Someone refers to a sci-fi-esque (more imaginative than scientifically accurate) virtual rendition of an interesting scientific phenomenon (black hole) in a fanous sci-fi movie (Interstellar), in their scientific analysis/critique comment on a HN thread about the virtual sci-fi-esque rentition of such a sci-fi object (black hole)(yes, a simplified easy-on-eyes pseudo-accurate rendition of a black hole, for VR/AR immersion at home, counts as sci-fi-esque, IMHO), and someone else who worked on such famous object (black hole) depicted in that exact sci-fi movie, responds to the comment.

Peak HN, right here!

>of course this is a simplified visualization

Its titled a "physically accurate black hole"! Please don't do this, if its intentionally not physically accurate and heavily simplified! The general public on here don't know better, and it takes someone else with years of experience simulating black holes to dig through your code to show what you've simplified. There's like a few hundred people who have the right experience worldwide to know that you've got some of your equations incorrect

The issue is when you're communicating doppler, if you want to correctly show the change in doppler, you can't make the intensity or colour mapping arbitrary

There's two ways to communicate accurately an example linear change in emissive power:

1. Use a perceptual brightness system, so that a linear change in power represents a linear perceptual change in perceived brightness. This accurately communicates to a viewer the underlying shift in power emission, if you want to show off how a radio telescope perceives a black hole for example

2. Use an emitted power <-> sRGB mapping (with tonemapping), so that a linear change in power is perceived as if it were a physical light getting brighter. This is more "what would this look like to a person?"

At the moment the change in your image brightness doesn't correspond to anything, which means that its not really communicating any science, and it doesn't correspond to doppler. Which is fine if its just illustrative and that's clear, but again vanishingly few people will know this is a visualisation not a physically accurate render

Great job. Please consider turning on rotation by default (for those who missed it, it's in the parameters). The overwhelming majority of astrophysical black holes are expected to be spinning (Ker) black holes.

> completely arbitrary

You agree that it isn’t “physically accurate”, then… but seem to argue that you shouldn’t be called out for the false title?

It’s fair enough to be called clickbait when you really did score extra clicks with a slick falsehood, surely?

All they need to do is not put the label physically accurate on it then. If you call something physically accurate and decorate it with your credentials as a harvard phd in astrophysics building radiative transfer sims, people expect it to have a degree of accuracy. This sim, from a physical perspective, is wrong

That's 100% fine if you present it as a visualisation with limitations and I absolutely love people making fun side projects like this and presenting them. I built a whole tutorial series on doing this, because I think people getting stuck into the field is absolutely great, and more power to everyone who wants to write anything no matter how accurate it is

Its the fact that this is being presented and stated as if its a physically accurate sim made by someone with experience in the field so it must be spot on, when in reality its little better than an artists impression of a black hole, that bothers me. Its science miscommunication. Coming away from this, you might think:

1. Black hole accretion disks are red

2. Black holes do not warp the background around them, only the accretion disk

3. You might get notions about the intensity distribution of the doppler shift, or the way that cameras work near black holes etc

None of which is particularly correct, and there's a lot more wrong with it too

The person you’re replying to did not hold it to that standard — they only pointed out that the standard it claimed to hold itself to was not actual.

If correcting misinformation is “harsh”, reality is fucked.

They're blue, in general black hole accretion disks are very hot, and anything past a certain temperature looks pale blue as follows:

https://20k.github.io/assets/kerraccrete.PNG

This is a colour and relative brightness accurate example of a hot accretion disk. The size, emissivity and absorption are set to arbitrary parameters, but this is human-eye-colour accurate with correct doppler and radiative transfer for a spinning black hole. Its as correct as I can make a specific model, for what a human would see standing next to a black hole taking into account the limitations of the human visual system

You can get a red accretion disk like this:

https://i.postimg.cc/pV8VWKhw/verycold.png

But it requires the disk to be extremely cold, which is physically pretty suspect

One interesting feature is that the temperature and brightness scale differently, so that its actually hard to observe the colour shift, as the brightness changes much faster than the colour. So its not something you ever really see to the human eye

That said these don't do accretion disk within the ISCO, which is a major limitation

It's purely my color map choice – the underlying simulated image is simply a number at each pixel. Transforming that number to the actual displayed color is generally an arbitrary choice, as common for the vast majority of images in astronomy/astrophysics papers. The only difference is that I don't show a numeric colorbar here, for the sake of simplicity.

Keep your need for simplified representations of reality (which claim to be complete) out of our information-based community.