20 posts tagged universe
Is our universe a bubble in the multiverse?
Researchers at the Perimeter Institute for Theoretical Physics are working to bring the multiverse hypothesis — we are living in one universe of many — into the realm of testable science. Perimeter Associate Faculty member Matthew Johnson and his team are looking for clues for the existence of multiverses (a.ka. parallel universes) in the cosmic microwave background data, assumed to be left over from the Big Bang. To do that, “we simulate the whole universe,” he says. “We start with a multiverse that has two bubbles in it, we collide the bubbles on a computer to figure out what happens, and then we stick a virtual observer in various places and ask what that observer would see from there.” For example, if another universe had collided with ours n the early universe, it would have left evidence in the form of a “a disk on the sky,” creating a “bruise” in the pattern, he says. That the search for such a disk has so far come up empty makes certain collision-filled models less likely.
Meanwhile, the team is at work figuring out what other kinds of evidence a bubble collision might leave behind. It’s the first time, the team writes in their paper, that anyone has produced a direct quantitative set of predictions for the observable signatures of bubble collisions. And though none of those signatures has so far been found, some of them are possible to look for.
The real significance of this work is as a proof of principle: it shows that the multiverse can be testable. In other words, if we are living in a bubble universe, we might actually be able to tell.
Abstract of Journal of Cosmology and Astroparticle Physics paper
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. We develop and implement an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. We first simulate the collision spacetime by solving Einstein’s equations, starting from nucleation and ending at reheating. Taking advantage of the collision’s hyperbolic symmetry, the simulations are performed with a 1+1-dimensional fully relativistic code that uses adaptive mesh refinement. We then calculate the comoving curvature perturbation in an open Friedmann-Robertson-Walker universe, which is used to determine the temperature anisotropies of the cosmic microwave background radiation. For a fiducial Lagrangian, the anisotropies are well described by a power law in the cosine of the angular distance from the center of the collision signature. For a given form of the Lagrangian, the resulting observational predictions are inherently statistical due to stochastic elements of the bubble nucleation process. Further uncertainties arise due to our imperfect knowledge about inflationary and pre-recombination physics. We characterize observational predictions by computing the probability distributions over four phenomenological parameters which capture these intrinsic and model uncertainties. This represents the first fully-relativistic set of predictions from an ensemble of scalar field models giving rise to eternal inflation, yielding significant differences from previous non-relativistic approximations. Thus, our results provide a basis for a rigorous confrontation of these theories with cosmological data.
The Universe Is Programmable. We Need an API for Everything
Think about it like this: In the Book of Genesis, God is the ultimate programmer, creating all of existence in a monster six-day hackathon. Or, if you don’t like Biblical metaphors, you can think about it in simpler terms. Robert Moses was a programmer, shaping and re-shaping the layout of New York City for more than 50 years. Drug developers are programmers, twiddling enzymes to cure what ails us. Even pickup artists and conmen are programmers, running social scripts on people to elicit certain emotional results. The point is that, much like the computer on your desk or the iPhone in your hand, the entire Universe is programmable. Just as you can build apps for your smartphones and new services for the internet, so can you shape and re-shape almost anything in this world, from landscapes and buildings to medicines and surgeries to, well, ideas — as long as you know the code. That may sound like little more than an exercise in semantics. But it’s actually a meaningful shift in thinking. If we look at the Universe as programmable, we can start treating it like software. In short, we can improve almost everything we do with the same simple techniques that have remade the creation of software in recent years, things like APIs, open source code, and the massively popular code-sharing service GitHub. (via The Universe Is Programmable. We Need an API for Everything | Enterprise | WIRED)
A 10-dimensional theory of gravity makes the same predictions as standard quantum physics in fewer dimensions
A team of physicists has provided some of the clearest evidence yet that our universe could be just one big projection. In 1997, theoretical physicist Juan Maldacena proposed that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity. Maldacena’s idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing—and because it solved apparent inconsistencies between quantum physics and Einstein’s theory of gravity. It provided physicists with a mathematical Rosetta stone, a “duality,” that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa. But although the validity of Maldacena’s ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive. In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.
If different wavelengths of light experience spacetime differently, the big bang may never have happened
What if the universe had no beginning, and time stretched back infinitely without a big bang to start things off? That’s one possible consequence of an idea called “rainbow gravity,” so-named because it posits that gravity’s effects on spacetime are felt differently by different wavelengths of light, aka different colors in the rainbow. Rainbow gravity was first proposed 10 years ago as a possible step toward repairing the rifts between the theories of general relativity (covering the very big) and quantum mechanics (concerning the realm of the very small). The idea is not a complete theory for describing quantum effects on gravity, and is not widely accepted. Nevertheless, physicists have now applied the concept to the question of how the universe began, and found that if rainbow gravity is correct, spacetime may have a drastically different origin story than the widely accepted picture of the big bang.
What is the purpose of the Universe? Here is one possible answer.
The more we learn about the universe, the more we discover just how diverse all its planets, stars, nebulae and unexplained chunks of matter really are. So what is all this matter doing in our universe, other than just floating in space? Well, it just so happens that there is a theory that gives a kind of raison d’etre to our universe and all the objects flying through it. If true, it would mean that our universe is nothing more than a black hole generator, or a means to produce as many baby universes as possible. To learn more, we spoke to the man who came up with the idea. It’s called the theory of Cosmological Natural Selection and it was conjured by Lee Smolin, a researcher at the Perimeter Institute for Theoretical Physics and and an adjunct professor of physics at the University of Waterloo. (via What is the purpose of the Universe? Here is one possible answer.)
Has the cosmos existed forever, or did something bring it into existence? Time to grapple with the universe’s greatest mystery AS BIG questions go, it’s hard to beat. Has the universe existed forever? Over the years, some of the greatest minds in physics have argued that no matter how far back in time you go, the universe has always been here. Others have argued that the opposite must be true - something must have happened to bring the cosmos into existence. With both sides claiming that observations support their view, until recently an answer seemed as distant as ever. However, earlier this year, cosmologists Alex Vilenkin and Audrey Mithani claimed to have settled the debate. They have uncovered reasons why the universe cannot have existed forever. Yet what nature grudgingly gives with one hand, it takes back with the other - even though the universe has a beginning, its origins may be lost in the mists of time. Modern cosmology began in 1916 when Einstein applied his newly formulated theory of gravity, general relativity, to the biggest gravitating mass he could think of: the entire universe. Like Newton, Einstein favoured an unchanging universe - a universe that had existed forever and therefore had no beginning. To achieve this, Einstein realised that the gravity pulling together all the matter in the universe had to be countered by a weird cosmic repulsion of empty space. Einstein’s static universe was unfortunately unstable. As the English physicist Arthur Eddington pointed out, such a universe was balanced on a knife-edge between runaway expansion and runaway contraction. A further blow came in 1929 when American astronomer Edwin Hubble observed that galaxies were flying apart from each other like pieces of cosmic shrapnel. The conclusion was that the universe was expanding. Yet if the universe was expanding, an unavoidable consequence must be that it had been smaller in the past. Imagine rewinding that expansion back to a time when everything was compressed into the tiniest of volumes. This was the big bang.
The universe may grow like a giant brain, according to a new computer simulation. The results, published Nov. 16 in the journal Nature’s Scientific Reports, suggest that some undiscovered, fundamental laws may govern the growth of systems large and small, from the electrical firing between brain cells and growth of social networks to the expansion of galaxies. “Natural growth dynamics are the same for different real networks, like the Internet or the brain or social networks,” said study co-author Dmitri Krioukov, a physicist at the University of California San Diego. The new study suggests a single fundamental law of nature may govern these networks, said physicist Kevin Bassler of the University of Houston, who was not involved in the study. [ What’s That? Your Physics Questions Answered ] “At first blush they seem to be quite different systems, the question is, is there some kind of controlling laws can describe them?” he told LiveScience. By raising this question, “their work really makes a pretty important contribution,” he said. (via Universe may grow like a giant brain - Technology & science - Science - LiveScience | NBC News)