Despite the general rejection of science by American society today there are still many of us who delve into whatever science we can find and enjoy it. However, even among the well educated, there are a number of scientific misconceptions that have penetrated the popular consciousness. I believe that these incorrect ideas largely come from science classes in middle and high school, and are then perpetuated by a largely scientifically illiterate media. We all have heard and believe ideas that are probably incorrect, as we can't all be experts in everything.
Below I have listed a handful of them that bug me with the hopes that I can spread a little enlightenment. I don't mean to insult anyone if they believed one of these misconceptions, they have persisted because they make intuitive sense, even if they are wrong. Hopefully I can straighten things out a little bit.
1. "Survival of the fittest"
The term "survival of the fittest" has come a long way since Charles Darwin first used it in the fifth edition of his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Darwin himself didn't come up with the phrase; it was developed by an economist named Herbert Spencer after reading Darwin's book. Darwin had never really liked the term "natural selection" because he felt it implied that nature was making a conscious choice in selection.
However, as the phrase is used today has become something of a tautology. People often think of the colloquial use of the word "fitness" meaning physically fit, or strong. When they see a lion take down a gazelle, they think 'Oh, the lion was bigger and stronger than the gazelle, so he survives and the gazelle doesn't'. However, that usage of the term effectively means 'survival of those most able to survive' and isn't that useful of a scientific idea. In addition it ignores the most important aspect of Darwin's ideas, the nature of the heritability of traits.
An important point here is that we aren't merely talking about reproduction. Take, for example, a horse that only mates with a donkey. The pair may have several mule offspring but everyone of those offspring are infertile. Therefore, whatever genes that the horse passed to its offspring will not be added to the gene pool, and the horse's 'Darwinian fitness' is effectively zero. Darwinian fitness is best described thusly: If an individual possesses genes that give it an advantage in both survival and reproduction, and those genes impart a competitive advantage to its offspring for survival and reproduction. So if you want to look at the fitness of an individual, you should look at how many grandchildren it has, not how many kids it has, and certainly not at just the individual itself.
2. The replacement number
People who are concerned about overpopulation of our planet frequently talk about the "replacement number" or "replacement fertility": the number of children that a couple should have to keep a stable population size. Fewer than this number and the population will shrink, having more kids results in population growth. Ideally, assuming that everyone couples, and everyone has children, and everyone lives through their child-bearing years, every couple would have two children, one to replace each of them. In reality, none of the above caveats are true so the replacement number is higher, close to 2.1 in the United States, and around 2.33 worldwide.
However, while this number holds true for one generation, it falls apart in the second generation and is not particularly useful when attempting to figure out future population growth. That is because the number is gender neutral, and to be quite honest, when it comes to reproduction, men are irrelevant. Take for example, if you have 10 people and the ratio is 9 women to 1 man. Those women could theoretically give birth to 9 babies a year, allowing the population to explode. However, if the ratio if 1 woman to 9 men, she can only physically have about one baby a year, so the population would grow much more slowly. This is a problem that China is about to approach as there are a much higher ratio of men to women than most of the rest of the world.
This is why many population geneticists use a number referred to as the "net reproduction rate"; the number of girls that a woman births in her lifetime. So if you are having kids, and are conscious of your effect on population growth, stopping after two boys will prevent population growth in the next generation, and really slow it in the next. Two girls, on the other hand, will lead to greater population growth in the subsequent generations (not passing any judgment about numbers of children, just reporting the numbers used by the people who work on this stuff).
3. Glass is a liquid
This one probably bugs me more than it should because I am a geologist, but I am putting it up here anyway. We have all heard at some point that glass is a liquid (or a fluid solid) and that it flows very slowly. People frequently point to old windows that are thicker at the bottom than at the top. However, this is not caused by flow in the glass.
The reason ancient windows are often thicker at the bottom than at the top has to do with the way they were made. Anyone who has been to a renaissance festival has seen the resident glass blower, and that is how window glass used to be made. Effectively, molten glass would be spun, forming a disk. But this had the result of making the glass thicker at the edges of the disk than in the center. Later, when mass-production of glass for windows began in the 20th century, glass was formed by pouring it on a table. This created thicker glass where the molten glass was poured. When the glass was cut for the windows, it was installed with the thicker side down for several reasons, including it is more stable that way, and it served as a way to shunt rain away from the base of the window. If you visit the ghost towns of the American west where the houses popped up quickly, it is not uncommon to find windows where the thickest part is at the top or the sides because of sloppy work done for the sake of speed.
A favorite proof of mine that glass is not a liquid has to do with the birth of modern science. In the 17th century, Galileo made a number of very precise telescopes using glass lenses. Those telescopes are still in perfect focus. If glass flowed fast enough to cause a thickening in 100 year old windows, you would not be able to see the stars through Galileo's 400+ year old telescopes any more.
Glass, to a geologist, is an amorphous solid. That simply means that it does not have a distinct crystalline (read: repeated) structure. There are a number of natural glasses (obsidian comes readily to mind). And anyone who has seen an arrowhead knows that the edges can be very sharp even after several centuries.
4. Black holes are super-massive
The reason that gravity is so strong at a black hole has little to do with its mass. A simple thought experiment about the formation of a black hole can demonstrate this. Our current understanding is that black holes form as a result of a supernova of giant stars. So the star explodes, ejecting its mass into space, and some amount of that mass collapses into a black hole. By definition, the resulting black hole will be less massive than the star it formed from, yet the parent star still gave off light and mass.
While mass certainly does affect gravity, it is not what makes the powerful gravitational pull of a black hole. What it really comes down to is density. Specifically, the volume in which the mass is contained. This is because the force of gravity is a function of the square of the distance between two objects.
where F = gravitational force, G = gravitational constant, m1 and m2 are the masses of two objects in question, and r is the distance between the two objects.
The parent star, while more massive, had a nuclear fusion reactor in the center of it, and the energy from those reactions, aside from creating enormous amounts of light and heat, also propels gasses away from the star. This force acts in the opposite direction of the gravitational force pulling everything to the center of the star, and the size of the star is dictated by the distance at which the gravitational force is equal to the force applied on the escaping gasses. Eventually, as the star gets older it stops "burning" hydrogen and helium and starts moving on to heavier elements. There is less energy to be gained here, and eventually the amount of outward force applied by the nuclear engine becomes less than that of gravity, and the star begins to collapse. A process I don't totally understand then causes the star to explode, and subsequently the matter that has not escaped collapses in on itself. With no opposing force applied, gravity pulls the remaining matter into a super-dense object.
The point where nothing (not even light) cannot escape the gravitational pull around the black hole is called the event horizon. An important point here is that the event horizon will be much closer to the black hole than the original star's size.
Because a black hole is controlled by density and not by mass, you can theoretically create a black hole of any size. You could turn your coffee cup into a black hole, it is just the event horizon would be femto-meters across. In fact, there are thousands of so-called nano-black holes that form at the top of our atmosphere every day. The Large Hadron Collider (LHC) under Switzerland/France will create these nano-black holes in an attempt to study the origins of the universe.
It is also a myth that black holes never die. They also have a lifespan just as stars do, but their deaths are much less spectacular than the supernovas that produce them. But that is a story for another day.
5. "It's just a theory"
Most of you guys probably know this already, but this drives me absolutely nuts, so I have to include it but I won't belabor the point. The colloquial use of the term theory as simply an idea is completely wrong. In science, when we have an idea to explain something we call it a hypothesis. The expression "it's just a hypothesis" would be perfectly valid. But after hundreds to thousands of tests on a hypothesis has been unable to disprove it, the hypothesis becomes a theory. A theory is the strongest term we can use in science to describe a concept. Sure there are laws in physics, but we don't use laws in the natural sciences. So when a natural scientist describes something as a theory, you can generally take it to the bank as correct.
For those of you who made it this far, thank you for staying with me through my rant. This was very therapeutic. There are plenty of scientific misconceptions out there (Bernoulli's principle as the reason planes fly for example), through no fault of the general public, but if I went much longer I think I would start clogging the inter-tubes. Maybe I will post some more later.