How much can you 'laymanize' a PhD presentation? I am in my first year of a PhD in France. I recently attended a competition of best presentation by PhD students. It was a 15 minutes visual presentation and 7 minutes of questions. After the presentation, one of the members of review committee openly stated the following; 


  Since we have an audience from diverse areas of science, mathematics and technology the presentations should have been simple so that a layman can understand. I quote A. Einstein, "if you can't explain it simply you don't understand it well enough." 


Even though this communicates an obvious message, I feel layman bear a high level of ambiguity with it. The following questions crops up in my mind.


How much can you laymanize a particular research topic say, from theoretical physics, for example Non local wavefunction collapse?


The topic is chosen as random but for those who don't have exposure in basic quantum mechanics may not understand the technical terms.


Is it advisable to prepare such a presentation in assumption that the audience are completely nescient?


If I oversimplify the presentation, leaving all the technical terms, I highly doubt that there will not be any material for those who actually knows the subject.

One approach is to try to satisfy both the extremes, first explain the technical terms in detail and then move on to subject core which I found is difficult if not impossible to fit into the time limit.
First, it is important to recognize that every scientist is effectively a layman for almost all other science.  

For example, I am a computer scientist, and I have only a vague layman-level understanding that when you say "non-local waveform collapse" it's probably about quantum mechanics and Bell's theorem, and the math you put up on a slide will certainly be rather alien and fairly incomprehensible to me.  If I put up a slide on the semantics of field calculus, it would probably be likewise alien to you, and if a biologist of my acquaintance put up a slide on the chemical mechanisms of chromatin remodeling it would be alien to both you and I.  Think of a layman, then, not as some sort of idiot to be condescended to, but as an intelligent and interested person whose expertise happens to be in a different field.

Furthermore, our relative ignorance of one another's work is greatly amplified while listening to a talk: when I am puzzled and need to think about what you've just said, I miss the next things being said and have to try to catch up! In effect, only people who are extremely close to your own work, even within your field, will be able to follow deep technical details in a talk.  Every audience except the smallest and most intimate, then, is effectively composed mostly of laymen---but likely with a few experts as well.

So, how do you give a talk to heterogeneous audiences?  Personally, I find it effective to think of a talk as an advertisement, the goal of which is to make people interested enough and convinced enough by your work that they want talk with you about it afterward or to read the manuscripts that present it fully.  Start with a discussion of the goal of your work, how the work relates to other work and why its goals might be interesting, narrow down to a few key details (which might only be understood in detail by the few experts in the audience), present evidence for why your insights are correct, and widen back out to explain why what you just presented satisfies the goals you laid out in your introduction.   Such a structure can then "laymanize" even the most complex topic, by explaining how it fits into the larger world, while at the same time respecting the intelligence of the audience and not sacrificing communication to experts.

For the details of how to accomplish this effectively, I personally have found Patrick Winston's "How to Speak" lecture to be an excellent resource for heuristics and tips, and recommend it to others as well.