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According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in scientific literature. Being Universe Today if we occasionally stray into critically evaluating each other’s critical evaluations, that’s OK too. And of course, the first rule of Journal Club is… don’t talk about Journal Club.
So, without further ado – today’s journal article under the spotlight is about nothing.
The premise of the article is that to define nothing we need to look beyond a simple vacuum and think of nothing in terms of what there was before the Big Bang – i.e. really nothing.
For example, you can have a bubble of nothing (no topology, no geometry), a bubble of next to nothing (topology, but no geometry) or a bubble of something (which has topology, geometry and most importantly volume). The universe is a good example of a bubble of something.
The paper walks the reader through a train of logic which ends by defining nothing as ‘anti De Sitter space as the curvature length approaches zero’. De Sitter space is essentially a ‘vacuum solution’ of Einstein’s field equations – that is, a mathematically modelled universe with a positive cosmological constant. So it expands at an accelerating rate even though it is an empty vacuum. Anti De Sitter space is a vacuum solution with a negative cosmological constant – so it’s shrinking inward even though it is an empty vacuum. And as its curvature length approaches zero, you get nothing.
Having so defined nothing, the authors then explore how you might get a universe to spontaneously arise from that nothing – and nope, apparently it can’t be done. Although there are various ways to enable ‘tunnelling’ that can produce quantum fluctuations within an apparent vacuum – you can’t ‘up-tunnel’ from nothing (or at least you can’t up-tunnel from ‘anti-de Sitter space as the curvature length approaches zero’ ).
The paper acknowledges this is obviously a problem, since here we are. By explanation, the authors suggest:
- get past the problem by appealing to immeasurable extra dimensions (a common strategy in theoretical physics to explain impossible things without anyone being able to easily prove or disprove it);
- that their definition of nothing is just plain wrong; or
- that they (and we) are just not asking the right questions.
Clearly the third explanation is the authors’ favoured one as they end with the statement: ‘One thing seems clear… to truly understand everything, we must first understand nothing‘. Nice.
So – comments? Is appealing to extra dimensions just a way of dodging a need for evidence? Nothing to declare? Want to suggest an article for the next edition of Journal Club?
Brown and Dahlen On Nothing.