Is backward time travel possible? Can you change the past? My latest post for NOVA's The Nature of Reality blog explores the idea of using traversable wormholes as time machines:
Wormholes as Time Machines
Sunday, July 15, 2012
Saturday, June 2, 2012
The Mystery of Dark Flow
What is dark flow? My inaugural post for NOVA's "The Nature of Reality" blog describes the recent discovery
that hundreds of galaxy clusters are moving at about two million miles
per hour in the direction of a patch of sky between the constellations
Centaurus and Vela.
Dark Flow: Tugs from Beyond the Observable Universe?
Sunday, May 6, 2012
Edge of the Universe: A Voyage to the Cosmic Horizon and Beyond
I'm delighted to announce that my new book, "Edge of the Universe: A Voyage to the Cosmic Horizon and Beyond," an exploration of cutting-edge cosmology, is now available for preorder.
Preorder on Amazon.com
Preorder on Amazon.co.uk
More information about the book is at:
Edge of the Universe
Preorder on Amazon.com
Preorder on Amazon.co.uk
More information about the book is at:
Edge of the Universe
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?
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.
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?"
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?"
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