the concept of temperature and thermal equilibrium can be meaningfully applied? See http://philsci-archive.pitt.edu/2691/1/UffinkFinal.pdf We would be accusing statistical mechanics of 'mathiness' were it not the case that we know how to make it work for very many systems of practical interest. The main problem with economics is that it does not work as often.

[Mattasher]

Good points. I think the hidden terms here are "ratio variables" vs "interval variables". It's not obvious that 200 degrees (Kelvin) is twice as hot as 100 degrees. But almost everyone is going to agree that water at 300K feels hotter than water at 280K (though this may not work across materials, as you note).

What we can do with our temperature scale is build a model that says every time we convert n liters of oil into heat and direct it at x liters of water we get a change of temperature of y degrees. Reliably, and with small margin of error.

We can't do this with GPD, and if we declare that a 10% increase in education spending will lead to a 5% increase in GDP over 15 years, we don't have a testable scientific model, we have a guess based on our interpretation of extremely messy data.

[XorNot]

Not really. Temperature is one of those odd-ball scales where there's a real, absolute 0 to it. Years of debate converged on a physical reality.

[bbq]

A physical reality we describe with mathematical constructs - like 0.

People acting as groups exchanging capital is just as real as atoms acting as groups exchanging energy.

[TeMPOraL]

Except groups exchanging capital are still an GAI-complete system, unlike atoms - even if they behave predictably, they can start doing weird things completely at random. Also, atoms themselves don't have equal voting or influence rights to change the way we compute temperature when it suits them.

[robotresearcher]

The concept was well known and widely used before it was known to have a lowest possible value.

[jsprogrammer]

I don't believe anyone has ever shown something to measure at 0k.

[jonathankoren]

True, but irrelevant. The definition of temperature (average kinetic particle energy) means it exists. Conversely, Absolute Hot[1], is an open question.

[1] https://en.wikipedia.org/wiki/Absolute_hot

[jsprogrammer]

Irrelevant to what? The poster claimed that there was a real thing in a physical reality. If that is true, shouldn't we have observed it before? As the statement stands it claims as absolute reality something which no one has ever seen.

[TeMPOraL]

Ok, so we've never seen something to be exactly 0K. We've probably also never seen anything to be exactly 3.14159K. That doesn't mean objects with temperature of exactly 3.14159K are impossible, neither that we should assume they don't exist until you point out an example.

Temperature scale is a good model that maps the territory quite well. There is nothing to suggest it will suddenly stop working at 0K, if it works very well even as we get closer and closer to absolute zero.

Contrast with most economic models which as maps correspond to territory in a similar way the map of China corresponds to the Middle Earth - there are trees and not trees, you have to turn it around to make the sea be on the proper side, and... that's about how much it matches. Be wary of zooming too much in, lest you get eaten by an Orc.

[jsprogrammer]

It may be a good model, but that is not what the poster claimed. The poster claimed that is was an aspect of a real, physical reality. There is no evidence of that.

In fact, there is a good argument that 0k is unachievable [0].

[0] http://wordpress.mrreid.org/2014/07/03/why-cant-we-get-to-ab...

[akiselev]

》 If that is true, shouldn't we have observed it before?

No. The concept of temperature is based on the bulk interactions of matter due to the motion/collisions of atoms and molecules relative to an inertial reference frame. A frame that usually has to exist outside of the system for temperature to have practical meaning so it is a concept that by definition has an absolute zero, even if we haven't observed it yet.

In this case, absolute zero really means zero motion relative to the instrument measuring the sample so it is possible for a Type 1+ civilization to build a planet sized (or bigger, don't know how the math works out but it probably has something to do with constricting atoms to a precision within a planck length) laser or other electromagnetic trap to cool some nontrivial number of atoms to absolute zero like those used for Bose-Einsten condensate experiments.

[bobthechef]

Wrong. Nonsense invocations of nomenclature and pretentious obfuscations aside, your explanation came after the fact. When temperature scales were being constructed, neither thermodynamics nor atomic theory had been at the state you presuppose. What you state are not givens, they are conclusions of theories and explanations of the observations in terms of them. To say that temperature must by definition have an absolute zero isn't saying anything. Where did this definition come from? What is heat that temperature measures (yes, heat, not temperature)? Neither Fahrenheit nor Celsius knew. Current kinetic theory explains heat as exclusively the motion of microscopic things (not just atoms, btw) and it thus follows that the absence of motion must mean the absence of heat. In the 17th century, you might be telling us that absolute zero is complete dephlogistication. But why should temperature have an absolute zero? Without your theory of heat, or at least some intuition of it that frames heat as a quantity and cold merely the absence of heat, you have no reason to claim that temperature has a lower bound.

You really need to understand the order of dependence of explanations.

[jsprogrammer]

>it is possible for a Type 1+ civilization to build a planet sized...

It may be possible, but we seem to be a very long way away from being able to test such a hypothesis.

[Retra]

The temperature scale has a zero, and that's a fundamentally important temperature limit, so you'll want in on that scale.

[bobthechef]

Whether a scale has a zero is something that is decided after the fact. Whether it is "fundamentally important" is, again, dependent on the state of the theory it is bound up with and the result of.

[Terr_]

So? We haven't clocked a physical object moving at the speed of light either. That doesn't mean the math is wrong.

[sobkas]

Maybe because it's not possible to achieve 0K? It's physically not possible.

[bobthechef]

And how would you know that without a theory that told you that?

[hugh4]

No, we settled on temperature through years of careful, tedious experimentation involving the expansion of gases.

Much later, we figured out what it actually meant in terms of atoms.

[mxfh]

Temperature is one thing, but without knowing the air pressure you couldn't even cook an egg properly.

Assuming unstated conditions, like normal air pressure, is just as well an entry point for error if you want to reliably describe the assumed state of things.

http://biomodel.uah.es/Jmol/plots/phase-diagrams/

[meric]

With temperature we know what feeling each measurement corresponds to. When a politician ernestly does everything he can to raise the GDP per capita of his country often he is not aware of what real world consequences there will be. E.g. In China ten years ago everyone had motorbikes. Ten years later many families have cars but the roads are stuck in gigantic traffic jams and the the sky is covered in smog, and rivers covered in muck. GDP per capita and median incomes are going up, but is life getting better where people are getting more fulfilled and more contented?

[Gibbon1]

When you get into engineering one finds a strong caution to beware of optimizing the metric at the expense of the process. In your instance, GDP is up, median quality of life is down. Far as I can tell ordinary economists are totally blind to this.

[JoeAltmaier]

Accountants don't have the important columns in their spreadsheet: satisfaction, quality of life, health

[Gibbon1]

I've dated a few accountants, and my mother was one. You'd probably be surprised what's in their spread sheets.

[briandear]

How do you quantify quality of life and satisfaction? It's subjective. Health too is also subjective unless you go with binary: alive or dead.

[nickbauman]

Eh, there are Nobel laureates who work down the hall from each other who cannot agree on the definition of basic macroeconomic concepts such as what constitutes a "bubble" or whether "market failure" is even a valid concept to begin with.

[princeb]

that's because these are ambiguous layman descriptions of the state of the economy.

[nickbauman]

Yet serious economists openly argue about the term.

http://www.newyorker.com/magazine/2010/01/11/after-the-blowu...