Occam’s Machete

Lee Smolin has been one of the most articulate naysayers in modern cosmology, constantly finding a different path from the more popular multiple universe string theorists. He writes a lucid popular description of his philosophy here.  Since learning about the inflationary model of the big bang, which posits that the universe once expanded faster than the speed of light, I have wondered if things might be explained better the other way round.  Maybe the speed of light has not been constant during the life of the universe.  Unfortunately it will take some other slight of hand to make the math work out for that admittedly half-baked idea but you get the drift, what if the laws of nature have changed?

Many cosmologists think that time is an illusion.  We see the “superposition” of all the vastly many trajectories of the possible universes and turn that into what seems like the arrow of time.  A superposition is like placing all the possibilities on top of each other, if you squint you might think you see only one, kind of like the average.  This idea comes from the notion in quantum mechanics that a particle does not take a single path in getting from point A to point B.  It actually can be thought of as taking all possible paths between the two points.  What works for the tiny must work for the very big, right?

Smolin asks the question, how would things work out if time were really an underlying property of the universe?  What if there were only one universe and time really does flow in one direction.  Seems so old fashioned doesn’t it?  But in exploring the idea he has constructed a way to think about the unfolding of the universe from the big bang that models the emergence of our dimesions, the emergence of space-time itself.

Now a word about emergence is probably called for here.  Time is said to be emergent if it comes from the causal reality.  In other words if there are multiple universes all branching off at every instance and we see the illusion of time’s passage then time is emergent.  If, as Smolin thinks, space comes from a universe with time then the dimensions and space-time itself is emergent.

He has created a framework to explore this idea that he calls Quantum Graphity (sorry, his pun not mine).  It models the evolution of the universe with approximations of the quanta of space-time.  Smolin wrote an article in Scientific American about the idea of causal dynamical triangulations where he theorizes that the nature of space depends on how closely you look at it and when you look at it.

The old-fashoned idea that time is a property of the universe leads to further ideas exotic enough to challenge the best from string theorists, ideas like; the laws of the universe do not operate the same over time in fact cannot be removed from time, or the idea that the very number of dimensions we see have evolved from two to our present four (4.02 +/-0.1).

It is good to see that there is life in cosmology outside of string theory.

Recently I read a preso from Edward Witten, the High Priest of String Theory, where he talked about what was interesting to him outside of high energy physics.  In other words, what is interesting outside of the LHC world.  Being an amateur it is sometimes hard to tell the crackpot ideas from the merely improbable.  No matter what you think of String Theory you have to respect Witten–and after bringing up the idea of cosmic super strings as dark matter candidates he makes the following statement:

the physics landscape away from the energy frontier contains all kinds of other possibilities … fifth forces … breakdown of quantum mechanics … new signals in cosmic rays … who knows! — Ed Witten

It looks like quantum mechanics is real, how much weirder can it get?

I’ve noticed a couple of articles lately about old data that has recently been discovered to contain some gem of hidden import.  The first involves a planet discovered around a young star through indirect means.  But looking back through the archives of Hubble several infrared images were discovered of the star.  New techniques to remove the star’s glare from the image resulted in a couple really important pixels showing up.

Another is from a researcher who back in 1987 claimed to have detected gravity waves coming from a nearby supernova.  His claims were dismissed at the time when calculations showed his detector was not sensitive enough to detect those effects.  Recently it was discovered that gravity wave resonance may allow gravity waves to be drastically amplified in certain circumstances.  And it so happens that the supernova seen in 1987 fits those circumstances pretty well.

Packrats of the world rejoice.  The moral of the story is never throw away those old floppies–your Nobel prize may be waiting there for some future data miner to unearth.

One of my favorite Cosmology bloggers, Peter Coles, a Professor in Theoretical Physics at Cardiff University, has just published an important new theory explaining the flatness of the universe. I don’t want to spoil the story but it involves a few beers at the Half Moon Pub, the creator, and inscrutable Swedish furniture engineering techniques.  A must read.

If there are so many planets out there then many must have life and with lots of life there must be lots of television… SETI listens to the sky for the faint echos of alien Fred Flintsones–yaba daba dooo.  So where are all the aliens? If the galaxy is so old why haven’t they stopped by and left a calling card (I know, the pyramids…) This question is called Fermi’s paradox and a recent article on arxiv has a really interesting answer. Even if they are out there they would have to be above a certain density to notice each other.  Smith calculates that if there were only 200 communicating civilizations in our neighborhood we might never notice each other.  Maybe Drake’s equation needs a new term?

A recent analysis of galaxy clusters has given us some very nice images so I couldn’t resist posting them. The first shows a cluster and a computer analysis of the affect of gravitational lensing. You will notice in the image to the right that, if you scrape off all the spikes, there is a gradual bulge. Scraping off all the spikes amounts to removing all of the visible objects (seen as bright galaxies). The underlying bulge can be explained by the presence of large amounts of something that we can’t see—dark matter.

Gravitational Lensing of Galaxy Clusters

The second photo comes from another cluster. The left image is in visible light, the right in x-rays. The x-rays show a very hot gas halo around the cluster. This hot gas would have escaped into the void if not for a gravitational affect beyond what can be explained by the object in the visible light image.

X-Ray producing hot gas in the grip of dark matter.

This is nothing ground breaking but gives us a clearer picture of the shape of dark matter.  One more thing interesting in this arxiv paper is a discussion of dark matter stars as a candidate for dark matter.  How’s that for a recursive argument?

Update:  A new study of several globular galaxies shows indirectly the effects of dark matter.  The galaxies pictured were observed in the middle of a cluster where other galaxies were being ripped apart by tidal forces.  These remained undisturbed in the center of the gravity maelstrom hinting at a halo of dark matter which must be sheilding them.

I just got done reading Anathem by Neal Stephenson.  It describes the adventures of an avout from a remote Math and his numerous discourses on Cosmography.  It’s a great yarn and especially fun if you can see through the mystical trappings to the cosmology beneath.  The underlying rules of the universe, eternal inflation, supersymmetry, string theory, parallel universes–it’s all there with a dash of Pythagoras and Plato to spice it up.

It got me to thinking about how lots of cosmology seems to fall into what I think of as mathematical theoretical cosmology.  The type of things you find in this bucket tend to start from some mathematical construct that seems to be reflected in nature.  Often as not the idea starts from pure mathematics and is found to describe something in nature.  A mathematician/physicist picks up the idea with the hope that if they trudge far enough into the math that they will come out the other end with some novel predictions.  The whole approach appeals to anyone interested in the elusive concept of elegance–beauty in simplicity.  Here are some examples:

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  Standard Model - SUSY

  Supersymmetry (SUSY)–this theory starts by noticing that elementary particles of one spin each have a corresponding particle differing only by a spin of one half.  In other words for every boson there is a fermion.  So what?  Well if you stack up all the known particles and their super partners you will see that some of the array have not been observed in nature.  Does the elegance of the supersymmetrical “standard model” make it right?  Of course not but that is exactly what got people to looking.  The model comes with lots of math that follows along a train of thought leading to certain predictions about what these missing particles might look like.  So the theory fits observed reality and makes testable predictions.  Who cares that it sprang from a human need to find elegance?  Not me–especially if it proves out.

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  Calabi-Yau Shape

  String Theory–this is the famous idea that all the elementary particles come from different ways that a string (in ten dimensional space) can vibrate.  These modes of vibration correspond to the above mentioned SUSY particles and their super partners.  Many physicists have jumped on the subject and, given its intricacies, there are lots of avenues to pursue. The idea is profoundly elegant but quickly gets really complicated and it has been argued that it is untestable.  I find this last to be a bit silly since it implies a limit to testability that is unknown to me.

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  E8 Simple Lie Algebra

  E8 Simple Lie Algebra–here Garret Lisi uses the E8 simple lie algebra, a kind of structured mathematics, and applies it to describe the elementary particles of the standard model.  One interesting aspect of his unification theory is that is operates in regular old four dimensional space.   Once again Lisi’s grand unification theory (GUT) came from a mathematical construct of great elegance and beauty but does it lead anywhere?  Given Lisi’s interesting bio it would be nice.  Lisi’s TED talk is here.   Below is an animation showing different slices of the E8 in two dimensions.

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  F4-an eight dimensional quark in 4-D

  Octonions–another kind of structured mathematics is used by Tevian Dray and Corinne Manogue to describe things in eight dimensions.  One problem with String Theory is that we see only four dimensions, where are the rest of the ten dimensions required for the theory?  One answer is that they are all wound up tightly so we can’t see them.  Octionions give one way to describe how this happens and can also be used to maniplulate objects in String Theory.  The illustrations describes an eight dimensional quark on four.  How’s that for a nice trick?

I was reading the FQXi article above and following a reference brought me to a page full of tile patterns here.  They reminded me so much of the teglon in Anathem.  The great thing about elegance is that it appeals to right as well as left brain types–mathematicians, physicists, authors, and artists.  In mystical terms perhaps the unseen reality is throwing a shadow into our minds.  Don’t blame me for the mysticism, read your Plato.

One foundational element of modern cosmology is inflation theory. It states that shortly after the big bang the entire universe started expanding faster than the speed of light. It eventually slowed down and recently we have discovered that it is speeding up again. The original form of inflation was proposed by Alan Guth and explains many things we observe about the universe including why it seem to be so uniform.

One interesting side effect of this period of hyper fast expansion is that some of our universe is not visible to us. If you look out into the universe far enough you will reach the limit of what we can see. There is only so far that light can have traveled in the 13.7 billion years since the big bang. But the inflationary period put part of our universe so far out that light cannot have traveled to us. But the theory implies there may be stuff out there in the dark, past the observable limits.

This became more than speculation when it was recently noted that many galaxy clusters at the observable limit are rushing toward a point that appears to be beyond what we can see. Something big is out there sucking things towards it. Spooky! And here is a picture showing the action.

Nearby galaxy clusters are moving towards the purple dot.

An article in SPACE.com quoted Kashlinsky, the discoverer of the dark flow effect, as saying:

The structures responsible for this motion have been pushed so far away by inflation, I would guesstimate they may be hundreds of billions of light years away, that we cannot see even with the deepest telescopes because the light emitted there could not have reached us in the age of the universe.

Depending on your favorite flavor of Inflation Theory these structures may be very strange indeed.  if they can have an influence over billions of light year on more than 700 of galaxy clusters then they must be pretty big.