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After a while I noticed that the sun and all the stars in his neighborhood were ruddy. Those at the opposite pole of the heaven were of an icy blue. The explanation of this strange phenomenon flashed upon me. I was still traveling, and traveling so fast that light itself was not wholly indifferent to my passage. The…
Physicists love to think about systems that take only a little information to describe. So when they get a system that takes a lot of information to describe, they use a trick called 'statistical mechanics', where you try to ignore most of this information and focus on a few especially important variables. For…
Heisenberg’s idea had quickly been dubbed Unschärferelation, which transliterates to “unsharpness relationship,” but as there is really no such term in English ('blurred', 'fuzzy', 'vague' or 'ambiguous' have all been tried), the translation ended up as "the Uncertainty Principle"—when he had not used either term at…
Scent seems to have all the disadvantages and none of the advantages, as a long-range sense. However, under special circumstances even a modified nose may fill the need. In a story of my own some years ago ("Uncommon Sense," Astounding Science Fiction, September 1945), I assumed an airless planet, so that molecules…
The trick of magnifying a normal creature to menacing size is all too common. The giant amoeba is a familar example; monster insects (or whole populations of them) even more so. It might pay an author with this particular urge to ask himself why we don't actually have such creatures around. There is likely to be a…
The need for an internal skeleton stems largely from the nature of muscle tissue, which can exert force only by contracting and is therefore much more effective with a good lever system to work with. I belittle neither the intelligence nor the strength of the octopus; but in spite of Victor Hugo and most other writers…
The rocket equation contains three variables. Given any two of these, the third becomes cast in stone. Hope, wishing, or tantrums cannot alter this result. Although a momentum balance, these variables can be cast as energies. They are the energy expenditure against gravity (often called delta V or the change in rocket…
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…
awking has written down an equation which looks rather like Planck's equation. Hawking's equation is S = kA, where S is the entropy of a black hole, A is the area of its surface, and k is a constant which I call Hawking's constant. Entropy means roughly the same thing as the heat capacity of an object. It is measured…
In the year 1900 Max Planck wrote down an equation, E = hv, where E is the energy of a light wave, v is its frequency, and h is a constant which we now call Planck's constant. Planck's equation was the beginning of quantum theory. It said that energy and {22} frequency are the same thing measured in different units…
Our Sun is significantly enriched, having formed when the Universe was more than 9 billion years old in the plane of a spiral galaxy, one of the most enriched places in the Universe. Yet, when our Sun formed, it was still made out of — by mass — 71% hydrogen, 27% helium, and about 2% “other” stuff. If we convert that…
Milk production at a dairy farm was low, so the farmer wrote to the local university, asking for help from academia. A multidisciplinary team of professors was assembled, headed by a theoretical physicist, and two weeks of intensive on-site investigation took place. The scholars then returned to the university…
The basic physics of thermonuclear energy is seductively simple. Fission produces energy by atomic fracture, fusion by tiny acts of atomic union. Every atom contains at least one proton, and all protons are positively charged, which means that they repel one another, like identical ends of a magnet. As protons are…
It is called a tokamak—old Soviet shorthand for a more precise and geometrical name, toroidalnaya kamera s aksialnym magnitnym polem, or “toroidal chamber with an axial magnetic field.” Sakharov’s rough sketch depicted a doughnut-shaped vacuum chamber, or torus, ringed with electromagnets, and that is how iter’s core…
Those reductionists who try to reduce life to physics usually try to reduce it to primitive physics—not to good physics. Good physics is broad enough to contain life, to encompass life in its description since good physics allows a vast field of possible descriptions. There is no reason why living beings should be…
Everything is made of atoms. That is the key hypothesis. The most important hypothesis in all of biology, for example, is that everything that animals do, atoms do. In other words, there is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to…
I have settled down to the task of writing these lectures and have drawn up my chairs to my two tables. Two tables! Yes; there are duplicates of every object about me—two tables, two chairs, two pens.... One of them has been familiar to me from earliest years. It is a commonplace object of that environment which I…
Our sense of touch tells us quite definitely that one body is hot and another cold. But this is a purely quali- tative criterion, not sufficient for a quantitative descrip- tion and sometimes even ambiguous. This is shown by a well-known experiment: we have three vessels con- taining, respectively, cold, warm and hot…
A most fundamental problem, for thousands of years wholly obscured by its complications, is that of motion. All those motions we observe in nature that of a stone thrown into the air, a ship sailing the sea, a cart pushed along the street are in reality very intricate. To understand these phenomena it is wise to begin…
Laid up in bed during a brief illness and idly watching two clocks mounted in one case, Huygens noticed something strange: No matter how the pendulums started out, eventually they always ended up swinging in exactly opposite directions. Huygens wondered whether this odd sympathy might solve the longitude problem…