Blog

Achin Vanaik will be in Bengaluru to talk about the genocide in Palestine and the crisis in West Asia. We are having a talk at ICTS on Tuesday, 19 November 3:30-5 pm as part of our general talk series. Then, later in the evening, on the same day, there is a public talk at the AITUC office in Malleswaram organized by Bengaluru for Justice and Peace. Please spread the word about the public event and please come if you can.

IISc seems to think that this is the right time to promote an India-Israel business summit. More than 1500 students and faculty members from across the country, and other members of civil society have written to the Director of IISc expressing their concern. I think one measure of the depth of the outrage in the broader scientific and academic community is that these signatures were collected in a little more than 36 hours.

See the full letter and signatories here: https://docs.google.com/document/d/1KY3l-dfpjfj6oLtXSWhRI4Xv248RdYN2sfFhzO2GLFA/edit

Fun podcast discussion with Hassaan Saleem. We discussed physics and life and some politics and some other questions! https://youtu.be/Eu-vHy_lnkc

An email that I sent to Harvard’s interim president, Alan Garber, today.

Some of us have drafted a letter to the President of Columbia University. The letter is available here: https://docs.google.com/document/d/1siZzqg0PGXVvp3r7Cg4JEXm2_c_vSf37borLj_BmeBA/edit

If you would like to endorse this letter, please use this Google Form: https://docs.google.com/forms/d/114XlojgHuPxD-qk5UOj9SsN3VOpQV0EbeUCfqUSlq88/viewform?edit_requested=true

We plan to send it off to Shafik by the weekend.

The students at Columbia and other campuses are doing the right thing. Their actions are informed, empathetic and courageous.

Vasudev Shyam got Geoff Penington and me to be part of a podcast discussion today morning. We discussed whether islands and the Page curve are relevant for realistic black holes.

As Geoff pointed out at the end, it is good to broaden and democratize these discussions as much as possible, so you can see for yourself: https://www.youtube.com/watch?v=ZCIho8geEfI

The video itself is pretty long so here is, I believe, a reasonable summary of what we agreed and disagreed on:

We agree that information is always outside the black hole for a physical observer. Therefore, in a standard theory of gravity, information doesn’t “emerge” the way that Page argued that it does. I feel that this suggests that deriving a Page curve is not crucial for understanding the information problem. Geoff’s disagrees with this perspective.

We agree that it is possible to find a Page curve if one looks for it. One possibility is to modify the theory by coupling it to a nongravitational bath. In these theories the graviton is massive and information does emerge according to a Page curve.

Alternately, we agree that it is also possible to simply disallow the observer outside the black hole from measuring the components of the metric that correspond to the energy. Such an observer sees a Page curve even in standard gravity.

My perspective was that this Page curve reflects our voluntary choice of disregarding some information that is available at all times. Geoff argued that this was physically natural.

Since I spend some of my time thinking about how to localize observations in gravity, I couldn’t help thinking about this question today.

How do we decide that a structure we build today is at the same spatial location as another event that supposedly happened a few thousand years ago?

If we stick to a geocentric perspective, one possibility is to use some local reference frame like rivers or mountains. But these tend to shift quite considerably over the course of a few thousand years.

And why should we localize something just on the crust of the Earth, which is so small compared to the Earth as a whole? But if we broaden our perspective, we now have the problem that the continental plates drift by a couple of centimetres a year. This itself would give us a few tens of metres of drift over a few thousand years, which might be larger than the size of the structure we are building.

Moreover, we are taught to think from a Universal perspective in India. And some of these questions supposedly pertain to the Lord of the Universe. From that perspective, the Earth itself is rather small even within the solar system and our galaxy, let alone the Universe. The galaxies and stars themselves have moved quite a lot in a few thousand years. So, if one were to use a different coordinate system, the “spatial point” where something happened a few thousand years ago might now not lie within the Earth at all or even within the Earth’s orbital trajectory.

From the flags outside our house, I infer that many people around me seem to understand this very well, and so I must be missing something basic. Nevertheless, I can’t help being somewhat puzzled. Any answers?

A statement issued by an international group of theoretical physicists on the crisis in Palestine:

https://particlesforpalestine.org