#paperoftheday — Public Fediverse posts

My #paperOfTheDay was "Galilei invariance, action-reaction principle, and center of mass theorem" from 1983.
This is an article about #generalRelativity , without anything quantum. From daily experience, we know that every object has a mass, but thinking more closely, the parameter we call mass actually appears in different ways in #physics, and it is not a priory clear how they are logically related. Einstein's famous thought experiment was about the "falling elevator", that is, if you are in a box and can't look outside, you can not distinguish whether you fall freely, or you are located far away from a planet where there is no gravitational field. This "weak equivalence principle" asserts the equivalence between "inertial mass", the parameter which determines how hard it is to accelerate something, and "passive gravitational mass", the parameter that determines how strongly a gravitational field acts on an object.
But there is a third type of mass, the "active gravitational mass", which determines how much gravitational field is generated by an object. The "strong equivalence principle" asserts that all three masses are the same.
The present article demonstrates that, as far as classical celestial mechanics is concerned, the strong equivalence principle can not been distinguished from the weak one. That is, the observed motion of celestial bodies can already be explained by the weak equivalence principle, regardless of whether the strong one holds or not.
I don't know what the current state of affairs is in that question, in particular regarding quantum theory.
https://link.springer.com/article/10.1007/BF01889417

Today's #paperOfTheDay is "Why there is Nothing rather than something: A theory of the cosmological constant" from 1988. Like yesterday's paper, it deals with the intersection between quantum field theory and #generalRelativity, but the 30 years between them clearly show. Coleman's 1988 paper is an argument in the style of that time (which structurally is quite similar to much of the older #renormalon literature): Heuristic manipulations of formal objects such as the wave function of the universe, or divergent sums over all spacetime geometries. The outcome of this argument is that if #wormholes exist (caused by quantum effects at a scale that is much smaller than observations, but larger than the Planck scale), they can drive the cosmological constant to zero in an Euclidean path integral formulation of general relativity. As always with Coleman, the language is quite funny and frank about the paper's limitations: He writes "Although I find this theory in many ways very attractive, I must honestly stress its speculative character. It rests on wormhole dynamics and the Euclidean formulation of quantum gravity. This is doubly a house built on sand. [...] the Euclideon formulation of gravity is not a subject with firm foundations and clear rules of procedure; indeed, it is more like a trackless swamp". Observations like these have by now, 30 years later, led to a style of theoretical physics that is much more systematic and mathematical than in the 1980s, but also sometimes less intuitive. #dailyPaperChallenge https://doi.org/10.1016%2F0550-3213(88)90097-1

#paperoftheday

Amazing work showing that #genetic #disruption of the #kinase module (CDK) of Mediator complex in chimeric #antigen receptor T cell (CAR T) resulted in enhanced effector function and increased #antitumor activity (disruption of CDK module increases core Mediator #chromatin occupancy at #enhancers)

https://www.science.org/doi/10.1126/science.abn5647