Nemesis

But why should comets become more likely to hit us every million years? Here we launch ourselves into deep speculation. It has been suggested that the sun has a sister star, and the two orbit each other with a periodicity of about 26 million years. This hypothetical binary partner, which has never been seen but which has nevertheless been given the dramatic name Nemesis, passes, once per orbital rotation, through the so-called Oort Cloud, the belt of perhaps a trillion comets which orbits the...

 It is No Accident that We Inhabit a Veritable Paradise

Imagine a spaceship full of sleeping explorers, deep-frozen would-be colonists of some distant world. Perhaps the ship is on a forlorn mission to save the species before an unstoppable comet, like the one that killed the dinosaurs, hits the home planet. The voyagers go into the deep-freeze soberly reckoning the odds against their spaceship's ever chancing upon a planet friendly to life. If one in a million planets is suitable at best, and it takes centuries to travel from each star to the nex...

 Intellectual Exploration as Geographical Exploration

My own field of physics is passing today through a phase of exuberant freedom, a phase of passionate prodigality. Sometimes as I listen to the conversation of my young colleagues at Princeton, I feel as if I am lost in a rain forest, with insects and birds and flowers growing all around me in intricate profusion, growing too abundantly for my sixty-year-old brain to comprehend. But the young people are at home in the rain forest and walk confidently along trails which to me are almost invisib...

 The Comet Loss Cone

To understand why comet showers occur, we go back to the Oort Cloud. The theory of comet showers was worked out by Jack Hills, an American physicist now at Los Alamos. He realized that the movements of the comets in the Oort Cloud are not entirely random. Comets in the cloud are generally moving in random directions, but if a comet happens to be moving in an orbit almost exactly toward the Sun, it will not survive for long. A comet in an orbit coming close to the Sun may get boiled away and d...

 The Pretties

There was a certain kind of beauty, a prettiness that everyone could see. Big eyes and full lips like a kid’s; smooth, clear skin; symmetrical features; and a thousand other little clues. Somewhere in the backs of their minds, people were always looking for these markers. No one could help seeing them, no matter how they were brought up. A million years of evolution had made it part of the human brain. The big eyes and lips said: I’m young and vulnerable, I can’t hurt you, and you want...

 Science of a Second

The old definition of a second was based on the rotation of the Earth. As it takes the Sun one day to rise in the east, set in the west and rise again, a day was almost arbitrarily divided into 24 hours, the hour into 60 minutes, and the minute into 60 seconds. However, the Earth doesn’t rotate uniformly. In fact, it’s rotation decreases at a rate of about 20 millionths of a second every calendar year due to tidal friction caused by the Moon. Atomic time relies on the energy transition w...

 Fireside Conversation Sparked Storytelling

Control of fire and the capacity for cooking led to major anatomical and residential changes for early humans, starting more than a million years ago. However, little is known about what transpired when the day was extended by firelight. Data from the Ju/’hoan hunter-gatherers of southern Africa show major differences between day and night talk. Day talk centered on practicalities and sanctioning gossip; firelit activities centered on conversations that evoked the imagination, helped people...

 Human Respiration is Not a Source of Carbon Emissions

That's not a problem. The CO2 that's released by humans (and animals) is produced by metabolising carbon from food, and the food comes from plants that have been grown recently. During their growth, the plants have absorbed an equivalent amount of CO2 from the atmosphere. Even when eating meat, the animals are typically only a few years old and were fed on recently grown plants. In contrast, the cars run on fossil fuels that are hundreds of million years old.

 Why Black Bears Sleep in Trees

The ancestors of modern North American bears evolved in Asia during the Pleistocene, wandering over to Alaska during several appearances of the Bering land bridge, between the Bering and Kamchatka Peninsulas. Advancing and receding glaciers, fueled by evaporating sea water, caused ocean levels to alternately drop and rise, exposing and resubmerging the Bering Strait. The ancestors of black bears came across half a million years ago, and it is suspected that black bears adapted to climbing tr...

 Human History is One of Neccessity VS Freedom

The history of mankind is one of continuous development from the realm of necessity to the realm of freedom. This process is never-ending. In any society in which classes exist class struggle will never end. In classless society the struggle between the new and the old and between truth and falsehood will never end. In the fields of the struggle for production and scientific experiment, mankind makes constant progress and nature undergoes constant change, they never remain at the same level. ...