Wednesday, June 21, 2017

Explaining Matter-Antimatter Asymmetry

I've long been an advocate of an approach to explaining the matter-antimatter asymmetry of the universe in which antimatter predominantly in a partner universe whose boundary with our own is at a shared Big Bang. A brief new paper explores the idea more formally, although the use of multiverse terminology is somewhat unfortunate for a proposal that lacks many of the flaws more commonly found in multiverse arguments.
In the multiverse, the universes can be created in entangled pairs with spacetimes that are both expanding in terms of the time variables experienced by internal observers in their particle physics experiments. The time variables of the two universes are related by an antipodal-like symmetry that might explain why there is no antimatter in our universe: at the origin, antimatter is created, by definition and for any observer, in the observer's partner universe. The Euclidean region of the spacetime that separates the two universes acts as a quantum barrier that prevents matter-antimatter from collapse.
Salvador J. Robles-Perez, "Restoration of matter-antimatter symmetry in the multiverse" (June 20, 2017).

An earlier version of the proposal from 2013 can be found here.

Why Are Hyaenas Smart?

Behavioural data indicate that there has been considerable convergence between primates and hyaenas with respect to their social cognitive abilities.
From here (hat tip to Razib Khan).

I have long attributed the exceptional intelligence of hyaenas, one of the most intelligent and successful African megafauna, to the fact that unlike most other mammals, the reproductive organs of hyaenas require both the male and female to be simultaneous aroused to reproduce. This has the effect of giving female hyaenas much more control of their reproductive decisions than comparable felines and canines. 

Hyaenas are the poster children for Planned Parenthood of the animal world.

Cosmopolitan Scandinavians Of Old And Y1K

In the Middle Ages in Europe it is commonly said that most people never traveled more than thirty miles from where they were born. But, then there were the Vikings:
In the centuries around and before 1000 A.D. there was a “Viking international” of sorts. Harald Hardrada may have died in England trying to become king of that nation, but he served for a time in the Varangian Guards in Constantinople. His connections to Kievan Rus were such that priests in the Eastern Christian tradition were brought in to aid in the conversion of Norway.
N.B. The time period that I call Y1K was a fascinating one all over the world. For example, Viking Lief Erikson makes it to the New World, the Gypsies start their migration from India, the Brahui migrate from the Deccan Peninsula to the Indus River Valley, the Crusades start one of the first very distant foreign wars in history, and more.

Even before the Vikings, the Bronze Age Scandinavians got around as well. There is evidence of trade of amber for Egyptian jewelry that brought goods, and probably people with them, from the Baltic Sea to Egypt.

Monday, June 19, 2017

Physics Is Culturally Neutral

Lubos Motl should know better than to make the ad hominem argument that a physics concept is discredited just because a Nobel Prize winning physicist who also became a Nazi at some point in his life toyed with the idea.

In this case he is attacking the loop quantum gravity approach to quantum gravity (he prefers the approach to quantum gravity based upon gravitons in 10-11 dimensional string theory), because the physicist who invented the cathode ray tube (which was at the heart of all video screens for half a century) toyed with a somewhat similar aether theory.

Loop quantum gravity (LQG) is a really a class of theories of quantum gravity that argues that, as in general relativity, gravity involves a background independent deformation of space-time, rather than a force mediated by a boson in the special relativistic space-time background of quantum-mechanics. Thus, in loop quantum gravity, there is quantization of space-time at the Planck scale, rather than quantization of a force acting between particles.

It is certainly fair game to criticize potential flaws in one of the two major approaches to quantum gravity, which is one of the great unsolved problems of physics, and eventually he does address some of his concerns on that score.

But, it is not fair game to field as an argument against LQG the politics of an admittedly technically accomplished physicist who explored a distant predecessor of the idea, any more than it is to denounce half a century of television screens as "Nazi Science". This is the kind of criticism that confuses people who don't know better while not informing or persuading anyone who does know better. It is particularly unseemly coming from someone whose own distasteful politics and poor social skills appear to have cost him a position in the physics department at Harvard, despite his clearly solid command of the discipline of physics itself, however, opinionated he might be in that regard towards rival approaches in his discipline.

Motl's offhand accusations of plagiarism directed at an academic rival (which having read many of the academic rival's papers, I can confidently tell you is hog wash), and his failure to engage in the real issues by offering up straw man versions of LQG, are likewise unworthy of a serious and sincere academic.