Occam's Machete

Cosmologists have long tried to come to grips with the implications of the expanding universe.  They follow the arrow of time back to what they assume must be a single point from which everything expanded.  They also assume that something happened all thos billions of years ago and everything afterward is a result of that single event.  I’m not sure why, in fact, those assumptions don’t seem logical to me.  Lately explanations for the Big Bang have pointed at possible interactions between parallel universes.  Why would a collision between two universes happen in a single point or at a single moment for that matter?

This might seem idle speculation; of the sort String Theorists are often accused, if it weren’t for recent observations of the cosmic background radiation.  Calculating the distribution of energy in the universe based on what we see in the microwave background recent research shows a lopsidedness amounting to 10%.  In other words one half of the observable universe has 10% more microwave radiation than the other.  The the radiation is thought to be from the very first light of the universe red shifted into microwave, it may be an indication of early structure to the universe.  In other word it may not have started from a uniform point source.  Furthermore some researchers have proposed an explanation of the structure.

Another data point is the recent work done by Quantum Physicists to model the early universe.  At very least their calculations hint that the universe has a smallest possible size which corresponds to the maximum allowable energy density.  General Relativity will run backwards to predict virtually infinite energy density but not so if you use quantum mechanical measures.  What happens when the universe gets so small that it reaches the maximum density—it expands.  If it can’t reach a point why would we think it every reaches a maximum?  Only if it starts to collapse will it every reach a maximum and currently we think if will expand at ever increasing rates forever. 

Let’s suppose that the universe began from some volume that magically appeared from nowhere—or from outside the current universe.  What is to say that this appearance happened at a point in time?  Why do we assume that this creation from outside isn’t still going on or at least did for some time after the universe came into being?  Might the early inflationary period be tied to some type of continuing creation event?  I have never heard a good explantation of teh inflationary period let alone any proof that it really happened.  As usual I’m left with more questions than I started with.

Gravitational lensing has been used to show the effects of massive objects between the observer and some distant observed objects.  It is easy to understand how a massive object will bend light and some rather striking images show the effect.  What is interesting is that gravitational lensing can actually be used to map dark matter in the universe.  If you know what an object should look like you know when its light has been bent causing the image to be distorted even when the light is bent by invisible dark matter. 

As with many ideas that seems complex the trick is rather simple.  Look first at this image of the galaxy cluster Abell 2218.  Here you can see that the shape of the distant galaxies have been distorted by the large galaxy at the center of the picture.  Our eye picks out the distortion easily because we are used to seeing elliptical galaxies, not the bent slivers in this image.  It turns out that the amount of the curve can be used to measure the magnitude of the lensing and therefore the magnitude of the gravitational effect.  In this image the gravitational effect is from a visible object but if you imagine the same picture with no central bright blob you would still notice the distorted curved galactic ellipses.  And that is exactly how gravitational lensing is used to measure dark matter. 

There are problems with this type of distortion measure though since dark matter is highly diffuse.  Any photon moving through the center of a diffuse cloud of dark matter will move straight through it since the effect of the dark matter is to tug equally in all directions.  But when a photon moves near a diffuse cloud of dark matter it will tug more in the direction of the center of mass, so the photon bends in that direction.  By measuring the very slight curve in what should be a nice regular ellipse astronomers can calculate a line to the the center of mass of the cloud of dark matter.  By measuring the curvature of several galaxies they can triangulate to find the location of the dark matter. To get more precise they need to subtract the lensing caused by visible matter but you get the idea.

By putting together many observations astronomers are getting a better idea of the large scale structure of dark matter in the universe.  Here is one map of dark matter structures.  And here is link to a new study that describes the process in much greater detail (though I can't find an image to go with it.)