Congratulations to my PhD student, Chiamaka Okoli, on her first paper being accepted for publication in Monthly Notice of Royal Astronomical Society.

Chiamaka has shown that you can use the simple idea of energy conservation, combined with knowing when an ellipsoid collapses, to predict how dense (and hot) a dark matter halo will be when it forms.  Previously, people had to rely on numerical simulations, and ad hoc extrapolations and fitting functions, which often led to contradictory conclusions for the densest dark matter haloes. However, her method is more robust, easy to use, and elegant (and I am in no way biased 🙂 ) ! You can also apply it to any cosmology or initial conditions.

Read more here. 

 

 

 

This weekend at Mann Fest, we celebrated the contributions of our colleague Robb Mann, on the occasion of his 60th birthday. Robb is very prolific, both in producing innovative scientific research, but also in training excellent undergraduate and graduate students. I met several of them during Mann Fest, who have now scattered across the globe, many as successful professors, and are engaged in diverse and exciting research. Not surprisingly, Robb is also an extraordinary lecturer.

You can find my talk at Mann Fest here. 

 

Einstein’s General theory of Relativity predicts the occasions of its own demise. These are known as spacetime singularities, where Einstein’s equations fail to predict the future. However, in most typical situations, we have found that the singularities lie behind event horizons of black holes. Since nothing moves faster than speed of light in Relativity, and light cannot escape event horizons, then it appears that most common singularities are invisible to us. Penrose promoted this observation to the Cosmic Censorship conjecture, proposing that singularities are generically censored by event horizons, to outside observers.

But what if something can travel faster (even infinitely faster) than speed of light? Would that render singularities naked and exposed?! My students Mike Meiers and Mehdi Saravani have just posted a paper on arXiv showing that even if gravity has an incompressible aether (with infinitely fast signals), it can still manage to censor its own singularities in collapsing charged and spinning black holes.

Also, congratulations to Mike on his first paper (and Mehdi for his 9th!), and the most beautiful Penrose diagrams that I have ever seen 🙂 (The red regions are censored by aether).

Read more here.

 

Congratulations to Dr. Farbod Kamiab @fkamiab on successful defence of his PhD dissertation: “Neutron Stars, the Exotica: From Modifying General Relativity to Strong Magnetic Fields”. He is now the world expert in the most exotic things that could happen to the most exotic stars in our universe!

Here is a quick run through his final presentation:

 

Update (23/12/2015): Here is a link to Farbod’s thesis.

Have you ever wondered why the universe is Lorentz-invariant?

In this letter, I attempt to prove that:

Cosmology+Quantum Mechanics ➞ Lorentz Symmetry

More precisely, if you require to live in a big universe, for a long time, and have a consistent  effective quantum field theory (which includes gravity), then high energy processes (that, for example, happen in Large Hadron Collider), cannot see a preferred reference frame, and thus must be Lorentz-invariant.

Read more here.

From his letter to his former PhD student, Koichi Mano.

This update is way overdue, but the talks for our Cosmic Flows workshop at PI are available at

http://pirsa.org/C15035

and here is our conference photo:

I have a new reading of “Alice in Wonderland”, celebrating the centennial of General Relativity, based on my colloquium at Western Math department:

“Down, down, down. Would the fall never come to an end! ‘I wonder how many miles I’ve fallen by this time?’ she said aloud. ‘I must be getting somewhere near the centre of the earth. “ wrote Charles Dodgson, the English writer and mathematician, of Alice’s fantastic adventure into a bizarre world of underground creatures. I shall retell the story of our centennial adventure into the relativistic wonderland, a tall tale of non-sensical creatures that includes blunders, black holes, Schrödinger’s cats, and a very vibrant vacuum! ”

Here are the slides in PDF and Keynote.

Perimeter Institute for Theoretical Physics invites applications for postdoctoral positions from new and recent PhDs working in fundamental theoretical physics. Our areas of strength include classical gravity, condensed matter theory, cosmology, particle physics, mathematical physics, quantum fields and strings, quantum foundations, quantum information, and quantum gravity. We also encourage applications from scientists whose work falls in more than one of these categories. Our postdoctoral positions are normally for a period of three years. Outstanding candidates may also be considered for a senior postdoctoral position with a five-year term.

Read More Here. 

So, I have successfully transitioned to my new homepage: https://nafshordi.wordpress.com/.

The plan is to centralize all my (semi-)professional communications, and bring them into 21st century!