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- As Nathan Budd aludes to, the 50% genetic similarity is an average. It applies to entire populations. Specific siblings will vary in how similar they are, though you can take the 50% as an estimate of how similar you can expect them to be. The 50% is also the probability that one of your genes will be shared with a sibling. I'm fairly sure the expected similarity and sharing probability will always be the same, but never went far enough in statistics to say this with absolute certainty.
In addition, the expected genetic similarity of an individual with two of their siblings (and the probability of sharing a gene with at least one of two siblings) isn't 100%, as the siblings will themselves share genes. The 100% counts some genes twice, so the 2nd counting has to be subtracted out. The probability of two independent events both happening is the product of their probabilities; the probability that a gene is shared with both siblings is 1/2 * 1/2 = 1/4. The probability that a gene is shared with at least one sibling is thus 1/2 + 1/2 - 1/4 = 3/4. That gives an expected genetic similarity of 75%.
- Sean M:
"Quantum" isn't synonymous with "chaos", nor with "random". Neither are the latter the same; they often get confused as both meaning "unpredictable", which they don't in technical fields. Newtonian systems can be chaotic; witness the Lorenzian Waterwheel (http://www.ace.gatech.edu/experiments2/2413/lorenz/fall02/). Quantum systems can be periodic, such as the arrangement of orbitals in elements. Furthermore, quantum systems don't meet the technical definition of "chaotic systems" as they are not deterministic.
Both the position and momentum of a particle can be known, but only up to a certain degree of accuracy. There is a tradeoff in the accuracy between the two, but it isn't all or nothing.
Whether two unbridged worlds you spoke of are the quantum and classical or the atomic and macroscopic, a bridge does exist. It's called the correspondence principle (http://en.wikipedia.org/wiki/Correspondence_principle). It's why everything observable at the macroscopic level has a quantum explanation, such as superconductors, the iridescence of oil sheens and feathers, permanent magnets and atomic bombs (see also http://www.quora.com/What-macroscopic-phenomena-can-only-be-explained-through-quantum-mechanics). What has yet to be bridged are the quantum and cosmic scales which can hopefully be done at extremely high energies, though higher than can currently be reached in colliders.
The chaotic nature of weather doesn't necessarily arise from quantum effects. A basic property of chaotic systems is that differences compound over time, so that slight initial differences result in systems that diverge rapidly, look nothing alike as they evolve. Weather models (which aren't based on quantum mechanics) exhibit this behavior, the same as real weather. The decreasing accuracy of predictions going into the future is a consequence of this divergence property and the differences between measured and actual (whatever that means) quantities.
One more page of interest: http://www.people.carleton.edu/~apattana/Research/RiceTalk.html
Science is a subtle thing.
- The CalTech scientists mentioned are those of the Elowitz Lab. The lab site features some movies and publications.
Nature has grouped the work of the Elowitz lab along with many others in a section on biological noise.
- @hawkotaco: that sounds more like clumping (the tendency of random events to happen in clumps, rather than being more evenly distributed) than emergence. There could also be other factors, which might be revealed by plotting arrivals by minutes of the hour. Read the last chapter of Martin Gardner's "Aha! Gotcha: Paradoxes To Puzzle And Delight" for more.
