Occam's Machete: Cosmology

Woit and Motl agree on something and that is that Verlinde is on the wrong track, maybe even a crackpot.  But neither seem to have torn apart the math with a critical eye and, well let’s just say they have strong pre-existing opinions about the proper way to think.  They are both smart but extreme enough that I sometimes question their opinions only because they hold them.  What’s an amateur to do to get a balanced analysis?

Enter Sabine Hossenfelder or Bee as she is known to her blog readers.  She has recently spent time examining Verlinde’s paper producing a blog post and arXiv paper.  She offers some thoughtful criticism and asks the question, “so what?”  Some sort of equivalence between entropy and gravity is only useful if it can be used as a bridge to apply gravity to the quantum world.  And she finds that part still lacking.

The year of Entropy continues with a paper referencing Verlinde but describing gravity and dark energy as effects of entanglement entropy. Read it on arXiv.

Something that has alway bothered me is the opinion expressed by moralistic politicians that faith and belief are virtues. Why? Doesn’t the skeptic who searches for evidence and rejects wishful thinking embody real virtue?  Would you be persuaded by someone’s belief that aliens crashed in a volcano and spread to infect all of humanity causing our combined ill-fortunes?  Oh, wait some people do believe that even though most of us would call that belief silly.  It is not backed by evidence and without evidence is not worthy of serious consideration. Which brings me to the quote of the day.

“I don’t ‘believe’ in string theory”, Brian Greene (the popular face of string theory and author of The Elegant Universe) in a Discover interview here.

Of course he goes on to make the distinction between belief and the virtuous pursuit of scientific skepticism in examining string theory. This balance of conviction and skepticism is the hallmark of good science. Greene is clearly a proponent of string theory and has written much about it but he is making a point about thought hygiene that ought to be applied broadly.

So the next time you are asked to vote for a politician who professes “faith” ask yourself if that lack of intellectual rigor is a good thing in a leader.  Faith is generally not a virtue.

Some folks at Colgate (Patrick Crotty, Daniel Schult, Ken Segall) have proposed a Josephson Junction array that simulates many of the physical properties of a biological neuron but operates orders of magnitude faster.  Now if that doesn’t get the SciFi writer in you going nothing will.

Entropy is big lately.  A new paper on arxiv (The Entropic Lanscape, Bousso and Harnik) uses entropic principles to derive predictions about such things as the cosmological constant and the nature of entropic radiation.  These predictions match well with observations in our corner of the universe and give a framework that applies to any part of the universe, even in other vacua.  This paper relates to examinations of the vacuum lanscape that usually end up relying on anthropic arguments.  In other words things are the way they are because we wouldn’t be here to observe them if they were different.  Bousso and Harnik replace arguments like that with ones that favor the maximiztion of entropy.

Also in a comment to a previous post here Nisheeth points to his arxiv article (The relativity of theory, Nisheeth) where he describes a framework for deriving physical laws from information-theoretic first principles.  He too relies on the maximiztion of entropy.

Lately I’ve seen a several papers describing how one fundamental way of measuring the universe or another is actually emergent from a different way of looking at things.  There are those that claim time does not exist in any fundamental way, we are just looking at things wrong. So what is fundamental?

Entropy.

Understand entropy and gravity emerges.  Understand it in a moving frame and General Relativity emerges.  The idea is published on arxiv (On the Origin of Gravity and the Laws of Newton, Erik Verlinde) and even made it to Slashdot.  Woit surveys other entropy related ideas.

As a computer scientist there is something appealing in the notion that information is fundamental and that all the laws of nature are derived from the way information works.

Update: There is a long post from Verlinde on Motl’s blog here.  It illuminates some of his ideas and explains their history.  If you can stomach Motl’s bullying read the comments too, there are many.

Motl has a nice post about the place of thought experiments in physics. How do you run an experiment when you have to have a train that moves at the speed of light and is smaller than the Planck scale—run a thought experiment.