This blog enables you to understand about Black holes. It also explains related terms and theory.
Wednesday, 5 November 2014
Parallel universes – worlds where the dinosaur-killing asteroid never hit, or where Australia was colonised by the Portuguese – are a staple of science fiction. But are they real?
In a radical paper published this week in Physical Review X, we (Dr Michael Hall and I from Griffith University and Dr Dirk-André Deckert from the University of California) propose not only that parallel universes are real, but that they are not quite parallel – they can “collide”.
In our theory, the interaction between nearby worlds is the source of all of the bizarre features of quantum mechanics that are revealed by experiment. Super Weekend – Flat 40% off on over 15000 styles.
Many worlds in existing interpretations
The existence of parallel worlds in quantum mechanics is not a new idea in itself – they are a feature of one of the leading interpretations of quantum mechanics, the 1957 “many worlds interpretation” (MWI).
Now quantum mechanics is the most widely applicable and successful physical theory of all time, so you might wonder why it needs interpreting. There are two reasons.
First, its formalism is extremely remote from everyday experience. It is all based on a “wavefunction” which is like a wave, except that it lives not in ordinary three-dimensional space but in an infinite dimensional space.
Second, the so-called Bell correlations, which can be experimentally measured using distant quantum systems originating from a common source, violate the usual laws of local cause and effect.
This implies that the wavefunction formalism can’t be replaced by anything in ordinary space.
There are several competing interpretations of quantum mechanics and each one gives a quite different portrayal of the ultimate nature of reality. But each portrayal is profoundly strange in some way, because of the weirdness of quantum mechanics itself.
The strangeness of the MWI is in postulating that any time any quantum system is observed in a universe, that universe “branches” into a bunch of new universes, one for each possible outcome of the observation.
The MWI has been criticised for the fact that it doesn’t define precisely when an observation occurs. Thus it is vague about how many worlds there are at any given time, and each world is somewhat fuzzy in its properties, being described by a wavefunction.
Also, because different outcomes happen with different probabilities, the MWI has to postulate that different worlds have different “weights” – some worlds are more important than others even though they are all supposed to be real.
Finally, once they are created, these different worlds don’t interact, so some critics say they are purely hypothetical and serve no purpose.
Many interacting worlds
Our new theory also involves many worlds but there the similarity to the standard MWI ends.
First, we postulate a fixed, although truly gigantic, number of worlds. All of these exist continuously through time – there is no “branching”.
Second, our worlds are not “fuzzy” – they have precisely defined properties. In our approach, a world is specified by the exact position and velocity of every particle in that world – there is no Heisenberg uncertainty principle that applies to a single world. Indeed, if there were only one world in our theory, it would evolve exactly according to Newtonian mechanics, not quantum mechanics.
Third, our worlds do interact and that interaction is the source of all quantum effects. Specifically, there is a repulsive force of a very particular kind, between worlds with nearly the same configuration (that is, having nearly the same position for every single particle). This “interstitial” force prevents nearby worlds from ever coming to have the same configuration, and tends to make nearby worlds diverge.
Fourth, each one of our worlds is equally real. Probability only enters the theory because an observer, made up of particles in a certain world, does not know for sure which world she is in, out of the set of all worlds. Hence she will assign equal probability to every member of that set which is compatible with her experiences (which are very coarse-grained, because she is a macroscopic collection of particles). After performing an experiment she can learn more about which world she is in, and thereby rule out a whole host of worlds that she previously thought she might be in.
Putting all of the above together gives our theory – the Many Interacting Worlds approach to quantum mechanics. There is nothing else in the theory. There is no wavefunction, no special role for observation and no fundamental distinction between macroscopic and microscopic.
Nevertheless, we argue, our approach can reproduce all the standard features of quantum mechanics, including twin-slit interference, zero-point energy, barrier tunnelling, unpredictability and the Bell correlations mentioned above. Up to 50% off on Women’s Apparel.
We call our theory an “approach” rather than an “interpretation” because for any finite number of worlds our theory is only an approximation to quantum mechanics. This gives the exciting possibility that it might be possible to test for the existence of these other worlds.
The ability to approximate quantum evolution using a finite number of worlds could also be very useful. Specifically, it could be to model molecular dynamics, which is important for understanding chemical reactions and the action of drugs.
Quantum mechanics has always been a puzzle because of the subtle but deep ways it deviates from Newtonian mechanics. That these deviations could be due to a delicate interaction of essentially Newtonian worlds with “nearby” parallel worlds is an entirely new solution to the quantum puzzle.
For us at least there is nothing inherently implausible in the idea, and for fans of science fiction it makes those plots involving communication between parallel worlds not quite so far-fetched after all.
Tuesday, 4 November 2014
Multi_ _ _iverse affect ours
Parallel universes have long been a staple of science fiction. But according to a radical new theory of quantum mechanics published Oct. 23 in the journal Physical Review X, other universes are real--and they exist in vast numbers.
What's more, the scientists behind the theory say the other universes exert a subtle repulsive force on our own universe--and that this force is what makes the quantum realm so mind-bendingly bizarre.
"Any explanation of quantum phenomena is going to be weird, and standard quantum mechanics does not really offer any explanation at all--it just makes predictions for laboratory experiments," Prof. Howard Wiseman, a physicist at Griffith University in Brisbane, Australia, and one of the creators of the new "many interacting worlds" theory, told The Huffington Post in an email. "Our new explanation...is that there are ordinary (non-quantum) parallel worlds which interact in a particular and subtle way."
The theory is a new twist on the so-called "many worlds interpretation" of quantum mechanics, which dates back to the 1950s. As Wiseman explained in a written statement issued by the university:
"In the well-known 'many worlds interpretation,' each universe branches into a bunch of new universes each time a quantum measurement is made. All possibilities are therefore realized--in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese. But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our 'many interacting worlds' approach is completely different, as the name implies."
Wiseman and his collaborators--Dr. Michael Hall, also of Griffith University, and University of California, Davis mathematician Dr. Dirk-Andre Deckert--say that their theory may have important implications in the field of molecular dynamics, which is critical to understanding chemical reactions.
Does it also suggest that humans might someday be able to interact with other universes?
"It's not part of our theory...," Wiseman told Motherboard. "But the idea of interactions with other universes is no longer pure fantasy."
What do other experts make of the new theory?
Dr. Lawrence Krauss, a theoretical physicist at Arizona State University in Tempe, told The Huffington Post in an email that he was "skeptical." And a popular Czech Republic physicist wrote on his blog that while Wiseman and his collaborators had "managed to present some ideas that are at least slightly original," their paper was "another example of the fact that such efforts are a hopeless enterprise and a huge waste of time."
But Charles Sebens, a philosopher of physics at the University of Michigan in Ann Arbor, told Nature that he was excited by the approach taken by Wiseman and his collaborators.
“They give very nice analyses of particular phenomena like ground-state energy and quantum tunneling," he told the journal. “I think that together they do a nice job presenting this exciting new idea.”
Dr. L. William Poirer, professor of chemistry at Texas Tech University in Lubbock, also expressed support for the "many interacting worlds" theory. He told HuffPost Science in an email that Wiseman and his collaborators had made "an important contribution...There is no experimental evidence to support this yet, but if true, it means that their theory will make different experimental predictions than standard quantum mechanics does."
Clearly, there's no consensus. But if Wiseman is dismayed by the uneven reaction to the theory, he's not letting on.
"There are some who are completely happy with their own interpretations of QM, and we are unlikely to change their minds," he said in the email. "But I think there are many who are not happy with any of the current interpretations, and it is those who will probably be most interested in ours. I hope some will be interested enough to start working on it soon, because there are so many questions to answer."
In the meantime, the last word should probably belong to Nobel Prize-winning theoretical physicist Richard Feynman (1918-1988), who once said, "I believe I can safely say that nobody understands quantum mechanics."
_______ Theory _________ Quantum Mechanics?
Two USC researchers have proposed a link between string field theory and quantum mechanics that could open the door to using string field theory — or a broader version of it, called M-theory — as the basis of all physics.
“This could solve the mystery of where quantum mechanics comes from,” said Itzhak Bars, USC Dornsife College of Letters, Arts and Sciences professor and lead author of the paper.
Bars collaborated with Dmitry Rychkov, his Ph.D. student at USC. The paper was published online on Oct. 27 by the journal Physics Letters.
Rather than use quantum mechanics to validate string field theory, the researchers worked backwards and used string field theory to try to validate quantum mechanics.
In their paper, which reformulated string field theory in a clearer language, Bars and Rychov showed that a set of fundamental quantum mechanical principles known as “commutation rules’’ that may be derived from the geometry of strings joining and splitting.
“Our argument can be presented in bare bones in a hugely simplified mathematical structure,” Bars said. “The essential ingredient is the assumption that all matter is made up of strings and that the only possible interaction is joining/splitting as specified in their version of string field theory.”
The history of string theory
Physicists have long sought to unite quantum mechanics and general relativity, and to explain why both work in their respective domains. First proposed in the 1970s, string theory resolved inconsistencies of quantum gravity and suggested that the fundamental unit of matter was a tiny string, not a point, and that the only possible interactions of matter are strings either joining or splitting.
At present, no single set of rules can be used to explain all of the physical interactions that occur in the observable universe.
Four decades later, physicists are still trying to hash out the rules of string theory, which seem to demand some interesting starting conditions to work (like extra dimensions, which may explain why quarks and leptons have electric charge, color and “flavor” that distinguish them from one another).
At present, no single set of rules can be used to explain all of the physical interactions that occur in the observable universe.
On large scales, scientists use classical, Newtonian mechanics to describe how gravity holds the moon in its orbit or why the force of a jet engine propels a jet forward. Newtonian mechanics is intuitive and can often be observed with the naked eye.
On incredibly tiny scales, such as 100 million times smaller than an atom, scientists use relativistic quantum field theory to describe the interactions of subatomic particles and the forces that hold quarks and leptons together inside protons, neutrons, nuclei and atoms.
An invaluable framework
Quantum mechanics is often counterintuitive, allowing for particles to be in two places at once, but has been repeatedly validated from the atom to the quarks. It has become an invaluable and accurate framework for understanding the interactions of matter and energy at small distances.
Quantum mechanics is extremely successful as a model for how things work on small scales, but it contains a big mystery: the unexplained foundational quantum commutation rules that predict uncertainty in the position and momentum of every point in the universe.
“The commutation rules don’t have an explanation from a more fundamental perspective, but have been experimentally verified down to the smallest distances probed by the most powerful accelerators. Clearly the rules are correct, but they beg for an explanation of their origins in some physical phenomena that are even deeper,” Bars said.
The difficulty lies in the fact that there’s no experimental data on the topic — testing things on such a small scale is currently beyond a scientist’s technological ability.
Ans.
String Theory Underpins Quantum Mechanics?
In a radical new theory, scientists have proposed that parallel universes really do exist and they interact with one another.
Professor Howard Wiseman and Dr Michael Hall from Griffith University's Centre for Quantum Dynamics in Australia, and Dr Dirk-Andre Deckert from the University of California, have proposed that parallel universes exist, and rather than evolving independently, nearby worlds influence one another by a subtle force of repulsion.
The researchers said that such an interaction could explain everything that is bizarre about quantum mechanics.
Quantum theory is needed to explain how the universe works at the microscopic scale, and is believed to apply to all matter. But it is notoriously difficult to fathom, exhibiting weird phenomena which seem to violate the laws of cause and effect.
The "Many-Interacting Worlds" approach developed at Griffith University provides a new perspective on this.
"The idea of parallel universes in quantum mechanics has been around since 1957," said Wiseman.
"In the well-known "Many-Worlds Interpretation," each universe branches into a bunch of new universes every time a quantum measurement is made.
"All possibilities are therefore realised - in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese.
"But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our "Many Interacting Worlds" approach is completely different, as its name implies," he said.
Wiseman and his colleagues proposed that the universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different.
All of these worlds are equally real, exist continuously through time, and possess precisely defined properties, they said.
All quantum phenomena arise from a universal force of repulsion between 'nearby' (ie similar) worlds which tends to make them more dissimilar, they added.
Hall said the "Many-Interacting Worlds" theory may even create the extraordinary possibility of testing for the existence of other worlds.
"The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics," he said.
"In between it predicts something new that is neither Newton's theory nor quantum theory.
"We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena," Hall said.
The study was published in the journal Physical Review X.
Monday, 27 October 2014
The scent of a comet: Rotten ____ and __e
Eau de Comet isn't, we now know, the most seductive scent floating around in our galaxy. The Rosetta probe's Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) has been using its two mass spectrometers to detect the "smell" of 67P/Churyumov-Gerasimenko.
From its position in orbit around the comet, ROSINA was able to detect the chemical makeup of 67P/C-G's coma -- the halo of material surrounding the comet, which increases in intensity as the comet nears the sun and heats up, causing parts of it to sublimate.
As of September 11, the ROSINA team knew that the coma contained (in gas form) water, carbon monoxide, carbon dioxide, ammonia, methane and methanol.At 400 million kilometres (250 million miles) from the sun, the Rosetta team thought the coma would only contain the comet's most volatile molecules -- carbon dioxide and carbon monoxide -- but it is much richer than previously thought.
The new measurements have detected the presence of formaldehyde, hydrogen sulphide, hydrogen cyanide, sulphur dioxide and carbon disulphide -- albeit in relatively low density.
This heady melange -- aside from being quit toxic to humans -- would smell quite vile.
"The perfume of 67P/C-G is quite strong, with the odour of rotten eggs (hydrogen sulphide), horse stable (ammonia), and the pungent, suffocating odour of formaldehyde. This is mixed with the faint, bitter, almond-like aroma of hydrogen cyanide," said ROSINA principal investigator Kathrin Altwegg.
"Add some whiff of alcohol (methanol) to this mixture, paired with the vinegar-like aroma of sulphur dioxide and a hint of the sweet aromatic scent of carbon disulphide, and you arrive at the 'perfume' of our comet."
As 67P/C-G draws closer to the sun, it's expected that it will begin releasing more molecules. These -- and the changes in the comet's coma -- will allow the scientists to determine the composition of the comet itself. This, in turn, will allow comparison with other comets -- such as Siding Spring, which recently flew past Mars.
The 67P/C-G hails from the Kuiper Belt, within our solar system, and Siding Spring is from the Oort Cloud -- over 1,000 times further away from the sun than the Kuiper Belt. Comparing the two comets could help determine the composition of the nebula that gave birth to the sun and solar system.
Given all that, how do we know the universe as a whole is flat? One way is to look at the distribution of galaxies in the universe. One principle of cosmology is that on large enough scales the universe is homogeneous and isotropic. In other words, galaxies are distributed fairly evenly, and the universe looks pretty much the same in all directions. That isn’t true on the scale of galaxy clusters, but on a cosmic scale across billions of light years it seems to be true. If the universe wasn’t flat, then the light from distant galaxies would be distorted similar to gravitational lensing, but on a cosmic scale. We don’t see such an effect, so it seems the universe is flat. A more precise test of cosmic flatness uses the cosmic microwave background (CMB). From fluctuations in the CMB we can determine both the Hubble constant of the universe and the mass density. From these we can calculate the flatness of the universe. What we find is that to the limits of observation, the universe appears to be flat.
Although we know with high certainty that the universe is flat (or very, very close to flat), we still aren’t sure why it’s flat. It is sometimes referred to as the flatness problem, and it remains an unsolved mystery in cosmology.
Friday, 12 September 2014
The Hologram Cosmos
There has been a flurry of news articles about a new experiment that could prove we live in a two-dimensional hologram. Needless to say, we do not live in a 2-D hologram, and even if successful this new experiment would prove nothing of the sort. Unfortunately the “universe is a hologram” headlines always make great link-bait, and it doesn’t help that the press release for this experiment uses a similar link-bait headline. That said, the experiment is is very real, and if it succeeds it could revolutionize our understanding of the cosmos, so it is worth talking about.
The experiment in question is known as the Holometer, being run at Fermilab, and its goal is to detect very small fluctuations in space itself. In physics there are two main theoretical frameworks to describe the universe: general relativity and quantum mechanics. Both of these theories have been verified numerous times by experiment, and both are extraordinarily accurate descriptions of their respective regimes. The problem is that each of them paint the universe in very different ways.
In general relativity, objects are solid and continuous. Space and time can be warped by the presence of mass, and can in turn cause masses to deviate from their normal, linear paths. General relativity is a classical theory, using many of the same assumptions about physical objects that Newton did in the 1600s. Quantum mechanics, on the other hand, proposes that objects are not solid. Instead they possess a duality of particle-like and wave-like characteristics. Quantum objects are typically described within a space and time that is fixed and unaffected by things like mass.
For large objects like apples and planets, you don’t typically need to worry about their quantum nature, so the assumptions of general relativity are perfectly fine. For small objects like atoms, you don’t typically need to worry about gravity, so the assumptions of quantum mechanics are fine. The problem comes with things that are both massive and small, such as black holes and the earliest moments of the big bang. In those cases we aren’t sure where the assumptions break down, and trying to figure out the physics gets problematic at best.
It’s generally thought that at some point the quantum nature of space and time can’t be ignored. This presumes that general relativity must give way to a quantum description of space and time. Two main approaches to quantum gravity are string theory (which generalizes particle physics to include gravity) and loop quantum gravity (which strives to quantize general relativity directly). One idea that seems central to both of these approaches is known as the holographic principle, from which all the “universe is a hologram” statements arise.
The holographic principle states that the information contained within a region of space can be determined by the information at the surface that contains it. For example, suppose there is a road 10 miles long, and its is “contained” by a start line and a finish line. Suppose the speed limit on this road is 60 mph, and I want to determine if a car has been speeding. One way I could do this is to watch a car the whole length of the road, measuring its speed the whole time. But another way is to simply measure when a car crosses the start line and finish line. At a speed of 60 mph, a car travels a mile a minute, so if the time between start and finish is less than 10 minutes, I know the car was speeding. The holographic principle applies this idea to quantum gravity. Just as its much easier to measure the start and finish times than constantly measure the speed of the car, it is much easier to do physics on the surface “hologram” than it is to do physics in the whole volume.
If the holographic principle is correct, then (so the Holometer team argues) there should be quantum fluctuations within space itself due to its dual nature. This would produce a background of “holographic noise” that could in principle be detected. The Holometer team hope to detect this quantum noise over the next few years.
It should be noted that this experiment is somewhat controversial. Theoretical calculations don’t clearly support the existence of holographic noise, and observations of gamma ray bursts seem to disprove its existence at a level detectable by the Holometer experiment. This is really cutting edge science, so it’s difficult to predict what the outcome will be.
What we do know for sure is that if the project is successful there will be lots of headlines declaring that the universe is a hologram. They will be wrong. It would just be the first direct detection of the quantum nature of gravity, which we’ve long suspected but haven’t been able to prove.
Sunday, 17 August 2014
Light is not the fastest
One of the fundamental principles of modern physics is that nothing can travel faster than light. Of course when this is mentioned, someone usually suggests a way to get around that limit. What about warp drive, for example. Or what about tachyons? These are hypothetical particles that can never go slower than the speed of light. What I like about tachyons is that it’s a good example of how what seems like a simple and obvious solution turns out to be deeply complex when you take it seriously.
The basic idea of tachyons comes from special relativity. One of the things we know is that the observed speed of light is the same no matter what frame of reference you are in. Two observers could be moving away from each other at nearly the speed of light, and they would each measure the same light speed. In order for this to work, some strange physics has to occur. As you approach the speed of light (as seen from another observer), your time would appear to slow down, and your mass would appear to increase. Both of these conspire to ensure that you can never reach the speed of light. It would take an infinite amount of energy to do so, which simply isn’t possible.
But many people have pointed out that technically special relativity prevents you from crossing light speed, not moving faster than light. In principle you could start with a speed faster than light, and special relativity would require that you never move slower than light. These hypothetical objects are often called tachyons. It seems light a clear solution to light’s speed limit, but it turns out things are not so simple.
To begin with, any faster-than-light object would still be viewed by the light coming from the object. Since light is governed by the cosmic speed limit, we wouldn’t actually observe something moving faster than light. Instead, as a tachyon raced past us, we would observe two particles racing away from each other. One as an echo of the object as it speeds away from us, the other as a “past” echo from when the object was speeding toward us. Both of these echo particles would appear to move slower than light.
Then there is the problem with special relativity itself. If you presume a particle is always moving faster than light, but obeys special relativity, then the math requires that the mass of tachyons be imaginary. As far as we know, all particles have positive mass. Some have speculated that antiparticles might have negative mass, but there is no evidence to support that idea. Still, you might argue, photons have zero mass, so perhaps imaginary mass is possible. We shouldn’t discard an idea just because of imaginary mass.
Fair enough, but even if we allow for imaginary mass tachyons, they should still conform to quantum theory. In quantum theory, objects are described as quantum fields, from which we can observe non-local “wave-like” effects and local “particle-like” effects. The mathematics of quantum theory is very clear, so it is relatively straightforward to plug an imaginary mass into the equations to see what happens. When you do that, it looks like a description of a faster-than-light particle, but when you look closely what you find is that the “particle” aspect of the quantum field actually travels slower than light. So what started as a simply solution to move faster than light turns out to be something that moves slower than light.
Interestingly, imaginary mass does appear in certain areas of physics. In superconductivity, for example, quantum fields can have an “effective” imaginary mass through the superconductor. Particles don’t really have imaginary mass, but the interaction between materials and currents makes it easy to describe in that way.
Often in “alternative” physics you will see simple answers proposed to difficult problems. Just break a basic physical law or propose a radically different interpretation to standard science, and the solution is “obviously” clear. But as we can see, even a small tweak of known physical theories has a kind of cascade effect, which only appear when you look at things closely. Even then, the effect can be radically different than you initially thought.
