Black Hole Interior Operators and Dilatation Symmetry in Planar Black Branes Planar AdS black branes have a scaling symmetry that maps a brane solution at one temperature to a solution at another. It is natural to expect that boundary representations of bulk field modes should...

I wrote up a small observation I had on the interplay between symmetries and state-dependent operators.

arxiv.org/abs/2604.03003

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Holographic One-Point Function and Geodesics in SdS$_3$ Grinberg-Maldacena showed that, for AdS/CFT, the thermal one-point function of a heavy boundary operator in the dual conformal field theory encodes the complex geodesic length from the boundary insert...

New preprint, with my students Arundhati Goldar and Rhitaparna Pal!

We extend Grinberg-Maldacena's result that the boundary thermal one-point function encodes the bulk geodesic distance from boundary to singularity in AdS black holes, to 3D de Sitter black holes.

arxiv.org/abs/2603.21425

My students printed out my General Relativity lecture notes from a few years ago and made this cover for it!

Haha that's amazing!

mathematica codes? or python?

*Takes the tiniest possible bite*
"That's a big bite!"

If I didn't read the description, I would have thought this was a comedy skit

Me: will you please get on with it

Chatbot: (thought for 49 minutes):

Right, let me solve the equation in the spirit of "getting on with it."

Here's the trick most people miss. We divide both sides by 2 to get x=4.

Do you want me to carry on and solve for y?

me: 😭

3/3

Me: thought I did

Chatbot: (thought for 1 minute)
Very good. The equations you want solved are x+y=5, x-y=3. Here comes the crucial step. Are you ready for the crucial step?

We add the two equations and get 2x=8.

The next step will be to solve for x.

2/3

Me: solve the equations x+y=5, x-y=3

Chatbot: (thought for 17 minutes)
Simultaneous equations can be tricky. The equations you want solved are x+y=5, x-y=3.

If we substitute x=z, y=w, the equations simplify to z+w=5, z-w=3.

The next step would be to solve it. Just say the word.

1/3

You got to improve these slides my dude, impossible to read now

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Faster than Light Travel, Free from Paradoxes No grandfathers were hurt in the writing of this article

Special relativity does not rule out faster-than-light signals? There's a strong argument showing that it need not.

Hat tip to @uberwensch.bsky.social who shared a paper and initiated a discussion that inspired this post

nirmalyakajuri.substack.com/p/faster-tha...

Faster than Light Travel, Free from Paradoxes No grandfathers were hurt in the writing of this article

It will be interesting to construct a toy model, like electrodynamics coupled to a superluminal fluid, and see it play out.

btw your post led me to write a popsci piece about the paper: nirmalyakajuri.substack.com/p/faster-tha...

Geroch's point is that for theories which disallow causal loops, faster than light propagation is not a problem in itself. I don't think anyone disagrees with that.

I imagine this came out when the whole faster-than-light neutrino detection thing happened.

The argument against ftl in SR textbooks is incomplete: we say FTL implies some observers will see effect before cause. But that's not a problem in itself. The problem is if causal loops form.

Agree

Clock with no hands

Thinking about hanging this clock in my office to remind me of the problem of time in canonical quantum gravity

There was a fair amount of discussion in old twitter

So if you like to play with such ideas, the scenario you should think of are the 2D sky creatures and what could possibly stop them from detecting the existence of the height dimension. Two kinds of particles does not help--they don't prevent access to height.

Now in your picture, we are the sky creatures. We should constantly see stuff drift off into other dimensions.

Any good model of extra dims must have a way to stop this. Rolled up dimensions are too small for things to drift off in. Large extra dimension models have mechanisms to make stuff stick

Let's suppose, like you did, there are 2 categories of particles and they don't interact. Fine. But what stops the particles from traveling across dimensions?

The sky creatures, for example, would see their particles fall down (you have allowed gravity to pass across dimensions) all the time.

You are probably thinking of dimensions as they are depicted in fiction--some kind of portal where people can enter. But dimensions in physics are mundane like length, breadth, width.

As an example, take hypothetical 2-dimensional creatures living on a slice of the sky. The third dim is height.

That is true, but on the other hand, these are one of the few forums where you have a bunch of experts gathered together. I have certainly seen some enlightening conversations and threads on X.

This is the good stuff.

Also astro folks seem on the average more interested in, and somehow able to make a lot more time for sci-comm.

But I found on X that there is an audience for the more abstract stuff. Particle physicist Martin Bauer has 100K followers over there, posting mostly quantum field theory content :)

There were certainly more discussions on X. I think lack of algorithm is part of the issue--both in terms of not showing people the content they would like to see and also not being addictive enough for people to spend much time on.

I don't log in here every day so it could be that, and the lack of any algorithm doesn't help either since people have stopped using feeds.

There's so many physicists here on Blusky yet I never see any real discussion or dialogue on any physics topic despite following the physics feed and every physicist in my areas of interest.

Am I missing them? What can we do to spark some physics conversations?

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