## Metadata - Author: [[Brian Greene]] - Full Title: The Hidden Reality - Category: #books ## Highlights - General relativity then establishes that objects move toward regions where time elapses more slowly; in a sense, all objects “want” to age as slowly as possible. From an Einsteinian perspective, that explains why an object falls when you let go of it. ([Location 772](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=772)) - The speed limit set by light refers solely to the motion of objects through space. But galaxies recede from one another not because they are traveling through space—galaxies don’t have jet engines—but rather because space itself is swelling and the galaxies are being dragged along by the overall flow. ([Location 918](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=918)) - In Newton’s theory, gravity arises solely from an object’s mass. The bigger the mass, the bigger the object’s gravitational pull. In Einstein’s theory, gravity arises from an object’s mass (and energy) but also from its pressure. ([Location 957](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=957)) - And much as general relativity shows that positive pressure gives rise to attractive gravity, it shows that negative pressure gives rise to the opposite: repulsive gravity. ([Location 969](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=969)) - You know those vapor tendrils you see near the bottle’s neck when the cork is out? They form because the energy expended by the champagne in pushing against the cork results in a drop in temperature, which, much as with your breath on a wintry day, causes surrounding water vapor to condense. ([Location 1037](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=1037)) - Assuming unlimited Schrödinger hegemony, linearity applies here too, so not only will the device simultaneously display both locations but also your brain will be caught up in the confusion, thinking that the electron is simultaneously positioned at both. ([Location 4066](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4066)) - Everett argued that probabilities find their way into the Many Worlds approach because an analogous ignorance, from a thoroughly different source, necessarily creeps in. Inhabitants of the Many Worlds only have access to their own single world; they do not experience the others. Everett argued that with such a limited perspective comes an infusion of probability. ([Location 4399](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4399)) - Initially introduced in the mid-nineteenth century to quantify energy dissipation in combustion engines, the modern view, emerging from Ludwig Boltzmann’s work in the 1870s, is that entropy provides a characterization of how finely arranged—or not—the constituents of a given system need to be for it to have the overall appearance that it does. ([Location 4644](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4644)) - Take any system and count the number of ways its constituents can be rearranged without affecting its gross, overall, macroscopic appearance. That number is the system’s entropy.* If there’s a large number of such rearrangements, then entropy is high: the system is highly disordered. If the number of such rearrangements is small, entropy is low: the system is highly ordered (or, equivalently, has low disorder). ([Location 4659](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4659)) - Any object with a nonzero temperature radiates. Hot coal radiates visible light; we humans, typically, radiate in the infrared. If a black hole has a nonzero temperature, the very laws of thermodynamics that Bekenstein was seeking to preserve state that it too should radiate. ([Location 4722](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4722)) - So by the end of 1974, the Second Law was law once again. The insights of Bekenstein and Hawking established that in any situation, total entropy increases, as long as you account for not only the entropy of ordinary matter and radiation but also that contained within black holes, as measured by their total surface area. Rather than being entropy sinks that subvert the Second Law, black holes play an active part in upholding the law’s pronouncement of a universe with ever-increasing disorder. ([Location 4789](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4789)) - What actually is information, and what does it do? Your response is simple and direct. Information answers questions. Years of research by mathematicians, physicists, and computer scientists have made this precise. Their investigations have established that the most useful measure of information content is the number of distinct yes-no questions the information can answer. ([Location 4935](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4935)) - a system’s entropy is the number of yes-no questions that its microscopic details have the capacity to answer, and so the entropy is a measure of the system’s hidden information content. ([Location 4952](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4952)) - Although Bekenstein and Hawking tell us how much information is hidden within a black hole, they don’t tell us what that information is. They don’t tell us the specific yes-no questions the information answers, nor do they even specify the microscopic constituents that the information is meant to describe. The mathematical analyses pinned down the quantity of information a given black hole contains, without providing insight into the information itself. ([Location 4973](https://readwise.io/to_kindle?action=open&asin=B004C43ETO&location=4973))