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Next week, we are planning to have three talks by Natasha and Devangana who will discuss the UAPA and its misuse through the lens of their own experience. Two of the talks are aimed at students in ICTS and IISc—a discussion we really need to have in our scientific institutions. Finally, there is a public talk at the Ashirvad centre. Please come for at least one of these events if you can. Please also share this announcement and spread the word to others who might be interested.

Schedule

ICTS: Date : 26th June (Monday) Venue : ICTS , Emmy Noether Seminar Hall Directions : https://goo.gl/maps/mFF8K3wkkP6vDGwh6 Time : 4pm

IISc: Date. : 28th June (Wednesday) Venue. : IISc, CCE Lecture Hall Directions : https://goo.gl/maps/NsFCKzeyEPG5ZYV7A Time : 5:30pm

Public Event: Date. : 29th June (Thursday) Venue. : Ashirvad Centre , 31, St Mark’s Rd, Ashok Nagar, Bengaluru 560001 Directions. : https://goo.gl/maps/1yL9CKv3DMDkipek6 Time. : 5:30pm

The Injustice of Law: UAPA, Prisons and The Criminal Justice System" (29 June, 5:30 pm at Ashirvad)

Speakers: Natasha Narwal and Devangana Kalita

Details: Natasha and Devangana will take us through their journey of being charged under the Unlawful Activities Prevention Act (UAPA) elaborating on how this draconian law which stands in violation of many fundamental constitutional values, has become an instrument for suppressing dissent by those in power. They will look at the history of the use of such ’exceptional laws’ and how they contribute to enhancing the power of authoritarian regimes. Drawing on their experiences of incarceration, they will also share their reflections on the urgent need for thinking politically about prisons – how our criminal justice system disproportionately incarcerates the most marginalised communities in our country, making access to justice contingent on one’s caste-class-gender locations.

This event is organized by Sthayi (ICTS), Breaking the silence (IISc), Academics for Democratic Rights (www.acdr.in) and the India Academic Freedom Network.

Contact: +91-9819165832

I have always found the Nature publishing model distasteful. Fortunately, in high-energy theory we have rid ourselves of these scientific gatekeepers and publication is largely via the arXiv, with peer-review being done through community journals. But I still sometimes get requests to review manuscripts when someone in HET decides to submit there.

I decided a while back that I would decline to review manuscripts for journals that forced authors to pay an exorbitant APC, as some of the Springer-Nature journals do.

It would be useful if more members of the scientific community were to do likewise.

Here is a sample email that I sent to Nature Communications a few months back.

And here is the second one (again with Tuneer, Joydeep, Victor, and Priyadarshi. )

https://arxiv.org/pdf/2303.16316.pdf

The question we ask and answer here is: how does the holography of information work in de Sitter space.

The background to this is the idea that gravity localizes information differently from nongravitational theories. In both flat space and in AdS, one can argue that all information on a spatial slice is available near its boundary. This argument doesn’t require AdS/CFT; rather it explains why gravitational theories are holographic.

How should this idea work in dS, where spatial slices have no boundaries?

It turns out that there is a remarkable answer in terms of “cosmological correlators”: cosmological correlators in any small patch of the late-time slice in dS are sufficient to uniquely identify the state!

Intuitively, this result goes back to the symmetries of the states in the dS Hilbert space. The WDW analysis tells us that all valid states have the same symmetries as the Hartle-Hawking state. This leads cosmological correlators to manifest a version of conformal symmetry in all states. Therefore, knowing them in a small open set is equivalent to knowing them everywhere on the spatial slice. Somewhat surprisingly (and somewhat unlike AdS and flat space) our result remains true even if one switches off gravity completely while preserving the Gauss law in the Hilbert space.

The analysis is somewhat technical even if the final result is simple.

We had to start by understanding observables in the de Sitter Hilbert space. We propose that the expectation value of an observable is described by integrating it with a squared wavefunctionals over all field configurations and dividing by the volume of the diff and Weyl group. This is like the functional integral that appears in worldsheet string theory, and we spend a fair amount of time teasing out its form and examining various subtleties.

Moreover, Cosmological correlators, defined as expectation values of products of fields on the late-time de Sitter slice, are not gauge invariant by themselves. So we define them as gauge-fixed observables. Such correlators are labelled by coordinates on the late-time slice but they are secretly nonlocal. So a physical observer (which, separately, is a tricky thing to model in cosmology ) cannot discern the state of the Universe by looking at just a small patch. But, nevertheless, this result is a sharp mathematical difference between theories with gravity and theories without gravity.

I am quite excited about a pair of papers that we put out today with Tuneer, Joydeep, Victor, and Priyadarshi. Here is the first one:

https://arxiv.org/pdf/2303.16315.pdf

The question we ask and answer here is: “What is the right Hilbert space for quantum gravity in de Sitter space?”

At first sight, this might seem trivial: at least perturbatively, why not just start with the Hartle-Hawking vacuum and build a Fock space? This isn’t the right answer because even in the weakly coupled limit it is necessary to impose the Gauss law in a gravitational theory. But the spatial slices of de Sitter are compact. So the Gauss law tells us that valid states should have no charges under any of the de Sitter isometries. In the usual Fock space, the only such space is the vacuum. So does the dS Hilbert space have only one state? :-)

Higuchi studied this question and proposed an answer more than 30 years ago in a paper that is far less known than it should be. Higuchi’s idea was that one should take each element of the Fock space, as a “seed state”, and then “average it” over the isometry group. To define the norm of the group-averaged state, Higuchi proposed that one should use the usual norm divided by the volume of the isometry group.

As someone once said to me, “that sounds crazy. In flat space, we don’t take states and average them over the Poincare group!”

So we went back to the basics. We started with the Wheeler-DeWitt (WDW) equation, which is the fundamental constraint on the gravitational Hilbert space. The technical idea is that the WDW equation — which is usually intractable — simplifies at late times in de Sitter because the volume of the spatial slices becomes large. We don’t even to work perturbatively and, in this limit, can find solutions, whose form is preserved at all orders in perturbation theory.

This leads to many interesting results.

1. When states are described in terms of wavefunctionals. then we show that a basis of solutions is given by wavefunctional that have a universal phase factor, e^{i S} multiplied with Z, where Z obeys the same Ward identities as a CFT partition function. (The central charge is imaginary, and there are no constraints of unitarity of locality on Z)
2. The Hartle-Hawking state has this form, but it corresponds to one possible choice of Z. Other choices of Z are perfectly fine. In this sense, our state space is like “theory space.”
3. All states have the same symmetries as the Hartle-Hawking state. So approximate conformal invariance of the early Universe, were it to be confirmed, would not provide evidence for the no-boundary proposal. It is a general prediction of inflation.
4. When written in a particular basis, our states reduce to Higuchi’s group averaged states in the nongravitational limit. But beyond G_N -> 0, Higuchi’s construction must be corrected and we show how to do that.

Our recent statement expressing our dismay at the government’s decision to block the BBC Documentary, India: the Modi question.

https://docs.google.com/document/d/165atZGawZu_oST8y63iGe9NuC55G2p6nz0yXl4fN-Vc/edit

Some news coverage is here: https://scroll.in/latest/1043170/blocking-of-bbc-modi-documentary-violates-indians-rights-say-over-500-scientists-and-academicians

and here:

https://thewire.in/rights/500-indian-scientists-academic-slam-blocking-bbc-documentary-modi

and a few other places.

nice non-technical summary by Nirmalya Kajuri of some of the recent debates on black-hole information.

https://science.thewire.in/the-sciences/unitarity-entanglement-islands-holography-information/

I’m often struck by how differently children think.

My 9.5 year old son is fond of playing the following “magic trick” on his friends. The magician asks the subject to think of a number between, say, 1 and 63. Then the magician shows the subject a set of 6 cards, each of which has numbers written on it, and asks the subject to state “yes” or “no” depending on whether the chosen number is printed on the card. At the end the magician guesses the number.

The principle is simple: n “yes” or “no” answers yield n bits of information and can be used to uniquely encode a number up to 2^n-1. But it appears surprising if one hasn’t thought about it.

The kid wanted to go up to higher powers of 2. So he needed to generate his own “magic cards”, which he decided to do via a small Scratch program. (His initial plan was to print cards up to 2^21 but strict rationing of the use of the printer has limited him to 2^10. )

In any case, the precise question is as follows: “given a number, 2^n, generate n lists so that the k^th list has the property that it contains all numbers up to 2^n whose binary representation has 1 in the k^th place.”

Here is what the kid came up with (see image). Or test the full code here: https://scratch.mit.edu/projects/740194941/

To me, this is a perfect example of obfuscated code! I can never imagine writing this code to solve the problem above. I challenge any of the adults reading this to figure out how the code works without reading it at least thrice. But this was perfectly natural for the child. He wrote it pretty quickly — in under 15 min. And, remarkably, it is not particularly inefficient either in terms of code-size or running-time. (For those who still find the code crytpic, see the discussion with Rukmini below.)

I am sure, in a few years, when he has had more formal training, he will write a “more standard” algorithm for this problem. Just as formal training makes us see hats instead of boa constrictors with elephants.

A small outreach video on black hole information that we prepared recently. Many thanks to Anupam Ghosh and the ICTS outreach team for putting this together.

Let me know if you have comments. (Even if they are critical, especially given that I’ve been critical of outreach in the subject in the recent past 😀 )

Nishina Prize 2022 — A discussion with Suvrat Raju