Greg Egan @gregeganSF Twitter profile | Pikagi

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Greg Egan

@gregeganSF

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SF writer / computer programmer Latest novel: MORPHOTROPHIC Latest collection: SLEEP AND THE SOUL Web site: Also: @gregeganSF @mathstodon .xyz

https://t.co/6iQ66NAtjK

Joined December 2016

Don't wanna be here? Send us removal request.

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@gregeganSF

Greg Egan

2 years

When Cara Leon goes missing, Sam Mujrif is hired to investigate. Cara is 8 times taller than Sam, but evidence points to players much smaller than either of them—and technology with the potential to radically alter the balance of power between the scales.

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@gregeganSF

Greg Egan

3 months

Crowdstrike have advised that the world will be reverted to its last valid backup set, dated 7 Jan 2014, within the next 30 minutes. Please make paper notes of anything important to you from the intervening period, and tape them to your refrigerator door in a prominent position.

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Greg Egan

3 years

Every time I read new research about the Antikythera mechanism my jaw drops a little lower. I can’t decide which is most impressive — that anyone (even a genius like Archimedes) could design such a thing, or that anyone could build it, ~2100 years ago.

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Greg Egan

4 years

Why do we never hear about the brave free thinkers who spent the Blitz telling everyone in sight that blackout curtains were just a scam cooked up by Big Fabric, and that the Luftwaffe had killed fewer people than the last war with Spain?

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Greg Egan

4 years

“Zeus!” gulped Otto. “Deplug Suez!”

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Greg Egan

5 years

When you die, there is a tug of war between the people you helped, trying to drag you to paradise, and the people you let down, trying to drag you to hell. So, always be kind to Sumo wrestlers.

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Greg Egan

2 years

After dying, we strongly recommend that you do *not* disclose any personal information to superficially angelic-looking interlocutors, as this is likely to be a phishing attempt. Type the URL for paradise manually into your soul’s browser, and double-check for a padlock symbol.

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Greg Egan

7 years

No individual colour making up this wave travels faster than the grid lines, but the sum of all components appears to outrace the grid. This is how “group velocities” can exceed the speed of light without carrying information.

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Greg Egan

4 years

In a sphere of uniform density, the best tunnels to dig for your gravity-driven parcel delivery tubes are hypocycloids (left), with total time proportional to √[θ(2π–θ)] Straight line tunnels are, umm, consistent: the parcel will take the same time, regardless of distance.

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Greg Egan

5 years

[1/2] It’s well known that an ellipse will reflect any straight line trajectory from one focus so it passes through the other focus, but what about the parabolic trajectories of an object moving under gravity? Here the red curve will reflect any object leaving the “launch point”

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Greg Egan

2 years

[1/10] Here’s an example of how to calculate the difference between quantum and classical correlations — of the kind that led to the 2022 Nobel Prize — with a few lines of high school mathematics. Let’s start with a simple inequality: |x + y + z + ... | ≤ |x| + |y| + |z| + ...

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@gregeganSF

Greg Egan

6 years

Sports where the ball is a classical object are so last millennium. In quantum soccer, the ball is a wave function that you shape so that there’s more than a 50% probability of it being in the goal.

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Greg Egan

5 years

[1/2] My new eBook, INSTANTIATION, has 11 stories: • “The Discrete Charm of the Turing Machine” • “Zero For Conduct” • “Uncanny Valley” • “Seventh Sight” • “The Nearest” • “Shadow Flock” • “Bit Players” • “Break My Fall” • “3-adica” • “The Slipway” • “Instantiation”

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Greg Egan

4 years

Just watched the anime “Your Name” (which was apparently inspired to some degree by my short story “The Safe-Deposit Box” (!) though the plot is entirely different []). It was a bit saccharine in parts, but overall pretty good, and visually ravishing.

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Your Name - Wikipedia

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Greg Egan

5 years

@xenohuntero @markhumphries Yes, it’s horrifying that these comedians are undermining your enormously important efforts on this front, which would otherwise have opened the eyes of tens of thousands of scientifically illiterate politicians and pundits. When we all fry, I will be sure to blame the satirists.

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Greg Egan

1 year

[1/2] Given two people (red and blue dots) between two parallel mirrors, there are an infinite number of light paths joining them, involving ever more reflections. But *all* those paths can be blocked by obstructing just 4 points (black dots)! This is because the virtual images

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Greg Egan

7 months

It’s 30 years this month since PERMUTATION CITY was first published. But of course, all the same letters had been present in other books for centuries before, they just hadn’t been read in that order. Excerpt at:

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Greg Egan

3 years

The level sets of q(x,y) = ½(x^2 + 2xy + y^2 + 3x + y) are parabolas. For some reason, Georg Cantor *really* liked this quadratic, but I can’t imagine why. I mean, its values on integer pairs (x,y) are integers, as shown, but that’s true of many quadratics. Oh, hang on ...

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Greg Egan

5 years

After 14 yrs, the intake valve for my $95 toilet cistern needed a new seal. $5 part, 1 min of my time, no tools. After 2 yrs, 2 of the rubber feet on my $200 Apple keyboard have fallen off, because they were affixed with some cheap glue. And the masters of design are ... ?

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Greg Egan

5 years

Take a 600-cell in 4D with 120 vertices ±v_i, i=1…60 Define F(x)=𝚷_i v_i·x Stereographically project F from a 4-sphere to 3D, then Fourier-transform from momentum space to position space. Result: this hydrogen wave function, with energy level n=61.

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Greg Egan

5 years

Next time someone asks you to name a computable irrational number that has been proved *not* to be normal in any base (i.e. does *not* contain every finite sequence of digits with equal density) you can turn to this beautiful example from Greg Martin:

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Greg Egan

2 years

It’s hilarious that after 70 years of ingenious people programming computers to do thousands of valuable tasks millions of times faster, more reliably & accurately than humans, the ability to write bad poetry and inaccurately summarise text is trumpeted as the dawn of a new era.

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Greg Egan

3 years

[1/2] A recent fun video by @3blue1brown showed how easy it is to find the average area (over all orientations) of the shadow of a convex solid due to an infinitely distant light source. So, I wondered whether any case with a light source at a finite distance is exactly soluble.

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@gregeganSF

Greg Egan

5 years

I am constantly awestruck by Peter Doherty’s patience. Doherty got a Nobel for his discoveries in immunology, and he’s just been called a “boomer retard” by a random guy with 2 followers whose profile pic is a selfie flexing in the gym. And yet he still replies calmly on topic.

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@gregeganSF

Greg Egan

5 years

A satellite has the least kinetic energy when farthest from the central mass. If it releases mini-satellites moving tangentially to its orbit, but whose KE per kg is less than its own by that minimum, they will all pass through the 2nd focus of its orbit, all at the same speed.

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@gregeganSF

Greg Egan

3 years

My new novel, THE BOOK OF ALL SKIES, is set on a world where you can walk through a “Hoop” and find yourself beneath different constellations. More details & a link to an excerpt here: Currently an ebook from Amazon, Smashwords; other stores & POD soon.

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Greg Egan

4 years

Caffeine is a spectacular impressive substance! Less than 10% of the lethal dose, administered regularly, can elevate the cognitive performance of caffeine-habituated people to almost 90% of the level of non-habituated people.

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Greg Egan

1 year

Oh wow, someone thinks they proved a conjecture I made in 2014, about fitting a simplex between two nested spheres in n dimensions! Their proof: The conjecture was here:

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Greg Egan

10 months

Wireless keyboards shouldn’t need to be charged, they should just power themselves by trapping and metabolising spilt crumbs.

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Greg Egan

2 years

I want David Cronenberg to design the new USB standard, so all the ports and plugs sigh and moan and writhe before finally accommodating each other’s anatomy in a blissful, disturbing union that allows charging and data transfer to occur effortlessly between all equipment.

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Greg Egan

3 years

Again, I am left quaking in fear at the awesome powers of the coming superintelligence.

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Greg Egan

6 years

Douglas Hofstadter’s wonderful book “Gödel, Escher, Bach” features images of a wooden block whose three orthogonal shadows form three distinct letters. A single 5D block can (with similar care in the choice of letter shape) have ten projections to 2D that form ten letters.

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Greg Egan

9 months

Me: Please simplify this horrible expression. Mathematica: No, I have no idea how to make that any simpler. Me: What if all those πs were just ... anything? Say, z? Mathematica: Oh, sure, that can be simplified enormously! Me: What if it was e instead of π? Mathematica: Nope.

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Greg Egan

2 years

I’m just waiting for someone to train an LLM exclusively on a religion’s sacred texts, and then market it as a way to converse with the associated deity or deities.

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Greg Egan

7 months

Saw someone hyperventilating over LLMs “passing the mirror test”, so … TL;DR This short program “recognises itself”: show it a file containing its own source code and it will print “This is me!” Underwhelmed? You should be! But I did have to type a lot of backslashes.

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Greg Egan

4 years

If mathematics is so “unreasonably effective”, Wigner, why can’t I sweep the floor 52 times now and be done for the whole year? Why can’t I make my saucepans negatively dirty prior to cooking so they’ll be clean straight after? You have a very low threshold for “unreasonable”.

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Greg Egan

6 years

In the Euclidean plane, lattices can only have exact rotational symmetry under rotations of 180, 120, 90 or 60 degrees. In the Lorentzian plane, lattices can be constructed that are symmetric under “boosts” with parameter arccosh(n/2) for any integer n>2. For this lattice, n=3.

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Greg Egan

9 months

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Greg Egan

5 years

@xenohuntero @markhumphries However counterproductive it is to ridicule a sincere but misinformed person face-to-face, it’s actually a good idea to publicly mock the most bizarre behaviour, e.g. babbling apoplectically about brainwashing when a girl says “Trust science.” The Overton window needs that nudge.

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Greg Egan

8 years

“Girih”, the Persian word for “knot”, describes the strapwork decorating some beautiful kinds of Islamic tiling.

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Greg Egan

2 years

Am I dead again? I hate it when that happens.

@clemRussoNazet

The Sourcerer 🤓 🧙‍♂️

@clemRussoNazet

2 years

@HungLee The late Greg Egan thought about it in the 90's in one of his anticipation shorts, 'Learning to Be Me'. Not spoiling, but taking this concept too far makes black mirror feel light-hearted in comparison😅 Great read, highly recommend if you're into Science Fiction👍

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Greg Egan

5 years

That passage in the Necronomicon where they explain that the Circle of Protection will *only* keep the demon you summoned at bay if you can extemporise a rigorous proof of the Jordan Curve Theorem really ought to be moved from Appendix 17 to the preface.

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Greg Egan

5 years

[1/3] You can carve a tunnel through a cube that another cube the same size can pass through. All the Platonic solids share this property, and so do all n-cubes: Wallis credits Prince Rupert of the Rhine with noting this of the cube, so mathematicians

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Greg Egan

4 years

The best way to annoy a topologist is to cut a very thin slice through the handle of their favourite coffee cup — so thin as to have no effect on its function, but thick enough so that every time they look at it, they will be in no doubt that it is now homeomorphic to a ball.

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Greg Egan

5 years

This is my favourite dissection of the cube: 6 pieces, with the 6 ways of permuting the coordinates in ascending order: x ≤ y ≤ z x ≤ z ≤ y y ≤ x ≤ z y ≤ z ≤ x z ≤ x ≤ y z ≤ y ≤ x In higher dimensions, the n-cube can be dissected in the same way into n! pieces.

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Greg Egan

6 years

The black hole Taraxippus is about to enter the solar system. But it’s only a tenth the mass of the sun, and it’s not expected to pass too close to the Earth. What could possibly go wrong? My new novella, PERIHELION SUMMER, 16 April from Books.

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@gregeganSF

Greg Egan

1 year

When I’m king of the world it will be forbidden to teach Pythagoras’s c^2 = a^2 + b^2 without giving equal time to Minkowski’s s^2 = –(c t)^2 + x^2 thus destroying a whole cottage industry of bores pretending that special relativity is harder than Euclidean geometry.

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Greg Egan

5 years

After years of painstaking research, some of it in cafés quite close to the Bodleian Library, I have discovered the correct term for this: aridition (n) The quality of appearing to have great knowledge or learning that turns out upon closer inspection to be entirely superficial.

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Greg Egan

7 years

Just another black hole passing by in the distance ...

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Greg Egan

3 years

How to annoy your high school mathematics teacher: “I asked you to plot a sine curve!” “This is a sine curve: y=sin(s), where s is the distance along the curve from (0,0).”

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Greg Egan

4 years

It still astonishes me that it took till 2018—and a full classification of geodesics on a dodecahedron—for anyone in the world to find *this* one: from a vertex back to itself, passing through no others. With the net drawn the right way, it’s so obvious!

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Greg Egan

7 months

My new novel MORPHOTROPHIC is available now! You can read the first two chapters here:

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Greg Egan

4 years

If you have no bubble wrap to pop or cellophane to crinkle, the next best thing is to listen to the sound that MacOS makes when deleting files.

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Greg Egan

2 months

“Scavengers Reign” is something else — it’s as if Miyazaki decided to remake Tarkovsky’s “Solaris”. I have absolutely no idea what’s going on, but as a gloriously hallucinatory xenobiological dream, I’m happy to just sit and stare at all the strange creatures chittering around.

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Greg Egan

7 months

My new novel MORPHOTROPHIC will be published on 9 April. Amazon is now accepting preorders for the ebook; other venues will follow soon. There will also be print-on-demand editions from Amazon available on 9 April, but they can't be pre-ordered.

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In a world where the cells that make up our bodies are not committed to any one organism, Marla is confronted by the fickleness of her cytes, and resolves to understand them with help from Ada, a...

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@gregeganSF

Greg Egan

1 year

@Quasilocal Yeah, but if you take a photo of a corpse, AI-powered “wind this back to show every second for the last 24 hours” will reveal the killer.

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Greg Egan

4 years

This function whose derivative is also its inverse is pretty cute, and deserves to be better known! H/T @sfera314

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Greg Egan

6 years

Gosh, these “Mr. Robot” episode titles are *really* starting to capture the authentic feel of modern computing.

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Greg Egan

4 years

Some people think the theory of divergent series has no relevance in the real world — but they haven’t seen me adding ever smaller quantities of flour and water to dough in a vain attempt to get the consistency right without consuming an infinite amount of resources.

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@gregeganSF

Greg Egan

1 year

My new collection, SLEEP AND THE SOUL, is now available. You can get it as an eBook from most venues, or as print-on-demand from Amazon. This collection includes the story “Solidity”, a current finalist in the Locus Awards for best novelette of 2022.

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Greg Egan

5 years

I wish I could spend a few days as 1983-me again. He didn’t own a computer, but he had legible handwriting, wrote clear, helpful notes, and possessed enough patience to do useful things with graph paper and a calculator.

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Greg Egan

2 years

The script that runs on my computer when I die will rename the story ideas file “TL;DW”.

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@gregeganSF

Greg Egan

7 years

Dan Piponi @sigfpe has been plotting the eigenvalues of random matrices! Here’s a variation: with A, B, C 200×200, real/imaginary parts from std normal, each frame is eigenvalues of A+exp(i t) B/5+exp(i u) C/10, coloured by u, while t increases over time.

@sigfpe

@[email protected]

7 years

Here's a version using eigenvalues of an "animated" matrix. Note that this is approx. 4 second animation, but individual particles have paths 4n seconds long with various n.

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Greg Egan

4 years

Breaking: Hollywood is in crisis after criminals hacked into multiple CGI companies and enforced conservation of momentum in all superhero rendering code. Detailed ransom demands have not been disclosed but sources say it likely includes green-lighting several unproduced scripts.

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Greg Egan

2 years

This is the kind of interface for search that I fantasised about having by 2055 in my 1995 novel DISTRESS. We could, of course, still have something like this well before 2055 … but not if people keep lowering the bar and pretending that garbage like Sydney/Bing is even close.

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Greg Egan

1 year

[1/3] Here is a mathematical idealisation of a Möbius strip made from a paper band — where the paper can bend, but it can’t be stretched or sheared. Because the cylinders are intrinsically flat, we know we can wrap the band around them without distorting its shape at all!

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Greg Egan

3 years

A sphere knotted in four dimensions (rotating in R^4 and projected down to R^3), built by taking trefoil knots in R^3 scaled by sin u, and given a 4th coord of cos u. This construction was discussed by @stevenstrogatz and Colin Adams in this fun podcast:

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Greg Egan

2 years

Writing a book is so easy, you just type 100,000 random words then use gradient descent to make them better.

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@gregeganSF

Greg Egan

5 years

[1/2] The interior of a hypocycloid with n cusps can be “swept out” by a rotating hypocycloid with n–1 cusps (which in turn can be swept out by a rotating hypocycloid with n–2 cusps …) If you take the trace of every matrix in the group SU(n), you get a hypocycloid with n cusps

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Greg Egan

1 year

On a sphere, if you start at ANY point, and set off along a geodesic in ANY direction, you will ALWAYS return to exactly where you started, facing in THE SAME direction. But spheres are exceptional. Even on an ellipsoid with two axes the same, the meridians and the equator are…

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Greg Egan

5 years

The 5 stages of denial: [1] The planet isn’t warming. [2] It’s warming, but it’s natural variation. [3] It’s human-induced warming, but it will have a net benefit. [4] The warming’s not beneficial, but adapting will be cheaper. [5] Adapting is ruinous, but we never had a choice.

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Greg Egan

4 years

I just received a copy of Hayakawa SF magazine, February 2020, with this beautiful illustration for a story of mine.

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Greg Egan

2 years

The dream was for all scientific literature to be open access, hyperlinked, and when possible, rigorously checked by software that could catch errors (e.g. proof assistants). Instead, we get software that spews out faux-coherent garbage, adding errors, polluting the infosphere.

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Greg Egan

3 years

Any sufficiently misunderstood natural phenomenon can be mistaken for advanced technology.

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Greg Egan

5 months

Two Chinese editions arrived in the mail today. PERMUTATION CITY is the first of my novels to be published in Chinese; the previous books have all been short story collections (like the other one here, OCEANIC).

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Greg Egan

5 years

[1/2] The red dot accelerates at a constant rate and direction. The black dots can accelerate faster. How can they match the red’s position *and* velocity as soon as possible? The calculus of variations shows the optimal trajectories obey a simple rule:

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Greg Egan

3 years

Breaking: leaked memo shows that WHO contemplated renaming COVID variants “covariants” just to mess with mathematicians and physicists, but backed down at the last minute after intensive lobbying from IAS and Perimeter Institute.

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Greg Egan

7 months

You can read the first two chapters of my new novel MORPHOTROPHIC here: Publication is on 9 April.

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Greg Egan

5 months

Wow, thanks to my brilliant Japanese translator Makoto Yamagishi, my story “Solidity” just won the Japanese Seiun Award for Best Translated Short Fiction! [For English-speaking readers, this story is in “Sleep and the Soul”: ]

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Delicious in Dungeon, Godzilla -1.0, Kia Asamiya Win Seiun Awards

www.animenewsnetwork.com

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Greg Egan

29 days

I was impressed by X’s spectacular AI skills, which enabled them to swiftly identify, report & block the 50 or so pornbot accounts with identical profile pics, 0 followers and 1 follow who liked random posts of mine in the past 24 hours. Oh wait, that was me, doing it manually.

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Greg Egan

4 years

Twitter beta-tests new “infinite scroll-up” feature to selected users’ timelines, allowing them to see algorithmic predictions of future tweets from everyone they follow.

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Greg Egan

2 years

So, tonight the whole ceiling above my living room / writing room fell down. I heard what I thought was a possum moving around in the roof last week, and again today, so apparently it was even heavier than I realised. No injuries, I wasn't in the room, so I was lucky.

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Greg Egan

4 years

What harm could there be in releasing my recursive LaTeX macro into the wild ... ?

@chmonke

Dᵇ(Monkey) Alex Scheffelin

4 years

You walk into your Calc 2 final and see this. What are you gonna do?

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Greg Egan

3 years

I didn’t really *need* to spend 2 h 18 m watching a comprehensive takedown of the cryptocurrency cults, but this is also funny enough along the way that it was worth watching to the end. YMMV.

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Greg Egan

4 years

Penrose-deBruijn tilings come from picking a plane in R^n, finding a set of squares with vertices in Z^n that approximate the plane, then projecting them onto the plane. Here is a tiling using R^6, where the contours show the orthogonal distance from the squares to the plane.

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Greg Egan

5 years

By tweaking the usual Binet formula for the Fibonacci numbers in terms of the golden ration ϕ, you can write a real-valued function F(x) of the real numbers that obeys: F(x+2) = F(x) + F(x+1) for all x, real or complex. H/T @octonion , @AndrewM_Webb , @hvairinhos , @stephentyrone

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Greg Egan

5 years

[1/2] The square and the equilateral triangle are highly symmetrical shapes, but curiously, the dissection of one into the other with the fewest pieces breaks all that symmetry. This hinged dissection was discovered by the English mathematician in 1903.

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Greg Egan

9 months

My novel “Scale” — a political thriller set in a world where people belong to seven groups that differ vastly in size — is included in the 2023 Locus recommended reading list.

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Greg Egan

4 years

I guess I should make more effort to target my work to my biggest fans — Twitterbots — by including more positive representations of characters that are irritating, insentient software.

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Greg Egan

5 years

What these wondrous numbers giveth with one hand, they taketh with the other. — Leonardo Bigollo Pisano, Liber Abaci (1202)

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Greg Egan

5 years

You have a pack of 52 playing cards. • Shuffle the cards. • Pick a card at random. • Note what it is. • Return it to the deck. • If you’ve now seen every card, you’re done. • Otherwise, repeat. What is the expected number of cards picked, rounded to the nearest integer?

153

155

236

531

1378

659

2116047814278053667325

2202

45

82

234

@gregeganSF

Greg Egan

3 years

When Google started putting photos of random people in its “knowledge graph” box alongside my biographical details, I said, “One day, they’re going to seriously libel someone with their incompetence”. Lo and behold:

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@gregeganSF

Greg Egan

4 years

Wow, I’ve never even *been* to America, and I’ve still paid the American IRS more than the American President over the last four years.

7

20

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@gregeganSF

Greg Egan

5 years

They laughed at my perpendicular slide rule — but when the computers have been smashed, and no one can remember what a logarithm is, the quadratic green scale will come to the rescue!

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@gregeganSF

Greg Egan

4 years

This is beyond hilarious: Google’s “Knowledge Panel” for the French mathematical collective that published as “Nicolas Bourbaki”. H/T @_onionesque

Tweet media one

10

61

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@gregeganSF

Greg Egan

1 year

[1/6] You’ve probably seen a pattern like this on Christmas decorations or chocolates, but it’s actually a demonstration of a technique I just learned from @ZenoRogue for creating a coordinate system (u,v) on a surface such that moving along a grid line of constant v from

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Greg Egan

1 year

Scientists publish studies on how too much sitting will kill you, and how standing desks aren’t much better … but how about a study of people who plant their feet against the nearest surface and tip back and forth on their chair, the way their teachers always told them not to?

18

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@gregeganSF

Greg Egan

4 years

If you don’t empathise with the protagonist of “Memento” you’ve probably never looked at any software you wrote two years ago.

7

26

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@gregeganSF

Greg Egan

6 years

When the cone you’re slicing is the light cone, instead of ellipses, you just get different circles.

3

48

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@gregeganSF

Greg Egan

2 years

@AdamRutherford My new EpiFace™ algorithm supplements the raw base pairs of DNA by examining the well-known epigenetic markers laid down when the suspect shaves, cuts his hair, gets a prescription for glasses, or buys a hat.

5

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