Category Archives: Science

Do Eggs Gain Weight?

A second grade classroom at my school incubated chicken eggs until they hatched. When their feathers had dried, the fluffy chicks looked too big to have been enclosed within the broken shells still lying in the incubator.

One of the eggs did not hatch. For some reason, the chick inside had gone lifeless and would never break out into the wide world. Mr. Watts, the teacher who had run the whole project, handed it to me. “Feel this,” he said. “It seems heavier than it was in the beginning.”

I gently shook the egg from side to side, feeling the dead weight shift within the shell. Truly, it felt heavier than the eggs I buy for omelets. Was it because this egg had been fertilized and transformed into a nearly-finished young bird? Is it possible for an egg to gain weight while the chick grows inside?

My first thought was that it could not have gained any mass, because it had not eaten anything from outside the shell. Everything inside an egg until it hatches was in there since the moment it was laid. The chick forms from a small part of the material, and absorbs most of the rest as it grows. Since it does not eat or absorb anything from outside the egg, it seemed unlikely that it would actually weigh more at the end of incubation than it had at the beginning.

Since I am not an expert in birds or their eggs, I decided to do some research. The best article I found was on the Poultry Club of Great Britain website, which you can read here if you like. According to the article, a healthy chicken egg loses about 13% of its mass during incubation. Otherwise, the chick does not have room to move around enough to break the shell with its egg tooth, and dies inside the egg as a result. Maybe that is what happened to the egg that inspired this article.


There was one other thing I was unsure of. A chicken breathes oxygen and wastes carbon dioxide, like all animals on Earth. Would it not have to breathe through the shell? If so, there might be gases coming into the egg from outside, which might add mass.

It turns out that there is an exchange of oxygen and carbon dioxide through the shell, but since carbon dioxide is heavier than oxygen, this would reduce, rather than increase, the egg’s mass; indeed, this is one of the reasons – humidity being the other – that the egg loses weight.

Why did the egg feel heavy? Probably because an unfertilized egg – like the ones I get at the grocery store for my omelets – is all liquid inside. The egg with the unhatched chick had much less liquid, a larger amount of air, and a solid mass shifting around, which gave an illusion of added weight. I am reminded of when my children were small. When they would fall asleep and I carried them to bed, they felt heavier than when I would give them a piggyback ride. Their limp and sleeping bodies felt heavier, even though their weight had not changed.

My sons are much too big and heavy for me to carry anymore. But getting old has nothing to do with the weight of chicken eggs, so I suppose this post is done.

What You Don't Know Can't Hurt You…Right?

Gravity, it seems, has become a controversial subject once again! For most of my life I had been under the impression that gravity is an attractive force; every reference work I have found describes gravity as being attractive; yet apparently there is a portion of the population who disagrees. Let me elaborate.

The school where I work is, on election days, a polling station. Upon such occasions, the polling booths are set up near the main entrance; students are routed away from there, and everything proceeds as normal. I appreciate the dedication of the volunteers who monitor the polls all day, and usually stop on my way out to exchange a thankful comment or a bit of polite banter, depending on how tired they appear. A couple of weeks ago, one of the volunteers seemed to have had a very hard day. His face bore a heavy frown of weary disgust. I made the mistake of trying to cheer him up. My new business cards had just arrived from the print shop, and I handed him one with a friendly smile. The cards advertise this website; the front side asks “Are you terribly curious?” and the back reads simply “”. When I give someone a card, the usual response is to read the front and ask, “What’s this?” Whereupon I reply, “You see? It works!” Not the cleverest thing in the world, but it’s nearly always good for a quick grin.

Not that day! My disgruntled victim looked at the card and sneered, “What’s this?” I was already regretting my choice of daily public relations, and decided against the banter.

“It’s a general knowledge website,” I explained. Waving my hand about in an awkward fashion, I added needlessly, “I’m a teacher.”

His sneer grew into a snarl. “Hah!” he spat, obviously of the persuasion that teachers fall somewhere between pickpockets and drug dealers on the scale of social undesirables. “All right then!” he continued, as if to say let’s see if you know your stuff. “Is gravity a push or a pull?”

I hesitated for a second. My class had just finished experimenting with gravity; we had established to our satisfaction that an object held above the floor will, upon being released, fall to the floor. We had furthermore concluded that this behavior was due to a pulling force known as “gravity”. I considered the possibility that the gentleman confronting me was joking in a strangely belligerent mode, but a second glance at his expression rendered that hypothesis incredible. I gave the most concise answer I could: “Gravity is an attractive, or pulling, force.”

“Huh!” My antagonist tossed the card on the registration table in an overt gesture of perceived worthlessness. “Shows how much you know. Gravity is a push! Look!” And he pulled a pen from his pocket, held it high above his head, and dropped it. As it hit the tabletop, he threw his head back and fixed me with a glare of triumph worthy of Louis Pasteur showing a germ through a microscope to a disbelieving critic.

I tried to smile without showing my teeth. “I’m afraid I have to disagree. You see, the pen falls to the table because of the Earth’s gravitational field. The origin of that field is the Earth’s center of gravity; the pen falls toward the origin, thus the force is attractive, or a pulling force.”

He was utterly unimpressed. With a final contemptuous grunt, he dismissed me and all my heresy with a dismissive wave and turned away; the interview had come to an end. I walked away mystified. How had this poor man grown as old as I with so little understanding of basic scientific principles?

Alas, in our time science has become politically useful, and therefore subject to controversy. The USA has the dubious distinction of being the only nation in the industrialized world in which a significant percentage of the citizenry flatly disbelieves what passes for common knowledge in the rest of the planet.

We need conservatives to make sure we keep those things worth keeping as we travel, each moment of every year, from past to future. Just as importantly, we need liberals to make sure we continue seeking the best possible future instead of clinging to a past which, every second, disappears beyond recall. As an educator, my nature is to work for the increase of knowledge. Our nation will not long remain competitive if we reject any knowledge gained simply because it does not fit our current understanding. The result would be a scientific community made up of individuals like my befuddled friend at the polling station. Our national pride would be the least of our losses. What we don’t know can indeed hurt us.

Why Can't We Travel Faster Than Light?

James writes: I know light is the fastest thing in the universe, but why can’t anything else go that fast? Is it just that we haven’t built a ship fast enough yet?

James, I am no physicist. I believe I understand the reason for “lightspeed” being the cosmic speed limit, but I could be wrong. Here goes my best shot:

The hard part, to me, is why light travels at a constant velocity – and why that velocity is 299,792,458 meters per second (in a vacuum; going through air or other media slows it down). I have no idea why light travels at exactly that speed, instead of going faster or slower. But Albert Einstein’s famous relativity equation – E=mc² – explains why we cannot build a ship that goes that fast.

In the relativity equation, “E” stands for the energy of an object. The “m” on the right side of the equation is the object’s mass. And “c” means “constant”: the velocity of light. In math, a constant is a value that does not change. Variables are properties that can change. “E” is a variable, because the energy an object has can change. For example, if a karate master moves his fist very slowly towards a wooden board, he might push it out of the way, but the board will not break. But if the karate master throws a fast punch at the board, his fist will break through it easily. Why? Because his fist had much more energy when it was moving fast. Energy increases with speed; this is why cars (and passengers) are damaged a lot worse if they crash at high speeds than if they crash when moving slowly.

An equation is a statement that both sides are equal, like 3+2=5. The left side equals the right side. If we add to the left side, we must add the same value to the right side for the equation to be true: 3+2+1=5+1. Einstein’s relativity equation states that an object’s energy is equal to its mass multiplied by the square of a constant, “c”. The constant does not change, so if “E” changes, “m” must also change. In effect, an object moving very quickly becomes more massive.

More mass means that it takes more energy to accelerate. This is why a Ferrari can accelerate faster than a dump truck, even if the dump truck has more power. So if we build a starship and move it faster and faster, its mass will begin to increase. The more massive it is, the more energy it takes to make it go faster. As we approach the speed of light, the mass becomes so great that it would take an infinite amount of energy to make it go as fast as light. Since we do not have an infinite amount of energy, we cannot reach lightspeed.

That is as much as I understand about your question, James. I hope it helps. If there are any physicists in the audience who can explain it better, or correct any mistakes I have made, I will appreciate it.

Stay curious, my friends!

It's Bad Luck to be Superstitious

“Superstition brings bad luck.” – Raymond Smullyan

Do you avoid stepping on cracks? Does it make you worried if you spill the salt, or break a mirror, or walk under a ladder? Are you afraid something bad will happen if a black cat crosses your path? If so, you are not alone. Many people share these – and many other – superstitions. But where did all these beliefs come from?

Merriam-Webster’s online dictionary defines superstition as “a belief or practice resulting from ignorance, fear of the unknown, trust in magic or chance, or a false conception of causation”.

In everyday English, there are several reasons why the world seems not to make sense. One of these reasons is not having enough information to understand why things happen. It is easy to see patterns in the world around us; the human brain seems to be hard-wired for recognizing patterns. When we detect a pattern, we like to find the cause for the pattern. For example: on the twentieth day of every month, I feel a little more happy and relaxed than on other days. Why could this be? Is there something magical about the number 20? Not at all: I get paid on the twentieth of each month. But if you didn’t know that, and failed to guess the truth, you might find some other explanation.

Another reason for being superstitious is feeling afraid of what might happen. Nobody knows exactly what will happen in the future; yet some of us fear it and others do not. If you feel that you are in control of your life (whether this is true or not), you will not fear the future. If you feel that you have little or no choice in your life’s events, you will probably feel some degree of fear when imagining the future.

Finally, it is possible to believe that things happen for a reason, and still be wrong about the reason. For example, before discovering germs, most people around the world believed that diseases were a punishment from Heaven, or caused by evil spirits hovering in the air! (When Dr. Semmelweiss proposed in 1847 that diseases were caused by germs, the other doctors made fun of him. They got him kicked out of the hospital where he worked. They even had him declared insane and locked up. But that is another story!)

It is pretty easy to prove that diseases are caused by germs, so not many people are superstitious about sickness anymore. But many old superstitions are still popular, probably because there is a bit of truth to them!

Walking Under a Ladder

Walking under a ladder is considered bad luck in many parts of the world. The reason for this one is fairly obvious: the more you walk under ladders, the more likely you are to knock them over and get pelted with buckets of paint, metal tools, construction workers, and whatever else is at the top of the ladder. There is really no reason to be superstitious about ladders; it is just good common sense to walk around them instead of under them.

Breaking a Mirror

Breaking a mirror is supposed to bring seven years of bad luck. The reason for this is not quite as obvious as the one about ladders. Yes, when you break a mirror, there is always the risk of cutting yourself while picking up the pieces; but a cut will heal in seven days, not seven years. Why would anyone believe seven years of bad luck?

You may not think of a mirror as a valuable and prized possession, but they were until about 300 years ago. Before then, mirrors were hand-made by artisans who knew the secret of producing sheets of glass with a backing made from mixing tin and mercury. The process was difficult and only known to mirror-makers in the city of Venice, and mirrors were extremely expensive. Most people could not afford to own a mirror. If your family had a mirror, and you broke it, they would probably be upset with you for seven years or so! Thus the superstition.

Spilling the Salt

Like mirrors, salt was difficult to produce in the ancient world. This made it so valuable that the Roman army even paid their soldiers in salt (better than gold for a soldier, as salt also can disinfect wounds and keep meat from spoiling); this is the origin of the word “salary”. The only bad thing about getting paid in salt is that it dissolves in water; if you drop it in a puddle, your salary is gone. Bad luck indeed.

Black cats

As opposed to ladders, mirrors, and salt, there is no real link between black cats and bad luck. But to the superstitious mind, always looking for a reason (and not really caring if the reason is a logical one or not), black cats are handy scapegoats. Why? Because there are so many of them all over the place. Chances are, if something good happens unexpectedly, there will be a black cat nearby. The difference is that we never look for a reason when something good happens; we seem to think we had it coming. On the other hand, when misfortune strikes, it must have been that cat!

The comedian Groucho Marx famously said, “A black cat crossing your path signifies that the animal is going somewhere.”  Which makes sense to me.

Superstition in Sports

Superstitions are most often due to a sense of not being in control of things, of wanting to gain control, but without any real plan for doing this. It is interesting – and perhaps instructive – that superstition is much more common in some sports than others. More to the point, the sports that breed superstition are the ones where the player has the least control. Baseball players are famously superstitious; golfers a bit less. These sports involve hitting hard balls with hard clubs at very high speeds and at distances that allow the wind to become a factor. Tennis players are not prone to superstition. They are hitting a soft ball with a flexible racquet over a short distance, and are able to control the ball with a high degree of confidence. Likewise, you will never hear an archer or a rifle marksman talk of superstition. Their equipment is very precise and allows almost total control of the results. Tennis players, archers, and marksmen talk about skill, not luck.

And that is why I titled this post “It’s Bad Luck to be Superstitious”. The way to achieve success is to maximize your control over as many factors as possible. Anything else is probably a waste of your time and energy. Of course, control starts with yourself – which is why it is such an unpopular word. Until you are in control of yourself – words, actions, and thoughts – you can never really be in control of anything outside yourself either. Self-control is the key to every kind of success. It is also the end of superstition.

Were the Apollo Moon Landings Real, or Not?

This summer, I took my two sons and my nephew to the Frontiers of Flight Museum at Love Field Airport in Dallas.

If you like airplanes half as much as I do, you will want to visit Frontiers of Flight next time you are in the Dallas area. The exhibits cover the entire history of human flight, from Leonardo da Vinci’s sketches to the current space program. What sets this flight museum apart from most others is the sheer number of real planes on display; an aircraft enthusiast could easily spend all day there learning and exploring, and every time I visit, there seems to be something new to see.


The best piece of all is the Apollo capsule. This is not a replica. It is the actual command module from the Apollo 7 mission. That fact in itself is enough to make me stand silently for a few moments every time I visit, and reflect on the audacity of the human spirit. Three human beings sat in that very box for eleven days, the rude metal cone hurtling through the vacuum of space at 50,000 miles per hour, guided by a primitive calculating machine with far less power than any cellphone you can buy today. Their courage and skill paved the way for the triumphant moment a year later, when an air-breathing mammal from Earth set foot on the dusty, airless surface of the Moon with the unforgettable words “one small step for a man; one giant leap for mankind.”


The Apollo capsule represents something that makes me proud to be a man. That’s why it makes me sad when a student asks me if the moon landings were real – because they read some silly web page (written by someone too ordinary to capture anyone’s attention without capitalizing on fear, distrust, and ignorance) about how the whole space program was faked.


The Apollo program was a giant leap for humankind. It was a gigantic push, by a nation of dreamers, to go where no one had gone before, to do the impossible. It took a decade and cost $25 billion, which sounds like a lot of money until you compare it with the amount we spend on other kinds of hardware from stealth bombers to aircraft carriers (if you care to research this, make sure you look at operating costs, not just cost to build). And I have no doubt whatsoever that Apollo was a genuine program that delivered genuine results – among the most spectacular results ever achieved by any human enterprise. The reason for my lack of doubt is called Occam’s Razor.

Occam’s Razor is a general rule of logic, the idea being that when you have to choose between a number of explanations, the simplest one – the explanation that requires the fewest assumptions to support it – is the most reliable.

There are many websites devoted to the idea that the Apollo moon missions – if not the entire U.S. space program – were a hoax. I will not list all the arguments here; you can find them easily enough if you are interested (or more likely, if you are really bored). The most obvious weakness of these theories is that they fail the test of Occam’s Razor. They depend on many more assumptions without evidence to support them – let alone the fact that they fail to explain how GPS works if we never went into space. But the thing that annoys me the most about these people is the way they disrespect all the courageous astronauts who risked their lives – and a few who lost their lives – for the sake of lifting a nation’s eyes and spirits to the stars. I wonder if they would have the nerve to look Buzz Aldrin in the face and call him a liar. Somehow I doubt it.

How Can I Stop Hiccuping?

A hiccup (or for all good folks of the British persuasion, a hiccough) is defined by the National Library of Medicine as “an unintentional movement (spasm) of the diaphragm, the muscle at the base of the lungs. The spasm is followed by quick closing of the vocal cords, which produces a distinctive sound.”

Which would make a hiccup an onomatopoeion, too.

Getting hiccups seems to be an integral part of the human experience. There are all kinds of supposed remedies for hiccups, most of them less than satisfactory. If aspirin had the same failure rate as all the different home remedies for hiccups, nobody would buy it anymore. Some people will advise you to drink a glass of water; others will tell you to drink it upside down (hey, if you start choking, maybe the hiccups will go away). One common trick is to hold your breath. Another is to have someone startle you, which usually only works after you have forgotten to expect them to startle you, by which time the hiccups may have stopped on their own. Personally, I have had the best luck emptying my lungs and holding my breath out. Nothing works all the time; some of them may not work for you at all. Still, I would bet that every one of us has been able to beat the hiccups at least sometimes. What is the best way to make them stop?

Going back to the definition of hiccups, we see that they are spasms (or quick involuntary movements) of the diaphragm, which is the large flat muscle dividing the chest cavity from the abdomen, and which we use to force air in and out of the lungs. So hiccups don’t just make it hard to breathe; they do so because they take over the function of the breathing muscle.

The trick to making hiccups go away is to regain breathing control. Any exercise, involving water or not, that helps you control your breath will also help rid you of hiccups. If it doesn’t work immediately, don’t give up. You are taking back control of your own muscle, and it will work if you persist.

Some cases of hiccups have a pathological cause, and need to be treated medically. The Guinness Book of World Records has Charles Osborne as the hiccup champion of all time; he was unfortunate enough to have hiccuped more or less continually for 68 years. There is no record of a cause for this lifelong affliction; but another man, Christopher Sands, suffered from hiccups for over two years due to a brain tumor putting pressure on certain nerves.

One thing makes more sense to me than the rest. The phrenic nerve is connected to the diaphragm, and seems to be involved in hiccuping. Some doctors advise pinching the skin over the deltoid muscle (the deltoid is the big muscle on the outside of the shoulder that looks like a triangle – or the Greek letter delta); a branch of the phrenic nerve passes over this muscle. Even if this doesn’t take care of the hiccups, it always feels nice to get a shoulder massage. I think next time I have hiccups, I will ask for a shoulder rub! If I can hold my breath and drink a glass of water while getting my shoulders rubbed, I think my chances are pretty good.

Good luck fighting the hiccups!

Will We Ever Find A Dinosaur Frozen In A Block Of Ice?

I love the “Ice Age” movies. Who doesn’t? Granted, they kind of go downhill after the first one, but it’s a gentle slope, and making a sequel better than the original is arguably impossible. Don’t get me started on Star Wars.

One of my favorite scenes from “Ice Age” is the one where the oblivious Sid, lost in the ice cave and peering at the walls with his natural curiosity, is startled by a frozen fish with large needle-sharp teeth. He turns quickly away, only to be confronted with a much larger, much scarier specimen: a Tyrannosaurus Rex, razor jaws gaping, frozen into the icy wall. Sid continues past a row of frozen fossils in phylogenetic order; all share features in common with Sid. As he reached the end, he stops, completing a tableau of his own evolutionary history.

The last time I saw the movie, someone asked if a dinosaur had ever been discovered frozen in the ice. I said that we haven’t, which prompted the question whether we ever would make such a discovery. What a find that would be! Much as I love the idea, it is very unlikely. I don’t like to say “impossible” – too many things once considered impossible have already become reality – but in this case, it might not be too strong a word.

The frozen dinosaur in the movie was buried deep in a glacier. Glaciers are frozen rivers; they flow downhill towards the ocean just like any other river, but much more slowly. As the bottom of the glacier melts, the top is being formed out of snow that falls high in the mountains where the glacier begins.

For an animal to become trapped in a glacier, it would have to die high up in the snowy mountains where glaciers form. The animal would be covered over with snow that would slowly turn to ice as it built up over centuries. After some thousands of years, it might be found deep inside a glacier like the frozen dinosaur in “Ice Age”.

As far as I know, nobody has ever found an animal frozen inside a glacier. It may have happened, but I doubt it. Animals need food, and there is nothing to eat high up in the eternal snows where glaciers begin. Humans are the only things that climb around glaciers on purpose. If an animal got lost in the mountains, it would die long before it could reach the source of a glacier.

We have learned many things about dinosaurs since I was a child. Some scientists think that certain dinosaurs may even have been partly warm-blooded, like some fish are. But no one is suggesting that dinosaurs were able to live in icy Arctic conditions. There may have been mountains with glaciers during the Triassic, Jurassic, and Cretaceous Periods when dinosaurs were alive, but the dinosaurs would never have been anywhere near the tops of those mountains.

It is a pretty sure thing that no animal, much less a dinosaur, will be found preserved inside a glacier. But I still love the movie.

Why Is Our Clock So Messed Up?

One of my pet peeves – which, unfortunately, will almost certainly never change – is our system of counting time.

The standard number system for everything else in the world is the decimal system, or base-10. Place value in the decimal system is ten times greater to the left and ten times less to the right. For example, “333” means three ones, three tens, and three hundreds; “3.33” means three ones, three tenths, and three hundredths. Since five is half of ten, one half is written “0.5”. One fourth (half of one half) is “0.25”. Anyone who can read a price tag at the store can use the decimal system. It is beautifully simple to use; if you think I am exaggerating, try doing some long division with Roman numerals, or add up some groceries in binary (if you really enjoy suffering, use hexadecimal).

The decimal system is great. So why don’t we use it to measure time? An hour and a half is 1.5 hours, but when we write it in hours and minutes, it comes out 1:30 instead. This makes it difficult to calculate the cost of something per hour, because minutes are sixtieths of an hour instead of hundredths. If I rent a boat for $6.50 per hour, and I want it for three hours and fifteen minutes, I might try to multiply 6.5 times 3.15; I will end up owing money. Three hours and fifteen minutes equals 3.25 hours, not 3.15.

Here’s a simpler example. Imagine that I pay my son minimum wage – $7.25 per hour – to mow the lawn. When he finishes, the timer reads 0:35, or 35 minutes. To pay him, I have to divide $7.25 by 60 and multiply by 35. This is no fun.

What if there were 100 minutes in an hour instead of 60? Then I could just multiply $7.25 by 0.35 – a single operation instead of two.

If we divided the day (from sunrise to sunrise, or midnight to midnight) into 10 hours, each hour into 100 minutes, and each minute into 100 seconds, our timekeeping would be much easier. Of course, the minutes and seconds would be a little longer than they are now, but not that much. It would be far easier to teach children to tell time without all the twelves and sixties. Everything would be better!

So how did our clock get messed up? Why do we use a 12-base clock when everything else is 10-base?

The answer goes all the way back to the beginning of clocks. The first clocks we know of were sundials in ancient Egypt. Sundials are great when the sun is shining, but less so when it is cloudy, and not at all during the night. Ancient Egyptians divided the daylight into ten hours (sensible people!) but added a twilight hour at the beginning and another at the end of the day. Since their sundials did not work at night, this gave them twelve hours. Much later, after inventing ways to keep time during the night, people doubled the daylight hours for the nighttime. From sunrise one day until sunrise the next day, there were 24 hours (and still are today).

The number 12 works well with another number system, 60-base, which was used by ancient Babylonians (who were very good astronomers despite having a horribly clunky number system). The ancient people of India and Sri Lanka were also great astronomers and used 60-base systems; our word “hour” comes from the Indic word “hora”.

No matter how good ancient people were at astronomy, I think we would be better off with a decimal time system. But that is not likely to happen, because all the systems used all over the world by 7 billion people use the 12-base clock. Oh well!

If You Fell Through a Black Hole, Where Would You Go?

Black holes are definitely some of the most mysterious things in the universe. A hole that looks the same from all sides is quite a puzzle!

If I were to go up into the attic and saw a circular hole around me, I would fall down into the living room. Likewise, if there were a hole in my living room floor, I might keep falling down into the basement. This is easy to imagine. It is not too much harder to picture gravity reversing, so that I would fall up from the basement through the hole in the living room floor, ending up back on the couch where I started. In each of the three places I had been – the living room, the attic, and the basement – I could look through (or fall through) a hole to another space.

Before I start talking about black holes, I should say that everything we know about them is based on math. Until 1971, there was no observed evidence that they even existed. Today, there are many known black holes, but we will never see one of them directly, so all our knowledge of black holes is based on measurements of things happening in space that cannot be explained without the math model of a black hole. Most of my readers are not math professors, so you may be wondering what I mean by “math model”. If I tell you that I am thinking of an object that is 5 cm long, 5 cm wide, and 5 cm tall, you could guess that it is a cube. But what if it is a sphere? All you really know is how big it is. Now, if I tell you that the object has six square sides, you know it is a cube. You can picture it in your mind. There is no real cube, but your image of it is based on numbers I gave you. The cube in your mind is a math model.

Remember the holes in my ceiling and floor? Now imagine a hole in the middle of empty space. It is not a hole in a wall or anything else; it is a hole in space. You might be able to see the hole if you got close enough, but you would not be able to see through it. If you moved in a big circle around the hole, it would look the same from any angle! If you were to throw an object – like a marshmallow – through a hole in a wall, you could look over the wall (or through the hole) and see the marshmallow on the other side. But if you threw a marshmallow into a black hole, there is no other side. It is gone forever!

How can this be? About 250 years ago, a scientist named John Michell imagined a thing nobody had thought of before.

(Scientists of his time already knew that objects had to reach a certain speed to escape the gravity of any planet or star; this speed is called the “escape velocity”. The more massive a planet or star is, the faster an object has to move to escape out into space. This is why a rocket can get to the moon, but a bullet from a gun cannot. It is not fast enough. A rocket fast enough to escape the Earth’s gravity would still not be able to escape the Sun, because the Sun is so much more massive than the Earth. You would need a much faster rocket. On the other hand, if you have seen pictures of the Apollo missions to the Moon, the rocket they used to get off the Moon was not very fast at all. It didn’t have to be; the Moon is much less massive than the Earth, so its gravity is much weaker.)

John Michell imagined a star so massive that even light would not have enough speed to escape its gravity. If the light from the star could not escape out into space, then nobody would be able to see it! John Michell called his imaginary star a “dark star”. Later scientists, including Albert Einstein and Karl Schwarzschild, made math models of dark stars to describe the behavior of light and of objects that got close to them. It was a scary but fascinating idea! In 1964, a journalist named Ann Ewing wrote a report about these math models. The report was called “Black Holes In Space”. Since then, people have been calling them “black holes”.

Even though many scientists made lots of math models of black holes, nobody had ever seen one. They are, after all, invisible! Between 1971 and 1973, a team of astronomers watched a giant star far out in space. It behaved unlike any other star. By 1973, they knew from their measurements that the star had a black hole next to it, just like you knew (after getting enough information) that the object I was describing was a cube. The star system fit the math model: it could only be a black hole!

That first observed black hole is called Cygnus X-1. Since then, we have observed many other black holes. Although they are invisible, we know they are black holes from observing what happens around them. If it fits the math model, it must be a black hole.

So what is the answer to the question we started with? If you fell into a black hole, where would you go? By now, you know that black holes are not really holes at all. They are objects with such strong gravity that nothing, not even light, can escape them, which is why they are perfectly dark. Because its gravity is so strong, anything that falls into a black hole is crushed into zero volume. Since one of the properties of matter is that it takes up space, objects falling into a black hole would really not even be objects anymore. The center of a black hole is called a “singularity”, and the math model for a singularity seems to break the rules for what we know about the universe.

Black holes may always be one of the universe’s mysteries!

How Do Baby Turtles Know To Crawl Towards the Water?

There is a beautiful park a couple of blocks from my house. Groves of big shady trees line the shores of the lake; the footpath winds through the trees, over bridges and around an open field perfect for flying kites. It is a nice place to go for a walk, or a bicycle ride, although the summer here is too hot to be outdoors except early in the morning or after sundown.

Yesterday we rose early and rode our bicycles down to the park. The air was still cool in the shade, but the sun was up and it would be hot before long. As we turned onto the path, I spotted a large turtle, a red-eared slider, in the grass near the path. It was a good fifteen meters from the water, which was strange; when the turtles pull themselves up onto the bank to bask in the sun, they usually stay right at the water’s edge, ready to slide back into the lake at the first sign of someone approaching. Why was this turtle so far from the safety of its habitat?


I stopped and signaled the boys to come slowly and quietly. As we watched, the red-eared slider dug into the ground with its hind legs and began laying a clutch of eggs! Slowly it began to scrape the soil back into the hole to cover them up.

Turtles, like all reptiles, are exothermic (or “cold-blooded”); they depend on the environment to warm or cool their bodies. If a turtle lying on the shore gets too hot, it goes back into the water to cool its body. But this turtle was a long way from the water (at least, for a turtle!) As I watched the turtle covering its eggs, I began to worry that it would overheat. The spot it had picked to dig its nest had been in the shade when it began digging, but now the sun beat down directly on the turtle’s shell. I wondered how long it would take for the turtle to finish covering its eggs and drag itself back down to the lake.

I need not have worried. A few minutes later, the nest covered and nearly invisible, Mother Red-Ear was on her way back to the cool water. She stopped in the shade of a hackberry tree to rest beside a fallen branch. Soon she was back in the water.


Andres asked, “When the baby turtles hatch, how will they find the lake? What if they go up onto the road instead, or get lost in the park?”

The short answer is that aquatic turtles hatch with the instinct to go straight for the water. They don’t know where the water is, or even what it is; they have no experience at all, yet they all head for the water as quickly as a baby turtle can (which is quite a bit faster than the adults, on land anyway). Instinct drives them; they can’t help it. The reason for this instinct is obvious: the ones, long ago, who went in any direction other than the water failed to survive, and never grew up to pass that trait on to their offspring. Today, all aquatic turtles are descended from turtles who survived by seeking the water as soon as they hatched, and so all aquatic turtles have that instinct.

So turtles go to water because of survival instinct. But what makes a hatchling turtle move in the right direction? There must be something a baby turtle can sense in order to trigger the instinct. Since gravity makes water lie in the lowest part of any area, it makes sense to think that newly hatched turtles would follow the slope of a beach or lakeshore down to the water. Another possibility is that the mother turtle leaves a scent trail for the hatchlings to follow, but since the eggs take two to three months to hatch, it seems unlikely that there would be much of a scent left to detect. Finally, researchers have observed that baby sea turtles can become confused by electric lights near the beach, becoming attracted to the lights instead of the water. On a beach with no electric lights, the brightest place is the water because it reflects moonlight or starlight from the sky. Maybe turtle hatchlings find their way by the difference in brightness between land and water.


Our turtle’s eggs should hatch towards the end of summer. We will be watching for the baby turtles to crawl down to the lake. One way or another, they will find the way!