Scientists on Reddit

Katie Mack

Cosmologist and author of The End of Everything

How we know it's theirs

The 2014 r/science AMA, posted from this account

We retrieved 2 posts and 96 comments from u/astro_katie, dated 2014 to 2025, most often in r/askscience, r/science and r/space.

Best moment

A redditor wrote in r/science

On “I'm Dr. Katie Mack, an astrophysicist studying dark matter, black holes, and the early universe, AMA.”

What is the most exciting thing that's happened in your job that you've directly been involved in?

u/astro_katie replied

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This is a really tough question. As a theorist, I don't often get to see new data come in that I've been involved with, and I haven't yet seen any of my ideas totally confirmed or falsified. There've been a LOT of exciting developments in cosmology in the last few years as new experiments have given us new data about the Universe, but as a theorist I can't say I've been directly involved in any of it.

I was pretty excited about the BICEP2 result, though, and although I certainly wasn't involved in it, the result does suggest that a dark matter model I wrote some papers about, the high-scale string theoretic axion, probably can't account for dark matter. So that was pretty cool. :-)

One time, back in the day, when I did experimental work in particle physics, I got to spend a few weeks going around in the Super Kamiokande neutrino detector in a boat, repairing photomultiplier tubes. That was pretty sweet.

Oh also I once gave a talk that Stephen Hawking attended. Though I'd call that more terrifying than exciting.

More moments

A redditor wrote in r/science

On “I'm Dr. Katie Mack, an astrophysicist studying dark matter, black holes, and the early universe, AMA.”

How do you explain dark matter to kids?

u/astro_katie replied

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I usually like to start with something like the intro to this piece -- I tell them that when they touch the table, what they're feeling is the electromagnetic repulsion (or, you know, I use some less jargony way of saying that) between that surface and their hand, and that's what makes it feel solid and what keeps you from passing right through it. Dark matter doesn't seem to have that force. It has gravity, but it doesn't do electromagnetic repulsion as far as we can tell. So if dark matter were in the room (which it probably is), it would pass through you unnoticed. And we know dark matter is out there because of the way it moves things around in galaxies and clusters of galaxies, and how its gravity bends light. And then I show them lots of pictures. :-)

A redditor wrote in r/askscience

On “AskScience AMA Series: I'm Dr. Katie Mack, theoretical astrophysicist, TED Fellow, and author of The End of Everything, which describes five possible ways the universe could end. I'm here to answer questions about cosmic apocalypses, the universe in general, and writing (or tweeting) about science!”

Congrats on getting your private pilot license! What was the skill you found the most difficult to master before doing your checkride?

u/astro_katie replied

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Thank you! The things I struggled with most were landings (which are always the hardest part, I suppose) -- especially short-field and soft-field landings -- and soft-field take-offs. And I still get super nervous whenever I have to talk to Air Traffic Control or really even just give radio calls at all, even just on the common frequency around an uncontrolled airport. You would think that someone who has given radio interviews for the BBC World Service would find ATC easy but no! It is terrifying!!