My PhD viva

In this post, I’ll discuss how I prepared for my PhD viva exam in cosmology, what the viva itself was like and what happened next.

I submitted my PhD thesis on the 4th of January 2021 (which also happened to be my birthday) and had my viva exam on the 3rd of February. This is a very quick turnaround, and it’s common to have gaps of two to three months between submission and viva. However, I had been offered a postdoc position back in April 2020 and I was keen to start that position as soon as possible, hence why I submitted my thesis ahead of the typical 31st of March deadline. My supervisor arranged the viva date with my examiners before I’d even handed in, and I sent them an unofficial copy of my thesis before Christmas so they could get a head start on reading it before I officially submitted.


The first thing I did to prepare was take a break. I found the week leading up to my unofficial hand-in before Christmas to be quite stressful and tiring, despite my careful planning and pacing of my writing. I wanted to make my thesis as good as possible and so I worked flat out that final week trying to catch any last mistakes or typos. Thanks to my timing, I could then take the couple of weeks over Christmas off and get some mental distance between myself and my thesis.

Next, I went through the list of potential questions I made during the writing process. As I was writing up, there were inevitably sections of my thesis which had to be cut or curtailed for the sake of brevity, and I noted down these areas as the sources of potential questions. I also listed some general questions, such as “describe the work you have done in this thesis” or “what was your contribution to knowledge?”, often borrowing from this extensive list of viva questions. I then went through these questions, testing myself to see if I could give a good explanation or answer.

Then, I summarised my thesis. I took notes on each chapter, reminding myself of all my results, equations and figures. I then further condensed these notes into a single sheet of A4, divided into six boxes for the six main chapters of my thesis. In each box I wrote the key, take-home points for each chapter. I had thought I could refer to these notes in the viva but in the end I didn’t need to.

The next thing I did was re-read key papers. I went through my thesis and picked out about fifteen papers which were especially important for my work. For example, one was a paper exploring the potential consequences of one of my simplifying assumptions, and another was a paper that had introduced a certain method that I later used in my own work. I made sure that I knew these papers back to front. A happy consequence of having the viva online was that I could annotate the pdf copy of my thesis with notes about these key papers next to where I referred to them in the text, and unobtrusively check these notes during the viva. However, in the end I didn’t actually need to look at the notes, as I remembered the necessary details.

Finally, I had a mock viva. This was conducted by my second and third supervisors. It lasted about an hour and most of their questions were on the background material, since they obviously did not have time to read my whole thesis. This was really helpful as it soothed my nerves a lot, and made me realise that it really is less of an exam and more of a chat. My supervisors gave me some suggestions of things to revise (although none of these topics actually came up in the real thing!), so if you have a mock make sure to organise it a week or so before the real thing, to give yourself time to act on any suggestions you might be given.

The viva

My viva was on a Wednesday morning, starting at 10am. It was online, on Zoom (thanks Covid!). My university has a policy that all online vivas must have a randomly appointed independent chair who is internal to the university, to ensure that the viva is conducted fairly. My chair was from the engineering department and he set up the Zoom meeting and explained the procedure when I joined. He then remained silent until the end of the viva. In the end, we didn’t actually start until around 10:30am, since the examiners discussed my thesis between themselves for some time before I was allowed to join the meeting. This was probably the most stressful part of the day, since I had psyched myself up to start at 10am! I didn’t try to study any more in the extra time, instead I just stood looking out the window and trying to stay calm until I got the email inviting me to join the Zoom meeting.

Once I’d joined, we got straight into the questions. The external examiner took the lead, asking most of what he called the “nit-picky” questions, whereas the internal examiner asked more general, big picture questions. They started with a soft question: “tell us about your thesis” and I gave a fairly short answer, not wanting to ramble on too much. They then asked me to expand a bit on my answer and talk about my results and findings. After that, we moved straight to Chapter 1 of my thesis, which was my background chapter. This was the chapter that I was least looking forward to answering questions on, as all the rest (barring Chapter 2, which was methodology) were based on my own research work, so I was naturally more confident with those.

Their first question on this chapter was “how do you obtain the Friedmann equations from the Einstein field equations of general relativity?”. I wonder if the viva had been in person whether they’d have asked me to do the derivation on the whiteboard, but of course that was pretty much impossible online. I stumbled through a sketchy answer (in my defence, I haven’t computed a Christoffel symbol in about five years!), but they didn’t mind that I didn’t have the details down pat. This was when I started to relax, since I realised that it was fine to say that I didn’t know the answer, or to just attempt a rough answer, guess or estimate. In fact, they prefaced some of their questions with “Do you know why [this result exists]? It’s fine if you don’t, it’s just an interesting bit of physics” or similar, so I felt very comfortable saying that I didn’t know.

We continued in that vein for about half an hour, until we got to the end of Chapter 1. They then skipped Chapter 2 completely (they literally said “Chapter 2 is fine, very happy with it” and moved straight on), which disappointed me because I was keen to talk about my methodology. Then we were on to the chapters containing my research work. This is where the general questions of the internal examiner came to the fore. For each of Chapters 3 to 6 he asked me the same questions: “describe what you have done in this chapter”, “what was your specific contribution to this work?” (since most of these chapters were based on papers done in collaboration with others) and “choose a plot from this chapter and tell me about it”. These were all easy questions to answer, thanks to my preparation for exactly this type of soft question.

The external then asked me more detailed questions about the results of each chapter, and we spent a while discussing the theory behind the specific models I had studied too. We hit the hour mark after going through Chapter 3, so we stopped then for a five minute break. I was glad of that, because I hadn’t managed to eat much breakfast thanks to nerves, so I had a quick drink and snack before rejoining the meeting.

We continued where we left off, going through the research chapters. I was not looking forward to discussing Chapter 5, as that was the one research chapter not based on a published paper, so I felt the results were the least secure and robust. However, both my examiners seemed to find that chapter the most interesting and we talked about the work that could be done to turn it into a paper.

We went over Chapter 6 very quickly, with the only questions being the general ones from the internal examiner. I was disappointed again with this, as I really liked the work I’d presented in that chapter, although it was at a bit of a tangent to the rest of my thesis. We were also reaching the two hour mark and it was clear that everyone was getting a bit of Zoom fatigue. They also asked no questions at all about my conclusions, which again I was a bit put out by, as I’d made an effort to discuss some of the methodological flaws common to the types of analysis I’d followed for most of thesis and I thought we could have had a very interesting discussion about that.

To close the viva, they asked me to summarise what we’d talked about, which was actually quite hard since we had discussed a lot and I was having trouble remembering the first part of the viva due to the stress! But they seemed happy with my answer nonetheless, and they asked me to leave the meeting to allow them to deliberate. Overall, the viva took almost exactly two hours — I think if it had been in person it would have certainly been longer. After about fifteen minutes they called me back in to tell me I’d passed with minor corrections!


I was obviously really happy with the result and spent the rest of the day celebrating with my family and later on, colleagues and friends on Zoom. My examiners had told me they’d send me the corrections by the end of the week, but after three weeks had passed without any word, I emailed them to chase them up. It turns out the internal had basically forgotten to forward them to me and I wish I’d asked for them earlier, as after three weeks it was quite hard to remember exactly what we’d talked about during the viva.

The corrections really were very minor (only ten points, one of which was optional) and were nothing technical. Mostly I had to add an extra sentence here or there to deepen my discussion slightly, and in one place I’d missed a square in two equations. In the course of my viva preparation I’d also found and corrected a few typos, so I made a list of those to send back with the corrections.

I think the most valuable piece of preparation I did was re-reading key papers. My examiners were quite impressed with my ability to confidently refer to results in certain papers when answering their questions and it gave me peace of mind beforehand as I felt that it really established in my own mind where my work sits in the literature. Apart from that, I would strongly suggest having a mock viva if you can (and not with your own supervisor), and practice answers to those general questions, so you can answer them smoothly during the viva.

I found that my revision of background material was not so helpful, as there were so many potential topics to revise that I simply couldn’t cover everything and just ended up feeling overwhelmed. As I found, it didn’t matter anyway that I didn’t know the answer to some of these background questions, so I would suggest to anyone preparing for their viva to focus on their own work and the key papers in their field. You know more than you think you do!

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2 responses to “My PhD viva”

  1. […] thesis at the beginning of January 2021 (in practice, I had it finished by mid-December) and having my viva in early February, the intention being that I would travel to Madrid and start the job in mid-February this […]


  2. Many thanks for this!


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