This post is the next in a series that dates back several years. In fact, it's been going on so long that I ended up upgrading the title from "50 Years of Science" to "60 Years of Science". And, ignoring the change, this is the seventeenth entry in the series. You can go to sigma5.blogspot.com/2017/04/50-years-of-science-links.html for a post that contains links to all the posts in the series. I will update that post to include a link to this entry as soon as I have posted it.
I take Isaac Asimov's book "The Intelligent Man's Guide to the Physical Sciences" as my baseline for the state of science when he wrote the book (1959 - 60). In this post I am reviewing what he reported then noting what has changed since. For this post I will be reviewing two sections: "Heat" and "Mass and Energy". Both are from the chapter he titled "The Waves".
As he points out, many discussions of "light" are accompanied by a discussion of "heat". A candle, for instance, gives off both light and heat. The quantitative (assigning numbers to things) as opposed to qualitative (generalities such as "it's hot out today") understanding of this subject was completely missing until what he describes as "modern times". If you can't measure it, you can't study it quantitatively.
The observation that kicked off the change from qualitative study to quantitative study was the observation that warming many materials up caused them to expand. Galileo kicked things off in 1603 by plunging a tube of heated air into room temperature water. The water cooled the air, which compressed and drew water up into the tube. He called the device a "thermometer". Unfortunately, the height of the water in the tube could be changed not only by changes in room temperature but also by changes in air pressure (a phenomenon not well understood at the time).
In 1654 the Grand Duke of Tuscany came up with a better design. He sealed the tube. That fixed the problem caused by changes in air pressure. He also switched to a liquid. To magnify the change he placed a large bulb full of the liquid at the bottom of the tube then forced the liquid to expand up a narrow tube. If that sounds familiar, it's because all thermometers were designed that way until the electronic thermometer took over. And that change happened long after Asimov's book came out.
The Duke's design was good enough to permit some serious science to happen. Boyle figured out that human body temperature is (relatively) constant and substantially higher than any ambient temperature people find comfortable. Amontons led the switch from water to mercury as the liquid in the tube. "Mercury thermometers" were ubiquitous until a decade or so ago. They are still pretty easy to find. But, given that electronic thermometers are now cheap and contain no dangerous mercury, I don't expect that to last much longer.
Fahrenheit added a scale. Much of the world, including the US, still lives by his scale. On his scale water freezes at 32 degrees and boils at 212 degrees. On the Celsius scale (invented by a Swedish astronomer named Celsius in 1842) that is part of the Metric System that the rest of the world uses, these numbers are 0 degrees and 100 degrees.
Originally called Centigrade, in 1948 various tiny technical changes were made and the name was changed to Celsius. Given the rampant hostility to science that various groups succeeded in have fomenting, it is unlikely that the US will switch from Fahrenheit to Celsius any time soon.
Temperature is a measure of intensity, not quantity. In 1760 Black started measuring how much heat it took to change the temperature of various materials by a degree. It turns out that this quantity varies a lot. A further source of confusion came from the fact that under certain circumstances you can insert heat and the temperature doesn't change. If you add heat to ice the temperature stops changing when it reaches 0 degrees Celsius (see how much handier the Celsius scale is). Instead, some of the ice melts. There's nothing simple about heat.
What really sent the study of heat into high gear was the invention of the steam engine. The people who bought them didn't just care that they worked. They also cared how much they cost to run. If the same job could be done with less fuel (and fewer people to feed the fuel into the engine) then that was a good thing. But to understand how to make steam engines more efficient scientists had to understand how heat worked.
The first "theory of heat" was that it consisted of something called "caloric". Various materials contained various amounts of caloric, which could flow from here to there, presumably according to a set of rules. But no matter what rules they came up with, one obstacle or another inevitably popped up.
Scientists hunted for alternatives and eventually came up with the idea that heat was the manifestation of some kind of vibration. Thompson studied the way cannon barrels were bored, a process that produces tremendous quantities of heat. He decided that the mechanical friction of hard metal scraping against hard metal was causing some kind of vibration.
Davy then caused two pieces of ice to be rubbed together in a way that produced no caloric and observed that the ice melted. Caloric couldn't explain the result. But again mechanical friction could produce some kind of vibration that could.
Several scientists, most notably Carnot, studied how heat flowed. This later led scientists to crown Carnot as the founder of "thermodynamics", the study of heat and heat flow. Carnot developed a theory that explained how steam engines worked. The theory told scientists and engineers what to do to make them more efficient. It also allowed them to calculate exactly how efficient a steam engine could possibly be made. No actual steam engine is anywhere near as efficient as theory says it can be. But they are now way more efficient than early designs were.
Another pioneer was Joule. He spent 35 years studying how heat behaved in various situations. He developed Joule's Law: A given amount of "work" always produces the same amount of heat. And that meant that heat was just another form of energy. This led to the idea of "conservation of energy". Unfortunately for Joule, it was Helmholtz who formally proposed the idea in 1847. Conservation of Energy means that you can convert energy back and forth from one form to another. But you can neither create nor destroy it.
At roughly the same time it was observed that, with one exception, the conversion of one form of energy to another was never 100% efficient. Every time you did a conversion you got some heat whether you wanted to or not. So the only 100% efficient conversion is from any other form of energy into heat.
A study of the opposite, turning heat into other forms of energy, resulted in the introduction of the concept of "Absolute Zero". (Asimov doesn't talk about it here but that doesn't stop me from talking about it below.) The process of converting heat into other forms of energy involves two reservoirs; a hot reservoir and a cold reservoir. Heat can be turned into other forms of energy by taking some of the contents of the hot reservoir and reducing its temperature to that of the cold reservoir.
It turns out that's what a steam engine does. You heat water and turn it into steam. That's the hot reservoir. The general environment is the cold reservoir. If you process the steam cleverly it's temperature is reduced to that of the cold reservoir and energy is available to turn a flywheel. But the temperature of the cold reservoir imposes a limit on how much of the energy present in the hot steam is available to be converted into the energy of mechanical motion.
The laws of thermodynamics don't let you cool the steam to a temperature below that of the cold reservoir. But it's worse than that. It turns out that as a practical matte, some of the heat goes to warm up the machinery and for other non-productive purposes. The first law of thermodynamics is waggishly stated as "you can't win". The second law is waggishly stated as "you can't even break even". And a similar rendering of the third law yields "you can't even get out of the game".
The part of the theoretically available energy that is actually available is called "free energy". The part that is inevitably lost eventually became associated with the term "entropy". Entropy always goes up. Clausius invented the term in 1850.
At this point scientists knew in general terms how things worked. But they had no idea how the underlying mechanism worked. In 1870 Maxwell and Boltzmann developed the "kinetic theory of gasses". Heat came from the microscopic vibration of each molecule of gas. It turns out that molecules in a liquid can vibrate. Even molecules in a solid can (and do) vibrate. That's where the energy that heat represented was hiding. There was no caloric fluid.
Vibrating molecules can pass on their vibrations to other molecules. The energy contained in a certain rate of vibration depends, among other thins, on the weight of the vibrating molecule. The details are complicated. But the bottom line is that scientists figured out how to make this vibration approach explain all the details of how thermodynamics worked.
The energy involved in melting ice (or turning liquid water into steam) could be explained by the energy necessary to break (thaw, boil) the bonds that make a solid a solid (or a liquid a liquid). The same was true of the freezing (and condensation) processes. Making the bonds freed energy.
And in 1870 Gibbs extended the idea to chemical bonds. Chemical processes could be explained by attributing a certain amount of energy to a chemical bond. The energy was released when the bond formed and absorbed when the bond was broken. That brought chemistry into the thermodynamic fold.
That brings us to the section titled "Mass to Energy". Radioactivity, discovered in 1896, initially presented a challenge. The energies involved were gigantic. Where could that much energy come from? Einstein supplied the answer with his famous "E" equals "M" times the square of the speed of light. "E" is energy. "M" is mass. It turns out that a tiny amount of mass contains a gigantic amount of energy. The square of the speed of light is just a truly enormous constant number. But all it does is tell you exactly how much energy you get when you annihilate a tiny amount of mass.
Doing away with a tiny amount of matter is all it takes to produce the enormous amounts of energy we see coming from radioactive decay. And, of course, if you annihilate a "large" amount of mass, say a pinch of salt's worth, you get enough energy to level a city. Atomic (fission) and Hydrogen (fusion) bombs are just machines for the annihilation of what would otherwise be considered small amounts of mass.
A side effect of all this was the loss of Lavoisier's "conservation of mass" law. It was replace by the "conservation of mass-energy" law. And Einstein's idea soon transitioned from the theoretical to the practical.
Aston was able to experimentally confirm that Einstein's equation was correct. He was able to make measurements involving radioactive decay that were delicate enough to measure the mass loss in some situations. It was the right amount to match the amount of energy that was produced when, of course, you used Einstein's conversion factor.
Before I finish, I want to cover one subject that Asimov didn't. Scientists were able to do complex sets of experiments and calculations to determine how much energy was produced by reducing the temperature of water from say a hundred degrees to zero degrees. (We are using the Celsius scale here where water boils at 100 and freezes at zero.) It turns out the process released 373/273 of the energy theoretically available. Other experiments produced a similar result if you just added 273 to all the temperatures.
That got these scientists to ask themselves "is there such a thing as the lowest possible temperature, an absolute zero?" If there was, it appeared to be -273 degrees. (It's actually 273 and a fraction but I am going to ignore the fraction in order to keep things simple.) That led to the development of the Kelvin temperature scale.
A Kelvin degree is exactly the same as a Celsius degree. But 0 degrees Celsius is the same as 273 degrees Kelvin. 100 degrees Celsius becomes 373 degrees Kelvin. If you convert all temperatures to Kelvin then the ratio of the temperature of the hot reservoir to the temperature of the cold reservoir gives you the answer the question of how much heat energy can be converted to free energy.
Since the environment tends to be at roughly 300 degrees Kelvin (80 degrees Fahrenheit) you have to operate your hot reservoir at 600 degrees Kelvin to have access to even 50% of what's theoretically available. That's about 620 degrees Fahrenheit. This kind of analysis explains why engineers are always trying to increase the "operating temperatures" of things like jet engines.
An operating temperature of 1,100 degrees Celsius, something that the most efficient jet engines can now do, translates to a Kelvin temperature (again ignoring the fraction) of 1,400 degrees. That means that over 70% of the heat energy can theoretically be turned into free energy.
Cars, whose engines don't run anywhere near that hot, are doomed by thermodynamics to have a very low percentage of the heat energy the fuel produces translated into the free energy that can be used to "make the wheels go round and round".
Bottom line: Very little has changed in these areas. These subjects are foundational. And, for the most part, the foundations in these two areas were laid well before Asimov wrote his book. Science has since built on these areas. But for these specific areas, the foundations themselves have seen no changes. And little of a foundational nature has been added in the interval since the book came out.
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