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1/ Today is #BlackHoleFriday, an annual science outreach event that, by complete coincidence I’m sure, is done on #BlackFriday. You’ll read lots of cool stuff about black holes on the hashtag. Here’s mine.

 2/ Black holes are weird. Duh. People like to think of them as something like incredibly dense nuggets of stuff that sucks other stuff in. But they’re not like that.
3/ If you squeeze enough mass into a small enough volume, the gravity gets so intense that it’s impossible to escape them *if you get too close*. From far away, though, gravitationally they more or less act like anything with that much mass.
4/ So if the Sun turns into a black hole we wouldn’t get drawn in. In fact, we’d orbit it almost exactly the same way as we do now, though we’d freeze to death pretty rapidly, which, in the end, would still kinda suck.
5/ Black holes get weird *when you get close*. Anything with mass warps space — we feel that warp as gravity! — but black holes stretch space to its limit.
6/ It’s like falling down an infinitely deep hole with perfectly vertical and frictionless sides. Down you go, and that’s that. Even light can’t get out if it gets too close.
7/ But because they warp space so much, there are weird effects. Take, for example, the size of a black hole. Imagine an infinitely deep circular hole in the ground. Literally bottomless. What’s the hole’s radius?
8/ Well, if you walk around it it has a circumference. Divide by 2 pi and you get the radius. But now try to go *through* it, down the hole and back up. You’d have to travel forever. The radius in that sense is ∞.
9/ I know, right? It gets weirder. A black hole in general is a sphere. That means you can measure the radius by going around it. How does that depend on mass?
10/ Turns out, if you double the mass of a black hole, you double the radius (see: https://t.co/jIYeYG3THl). That’s the way the math works out. BUT think about geometry. The volume of a sphere goes up as the radius CUBED.
11/ So when you double the mass of a black hole, the volume goes up by 2 x 2 x 2 = 8 times. That leads to an interesting idea. Density is mass / volume. What happens to a black hole’s overall density as it consumes material?
12/ Double the mass and the volume goes up by 8. That means the density goes DOWN by 2/8 = a factor of 4. As a black hole gets more massive *its density gets lower*. 10 times the mass = 1/100th the density.
13/ At some point a black hole gets so big its density becomes very small. A black hole with 4 billion times the Sun’s mass would have a diameter of 24 billion km (big!) but have the density of… air.
14/ In other words, if you took a sphere 24 billion km across and filled it with *air* at Earth’s sea level density, it would be so massive it would be a black hole.
15/ Mind you, we see some black holes this massive! They’re in the centers of distant galaxies, but still. They exist. Supermassive, but very low density.
16/ Come to think of it, they’d float if you had a bathtub big enough. And could keep the water from collapsing into a black hole. And had a uniform 1g gravitational field under it to counteract buoyancy. Hmm. This idea has issues. I’ll have to write more about it some day.
17/ Anyway, I had a conversation with a leading black hole physicist some years ago, and mentioned this to him. He got thoughtful, and then nodded. “Yeah,” he said. “That’s right!” I was pretty chuffed to a) be right, and 2) have thought of something he hadn’t thought of.
18/18 Honestly, I wondered if I had missed something obvious, but nope. This is correct. So, to summarize: Black holes are weird. And that’s my #BlackHoleFriday thread. /fin
19/18 (yeah, I know) BTW here’s my Crash Course Astronomy episode on black holes.

https://t.co/QetnodyE72

#BlackHoleFriday

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1/

Get a cup of coffee.

In this thread, I'll help you understand the basics of Binomial Thinking.

The future is always uncertain. There are many different ways it can unfold -- some more likely than others. Binomial thinking helps us embrace this view.


2/

The S&P 500 index is at ~3768 today.

Suppose we want to predict where it will be 10 years from now.

Historically, we know that this index has returned ~10% per year.

If we simply extrapolate this, we get an estimate of ~9773 for the index 10 years from now:


3/

What we just did is called a "point estimate" -- a prediction about the future that's a single number (9773).

But of course, we know the future is uncertain. It's impossible to predict it so precisely.

So, there's a sense of *false precision* in point estimates like this.

4/

To emphasize the uncertainty inherent in such predictions, a better approach is to predict a *range* of values rather than a single number.

For example, we may say the index will return somewhere in the *range* of 8% to 12% (instead of a fixed 10%) per year.

5/

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It was great to talk about reproducible workflows for @riotscienceclub @riotscience_wlv. You can watch the recording below, but if you don't want to listen to me talk for 40 minutes, I thought I would summarise my talk in a thread:


My inspiration was making open science accessible. I wanted to outline the mistakes I've made along the way so people would feel empowered to give it a go. Increased accountability is seen as a barrier to adopting open science practices as an ECR

It also comes across as all or nothing. You are either fully open science or your research won't get anywhere. However, that can be quite intimidating, so I wanted to emphasise this incremental approach to adapting your workflow

There are two sides to why you should work towards reproducibility. The first is communal. It's going to help the field if you or someone else can reproduce your whole pipeline.


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Rebecca \U0001f983 "Stay the Fuck Home" \U0001f983 Watson
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So it turns out that an organization I thought was doing good work, the False Memory Syndrome Foundation (associated with Center for Inquiry, James Randi, and Martin Gardner) was actually caping for pedophiles. Uhhhh oops?


Since this, bizarrely, turned out to be one of my longest videos ever (??) here's a quick thread to sum it up for those of you like myself with short attention spans. 1/10

In the '90s the False Memory Syndrome Foundation was founded to call attention to the problem of adults suddenly "remembering" child abuse that never actually happened, often under hypnosis. Skeptics like James Randi & Martin Gardner joined their board. 2/10

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