Archive for Early Universe

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , on February 2, 2021 by telescoper

Time to announce the first publication of 2021 in the Open Journal of Astrophysics. This one was actually published a few days ago but  it took a bit of time to get the metadata and DOI registered so I held off announcing it until that was done.

The latest publication is a lengthy and comprehensive review article (67 pages altogether) by Allahverdi et al. which has 26 authors from all round the world. It is entitled The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe and is a study of the various possible evolutionary histories of cosmic expansion possible with a wide range of cosmological models with their implications for baryogenesis, nucleosynthesis, primordial gravitational wave production, and many other things besides.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here. This is one for the Cosmology and Nongalactic Astrophysics folder.

And so Volume 4 begins. Volume 3 had 15 papers, Volume 2 had 12 , and Volume 1 just 4 so we’re growing slowly but surely! Let’s see how many we publish in 2021. I can tell you  we have some very exciting papers in the pipeline…

Primordial Figures

Posted in Biographical, The Universe and Stuff with tags , , , , on August 28, 2020 by telescoper

I was rummaging around looking for some things related to a paper I’m struggling to finish before term starts and I found some vintage diagrams. They brought back a lot of memories of working on the textbook I wrote with Francesco Lucchin way back in the 1990s. In particular I remember how long it took to make these figures, when nowadays it would take a few minutes. In fact I’m thinking of setting this as a Computational Physics project for next year. These are not full computations either, just a simple fluid-based approach.

The curves show the evolution of fluctuations in both matter δm and radiation δr on a particular scale (i.e. a Fourier mode of given wavelength) defined as δm=δρmm, etc.  The x-axis shows the cosmic scale factor, which represents the expansion of the Universe and in both cases the universe is flat, i.e. it has a critical density. The first graph shows a universe with only baryonic matter:

Notice the strongly coupled oscillations in matter and radiation until a scale factor of around 10-3, corresponding to a redshift of a thousand or so, which is when matter and radiation decouple. The y-axis is logarithmic so the downward spikes represent zero points.

It is these oscillations which are responsible for the bumps and wiggles in the spectrum of the cosmic microwave background spectrum, as different Fourier modes arrive at the last scattering surface at a different phase of its oscillation. Of course going from the Figure above to the CMB fluctuation spectrum (see below) involves more calculations, and there is now a well-established machinery for doing these with full physical descriptions, but I think the above diagram makes the physical origin of these features clear.

The CMB power spectrum from Planck

The second diagram shows what happens if you add a third component called `X’ in the Figure below which we take to be cold non-baryonic matter. Because  this stuff doesn’t interact directly with radiation (while baryons do) it doesn’t participate in the oscillations but the density perturbations just carry on growing:

Notice too that at late times (i.e. after the baryonic matter and radiation have decoupled) the baryonic component grows much more quickly than in the first Figure. This is because, when released from the effect of the photon background, baryons start to feel the gravitational pull of the dark matter perturbations.

There’s nothing new in this of course – these Figures are thirty years old and similar were produced even earlier than that – but I still think pictures like these are pedagogically useful,

 

R.I.P. Tom Kibble (1932-2016)

Posted in The Universe and Stuff with tags , , , , , on June 2, 2016 by telescoper

Yet again, I find myself having to use this blog pass on some very sad news. Distinguished theoretical physicist Tom Kibble (below) passed away today, at the age of 83.

Kibble

Sir Thomas Walter Bannerman Kibble FRS (to give his full name) worked on  quantum field theory, especially the interface between high-energy particle physics and cosmology. He has worked on mechanisms ofsymmetry breaking, phase transitions and the topological defects (monopoles, cosmic strings or domain walls) that can be formed in some theories of the early Universe;  he is  probably most famous for introducing the idea of cosmic strings to modern cosmology in a paper with Mark Hindmarsh. Although there isn’t yet any observational support for this idea, it has generated a great deal of very interesting research.

Tom was indeed an extremely distinguished scientist, but what most people will remember best is that he was an absolutely lovely human being. Gently spoken and impeccably courteous, he was always receptive to new ideas and gave enormous support to younger researchers. He will be very sadly missed by friends and colleagues across the physics world.

Rest in peace, Tom Kibble (1932-2016).