Could there be an undiscovered integer between 6 and 7？
Could there be an undiscovered chemical element between atomic number 6 （which is carbon） and atomic number 7 （which is nitrogen）？
Yes， the new preservative causes cancer in rats. But what if you have to give a person， who weighs much more than a rat， a pound a day of the stuff to induce cancer？ In that case， maybe the new preservative isn’t all that dangerous. Might the benefit of having food preserved for long periods outweigh the small additional risk of cancer？ Who decides？ What data do they need to make a prudent decision？
In a 3.8 billion-year-old rock， you find a ratio of carbon isotopes typical of living things today， and different from inorganic sediments. Do you deduce abundant life on Earth 3.8 billion years ago？ Or could the chemical remains of more modern organisms have infiltrated into the rock？ Or is there a way for isotopes to separate in the rock apart from biological processes？ Sensitive measurements of electrical currents in the human brain show that when certain memories or mental processes occur， particular regions of the brain go into action. Can our thoughts， memories and passions all be generated by particular circuitry of the brain neurons？ Might it ever be possible to simulate such circuitry in a robot？ Would it ever be feasible to insert new circuits or alter old ones in the brain in such a way as to change opinions， memories， emotions， logical deductions？ Is such tampering wildly dangerous？
Your theory of the origin of the solar system predicts many flat discs of gas and dust all over the Milky Way galaxy. You look through the telescope and you find flat discs everywhere. You happily conclude that your theory is confirmed. But it turns out the discs you sighted were spiral galaxies far beyond the Milky Way， and much too big to be nascent solar systems.
Should you abandon your theory？ Or should you look for a different kind of disc？ Or is this just an expression of your unwillingness to abandon a discredited hypothesis？
A growing cancer sends out an all-points bulletin to the cells lining adjacent blood vessels： ‘We need blood，’ the message says. The endothelial cells obligingly build blood vessel bridges to supply the cancer cells with blood. How does this come about？ Can the message be intercepted or cancelled？ You mix violet， blue， green， yellow， orange and red paints and make a murky brown. Then you mix light of the same colours and you get white. What’s going on？
In the genes of humans and many other animals there are long， repetitive sequences of hereditary information （called ‘nonsense’）. Sorne of these sequences cause genetic diseases. Could it be that segments of the DNA are rogue nucleic acids， reproducing on their own， in business for themselves， disdaining the well-being of the organism they inhabit？
Many animals behave strangely just before an earthquake.What do they know that seismologists don’t？
The ancient Aztec and the ancient Greek words for ‘God’ are nearly the same. Is this evidence of some contact or cornmonality between the two civilizations， or should we expect occasional such coincidences between two wholly unrelated langt’ages merely by chance？ Or could， as Plato thought in the Cratylus， certain words be built into us from birth？
The Second Law of Thermodynamics states that in the Universe as a whole， disorder increases as time goes on. （Of course， locally worlds and life and intelligence can emerge， at the cost of a decrease in order elsewhere in the Universe.） But if we live in a Universe in which the present Big Bang expansion will slow， stop， and be replaced by a contraction， might the Second Law then be reversed？ Can effects precede causes？
The human body uses concentrated hydrochloric acid in the stomach to dissolve food and aid digestion. Why doesn’t the hydrochloric acid dissolve the stomach？
The oldest stars seem to be， at the time I’m writing， older than the Universe. Like the claim that an acquaintance has children older than she is， you don’t have to know very much to recognize that someone has made a mistake. Who？
The technology now exists to move individual atoms around， so long and complex messages can be written on an ultramicroscopic scale. It is also possible to make machines the size of molecules. Rudimentary examples of both these ‘nanotechnologies’ are now well demonstrated. Where does this take us in another few decades？
In several different laboratories， complex molecules have been found that under suitable conditions make copies of themselves in the test tube. Some of these molecules are， like DNA and RNA， built out of nucleotides； others are not. Some use enzymes to hasten the pace of the chemistry； others do not. Sometimes there is a mistake in copying； from that point forward the mistake is copied in successive generations of molecules. Thus there get to be slightly different species of self-replicating molecules； some of which reproduce faster or more efficiently than others. These preferentially thrive. As time goes on， the molecules in the test tube become more and more efficient. We are beginning to witness the evolution of molecules. How much insight does this provide about the origin of life？
Why is ordinary ice white， but pure glacial ice blue？
Life has been found miles below the surface of the Earth. How deep does it go？ The Dogon people in the Republic of Mali are said by a French anthropologist to have a legend that the star Sirius has an extremely dense companion star. Sirius in fact does have such a companion， although it requires fairly sophisticated astronomy to detect it. So （1） did the Dogon people descend from a forgotten civilization that had large optical telescopes and theoretical astrophysics？ Or， （2） were they instructed by extraterrestrials？ Or， （3） did the Dogon hear about the white dwarf companion of Sirius from a visiting European？ Or， （4） was the French anthropologist mistaken and the Dogon in fact never had such a legend？