Scientific American Editors - Physics: New Frontiers

Physics: New Frontiers

From the Editors of Scientific American
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Letters to the Editor
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Better Than Sci-Fi

Science fiction has imagined some pretty wild ideas about the universeand our place in it. Parallel or alternative universes have been a recurrent themein Star Trek. In Interstellar, an astronaut explores hidden extra dimensions. TheMatrix and other movies have depicted ordinary life on Earth as nothing but aholographic or mental projection. But these imaginings all seem downright tamecompared with the mind-bending science now coming out of physics and astronomy.

The weirdness begins at the moment of creation. We have long thought of the big bangas the beginning of time, but theorists now have an idea of what might have come before.Could our 3-D universe have sprung from the formation of a black hole in a 4-D cosmos?The math says: maybe.

Then again, black holes might be quite different from the conventional picture of a pointlikesingularity surrounded by an invisible event horizonthe boundary beyond whichescape is impossible. As physicist Joseph Polchinski explains, the laws of quantumphysics suggest instead that black holes may literally be large, spherical holes devoid ofspace and time. If so, then event horizons might actually be solid shells. And they should bequite visible, seething with an intense, instantly lethal fire of high-energy particles.

Increasingly, it seems as though hardly anything out there is what it first appears to be.The first stars to form may have been so huge they arguably deserve a new label.Our own Milky Way galaxy has a gigantic dumbbell of glowing gas skewering its centerthat no one noticed until recently. Even our most fundamental notions of whatreality is are now up for debatealthough there may be less dramaticways to interpret the bizarre behaviors seen in the quantum realm.

Much of this new science is made possible by technological innovations. They include5,000-odd sensors frozen deep within a cubic kilometer of crystal-clear ice in Antarcticaan array that might shine light on the puzzling nature of dark matter. Scientistsare also dissecting molecules with the most powerful x-ray laser in the worldand using a 570-megapixel camera to scan the heavens for clues to the mystery of dark energy. And dont forget the most useful tool of all for physics: mathematics.

Advanced physics can seem abstract, but it does connect to everyday life. Living things, too, must abide by the rules of quantum mechanics. And physics may eventually set an upper limit to human intelligence. In the meantime, it makes us smarter.

--W. Wayt Gibbs
Book 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 prisoners who have spent their entire lives chained to the wall of a dark cavern. Behind the prisonerslies a flame, and between the flame and prisoners parade objects that cast shadowsonto a wall in the prisoners field of view. These two-dimensional shadows are the onlythings that the prisoners have ever seentheir only reality. Their shackles have preventedthem from perceiving the true world, a realm with one additional dimension to theworld 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, theuniverse came into being during a bigbang that started from an infinitelydense point. But according to recent calculationsthat we have carried out, wemay be able to track the start of the universeback to an era before the big bang, an era with an additional dimension ofspace. This protouniverse may have leftvisible traces that upcoming astronomicalobservations could 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-dimensional universeis merely the shadow of a world that hasfour spatial dimensions. Specifically, ourentire universe came into being during astellar implosion in this suprauniverse, animplosion 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 ofholography, a set of mathematical toolsthat al lows them to translate descriptionsof events in one dimension to the physicsof a different dimension. For example, researchers can solve relatively straightforwardequations of fluid dynamics in twodimensions and use those solutions tounderstand what is go ing on in a muchmore complicated systemfor example,the dynamics of a three-dimensional blackhole. Mathematically, the two descriptionsare interchangeablethe fluid serves asa perfect analogue for the extraordinaryblack 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-dimensional universe 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 rapidexpansion of space in which the early universein creased its volume by a factor of1078 (or more). Yet this expansion providesno insight into what caused the bigbang. Our four-dimensional universe, incontrast, gives us an answer to the ultimatemystery: Where did the universecome from?