Blog

Op-ed with Mv Ramana for the Hindu today: https://www.thehindu.com/opinion/op-ed/pushing-the-wrong-energy-buttons/article30965454.ece The idea that India should import reactors from the United States is a zombie idea that should have been dead long ago but keeps rearing its head from time to time. This happened again during Trump’s recent visit. It didn’t get much media attention because of everything else that is happening in the country. But given the scale of the deal (lakhs of crores) and its potential for long-term damage, one shouldn’t allow its progress to pass under the radar.

The holographic nature of null infinity! With Alok, Siddharth and Pushkal. https://arxiv.org/abs/2002.02448

I think that we have some exciting and interesting results. We clarify an important aspect of how holography should work in flat space — the question of how null infinity stores information about the bulk state. The answer seems to be that null infinity stores information more intricately than the AdS boundary. A small region near the past boundary of I^+ already has all information about massless excitations. But, as we go towards the future (on I^+) we may “lose” information. This means that a cut on I^+ always contains at least as much information as any cut to its future but not necessarily as much as a cut to its past. (The opposite is true on past null infinity.)

Its fun to explore what this means for the information paradox. Usually, people ask questions about how the information should “come out” of a black hole. But our results suggest that even in flat space, the information is always outside and so this is just the wrong question to ask. More specifically, this suggests that the von Neumann entropy of the state reduced on a segment on I^{+} doesn’t obey the Page curve but rather is trivially constant as one extends the segment to the future. Our results are not inconsistent with the recent discussions of the Page curve, where gravity it turned off at some point to obtain a factorized Hilbert space. But they do imply that those discussions are not immediately relevant for the evaporation of black holes in our world where gravity doesn’t suddenly get turned off.

An interview that I did with rediff.com a few days ago: https://www.rediff.com/news/interview/protests-have-forced-govt-on-backfoot/20200121.htm Its mostly just a set of simple questions and answers but some aspects might still be of interest.

An absolutely incredible march organized by IISc students yesterday night, in which at least several hundred students marched through the campus. The video is very poor because I’m a poor videographer and because the light was too low for my phone but it should give you a sense of the atmosphere.

And here is an audio recording with slightly clearer content

https://soundcloud.com/user-526258477/iisc-protest-slogans

If you don’t find it remarkable to see and hear this in IISc, this can only be because you are unfamiliar with the campus!

Members of scientific research institutes are discouraged all the time — both tacitly and directly — from engaging with critical social issues and I’m very happy to see them rejecting this repressive attitude all over the country. I’m also very glad that an event is being planned at ICTS tomorrow.

A simple quantum test for smooth horizons, with Kyriakos and Pushkal.

https://arxiv.org/abs/1910.02992

We use the short distance behaviour of the two-point function to set out some very general necessary conditions for a quantum state of the fields to be smooth at any null surface. In the case of black holes with both an inner and an outer horizon, where we apply our test, these conditions require that the degrees of freedom near both horizons be occupied at just the right temperature and also be entangled with partners just behind the horizons.

There is an interesting story here. If you talked to me a couple of months ago, I would have explained to you (as I did explain to several people!) that this meant that quantum mechanical effects always imposed strong cosmic censorship regardless of all the recent classical discussions on the subject. Note how tricky it is for all the conditions above to be satisfied. The modes near the outer horizon have to be automatically “heated” by the geometry to attain the temperature of the inner horizon when they reach there. Moreover, in attempting to cross the inner horizon, we have the problem of the monogamy of entanglement: since the modes between the inner and outer horizon are entangled with partners outside the outer horizon they cannot be entangled with fresh modes behind the inner horizon. So, surely, one would be unable to extend the field into that region?

This intuition is right in higher dimensions. But for the BTZ black hole, this naive conclusion is just wrong! In that case (and, as far as we know, only in that case) the geometry does magically heat the field by just the right amount as they reach the inner horizon; and the existing degrees of freedom can then be cleverly juggled to extend the field behind the inner horizon.

Does this mean that strong cosmic censorship is violated for the BTZ black hole as Dias, Reall and Santos argued a few months back? What would this mean for AdS/CFT? We think that quantum effects could still have a few tricks up their sleeve at very late times, but I now think this is a very interesting question.

Many of us have been disturbed by what is happening in Kashmir, and have felt helpless at our inability to do anything about it.

Some of us felt that it would be very useful to have a statement from members of the academic and scientific community registering our opposition to the government’s policies. Our objective was to (a) at least marginally modify the public narrative by emphasizing that not everyone in India agrees with the Indian government’s policies (b) extend solidarity to our own Kashmiri colleagues and friends, who are obviously going through very difficult circumstances.

We were able to gather more than 500 signatures in about 24 hours.

This is the statement that we issued https://docs.google.com/document/d/1aGJ8jmPJcsTnrsx9FCqQQEKuhn4o2pUeEW0gUg0JQLk/edit?usp=sharing

The statement has had some broader impact and today, several media outlets have reported on it. Here are a few reports. The BBC newshour also recorded a brief story on the issue (update: link below)

https://www.thehindu.com/news/national/detaining-opposition-leaders-in-jk-deeply-undemocratic/article29478999.ece

https://www.telegraphindia.com/india/500-scientists-and-academics-condemn-communication-block-in-kashmir/cid/1706556

https://scroll.in/latest/938047/jammu-and-kashmir-over-500-academics-scientists-issue-statement-calling-for-end-of-curfew

https://thewire.in/rights/appalled-by-restrictions-504-academics-scientists-express-concern-over-kashmir

https://www.thenewsminute.com/article/restore-communication-kashmir-indian-academics-write-letter-indian-govt-109269

BBC Newshour: https://www.bbc.co.uk/sounds/play/w172wq4whqzlbmv (from 14:00)

This is an op-ed I wrote for the Hindu on the U.S.-Iran conflict. https://www.thehindu.com/opinion/op-ed/talking-sanctions-endangering-peace/article28287389.ece?homepage=true

My views on what is happening in Iran (for the blog and next issue of Aspects of India’s Economy). This piece is a little long — 6500 words — but I’ll try and write a shorter summary soon. (Update: see Hindu op-ed above.) https://rupeindia.wordpress.com/2019/06/27/imperial-overreach-in-iran/