Can you hear the echoes from the abyss? If not, come to my talk!

Image Credit: NASA/Ames Research Center/C. Henze

Recently, with Jahed Abedi and Hannah Dykaar, we found gravitational wave signatures for quantum gravity effects near black hole horizons. If you’d like to hear more about this, and you’re in Waterloo, come to my seminar tomorrow:


Our original paper can be found here, with additional press coverage (in various languages):

In a second paper, which just appeared on arXiv, we clarify some of the misunderstandings about our finding.

Delayed echoes from Planck-scale structure near black hole horizons predict a peak at x=1 in this plot. As can be seen, analysis of LIGO gravitational wave data indeed shows such a peak with >99% confidence level (from arXiv:1701.03485)

He will be eternally lost in his hopeless oblivion!


Today, a friend on facebook was asking for a translation of the famous Persian poem by Ibn Yamin:

آن کس که بداند و بداند که بداند
اسب خرد از گنبد گردون بجهاند
آن کس که بداند و نداند که بداند
آگاه نمایید که بس خفته نماند
آن کس که نداند و بداند که نداند
لنگان خرک خویش به منزل برساند
آن کس که نداند و نداند که نداند
در جهل مرکب ابدالدهر بماند
It turns out that back in Sep. 2011, my colleague Kris Sigurdson wanted to use this in one of his talks. He had found it originally on the “There are known knowns” entry on wikipedia, which reflects on Donald Rumsfeld’s words of wisdom. Back in 2011, the page quoted Ib Yamin’s poem as an older version  of a similar philosophy, but provided a very poor English translation. So, I gave Kris a much better translation (in my opinion), and updated the wikipedia entry:
One who knows and knows that he knows…
His horse of wisdom will reach the skies.
One who knows, but doesn’t know that he knows…
He is fast asleep, so you should wake him up!
One who doesn’t know, but knows that he doesn’t know…
His limping mule will eventually get him home.
One who doesn’t know and doesn’t know that he doesn’t know…
He will be eternally lost in his hopeless oblivion! 
However, when I checked today, the wikipedia page had lost all the reference to the poem. In fact, Ibn Yamin doesn’t even have any English wikipedia entry. However, my translation had lived on, with more than 1300 hits on Google as of now, which use it verbatim, either with no reference, or citing the now non-existent wikipedia page.
That’s why I decided to write this and set the record straight, so that the next time you wanted a more eloquent and original version of Rumsfeld’s wisdom, you know where to find it.

Battle for the heart of democracy: The case for Bernie Sanders


There is a battle brewing less than a hundred miles from where I’m sitting right now. On the face of it, it’s just a political campaign the likes of which happen every four years in the US, and frequently across the world. But on closer examination, I argue, it is something much more significant and unique. It is a battle for the heart and soul of democracy; do people have a right or desire for self-determination, or do they ultimately opt to give up that right, and be subjects to the elite ruling class, to the rich and powerful, to the Oligarchy?

But let’s start with a naive question: How are the liberal democracies of the 21st century different from the dynasties that have governed our civilizations for millennia?

There are, of course, the civil rights and liberties of the citizenry, but they have existed in some shape or form, albeit imperfectly, in various authoritarian governments of the past. Rather, the most characteristic trait of a democracy must be the people’s right to self-determination through the ballot box, either directly or via their elected representatives.

In a dynasty, a family is entrusted with ensuring the good of a country. The children are groomed from an early age to be effective leaders, and then are trusted to maintain a happy and prosperous nation. In contrast, in a liberal democracy, citizens can freely elect the representatives who most closely represent their interests, and keep them in power, or kick them out, depending on their performance.

Or can they?!  In fact, is there any reason to believe that the authoritarian systems that have evolved and perfected within our societies over millennia would suddenly and spontaneously change in any fundamental way? Could it be that, instead of citizens picking their leaders in a democracy, the ruling class “manufactures our consent” through money and media, with the ultimate goal of keeping themselves in power?  

If this vision is too dystopian for your taste, you may feel comfort in the fact that the answer to this question is not written yet. People of New York are to decide in a few days whether they prefer a decades-old dynasty, entangled and paid for by the world’s biggest banks and corporations, to rule them. Or may they opt for the much more radical alternative, to elect someone who represents the people not the billionaires, the big money, and the political establishment?  

Bernie Sanders 2016 logo

So, this is the gist of why I support Senator Bernie Sanders’ bid for the presidency of the United States, against Secretary Hillary Clinton. It is because he has always supported the rights of ordinary people across the world, from the US to Central America, Iran, Iraq, or Palestine, over dogma and ambitions of the ruling elite, moneyed influence, and political expediency. It is because I think the most powerful military in the world can only be entrusted with someone who believes the state “should not be in the business of killing people“, in the US or anywhere else.  It is because he appreciates that bringing back the power from the top 1% to the people, via universal healthcare, free public education, and a healthy campaign finance system, while uncharted territory, is worth fighting for and the true cost of a democracy. It is because his proudest foreign policy accomplishment IS NOT putting in place brutal sanctions on poor people of a 3rd world country.

So, there are still a few days left to save the biggest democracy on this side of the world. But that all depends on who wins the Battle of New York 🙂



Critical geometry of a thermal big bang (and how it exactly matches CMB with no fine-tuning)


Here is something bizarre that Joao Magueijo and I have discovered. You can have a purely thermal big bang, all the way through,  and reproduce the exact same deviation from scale-invariant primordial power spectrum, as observed in CMB data, without ANY fine-tuning or free parameters! This is more predictive (and falsifiable) than ANY inflationary (or non-inflationary) theory of early universe.

What’s the catch? The acoustic speed in the primordial plasma should suddenly diverge (i.e. become much faster than speed of light) at 4 orders of magnitude below Planck temperature. This is what my student and I had called Thermal Tachyacoustic Cosmology (TTC) before. What’s new is that there is a unique critical version of this model, with a geometric interpretation involving a membrane moving in a very special geometry (with two times 😜). Amazingly, it has a very sharp prediction for deviation from scale-invariance (n=0.9648) which matches CMB observations (n=0.9667 +/- 0.0040) to 3 significant digits!

So, there you have it! The most predictive theory of early universe, but it costs you a new time dimension 😀

Tree rings in the sky: How dark matter haloes age


In a recent paper, entitled: “Universal Clustering of dark matter in phase space”,  Jesus and I have showed that dark matter haloes age very similarly to how trees age! To see how old a tree is, you look at the cross-section of the trunk and count the rings. To see how old a dark matter halo is, you look at the clustering of its phase space (what we call P2SAD), and count by how many decades it changes.

Why does this matter? It turns out that understanding this phase space structure on very small scales is very important in planning and interpreting our efforts to find dark matter. The fact that it’s universal certainly helps!

Clustering in the phase space of simulated dark matter haloes. The blue surface includes all the sub-structure, which could be many orders of magnitude above the red surface (the smooth halo).

The paper (for which, Jesus should get all the credit) was just accepted for publication in MNRAS.


How dense are the densest dark matter haloes?

Chiamaka Okoli

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. 


Concentration of dark matter haloes, across 20 orders of magnitude in mass



Mann Fest: Happy Birthday Robb Mann!!


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. 


How aether censors singularities (and the most beautiful penrose diagrams you’ll ever see)

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.


Why is High Energy Physics Lorentz Invariant? [Hint: It’s not what you think!]

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.

Two inverse lorentz boosts equals boost and thomas rotation 2