How has the universe come into existence?
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Answers
Answer:
Explanation:
Fundamental mysteries
According to the standard Big Bang model, the universe was born during a period of inflation that began about 13.8 billion years ago. Like a rapidly expanding balloon, it swelled from a size smaller than an electron to nearly its current size within a tiny fraction of a second.
Initially, the universe was permeated only by energy. Some of this energy congealed into particles, which assembled into light atoms like hydrogen and helium. These atoms clumped first into galaxies, then stars, inside whose fiery furnaces all the other elements were forged.
That, in a nutshell, is the Big Bang theory, which virtually all cosmologists and theoretical physicists endorse. The evidence supporting the idea is extensive and convincing. We know, for example, that the universe is still expanding even now, at an ever-accelerating rate.
Scientists have also discovered a predicted thermal imprint of the Big Bang, the universe-pervading cosmic microwave background radiation. And we don't see any objects obviously older than 13.7 billion years, suggesting that our universe came into being around that time.
This is the generally agreed-upon picture of our universe's origins as depicted by scientists. It is a powerful model that explains many of the things scientists see when they look up in the sky, such as the remarkable smoothness of space-time on large scales and the even distribution of galaxies on opposite sides of the universe.
But there are things about this story that make some scientists uneasy. For starters, the idea that the universe underwent a period of rapid inflation early in its history cannot be directly tested, and it relies on the existence of a mysterious form of energy in the universe's beginning that has long since disappeared."Inflation is an extremely powerful theory, and yet we still have no idea what caused inflation or whether it is even the correct theory, although it works extremely well," said Eric Agol, an astrophysicist at the University of Washington.
For some scientists, inflation is a clunky addition to the Big Bang model, a necessary complexity appended to make it fit with observations. This wouldn't be the last addition.
"We've also learned there has to be dark matter in the universe, and now dark energy," said Paul Steinhardt, a theoretical physicist at Princeton University. "So the way the model works today is you say, 'OK, you take some Big Bang, you take some inflation, you tune that to have the following properties, then you add a certain amount of dark matter and dark energy.' These things aren't connected in a coherent theory."
Steinhardt worries cosmologists are acting more as engineers than scientists. If an observation doesn't match the current model, they attach another component or tinker with existing ones to fit. The components aren't connected and there's no reason to add them except to match observations. It's like trying to fix an old car by adding new parts from newer but different models. Those parts may work in the short term, but eventually, you need a new car.
An ageless universe
In recent years, Steinhardt has been working with Anna Ijjas, a theoretical physicist at Harvard University, on a radical alternative to the standard Big Bang model.
According to their idea, called bouncing cosmology, the universe was born not just once, but possibly multiple times in endless cycles of contraction and expansion. The theory replaces the "big bang" with a "big bounce", which smoothly connects periods of contraction and expansion of the universe and solves many of the issues that plague the inflation theory.
The pair claims that their ekpyrotic, or "cyclic," theory would explain not only inflation, but other cosmic mysteries as well, including dark matter, dark energy and why the universe appears to be expanding at an ever-accelerating clip. [The 18 Biggest Unsolved Mysteries in Physics]
While controversial, bouncing cosmology raises the possibility that the universe is ageless and self-renewing. It is a prospect perhaps even more awe-inspiring than a universe with a definite beginning and end, for it would mean that the stars in the sky, even the oldest ones, are like short-lived fireflies in the grand scheme of things.
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