A Matter of Degrees by Gino Segre

• Since all the [biological] circuity is temperature-dependent, having a constant body temperature--one with a little leeway for special circumstances--is simple the best evolutionary choice for animals as complex as we are. Fluctuating brain temperature would lead to unpredictable reactions, ones that might not occur in the same sequence if the learning had taken place at a different brain temperature.
• Calories are units of heats. It takes one calore to raise one gram of water 1 degree Celsius, or 100 calories to go from 0 to 100 degrees Celsius. But more than 500 calories are necessary to change a gram of water at 100 degrees Celsius into a gram of steam at the same temperature. In other words, the amount of heat employed in the simple transition from water to water vapor is more than five times as great as that in going all the way from freezing to boiling temperature. This means the conversion of water to water vapor in the body is a very efficient way to cool down.
• The key to dressing well in very cold climates is remembering that air conducts heat poorly.
• There are two ways to change the set temperature value in the hypothalamus back to normal when you have a fever. One is to remove the pyrogens--that is, kill the bacteria that are leading to the cytokines. The second is to administer aspirin or similar drugs that inhibit the synthesis of prostaglandin. In plain language, destroy the message or kill the messenger.
• We should remember that the germ theory of disease, largely the work of Louis Pasteur, is little more than a hundred years old.
• Excess or prolonged fever is harmful to a patient, but it is less clear that a fever is always harmful.
• Fever diminished mental functioning and can produce delirium in even nonfatal episodes. It shocks the system, so much that mental patients were sometimes treated by having fevers induced.
• Rising temperature is only one of many environmental stresses that lead to the deforming or improper folding of molecules in the cell. Poisons, heavy metals, and pollutants of one sort or another are often just as bad or worse.
• Beyond diet, fire changed the way people lived. A blazing bonfire scares animals away. A fire at the entrance to a cave keeps out even the most determined predators. First also provides light in that cave, enabling habitation of its deeper reaches. Fire meant that humans could move from the temperate zones in which they had evolved toward harsher climate, particularly if they had tools to help them hunt and make clothing.
• Measurement is only interesting when you know what you are measuring--when there is a purpose.
• Since pressure and volume are both positive at fixed quantities, zero is the smallest value they can take.
• Heat is simply a form of energy, one of many, and the sum of all forms of energy in an isolated system is conserved. This has come to be known as the First Law of Thermodynamics.
• Mechanical energy can be transformed into thermal energy with 100 percent efficiency, but thermal energy can be transformed into mechanical energy only if you have a sink at absolute zero. Of course, since no temperature can be lower than absolute zero, the efficiency can be greater than 100 percent.
• In essence, the First Law of Thermodynamics says heat is just another form of energy and energy as a whole is conserved. The Second Law says you can’t build a machine that will convert thermal energy into mechanical energy with 100 percent efficiency.
• Nernst’s Theorem, sometimes known as the Third Law of Thermodynamics. It states that an object’s entropy goes to zero as its temperature goes to absolute zero. Absolute zero temperature is a state of complete order.
• Absolute zero is no longer a mystery. Kinetic energies are always positive. The average value of positive quantities is necessarily positive so the smallest value the average can take is zero and that value is reached only if all kinetic energies are zero. Zero is the average of a string of zeros.
• Absolute zero is absolute rest for all molecules.
• The meaning of the First Law of Thermodynamics is simple. The heat in the container is simply the sum of all the molecular kinetic energies. Thermal energy is just another way of describing motion energy, a summing of the very small mechanical kinetic energies of a very large number of molecules. The First Law of Thermodynamics is conservation of that energy; energy either appears or disappears.
• The warming of the Arctic regions has been dramatic.
• A rise in temperature at one place can trigger climatic conditions that will set off an environmental disaster elsewhere; a rise in air temperature can have a big impact in changing ocean levels.
• There are four main contributors to the temperature of the Earth’s surface. The first is the Sun, our principal source of heat. [...] The second contributor is the heat generated directly in the Earth. [...] Third, oceans are big contributors to global temperature shifts, largely through the round-the-world motion of giant mass of water in what looks like a conveyor belt system. [...] The fourth and final major contributor to global temperature is the blanketing of the Earth in its atmosphere, a cover that both shields the Earth from harmful radiation and keeps much of the terrestrial warmth generated by the Sun from escaping into space.
• In other words, Sun, Earth, water, and air explain Earth’s temperature.
• Ice is one of the best places to look for a record of warming and cooling, for evidence of Milankovitch cycles, and for sudden shifts in temperature.
• All radiation, including, of course, sunlight, can be characterized by its energy density or intensity and its frequency, the latter being the number of waves per second emitted by the sender.
• Sunlight filters through the upper layers of the ocean, but by a thousand feet down there isn’t enough light to sustain photosynthesis, the process by which plants convert water and carbon dioxide into oxygen and organic material. Plant growth ceases at that point, but life continues, sustained by nutrients that have drifted slowly downward from the upper, life-rich layers.
• By fifty miles down, the temperature is 2000 degrees Fahrenheit; there is enough heat to create volcanoes, enough to sustain the motion of continents and of ocean floors.
• The secret to life on the vents lies in a discovery that emerged more or less simultaneously with the discovery of the vents: bacteria with extraordinary tolerance to high temperatures.
• The prerequisites for life anywhere in the solar system and possibly the universe are threefold. The first is an energy force capable of driving the chemical reactions that lead to life; the second is the presence of organic molecules that carry genetic information; the third is water. Liquid water is a sine qua non, the solvent and the medium for the chemical reactions.
• Other liquids such as methane or ammonia have been considered from time to time, and there might even be special circumstances under which one of them works, but life as we know it needs liquid water.
• Liquid water sets unambiguous temperature limits to the internal settings of a living creature: 212 degrees Fahrenheit as a maximum and 32 degrees as a minimum. The limits are not altogether sharp because salinity lowers the freezing point of water and pressure raises the boiling point, but there is not much leeway.
• Plants make complex organic molecules out of simple ones through photosynthesis. With light as an energy source, they combine water and carbon dioxide to from oxygen and carbohydrates. Animals breathe oxygen and eat carbohydrates: life abounds.
• Carbon dioxide is normally kept in check through absorption from plants as well as by burial in rocks washed into the oceans after erosion and exposure to rainfall. It’s a delicate balance.
• Most scientists think the chances of independent evolution are higher than those of any form of panspermia, but there is no substitute for hard evidence. The conditions on early Mars were one favorable and Mars still remains a candidate despite its present frigidity. The moons of Jupiter may be a better bet.
• Mars and the outer planets are too cold, too far away from the Sun for life above ground. But we know from the creatures found on the Earth’s hydrothermal vents that life can exist even in the absence of sunlight provided an energy source is present and the temperature is high enough for water to remain liquid.
• The extraterrestrial candidate most likely to harbor life is an unlikely one: Europa, one of the moons of Jupiter.
• The Sun’s core is a giant nuclear reactor in which a thousand billion pounds of hydrogen nuclei are converted every second into helium nuclei. I say nuclei rather than atoms because the ambient temperature is so high that the electrons, stripped from the atoms, constitute a kind of gas through which the nuclei move.
• Each pound of hydrogen produces as much energy in fussing as the burning of twenty million pounds of coal, employing the same process as the one that fuels the hydrogen bomb.
• Understanding superconductivity or knowing why some materials are electrical conductors and others insulators requires a bit of quantum mechanics. Without quantum mechanics, the periodic table of elements is simply a set of rules for grouping similar chemicals. With quantum mechanics, the behavior of elements is comprehensible and predictable. Without quantum mechanics, atomic behavior near absolute zero temperature is bizarre.
• The photon is neither a particle disguised as a wave nor a wave disguised as a particle. It is both.
• Pauli’s exclusion principle sets the number of electrons that can be in each atomic orbit and explains why, once that number is reached, any additional electrons have to be in the next higher orbit.
• Proceeding from element to element, the exclusion principle describes the level of chemical activity of each type of atom and anticipates what sort of molecular bonds atoms will form.