Cosmology 101: The End

Welcome back to the third, and last, installment of Cosmology 101. So far, we’ve covered the history of the universe up to the present moment. But what happens next? How will our universe end? And how can we be so sure that this is how the story unfolded?
Read more...

Full story at Universe Today.

Cosmology 101: The Beginning

How did the universe get its start? It’s one of the most pressing questions in cosmology, and likely one that will be around for a while. Here, I’ll begin by explaining what scientists think they know about the first formative seconds of the universe’s life. More than likely, the story isn’t quite what you might think.
Read more...


Full story at Universe Today.

The greatest story ever told.

13.7 billion years ago, an event occurred. Space itself swelled terrifically into being. Suddenly, there appeared a burgeoning cosmos where before there had been nothing. The explosion left behind a molten sea of charged particles that would eventually give life to everything in the universe. The churning plasma expanded along with space for 300,000 years until its constituent protons and electrons had finally cooled enough to combine. Consequently, the entire universe was soon clouded by neutral hydrogen gas. Such gas absorbs radiation exceptionally well, and so space was plunged into darkness for another billion or so years.

At this point, it was gravity that dispelled the haze. Clumps of gas soon condensed under its influence, slowly becoming dense furnaces for nuclear fusion. The high energy UV radiation emitted by these young stars leaked out across the universe, heating the surrounding gas to temperatures they had not faced since the big bang. Electrons that had been trapped within the nuclei of light atoms were suddenly released, reionizing hydrogen and rendering space transparent once more. As the universe expanded, overdense regions of structure contracted under gravity. Over the course of a few billion years, a familiar cosmos took shape. Stars came together into galaxies, galaxies came together into clusters, wacky objects like quasars came and went, supernovae went off, our Solar System formed, and the universe painstakingly plodded into its current configuration.

You may have noticed that some details are a little murky. As of yet, astronomers have no idea how the first stars formed out of the ambient fog. One pair of scientists is now hoping to change that. Alan Rogers of MIT and Judd Bowman of Arizona State University have developed a method using the 21cm spectral line of hydrogen. This line appears in the spectra of hydrogen atoms that have undergone an excitation. According to Rogers and Bowman, the specific way in which the radio spectrum of hydrogen evolves with time tells us that reionization itself lasted about 5 million years. Thus, the first stars and galaxies were most likely born during this time. Understanding the stellar mechanics that occurred during reionization is one of the most active quests in cosmology today. The team hopes to learn more with future observation and fine-tuning of their instrument, the EDGES antenna at the MIT Haystack Observatory.

Could the Big Bang be a bust?

Once upon a time, our universe was a hot, dense place. Then, out of nowhere (and no-when), it suddenly underwent a monstrous expansion. 13.7 billion years later, we look back upon this moment of extraordinary inflation and call it the "big bang." Over the years, cosmologists have collected a hefty stock of evidence that strongly supports this story. But what if there were another explanation for how we came to be? What if nothing "banged?" What if the universe has always existed? A group of Taiwanese researchers is now suggesting a new cosmological model - one that doesn't require a big bang at all.

In his recent paper, professor Wun-Yi Shu from the Institute of Statistics at the National Tsing Hua University suggests that many of the current problems plaguing cosmology can be solved by his new model. For instance, it renders the horizon and flatness problems obsolete based on new geometry. It also does away with the seemingly improvised explanation that physicists currently give when asked about the accelerated expansion of the universe: an exotic form of anti-gravity called "dark energy." Based on cosmological evidence, dark energy is believed to be responsible for about 75% of the universe's energy density (for comparison, the kind of matter we see all around us only accounts for about 5%). There is only one problem with this theory: researchers have never seen or detected this mysterious form of energy. In general relativity, dark energy is represented by the cosmological constant, a fudge factor inserted by Einstein in order to prevent the universe from collapsing on itself. But according to Shu, dark energy is unnecessary.


The current cosmological model. Image courtesy of NASA/WMAP.

His model makes four major claims. First of all, the speed of light and gravity are not constant; instead, they vary with time as the universe evolves. Secondly, time is infinite. Shu also states that the spatial portion of the universe (that is, the part of spacetime that is not temporal) takes the form of a 3-sphere, the four-dimensional counterpart to a sphere. Lastly, Shu states that although we know that the universe is accelerating now, that doesn't mean it always has been. In his reality, the universe spends time decelerating as well.

Shu's spacetime illustrates a type of eternal, cyclic universe with dynamic physical laws. And perhaps surprisingly, all of this is more than a simple thought experiment. Shu actually compared his model with existing data from the analysis of type 1a supernovae and found that his "theoretical predictions... fit the observations quite well." Einstein once called the cosmological constant the "biggest blunder" of his life. A model such as Shu's could pave the way to vanquishing it and dark energy for once and for all.