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What are people made of?
All life on earth is carbon-based. Carbon is the only atom that you can string together into an infinite variety of flexible chains, loops, and branches, decorated with a sprinkling of other atoms. In order for these large molecules to move, wiggle, change shape and interact with their neighbors, they need to be able to swim around in water. Thus, we are mostly made of water. In fact, Captain Jean-Luc Picard of the Starship Enterprise was once insulted by being called an ugly bag of mostly water.
Since there is no other system of chemicals that allows such variety,
scientists think that life in other parts of the universe also depends on water, and is based
on carbon. So when you want to look for life on Mars, or anywhere else,
the first thing
you have to look for is water.
As you can see, the Hydrogen and Oxygen that make up the water are prominent, and Carbon of course also. All the othe red dots show that other elements, all the way up to Uranium at 92, occur in minuscule amounts. There are better ways to plot the data, and I also looked up data for the composition of the Earth's crust, the solar system and more. Since all that is a bit much for this web page, have a look here for much more on this subject. There are some amazing tidbits to be seen in these raw distributions of elements.
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Aliens and UFOs
These come up every year, and there is a fair bit to say about it. According to the INS, I am an alien myself, so I always bring in my green card to prove that aliens actually exist. 6-Graders usually don't think that is very funny.
I - Are there any?
II - Where are they all?
Next there is the matter of time: Mammal species on earth last for about a million years or so, and although
humans may last longer than dolphins, we may not last forever, especially if we manage to wipe ourselves out
in some man-made catastrophe. The earth itself is only 4.5 billion years old, and will be gone in a few
billion more. Even if the earth got a dozen visits by aliens in its lifetime, there is only a
1/1000 chance that they would arrive during the existence of the human race.
II - Listening and looking
III - Speaking
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What are quarks?
Until recently, I always started this story with the Greek philosopher Democritus (5th century BC), but I learned on Wikipedia about even older Indian atomic philosophies, as well as how Arabic scholars developed their atomic theories in the 11th century. Anyway, bring an apple and a big. sharp knife to show that the 'essence of apple-ness' remains present as you cut smaller and smaller pieces. Modern concepts of atoms flowed out of chemical experiments, and was formulated by John Dalton, about 200 years ago.
Early in the 20th century, atoms were found to to be
not hard spheres, but mostly empty, with a small nucleus in the center, and
lightweight electrons buzzing around it (the Rutherford
scattering experiment). This is like trying to infer the shape of a peach by tossing
peas at it. By observing how they bounce off, or pass by without hitting, you could
eventually infer the size of the peach, about 3-4 inches. However, if you try to do the
same thing by shooting beebees
at the peach, and see how they scatter, you would get a very different answer. Beebees
would pass straight through the soft peach, and only scatter when they hit the pit, which
is less than 1 inch. So what you measure depends on how energetic the probe is that is
used to do the measurements. Producing high-energy particles to do this leads to bigger
and bigger machines, and I put up a poster showing an
aerial photograph of CERN,
where I used to work. The biggest accelerator ring is 30 km around.
At the next level down, the nucleus is made up of protons and neutrons, and by doing scattering experiments at even higher energies, the protons and neutrons are found to be made up of quarks, called 'up' and 'down'. Although everything we can see and touch is made up of up quarks, down quarks and electrons, that is not the whole story. These particlea each have 2 heavier cousins, which have only a fleeting existence, and can only be seen in high-energy experiments. Links:
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