Why is there an arrow of time?

Time moves forward because a property of the universe called "entropy," roughly defined as the level of disorder, only increases, and so there is no way to reverse a rise in entropy after it has occurred. The fact that entropy increases is a matter of logic: There are more disordered arrangements of particles than there are ordered arrangements, and so as things change, they tend to fall into disarray. But the underlying question here is, why was entropy so low in the past? Put differently, why was the universe so ordered at its beginning, when a huge amount of energy was crammed together in a small amount of space?

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Einstein’s Lost Theory Describes a Universe Without a Big Bang

Einstein with Edwin Hubble, in 1931, at the Mount Wilson Observatory in California, looking through the lens of the 100-inch telescope through which Hubble discovered the expansion of the universe in 1929. Courtesy of the Archives, Calif Inst of Technology. In 1917, a year after Albert Einstein’s general theory of relativity was published—but still two years before he would become the international celebrity we know—Einstein chose to tackle the entire universe . For anyone else, this might seem an exceedingly ambitious task—but this was Einstein. Einstein began by applying his field equations of gravitation to what he considered to be the entire universe. The field equations were the mathematical essence of his general theory of relativity, which extended Newton’s theory of gravity to realms where speeds approach that of light and masses are very large. But his math was better than he wanted to believe—...

There’s a Previously Undiscovered Organ in Your Body, And It Could Explain How Cancer Spreads

Ever heard of the interstitium? No? That’s OK, you’re not alone — scientists hadn’t either. Until recently. And, hey, guess what — you’ve got one! The interstitium is your newest organ. Scientists identified it for the first time because they are better able to observe living tissues at a microscopic scale, according to a recent study published in Scientific Reports , Scientists had long believed that connective tissue surrounding our organs was a thick, compact layer. That’s what they saw when they looked at it in the lab, outside the body, at least. But in a routine endoscopy (exploration of the gastrointestinal tract), a micro camera revealed something unexpected: When observed in a living body, the connective tissue turned out to be “an open, fluid-filled space supported by a lattice made of thick collagen bundles,” pathologist and study author Neil Theise told Research Gate . This network of channels is present throughout ...

First light-bending calculator designed with metamaterials

Exotic materials that bend light in extreme ways could be used to perform complex mathematical operations, creating a new kind of analogue computer. Tools for manipulating light waves have taken off in recent years thanks to the development of metamaterials . These materials have complex internal structures on scales smaller than the wavelength of the light they interact with, and so they produce unusual effects. Most famously, metamaterials promise to deliver " invisibility cloaks " that can route light around an object, making it seem to disappear. Nader Engheta at the University of Pennsylvania, Philadelphia, and his colleagues decided to explore a different use for metamaterials, one that adapts the old idea of analogue computing . Today's digital computers are based on electrical switches that are either on or off. But before these machines were analogue computers based on varying electrical or mechanical properties. The slide rule is one example...

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