Tuesday, March 18, 2014

Gravitational Waves and Andrei Linde gets a surprise.

Yes the great gravitational wave breakthrough was as expected announced yesterday.  Stanford University Professor Andrei Linde, one of the founders of inflation theory, and his wife fellow Stanford Professor the string theorist Renata Kallosh got a surprise visit:

Assistant Professor Chao-Lin Kuo surprises Professor Andrei Linde with evidence that supports cosmic inflation theory. The discovery, made by Kuo and his colleagues at the BICEP2 experiment, represents the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang."
The original paper published yesterday at 10:45 a.m. is here.

Linde's shock at the result... "5σ r=0.2", Linde says "0.2!" in surprise.

It is surprising . The article on arXiv concludes:
Subtracting the various dust models and re-deriving the r
constraint still results in high significance of detection. For
the model which is perhaps the most likely to be close to re-
ality (DDM2 cross) the maximum likelihood value shifts to
r = 0.16 +0.06 −0.05 with r = 0 disfavored at 5.9σ. These high
values of r are in apparent tension with previous indirect limits
based on temperature measurements and we have discussed
some possible resolutions including modifications of the ini-
tial scalar perturbation spectrum such as running. However
we emphasize that we do not claim to know what the resolu-
tion is.
They are saying that their value of r which is the ratio of the tensor polarization from gravitational waves to the scalar polarization from the inflaton field, after correction for the effects of gravitational lensing, is incompatible with with the indirect limits established by satellite temperature measurements. From this r = 0.2 is surprisingly high.

These incompatibilities  need to be ironed out before this result is fully accepted.  This is just a
note of caution.  Lets hope everything is fine and we have witnessed a scientific revolution as big as that introduced by the CMB anisotropy results and the birth of precision cosmology.

Monday, March 17, 2014

The Landscapes of Science

 I have always been interested in the concept of a "landscape" in scientific theories.  A "landscape" is a representation of a higher dimensioned potential energy surface in a simplified three dimensional plot.  A couple of years ago I posted this comment in a thread about Conrad Hal Waddington's ideas on epigenetics (his term for developmental processes in biology not to be confused with the current misuse and abuse of the terminology):

"I can still remember the shock of insight from seeing a diagram of the epigenetic landscape in one of C.H. Waddington’s books when reading it over 40 years ago now.
I am impressed to this day by the usefulness of the “landscape” concept in diverse fields of science. In chemistry the potential energy surfaces of molecules and reactions are a landscape representation. In evolutionary theory there are of course fitness landscapes and finally on the grandest scale the cosmological landscape of string theory.
They are all of course higher dimensioned potential energy surfaces simplified to a 3-D representation in a 2-D projection. I wish the current evolutionary biologists would draw them the right way though, like physicists, chemists and the late great C. H. Waddingtion did. The vertical axis is potential energy and stable states are the lowest levels on this axis. So there are fitness valleys not fitness hills. A test “marble”, “ping-pong ball” atom or organism will tend to roll down to the lowest level in the metaphor of terrestrial gravity operating in a landscape."
 Comment in Why Evolution Is True

I have continued to think about the landscape metaphor in science.  The landscape is a simplified representation of a mathematical object in a potentially highly dimensioned hyperspace.  The usefulness of the concept in such diverse scientific fields  must represent some underlying similarities of the mathematics involved.

An example of a chemical potential energy surface from the article When is a Minimum not a Minimum

Here is Waddington's epigentic landscape from 1957 showing the potential developmental pathways for the ball (embryonic cell) as it rolls down the landscape.

What is the fundamental difference between difference between the two landscape representations ?  More to come.