Skip to main content

Dark Energy and the knights of the razor


Sabine Hossenfelder, a theoretical physicist (she did a doctoral thesis on black hole production) and a prolific science popularizer, discussed in her blog recently whether physicists have any good reason to posit the existence of "dark energy."

About the turn of the millennium, physicists determined that the expansion of the universe is accelerating. They didn't know why, so they proposed a "dark (otherwise unobservable) energy" that was driving this acceleration. There is a key paper by Chevalier and Polarski in the International Journal of Modern Physics from 2001.  

But the simple idea, once postulated, didn't stay simple.  Theorists were soon explaining why dark energy has to be understood to be "evolving," and competing scenarios for that evolution themselves evolved.  

Now quite recently, a group of mathematicians have looked at the numbers and have decided that this work may all have been a wild goose chase.  There need be no dark energy to evolve or to argue about. Alexander, Temple and Vogler, writing in Proceedings of the Royal Society A.]

You can make the numbers work re accelerating without dark energy by supposing uneven distribution of matter through the universe, a "chunky" universe even at the largest scales.  That presumably is what Ockham would prefer.  Physicists typically use their "cosmological principle" in modelling the world -- the principle that the universe is smooth and directionless at those largest scales. But if the smooth and directionless stuff gets us into unending further postulations, one should feel free to reject it.

Actually, Hossenfelder doesn't go that far.  She says the paper has good mathematics, but physicists will want to test its chunky-universe premise against a lot of data and the assessment could take years.  And they already have posters printed up for the next conference on new models for the dark energy evolution!    
Labels:

Comments

Post a Comment

Popular posts from this blog

Searle: The Chinese Room

John Searle has become the object of accusations of improper conduct. These accusations even have some people in the world of academic philosophy saying that instructors in that world should try to avoid teaching Searle's views. That is an odd contention, and has given rise to heated exchanges in certain corners of the blogosphere.  At Leiter Reports, I encountered a comment from someone describing himself as "grad student drop out." GSDO said: " This is a side question (and not at all an attempt to answer the question BL posed): How important is John Searle's work? Are people still working on speech act theory or is that just another dead end in the history of 20th century philosophy? My impression is that his reputation is somewhat inflated from all of his speaking engagements and NYRoB reviews. The Chinese room argument is a classic, but is there much more to his work than that?" I took it upon myself to answer that on LR. But here I'll tak...
24 comments
Read more

A Story About Coleridge

This is a quote from a memoir by Dorothy Wordsworth, reflecting on a trip she took with two famous poets, her brother, William Wordsworth, and their similarly gifted companion, Samuel Taylor Coleridge.   We sat upon a bench, placed for the sake of one of these views, whence we looked down upon the waterfall, and over the open country ... A lady and gentleman, more expeditious tourists than ourselves, came to the spot; they left us at the seat, and we found them again at another station above the Falls. Coleridge, who is always good-natured enough to enter into conversation with anybody whom he meets in his way, began to talk with the gentleman, who observed that it was a majestic waterfall. Coleridge was delighted with the accuracy of the epithet, particularly as he had been settling in his own mind the precise meaning of the words grand, majestic, sublime, etc., and had discussed the subject with William at some length the day before. “Yes, sir,” says Coleridge, “it is a maj...
10 comments
Read more

The Growing Block Theory of Time

My own disposition, in regard to the philosophy of time, is toward the "growing block" theory. This is the view that past events remain realities, that present-moment events are also realities, but that future events are not yet real. The image is of the universe as a block with an edge on (say) the right-hand side. The block is expanding because that edge is moving ever further right, and that edge is what we call the present, or, simply, "now." Everything to the left of that edge is both static (the past is complete) and, still and forever, real. Think of the phrase "the moving finger writes." The chief alternatives to the growing-block theory are "presentism" (only the now-edge itself is real) and "eternalism" (past, present, and future are all real." I believe that time is a growing block because (1) that's what it feels like, (2) we should stick with the introspective phenomenon unless we have good reason to abandon ...
8 comments
Read more