Finding a Fourth Dimension
Braneworld challenges Einstein’s general relativity.
Scientists have been intrigued for years about the possibility that there are additional dimensions beyond the three we humans can understand. Now researchers from Duke and Rutgers universities think there’s a way to test for five-dimensional theory (4 spatial dimensions plus time) of gravity that competes with Einstein’s General Theory of Relativity. This extra dimension should have effects in the cosmos which are detectable by satellites scheduled to launch in the next few years.
Scientists at Duke and Rutgers universities have developed a mathematical framework they say will enable astronomers to test a new five-dimensional theory of gravity that competes with Einstein’s General Theory of Relativity.
Charles R. Keeton of Rutgers and Arlie O. Petters of Duke base their work on a recent theory called the type II Randall-Sundrum braneworld gravity model. The theory holds that the visible universe is a membrane (hence “braneworld”) embedded within a larger universe, much like a strand of filmy seaweed floating in the ocean. The “braneworld universe” has five dimensions — four spatial dimensions plus time — compared with the four dimensions — three spatial, plus time — laid out in the General Theory of Relativity.
The framework Keeton and Petters developed predicts certain cosmological effects that, if observed, should help scientists validate the braneworld theory. The observations, they said, should be possible with satellites scheduled to launch in the next few years.
If the braneworld theory proves to be true, “this would upset the applecart,” Petters said. “It would confirm that there is a 4th dimension to space, which would create a philosophical shift in our understanding of the natural world.”
The scientists’ findings appeared May 24, 2006, in the online edition of the journal Physical Review D. Keeton is an astronomy and physics professor at Rutgers, and Petters is a mathematics and physics professor at Duke. Their research is funded by the National Science Foundation.
The Randall-Sundrum braneworld model — named for its originators, physicists Lisa Randall of Harvard University and Raman Sundrum of Johns Hopkins University — provides a mathematical description of how gravity shapes the universe that differs from the description offered by the General Theory of Relativity.
Keeton and Petters focused on one particular gravitational consequence of the braneworld theory that distinguishes it from Einstein’s theory.
The braneworld theory predicts that relatively small “black holes” created in the early universe have survived to the present. The black holes, with mass similar to a tiny asteroid, would be part of the “dark matter” in the universe. As the name suggests, dark matter does not emit or reflect light, but does exert a gravitational force.
The General Theory of Relativity, on the other hand, predicts that such primordial black holes no longer exist, as they would have evaporated by now.
“When we estimated how far braneworld black holes might be from Earth, we were surprised to find that the nearest ones would lie well inside Pluto‘s orbit,” Keeton said.
Petters added, “If braneworld black holes form even 1 percent of the dark matter in our part of the galaxy — a cautious assumption — there should be several thousand braneworld black holes in our solar system.”
But do braneworld black holes really exist — and therefore stand as evidence for the 5-D braneworld theory?
The scientists showed that it should be possible to answer this question by observing the effects that braneworld black holes would exert on electromagnetic radiation traveling to Earth from other galaxies. Any such radiation passing near a black hole will be acted upon by the object’s tremendous gravitational forces — an effect called “gravitational lensing.”
“A good place to look for gravitational lensing by braneworld black holes is in bursts of gamma rays coming to Earth,” Keeton said. These gamma-ray bursts are thought to be produced by enormous explosions throughout the universe. Such bursts from outer space were discovered inadvertently by the U.S. Air Force in the 1960s.
Keeton and Petters calculated that braneworld black holes would impede the gamma rays in the same way a rock in a pond obstructs passing ripples. The rock produces an “interference pattern” in its wake in which some ripple peaks are higher, some troughs are deeper, and some peaks and troughs cancel each other out. The interference pattern bears the signature of the characteristics of both the rock and the water.
Similarly, a braneworld black hole would produce an interference pattern in a passing burst of gamma rays as they travel to Earth, said Keeton and Petters. The scientists predicted the resulting bright and dark “fringes” in the interference pattern, which they said provides a means of inferring characteristics of braneworld black holes and, in turn, of space and time.
“We discovered that the signature of a fourth dimension of space appears in the interference patterns,” Petters said. “This extra spatial dimension creates a contraction between the fringes compared to what you’d get in General Relativity.”
Petters and Keeton said it should be possible to measure the predicted gamma-ray fringe patterns using the Gamma-ray Large Area Space Telescope, which is scheduled to be launched on a spacecraft in August 2007. The telescope is a joint effort between NASA, the U.S. Department of Energy, and institutions in France, Germany, Japan, Italy and Sweden.
The scientists said their prediction would apply to all braneworld black holes, whether in our solar system or beyond.
“If the braneworld theory is correct,” they said, “there should be many, many more braneworld black holes throughout the universe, each carrying the signature of a fourth dimension of space.”
Original Source: Duke University
Friday, January 28, 2011
Wednesday, January 19, 2011
Top 10 science mistake
Take a deep breath: Believe it or not, scientists are not always right. We really put them up on a pedestal, though, don't we? We quote scientists as experts, buy things if they're "scientifically proven" to work better … but scientists are human, too. It's just not fair to expect perfection out of them, is it? But come on, can't we at least ask for a reasonable level of competency?
Top 10 Science Mistakes
10: Alchemy
The idea of morphing lead into gold may seem a little crazy these days, but take a step back and pretend you live in ancient or medieval times.
Pretend you never took high-school chemistry and know nothing about elements or atomic numbers or the periodic table. What you do know is that you've seen chemical reactions that seemed pretty impressive: substances change colors, spark, explode, evaporate, grow, shrink, make strange smells - all before your eyes.
Now, if chemistry can do all that, it seems pretty reasonable that it might be able to turn a dull, drab, gray metal into a bright, shiny yellow one, right? In the hopes of getting that job done, alchemists sought out the mythical "philosopher's stone," a substance that they believed would amplify their alchemical powers.
They also spent a lot of time looking for the "elixir of life." Never found that, either.
9: Heavier Objects Fall Faster
OK, trick question: do heavier objects fall faster than lighter ones? Today, we all know that they don't, but it's understandable how Aristotle could've gotten this one wrong.
It wasn't until Galileo came along in the late 16th century that anyone really tested this out. Though he most likely did not, as legend holds, drop weights from the tower of Pisa, Galileo did perform experiments to back up his theory that gravity accelerated all objects at the same rate. In the 17th century, Isaac Newton took us a step further, describing gravity as the attraction between two objects: on Earth, the most important being the attraction between one very massive object (our planet) and everything on it.
A couple of hundred years later, Albert Einstein's work would take us in a whole new direction, viewing gravity as the curvature that objects cause in space-time. And it's not over. To this day, physicists are ironing out the kinks and trying to find a theory that works equally well for the macroscopic, microscopic and even subatomic. Good luck with that.
8: Phlogiston
What? You've never heard of phlogiston? Well, don't beat yourself up about it, because it's not real.
Phlogiston, proposed in 1667 by Johann Joachim Becher, was another element to add to the list (earth, water, air, fire and sometimes ether); it wasn't fire itself, but the stuff fire was made of. All combustible objects contained this stuff, Becher insisted, and they released it when they burned.
Scientists bought into the theory and used it to explain a few things about fire and burning: why things burned out (must have run out of phlogiston), why fire needed air to burn (air must absorb phlogiston), why we breathe (to get rid of phlogiston in the body).
Today, we know that we breathe to get oxygen to support cellular respiration, that objects need oxygen (or an oxidizing agent) to burn and that phlogiston just doesn't exist
7: The Rain Follows the Plow
If only it were so easy. It's actually kind of shocking that humanity held on to the idea that land would become fertile through farming for so long. Didn't anyone look around and see that all this farming of arid land wasn't doing much?
So much for observation.
In reality, this quite erroneous theory (popular during the American and Australian expansions) may have stayed alive in part because it did sometimes work -- or at least it seemed to work.
What we know now is that the plow wasn't actually bringing the rain; long-term weather patterns were. Arid regions (like the American West, for example) go through long-term cyclical droughts, followed by cycles of wetter years. Wait long enough and you'll get a few wet ones.
There's just one problem: wait a few more years and all the rain just goes away - only now, you've got a civilization to support.
6: The Earth Is Only 6,000 Years Old
Once upon a time, the Bible was considered a scientific work. Really. People just kind of assumed it was accurate, even when it didn't make much sense.
Take the age of the planet, for example.
Back in the 17th century, a religious scholar took a hard look at the Bible and estimated that creation happened around 4004 B.C. (you know, approximately). Add in nearly 2,000 more years to get to the 18th century, when Western, Bible-reading geologists started to realize that the Earth was constantly shifting and changing, and you get about 6,000 years.
Hmm ... those biblical scholars may have been a bit off. Current estimates, based on radioactive dating, place the age of the planet at around, oh, 4.5 BILLION years.
By the 19th century, geologists started putting the pieces together to realize that if geologic change was happening as slowly as they thought it was, and if this Darwin guy was at all right about evolution (which was also a slow process), the Earth had to be WAY older than they had thought. The emergence of radioactive dating in the early 20th century would eventually prove them right.
5: The Atom Is the Smallest Particle in Existence
Believe it or not, we weren't actually all that stupid in ancient times. The idea that matter was composed of smaller, individual units (atoms) has been around for thousands of years -- but the idea that there was something smaller than that was a bit harder to come by.
It wasn't until the early 20th century, when physicists like J.J. Thompson, Ernest Rutherford, James Chadwick and Neils Bohr came along, that we started to sort out the basics of particle physics: protons, neutrons and electrons and how they make an atom what it is. Since then, we've come a long way: on to charmed quarks and Higgs bosons, anti-electrons and muon neutrinos. Let's hope it doesn't get too much more complicated than that.
4: DNA: Not So Important
DNA was discovered in 1869, but for a long time, it was kind of the unappreciated assistant: doing all the work with none of the credit, always overshadowed by its flashier protein counterparts.
Even after experiments in the middle part of the 20th century offered proof that DNA was indeed the genetic material, many scientists held firmly that proteins, not DNA, were the key to heredity. DNA, they thought, was just too simple to carry so much information.
It wasn't until Watson and Crick published their all-important double-helical model of the structure of DNA in 1953 that biologists finally started to understand how such a simple molecule could do so much. Perhaps they were confusing simplicity with elegance.
3: Germs in Surgery
Laugh or cry (take your pick), but up until the late 19th century, doctors didn't really see the need to wash their hands before picking up a scalpel.
The result? A lot of gangrene. Most early-19th century doctors tended to attribute contagion to "bad air" and blamed disease on imbalances of the "four humors" (that's blood, phlegm, yellow bile and black bile, in case you weren't familiar).
"Germ theory" (the revolutionary idea that germs cause disease) had been around for a while, but it wasn't till Louis Pasteur got behind it in the 1860s that people started listening. It took a while, but doctors like Joseph Lister eventually connected the dots and realized that hospitals and doctors had the potential to pass on life-threatening germs to patients.
Lister went on to pioneer the idea of actually cleaning wounds and using disinfectant. Remember him next time you reach for the Purell.
2: The Earth Is the Center of the Universe
Chalk it up to humanity's collectively huge ego. Second-century astronomer Ptolemy's (blatantly wrong) Earth-centered model of the solar system didn't just stay in vogue for 20 or 30 years; it stuck around for a millennium and then some.
It wasn't until almost 1,400 years later that Copernicus published his heliocentric (sun-centered) model in 1543. Copernicus wasn't the first to suggest that the we orbited the sun, but his theory was the first to gain traction.
Ninety years after its publication, the Catholic Church was still clinging to the idea that we were at the center of it all and duking it out with Galileo over his defense of the Copernican view. Old habits die hard.
1: The Circulatory System
You don't have to be a doctor to know how important the heart is...but back in ancient Greece, you could be a doctor and STILL have no idea how important the heart is.
Back then, doctors like second-century Greek physician Galen believed (no kidding) that the liver (not the heart) circulated blood (along with some bile and phlegm), while the heart (really) circulated "vital spirit"(whatever that is).
How could they be so wrong? It gets worse.
Galen hypothesized that the blood moved in a back-and-forth motion and was consumed by the organs as fuel. What's more, these ideas stuck around for a very long time. How long?
It wasn't until 1628 that English physician William Harvey let us in on our heart's big secret. His "An Anatomical Study of the Motion of the Heart and of the Blood in Animals" took a while to catch on, but a few hundred years later, it seems beyond common sense -- perhaps the ultimate compliment for a scientific idea.
Top 10 Science Mistakes
10: Alchemy
The idea of morphing lead into gold may seem a little crazy these days, but take a step back and pretend you live in ancient or medieval times.
Pretend you never took high-school chemistry and know nothing about elements or atomic numbers or the periodic table. What you do know is that you've seen chemical reactions that seemed pretty impressive: substances change colors, spark, explode, evaporate, grow, shrink, make strange smells - all before your eyes.
Now, if chemistry can do all that, it seems pretty reasonable that it might be able to turn a dull, drab, gray metal into a bright, shiny yellow one, right? In the hopes of getting that job done, alchemists sought out the mythical "philosopher's stone," a substance that they believed would amplify their alchemical powers.
They also spent a lot of time looking for the "elixir of life." Never found that, either.
9: Heavier Objects Fall Faster
OK, trick question: do heavier objects fall faster than lighter ones? Today, we all know that they don't, but it's understandable how Aristotle could've gotten this one wrong.
It wasn't until Galileo came along in the late 16th century that anyone really tested this out. Though he most likely did not, as legend holds, drop weights from the tower of Pisa, Galileo did perform experiments to back up his theory that gravity accelerated all objects at the same rate. In the 17th century, Isaac Newton took us a step further, describing gravity as the attraction between two objects: on Earth, the most important being the attraction between one very massive object (our planet) and everything on it.
A couple of hundred years later, Albert Einstein's work would take us in a whole new direction, viewing gravity as the curvature that objects cause in space-time. And it's not over. To this day, physicists are ironing out the kinks and trying to find a theory that works equally well for the macroscopic, microscopic and even subatomic. Good luck with that.
8: Phlogiston
What? You've never heard of phlogiston? Well, don't beat yourself up about it, because it's not real.
Phlogiston, proposed in 1667 by Johann Joachim Becher, was another element to add to the list (earth, water, air, fire and sometimes ether); it wasn't fire itself, but the stuff fire was made of. All combustible objects contained this stuff, Becher insisted, and they released it when they burned.
Scientists bought into the theory and used it to explain a few things about fire and burning: why things burned out (must have run out of phlogiston), why fire needed air to burn (air must absorb phlogiston), why we breathe (to get rid of phlogiston in the body).
Today, we know that we breathe to get oxygen to support cellular respiration, that objects need oxygen (or an oxidizing agent) to burn and that phlogiston just doesn't exist
7: The Rain Follows the Plow
If only it were so easy. It's actually kind of shocking that humanity held on to the idea that land would become fertile through farming for so long. Didn't anyone look around and see that all this farming of arid land wasn't doing much?
So much for observation.
In reality, this quite erroneous theory (popular during the American and Australian expansions) may have stayed alive in part because it did sometimes work -- or at least it seemed to work.
What we know now is that the plow wasn't actually bringing the rain; long-term weather patterns were. Arid regions (like the American West, for example) go through long-term cyclical droughts, followed by cycles of wetter years. Wait long enough and you'll get a few wet ones.
There's just one problem: wait a few more years and all the rain just goes away - only now, you've got a civilization to support.
6: The Earth Is Only 6,000 Years Old
Once upon a time, the Bible was considered a scientific work. Really. People just kind of assumed it was accurate, even when it didn't make much sense.
Take the age of the planet, for example.
Back in the 17th century, a religious scholar took a hard look at the Bible and estimated that creation happened around 4004 B.C. (you know, approximately). Add in nearly 2,000 more years to get to the 18th century, when Western, Bible-reading geologists started to realize that the Earth was constantly shifting and changing, and you get about 6,000 years.
Hmm ... those biblical scholars may have been a bit off. Current estimates, based on radioactive dating, place the age of the planet at around, oh, 4.5 BILLION years.
By the 19th century, geologists started putting the pieces together to realize that if geologic change was happening as slowly as they thought it was, and if this Darwin guy was at all right about evolution (which was also a slow process), the Earth had to be WAY older than they had thought. The emergence of radioactive dating in the early 20th century would eventually prove them right.
5: The Atom Is the Smallest Particle in Existence
Believe it or not, we weren't actually all that stupid in ancient times. The idea that matter was composed of smaller, individual units (atoms) has been around for thousands of years -- but the idea that there was something smaller than that was a bit harder to come by.
It wasn't until the early 20th century, when physicists like J.J. Thompson, Ernest Rutherford, James Chadwick and Neils Bohr came along, that we started to sort out the basics of particle physics: protons, neutrons and electrons and how they make an atom what it is. Since then, we've come a long way: on to charmed quarks and Higgs bosons, anti-electrons and muon neutrinos. Let's hope it doesn't get too much more complicated than that.
4: DNA: Not So Important
DNA was discovered in 1869, but for a long time, it was kind of the unappreciated assistant: doing all the work with none of the credit, always overshadowed by its flashier protein counterparts.
Even after experiments in the middle part of the 20th century offered proof that DNA was indeed the genetic material, many scientists held firmly that proteins, not DNA, were the key to heredity. DNA, they thought, was just too simple to carry so much information.
It wasn't until Watson and Crick published their all-important double-helical model of the structure of DNA in 1953 that biologists finally started to understand how such a simple molecule could do so much. Perhaps they were confusing simplicity with elegance.
3: Germs in Surgery
Laugh or cry (take your pick), but up until the late 19th century, doctors didn't really see the need to wash their hands before picking up a scalpel.
The result? A lot of gangrene. Most early-19th century doctors tended to attribute contagion to "bad air" and blamed disease on imbalances of the "four humors" (that's blood, phlegm, yellow bile and black bile, in case you weren't familiar).
"Germ theory" (the revolutionary idea that germs cause disease) had been around for a while, but it wasn't till Louis Pasteur got behind it in the 1860s that people started listening. It took a while, but doctors like Joseph Lister eventually connected the dots and realized that hospitals and doctors had the potential to pass on life-threatening germs to patients.
Lister went on to pioneer the idea of actually cleaning wounds and using disinfectant. Remember him next time you reach for the Purell.
2: The Earth Is the Center of the Universe
Chalk it up to humanity's collectively huge ego. Second-century astronomer Ptolemy's (blatantly wrong) Earth-centered model of the solar system didn't just stay in vogue for 20 or 30 years; it stuck around for a millennium and then some.
It wasn't until almost 1,400 years later that Copernicus published his heliocentric (sun-centered) model in 1543. Copernicus wasn't the first to suggest that the we orbited the sun, but his theory was the first to gain traction.
Ninety years after its publication, the Catholic Church was still clinging to the idea that we were at the center of it all and duking it out with Galileo over his defense of the Copernican view. Old habits die hard.
1: The Circulatory System
You don't have to be a doctor to know how important the heart is...but back in ancient Greece, you could be a doctor and STILL have no idea how important the heart is.
Back then, doctors like second-century Greek physician Galen believed (no kidding) that the liver (not the heart) circulated blood (along with some bile and phlegm), while the heart (really) circulated "vital spirit"(whatever that is).
How could they be so wrong? It gets worse.
Galen hypothesized that the blood moved in a back-and-forth motion and was consumed by the organs as fuel. What's more, these ideas stuck around for a very long time. How long?
It wasn't until 1628 that English physician William Harvey let us in on our heart's big secret. His "An Anatomical Study of the Motion of the Heart and of the Blood in Animals" took a while to catch on, but a few hundred years later, it seems beyond common sense -- perhaps the ultimate compliment for a scientific idea.
Wednesday, January 5, 2011
The Start of the Universe with String Theory
The Start of the Universe with String Theory
By Andrew Zimmerman Jones and Daniel Robbins
The big bang theory doesn’t offer any explanation for what started the original expansion of the universe. This is a major theoretical question for cosmologists, and many are applying the concepts of string theory in attempts to answer it. One controversial conjecture is a cyclic universe model called the ekpyrotic universe theory, which suggests that our own universe is the result of branes colliding with each other.
The banging of strings
Well before the introduction of M-theory or brane world scenarios, there was a string theory conjecture of why the universe had the number of dimensions we see: A compact space of nine symmetrical space dimensions began expanding in three of those dimensions. Under this analysis, a universe with three space dimensions (like ours) is the most likely space-time geometry.
In this idea, initially posed in the 1980s by Robert Brandenberger and Cumrun Vafa, the universe began as a tightly wound string with all dimensions symmetrically confined to the Planck length. The strings, in effect, bound the dimensions up to that size.
Brandenberger and Vafa argued that in three or fewer dimensions, it would be likely for the strings to collide with anti-strings. (An anti-string is essentially a string that winds in a direction opposite the string.) The collision annihilates the string which, in turn, unleashes the dimensions it was confining. They thus begin expanding, as in the inflationary and big bang theories.
Instead of thinking about strings and anti-strings, picture a room that has a bunch of cables attached to random points on the walls. Imagine that the room wants to expand with the walls and floor and ceiling trying to move away from each other — but they can’t because of the cables. Now imagine that the cables can move, and every time they intersect, they can recombine. Picture two taut cables stretching from the floor to the ceiling that intersect to form a tall, skinny X. They can recombine to become two loose cables — one attached to the floor and one attached to the ceiling. If these had been the only two cables stretching from floor to ceiling, then after this interaction, the floor and ceiling are free to move apart from each other.
In the Brandenberger and Vafa scenario, this dimension (up-down), as well as two others, are free to grow large. The final step is that in four or more space dimensions, the moving strings will typically never meet. (Think about how points moving in two space dimensions will probably never meet, and the rationale gets extended to higher dimensions.) So this mechanism only works to free three space dimensions from their cables.
In other words, the very geometry of string theory implies that this scenario would lead to us seeing fewer than four space dimensions — dimensions of four or more are less likely to go through the string/anti-string collisions required to “liberate” them from the tightly bound configuration. The higher dimensions continue to be bound up by the strings at the Planck length and are therefore unseen.
With the inclusion of branes, this picture gets more elaborate and harder to interpret. Research into this approach in recent years hasn’t been reassuring. Many problems arise when scientists try to embed this idea more rigorously into the mathematics of string theory. Still, this is one of the few explanations of why there are four dimensions that make any sense, so string theorists haven’t completely abandoned it as a possible reason for the big bang.
The ekpyrotic universe
In the ekpyrotic universe scenario, our universe is created from the collision of branes. The matter and radiation of our universe comes from the kinetic energy created by the collision of these two branes.
The theory builds on the ideas that some M-theory brane world scenarios show that the extra dimensions of string theory may be extended, perhaps even infinite in size. They are also probably not expanding (or at least string theorists have no reason to think they are) the way that our own three space dimensions are. When you play the video of the universe backward in time, these dimensions don’t contract.
Now imagine that within these dimensions you have two infinite 3-branes. Some mechanism (such as gravity) draws the branes together through the infinite extra dimensions, and they collide with each other. Energy is generated, creating the matter for our universe and pushing the two branes apart. Eventually, the energy from the collision dissipates and the branes are drawn back together to collide yet again.
The ekpyrotic model is divided into various epochs (periods of time), based upon what influences dominate:
The big bang
The radiation-dominated epoch
The matter-dominated epoch
The dark energy–dominated epoch
The contraction epoch
The big crunch
The story up until the contraction epoch is essentially identical to that made by regular big bang cosmology. The radiation that is spawned by the brane collision (the big bang) means the radiation-dominated epoch is fairly uniform (save for quantum fluctuations), so inflation may be unnecessary. After about 75,000 years, the universe becomes a particle soup during the matter-dominated epoch. Today and for many years, we are in the dark energy–dominated epoch, until the dark energy decays and the universe begins contracting once again.
Because the theory involves two branes colliding, some called this the “big splat” theory or the “brane smash” theory, which is certainly easier to pronounce than ekpyrotic. The word “ekpyrotic” comes from the Greek word “ekpyrosis,” which was an ancient Greek belief that the world was born out of fire.
Some feel that the ekpyrotic universe model has a lot going for it — it solves the flatness and horizon problems like inflationary theory does, while also providing an explanation for why the universe started in the first place — but the creators are still far from proving it. Stephen Hawking has bet Neil Turok that findings from the European Space Agency’s Planck satellite will verify the inflationary model and rule out the ekpyrotic model, but Hawking has been known to have to pay out on these sorts of bets in the past.
By Andrew Zimmerman Jones and Daniel Robbins
The big bang theory doesn’t offer any explanation for what started the original expansion of the universe. This is a major theoretical question for cosmologists, and many are applying the concepts of string theory in attempts to answer it. One controversial conjecture is a cyclic universe model called the ekpyrotic universe theory, which suggests that our own universe is the result of branes colliding with each other.
The banging of strings
Well before the introduction of M-theory or brane world scenarios, there was a string theory conjecture of why the universe had the number of dimensions we see: A compact space of nine symmetrical space dimensions began expanding in three of those dimensions. Under this analysis, a universe with three space dimensions (like ours) is the most likely space-time geometry.
In this idea, initially posed in the 1980s by Robert Brandenberger and Cumrun Vafa, the universe began as a tightly wound string with all dimensions symmetrically confined to the Planck length. The strings, in effect, bound the dimensions up to that size.
Brandenberger and Vafa argued that in three or fewer dimensions, it would be likely for the strings to collide with anti-strings. (An anti-string is essentially a string that winds in a direction opposite the string.) The collision annihilates the string which, in turn, unleashes the dimensions it was confining. They thus begin expanding, as in the inflationary and big bang theories.
Instead of thinking about strings and anti-strings, picture a room that has a bunch of cables attached to random points on the walls. Imagine that the room wants to expand with the walls and floor and ceiling trying to move away from each other — but they can’t because of the cables. Now imagine that the cables can move, and every time they intersect, they can recombine. Picture two taut cables stretching from the floor to the ceiling that intersect to form a tall, skinny X. They can recombine to become two loose cables — one attached to the floor and one attached to the ceiling. If these had been the only two cables stretching from floor to ceiling, then after this interaction, the floor and ceiling are free to move apart from each other.
In the Brandenberger and Vafa scenario, this dimension (up-down), as well as two others, are free to grow large. The final step is that in four or more space dimensions, the moving strings will typically never meet. (Think about how points moving in two space dimensions will probably never meet, and the rationale gets extended to higher dimensions.) So this mechanism only works to free three space dimensions from their cables.
In other words, the very geometry of string theory implies that this scenario would lead to us seeing fewer than four space dimensions — dimensions of four or more are less likely to go through the string/anti-string collisions required to “liberate” them from the tightly bound configuration. The higher dimensions continue to be bound up by the strings at the Planck length and are therefore unseen.
With the inclusion of branes, this picture gets more elaborate and harder to interpret. Research into this approach in recent years hasn’t been reassuring. Many problems arise when scientists try to embed this idea more rigorously into the mathematics of string theory. Still, this is one of the few explanations of why there are four dimensions that make any sense, so string theorists haven’t completely abandoned it as a possible reason for the big bang.
The ekpyrotic universe
In the ekpyrotic universe scenario, our universe is created from the collision of branes. The matter and radiation of our universe comes from the kinetic energy created by the collision of these two branes.
The theory builds on the ideas that some M-theory brane world scenarios show that the extra dimensions of string theory may be extended, perhaps even infinite in size. They are also probably not expanding (or at least string theorists have no reason to think they are) the way that our own three space dimensions are. When you play the video of the universe backward in time, these dimensions don’t contract.
Now imagine that within these dimensions you have two infinite 3-branes. Some mechanism (such as gravity) draws the branes together through the infinite extra dimensions, and they collide with each other. Energy is generated, creating the matter for our universe and pushing the two branes apart. Eventually, the energy from the collision dissipates and the branes are drawn back together to collide yet again.
The ekpyrotic model is divided into various epochs (periods of time), based upon what influences dominate:
The big bang
The radiation-dominated epoch
The matter-dominated epoch
The dark energy–dominated epoch
The contraction epoch
The big crunch
The story up until the contraction epoch is essentially identical to that made by regular big bang cosmology. The radiation that is spawned by the brane collision (the big bang) means the radiation-dominated epoch is fairly uniform (save for quantum fluctuations), so inflation may be unnecessary. After about 75,000 years, the universe becomes a particle soup during the matter-dominated epoch. Today and for many years, we are in the dark energy–dominated epoch, until the dark energy decays and the universe begins contracting once again.
Because the theory involves two branes colliding, some called this the “big splat” theory or the “brane smash” theory, which is certainly easier to pronounce than ekpyrotic. The word “ekpyrotic” comes from the Greek word “ekpyrosis,” which was an ancient Greek belief that the world was born out of fire.
Some feel that the ekpyrotic universe model has a lot going for it — it solves the flatness and horizon problems like inflationary theory does, while also providing an explanation for why the universe started in the first place — but the creators are still far from proving it. Stephen Hawking has bet Neil Turok that findings from the European Space Agency’s Planck satellite will verify the inflationary model and rule out the ekpyrotic model, but Hawking has been known to have to pay out on these sorts of bets in the past.
Parallel Universe
Everything you're about to read here seems impossible and insane, beyond science fiction. Yet it's all true.
Scientists now believe there may really be a parallel universe - in fact, there may be an infinite number of parallel universes, and we just happen to live in one of them. These other universes contain space, time and strange forms of exotic matter. Some of them may even contain you, in a slightly different form. Astonishingly, scientists believe that these parallel universes exist less than one millimetre away from us. In fact, our gravity is just a weak signal leaking out of another universe into ours.
The same but different
For years parallel universes were a staple of the Twilight Zone. Science fiction writers loved to speculate on the possible other universes which might exist. In one, they said, Elvis Presley might still be alive or in another the British Empire might still be going strong. Serious scientists dismissed all this speculation as absurd. But now it seems the speculation wasn't absurd enough. Parallel universes really do exist and they are much stranger than even the science fiction writers dared to imagine.
Greater dimensions
It all started when superstring theory, hyperspace and dark matter made physicists realise that the three dimensions we thought described the Universe weren't enough. There are actually 11 dimensions. By the time they had finished they'd come to the conclusion that our Universe is just one bubble among an infinite number of membranous bubbles which ripple as they wobble through the eleventh dimension.
Scientists now believe there may really be a parallel universe - in fact, there may be an infinite number of parallel universes, and we just happen to live in one of them. These other universes contain space, time and strange forms of exotic matter. Some of them may even contain you, in a slightly different form. Astonishingly, scientists believe that these parallel universes exist less than one millimetre away from us. In fact, our gravity is just a weak signal leaking out of another universe into ours.
The same but different
For years parallel universes were a staple of the Twilight Zone. Science fiction writers loved to speculate on the possible other universes which might exist. In one, they said, Elvis Presley might still be alive or in another the British Empire might still be going strong. Serious scientists dismissed all this speculation as absurd. But now it seems the speculation wasn't absurd enough. Parallel universes really do exist and they are much stranger than even the science fiction writers dared to imagine.
Greater dimensions
It all started when superstring theory, hyperspace and dark matter made physicists realise that the three dimensions we thought described the Universe weren't enough. There are actually 11 dimensions. By the time they had finished they'd come to the conclusion that our Universe is just one bubble among an infinite number of membranous bubbles which ripple as they wobble through the eleventh dimension.
Subscribe to:
Posts (Atom)