Putting the Pop in Soda

What a better way to beat the heat this summer than by enjoying a nice cold soft drink. It’s also a great excuse to learn a little chemistry! We all know that carbon dioxide is what puts the fizz in soda pop, but why not some other gas, say nitrogen for example?
   First a bit of history. In 1767, Joseph Priestley discovered a method of making carbonated water by hanging a bowl of distilled water above a beer vat at a local brewery. Priestley found that water treated this way had a pleasing taste, and he offered it to friends as a refreshing beverage. 
   In 1772, Priestley published a paper that described dripping sulfuric acid onto chalk to create carbon dioxide gas, then dissolving it into a bowl of agitated water. This process would be improved upon by others and eventually sold to pharmacies for commercial use. Before long, pharmacies were adding flavors to their soda water and the soft drink was born.
   Now back to our original question. Why carbon dioxide instead or nitrogen or oxygen? Carbon dioxide is used in fizzy drinks because it’s more soluble in water than nitrogen or other potentially suitable gases. At room temperature, you can dissolve about 1.75g of carbon dioxide into a liter of water, compared to about 0.02g of nitrogen per liter of water, and about 0.04g of oxygen in one liter of water. So, out of the readily available, nonpoisonous gasses in our atmosphere, carbon dioxide is by far the most soluble.
   Carbon dioxide dissolved in water at a 0.2–1.0% concentration and creates carbonic acid. This gives the water a slightly sour taste with a weakly-acidic pH of about 3.7 at normal bottling pressure. An alkaline salt, such as sodium bicarbonate, may be added to reduce the acidity and mimic the taste of natural spring water. This is how carbonated water came to be known as soda water, and is also the difference between seltzer water and club soda—the former does not have any sodium bicarbonate added to it.

Stromatolites

A cross section of a stromatolite showing
its characteristic dome layering.

The Pilbara region of western Australia is home to some of the Earth’s oldest rock formations, and among these formations are remnants of an ancient reef. This is no ordinary reef made of coral; it’s made of stromatolites—structures left behind by microorganisms that lived 3.5 billion years ago.
   Stromatolites are formed by algae that live on the floors of shallow seas. They collect fine layers of sediment that are built up into cones, domes and other shapes over many millions of years. A stromatolite is not alive, but is a structure made by living things. When we find one in the fossil record, it's like finding an ancient footprint. 
   The microbes that make these structures are almost never preserved as fossils inside the stromatolites. And without that it's difficult to be sure an ancient stromatolite is proof of life. But the Pilbara stromatolites are not only biologically produced, but possibly the oldest evidence of life on our planet. 
   These amazing structures have a pronounced conical shape unlike any kind of ripple pattern you would expect to see on a lifeless sea floor. Instead, stromatolites are sedimentary structures formed usually by cyanobacteria (also known as blue-green algae) that live in the interface between sediment and ocean. By examining these structures, we can tell that some lived almost 3.5 billion years ago, forming near rocky coastlines with shallow water environments. They have not been found in deep water areas that were also in existence at that time. 

Stromatolites at Shark’s Bay are fossil ancestors
to the oldest known life form on Earth.

   These fossilized ecosystems provide a glimpse of the Earth’s early history and possibly the beginning of life on our planet, as they are thought to be largely responsible for oxygenating Earth’s early atmosphere. Could life have existed even earlier? It’s possible. We don’t have any geologic record of the first 500 million years of Earth’s existence, so there is a pretty big gap in our knowledge. What's not preserved in the fossil record is how life formed in the first place. One thing we do know: that stromatolites are very distinctive and these structures are nearly identical with those of living stromatolites found at Shark's Bay, in western Australia. That means these living fossils have a family tree that stretches back farther than any other living thing on the planet. Remarkable, when you think about it.

Dragons of the Cretaceous

A giant azhdarchid compared to a giraffe.
Illustration by Mark Witton/University of Portsmouth.

Pterosaurs are flying reptiles that lived between about 230 and 65 million years ago. Although often called dinosaurs, they are actually a distinct branch of reptiles that independently evolved flight. There have been about 100 species of pterosaurs discovered so far, and one group of about a dozen species—the azhdarchids—is of particular interest. 
   In 1971, a student from the University of Texas working at Big Bend National Park discovered a long, hollow fossil bone that was from an enormous azhdarchid wing. Excavations recovered more wing bones, but no body bones could be found. It was named Quetzalcoatlus northropi, after the feathered snake god worshipped by the Aztecs. Eventually, other specimens of Quetzalcoatlus were found at the park. These specimens were smaller but more complete than the original, and by comparing them with the massive bones of the original, they were able to calculate the body size of the original specimen. This creature had an estimated wingspan of 10 meters or more and a height of over 5 meters. With a massive, elongate head, long, stiff neck and long hind limbs, this was a real-life dragon (minus the fire-breathing of course!) and the largest flying creature to have ever been found.
   Despite their huge size, azhdarchids were able to quickly launch themselves into flight from level ground by leaping from all four limbs from a standstill, without the need of cliffs. Azhdarchids were most-likely flap-gliders—capable of short bursts of powered flight while covering long distances by soaring on thermal currents.

A group of Quetzalcoatlus northropi, foraging
on a Cretaceous fern prairie. Illustration by
Mark Witton/University of Portsmouth.

   Azhdarchids have often been portrayed as feeding by grabbing fish as they skimmed the water, but it is more likely that they stalked their prey on land. Their fossils are usually found with terrestrial dinosaurs more typically found in semi-arid inland plains. They were well suited for walking and had feet that were small and padded, better for walking on solid ground rather than wading. They preyed on small dinosaurs and other animals up to the size of a large dog. Like a modern-day stork, an azhdarchid would pick up its prey, toss it to the back of its mouth, and swallow it whole.

Photons Are Weird

Single-slit pattern (above) and
double-slit pattern (below).

The classic double-slit experiment is a really good example of an amazing quantum phenomenon: interference of photons, and gets to the heart of the wave-particle duality that photons exhibit. Imagine a small light source in an otherwise dark room. On the other side of the room is a photographic plate. If we shoot a stream of photons at it, the plate will turn black. If we place a sheet of metal in between the two, the photographic plate will not turn black. 
   Now, let’s cut two thin parallel slits in the sheet metal and run a few experiments. If we cover the right slit and turn on the light, after a while we will get a black band on the film where the light has passed though the left slit. Next, open the right slit and  cover the left slit. That will give us another black band that partially overlaps the first one.
   Next, with a fresh photographic plate, open both slits. Surprisingly, you do not get the same pattern on the plate. Instead, you will get a zebra striped pattern—a series of dark and light bands. the light bands are areas of destructive interference, a well-know property of waves. This is where the light going through both slits cancel out.
   Let’s try doing the whole experiment again, but this time we will turn down the intensity of the light source so that only one photon comes through at a time, like a dripping faucet. When we cover one slit and expose the plate for a short while, we will see a few dark dots appear where the  individual photons landed. If we let it run some more, we get more dots, and if we let it run long enough we will reproduce the results of the first experiment. The photons are arriving randomly, and only after enough of them accumulate do we see the original pattern.

   Finally, let’s run this new experiment with both slits open. Remember, only one photon is passing through either slit at a time. Yet in this experiment, the photon do not land where the destructive interference took place [The figure at right is the result of a double-slit experiment showing the build-up of an interference pattern of single electrons. The numbers of electrons are 11 (a), 200 (b), 6,000 (c), 40,000 (d), and 140,000 (e).] This is despite the fact that photons can and do arrive at the very same spot if only one slit is open. In other words, if the left slit is open and the rights slit is closed, or if the right slit is open and the left slit is closed, the photon can reach the point where destructive interference takes place. But if both slits are open, not a single photon will get to that same spot. How can a single photon destructively interfere with itself? How would a photon, about to pass through the right slit, know whether or not the left slit was closed? The truth is hard to explain, but in reality the photon is not passing through either slit. It is instead going through both paths at the same time, destructively interfering with itself. 
   The double-slit experiment is remarkable in that it clearly  expresses the puzzling nature of the quantum world. The great physicist Richard Feynman said that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment: "One would normally think that opening a second hole would always increase the amount of light reaching the detector, but that's not what actually happens. And so saying that light goes either one way or the other is false. I still catch myself saying, Well, it goes either this way or that way, but when I say that, I have to keep in mind that I mean in the sense of adding amplitudes: the photon has an amplitude to go one way, and an amplitude to go the other way." I told you photons are weird!

“I am a Scientist!” Day

On Friday I had the pleasure of talking to about 60 fifth graders from Robinson Elementary School in Redondo Beach. The school was having its annual “I am a Scientist!” Day which gets students excited about science through fun demonstrations and talks from members of the science community. The presentations this year included a wide-variety of topics such as the science of magic, science and engineering in a refinery, robotics, and matter and reactions. 
   My talk was about physics. We learned that physics is the study of matter and energy, that matter is anything that takes up space and has mass, and that energy is the ability to do work. I told them that Einstein is regarded as the father of modern physics because he was able to relate matter and energy through his world-famous equation. 

The air flow from the wing of this airplane is shown
by colored smoke rising from the ground. The swirl
at the wingtip traces the aircraft’s wake vortex.

   Then we talked a bit about fluid mechanics, the study of fluids and the forces acting on them. As an example I talked about a program created by NASA and the Federal Aviation Administration in 1990 where they studied wake vortexes. The swirling airflow from the wingtip of an airplane is its wake vortex, which exerts a powerful influence on the airflow behind the plane. Because of wake vortex, the FAA requires aircraft to keep a minimum distance between each other when they land and take off. The goal of the program was to boost airport capacity by determining conditions under which planes could fly closer together. They studied wake vortexes using wind tunnels, flight tests and supercomputers in order to fully understand the phenomenon. Then they used what they learned to create an automated system that could predict changing wake vortex conditions at airports. For example, they confirmed that pilots don’t have to worry as much about wake vortex in rough weather because turbulent, windy conditions cause them to dissipate more quickly. 
   Afterwards, we did a neat demonstration of how to create a vortex using a closed cardboard box with a circle cut out of the side and a fog machine. Everyone in the class was able to create a vortex and use it to knock over a stacked pyramid of styrofoam cups. It was a fun day and I was very impressed by how knowledgeable the kids were. Also, a big thanks to my daughter Daniella who was my capable assistant for the day. Hopefully we can do it again next year!

Water on the Moon

LCROSS mapping of the lunar south pole showing
Cabeus and Shackleton craters, which have been
found to contain ice.

There is water on the Moon—lots of it. Permanently-shadowed craters at both poles have been trapping and accumulating ice for billions of years, research has shown. These cold traps contain at least 600 million tons of ice according to research done over the last few years. 
   Concentrated stores of ice on the Moon could revolutionize space travel. Lunar ice could be mined and split into its component elements hydrogen and oxygen to make rocket fuel, then brought to low Earth orbit and sold. An orbiting filling station could spur a wave of space travel because spaceships wouldn’t have to bring all the fuel they need from Earth. Considering that it costs about $10,000 to put one kilogram of payload into low earth orbit, there is a huge incentive to set up a mining camp on the Moon to tap these vast deposits of water to create a sustainable expansion into space.
   The lunar poles are unique because they have craters that never get a drop of sunlight, making them super cold. Shackleton crater, named after the famous Antarctic explorer Ernest Shackleton, is one that has been studied in detail. Situated at the Moon’s south pole, the interior of Shackleton crater is in permanent shadow. Also, the rim of this crater is in constant sunlight, making it an ideal location as a lunar outpost. Sunlight on the rim could provide energy for solar panels which in turn could provide the energy needed to harvest the water in the crater, and NASA is planning on setting up an outpost there by 2020. NASA’s Lunar Reconnaissance Orbiter (LRO) probed this impact crater with radar back in 2009. Shackleton crater was a good candidate because it is so massive—4.2 km deep and 21 km across, making it one of the deepest crater on the Moon. By analyzing the reflections off Shackleton crater, researchers discovered that is contains radar-transparent material which is consistent with ice. 

   Several other Moon missions have corroborated the existence of water on the Moon. In 2008, India’s Chandrayaan-1 spacecraft found evidence of water molecules on the lunar surface by deploying an impact probe onto the surface of the moon and then flying through the cloud of debris it kicked up. Chandrayaan-1 also mapped the moon with radar from 2008 to 2009 and found that the polar regions contained ice within the depths of permanently-shadowed craters. In 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) also discovered water and ice kicked up after an impact probe smashed into the Cabeus crater near the Moon’s south pole.

Science vs. Engineering

A solar furnace in France.

Scientists explore the world around us and make discoveries about the universe and how it works. Engineers then apply that knowledge to solve real-world problems, usually with the goal of optimizing cost and efficiency. In other words, if science is the discovery of what is possible, then engineering takes that knowledge and makes it economical.
   For example, a few weeks ago I wrote about a process for making eco-friendly cement. Researchers from George Washington University developed what they called Solar Thermal Electrochemical Production (STEP), which eliminates carbon dioxide from the cement-production process. The claim was that not only would it be more eco-friendly, but also less expensive than traditional methods. STEP would use solar energy in two ways. It would eliminate the needs for fossil fuels by using solar thermal energy to melt the limestone. It would also use solar energy to electrolyze the melt to produce lime (the main ingredient in cement), oxygen and carbon monoxide. 
   Scientifically, a very interesting idea. But let’s play devil’s advocate and take a closer look with our engineering hardhat on. Even if something can be done experimentally, it's a far cry from being profitable in the short term. One drawback of the STEP process is that it adds complexity to the production of cement, which is rarely cost-effective. 
   The research claims that by selling the carbon monoxide by-product, they could make $300 per ton of cement produced. I view this claim with suspicion. Carbon monoxide has a small and specialized market when sold by the bottle, so if this process was implemented broadly, the demand for this by-product would drop sharply. Most carbon monoxide that is currently needed is produced on-site to avoid shipping costs.
   Another point to consider is whether or not the STEP process could be portable. Most cement made today is produced by trailer-mounted units that are taken to the quarry and assembled in the field. By making the cement on-site it eliminates the need to transport tons of raw materials, especially for cement where it takes about five tons of raw materials to make one ton of finished product. It's hard to envision how a vast array of solar panels and mirrors could be transported and assembled efficiently. Another potential problem with solar power is that solar panels work best in a dust-free environment. Cement production creates a lot of dust and it would be difficult to keep the solar panels clean and operating at maximum efficiency. Also, it goes without saying that this process would not work too well in colder climates.
   One of the truths of scientific research is that much of it never ends up as part of a real production process. That’s just the nature of the game. But even if only one idea in a hundred is successful, it’s worth the price in my opinion. And even if an idea ends up not being feasible, sometimes it will lead to another discovery. Even plastic was invented by accident in an attempt to create a cheap substitute for shellac.