Special Relativity and Sibling Rivalry
One of the twins goes away very fast, travels for a year and returns home. His brother is 70 years old and enjoying retirement. The traveler is upset: "I was sitting in my rocket while you and your solar system were traveling relative to me. Why am I still a teenager, while you can buy as much liquor in the State of New York as you wish with your pension?" This argument cannot be resolved in the framework of special relativity.
General Relativity and Cosmology
The universe is not straight. Sum of the three angles in a large triangle is not 180?; nobody really knows what it is, but the matter is debated. According to some, the universe may be closed like a hypersurface of a hyperball. Even so, going one way, however fast, one may never come back from the other side, because the length of the required journey keeps expanding. It is like paying off your debts with an income that is less than the interest. Some people still do it using methods that go beyond general relativity.
Atoms and Dialectical Materialism
The word atom means indivisible. This is a misnomer, there is a positively charged nucleus inside and negatively charged electrons flying around. Dividing atoms is easy. Even the nucleus can be cracked by a speedy neutron. Some nuclei when cracked release two speedy neutrons, ready to crack other nuclei. This may lead to a chain reaction, which can be used in atomic bombs. Anticipating that everything may eventually be cracked in smaller and smaller pieces to benefit of mankind, Vladimir Ilich Lenin wrote the prophetic words: "dialectics insists ... an electron is as inexhaustible as the atom itself". So far nobody has figured out how to split an electron.
Time is of the Essence
Laws of nature admit evolution backward in time on equal footing. Why is it that we cannot remember the future and make plans for the past?