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How to make sparks fly in your mouth
We're issuing a science-based exception to the "don't chew with your mouth open" rule for this one. If you crunch Wint-O-Green Life Savers with your mouth open in the dark in front of a mirror, you should see some sparks start to fly. The light you see is due to a phenomenon called "triboluminescence."
When you chomp down on a mint, your teeth are fracturing crystals of sugar. This fracturing happens all the way down at the molecular level, where chemical bonds are broken. Because of the structure of the sugar crystal, the breaking of these chemical bonds causes a build-up of electrons that creates a miniature electrical field. Eventually, the electrons glom onto molecules like oxygen or nitrogen in the air, and emit a bit of light in the process. Usually we can't see this light because it's in the ultraviolet part of the spectrum. But wintergreen candies contain a compound called methyl salicylate that fluoresces, converting that UV light into visible blue light.
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Why do Pop Rocks pop?
Carbon dioxide gas is the chemical key to making Pop Rocks crackle in your mouth. Pop Rocks are made by heating a mixture of carbon dioxide and candy (a combination of sugar, corn syrup, lactose, and flavoring) to temperatures above 320 degrees Fahrenheit inside a pressurized chamber. While there's still 600 pounds per square inch of pressure on the mixture, the candy-carbon dioxide combination is cooled. After cooling, the pressure is released and the candy shatters into pieces full of tiny bubbles of carbon dioxide gas.
When you stick some Pop Rocks in your mouth, the candy melts and the carbon dioxide bubbles escape from their sugary prisons with satisfying pops.
And, despite any rumors you might have heard, eating Pop Rocks and drinking soda together won't cause your stomach to explode. That urban legend seems to have spread based on the false notion that pop rocks and soda would combine like an acid and a base and react violently — but since they both just get their fizz from carbon dioxide, the worst thing that would happen to you would be a really big burp.
Why do Mentos and Diet Coke create a geyser?
While you won't get much of a thrill from mixing Pop Rocks and Coke, if you pop some Mentos mints into a bottle of Diet Coke, you'll get to see an impressive geyser:
In some ways, the reaction looks like a science fair volcano. But unlike a baking soda-vinegar geyser, the candy isn't combining with the Coke in an acid-base reaction (none of the ingredients in Mentos are basic). Instead, the Mentos serves as a little factory and launchpad for carbon dioxide bubbles — supercharging the normal bubble-formation process in the Coke. The mint's rough surface has thousands of tiny pores, an ideal landscape for lots of bubbles to form (a process called nucleation). As the bubbles grow they become more buoyant and float up to the top of the soda. The process keeps chugging along, creating more and more bubbles until it explodes out the top of the bottle in a foamy overflow.
Certain ingredients in Mentos, like aspartame and potassium benzoate, also speed the process by acting as surfactants — chemicals that lower the surface tension of the soda. This makes it even easier for bubbles to form on the candy. Too much surface tension in a liquid doesn't allow for much bubble formation — the attractions between molecules in the liquid are strong enough that the molecules at the surface resist moving up and away. Adding a surfactant, like Mentos in Coke or soap in water, loosens the liquid molecules' hold on each other a little bit, allowing for bubbles to form.
Appalachian State University physicist Tonya Coffey wrote an in-depth paper on the science behind the Coke-Mentos reaction published in the American Journal of Physics in 2008. Coffey found that combining Diet Coke and Fruit Mentos yielded the most impressive horizontal spray distance, flinging the soda nearly 17 feet from the bottle.
Making candy dance
For a less explosive demonstration of the powers of carbon dioxide fizziness, you can drop a few pieces of various kinds of candy or food into a glass of clear soda and see what happens. Anything with a rough surface — like raisins, or Valentine's Day conversation hearts — should provide a good surface for bubbles to form, as we saw with the Mentos. If the candy (or raisin) is light enough, the carbon dioxide bubbles should be able to buoy it up to the surface; when the bubble pops, the candy (or raisin) falls back down again. This up-and-down "dance" should last until the soda goes flat.
See the spectrum in black jellybeans
Plunk a wet black jellybean down on a piece of filter paper, and you'll be able to see that its blackness is actually made from a combination of hues. The various dyes in the bean will travel different distances away from the jellybean on the filter paper due to their different properties. Some shades of dye are more water-soluble, meaning they dissolve more easily and can be carried along the paper further. Some colors will be more attracted to the paper. The resulting rings of colors are called a separation pattern — something chemists use all the time to figure out what different chemical ingredients are in a mixture. You can try this same experiment with other colors of jellybeans and with other candies as well.
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How to grow giant gummy bears
If you leave gummy bears in tap water for a while, they'll swell up into something more like Gummy Grizzlies. The reason for this is the process of osmosis — the tendency for water to perform a balancing act where it flows from a solution with fewer molecules dissolved into it into a solution that has more molecules in it (provided the two solutions are accessible to each other through a semipermeable membrane that allows certain molecules to cross its border, but which screens out others).
Gummy bears are actually a solution of water. These candies start out as a liquid mixture of water and gelatin, which is heated and then cooled, a process that draws water out of the bear and hardens it into a chewier texture. But there's still some water trapped in the matrix of gelatin that forms the bear. When you stick a gummy bear in water, osmotic pressure forces water molecules into the gummy bear, making the candy swell up like a sponge.
How to take the M off an M&M
If you leave an M&M or a Skittle in water for a little while, the 'M' or 'S' should peel off and float up to the surface. That's because the letters on the candy are made out of white edible ink that doesn't dissolve, unlike the dyes that color the candy shell.
Making soap bubbles with candy corn
This is one experiment you won't be able to do at home, unless you happen to live in a low-gravity environment:
NASA astronaut Don Pettit used his special stash of candy corn on the International Space Station to model how soap works. Soap molecules have a hydrophobic (water-hating) end and a hydrophilic (water-loving) end. When you scrub something with soap, the hydrophobic ends of the soap molecules automatically point towards little globules of grease and oil on your clothes (or your dishes, or your skin); eventually, the particles of grease are encased in little bubbles of soap and can be rinsed off with water.
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With his candy corn experiment, Pettit did the same trick, but in reverse: He coated one end of his candy corn pieces with oil, making it hydrophobic, then started adding kernels to a floating sphere of water. The hydrophobic ends naturally oriented themselves away from the center. After Pettit added enough candy corn, the sphere reached what's known as the "critical micelle concentration." The candy corn sphere wasn't mushy anymore, but behaved like a solid ball — or like a soap-coated grease globule ready to be rinsed off and away.
Why microwaved marshmallows puff up
Put a couple marshmallows in the microwave for about a minute, and you'll see them puff up. This is because the heat from the microwave softens the sugar in the marshmallow, and also causes the air pockets inside the sweet to expand. Because the sugary walls of the marshmallow are softer, the marshmallow puffs up. When cooled, the marshmallow shrinks down again — but is usually a bit crunchier than before, probably because some of the water inside it evaporated in the heat of the microwave.
Earth's climate is changing rapidly. We know this from billions of observations, documented in thousands of journal papers and texts, and summarized every few years by the United Nations' Intergovernmental Panel on Climate Change. The primary cause of that change is the release of carbon dioxide from burning coal, oil, and natural gas.
Negotiations about reducing emissions grind on. But in the meantime, how much warming are we already locked into? If we stop emitting greenhouse gases tomorrow, why would the temperature continue to rise?
The basics of carbon and climate
The carbon dioxide that accumulates in the atmosphere insulates the surface of the Earth. It's like a warming blanket that holds in heat. This energy increases the Earth's surface average temperature, heats the oceans, and melts polar ice. As consequences, sea level rises and weather changes.
Since 1880, after carbon dioxide emissions took off with the Industrial Revolution, the average global temperature has increased about 1.5F (0.85C). Each of the last three decades has been warmer than the preceding decade, as well as warmer than the entire previous century.
The Arctic is warming much faster than the average global temperature; ice in the Arctic Ocean is melting and the permafrost is thawing. Ice sheets in both the Arctic and Antarctic are melting. Ecosystems on both land and in the sea are changing. The observed changes are coherent and consistent with our theoretical understanding of the Earth's energy balance and simulations from models that are used to understand past variability and to help us think about the future.
Slam on the climate brakes
What would happen to the climate if we were to stop emitting carbon dioxide today, right now? Would we return to the climate of our elders? The simple answer is no. Once we release the carbon dioxide stored in the fossil fuels we burn, it accumulates in and moves amongst the atmosphere, the oceans, the land, and the plants and animals of the biosphere. The released carbon dioxide will remain in the atmosphere for thousands of years. Only after many millennia will it return to rocks, for example, through the formation of calcium carbonate — limestone — as marine organisms' shells settle to the bottom of the ocean. But on time spans relevant to humans, once released the carbon dioxide is in our environment essentially forever. It does not go away, unless we, ourselves, remove it.
If we stop emitting today, it's not the end of the story for global warming. There's a delay in temperature increase as the climate catches up with all the carbon that's in the atmosphere. After maybe 40 more years, the climate will stabilize at a temperature higher than what was normal for previous generations.
This decades-long lag between cause and effect is due to the long time it takes to heat the the ocean's huge mass. The energy that is held at the Earth by the increased carbon dioxide does more than heat the air. It melts ice; it heats the ocean. Compared to air, it's harder to raise the temperature of water — it takes time, decades. However, once the ocean temperature is elevated, it adds to the warming of the Earth's surface.
So even if carbon emissions stopped completely right now, as the oceans catch up with the atmosphere, the Earth's temperature would rise about another 1.1F (0.6C). Scientists refer to this as committed warming. Ice, also responding to increasing heat in the ocean, will continue to melt. There's already convincing evidence that significant glaciers in the West Antarctic ice sheets are lost. Ice, water, and air — the extra heat held on the Earth by carbon dioxide affects them all. That which has melted will stay melted — and more will melt.
Ecosystems are altered by natural and manmade occurrences. As they recover, it will be in a different climate from that in which they evolved. The climate in which they recover will not be stable; it will be continuing to warm. There will be no new normal, only more change.
Glacial ice loss over Greenland and Antarctica from 2003 to 2010.
Best of the worst case scenarios
In any event, it's not possible to stop emitting carbon dioxide today, right now. Despite significant advances in renewable energy sources, total demand for energy accelerates and carbon dioxide emissions increase. I teach my students that they need to plan for a world 7F (4C) warmer. A 2011 report from the International Energy Agency states that if we don't get off our current path, then we're looking at an Earth 11F (6C) warmer. Our current Earth is just over 1F warmer, and the observed changes are already disturbing.
There are many reasons that we need to essentially eliminate our carbon dioxide emissions. The climate is changing rapidly; if that pace is slowed, the affairs of nature and human beings can adapt more readily. The total amount of change, including sea-level rise, can be limited. The further we get away from the climate that we have known, the more unreliable the guidance from our models and the less likely we will be able to prepare. The warmer the planet gets, the more likely reservoirs of carbon dioxide and methane, another greenhouse gas that warms the planet, will be released from storage in the frozen Arctic permafrost — further adding to the problem.
If we stop our emissions today, we won't go back to the past. This is not reason, however, to continue with unbridled emissions. We are adaptable creatures, with credible knowledge of our climate's future and how we can frame that future. We're already stuck with some amount of guaranteed climate change at this point. Rather than trying to recover the past, we need to be thinking about best possible futures.
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The Universe should be teeming with gravity waves. As near as we can tell, just about every galaxy has at least one supermassive black hole at its core. Most large galaxies were formed by multiple mergers, which would put more than one of these supermassive black holes in close proximity. As they get close enough to start spiraling in towards a merger, their orbital interactions should produce gravity waves. As long as this process doesn't end in a merger too quickly, the Universe's population of merging black holes should fill space with a gravity wave background.
Our Earth-bound detectors aren't sensitive enough to pick this background up. Conveniently, however, nature has provided us with its own detector: pulsars. Unfortunately, a detailed study of a handful of pulsars has failed to turn up any sign of gravity waves, suggesting it might be time to revisit some of our models.
A pulsar is a rapidly spinning neutron star. Each revolution, it sends flashes of light towards Earth, often separated by a handful of milliseconds. The timing of these pulses can sometimes be tracked with a precision of 20 nanoseconds, providing an extremely tight constraint on their expected behavior. If a gravity wave happened to ripple through the right patch of space-time as the light pulse was on its way to Earth, it could distort the timing enough to be detectable.
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