What is a Gas?
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| A simple lab apparatus for studying the properties of gases |
A sample of a gas is trapped in the closed end of a narrow glass tube by a quantity of mercury (a silvery, dense liquid metal, shown in green). Adding mercury through the open end increases the pressure on the gas. The height of the gas sample is a measure of its volume, while the difference in height between the two ends of the mercury column is a measure of the pressure. Start with a gas height (V) of 60 cm and a mercury height (P) of 20 cm of mercury. Add mercury until the pressure is 40 cm, and you will find that the gas height is squeezed down to 30 cm. Further additions of mercury produce these results:
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You can see that multiplying P and V always gives 1200, or to put it another way, the product P times V is constant. So there is a regular pattern of behavior of the gas as we alter the pressure exerted on it.
What is a gas, that it should behave this way?
Hurrah for positive science!
Hurrah for positive science! long live exact demonstration!
Fetch stonecrop mixt with cedar and branches of lilac,
This is the lexicographer, this the chemist, this made a grammar of the old cartouches,
These mariners put the ship through dangerous unknown seas.
This is the geologist, this works with the scalpel, and this is a mathematician.
Gentlemen, to you the first honors always!
Your facts are useful, and yet they are not my dwelling,
I but enter by them to an area of my dwelling.
Walt Whitman (2)
From an interview
I like the scientific spirit—the holding off, the being sure but not too sure, the willingness to surrender ideas when the evidence is against them: this is ultimately fine—it always keeps the way beyond open.
Walt Whitman (3)
What is science?
I hope that these essays, among their other benefits, equip you to defend science when someone claims that science is a bad thing for our society, or that science is responsible for environmental degradation, the bewildering complexity of modern life, or social unrest.
Your first line of defense is knowing what science is, which will help you to define precisely what anti-science claims mean. Often a person who claims to oppose science is voicing a legitimate concern, but uses the term science when they really mean something else. So here is what science is, as well as what other things critics might mean when they say science.
Science is a process for discovering the truth about nature. By truth, I mean reliable knowledge—knowledge on which you can act or base decisions. Science is the attempt to see the physical world clearly and accurately, despite the sometimes obvious, and sometimes quite subtle, limitations and distortions of our senses and our minds. Science grows out of observation and experiment, which produces data, the facts of science. In the data, scientists can often discern patterns, called laws. These laws are useful, but they also cry out for explanation, and we call the explanations theories.
All of these elements of scientific thinking—data, laws, and theories—are self-correcting. By that I mean that they, like all findings of science, are public knowledge, and can be (and are) constantly being checked, and if necessary, corrected or extended. This is what Walt Whitman said that he liked about what he called the scientific spirit, the
holding off, the being sure but not too sure, the willingness to surrender ideas when the evidence is against them ...
Self-correction helps science to construct knowledge that is, in the words of philosopher John Searle (4), true, objective, and universal: true, despite all truth being subject to revision; objective, despite the presence of subjective elements in the judgments that accept it; universal (true in all times and places), despite having been discovered in specific instances. Self-correction makes science a more powerful process than philosophers of the past thought possible.
Data
Data
Now to get concrete about data, laws, and theories. An example of data is the list of measurements of gas pressure versus volume, as a gas is squeezed into smaller and smaller volumes—the table of data at the beginning of this essay. The data are numbers (with their associated units, such as cm of mercury), the pressure and the volume each time the measurements are made. To make the data complete, we need to know just how the pressure and volume were measured, so that we could do the experiment ourselves if we wish, and verify the data. It is good data only if it can be verified by others. If, by the word fact, you mean something unarguably true, that everyone can agree on, then data are the closest things to facts that you will find in science.
Like all elements of scientific thought, facts or data are self-correcting; that is, errors in data can be discovered by others, because scientists publish not only the results of an experiment, but its design, and its expected precision, so that others can check it. Often, scientists begin to expand or extend a published result by re-measuring some of the published data. This establishes (or calls into question) the reliability of the data and the method that produced it.
Laws
Laws
Next, laws. It is natural when we look at data to search for or notice patterns or trends. If these patterns are reliable, we call them laws. In the data table, we see that squeezing to reduce the volume of the trapped gas increases its pressure, and it does so in a very simple way: the product of pressure and volume is always the same. In this case, P times V equals 1200. This relationship is a good example of a law—it describes a trend or regular pattern in data. Laws are useful because they can guide action. For example, if we know that the gas container will burst at a pressure of 200 cm of mercury, then we know to stop this experiment before approaching a gas volume of 6 cm (giving an internal pressure of 1200/6 = 200).
Like data, laws are self-correcting. Any informed scientist can examine the fit of data to law, and can point out discrepancies, or even describe other patterns that cohere with the data, perhaps better than the law as originally stated. Sometimes, several different statements of a law turn out to be equivalent. In other cases, two different patterns that fit the data make different predictions about data outside the measured range. New, extended data allow scientists to decide which statement of the law is more general—that is, which pattern fits the data over a wider range.
I am not saying that a law is a pattern that nature must obey. I am saying that a law is a pattern that, when we judge by the data, nature appears to obey. Stating a law is much like asking whether nature always does things in the manner we have noticed. If so, that is useful information.
Obviously, in science, the word law means something very different from what it means in court.
Theories
Theories
Finally, theories. It is natural, when thinking about a law, to ask why. Why does the law hold? A theory is an attempt to explain why a law or set of laws holds, or why the data shows a trend or pattern. When scientists try to formulate a theory to explain why the product of pressure and volume of a gas is constant, they are asking, “What is a gas, that it should behave like this?”
The tested and widely accepted explanation for this simple gas law is called kinetic-molecular theory or KMT, a fancy term for the notion that a gas consists of tiny particles (atoms or molecules) that are in constant motion, and that these particles produce pressure by endlessly banging against the walls of their container. These collisions, for example, prevent an inflated balloon from collapsing. The pressure that supports the balloon is the sum of many small collisions with the container walls. The more frequently the particles bang, the higher the pressure. If the gas is forced into a smaller volume, with the same number of molecules banging around inside, there will be more bangs per second against the walls, and thus more pressure.
To see a vivid simulation of gas behavior as described by KMT, visit this site:
KMT Simulation (requires Java).
To see a vivid simulation of gas behavior as described by KMT, visit this site:
KMT Simulation (requires Java).
This simple idea or model has stood up to many experimental tests. I am not saying that KMT is true, but that it is widely accepted because it has withstood all experimental tests thus far, and it fits with other reliable knowledge. A theory that has withstood years of scrutiny and testing is the best product that science has to offer.
In the wider world, theories are the most likely elements of the scientific process to be misunderstood and mistakenly undervalued. Sound theories, which accurately explain why certain laws hold, and which hold up to diverse tests of their appropriateness, are the loftiest goals and the loveliest creations of science, its most powerful harbinger of progress, and its most useful product. When someone uses the expression “merely a theory,” as antievolutionists often say of Darwin’s powerful theory, then you can rest assured that they are completely ignorant of what I have just been telling you about science. Saying that evolution is “merely a theory” is like saying that a stone is merely a diamond.
Like data and laws, theories are self-correcting. They can be, and are, scrutinized by anyone sufficiently informed to understand them. Through publication, the first stage of which is peer review—careful examination by other scientists qualified to understand the work—the fit of theory to law, law to data, and data to the methods that produce it, all receive critical scrutiny from anyone who is interested, and who might find the theory to be a useful guide in their own work.
Facts, laws, and theories represent three important (but not the only) kinds of thinking that lie at the foundation of science. They are also at the basis of all rational thought. The psalmist quoted at the beginning of this essay is asking for a theory, an explanation for patterns in his life. He has been told by tribal or religious authority that his God made the world for humans, and he rightly wonders what this says about what we are, that an all-powerful being would give us charge of such wondrous creation. What is humanity, that it should deserve such consideration? Although we see now how much damage is done by the tacit assumption that the world is for us to use as we wish, the thinking that underlies this psalm is simply rational thinking, in which we seek explanations (theories) for the arrangement of things around us. (5)
Modern science: Sometimes the law IS the theory.
In such modern areas of science as relativity and quantum theory, it can turn out to be impossible to explain why the laws hold. That is, although the laws are incredibly accurate at predicting how systems will behave and at calculating the exact results of experiments, it turns out that classical, mechanical, cause-and-effect explanations (theories in the sense used in this essay) simply don't work; in order to make them fit the laws, they always have to contain something nonintuitive or physically implausible. For example, two-slit interference (add link to description) occurs with electrons even if only one electron at a time passes through the slits and reaches the detector. One could say that each single electron passes through both slits and interferes with itself. That explanation would certainly produce the interference pattern observed; but it certainly makes no sense with regard to objects in our visible, macroscopic world. No one has come up with classical cause-and-effect explanations for any quantum phenomena. This does not bother most modern scientists. The laws -- the equations of quantum mechanics -- are useful in their own right, and no underlying classical mechanism is needed to use them. And whenever scientists have tested the most outlandish and non-classical predictions of quantum mechanics -- the ones that most plainly defy common sense -- the laws have always held, and common sense thinking has failed to lead in the right direction.
This problem did not first emerge with quantum mechanics. In the nineteenth century, Faraday, Maxwell, and others struggled to explain electricity and magnetism with mechanical models. Faraday believed that undetectable, massless fields of force surrounded magnets or objects that were electrically charged. No mechanical analogs have yet replaced these fields and their lines of force, even though Maxwell was able to use such models to guide him towards equations that describe electromagnetism with great precision. In the end, he cast away the classical models and declared that the lines of force are real, and the equations themselves describe reality. Heinrich Hertz said, “I know of no shorter or more definite answer than the following—Maxwell's theory is Maxwell's system of equations.”
Facts, laws, and theories represent three important (but not the only) kinds of thinking that lie at the foundation of science. They are also at the basis of all rational thought. The psalmist quoted at the beginning of this essay is asking for a theory, an explanation for patterns in his life. He has been told by tribal or religious authority that his God made the world for humans, and he rightly wonders what this says about what we are, that an all-powerful being would give us charge of such wondrous creation. What is humanity, that it should deserve such consideration? Although we see now how much damage is done by the tacit assumption that the world is for us to use as we wish, the thinking that underlies this psalm is simply rational thinking, in which we seek explanations (theories) for the arrangement of things around us. (5)
Modern science: Sometimes the law IS the theory.
In such modern areas of science as relativity and quantum theory, it can turn out to be impossible to explain why the laws hold. That is, although the laws are incredibly accurate at predicting how systems will behave and at calculating the exact results of experiments, it turns out that classical, mechanical, cause-and-effect explanations (theories in the sense used in this essay) simply don't work; in order to make them fit the laws, they always have to contain something nonintuitive or physically implausible. For example, two-slit interference (add link to description) occurs with electrons even if only one electron at a time passes through the slits and reaches the detector. One could say that each single electron passes through both slits and interferes with itself. That explanation would certainly produce the interference pattern observed; but it certainly makes no sense with regard to objects in our visible, macroscopic world. No one has come up with classical cause-and-effect explanations for any quantum phenomena. This does not bother most modern scientists. The laws -- the equations of quantum mechanics -- are useful in their own right, and no underlying classical mechanism is needed to use them. And whenever scientists have tested the most outlandish and non-classical predictions of quantum mechanics -- the ones that most plainly defy common sense -- the laws have always held, and common sense thinking has failed to lead in the right direction.
This problem did not first emerge with quantum mechanics. In the nineteenth century, Faraday, Maxwell, and others struggled to explain electricity and magnetism with mechanical models. Faraday believed that undetectable, massless fields of force surrounded magnets or objects that were electrically charged. No mechanical analogs have yet replaced these fields and their lines of force, even though Maxwell was able to use such models to guide him towards equations that describe electromagnetism with great precision. In the end, he cast away the classical models and declared that the lines of force are real, and the equations themselves describe reality. Heinrich Hertz said, “I know of no shorter or more definite answer than the following—Maxwell's theory is Maxwell's system of equations.”
Come to think about it, Newton's theory of gravitation -- that gravity is a force between masses that acts instantaneously at a distance -- doesn't exactly make sense, does it?
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It's not easy being anti-science
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It's not easy being anti-science
So that’s what science is. It is really nothing more than being rational in the search for what is true—for reliable knowledge—about the world around us. If science is defined in this way, there is not a lot to dislike about it. So when someone has a beef with science, and blames it for all sorts of ills, are they saying that trying to find out the truth about nature is a bad thing?
Not likely. Instead, they may not be talking about science at all, but about specific scientific findings, which they wish were not true, perhaps because they are inconvenient or clash with cherished beliefs. Or they may be talking about technology, which like science is also a process, this time of turning truth about nature into useful products or procedures. There’s not a lot to dislike about technology, defined in this way. What’s wrong with the general practice of trying to turn reliable knowledge into reliable services?
So instead of complaining about science, or about technology, critics may well be complaining about specific products of technology, like the computer, or the morning-after pill, or napalm. Or even more likely, they may be talking about how specific products are used, like the use of herbicides, which can improve crop yields, as weapons of war. In this case, their gripe is with political policy, not with science.
When someone tells you that science makes the world more unpleasant or dangerous or impersonal, find out what they think they mean by science. Help them to decide whether it is science’s findings, or technology’s products, or the uses of those findings or products, that get under their skin. You may be helping them to define what is bothering them, and to find a productive course of action, one that does not involve the impossible and ill-advised measure of trying to put an end to science, or of simply ignoring what science can tell us about our world and ourselves.
Science is not all that there is
Science is not all that there is
The narrator’s praise of science in “Song of Myself” is not unqualified praise:
Your facts are useful, and yet they are not my dwelling,
I but enter by them to an area of my dwelling.
The narrator appears to be saying that science’s findings (which, I believe, the narrator means by "facts") are not all there is to our existence. What “area of our dwelling” is he or she speaking of, and how do the findings of science allow that access? Finally, what other areas are there, and how is science related to them? More about these questions awaits you in essays that follow.
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(1) Psalms 8:4, Holy Bible, King James Version, Cambridge Edition. Notice particularly verse 6; you might be interested in Lynn White's 1967 (!) take on Christianity's role in our climate crisis. Click HERE.
(2) from “Song of Myself,” by Walt Whitman, Complete Poetry and Selected Verse, James E. Miller, Jr., ed, Boston, Houghton Mifflin, 1959, p. 25.
(3) Quoted in In Horace Traubel, With Walt Whitman in Camden (1906), Vol. 1, 101, cited at http://www.todayinsci.com/W/Whitman_Walt/WhitmanWalt-Quotations.htm.
(4) John Searle, Philosophy in a New Century, Cambridge University Press, 2008, Chapter 1.
(5) You might be interested in the more technical article from which these arguments were distilled: Gale Rhodes, "Does a One-Molecule Gas Obey Boyle's Law?", Journal of Chemical Education, 69, 16, 1992. READ the article, using the Page arrow at the top of page 1 to see the next pages.
(5) You might be interested in the more technical article from which these arguments were distilled: Gale Rhodes, "Does a One-Molecule Gas Obey Boyle's Law?", Journal of Chemical Education, 69, 16, 1992. READ the article, using the Page arrow at the top of page 1 to see the next pages.
