On Friday Robert Mann gave a very nice colloquium at UQ, The Black Hole at the Beginning of Time. The video is below.
The (end of) the talk is based on the recent paper
Out of the white hole: a holographic origin for the Big Bang
Razieh Pourhasan, Niayesh Afshordi, and Robert B. Mann
The key idea is to consider our universe as the 4-dimensional boundary (brane or hologram) of a 5-dimensional space-time in which there is a black hole.
In our universe one then has not just 4D gravity and matter, but also induced gravity and an effective fluid from the 5D "bulk".
(For better or worse) this work was recently featured on the cover of Scientific American.
Robert covered a massive amount of material moving through special relativity, general relativity, black holes, big bang, cosmology, recent results from the Planck satellite, inflation, the multiverse,... and finally his alternative model.
I took several pages of notes.
He went overtime. I think this was one of the rare cases where I did not mind the speaker doing it.
Besides learning some interesting physics, what was most interesting to me was the refreshing way the work was presented. The tone was something like, "cosmology has some amazing successes but there are a few paradoxes, inflation is an interesting idea but also presents some problems, ...fine tuning is a challenge, ... so let me throw out a different idea.... it is a bit weird... but lets see where it goes ... it also has some strengths and weaknesses .... I am not sure this is better than inflation, but it is worth looking at." There was no hype or sweeping things under the rug.
Many in the audience were undergrads. I thought it was a great talk for them to hear. It was largely tutorial, there was some fascinating physics, connections to experiment were emphasised, healthy skepticism was modelled, and there was no hype.
I also liked the talk because it confirms my prejudice that people need to work harder, more creatively, and more critically, on foundational problems in cosmology. Dark matter, dark energy, inflation, and fine tuning are all really weird. They may be right. But they may not be. I think just accepting them as the only option and regressing to even weirder ideas like the multiverse is a mistake. [Of course, it is easy as an outsider to tell colleagues to work harder and more creatively.]
The physical model of the early universe that was presented was completely different to inflation. Yet it solves most of the same problems (horizon, flatness, and no monopoles). Its biggest problem is that it does not predict the observed 4 per cent deviation from scale invariance.
The most important and interesting bits are from about 52:00 to 58:00.