Scientific American - Wonders of the Cosmos

Wonders of the Cosmos

From the Editors of Scientific American
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Mysterious Universe

On what would become the most watched show in the history ofPBS, astronomer Carl Sagan opined that the Earth is a very small stage in avast cosmic arena ... our planet is a lonely speck in the great enveloping cosmicdark. The original Cosmos series, which aired nearly 40 years ago, instilledthe haunting sense that there is much we dont understand about our universe.Indeed, the human mind may not even have the capacity to comprehend what gave rise to allmatter since we are three-dimensional creatures living in a potentially 10-dimensional world.

The good news is that we are steadily gaining clarity. In this special edition, we presentthe most riveting discoveries about our cosmic home, from what we know of the origins ofthe universe and the cartography of space to the most bizarre phenomena and the enduringquestion: Are we alone in the universe?

Back to the problem of perception: Recent calculations by Niayesh Afshordi, Robert B.Mann and Razieh Pourhasan hint at a protouniversea fourth spatial dimension that existedeven before the big bang and eventually exploded, casting a visual projection of that explosion.The resulting image could be the universe as we see it today. Another possibility isthat during the initial expansion of the universe after the big bang, cosmic bubbles createdmultipleif not an infinite number ofuniverses, of which ours is just one iteration.

Also in the mind-boggling department: Researchers speculate that entangled black holescould serve as wormholelike corridors around the universe. We are discoveringfreak molecules floating in space that could never exist on Earth and enormousblack holes that tear apart stars. Our universe certainly has a flare for the dramatic,though perhaps not when it comes to living things. Whether or not Earth is the only placethat harbors animals, plants and microbes remains an open question, but we arescouring planets and moons for signs of life.

The scale of these stories seems massive and shadowy at once, but Sagan might say that weare more capable and entitled to understand it than we know. We are made of starstuff, hesaid. We are a way for the cosmos to know itself.

- Andrea Gawrylewski
Collections Editor

The Black Hole at the Beginning of Time

by Niayesh Afshordi, Robert B. Mann and Razieh Pourhasan

In his allegory of the cave, Greek philosopher Plato described prisonerswho have spent their entire lives chained to the wall of a dark cavern. Behind theprisoners lies a flame, and between the flame and prisoners parade objects that castshadows onto a wall in the prisoners field of view. These two-dimensional shadowsare the only things that the prisoners have ever seentheir only reality. Their shackleshave prevented them from perceiving the true world, a realm with one additionaldimension to the world that they know, a dimension rich with complexity andunbeknownst to the prisonerscapable of explaining all that they see.

Plato was on to something.

We may all be living in a giant cosmiccave, created in the very first moments ofexistence. In the standard telling, the universecame into being during a big bangthat started from an infinitely densepoint. But according to recent calculationsthat we have carried out, we may beable to track the start of the universe backto an era before the big bangan era withan additional dimension of space. Thisprotouniverse may have left visible tracesthat upcoming astronomical observationscould uncover.

The universe appears to us to exist inthree dimensions of space and one oftimea geometry that we will refer to asthe three-dimensional universe. In ourscenario, this three-dimensionaluniverse is merely the shadow of a world that has four spatial dimensions. Specifically, ourentire universe came into being during astellar implosion in this suprauniverse,an implosion that created a three-dimensionalshell around a four-dimensionalblack hole. Our universe is that shell.

Why would we postulate somethingthat sounds, on the face of it, so absurd?We have two reasons. First, our ideas arenot idle speculationthey are firmlygrounded in the mathematics that describespace and time.

Over the past couple of decades physicistshave developed a rich theory of holography,a set of mathematical tools thatallows them to translate descriptions ofevents in one dimension to the physics ofa different dimension. Researcherscan solve relatively straightforward equationsof fluid dynamics in two dimensions anduse those solutions to understand what isgoing on in a much more complicatedsystemfor example, the dynamics of athree-dimensional black hole. Mathematically,the two descriptions are interchangeablethe fluid serves as a perfect analoguefor the extraordinary black hole.

The success of holography has convincedmany scientists that more is atwork here than a simple mathematicaltransformation. Perhaps the boundariesbetween dimensions are less stable thanwe thought. Perhaps the rules of the cosmosare written in another set of dimensionsand translated into the three weperceive. Perhaps, like Platos prisoners,our personal circumstances have trickedus into believing the world is three-dimensionalwhen in fact a deeper understandingof what we perceive will comeonly when we look for explanations in thefourth dimension.

There is a second reason that our four-dimensionaluniverse is worth thinkingabout. A close study of this universe couldhelp us understand deep questions aboutthe origin and nature of the cosmos. Consider,for example, the big bang, the primordialflash that brought our universeinto existence. Modern cosmology holdsthat the big bang was immediately followedby inflationa period of rapid expansionof space in which the early universeincreased its volume by a factor of1078 (or more). Yet this expansion providesno insight into what caused the big bang.Our four-dimensional universe, in contrast,gives us an answer to the ultimate mystery:Where did the universe come from?