Assortments of Thought

Some Surprising Science

Posted on: July 20th, 2009

In science, as with any subject, there’re plenty of things a lot of people don’t know. Then there’re things they think they do know because they seem so intuitive, but which they’re actually wrong about. This is probably so more with physics than anything else, but it’s certainly so with other scientific fields as well. Therefore, in this post, I’d like to recount a few things that really surprised me personally when I first came across them, things that seem almost counter-intuitive at first. Specifically, I’ll discuss the notions of water only freezing at 0 ºC; people freezing in space; and one temperature that’s twice that of another being twice as hot.

So, to get started, water doesn’t just freeze at 0 ºC. Rather, it can freeze along a wide range of temperatures, meaning among other things that it can remain liquid well below 0 ºC as well. The reason for this is that in addition to temperature, pressure is also a variable that determines what phase something will be in (solid, liquid, or gas). To illustrate, consider some water at a given temperature and pressure. If the temperature is lowered enough, eventually, the molecules will lose enough kinetic energy such that they’ll slow down and interact strongly enough for the water to freeze into ice. On the other hand, if the pressure is increased enough, eventually, the extra force in pushing the molecules together will also allow them to interact strongly enough for the water to freeze into ice. Hence, it is temperature and pressure as a combination that determines what temperature water and other liquids will freeze at, as well as what temperatures they’ll boil at, what temperatures they’ll sublimate at (go from solid to gas at, like dry ice becoming carbon dioxide), and so on and so on.

In fact, for any substance, a phase diagram can be constructed to show what phase that substance will be in at any given combination of temperature and pressure. Such a diagram is simply a plot, or graph, with temperature along the horizontal axis and pressure along the vertical. As a review of phase diagrams would show, nearly all substances can exist in all three phases at certain temperatures and pressures. Further, there are more limited sets of temperature and pressure at which a substance exists at an equilibrium between any two phases. Finally, there’s often even a point at which a substance can exist in all three phases simultaneously, the triple point. If, for instance, you were to mix ice, water, and water vapor in a container at 0.01 ºC and 0.0060 atm (atmospheric pressure is 1 atm), then all three would remain in their original phases. More basically, at 0 ºC and 1 atm, ice and water would do that as well. In any case, the main point here is that, perhaps surprisingly, freezing points, boiling points, and other such phase-transitioning points are not fixed at definite temperatures, because pressure determines them as well.

Moving on, given that space is extremely cold, it’s often thought that if a person is exposed to space, they’ll instantly freeze. In fact, as space has a near-zero pressure, a person’s body fluids will actually boil in space rather than freeze. Of course, it might still seem that a person will rapidly lose heat, but that’s incorrect as well. Heat energy can only flow from hotter matter to colder matter, and since space is a near-vacuum, there simply isn’t be a place for a person’s heat energy to rapidly go. Hence, if exposed to space, a person won’t freeze, and they won’t rapidly lose heat. Rather, their body fluids will boil, and they’ll remain more or less at normal body temperature. The real immediate dangers of space exposure are thus boiling body fluids and a lack of oxygen (although according to the Wikipedia article “Vacuum,” sec. 4, para. 2, people with short exposures can still make complete recoveries).

Still, with regards to losing heat, whether for a body or any other object, what what happen immediately and what would happen in time are different matters. Space is not a total vacuum because it contains stray gas particles (though not liquids), virtually all of which are at extremely low temperatures. Hence, contact with such particles would gradually cool an object considerably, eventually almost to absolute zero (0 K, or -273.15 ºC), as they gradually took away heat energy. How long “gradually” would be, I’m not sure, and it would vary from case to case. In any case, the main point here is that although an object in space will indeed lose its heat energy eventually, it won’t be for quite awhile.

Finally, if one temperature is numerically twice another, it’s very tempting to say that the first temperature is, in fact, twice as hot as the other. However, unless the Kelvin scale is being used, that would be wrong. Consider 20 ºC and 40 ºC. Numerically, 40 is certainly twice that of 20, but 40 ºC is not twice as hot as 20 ºC, because 0 ºC is not the true zero point of the Celsius temperature scale. Rather, -273.15 ºC is, so relative to the true zero point (the temperature plus 273.15), 20 ºC and 40 ºC are, respectively, 293.15 ºC and 313.15 ºC. In other words, they’re not even that far apart, much less related by one being twice the other. On the other hand, consider 0 ºC and 273.15 ºC. The latter temperature is, in fact, twice as hot as 0 ºC even as count-intuitive as that seems, because, again, the zero point of the Celsius scale is not 0 ºC, but -273.15 ºC.

Of course, not all measurements have this property of ratios not being physically significant. On the Kelvin scale, for instance, 40 K really is twice as hot as 20 K, because 0 K is the true zero point. All of this in fact ties into the statistical concept of levels of measurement, of which there’re four: nominal, ordinal, interval, and ratio. At the nominal level, items can only be categorized but not ranked, like marbles being classified by color. No one category is higher or lower than another. Next up, the ordinal allows for rank, but with an indefinite distance between measurements, like ‘poor’, ‘average’, and ‘great’ on a survey. The order is clear, but individual points are not separated by a consistent or even definable distance. With the interval, however, there’s rank as well as a definite distance between measurements, but the zero point is not 0, as with the Celsius and Fahrenheit temperature scales. Consequently, ratios are not physically valid even though other mathematical operations are. Finally, the ratio is just like the interval except the zero point actually is 0, making it the most precise level complete with valid ratios. Thus, the main point here is that depending on the level of measurement, numerical ratios may not have physical significance, as is the case with the Celsius and Fahrenheit temperature scales.

So there you have it, the truth about a few things in science that are potentially very surprising in that they go against the intuitive. Certainly there’re many more, but those are some I personally found very surprising and so thought I’d discuss. Indeed, the world is sometimes not how it seems … and compared with quantum mechanical stuff, I’m sure these examples are truly mundane at that.

Reference:

en.Wikipedia.org: “Vacuum,” at Wikipedia as of July 20th, 2009
[http://en.wikipedia.org/wiki/Vacuum].

©2009, D.S. Applemin. All rights reserved.

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