Tuesday, August 2, 2011

Is Time Travel Possible?

A recent news story, based on a research article about light signals, proclaimed time travel to be an impossibility. Here is my response:

Is Time Travel Possible?

Sunday, May 29, 2011

The House Where Spacetime Began

Modern cosmology is described through Einstein's elegant general theory of relativity, which shows how matter and energy warp the fabric of spacetime--akin to placing heavy objects on a trampoline. Spacetime is the amalgamation of space and time into a single four-dimensional whole. Instead of considering the distance between points in space, or the duration between one moment in time and another, general relativists refer to spacetime intervals that link two "events."

There are a number of popular misconceptions about the idea of time as the fourth dimension. First of all, the notion did not originate with Einstein. In fact, when Einstein proposed special relativity in 1905 (briefly, his theory of reference frames moving at high constant speeds relative to each other), he expressed it in equations that did not involve a fourth dimension at all.

Moreover, the concept of time as the fourth dimension predated Einstein's work by a century and a half. In the 1754 work, "Encyclopedie," French mathematician Jean d’Alembert represented duration by use of the fourth dimension. Joseph Lagrange used similar terminology in his 1797 text, "The Theory of Analytical Functions." Both works made use of the reference in Newtonian physics to movement in space over time, signified by three components of space and one of time.

In 1885 a paper appeared in Nature written by someone who signed his name only "S." It proposed that reality could be best expressed by combining time and space into "time-space." As the writer put this:

“We must ... conceive that there is a new three-dimensional space for each successive instant of time; and, by picturing to ourselves the aggregate formed by the successive positions in time-space of a given solid during a given time, we shall get the idea of a four-dimensional solid, which we may call a sur-solid... Let any man picture to himself the aggregate of his own bodily forms from birth to the present time, and he will have a clear idea of a sur-solid in time-space.”

Soon thereafter, H. G. Wells, who was a student at what would later become Imperial College, London, wrote a short story, "The Chronic Argonauts," involving travel through time. The story would become the basis of his 1895 novella, "The Time Machine." In that work, he spoke very clearly of time as the fourth dimension.

Ten years later, when Einstein proposed special relativity, the idea of the fourth dimension was far from his mind. However, in Goettingen, Hermann Minkowski, who happened to be one of Einstein's former university instructors, realized that special relativity could be simply expressed in four-dimensional fashion. In a well-known public lecture in Cologne, Germany, Minkowski proclaimed the demise of space and time as independent ideas, to be replaced by a united spacetime. As Minkowski said:

“The views of space and time which I wish to lay before you have sprung from the soil of experimental physics and therein lies their strength. They are radical. Henceforth space by itself and time by itself are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent identity.”

Here are two photos of the house where Minkowski lived in Goettingen during the era when he proposed spacetime (I call it the "house where spacetime began," because only after Minkowski's proposal did the concept truly take flight):

Unfortunately, in 1909 Minkowski met an untimely death at the age of 44 when his appendix burst. He did not live long enough to see Einstein come to accept the fourth dimension and include spacetime manifolds as a key component of general relativity-a theory published in 1915.

Friday, May 6, 2011

The Search for a Theory of Everything

Ever since Maxwell combined electricity and magnetism into a single theory called electromagnetism, physicists have been tantalized by the possibility of describing all the forces of nature through a common set of equations. In my third contribution to the AT&T Science and Technology Author Series I discuss the scientific world's search for a theory that unites all four natural forces: gravity, electromagnetism, the weak force, and the strong force.

Saturday, April 9, 2011

Voyage to the Moments of Creation

Historians debate the role of various players in events that happened only hundreds of years ago. Prognosticators are uncertain what twists and turns worldly events might take little more than years, months or even weeks from now. Yet, thanks to the steady, predictable nature of many of the laws of physics, such as Einstein's general theory of relativity, along with space probes and telescopes able to collect ancient light from remote objects, cosmologists feel comfortable discussing events billions of years ago or speculating about possibilities billions of years hence. The precise sequence of what happened only a fraction of a second after the Big Bang, some 13.75 billion years ago, has become a central part of modern cosmological discussion.

In this second installment of my contribution to the AT&T Science and Technology Series I discuss the profound question, "What was the universe like when it was formed?"

Sunday, April 3, 2011

Mysterious Cosmic Flow to Reaches Unknown

While scanning the sky for telltale patterns is an ancient endeavour, modern astronomical tools and methods have tremendously sharpened the precision and broadened the scope. Thanks to contemporary instruments such as the Hubble Space Telescope, astronomers have been able to map out the expansive reach of the observable universe, pinning down precise values of locations and speeds of the galaxies, clusters of galaxies, and other celestial objects.

We have long known that the universe is expanding. Because of the growth of space, galaxies (except for nearest neighbors clinging together) are moving away from each other at an ever-increasing pace, like suburban sprawl gone mad. Unlike the spreading out of our own communities, there is apparently no limit to spatial growth -- cosmic real estate seems unlimited.

Much attention has been paid to measuring the exact expansion rate of the universe, gauging how it has changed over time. Such information can be used to help ascertain the origin and fate of the cosmos. That's one reason why pinning down the coordinates of galaxies, such as those of the spiral shown below, is so important (NGC 5584. Credit: NASA, ESA, A. Riess, L. Macri, et al., Hubble Heritage):
As humble dwellers on a middling planet in a peripheral region of the Milky Way galaxy, we have long thought that there is no special part of space. We have assumed that, aside from space's uniform expansion, galactic motions should be as haphazard as fish swimming in a tank--before any food pellets are dropped in, that is. Yet, remarkably, several recent studies have pointed to an improbable flow of clusters of galaxies in a particular direction--like fish swarming toward a certain point after tasty morsels had been dropped into their tank. What is the lure that draws all these clusters? Strangely enough there are no known agents powerful enough to provide such attraction.

Could there be incredibly vast collections of mass just beyond observation (or, alternatively, composed of undetected dark matter) providing the gravitational incentive for such an enormous cosmic flow? Or could it be that we live in a special part of the cosmos that happens by chance to have a greater than usual flow in a certain direction?

The latter possibility would negate the long-cherished Copernican Principle that no part of the universe is central or otherwise different from any other region. We expect Earth to lie in an average location, not an unusual locale. But could we be defying the odds?

As researcher Mike Hudson of the University of Waterloo remarked in a recent talk on the subject at the University of Pennsylvania:
"It is possible that we just happen to live in an unusual place where the velocity is that high. It is possible, but not likely."

Cosmic flow is a truly profound mystery. Its resolution could determine whether or not our part of space is truly special after all, despite the legacy of Copernicus. For the first time in centuries, Earth's normality hangs in the balance!

Tuesday, March 22, 2011

Welcome to Cosmic Quest

Welcome to the new Cosmic Quest blog, an expedition of the mind to the frontiers of the universe. Cosmology, the science of the universe, has made extraordinary progress in recent years tackling many long-standing questions. We now know the age of the cosmos with unprecedented precision: 13.75 billion years, give or take several hundred million. We also know the geometry and material composition of the universe.

Yet many deep mysteries remain. What is dark matter, the elusive gravitational "glue" that cements galaxies and clusters of galaxies together, yet cannot be seen? What is dark energy, the hidden cause of the universe's accelerated expansion? Is our universe part of a vaster multiverse? Could regions beyond the cosmic horizon affect ours through their unseen influences? Is the cosmos a hologram with its information encoded on a kind of surface? Were there other cycles of time before the Big Bang? Will time end in a Big Rip, a Big Stretch, a cosmic collision, or another scenario?

To begin this journey I am posting a video I recorded as part of the AT&T Science & Technology Author Series. In it I discuss cosmological milestones in recent history, as well as the ongoing search for dark matter and dark energy.