This is a short compilation of snapshots of memories about aneminent mathematician who was a great friend, philosopherand guide for the author.

I first met Varadarajan in January 1958, and maintained a closefriendship with him till he passed away in April 2019. He wasknown to all his friends as Raja, and that is how I shall referto him in the rest of this article. I learned much from him andcollaborated with him on two book-sized works.I am honoured to be asked to write about him. In my view, he wasone of the best mathematicians of Indian origin to have workedin the second half of the 20th century. I have divided this articleinto three parts. The first gives a brief description of his life. Thesecond part deals with some highlights of his work. The last partis devoted to some personal recollections. There I will describesome vignettes of our long friendship.

We forget often. But some memories last a lifetime. Thismeans that our brain is capable of protecting memories foryears. This is a remarkable feat given that the biochemicalhardware involved in creating new memories is a hostile placefor its storage. What are the challenges involved? And whattype of biochemical mechanisms may overcome them? Thisarticle explores a major hypothesis that molecular switchesmay be behind our remarkable ability to remember for a lifetime.

Observations show that the expansion of the Universe is accelerating.This requires that the dominant constituent ofmatter in the Universe has some unusual properties like negativepressure. This exotic component has been given the namedark energy. We work with the simplest model of dark energy,the cosmological constant introduced by Einstein. Westudy the evolution of spherical over-densities in such a modeland show that there is a minimum over-density required forcollapse; perturbations with a smaller amplitude do not collapse.This threshold is interesting as even perturbations witha positive over-density and negative energy do not collapse infinite time. Further, we show that perturbations with an amplitudelarger than, but comparable to the threshold value,take a very long time to collapse. We compare the solutionswith the case when dark energy is absent.

In this article, we move from sensory physiology to psychologyand consider the proverbially lazy drone. I will describehow some simple experiments permitted us to understandwhy males in the Indian paper wasp Ropalidia marginata dono work in the colony even during the time they live in it. Takingthe behaviour of feeding larvae as an example of work,we show that male wasps normally do not feed larvae, not becausethey are incapable of doing so, but because they do nothave access to enough food and also because female wasps areso much better at this job. As a confirmation of this conclusion,we could cure the males of their laziness, i.e., get themto feed the larvae by providing them with excess food andleaving them in the presence of hungry larvae, without thepresence of females.

A set of basic notes, or ‘scale’, forms the basis of music. Scalesare specific to specific genre of music. In this second articleof the series, we explore the development of various scalesassociated with Western classical music, arguably the mostinfluential genre of music of the present time.

A team working from IISER Pune, India has developed teachingresources to integrate climate change-related topics withthe core curriculum at school and/or undergraduate level toincrease the awareness of cause and effect of climate changeamong students. Their work is part of the global vision todemocratise knowledge such that all of humanity would investtheir talent, skills and ambition in a focused way to addressthe problems of climate change, which requires locally rootedsolutions, but based on global science.