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Hrvoje Crvelin

LHC needs you!

Posted by Hrvoje Crvelin Sep 27, 2011

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature.  In essence, our reality.  The data volume produces by run tests is huge. Data produced by LHC, as well as LHC-related simulation, will total approximately 15 petabytes per year (max throughput while running not stated).  Yeah, that's 15 million gigabytes which goes against 1.7 million dual layer DVDs.  Per year.  And for some reason I expect more than that.

 

The distributed computing project LHC@home was started to support the construction and calibration of the LHC. The project uses the BOINC platform, enabling anybody with an Internet connection and either Windows, Mac OS X or Linux to use their computer's idle time to simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine how the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.  At the moment, this project is not very active as all those have been done already.  BUT!  There is LHC 2.0!  It is known as Test4Theory too.

 

This is a test project, to demonstrate the use of the CERN-developed CernVM and BOINCVM systems to harness volunteer cloud computing power for full-fledged LHC event physics simulation on volunteer computers.  It is the first of what is expected to be a series of physics applications running on the LHC@home 2.0 platform. These applications will exploit virtual machine technology, enabling volunteers to contribute to the huge computational task of searching for new fundamental particles at CERN's LHC.

 

Initial call for help supressed all expectations and almost crashed whole system so engineers worked hard to make this work flawlessly and you can join via invitations.  I did!

 

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Invitations are open again.  If you want to test the project, please, sign up for an invite!

 

If the number of requests remains very high, we won't be able to accommodate everyone, so we'll be picking users randomly each week and sending them invitation codes – an invitation lottery. Thus, if you want to try the project and help debugging it sign up and good luck!

 

P:S. You will also see I use Einstein@Home.  It is another project, outside LHC realm.  Einstein@Home searches through data from the LIGO detectors for evidence of continuous gravitational-wave sources, which are expected for instance from rapidly spinning non-axisymmetric neutron stars. Einstein@Home also searches radio telescope data from the Arecibo Observatory for radio pulsars. On August 12, 2010, the first discovery by Einstein@Home of a previously undetected radio pulsar J2007+2722, found in data from the Arecibo Observatory, was published in Science.  Search continues.  Happy number crunching!

Hrvoje Crvelin

Braneworld Multiverse

Posted by Hrvoje Crvelin Sep 24, 2011

Physicists routinely use simplifications - ignoring Pluto’s gravity or treating the sun as perfectly round - that make the mathematics easier and bring approximate solutions within reach.   In physics, a coupling constant is a number that determines the strength of an interaction.  In string theory there is string coupling and it is assumed to be low.  If the string coupling is small, these approximate calculations are expected to accurately reflect the physics of string theory. But what if it isn’t?  Until '95 there were several version of string theory which came along with different coupling constants. Then in '95 Edward Witten showed the world all these different string theories were the one - with several different approaches to the same thing.   Each appeared different when examined in a limited context - small values of its particular coupling constant - but when this restriction is lifted, each string theory transforms into the others.  This might not be your cup of tea - first we have different things and then they eventually get fixed by saying they all talk about the same thing?  Consider following picture:

albert-einstein-marilyn-monroe.jpg

You probably have seen this one as I remember being popular few years ago and everyone kept mailing it around trying to figure out what was the secret of illusion.  If unfamiliar, when you look at this picture close range you see Albert Einstein.  If you take dozen of steps back (or a bit less) it morphs into Marilyn Monroe.  But hey, it is the same picture!  The morphing from Einstein to Monroe is sort of fun. The morphing of one string theory into another is transformative. It implies that if perturbative calculations in one string theory can't be undertaken because that theory’s coupling is too large, the calculations can be faithfully translated into the language of another formulation of string theory, one in which a perturbative approach succeeds because the coupling is small. Physicists call the transition between naively distinct theories duality. By providing two mathematical descriptions of one and the same physics, duality doubles our calculational arsenal. Calculations that are impossibly difficult from one perspective become perfectly doable from another.  Union of these theories was called M theory and it showed there’s much more to string theory than strings.

 

With the new calculational methods, physicists started analyzing again their equations with much more precision and produced a range of unexpected results. They established that ingredients with various numbers of spatial dimensions do lurk in string theory’s mathematical shadows.  The analyses revealed objects, shaped like Frisbees or flying carpets, with two spatial dimensions: membranes (one meaning of the "M" of M theory), also called two-branes. But there was more. The analyses revealed objects with three spatial dimensions, so-called three-branes; objects with four spatial dimensions, four-branes, and so on, all the way up to nine-branes. The mathematics made clear that all of these entities could vibrate and wiggle, much like strings; indeed, in this context, strings are best thought of as one-branes.  The more precise methods rectified this failing, revealing a string/M-theory universe with ten dimensions of space and one of time, for a total of eleven spacetime dimensions.  For the multiverse story, it is the branes that are central. Using them, researchers have been led by the hand to another variety of parallel universes.

 

Usually we imagine strings as very very tiny.  Indeed, they are, but with enough energy injected you could stretch it and string would become large.  We do not have enough energy on Earth to do so, but someone somewhere might just have it enough to do so.  If string theory is right, an advanced civilization would be able to pump strings up to whatever size it liked.  Natural cosmological phenomena also have the capacity to produce long strings; for example, strings can wrap around a portion of space and get caught up in the cosmological expansion, stretching long in the process (this would cause gravitational waves by the way). Like strings, higher-dimensional branes can be big too. Imagine a long string, as long as an overhead electric cable that runs as far as the eye can see. Next, picture a large two-brane, like an enormous tablecloth, whose surface extends indefinitely.  These are both easy to visualize because we can picture them located within the three dimensions of common experience.  If a three-brane is enormous, perhaps infinitely big, the situation changes. A three-brane of this sort would fill the space we occupy, like water filling a huge fish tank. Such ubiquity suggests that rather than think of the three-brane as an object that happens to be situated within our three spatial dimensions, we should envision it as the very substrate of space itself.  Just as fish inhabit the water, we would inhabit a space-filling three-brane. As we run and walk, as we live and breathe, we move in and through a three-brane. String theorists call this the braneworld scenario.

 

Braneworld models have attracted a lot of interest in recent years. The central idea of braneworld scenarios is that the visible universe is restricted to a four-dimensional brane (3 space and one time dimension) inside a higher-dimensional space, called the bulk. The additional dimensions are taken to be compact and other branes may be moving through the bulk. Interactions of the visible brane with the bulk and hidden branes introduce effects not seen in standard physics.  You may find difficult to picture this. Evolution has prepared us to identify objects, those presenting opportunity as well as danger, that sit squarely within 3D space. Although we can easily picture two ordinary 3D objects inhabiting a region of space, few can picture two coexisting but separate 3D entities, each of which could fully fill 3D space.

 

brane_world.jpg

Remember two-dimensional life on sheet of paper in previous blog?  This is analogous to living on a sheet of paper as a two-dimensional figure. You would have no concept of depth - it is simply not a part of your physical world. This is the concept behind braneworld theory, which says that our four dimensional spacetime is like the sheet of paper, simply a subspace of some bigger, multi-dimensional space that we cannot perceive because all matter and forces (except possibly gravity) we experience are constrained to this subspace (or brane).

 

string-braneworld.jpg

The same fundamental laws of physics would apply all across the collection of branes, since they all emerge from a single theory - string (M) theory.  Nevertheless, as with bubbles in Inflationary Multiverse, environmental details such as the value of this or that field permeating a brane, or even the number of spatial dimensions defining a brane, can profoundly affect its physical features. Some braneworlds might be much like our own while others might be very different.  In the braneworld scenario, our universe is just one of many that populate the Brane Multiverse.

 

If there are giant branes right next door, why don't we see them?  It turns out strings come in two shapes, loops and snippets. Can these strings fly off a brane? A loop ones can. A snippet can’t.  String snippets can freely move within and through a brane, gliding from here to there, but they can't leave it. In a braneworld, the strings that make you up and the rest of ordinary matter are snippets. The same is valid for the particles that transmit the three nongravitational forces (EM, strong and weak force). Visible light (stream of photons), can therefore travel freely through the brane, but is also unable to leave brane.

 

Two or three branes (as in picture above) or even more might be millimeters away - and light would not travel from one to another.  Would there be any hint of presence for neighbor brane then at all?  The only remaining force, gravity, is different player. 

 

Gravitons2.jpgIn physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton must be massless (because the gravitational force has unlimited range) and must have a spin of 2.  Spin 2 is twice than the particles arising from string snippets (such as photons).  That gravitons have twice the spin of an individual string snippet means you can think of gravitons as being built of two such snippets, the two ends of one melding with those of the other, yielding a closed loop.  Since loops have no endpoints, branes can't trap them. Gravitons can therefore leave and reenter a braneworld. In a braneworld scenario, then, gravity provides our only means of probing beyond our three-dimensional spatial expanse.

 

When objects attract each other gravitationally they exchange streams of gravitons.  The more gravitons the objects exchange, the stronger the mutual gravitational pull. When some of these streaming gravitons leak off our brane and flow into the extra dimensions, the gravitational attraction between objects will be diluted. The larger the extra dimensions, the more the dilution, and the weaker gravity appears. If we can establish that we are living on a brane, the mathematics gives us no reason to expect that ours is the only one.  If branes float in bulk, can they crash against each other?  According to theory - yes. Even more, many theorists speculate such crash would mark beginning where initial state would be very close to what we describe as the Big Bang today.  In theory this is known as the Big Splat.  Splat here might not be right word as branes actually bounce from each other (they don't merge or split or anything similar).  In such setup, we come to the point of cyclic universe.  This is because branes can collide and as they bounce of each other they go through universe rebirth process within.  Theorists close to this concept calculate life frame (birth, evolution and finally death) to be some trillion years.  What is interesting here is that both level I and level II universes exist within single brane (for level II see note about inflation below).   Given the cyclic feature, theory gives birth to something called Cyclic Multiverse.  Still, Max Tegmark for example, warns it is unclear whether such a world (brane) deserves be be called a parallel universe separate from our own, since we may be able to interact with it gravitationally much as we do with dark matter.

 

Part of the appeal of a cyclical cosmology is its apparent ability to avoid the knotty issue of how the universe began. If the universe goes through cycle after cycle, and if the cycles have always happened (and perhaps always will), then the problem of an ultimate beginning is sidestepped. Each cycle has its

own beginning, but the theory provides a concrete physical cause: the termination of the previous cycle. And if you ask about the beginning of the entire cycle of universes, the answer is simply that there was no such beginning, because the cycles have been repeating for eternity.  This may come as strange statement and first thing to be suspicious about is entropy which is supposed to rise with timeline.  That has been brought to attention in Herman Zanstra somewhere in 1950s and he did mathematical model to prove it.  Brane theorists were able to address this.   The branes themselves continually expand and they do so throughout each and every cycle. Entropy builds from one cycle to the next, but because the branes expand the entropy is spread over everlarger spatial volumes. So, total entropy goes up, but the entropy density goes down. By the end of each cycle, the entropy is so diluted that its density is driven very nearly to zero - a full reset or reboot if you want.  The cycles can continue indefinitely toward the future as well as the past and Cyclic Multiverse has no need for a beginning to time.

 

In inflationary cosmology, expansion in the early universe would have disturbed the spatial fabric that substantial gravitational waves would have been produced. These ripples would have left trace imprints on the CMB and we have missions seeking those out. A brane collision, creates a momentary maelstrom - but without inflationary stretching of space.  Still, there is inflation though.  A new theory, called brane inflation, suggests that inflation arises from the motion of D-branes in the compactified geometry, usually towards a stack of anti-D-branes. This theory, governed by the Dirac-Born-Infeld action, is very different from ordinary inflation. The dynamics are not completely understood so I won't go into any details (it appears special conditions are necessary since inflation occurs in tunneling between two vacua in the string landscape; process of tunneling between two vacua is a form of old inflation, but new inflation must then occur by some other mechanism).

 

Any gravitational waves produced would be too weak to create a lasting signal. So evidence of gravitational waves produced in the early universe would be strong evidence against the Cyclic Multiverse.  The Cyclic Multiverse is widely known within the physics community but is viewed, almost as widely, with much skepticism. Observations have the capacity to change this. If evidence for braneworlds emerges from LHC testing, and if signs of gravitational waves from the early universe remain elusive, the Cyclic Multiverse will likely gain increased support for sure.  Back in 2008, phenomena called Dark Flow has been found and certain views on it made connection to gravity pull by another brane, but model of Dark Flow met criticism as expected and as such it needs additional validation and research (2011 study done by University at Buffalo doesn't validate it for example).

 

Credits: Brian Greene, Wikipedia, Max Tegmark, Stephen Hawking

 

Related posts:

Deja vu Universe

Inflation

Landscape Multiverse

Many worlds

Holographic Principle to Multiverse Reality

Simulation Argument

In previous two blogs I discussed two models of parallel universes:

- quilted (or deja vu or level I universe)

- inflationary universe (or level II universe)

 

At this point we continue further, but before we hit the point we need a bit of a introduction to something else - string theory - as quantum wierdness itself generates Multiverse models.  Remember when at school you learned about molecules and atoms?  Usually you would start of atom as basic unit of matter and you would say it consists of central nucleus and cloud of electrons around it. References to the concept of atoms date back to ancient Greece and India.  It took some 3000 years to get from assumption to practice, but atoms become scholar reality.  Atoms group into molecules via chemical bonds to form electrically neutral group consisting of least two atoms (same or different ones).  Electrons, flying around nucleus, have been discovered in 1897 by J.J. Thomson.  They are also believed to be elementary particles as we are not aware of any substructure it consist from.  Electrons have negative charge.  Proton on the other hands have positive structure and they tend to form nucleus of an atom.  They have been theorized since 1815 and finally found in 1919 by Ernest Rutherford.  It was Ernest who theorized there might be another, with no electric charge particle making up nucleus.  Finally, this has been confirmed by James Chadwick who found neutron in 1932.  It took more than 30 years since to suggest and prove there is more if we look at it even smaller scale.

 

Period of mid 20s to mid 60s of last century was also the time when physicist search of theory of unification.  At that time it become apparent our best tooling to describe how things behave at large scale (eg. general relativity) and how they behave at very small scale (eg. quantum mechanical world description) simply didn't match - even though both did excellent job for what they were meant to be.  The idea was if we are all made of same particles then one single theory should be out there able to explain everything through laws for this particles itself.  Instead, we had this problems where whenever we tried to explain situations involving singularities (like Big Bang or Black Holes) math would just break.  At that time, only two forces in nature were known (out of 4 as we know it today); electromagnetism and gravitation (weak theory appeared in theory for the first time somewhere in 30s).

 

Then in mid 60s things started to happen.  In 1964 it has been suggested both neutrons and protons could be split to more elementary particles called quarks.  In 1968 this has been confirmed (there are 3 generations of quarks, 6 quarks in total and while first one was found in 1968 it was not before 1995 we found last one). Interesting thing about quarks is they never come along (isolated), but rather in pairs forming what is called hadron (you might get an idea what Large Hadron Collider stands for now).   Physicists realized that the methods of quantum field theory, which had been successfully applied to the electromagnetic force, also provided descriptions of the weak and strong nuclear forces.  Weak is responsible for, among other things, radioactive decay.  Strong one provides a powerful glue that holds together the nuclei of atoms (force carrying particles are called gluon).  The word strong is used since the strong interaction is the "strongest" of the four fundamental forces; its strength is 100 times that of the electromagnetic force, some 10^6 times as great as that of the weak force, and about 10^39 times that of gravitation.

 

knot.png

While certain structures that would become successful part of string theory were known in 20s, it was only around end of 60s and begin of 70s that string theory started its life.  The heart of string theory lied within previous work done under names like S-Matrix and Regge theory and bootstrap models and finally, dual resonance model.  In 70s, we find first records of representing nuclear forces as vibrating, one-dimensional strings.  As time progressed problems started to count up.  Initially this theories were not stable.  They included only bosons so fermions need to be included leading to supersymmetry to be invented (supersymmetry is nothing but mathematical relation between bosons and fermions).  At the end those string theories including fermionic vibrations were called superstring theories.  In 1984 so called first superstring revolution happened.   It was realized that string theory was capable of describing all elementary particles as well as the interactions between them.  Then in 1994 second revolution happened and M-theory has been born unifying different versions of superstring theory.  In 1997 Juan Macadena made some amazing math leading to AdS/CFT correspondence - what would become basis for a holographic principle later on (even though that used to be something Leonard Susskind was after in his continues battle with Stephen Hawking).  In 2000s, we further have discovered so called string theory landscape.  While this is all nice, can you describe also in sentence or two what really string theory is about?  Yes.  It is theory which states all objects in our universe are composed of vibrating filaments (strings) and membranes (or branes) of energy.  A string is an object with a one-dimensional spatial extent, unlike an elementary particle which is zero-dimensional, or point-like. Quarks and electrons are thought to be made of string(s) for example. An electron is less massive than a quark, which according to string theory means that the electron’s string vibrates less energetically than the quark’s string. The electron also has an electric charge whose magnitude exceeds that of a quark, and this difference translates into other, finer differences between the string vibration patterns associated with each. Much as different vibration patterns of strings on a guitar produce different musical notes, different vibration patterns of the filaments in string theory produce different particle properties. 

 

Strings was are also very very small, on the order of the Planck length - 10^-33 centimeters.  The Large Hadron Collidercan probe to scales of about 10^-19 cm; that’s a millionth of a billionth the width of a strand of hair, but still orders of magnitude too large to resolve phenomena at the Planck length.  During the summer 2011, just before I was headed for Croatia coast to enjoy some free time with family, ESA announced something unexpected.  While Einstein's General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric, yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach.  According to calculations, the tiny grains would affect the way that gamma rays travel through space. The grains should "twist" the light rays, changing the direction in which they oscillate, a property called polarization.  High-energy gamma rays should be twisted more than the lower energy ones, and the difference in the polarization can be used to estimate the size of the grains.  Some theories suggest that the quantum nature of space should manifest itself at the Planck scale: the minuscule 10^-33 cm.  However, observations are about 10000 times more accurate than any previous and show that any quantum graininess must be at a level of 10^-46 cm or smaller.  ESA Integral made a similar observation in 2006, when it detected polarized emission from the Crab Nebula, the remnant of a supernova explosion just 6500 light years from Earth in our own galaxy. This new observation is much more stringent, however, because GRB 041219A was at a distance estimated to be at least 300 million light years. In principle, the tiny twisting effect due to the quantum grains should have accumulated over the very large distance into a detectable signal. Because nothing was seen, the grains must be even smaller than previously suspected.

 

Another interesting fact coming out of the math of string theory is number of dimensions.  We are used to live in 4 dimensions, but string theory requires more dimension than those we are aware of.  Additional number of dimensions was first suggested on early days of 20st century.  It was Kaluza-Klein duo suggesting there are dimensions that are big and easily seen, and others that are tiny and thus more difficult to reveal - and the same might apply to the fabric of space itself.  If you are bird flying over sandy beach you see smooth two dimensional surface... but you fly down suddenly these sand grains start to reveal other dimensions.  Within same logic, very very high tower observed from long distance would appear as one dimensional line going to the sky.  But there is more then one dimension there, isn't.

 

Look at the letter S. Its shape is due to a single curved line. A splash of paint on a canvas also has a shape, but this is no longer that of a line but an area.  Solid objects have shapes too - cubes, spheres, people, cars all have geometric shapes called volumes.  The property that is different in the above three cases (line, surface and volume) is the number of dimensions required to define them. A line is said to be one-dimensional, an area is two-dimensional and volume is three-dimensional.  Is there some reason why we should stop here?  Well, our brains are hard-coded to three dimensions so we can't imagine worlds with higher number of dimensions very well.  Three space dimensions also define 3 arrows of movement we can do (up/down, left/right and forward/backwards).  In mathematics these three directions in which we are free to move are called mutually perpendicular, which is the mathematicians’ way of saying "at right angles to each other".  n dimensional life exists within n+1 world.  If you imagine 1 dimensional world (line, where you can only move within one direction) you would defined as dot or 0 dimensional being.  Below is the example:

 

1d.png

In both cases our dot is able to move along one dimension (backwards and forwards).  The only difference is that space within it lives (1 dimensional line) is flat in one case and in another it is curved.  In space, things get even more confusing when dealing with spacetime (which is 3 space dimensions and 1 time dimension) as gravity tends to curve both space and time.  To give you an idea of bent space and its influence on dimension consider following example:

 

2dbent.png

 

What we see on (a) is square (2 dimensions) on flat space.  On (b) and (c) we see square being bent within space.  On (d) we see space being bent and this reflects shape which as far as we are concern didn't change from (a).  In our world, it did of course.  But if you imagine to be one dimensional life living and following directions of lines we see as square - you would not be aware of this, would you?  To get an idea of life in two dimensional world imagine following picture:

 

life2d.png

We see 2 creatures living in two dimensional world (space wise).  From our point of view, they can move up/down and left/right.  That means they can't bypass each other (well, in 2D world you can solve this by one creature to lay down and second one to just walk over it).  They do not live on that surface, they live within that surface.  They also can't turn around... they can only start walking backwards (in this specific case, for being on left that would be left direction).  Now bare in mind, space wise, they live in 2D and you live in 3D.  You can see them, but they can't see you.  And this is all thanks to just one dimension (in this case we miss backward/forward to make it easier from our perspective).  Imagine you went with your hand through their world.  What would they see?  They would see line appearing from nowhere.  If you were to pick up one of the being and placing at somewhere else (for example left one behind right one) then this would be seen again as line appearing from nowhere which does something to left being and it moves us and then behind right without much logical explanation.  Exercises in two dimensional world with certain operations we perform daily in our 3D world may sometimes result in strange results.

 

We already mentioned curved space.  We take most of the things for granted and simplified in our everyday life.  As a kid, when I heard people used to believe Earth was flat I used to think people of the past were not so smart.  But, if nothing, I realize now they just followed sane logic.  Look through the window and look at distance.  It if flat.  If you start walking in one direction soon or later you will get back to the same point, but while doing that there would ne nothing to indicate that surface you walk is not flat.  Even the math you learn in school is the one which works for flat surface.  Check this out.  You are having fun with Polar bears on North Pole, but wish to stretch your legs so you start your journey until equator.  Then you turn left (that would 90 degrees) and you walk until let's say some point when you take another 90 degrees and walk back to North Pole.  Triangle has sum of 180 degrees for inner angles, but we already made that with two turns.  How is that?  Illustration helps again:

 

curve.png

 

As we can see, curvature of space makes difference.  So, there is number of challenges for scientists when dealing this space as we perceive it - let alone dimensions on top of that.  Whole story with dimensions tends to be interesting one, but if you followed carefully you would have noticed it started somewhere earlier... somewhere in '20s of last century.  What made those people think about dimensions at that time?

 

Kaluza revealed that in a universe with an additional dimension of space, gravity and electromagnetism can both be described in terms of spatial ripples. Gravity ripples through the familiar three spatial dimensions, while electromagnetism ripples through the fourth. An outstanding problem with this proposal was to explain why we don't see this fourth spatial dimension. Klein suggested resolution: dimensions beyond those we directly experience can elude our senses and our equipment if they are sufficiently small.  Almost half century later and string theory appeared requiring multiple dimensions to make sense.

 

One of the features of string theory is that particle properties are determined by the size and shape of the extra dimensions. Because strings are so tiny, they don't just vibrate within the three big dimensions of common experience; they also vibrate into the tiny, curled-up dimensions. And much as air streams flowing through a wind instrument have vibration patterns dictated by the instrument’s geometrical form, the strings in string theory have vibration patterns dictated by the geometrical form of the curled-up dimensions. If string vibration patterns determine particle properties such as mass and electrical charge, then these properties are determined by the geometry of the extra dimensions.

 

So, if you knew exactly what the extra dimensions of string theory looked like, you would be well on your way to predicting the detailed properties of vibrating strings (and so detailed properties of the elementary particles the strings vibrate into existence). The problem is, and has been for some time, that no one has been able to figure out the exact geometrical form of the extra dimensions. The equations of string theory place mathematical restrictions on the geometry of the extra dimensions, requiring them to belong to a particular class called Calabi-Yau shapes (Calabi-Yau manifolds).  There’s not a single, unique Calabi-Yau shape. Instead, like musical instruments, the shapes come in a wide variety of sizes and contours. And just as different instruments generate different sounds, extra dimensions that differ in size and shape generate different string vibration patterns and hence different sets of particle properties. An example of Calabi-Yau manifold is shown below.

 

Calabi-Yau.png

 

It is rather unimaginable that shape as this might be behind the shape of reality we see, but this is what modern theory suggests.  Even we still fail to figure out right shape, within string theory both general relativity and quantum mechanics finally join together harmoniously. That’s where string theory provides a vital advance.  Nevertheless, certain aspects remain to be proved in practice and scientists already have plans and tests ongoing or scheduled.  The failure to find supersymmetric particles might mean they don't exist, but it also might mean they are too heavy for even the LHC to produce (that would be current state); the failure to find evidence for extra dimensions might mean they don't exist, but it also might mean they are too small for our technologies to access; the failure to find microscopic black holes might mean that gravity does not get stronger on short scales, but it also might mean that our accelerators are too weak to burrow deeply enough into the microscopic terrain where the increase in strength is substantial; the failure to find stringy signatures in observations of gravitational waves (you may with to join Einstein @ Home as I did if too impatient) or the CMB might mean string theory is wrong, but it might also mean that the signatures are too meager for current equipment to measure. As of today, the most promising positive experimental results would most likely not be able to definitively prove string theory right, while negative results would most likely not be able to prove string theory wrong.  The theory will remain speculative until a convincing link to experiment or observation is forged.

 

In the mid-1990s, string theorists discovered that various mathematical approximations, widely used to analyze string theory, were overlooking some vital physics. As more precise mathematical methods were developed and applied, string theorists could finally step beyond the approximations; when they did, numerous unanticipated features of the theory came into focus. And among these were new types of parallel universes; one variety in particular may be the most experimentally accessible of all.  And this is where introduction for next blog entry stops.

 

Note: Most of illustrations and theory comes from either Brian Greene or Jim Al-Khalili papers.  I recommend both authors for anyone who wishes to dive more into the details on this matter.

 

Credits: Brian Greene, Jim Al-Khalili, Max Tegmark, Stephen Hawking, Wikipedia

In previous blog post, we have seen simplest example of multiverse.  Quilter universe or level I multiverse comes as logical consequence by limits of nature.  To far to been reached, but most likely out there.  This version of multiverse is sort of an upgrade.  Sort of an extension.  If you remember or just read previous blog post then you know our cosmic horizon is huge.  Beyond the reach it we do not know what exists, but we are sure our patch of universe extends further.  How much further we do not know nor does it matter.  What certainly is sure is that is huge.  What you are about to read discusses things at even grander scale. And its source lies within Big Bang theory.  More precisly, within processes which happened at very beginning of time (remember, time did not exist before Big Bang).  If this theory is correct, then we have multiple level II universes (kind I will explain in this post) and each of them have at least one (and most likely more) level I universes (as explained in previous post).

 

I already described what CMB is.  It is relic of Universe creation, Big Bang, which is spread across the Universe.  It has been discovered by chance and since then it has become important tooling for scientists.  It is out window to the past. No matter what advance we may have (based on EM waves), CMB remains oldest thing for us to see (those things before first 370000 years remain trapped in cosmic fog).   Calculations show that today there are about 400 million of these cosmic microwave photons racing through every cubic meter of space.  Before CMB has been discovered, Big Bang theory has already predicted its existence.  Our measurements from Earth show CMB being spread uniformly across the whole Universe we observe.  No matter when you measure, you will find leaving distinct signature of 2.725 degrees above absolute zero.  It might not be so obvious but the key question here is how can it be so uniform?

 

CMB.jpg

Above you see map of the CMB. The different spots of color correspond to different temperatures and in turn, different densities.  You may wonder how come now there is different temperature and density if we just said this is uniformly spread?  Although the temperature of the CMB is almost completely uniform at 2.7 K, there are very tiny variations, or anisotropies as they are called, in the temperature on the order of 10^-5K. The anisotropies appear on the map as cooler blue and warmer red patches. Ok, so there is this tiny difference, but what does that tell us?  These anisotropies correspond to areas of varying density fluctuations in the early universe. Eventually, gravity would draw the high-density fluctuations into even denser and more pronounced ones. After billions of years, these little ripples in the early universe evolved (through gravitational attraction) into the planets, stars, galaxies, and clusters of galaxies as we see it today.  OK, so it is sort of uniform then and this variations explain how things started, but they raise the question how did they get so uniform in the first place?  What mechanism does stand behind it?

 

Many people drink coffee (I don't).  Maybe better example here would be cup of tea, but it doesn't matter.  When served, cup is hot.  If you hold it on wrong spot you may get burned.  This is because surface of the cup is heated.  When objects are in contact, heat migrates from the hotter to the colder, until their temperatures are equal.  That's why cup will eventually get to the room temperature for example.  In model of Big Bang this fails!  Why?  Well, for places or objects to reach common temperature there is one essential requirement - mutual contact (direct or through information exchange to correlate it).  This exactly why thermos is designed to exactly prevent such interactions.  Locations in space that are very far apart.  If you look in the sky from north pole you see the first light which managed to reach us on Earth.  At the same time you have same situation on south pole.  These two distant sources of light never interacted, but however they are uniform. 

 

This brings us to the next puzzle.  If light travels at its speed which is limit how come that two objects that used to be close are now so far away?  The answer is quite simple though not so well explained by literature.  Speed of light is a limit of speed for an object traveling through the space.  But expansion we witness today (and since time started) is expansion of space itself.  There is no known limit on expansion of space so it may be faster than speed of light.  Mathematics of early space (and general relativity) indicates that too.  If this is the case, then how could have one object influence other you may ask?  In cosmology this is called horizon problem.

 

Solution to this problem, widely believed and accepted across science community, was given by Alan Guth in 1979.  The solution - inflationary cosmology.  At the time scientist realized problem was that regions have separated to quickly for thermal equality to happen.  The inflationary theory resolves the problem by stating there was a slow speed with which the regions were separating very early on, providing them time to come to the same temperature. It was then, theory proposes, when a brief burst of enormously fast and ever-quickening expansion happened - called inflationary expansion.  In such case, uniform conditions we observe no longer pose a mystery, since a common temperature was established before the regions were rapidly driven apart.  This is rather hard to grasp as in real life it has to find example for this, right?  There is also some sort of gravity which is slowing us down.  Einstein established long time ago that gravity comes down from mass, energy and pressure.  It is this pressure which is key to the inflation.  If you squeeze the ball, while mass remains the same, there is more weight due to the pressure.  This has been verified by multiple experiments.  The pressure you make in such example is called positive pressure (air pushes outward).  Positive pressure contributes to positive gravity (attraction) which leads to increased weight.  But pressure can be negative too.  In such case, it leads to repulsive gravity (stretched rubber band molecules for example pull inward).  OK, so pressure can be negative and gravity can be repulsive, but why would that happen at the Big Bang in the first place?  The answer lies in quantum fields.

 

You probably know what magnetic field is.  To refresh our memory, think of magnet above paper clip; clip jumps up and attach itself to magnet.  What happened there?  Magnet didn't even touch paper clip, but there was still some sort of interaction.  This interaction comes from something produced by magnet and called magnetic field.  Magnetic field is just one kind of field and as you may have guessed there are more.  For example electric field which is responsible for small electric shock I reach the metal doorknob of car sometimes.  These two fields are connected; changing one creates another one.  Turn on your mobile and place it next to radio or TV and you will hear electromagnetic waves.  In second half of 20th century scientists tried to apply EM to microworld of quantum mechanics and this is how quantum field theory was born.  With it, we found strong and weak nuclear fields, electron, quark and neutrino fields.  There is one field which still remains hypothetical though - inflation field.

 

We know fields carry energy (eg. magnet to pull paper clip).  A field’s value can vary from place to place, but should it be constant, taking the same value everywhere, it would fill space with the same energy at every point. Alan Guth noted such uniform field configurations would not only fill the space with uniform energy but also with uniform negative pressure and that exactly leads to physical mechanism to generate repulsive gravity. Guth also realized value of the field may change thus allowing bursts to happen and stop from happening.  If you think of the ball at the top of the hill, you know it has potential energy.  When it goes down potential energy is transformed to kinetic one.  This is typical. A system harboring potential energy will exploit any opportunity to release that energy.  I assume some physicist is responsible for saying "Don't throw away your potential".  Same applies to fields and it is described by something called potential energy curve.  So, in summary we have inflation field with high potential energy and negative pressure which gives a burst to expansion.  As potential energy drops during expansion so does negative pressure.  This energy is not lost (as energy level should always be the same); rather it transforms itself into a uniform bath of particles that fill space (think of cooling vat of steam producing water droplets).  I won't bother you with numbers here too much, but what math suggests is just outside imaginable;  they imply that a region of space the size of a pea would be stretched larger than the observable universe in a time interval so short that the blink of an eye would overestimate it by a factor larger than a million billion billion billion (if you insist on numbers that would be expansion for facto 10^30 within 10^-35 seconds).  While these are breath taking figures, they imply thermal equilibrium happened within small space which since has been stretched beyond observable horizon.  In inflation, a uniform temperature across space is inevitable.

 

If above is correct that we have enormous number of level I universes.  But this is not what defines level II universe.  Today there are many variations of inflationary theories and in many this burst is not one time event.  It goes on and on.  These theories indicate our universe is just a patch (or hole) in which rapid expansion stopped.  And there would be many other out there - all separate areas.  This gives birth to Inflationary Multiverse!  Inflation field has the same value for each point of space.  As it belongs to quantum world, it is subject to quantum uncertainty. This means its value will undergo random quantum jitters. Normally we are not aware of this due to our scale being small and thus they are too small to notice. Nevertheless, calculations show the larger the energy an inflaton has, the greater the fluctuations it will experience from quantum uncertainty (since the inflaton’s energy content during the inflationary burst was extremely high, the jitters in the early universe were big).

 

What this theory suggests is that we have ever-expanding spatial environment within which bubble universes are created (or pocket universes as they also called).  Each of those is huge and one of them is ours.  That one, ours, is the one which extends beyond cosmic horizon and which may host multiple level I universes.  Same applies to next bubble.  And next one.  And next one.  One way to imagine this it to look at following picture.

cheese.jpg

Yes, it is Swiss cheese.  I love it by the way.  Nevertheless, in this case cheese should be seen as spatial dimension carried by inflationary field.  Fluctuations result in certain regions to drop from warp speed of expansion and universes as ours form.  Those universes are holes in cheese.  If inflation theory is correct then the existence of an Inflationary Multiverse would be an inevitable consequence.  The number of parallel universes would be simply unimaginable and beyond any number you could think of.

 

Now let's go back to anisotropies seen on CMB map as briefly discussed before.  Even though the observed uniformity of the CMB was one of the prime motivations for developing the inflationary theory, it was realized rapid spatial expansion would not render the radiation perfectly uniform. Instead, it has been argued that quantum mechanical jitters stretched large by the inflationary expansion would overlay the uniformity with minuscule temperature variations, like tiny ripples on the surface of an otherwise smooth pond or lake.  Normally, such quantum variations are so tiny and happen over such minuscule scales that they are irrelevant over cosmological distances. 

 

The expansion of space was so rapid, even during the transition out of the inflationary phase, that the microscopic would have been stretched to the macroscopic.  Imagine placing a dot or some tiny written message on surface on balloon.  Now stretch it.  It becomes more visible, right?  Same happens here.  Tiny fluctuations during this expansion should leave certain signature behind.  Calculations show that the temperature differences wouldnt exactly be huge, but could be as large as a thousandth of a degree. If the temperature is 2.725K in one region, the stretched-out quantum jitters would result in its being a touch colder, say 2.7245K, or a touch hotter, 2.7255K, at nearby regions.  Scientist around the world were on mission to find this and compare it with what theory has suggested.  More impressive, the tiny temperature differences fit a pattern on the sky that is explained spoton by the theoretical calculations.  Not impressed?  Check it out:

graph.png

Above graph shows the good agreement of predictions of the inflation theory and observations. The magnitude of temperature variations in the CMB from the early Universe is plotted vertically against the multipole moment. The solid line represents the prediction of the simplest inflationary model and the data points are from satellites and ground-based experiments.  Now, that's just fascinating!  IMHO this has to be biggest thing cosmology in second part of 20th century if not more (just think of the scale of this whole thing and us as its consequence now figuring out what has happened).  Actually, this has been recognized in in 2006 Nobel prize for physics which went to George Smoot and John Mather, who led more than a thousand researchers on the Cosmic Background Explorer team in the early 1990s to the first detection of these temperature differences.  Despite all this, having our feet on the ground, inflation field (inflaton) remains hypothetical field and its potential energy curve hasn't been observed.  Still, other observations, above included, gives us peace of mind and theorist continue their work on developing existing models.

 

When we compare this level II universe with previously described level I universe we also see some differences.  In level I universe there is no obvious divide between parallel universes.  Things simply repeat themselves.  In level II universe there is divide.  In level I universe we have uniform distribution of content and laws of nature are equal given the circumstances.  Values (constants) are same here and in next patch.  In level II universe we expect same laws of nature to be present (as they have been created by same process), but constants may be different in value resulting in different aspects of content within each bubble.  If Inflationary Multiverse theory is correct is means we not only live in level I (quilted universe), but we are also part of level II universe (bubble or hole in cheese); level I universe exists within level II universe.  This also has implication of level I universe; if you had bird perspective level I universe would have spatially finite dimensions.

 

Credits: Brian Greene, Max Tegmark, Stephen Hawking, Wikipedia

 

Related posts:

Deja vu Universe

Braneworld

Landscape Multiverse

Many worlds

Holographic Principle to Multiverse Reality

Simulation Argument

In previous blog entry we encountered idea of infinite space.  Actually, we might claim space is infinite as we do not see the end of it plus there is no indication expansion would stop any time soon (it keeps speeding up).  Human notion of matter is such that there is nothing infinite and it is rather hard to cope with concept of infinite.  Infinity as per se is rather interesting, but I might more focus on that in some dedicated post one day - not now.  If we accept infinite space, does this mean there is infinite number of particles in space too?  Surprisingly, discussion on subject will lead us to concepts of multiverse, but we before we hit this theory concept let's check composition of Universe.

 

Whenever I think of modern view on what is out there I get flashes of history events showing evolution of idea about humans and our position in space.  Once upon the time we through Earth was flat.  We thought we were in center of Solar system.  Even space.  We thought world was spinning around us.  Since then we learned that we in rather different position; we oribit Sun, Solar system orbits galaxy center, galaxies group in clusters, clusters in super clusters.  From what we know, it stops there.  Nevertheless, in three polls conducted in 1996 and 1999, 19% of Britons, 18% of Americans, and 16% of Germans said that they believed the Sun orbits the Earth. We, you and me, screen which you use to read this, chair on which you seat, your partner and pet, planets... the whole material world around us - is made of atoms.  These atoms are made of nuclei and electrons and nuclei can  is made out of quarks.  Same particles in different layout as building blocks of everything around us.  Once again, it turns out this is not the case when it comes to Universe - this is only a small part of the content of the Universe.

 

Universe_Content.jpg

Atoms (matter) today made up for only 4.6%.  4% are free hydrogen and helium atoms.  0.5% are stars. Neutrinos are some 0.4% and heavy elements are are some 0.03% for an example.  So, it turns out space is not really space welcoming us at all.  We can romantically be described as star dust or nuclear waste to be less romantic (human composition contains traces of elements that may only come from stars during their nuclear processes).  While matter should be clear you may wonder what dak matter and dark energy are.  For both we can say more is unknown than known (even we do have some progress with dark matter and scientists expect to crack it down within next 20 years).

 

The mathematics shows that “just the right amount of matter,” the so-called critical density, weighs in today at about 2×10^–29 grams per cubic centimeter, which is about six hydrogen atoms per cubic meter (the equivalent of a single raindrop in every earth-sized volume).  Looking around, it would surely seem that the universe exceeds the critical density. The mathematical calculation of the critical density assumes that matter is uniformly spread throughout space. So you need to envision taking the earth, the moon, the sun, and everything else and evenly dispersing the atoms they contain across the cosmos.

Astronomers have been trying for long time to measure the average density of matter in the universe; with powerful telescopes they carefully observe large volumes of space and add up the masses of the stars they can see as well as the mass of other material whose presence they can infer by studying stellar and galactic motion. Until recently, the observations indicated that the average density was on the low side, about 27% of the critical density (equivalent of about two hydrogen atoms in each cubic meter).  In the late 1990s, astronomers realized that they had been leaving out an essential component of the tally: a diffuse energy that appears to be spread uniformly throughout space.  Even today, a decade after the initial observations, astronomers have yet to establish if the uniform energy is fixed or if the amount of energy in a given region of space varies over time. This energy does not give off light (explaining why it had for so long evaded detection) so we call it dark energy. "Dark" also describes well the many gaps in our understanding. No one can explain the dark energy’s origin, fundamental composition, or detailed properties - issues currently under intense investigation.  One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains cosmological constant makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.

 

We are much more certain what dark matter is not than we are what it is. First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 23% required by the observations. Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them. Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 23-25% dark matter contribution.  However, at this point, there are still a few dark matter possibilities that are viable. Baryonic matter could still make up the dark matter if it were all tied up in brown dwarfs or in small, dense chunks of heavy elements. These possibilities are known as massive compact halo objects, or MACHOs.  But the most common view is that dark matter is not baryonic at all, but that it is made up of other, more exotic particles like axions or WIMPs.

 

So if we rule out what we don't know, we are left with some 4% we believe we know enough.  Let's assume our universe expands into infinity (flat infinity, no tabletops or similar tricks that would make it finite please).  Now, for a moment, imagine large number of decks of cards.  You shuffle cards and key questions is can you have paterns repeating?  The answer depends on the number of decks. 52 cards can be arranged indifferent ways (52 possibilities for which card will be the first, times 51 remaining possibilities for which will be the second, times 50 remaining possibilities for the next card, and so on). If the number of decks we shuffle exceeds the number of different possible card orderings, then some of the shuffled decks would match. If you were to shuffle an infinite number of decks, the orderings of the cards would necessarily repeat an infinite number of times. An infinite number of occurrences with a finite number of possible configurations ensures that outcomes are infinitely repeated.  Can this be applied to Universe?

 

In an infinite universe, most regions lie beyond our ability to see, even using the most powerful telescopes possible (see previous blog entry on cosmic horizon).  Expansion of space increases the distance to objects whose light has long been traveling and has only just been received by us.  Same applies for light emitted by us for those who would have us out of their cosmic horizon.  Depending on the size of Universe (real one, not bounded by our cosmic horizon), in 2D world we might have as something seen on following picture:

Clip1.pngPicture on left shows us in center and ring around is our cosmic horizon.  On grand scale, depending on size of Universe, we might have many of those scattered around.  Going back to our cosmic horizon on left picture, we have radius of some 40+ billion light years (exact number hardly matters here).  We focus on matter and radiation particles.  How many different arrangements of the particles are possible?

 

The more matter and radiation you cram into the region the greater the number of possible arrangements. But you can’t cram pieces in indefinitely as particles carry energy, so more particles means more energy. If a region of space contains too much energy, it will collapse under its own weight and form a black hole.  And if after a black hole forms you try to cram yet more matter and energy into the region, the black hole’s event horizon will grow larger.  Thus there is a limit to how much matter and energy can exist fully within a region of space of a given size. For a region of space as large as today’s cosmic horizon, the limits involved are huge (about 10^56 grams).  Crucial here is not value of limit - it is a fact there is limit.  Something finite's in the air.

 

Finite energy within a cosmic horizon means finite number of particles (known or unknown). This also means each of these particles, lik has a finite number of distinct possible locations and speeds. Collectively, a finite number of particles, each of which can have finitely many distinct positions and velocities, means that within any cosmic horizon (picture right above) only a finite number of different particle arrangements are available (quantum states). Calculations reveals the number of distinct possible particle configurations within a cosmic horizon is around 10^10122  (huge but finite number).  The limited number of different card orderings ensures that with enough decks, shuffles will necessarily repeat. By the same reasoning, the limited number of particle arrangements ensures the particle arrangements must also somewhere repeat.  What does this mean?

 

As noted before, matter is pretty much made of same particles.  Different particle arrangement, but same particles (at present day there is no proof yet conscious might be coming from something else, but one may keep its mind open).  This indicates that out there there is a chance that very same you exists.  And both would be real.  Your second I would real as much as you (and if mental state comes out of physical properties it means indentical mentally as well).  Shocked?  There is more.  It turns out we can estimate location of next you too.  That is, in every region of space that’s roughly 10^10122 meters across, there should be a cosmic patch that replicates ours - you, Earth, Milky Way - everything else that inhabits our cosmic horizon.  As there is only one way to duplicate a region exactly, but many ways to almost duplicate it, we find approximate replicates way closed - some 10^10100 meters.  This is theory and it is theory which is quite possible.

 

Approach to such parallel Universe is called Quilted Multiverse by Brian Greene (I like to call it Deja Vu one, but probably there are other names too).  Brian wrote very nice book called "The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos".  I highly recommend this book and I plan to spend next few blog posts discussing various Multiverse concepts as described in Brian's book.  Nevertheless, it was another author who brought concept of multiple universes to my attention - Max Tegmark.  Max is known cosmologist (MIT) and has come up with a mathematical argument for the multiverse.  In his view, multiverse as described before is so called Level I Multiverse (IV levels in total).  You can find his paper on this subject here.  If you wish to visit his site where you can find multiple resources, click here.  Highly recommended.

Parallel_universe.jpg

Credits: Brian Greene, Max Tegmark, Stephen Hawking, Wikipedia

 

Related posts:

Inflation

Braneworld

Landscape Multiverse

Many worlds

Holographic Principle to Multiverse Reality

Simulation Argument

Space.  The final frontier.  Not that final as it turns.  Modern physics seems to be focused more and more on intriguing concepts of infinite space and multiverse concepts.  Before we even get there (few blogs later), we need to get some understanding of how far we can even see.  It's time for Universe sizing.

 

You probably read somewhere that current estimate on Universe age is some 13.7 billion years.  That's quite a huge number, but space is a huge place.  It is widely believed that was the moment when space and time were born and theory associated with is Big Bang.  Space is also cool place where we can perform sort of the time travel.  By using telescopes we take a peek into the past thanks to photons bringing us images of things as they once used to be.  The easiest way to understand this is to call for help our Sun.  Sun is 1.496×10^8km away from our planet.  When look at the Sun we believe we see it as it is now.  The truth is that photons travel from Sun to Earth using their constant speed - speed of light, which is around 300000 km/s.  That's rather speedy and there is no police out there to slow it down.  These little particles keep rushing at the same speed until absorbed.  With a little bit of math, we come to result which says light travels from Sun to us within 8 minutes and 19 seconds.  If Sun exploded now, we would become aware of that in 8 minutes and 19 seconds.  So, NOW on Earth and NOW next to Sun are are some 8 minutes apart.  When we look at the Sun we see past - as it was some 8 minutes ago.  When we look more distant, these values rise even more.  More distant we reach, more in past we travel.

 

Ok, so if Universe is 13.7 billion years old and light travels at speed of light (how original is that?) then the most distant light we see should 13.7 light years away, right?  Nope.  There is a catch called metric expansion of space.  At the start of 20th century Albert Einstein figure out from his equations space should expand.  He didn't believe it so he added something called cosmological constant to cancel this as he strongly believed space was stationary place.  Edwin Hubble then figure out distant galaxies were running away from us and that space was surely expanding.  Einstein considered failure to see this as "the biggest blunder" of his life.  Today, we not only know space is expanding; it is accelerating in its expansion.  For the last 7 billion years, contrary to long held expectations, the expansion of space has not been slowing down. It’s been speeding up!

 

At this point I have to do a small digression.  People not familiar with Big Bang and associated inflationary theories usually imagine this as some sort of explosion which spreads around some medium.  This is far from correct.  Big Bang is not explosion of something in some medium - it is theory which explains how our Universe started and deals with processes which happened at that point within certain time frames. At that point time has began for our Universe.  Since that time space has been expanding and latest observations show this expansion has accelerated.  I believe current observations is that space expands some 72km/s (there have been several measurements by the end of 1st decade of 21st century and their average is around mentioned value).  This expansion (regardless of speed) is unifrom from what we know and happens "everywhere".  As space, as we know it, does not have edge, you can imagine following picture.  Imagine you live in galaxy A while I live in galaxy B.  You would see following (illustration from UCLA):

A.gif

To you it appears as everything is running away from you, including my world, at uniform rate.  The way I see it is following:

B.gif

Well, I get the same result... So space expansion has no center.  It is space which is stretching itself.  At this point you may wonder does this mean Moon and Sun and rest is running away from us?  The answer is no.  We see these effects of space expansion at galaxy levels.  Actually, the space between galaxies is even not that much affected (when observed at level of galaxy clusters), but rather at level beyond that.  We believe today that what keeps galaxies together  (and its planets and stars) is due to gravitation where most of it comes from dark matter while expansion between them (can be seen as repulsive gravitation) is something attributed to dark energy.  I will discuss these more in separate blog dealing with content of Universe.

 

Why is this expansion important?  For number of reasons of course, but I will focus on the one related to distance calculation.  If the universe were static, light that had been traveling for the last 13.7 billion years and has only just reached us would indeed have been emitted from a distance of 13.7 billion light years as mentioned earlier. In an expanding universe, the object that emitted light has continued to recede during the billions of years the light was in transit. When we receive the light, the object is thus farther away (much farther than 13.7 billion light years).   This is why today when reading about certain object discoveries read "this and that has been found 27 billion years away" despite Universe age being 13.7 billion years. With all this numbers on our mind, how far can we see in terms of proper distance?  What is our observable Universe as seen from Earth?  It turns out that no matter where I place telescope I can go as far as 14.3 billion parsecs (about 46.6 billion light years).  If you imagine that as radius it turns out observable diameter is 93 billion light years.  And that's just what is observable from Earth!

 

So how big is the Universe?  Well, no one knows.  Period.  The universe is immensely large and possibly infinite in volume.  Infinity is world per se and as such you can imagine infinity as approximation of some unimaginable large (but finite) value if that makes you more comfortable.  OK, so we figure out that from our Earth there is a limit on how distant we can see due to expansion of space and time it takes for light to reach us.  How far can we see in the past.  Can we see Big Bang itself?  No, we can't.

 

The oldest object so far observed is galaxy named UDFy-38135539.  It is estimated that it has been created some 600 million years after Bing Bang (estimation goes galaxies started to form some 200 million years after Big Bang).   The oldest light captured is the one seen by Europe's Planck telescope in 2010 and goes very near the start of Universe.  WMAP also comes close, but there is something that obscures our view.  To see what we need to take a crash course on Big Bang and only instrument we use to probe the past - light (in spectrum invisible to our naked eye of course).

 

Everything radiates electromagnetic radiation (light), even our bodies. The wavelength of radiation or light depends on the temperature of the object.  If you ever visited ESA in Netherlands and their museum, you could test it on yourself.  If the entire universe was once condensed in a single particle, then the intense compression of all substances and energy would result in intense heat, which would have emitted radiation of a corresponding wavelength. The apparent temperature of this light would have cooled down as the universe expanded after the Big Bang. In 1965, Arno Penzias and Robert Woodrow Wilson, at Bell Laboratories, found it as what they believed to be noise.  It turns out this noise was the very light emitted when the universe was still hot. Although once hot, this radiation had cooled to an apparent temperature of 3 K (3 K = -270°C) since the time it first appeared along with the expansion of the universe. We call this today Cosmic Microwave Background Radiation (CMB).  This is the first light we can observe since Universe begun.  Can you see CMB yourself?  The cool thing is that you can! If you tune your TV between channels, a few percent of the "snow" that you see on your screen is noise caused by the background of microwaves.  You might need older TV set though and not some digital/cable thingy.  How close is this to very Big Bang time?  Very close, but in terms of human lifespan quite alot.  Some 370000 to 380000 years.  Why is that so?

 

Just after its birth, hot and dense universe experienced a frenzy of activity. Space rapidly expanded (inflation) and cooled, allowing a particle stew to congeal from the primordial plasma (we believe gluon quark plasma as the one created at LHC nowadays). For the first three minutes, the rapidly falling temperature remained sufficiently high for the universe to act like a cosmic nuclear furnace, synthesizing the simplest atomic nuclei: hydrogen, helium, and trace amounts of lithium. After just a few more minutes, the temperature dropped to about 108 Kelvin (K). Although immensely high by everyday standards (that's roughly 10,000 times the Sun's surface temperature), this temperature was too low to support further nuclear processes.  For eons that followed, not much happened except that space kept expanding and the particle bath kept cooling.  Then, some 370000 to 380000 years later, when the universe had cooled to about 3000 K (half the Sun’s surface temperature) we had great event. To that point, space had been filled with a plasma of particles carrying electric charge, mostly protons and electrons.  Because electrically charged particles have the unique ability to jostle photons - particles of light - the primordial plasma would have appeared as fog; the photons, incessantly buffeted by electrons and protons, would have provided a diffuse glow (imagine car’s lights cloaked by dense fog). But when the temperature dropped below 3000 K, the rapidly moving electrons and nuclei slowed sufficiently to amalgamate into atoms; electrons were captured by the atomic nuclei and drawn into orbit. This was a key transformation because protons and electrons have equal but opposite charges, their atomic unions are electrically neutral. Since plasma of electrically neutral composites allows photons to slip through it was the formation of atoms allowing the cosmic fog to clear and the luminous echo of the big bang to be released. The primordial photons have been streaming through space ever since and that's our CMB.  How come a light that would see (and probably get blind) now be invisible CMB to us?  Expansion.  As space expands, things on the move get weaker and cooler, including photons. Unlike particles of matter, photons don’t slow down when they cool; they always travel at light speed. Instead, when photons cool their vibrational frequencies decrease, which means they change color (violet photons will shift to blue, then to green, to yellow, to red, and then into the infrared, the microwave and finally into the domain of radio frequencies).  The bottom line is, it would be really hard for us to probe cosmic fog beyond 300000 years after Big Bang as we use light - and light was pretty much caged at those times.  Instead, we base our reverse engineering on theory, computer models, observations and other scientific methods in field.

 

If interested more in Big Bang chronology as used today, use wikipedia at http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang.

 

If you like music by Queen, then you probably know who Brian May is.  Brian May co-wrote book along with Sir Patrick Moore and Chris Lintott called "Bang! – The Complete History of the Universe".  It is nice and easily readable book with loads of informations and cool pictures - highly recommended to any reader of any age.  I bought few years ago and got chance to get it signed by Dr. Bri himself.  The picture below comes from NASA though.

 

CMB_Timeline.jpg

Universe is without any doubts bigger than we can imagine.  That's why infinity fits so well to description of Universe.  Holding a breath and focussing on what we can see we know we are limited by laws of nature and our current tooling to explore events and distances beyond what is considered observable space from Earth - cosmic horizon.  But this is just where it starts to be fun.  Next blog entry will deal with content of our Universe and once again I will touch the boundaries of space, but this time I will be able to go beyond those as well as introduction to some modern ideas which might have been Sci-Fi several years ago (to be discussed more in details on several blog posts to follow next week).

 

Credits: Brian Greene, Brian May, Sir Patrick Moore, Chris Lintott Stephen Hawking, Wikipedia

Hrvoje Crvelin

Exoplanets galore

Posted by Hrvoje Crvelin Sep 12, 2011

There is a small chance you never heard of term exoplanets, but then you never know... Exoplanet is short of extrasolar planet which again stands for a planet in some solar system.  Sun, as you might be aware, is nothing but star and we know there are plenty of stars out there.  Just our galaxy hosts some 200 to 400 billion stars.  That's a big number and bare in mind this is just our galaxy.  Current estimate is is there are some 170 billion galaxies in observable universe (which turns our to be some 28 billion parsecs in diamerar or 93 billion light years).  Our Milky Way is typical large galaxy.  So you would expect many suns out there and associated planets...  Not so.

 

While you might be under impression that planets always belong to some star, no matter what distance they keep, this is not correct.  We know today there are many free-floating planets out there.  They do not have orbit as we do around some star.  In May 2011, NASA suggested there might be even more of these objects out there than stars.  Obvious problem with these planets is being dark and thus more difficult to detect.  Anyway, I would like to get back focus on exoplanets now.  These planets orbit their parent star.  What is cool about them is that they just might be in right distance away (and with appropriate properties too) to host some sort of life form.  Life form here does not matter; bacteria, fish, humanoid, walking tree... you name it.  It might be even based on something else than carbon, but we still like to imagine things upon our own reflection so we search for similarities within frame reference we are familiar with.  Zone in which such exoplanet would orbit is called - habitable zone.

 

What is habitable zone or how does one defined it?  Quite simply, this zone is defined as distance between planet and star within star system where planet is capable of maintaining liquid water on surface and sustain Earth-like life (ok, no walking trees here).  Now, you way straight away say this is a bit fuzzy because this heavily depends on several factors like star size and phase, planet conditions (just ask yourself about all that liquid that one run on Mars surface), etc.  To make it more complicated, there is something called planetary habitability. Planetary habitabiliy deals only with conditions to sustain carbon-based life on the planet - HZ on the other hand deals with stellar conditions required to sustain carbon-based life (obivously, we may find life based on something else within this zone and that actually already happened on our planet in 2011 too). 

 

In search for planets of interest out there, for reasons of potential migration or research or simply life serach, astonomers focus on something they refer to as circumstellar habitable zone.  You can imagine this as a ring around star where conditions are just right.  This ring is sometimes called ecosphere.  Now what's the big deal with carbon based life (like us) and water.  It turns out liquid water is important because carbon compounds dissolved in water form the basis of all almost all life we know on Earth, so watery planets are good candidates to support similar biochemistries. So, we look out there for things as much as similar to our home.  This is why search for exoplanets is so important to us.  Strangly enough, it was all theory until recently though...

 

First confirmed dicovery of exoplanet happened in 1988.  Actually, it was published back then, but confirmed only in 2003.  Nevertheless, it is 1992 discovery by radio astronomers that is usually referenced as first exoplanet discovery.  It is fair to stay that we started to find in reality these planets by the closing of last century.  Today, we know 600+ of those and number is increasing. 

 

There are several ways used to detect these planets and mostly common used method is measuring radial velocity (but this is just one method though mostly used, but others are in use as well).  The HARPS (an acronym for High Accuracy Radial velocity Planet Searcher) spectrograph on the 3.6-metre telescope at ESO's La Silla Observatory in Chile is the world's most successful planet finder.  It has been announced today they found 60 new exoplanets where 15 of those turn out to be something called super Earths (results presented yesterday at the conference on Extreme Solar Systems held at the Grand Teton National Park, Wyoming, USA).  As you may have guessed, super here does not stand for free of politics, but rather size; planets with a mass between one and ten times that of Earth are called super-Earths. Interesting enough, tere are no such planets in our Solar System, but they appear to be very common around other stars.

 

In space, we have mission called Keppler. Keppler uses alternative method of detection; it searches for the slight drop in the brightness of a star as a planet passes in front of it and blocks some of the light. The majority of planets discovered by this transit method are very distant from us. In contrast, the planets found by HARPS are around stars close to the Sun. This makes them better targets for many kinds of additional follow-up observations.  Keppler has found some 1200 exoplanet candidates so far.

 

Finding these planets is crucial of us.  We detect their existance and can isolate those candidates for follow-up observations and research to find more about their chemistry.  We may find planets in various stages of life reflecting state of planetary habitat and can help us in further investigation and understanding of processes that might be applied to our planet.  Not to mention getting more puzzles in place in overall picture of Universe.  I can't not to remember early days of my elementary school when I stated to teacher I believe we will soon find Universe is blooming with life.  In return I was kicked out of the class for stating such thing.  Amazing, huh?  Exoplanet research helps us focus on potential spots where life migh exist and where conditions might be similar to what we have.  It is a long way yet to get there, but we started our journey and we should continue.  Let's hope JWST gets neede funding for us to be able to take a deeper peek into the space.  Whatever happens, we are starting to be more and more aware that we are not isolated condition wise.  All research so far, space wise or not, showed us repeatable paterns at all possible layers of reality and I expect this to be the same with exoplanet search results.  It should also speed up search for life in other regions of space.  The number of exoplanets continues to rise... and that's only for what we consider to be habitable zone according to our own standard.

 

exoplanet.jpg

 

Credits: Wikipedia

 

Related posts: Exoplanets galore II

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