# Talk: The skeleton of our universe

Tomorrow I give a talk to the Newcastle Astronomical Society entitled the Skeleton of Our Universe. This is particularly exciting to me as this is the first public talk I’ve given to adults. I have previously spoken to schools and children about science, but presenting to a society of astronomy enthusiastic adults will be a new experience. I anticipate receiving lots of interesting questions, and hopefully there will be good discussions.

The goal of this talk is to introduce the topic of my research, understanding the largest structures in the universe, to the members of the society. This begins by setting the stage for where cosmology takes place, and winding back the cosmic clock as far as we can to the early universe and the cosmic microwave background (CMB). From there, understanding that the very early universe is nearly the same everywhere, with only 10 parts per million deviation from the mean density, it becomes an obvious scientific question to understand how those tiny fluctuations grow into the rich structure of galaxies we see today. This is where my research takes place.

After touring through the history of the universe, we will take a detour into understanding how these huge distances and times are actually measured. This was a deliberate choice for the audience at hand. I anticipate many of the members of the Newcastle Astronomical Society will be much better versed in directly observing the very local universe than I am, so discussing the method of parallax, and the connections between stellar physics and cosmology seemed an appropriate was to tie together the fields (plus it’s an excuse for some nice space pictures).

The end point of the talk is the 6 numbers one needs to measure to construct the universe. These are based on the 6 parameters in $\Lambda$CDM (the standard cosmological model), slightly modified to make them more accessible to this general audience. These break down into:

• 2 numbers from the early universe: the amplitude and scale dependence of the fluctuations in the CMB ($n_s$ and $\Delta_R^2$).
• 2 numbers for the “pie recipe” of the universe: how much dark energy and dark matter do we have ($\Omega_{c}$, $\Omega_\Lambda$).
• 2 timescales for the universe: the age of the universe, $t_0$, and the time you have to wait for the first stars to form (related to the optical depth to reionisation, $\tau$).

A full recording of the talk should soon appear on the Newcastle Astronomical Society’s youtube page. This will be linked on both Newcastle’s Observational Astronomy Group page, and I will embed it here once it goes live.

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