Stringscape

Problems such as how to cool a 27 km-circumference, 37,000 tonne ring of superconducting magnets to a temperature of 1.9 K using truck-loads of liquid helium are not the kind of things that theoretical physicists normally get excited about.

Strings 07 kicked off their main conference this year with an update on the latest progress being made at the Large Hadron Collider (LHC) at CERN, which is due to switch on next May.

The possibility, that evidence for string theory might turn up in the LHC's 14 TeV proton–proton collisions was prominent among discussions at the five-day conference, held in Madrid in late June.

Talks were peppered with the language of real-world data, particles and fields - particularly in relation to cosmology. Admittedly these more tangible concepts were buried within the esoteric grammar of higher-dimensional mathematics, where things like "GUT-branes", "tadpoles" and "warped throats" lurk. However, Strings07 was clearly a physics event, and not one devoted to mathematics, philosophy or perhaps even theology.

Continue Reading: Stringscape Page One Superstring Revolution Page Two
Dimensions & Across the Landscape Page Three String Cosmology Page Four
The early universe may allow us to 'see' additional dimensions by Physics World
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CERN in 3 minutes
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Lisa Randall CERN 2007

Black Holes and Quantum Gravity at the LHC
The talk focused on models with higher dimensions of quantum gravity in the context of a low quantum gravity scale. How low ? Well, as low as one can hope for - about 1 TeV or so. Naturally, at the LHC one would expect quite dramatic signatures.

Should LHC be looking at black hole production or elsewhere ?
The questions experimentalists have to ask themselves at the start of a project like the LHC, which will explore unknown new energy scale and domains: - “Are we optimizing existing searches for the signatures we might have access to ?” and “Are we sure we are not missing possible searches ?”
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One interesting question, connected to the scope of Lisa’s talk, is: “If there is new physics, but it lies at a higher energy scale than the one directly accessible by the machine, how do we maximize our chances to see it ?”

Historically, the reason that black holes appear so promising as compared with other possible signatures is the predicted huge cross section for their production if there is a low quantum gravity scale. Lisa ventured to compute that if quantum gravity turns on at a scale of a TeV, one gets 100 pb which for 100 fb-1 luminosity would yield ten million events.

The basic reason why this cross section is so large compared to the production of a particle with TeV mass in a typical beyond the SM theory is the lack of any small couplings, such as gauge couplings in the cross section and absence of phase space suppression factors. However, this estimate ignores several major considerations and uncertainties in the black hole production and decay cross sections.

There is no suppression from gauge couplings, so it is indeed a large signal. Also, the signature is spectacular, since these objects are predicted to decay into large multiplicity final state, with highly spherical distributions. Very distinctive, unmistakable new physics.

But the problem is that the idyllic picture is not very realistic. The onset of a non-perturbative regime where black holes are produced and decay with those signatures is much above the QG scale, and this appears to be above the reach of even the LHC.

The Large Hadron Collider (LHC) at CERN has not emitted the first burp yet, and it is already criticized for being a midget. In any case, at threshold one would not see the striking signatures, but maybe something can be saved.

Randall was very clear in stating that the LHC is unlikely to make classical BH states decaying with Hawking radiation. She appeared to be interested in assessing the damage: and the answer is that, if you have a low quantum gravity scale and you cross it, you will have a change in the two-particle final states. Things are not calculable, but there appear to still be distincitve experimental signatures that are capable of distinguishing among different models.

You have to go well above M, the energy scale of quantum gravity, to be sure to hit the striking signatures publicized in the past. The parton distribution functions of the proton drop rapidly with the fraction of parton momentum, and since we are by necessity near threshold, the value of the latter is very important in determining what the rate of the new process is going to be. To make matters worse, M is convention-dependent. Factors of - fly around easily, and although one knows these are only conventions and what one cares for is just the actual threshold, there is a big difference between 1 TeV and 2 TeV for the LHC. So the picture is fuzzy.


Bubble Chamber: Leonard Susskind & Lisa Randall

Lisa discussed some of the models and the resulting conventions and equations for the schwarzschild radius, the energy scale, and the other main characteristics.

One point which looked important is that in the models considered, the black hole lifetime is bigger than the inverse of the energy scale of quantum gravity. This drives some of the phenomenology of the black hole decay. Another point is that every degree of freedom should carry an insignificant amount of energy with respect to the total; and since we are never going to get far above threshold at the LHC, we will have to be careful to call what we produce a real classical black hole. These things have low entropy close to threshold, and the multiplicity of the decay will be affected.

A critical factor in the computation of the number of particles emitted in the black hole decay is the assumption of the dimensionality of the space: particles emitted in the bulk have more directions in which to oscillate. Furthermore, since the threshold for producing black holes is not M, but a higher energy, even if we did see a black hole, we would not be able to extract M from the total cross section, because of inelasticity effects: not all the energy of the colliding partons goes in the creation of the black hole, due to initial state radiation.

The difficult question to answer is in fact, what fraction of the energy gets trapped inside the horizon? It is of course important since the PDF fall rapidly with energy. What is clear is that the inelasticity effectively increases the threshold. The reduction in cross section due to this effect is enormous, and it is the lack of considering it, which has brought some overoptimistic predictions in the past.

So, the upshot is that BH production threshold is higher than originally thought. It means a lower production cross section, a lower reach in black hole mass, and it translates into lower entropy reach as well. The conclusion of Lisa Randall is that we will not produce classical thermal black holes at the LHC. What will we still be able to produce, then ? And what kind of multiplicities should we expect ?

Lisa discussed the calculation of the multiplicity of final state particles. She said that the calculation is totally unreliable. But one thing stays clear: low multiplicity final states will dominate even if we call it black holes. So we have to face the facts, and study 2-body final states: jets and leptons. Can they be distinguished from backgrounds by rate, kinematics, bra size? Yes. For jets, transversality is the key. QCD is dominated by t-channel exchange, i.e., forward scattering. Black hole events are isotropic. So this is really becoming like any other compositeness search: massive states produced at low rapidity.

While describing a scenario where the LHC will have to walk the walk of unclear kinematical analyses rather than being hit in the face by those firework-like signatures that experimentalists have started to dream more and more frequently as of late, Randall was careful to insist that the LHC is indeed a powerful machine, although she fell short of declaring it will make everything clear about quantum gravity.

After discussing the signature of black holes, Randall delved into the possible signatures of the same kind from alternative models of quantum gravity, such as a weakly coupled string theory. There one apparently expects a resonance behaviour, followed by a dramatic drop in transverse cross section, which can be used to distinguish the stringy behavior from the simple production of a new Z’ boson, ...

In addition to the resonance, you would also see a drop in the quantity. This could also allow to distinguish models: you could decide you are finding a stringy state, and you could even distinguish different stringy models, because the correlation between and the cross section is different for different models. In summary, black holes are not as spectacular as advertised in the past. However, they may still provide lots of information about quantum gravity, through careful studies of processes.

Lisa also said she would love to see these studies done by Atlas and CMS: energy-dependent angle studies in dijet production.

Tommaso Dorigo asked the question: "I know from previous blogging on the issue that when one reaches a quantum gravity regime, the QCD cross section of dijet production has to go down, but Lisa had not discussed this feature." She explained that before one reaches the regime when QCD 2-particle cross section gets reduced, the cross section has to go up, in any case. So the dijet cross section reduction that Sabine has first studied happens at a regime that LHC will fail to cover.

Source: Lisa Randall: black holes out of reach of LHC
by Tommaso Dorigo @ A Quantum Diaries Survivor.
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Lisa Randall: Unification in warped extra dimensions and bulk holography
Lisa Randall: Smashing open the Universe @ Prospect Magazine.
Event probability for Production of Single Top Quarks using Matrix Elements

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M-branes & large X-tra dimensions

Itis courtesy of Barngoddess @ Ramblings from the Reservation

Straight from the horses mouth.

In String Theory, the myriad of particle types is replaced by a single fundamental building block, a `string'. These strings can be closed, like loops, or open, like a hair. As the string moves through time it traces out a tube or a sheet, according to whether it is closed or open. Furthermore, the string is free to vibrate, and different vibrational modes of the string represent the different particle types, since different modes are seen as different masses or spins.

One mode of vibration, or `note', makes the string appear as an electron, another as a photon. There is even a mode describing the graviton, the particle carrying the force of gravity, which is an important reason why String Theory has received so much attention. And gravity is not something we put in by hand. It has to be there in a theory of strings. So, the first great achievement of String Theory was to give a consistent theory of quantum gravity, which resembles GR at macroscopic distances.

In order to describe our world, strings must be extremely tiny objects. So when one studies string theory at low energies, it becomes difficult to see that strings are extended objects — they become effectively zero-dimensional (pointlike). Consequently, the quantum theory describing the low energy limit is a theory that describes the dynamics of these points moving in spacetime, rather than strings. Such theories are called quantum field theories.

However, since string theory also describes gravitational interactions, one expects the low-energy theory to describe particles moving in gravitational backgrounds. Finally, since superstring string theories are supersymmetric, one expects to see supersymmetry appearing in the low-energy approximation. These three facts imply that the low-energy approximation to a superstring theory is a supergravity theory.

Prior to M-theory, strings were thought to be the single fundamental constituent of the universe, according to string theory. When M-theory unified the five superstring theories, another fundamental ingredient was added to the makeup of the universe - membranes.

A membrane, or brane, is a multidimensional object, usually called a p-brane, p referring to the number of dimensions in which it exists.

Joseph Polchinski discovered a fairly obscure feature of string theory. He found that in certain situations the endpoints of strings (strings with "loose ends") would not be able to move with complete freedom as they were attached, or stuck within certain regions of space. Polchinski then reasoned that if the endpoints of open strings are restricted to move within some p-dimensional region of space, then that region of space must be occupied by a p-brane.

Not all strings are confined to p-branes. Strings with closed loops, like the graviton, are completely free to move from membrane to membrane. Of the four force carrier particles, the graviton is unique in this way. Researchers speculate that this is the reason why investigation through the weak force, the strong force, and the electromagnetic force have not hinted at the possibility of extra dimensions. These force carrier particles are strings with endpoints that confine them to their p-branes. Further testing is needed in order to show that extra spatial dimensions indeed exist through experimentation with gravity.

M-theory should be viewed as an 11 dimensional theory that looks 10 dimensional at some points in its space of parameters. Such a theory could have as a fundamental object a Membrane, as opposed to a string. Like a drinking straw seen at a distance, membranes would look like strings when we curl the 11th dimension into a small circle.

Could two 4 dimensional 'universes' have a region in common, like two lines of the same plane have a common point? If so, could something cross from one 'universe' to the other?

The M-Theory vision, although not yet complete, is of the whole observable universe being one of many extended 4 dimensional branes in an 11 dimensional spacetime.
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M-Theory Cambridge DAMPT University of Cambridge
The Elegant Universe with Brian Greene @ Nova Physics
Braneworld and the hierarchy in RS1 (Randall-Sundrum 1 Model) by Flip Tomato
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ALICE gets uk brain

As construction of the World`s largest machine, the Large Hadron Collider (LHC) at CERN in Geneva (Switzerland), gears up for completion next year, the four main experiments, that will study different aspects of the resulting high-energy particle collisions, are also gearing up. For one such experiment, called ALICE, this process got a step closer last week when a crucial part of the 10,000-ton detector, the British-built Central Trigger Processor (CTP), was installed in the ALICE cavern, some 150 feet underground.

The ALICE experiment will probe the mysteries surrounding the structure of matter. Head-on collisions of lead nuclei at the LHC will create sub-atomic sized fireballs with huge temperatures and densities and recreate the conditions that are believed to have existed less than a millionth of a second after an event commonly known as the Big Bang.

These 'mini Big Bangs' will produce temperatures of over a trillion degrees - 100,000 times hotter than the centre of the Sun – and neutrons and protons (which make up the nuclei of atoms) are expected to 'melt' into a new state of matter – quark-gluon plasma.

A quark-gluon plasma (QGP) is a phase of quantum chromodynamics (QCD) which exists at extremely high temperature and/or density. This phase consists of (almost) free quarks and gluons which are the basic building blocks of matter. QGP is believed to have existed during the first 20 to 30 microseconds after the universe came into existence in the process following a Big Bang.

Contrary to popular myth, ALICE is not likely to produce Black Holes, nor the singularities produced by matter in bulk.

ALICE, is the acronym for A Large Ion Collider Experiment, one of the largest experiments in the world devoted to research in the physics of matter at an infinitely small scale.

Scientists have found that everything in the Universe is made up from a small number of basic building blocks called elementary particles, governed by a few fundamental forces.

Some of these particles are stable and form the normal matter, the others live for fractions of a second and then decay to the stable ones. All of them would have coexisted for a few instants after the Big Bang.

Since then, only the enormous concentration of energy that can be reached in an accelerator at CERN can bring them back to life. Therefore, studying particle collisions is like "looking back in time", recreating the environment present at the origin of our Universe.

By studying particle collisions we hope to learn more about the force that holds atomic nuclei together (the strong force), the origin of the mass of nuclear matter and much, much more.

The most familiar basic force is gravity. It keeps our feet on the ground and the planets in motion around the Sun. On individual particles though, the effects of gravity are extremely small. Only when we have matter in bulk - as in ourselves or in planets - does gravity dominate.
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Microscopic microstate blackholes at the LHC by Lubos @ the Reference Frame
The Quark Gluon Plasma paradox by Dorigo @ A Quantum Diaries Survivor
NASA scientists pioneer technique for 'weighing' black holes EurekAlert!
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Universal Feast

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Photo thanks to Jimmy James @ Under The Ledge click image to enlarge


Logic would dictate that just as there is space time, there is Space outside TIME.

In spacetime we can take a snapshot and freeze time, we can even rewind a film on video or dvd, but we do this travelling forward thru time. Even when we look at the distant stars and galaxies in the universe, we are looking at the light that reaches us on Earth, from a time long past.
[+/-] Click here to expand

Time (and even Space) as we shall see is relative to the observer, and as humans we are travelling thru time (and ageing over time).

It is movement that creates the impermanence of time, but there must be a Space outside Time where motion (or movement) is possible without decay, ageing, disease, suffering or death - among the multiverses that Leonard Susskind & Alex Vilenkin would like us to be aware of (see or imagine) - they seem to have ommited the one Above All where Time itself does not exist.

Just for a moment imagine yourself looking at a film of yourself on a 2D or 3D screen, now take a further step back and look at yourself in 3D+T (from outside Time).

Quasar9

Stephen Hawking has worked on the basic laws which govern the universe. With Roger Penrose he showed that Einstein's General Theory of Relativity implied space and time would have a beginning in the Big Bang and an end in black holes.

These results indicated it was necessary to unify General Relativity with Quantum Theory, the other great Scientific development of the first half of the 20th Century. One consequence of such a unification that he discovered was that black holes should not be completely black, but should emit radiation and eventually evaporate and disappear.

Another conjecture is that the universe has no edge or boundary in imaginary time. This would imply that the way the universe began can be completely determined by the laws of science.

Stephen Hawking

We live in the aftermath of a great explosion. This awesome event, called somewhat frivolously the big bang, took place about 14 billion years ago. We can actually see some of the cosmic history unfolding before us since that moment—light from remote galaxies takes billions of years to reach our telescopes on earth, so we can see galaxies as they were in their youth.

But there is a limit to how far we can see into space. Our horizon is set by the maximum distance light could have traveled since the big bang. Sources more distant than the horizon cannot be observed, simply because their light has not yet had time to reach Earth.

And if there are parts of the universe we cannot detect, who can resist wondering what they look like? Until recently physicists thought that the answer to this question is rather boring: it’s just more of the same – more galaxies, more stars. But now, recent developments in cosmology have led to a drastic revision of that view.

According to the new picture, distant parts of the universe are in the state of explosive, accelerated expansion, called “inflation”. The expansion is so fast that in a tiny fraction of a second a region the size of an atom is blown to dimensions much greater than the entire currently observable universe. The expansion is caused by a peculiar form of matter, called “false vacuum”, which produces a strong repulsive force.

The word “false” refers to the fact that, unlike the normal “true” vacuum, this type of vacuum is unstable and typically decays after a brief period of time, releasing a large amount of energy. The energy ignites a hot fireball of particles and radiation. This is what happened in our cosmic neighborhood 14 billion years ago – the event we refer to as the big bang.

With inflation, the two competing processes are the decay of the false vacuum and its “reproduction” by rapid expansion of the inflating regions. My calculations, and those of Andrei Linde, show that false-vacuum regions multiply much faster than they decay, and thus their volume grows without bound.

At this very moment, some distant parts of the universe are undergoing exponential inflationary expansion. Other regions like ours, where inflation has ended, are also constantly being produced. They form “island universes” in the inflating sea of false vacuum. Because of inflation, the space between the islands rapidly expands, making room for more island universes to form.

Inflation is thus a runaway process that has stopped in our neighborhood, but still continues in other parts of the universe, causing them to expand at a furious rate and constantly spawning new island universes like our own. This never ending process is referred to as “eternal inflation”.


The role of the big bang in this scenario is played by the decay of the false vacuum. It is no longer a one-time event in our past: multiple bangs went off before it in remote parts of the universe, and countless others will erupt elsewhere in the future.

Analysis shows that the boundaries of island universes expand faster than the speed of light. (Einstein’s ban on super-luminal speeds applies to material bodies, but not to geometric entities such as the boundary of an island.) It follows that, regrettably, we will never be able to travel to another island, or even send a message there. Other island universes are unobservable, even in principle.

In the global view of eternal inflation, the boundaries of island universes are the regions where big bangs are happening right now. Newly formed islands are microscopically small, but they grow without limit as they get older. Central parts of large island universes are very old: big bangs once took place there long time ago. Now they are dark and barren: all stars have long since died there. But regions at the periphery of the islands are new and must be teeming with shining stars.

The inhabitants of island universes, like us, see a different picture. They do not perceive their universe as a finite island. For them it appears as a self-contained, infinite universe. That dramatic difference in perspective is a consequence of the differences imposed by the ways of keeping time appropriate to the global and internal views of the island universe. (According to Einstein's theory of relativity, time is not fixed, but instead is observer dependent.)

Perhaps the easiest way to see this is to count galaxies. In the global view, new galaxies are continually formed near the expanding boundaries, so as time passes, we have an infinite number of galaxies in the limit. In the internal view, all this infinity of galaxies exists simultaneously (say, at time 14 billion years). The implications are extraordinary.

Since each island universe is infinite from the viewpoint of its inhabitants, it can be divided into an infinite number of regions having the same size as our own observable region. My collaborator Jaume Garriga and I call them O-regions for short. As it happens, the most distant objects visible from Earth are about 40 billion light-years away, so the diameter of our own O-region is twice that number.

Quantum fluctuations in the course of eternal inflation ensure that all possible values of the constants are realized somewhere in the universe. As a result, remote regions of the universe may drastically differ in their properties from our observable region. The values of the constants in our vicinity are determined partly by chance and partly by how suitable they are for the evolution of life. The latter effect is called anthropic selection.

Another recent application of the principle of mediocrity, unrelated to string theory, is to the amount of dark matter in the universe. As its name suggests, dark matter cannot be seen directly, but its presence is manifested by the gravitational pull it exerts on visible objects. The composition of dark matter is unknown. One of the best motivated hypotheses is that it is made up of very light particles called axions. The density of axionic dark matter is set by quantum fluctuations during inflation and varies from one place in the universe to another.

Alex Vilenkin

However, it is clear that just as photons can be in many possible places but are only actually in one, we as humans though we can potentially be in many places are only actually ever in one, and that one place will be wherever we happen to be in 1) our physical body, and 2) our mind or mental state.

All our other states in Vilenkin's multiverses are effectively or conceptually in a different time frame, or outside Time - but they are unlikely to be at the same time. After all we can talk to many people in an auditorium or through tv, but we can only ever hold a one to one with one person at a time, and a dialogue or conversation with a few at most - even during video conferencing.

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The multiverse is like a flower from Dialogues of Eide
Quantum Phase Transitions from Science Daily releases
Universe offers 'eternal feast' by alinde@stanford.edu
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Extra Spatial Dimensions

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Physicists at the University of Wisconsin-Madison have devised an approach that may help unlock the hidden shapes of alternate dimensions of the universe.

A new study demonstrates that the shapes of extra dimensions can be "seen" by deciphering their influence on cosmic energy released by the violent birth of the universe 13 billion years ago. The method, published 02/02/07 in Physical Review Letters, provides evidence that physicists can use experimental data to discern the nature of these elusive dimensions.

String theory, proposes that everything in the universe is made of tiny, vibrating strings of energy, to encompass the physical principles of all objects from immense galaxies to subatomic particles. Though currently the front-runner to explain the framework of the cosmos, the theory remains, to date, untested.

The mathematics of string theory suggests that the world we know is not complete. In addition to our four familiar dimensions (three-dimensional space and time) string theory predicts the existence of six extra spatial "hidden" dimensions curled in tiny geometric shapes at every single point in our universe.

Maybe you can't picture a 10-dimensional world. Our minds are accustomed to only three spatial dimensions and lack a frame of reference for the other six, says UW-Madison physicist Gary Shiu, who led the new study. Though scientists use computers to visualize what these six-dimensional geometries could look like (see image), no one really knows for sure what shape they take.


A computer-generated rendering of a possible six-dimensional geometry similar to those studied by UW-Madison physicist Gary Shiu. (Image: courtesy Andrew J. Hanson, Indiana University)

According to string theory mathematics, the extra dimensions could adopt any of tens of thousands of possible shapes, each shape theoretically corresponding to its own universe with its own set of physical laws. For our universe, Nature picked one.

The many-dimensional shapes are far too small to see or measure through any usual means of observation, which makes testing this crucial aspect of string theory very difficult.

Just as a shadow can give an idea of the shape of an object, the pattern of cosmic energy in the sky can give an indication of the shape of the other six dimensions present, Shiu explains.

To learn how to read telltale signs of the six-dimensional geometry from the cosmic map, they worked backward. Starting with two different types of mathematically simple geometries, called warped throats, they calculated the predicted energy map that would be seen in the universe described by each shape. When they compared the two maps, they found small but significant differences between them.

The results show that specific patterns of cosmic energy can hold clues to the geometry of the six-dimensional shape.

Story adapted from a news release by University of Wisconsin-Madison
more Physicists Find Way To 'See' Extra Dimensions from Science Daily
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Calabi Yau from WMAP by Lubos Motl
Symmetry in psychological action by Plato
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Testing String Theory

Scientists have developed a test based on studies of how strongly W bosons scatter in high-energy particle collisions generated within a particle accelerator.

W bosons are special because they carry a property called the weak force, which provides a fundamental way for particles to interact with one another.

String Theory includes three mathematical assumptions — Lorentz invariance (the laws of physics are the same for all uniformly moving observers), analyticity (a smoothness criteria for the scattering of high-energy particles after a collision) and unitarity (all probabilities always add up to one). Our test sets bounds on these assumptions.

If the test does not find what the theory predicts about W boson scattering, it would be evidence that one of string theory's key mathematical assumptions is violated. In other words, string theory in its current form, would be proven impossible. If the bounds are satisfied, we would still not know that string theory is correct.


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Image Credit: Caltech - hologram

String theory attempts to unify nature's four fundamental forces — gravity, electromagnetism, and the strong and weak forces — by positing that everything at the most basic level consists of strands of energy that vibrate at various rates and in multiple, undiscovered dimensions. These "strings" produce all known forces and particles in the universe, thus reconciling Einstein's theory of general relativity (the large) with quantum mechanics (the small).

Proponents say that string theory is elegant and beautiful. Dissenters argue that it does not make predictions that can be tested experimentally, so the theory cannot be proven or falsified. And no particle accelerator yet exists that can attain the high energies needed to detect strings. Because of this technical limitation, tests of string theory have remained elusive until now.

Since we don't have a complete understanding of string theory, it's impossible to rule out all possible models that are based on strings. However, most string theory models are based upon certain mathematical assumptions, and what we've shown is that such string theories have some definite predictions that can be tested.
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Famous Quotes: It is true without lying, certain and most true. That which is Below is like that which is Above and that which is Above is like that which is Below to do the miracles of the Only Thing. And as all things have been and arose from One by the mediation of One, so all things have their birth from this One Thing by adaptation - Sir Isaac Newton
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Supersymmetry

Welcome to the mirror world, in which every particle in the known universe could have a counterpart. This cosmos would hold mirror planets, mirror stars, and even mirror life.

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Alice & the Cosmic Ballet, Now meet Higgins by Plato
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Seeing SUSY - desperately seeking Sushie
All current major high-energy collider experiments are desperately seeking SUSY and/or extra dimensions. One of the crucial searches is for a Higgs boson: SUSY suggests that one might well be visible at CERN's LEP electron-positron collider. Future collider experiments are also gearing up to look for new particles. The Fermilab Tevatron will resume the sparticle and Higgs searches after LEP is retired, and has quite good prospects. In the longer run, the LHC is expected to produce Higgs bosons and any supersymmetric particles. It will also be able to probe for extra dimensions at shorter scales than any previous experiments. There is optimism that the next generation of collider experiments will break out of the SM straitjacket. The issue of the cosmological constant - the energy density of free space - has been the most striking problem in quantum field theory for many years. Experimentally, it has long been known that it is very close to zero. According to the latest observations a (very) small non-zero value is now preferred, and this is further supported by cosmic microwave background observations by the BOOMERANG and MAXIMA collaborations. However, the result of theoretical calculations in quantum field theory is naturally a number at least 60 orders of magnitude bigger. SUSY has long held out the promise of a resolution to this dilemma, but so far has not been able to claim a solution. However, many new ideas of how to approach this problem are also suggested by brane theories and were discussed at SUSY2K.

Extra dimensions
Models predict The world we experience is complemented by extra (but to us invisible) spatial dimensions. These models have the common feature that our SM world is realized as localized degrees of freedom living on a generalized 3-spatial-dimensional membrane ("3-brane") embedded in a universe possessing a larger number of dimensions. In this approach, it is possible that the fundamental scale of gravity might be the TeV scale, rather than the embarrassingly distant Planck scale (1019 GeV), potentially eliminating the hierarchy problem (see "Particles and sparticles"). This requires a fundamental rethinking of cosmology and the high-energy behaviour of SM physics. Many questions are being reformulated in terms of the geometry of the extra dimensions - their sizes and shapes, and the fields localized on them. In the same way that general relativity introduced geometry as the natural explanation of gravity, so concepts of geometry and locality replace the ideas of symmetry usually used in field theory. Superstring theory naturally incorporates such branes and gives, at least in toy models, explicit realizations of the brane-world idea. One major question is the radiative stability of such models - that their predictions are compatible with accompanying virtual quantum effects. Without SUSY, the apparently haphazard hierarchy of the different forces of nature, with each force having very different associated mass scales, is not stable (or rather requires fine tuning). SUSY can take care of this problem, and new light may be cast by brane physics. At the moment there are two main approaches to the construction of extra-dimensional models. Originally, it was thought that the geometry of the extra coordinates should be distinct from our space - the universe at large could be viewed as the product of two spaces. In this case, a solution to the hierarchy problem requires large extra dimensions and quantum gravity physics at the TeV scale. In a more recent approach, highly-curved geometries have been proposed, which tightly constrain the brane in which we live. In this very different geometry, gravity is concentrated away from our world, explaining its observed weakness for us. Both schemes have very specific signatures for experiments at high-energy colliders.

Particles and sparticles
Standard Model (SM) particles come off the shelf in two kinds - fermions (matter particles) such as quarks, electrons, muons, etc.) and bosons (force carriers) such as photons, gluons, Ws and Zs. A feature of SUSY is that every matter particle (quark, electron...) has a boson counterpart (squark, selectron...) and every force carrier (photon, gluon) has a fermion counterpart (photino, gluino, chargino, neutralino...). This doubling of the spectrum is due to the fact that SUSY is a quantum-mechanical enhancement of the properties and symmetries of the space-time of our everyday experience - such as translations, rotations and Lorentz boosts. SUSY introduces a new form of dimension - one that is only defined quantum mechanically, and does not possess the classical properties we associate with a new dimension, such as continuous "extent". The doubling of the particle population can fix several of the problems afflicting today's SM, for instance why the different forces - gravity, electromagnetism, weak and strong - appear to operate at such vastly different and apparently arbitrary scales (the "hierarchy problem"). The extra particles provided by SUSY are also natural candidates for exotica such as the missing "dark matter" of the universe.

Mass communication
Many attractive new communication mechanisms for SUSY breaking were reviewed at the SUSY2K conference. In "archetypal" SUSY breaking, gravity takes on the role of communicating between the SUSY breaking sector and the conventional world, and, until recently, this gravity-mediated SUSY breaking was considered as the most plausible possibility. However, during the last few years many innovative new mechanisms have been proposed - "gauge mediation" (with heavy messenger particles communicating the breaking), "anomaly mediation" (via symmetries that are broken at the quantum but not at the classical level), and "gaugino mediation" (when the SUSY partners of the SM gauge bosons take on the mediating role). These different mechanisms have characteristic mass spectra and experimental signatures. Supersymmetry might not manifest itself as neutrino-like invisible events detectable only through "missing" energy, but in several other ways, for example in events producing additional photons or stable charged particles, or models with supersymmetric particles that are nearly degenerate in mass. Experiments at LEP and elsewhere have been looking for these various possibilities, but without any luck so far (see "Particles and sparticles" below).

Supersymmetry Physics on (and off) the brane
For all its spectacular experimental successes, the Standard Model (SM) fails to give us solutions to such basic problems as why there are three copies (generations) of quarks and leptons, why there are three different gauge forces (the strong, weak and electromagnetic, with differing strengths), and how gravity should be included in a consistent quantum theory along with the gauge forces. Supersymmetry (SUSY) is the leading contender for physics beyond the SM. Although SUSY has been around for some time and has so far had no direct experimental support, indirect experimental hints and progress in understanding the theoretical possibilities allowed for in a SUSY world have led to a new feeling of excitement. With these new ideas on the market, the Supersymmetry 2000 (SUSY2K) conference, held recently at CERN, attracted a large crowd and showed how the new SUSY ideas can help. SUSY makes precise predictions for the quantum numbers and selection rules for many new particles. What is much more difficult is predicting the masses of these additional supersymmetric particles. The reason for this is that SUSY must be a so-called "broken" or hidden symmetry, and the mechanism of communication of SUSY breaking to the SM and its superpartners is inevitably indirect, not well constrained, and is poorly understood. As a comparison, the unification of weak and electromagnetic gauge forces in the electroweak sector is also "broken" or hidden - with the Higgs mechanism leading to very different masses for the electromagnetic photon and the W and Z carriers of the weak force. For SUSY, such a direct coupling to the sector that breaks SUSY (analogous to the direct coupling of the electroweak force to the Higgs) is not possible, because such a coupling leads to sum rules for the masses of the unobserved superpartners (see box) that are definitively excluded. Thus an indirect communication of SUSY breaking must be employed
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Picture Dark Energy Harvard

Dark matter
If SUSY is correct then it would have played an important role in the Big Bang. For example, SUSY might have played a role in the generation of the observed matter in the universe. However, one of the most important issues is that of possible SUSY remnants of the Big Bang, which could play the role of the invisible "dark matter" known to pervade our universe. One of the most attractive features of SUSY is that it provides quite naturally a candidate, the "neutralino". Experimental searches for such particle dark matter are just beginning to reach the range suggested by theory. However, SUSY must also contend with the strong upper limits on various unwanted supersymmetric particles such as gravitinos. SUSY2K showed that supersymmetry is assured of an exciting future.

Original Text from CERN courier
Picture: wmc by William M Connolley stoat @ scienceblogs
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Strings in the Universe

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Credits for X-ray Image: NASA/CXC/ASU/J. Hester et al.

Weber's Oscillations
In the late 1950s, Weber became intrigued by the relationship between gravitational theory and laboratory experiments. His book, General Relativity and Gravitational Radiation, was published in 1961, and his paper describing how to build a gravitational wave detector first appeared in 1969. Weber's first detector consisted of a freely suspended aluminium cylinder weighing a few tonnes. In the late 1960s and early 1970s, Weber announced that he had recorded simultaneous oscillations in detectors 1000 km apart, waves he believed originated from an astrophysical event. Many physicists were sceptical about the results, but these early experiments initiated research into gravitational waves that is still ongoing. Current gravitational wave experiments, such as the Laser Interferometer Gravitational Wave Observatory (LIGO) and Laser Interferometer Space Antenna (LISA), are descendants of Weber's original work.
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Renaud Parentani's high frequencies
The study of acoustic black holes has been undertaken to provide new insights about the role of high frequencies in black hole evaporation. Because of the infinite gravitational redshift from the event horizon, Hawking quanta emerge from configurations which possessed ultra high (trans-Planckian) frequencies. Therefore Hawking radiation cannot be derived within the framework of a low energy effective theory; and in all derivations there are some assumptions concerning Planck scale physics. The analogy with condensed matter physics was thus introduced to see if the asymptotic properties of the Hawking phonons emitted by an acoustic black hole, namely stationarity and thermality, are sensitive to the high frequency physics which stems from the granular character of matter and which is governed by a non-linear dispersion relation. In 1995 Unruh showed that they are not sensitive in this respect, in spite of the fact that phonon propagation near the (acoustic) horizon drastically differs from that of photons. In 2000 the same analogy was used to establish the robustness of the spectrum of primordial density fluctuations in inflationary models. This analogy is currently stimulating research for experimenting Hawking radiation. Finally it could also be a useful guide for going beyond the semi-classical description of black hole evaporation.
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Strominger:
Boltzmann had one–the theory of molecules. We needed a microscopic theory for black holes that had to have three characteristics: One, it had to include quantum mechanics. Two, it obviously had to include gravity, because black holes are the quintessential gravitational objects. And three, it had to be a theory in which we would be able to do the hard computations of strong interactions. I say strong interactions because the forces inside a black hole are large, and whenever you have a system in which forces are large it becomes hard to do a calculation.
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String Theory
String theory grew out of attempts to find a simple and elegant way to account for the diversity of particles and forces observed in our universe. The starting point was to assume that there might be a way to account for that diversity in terms of a single fundamental physical entity (string) that can exist in many "vibrational" states. The various allowed vibrational states of string could theoretically account for all the observed particles and forces. Unfortunately, there are many potential string theories and no simple way of finding the one that accounts for the way things are in our universe.
One way to make progress is to assume that our universe arose through a process involving an initial hyperspace with supersymmetry that, upon cooling, underwent a unique process of symmetry breaking. The symmetry breaking process resulted in conventional 4 dimensional extended space-time AND some combination of additional compact dimensions.
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Quote of the Day:
We have, I fear, confused power with greatness.
Stewart L. Udall
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For further reading please visit:
grand quantum conjecture by Plato
bumblebee wing rotations and dancing by Plato
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Dimensions 4

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Image from Wikipedia: warning this image may be copyrighted.
Philosophy Science Physics Technorati tags

The question was actually intended to be, read as, or mean:

Does string theory: Lisa Randall & Lubos et al, think these subatomic forces and fields will be encountered (exist?) in the greater cosmos. ie: will space ships encounter and be affected by relatively speaking 'giant' strings & gravitons the size of galaxies and planets, - see angle and perspective of galaxy pic below - in these other 'dimensions' currently invisible to us in outer space - which is where some people's thinking and current thought is leading.

Dimensions (3+1): height, length, width + Time.

Three dimensions are all we see -- how could there be any more? Einstein's general theory of relativity tells us that space can expand, contract, and bend. If one direction were to contract down to an extremely tiny size, much smaller than an atom, it would be hidden from our view. If we could see on small enough scales, that hidden dimension might become visible.

See Plato for dimensional-referencing

At the very least, quantum gravity ought to describe physics on the smallest possible scales. Easy to find with dimensional analysis: Build a quantity with the dimensions of length using the speed of light, Planck's constant, and Newton's constant. Whether quantum gravity will yield a revolutionary shift in quantum theory, general relativity, or both remains to be seen.
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Are experiments in a collider or accelerator really representative of Nature & the lanscape in the big dark expanse of the cosmos or the known Universe.

Or are they more representative of the cosmos and the known Universe or the 'physical' reality - in the same way that films, animations and video games are representative of life outside in the real world?

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Quantum gravity is the field devoted to finding the microstructure of spacetime. Is space continuous? Does spacetime geometry make sense near the initial singularity? Deep inside a black hole? These are the sort of questions a theory of quantum gravity is expected to answer. The root of our search for the theory is an exploration of the quantum foundations of spacetime.

Do black holes exist? - do they lead to other universes?
Or are black holes matter where the mass of Sun or Star are compressed to the size of an ultra high density marblesized small sphere with the gravitational (magnetic?) field of the previous 'visible' Sun or Star.

Does information pass through a blackhole? - if not even light can escape a blackhole, then what information can possibly escape a blackhole?

Are we being metaphysical? - what goes past at death from the physical world to the Spirit world: memories, emotions, feelings? Preferences in tastes: music, fashion, flavours, smells ...

Picture credit: STSci & Hubble Heritage
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Dimensions 3

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Image from Wikipedia: warning this image may be copyrighted.
Philosophy Science Physics Technorati tags


Superstring theory stipulates ten dimensions.
The world around us appears to contain only four (including time).
Something needs to be done about the superfluous six. -
from Lisa Randall's "Warped Passages"

Because you may have 10 Dimensions at subatomic level, does it mean you 'must' have 10 dimensions in the 'physical' world around us
Q [Homepage] 06.29.06 - 3:27 pm #


If they are at the subatomic level they are still in the world around us, but we just can't detect them unequivocally yet with traditional science.
Rae Ann [Homepage] 06.29.06 - 5:14 pm #


These dimensions are very small-- think of a long cylinder(100m) with radius of say 2mm. If you look at it from far away, say 1 km, you will see a long line with no thickness.

But if you get close enough you will see the 2mm thickness.

Similarly to see the very small compactified dimensions you need a really powerful "microscope" (accelerator or something that produces very high energies).
Think of uncertainty principle for a better understanding-- the smaller length resolution you want, higher the momentum (energy) required.

Our everyday world is at an energy scale where these tiny lengths will simply not be "visible". This was a very handwaving analogy-- but this is roughly why we do not "see" these extra dimensions.

There is this completely wrong notion that somehow string theorists simply decided to throw in these extra dimensions-- they are in fact rather tightly controlled by the maths required to implement a physical condition which is necessary for any quantum theory to make sense.
I apologize to the experts who can certainly explain this much better than me, and perhaps manage to be more technically precise.
AR [Homepage] 06.29.06 - 9:14 pm #

"Regarding the Superfluous Six": Since Lubos is on a much-needed long-overdue hiatus, I will officially declare that it is "Amateur Night at The Reference Frame". Moreover, I will boldly volunteer to be the second amateur to take a mediocre stab at Q's thought-provoking question. Let me begin my figurative stabbing...

If one wants to conceptualize "the superfluous six", then one must gain a grasp of brane/bulk cosmology... First imagine dividing the cosmos into a higher dimensional bulk space and a lower dimensional brane space. Next imagine dividing strings into two distinct favors:

(1) open strings and
(2) closed strings.

As a general rule, non-graviton-particles act as open strings and are strictly confined to the lower dimensional brane(s).
By contrast, gravitons act exclusively as closed strings and uniquely behave as cosmic interlopers between the higher dimensional bulk and the lower dimensional brane(s).

Consequently, gravity is the only force in nature which is qualified to travel to-and-fro between the higher and lower dimensions. In addition, it is conjectured that supersymmetry partners exist upon a separate brane which runs parallel to a companion brane.

The closed-loop strings of gravity act as a mediator between these two branes.

Furthermore, gravitons have the potential to display two distinct modes of behavior:
(1) the gravitons - which run perpendicular to the brane - have the capacity to polarize the brane. This polarization leads to gravitational leakage into the bulk.
(2) the gravitons - which run parallel to the brane - lack the capacity to polarize the brane. Non-polarization maintains gravitational sequestration of the brane.

In conclusion: the most reasonable way to make sense of gravity in the universe is to view the universe as containing more than 3+1 dimensions. Best Wishes!
Cynthia [Homepage] 06.30.06 - 12:11 am #

Three dimensions are all we see -- how could there be any more? Einstein's general theory of relativity tells us that space can expand, contract, and bend. If one direction were to contract down to an extremely tiny size, much smaller than an atom, it would be hidden from our view. If we could see on small enough scales, that hidden dimension might become visible.

See Plato for dimensional-referencing
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Universe of Strings

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Image from Wikipedia: warning this image may be copyrighted


"The quest for a theory linking all matter and all forces led physicists deep into hyperspace, where they got horribly lost. But suddenly the way ahead has become clear",
-- says superstring theorist.

But what are these extra dimensions? see cosmicvariance:

"Imagine a tightrope stretched between skyscrapers," says JoAnne Hewett from SLAC. "If you are watching an acrobat walk across it - the tightrope looks like a line. But if you are watching an ant walk on the tightrope, you can see that the tightrope is thick and round." - The extra dimensions postulated in string theory are like the tightrope with an ant on it; they are too small to see unless you get really, really close.



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For further reading visit:

An ant's perspective
How particles came to be

Plato [Homepage]

Three dimensions are all we see -- how could there be any more? Einstein's general theory of relativity tells us that space can expand, contract, and bend. If one direction were to contract down to an extremely tiny size, much smaller than an atom, it would be hidden from our view. If we could see on small enough scales, that hidden dimension might become visible.

For further reading see Plato on dimensional-referencing

The earlier concept of a universe made of physical particles interacting according to fixed laws is no longer tenable. It is implicit in present findings that action rather than matter is basic ...

This good news, for it is no longer appropriate to think of the universe as a gradually subsiding agitation of billiard balls. The universe far from being a desert of inert particles is a theatre of increasingly complex organization, a stage for developmemt in which man has a definitive place, without an upper limit to his evolution.

Arthur M Young. The Reflexive Universe

For further reading visit: developing character in rhetoric
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4Qs to Leonard Susskind

2004 Reply from L. Susskind to Lee Smolin. edge145

In a nutshell, here is the view of physics and cosmology:

(1) In the remote past the universe inflated to an enormous size, many orders of magnitude bigger than the observed portion that we can see. Most of the universe is behind the cosmic horizon and cannot be directly detected.
(2) The mechanism of inflation leads to a diverse universe, filled with what Alan Guth calls pocket universes. We live in one such PU. Some people call this super-universe the Multiverse. I like the term Megaverse. This growth and continuous spawning of pocket universes is called, in the trade, eternal inflation.
(3) String theory leads to a stupendously large Landscape of possibilities for the local laws of nature in a given pocket. I'll call these possibilities environments. Most environments are very different from our own, and would not permit life: at least, life as we know it.

Combining 1,2 and 3—the universe is a megaverse filled with a tremendously large number of local environments. Most of the volume of the megaverse is absolutely lethal to life. Some small fraction is more hospitable. We live somewhere in that fraction. That's it.

QUASAR9 questions to Leonard Susskind.

(1) You claim a "Megaverse" with eternal inflation, expanding or evolving in perpetuity, without one iota of proof. Since most of the Universe as you clearly point out is behind or beyond the cosmic horizon and cannot be directly detected. Would it not be more logical, realistic and factual to say that our pocket universe, may or may not have been preceded by a big bang, and this would conform to our present models, explanations and theories of the present day detectable pocket universe, from whence we carry out our observations. And even then with our current limited knowledge of the universe, it would be purely conjectural to claim that it is expanding.

(2) This again an absolutely conjectural statement or premise with no more solid foundation than a claim that the universe beyond the cosmic horizon is green, blue or purple. In fact all you are saying is that forargument sake you will make that statement, which is corroborated by fellows of stature in the field of cosmology, and it cannot be refuted. No more than the existence of a Creator God can be refuted. A Creator God who for all we know may well be planting yet more pocket universes in this 'imaginary' Megaverse, just for something to do, like a landscape gardener doing weekend gardening.

(3) We already know this to be true in the observable universe, no one has encountered any aliens or lifeforms beyond Earth. So the statement per se is most likely true for our pocket universe. But it does not proceed hence that a Maegaverse exists. It simply states your support for string theory as a theory which will or may lead to a stupenduously large landscape of local physical laws in nature or environments. Well these are evident in nature in our very own pocket universe, on our very own planet in our very own bacykard.
You try living in the bottom of the ocean, if you know what I mean.
There is whole Megaverse of lifeforms, and local laws of nature or environments which permit marine life, and lifeforms we have not yet discovered which defy most laws of physics as known.

In a nutshell does a plane fly like a bird?

Therefore combining 1, 2 and 3 have only served to explain the concept of the pocket universe as it is perceived by big bang theorists, without I add one bit of proof, and then applied these same attributes to multiple (infinite?) pocket universes to create your preferred choice or vision of Megaverse. You even go as far as to point out that Lee Smolin does in fact agree with you on these three points.

Yet when we come to point 4, ie black holes or singularities, versus Lee Smolin's preferences for black holes as the gateway to the creation of these new (or other) pocket universes, you are silent. Though from other sections on the paper not in the nutshell above, yet I deduce you are still undecided or very non-descript in giving your own version of possible events in the occurring observable phenomena denominated blackholes or singularities.

(4) what is a blackhole, and what is a "singularity", and what in your opinion is on the other side of a blackhole? supposing the black hole has another side. No I am not asking if there are black holes or singularities or do we need to go look there, the fact that it is there is enough for us to want to go look there and/or know what is there. I am asking you to define whether a black hole is a hole or a "singularity" ie: high density matter a Sun or Star compressed to the size of a marble.

Cambridge Relativity black holes
This evolution doesn't produce a blackhole
This collapse does produce a blackhole (maybe)
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