Public

**Life in a universe with 2 time dimensions**

Greg Egan's novel

*Dichronauts*is now available on Amazon - and soon it will show up elsewhere. It's about life in a universe with 2 dimensions of space and and 2 dimensions of time!

I urge you to read the excerpt on his website and also check out the pages where he explains the physics! For example, the

**dark cone**. Ordinary physics has a

**light cone**: the directions in spacetime along with light can move. Egan's universe has a cone of directions in which light

*can't*move... but other things can. Paraphrasing from him:

*No light source can emit a beam in any of these directions, and no one would be able to see anything by looking in a direction that lies within the dark cone.*

*We are used to thinking of any restriction so powerful that even light must obey it as applying to all material objects as well: for example, when we hear that light can’t escape from a black hole, it follows that no ordinary object, travelling even more slowly, could hope to escape either. But in the case of the dark cone, nothing could be further from the truth!.*

*So, the dark cone contains no light, but material objects are free to move in these directions. And since sound waves are nothing but vibrations in material objects, sound is also free to move in the dark cone.*

When I was in grad school I took a course with the mathematical physicist Victor Guillemin, which touched on the beautiful things that happen in a universe with 2 space and 2 time dimensions. Since I was interested in real-world physics I thought this was a bit weird.

Only later did I learn enough math to realize that the

**split real form**of spacetime, with almost the same number of space and time dimensions, is mathematically the nicest in many ways: you can see the geometry coming from the O(n) Dynkin diagram most clearly in this case.

If you don't know what the hell "O(n) Dynkin diagram" means, well, now you see why I didn't understand it back then!

And if you're wondering why I said

*almost*the same number of space and time dimensions, well, if you've got an

*even*number of dimensions you can split them equally into space and time, like 2 = 1 + 1 or 4 = 2 + 2. And the cool part here is that then there's fundamentally there's

*no difference between which dimensions are space and which are time!*(If I understand correctly, Egan creates one by choosing a state of the universe that breaks this symmetry. I haven't read the book yet.)

But what if you have an

*odd*number of dimensions? Then you split these dimensions into space and time as equally as you can, like 3 = 2 + 1 or 5 = 3 + 2 or 7 = 4 + 3. That's what gives you the 'split real form', which is mathematically the nicest choice.

"Mathematically the nicest" does not mean the nicest for the physics we know and love - not in this case! Most physicists are appalled by the idea of 2 or more time dimensions. If you study theories like that they call you a dirty two-timing rat.

But Egan goes ahead and sees what it might be like.

**Dichronauts**

My new novel

**Dichronauts**is officially published in the US on July 11, but copies are already in stock at Amazon, and it might already be available from your favourite bookshop.

You can read an excerpt by following the link below, and supplementary material about the universe of the novel by following the links from that page.

http://www.gregegan.net/DICHRONAUTS/E1/Excerpt.html

View 34 previous comments

- +John Baez Enjoy! I think Rajaniemi is a fascinating new writer - and he's also doing exciting biotech stuff as well.33w
- Note from a British reader. I live in Oxford, and I'm disappointed at the difficulty of finding Greg's books in the shops. Oxford has the famous bookshop Blackwell's, founded in 1879. They have no Egan books, although a few years ago they had almost the complete set. They told me yesterday that none of their shops (of which there are a lot: see https://bookshop.blackwell.co.uk/bookshop/shops) plan to sell "Dichronauts". Waterstones aren't stocking it or any other Egan either, and said they couldn't order the book because it's only published in the US. And the only other bookshop left in Oxford, a small independent, don't have any Egan either. They told me they couldn't order "Dichronauts" for me, because all their books come via two wholesalers (one called Gardners; I forget the other), and these couldn't supply it. In the ruins, indeed.

I could probably order from Amazon. But it would be nice to support local shops, and even nicer to support ones which allow browsers the chance of discovering unsuspected books. I first discovered Greg's work that way, via "Unstable Orbits in the Space of Lies" in "Interzone", in WHSmith of all places. WHSmith no longer sell SF magazines.29w - +Jocelyn Ireson-Paine - sad. I've been to that Blackwell's, and it's huge! I was mildly upset that they didn't have any scholarship on Euclid in their classics section, but that's more forgivable.29w
- +Jocelyn Ireson-Paine My UK publisher dropped me because the
*Orthogonal*trilogy sold badly for them, so you can forget about any prospect of seeing new titles of mine in UK book shops. The US publisher does have the right to sell their print edition worldwide, but most UK distributors are uninterested in taking it because of previous low sales.

So, by all means support whatever bookshops you like by buying the books that they actually stock, but if you want to read anything new that I've written, that will come down to mail order from Amazon etc., or the ebook.29w - +Greg Egan, your UK publisher is crazy, but at least it doesn't actually mean that UK readers can't get your stuff any more, just that it's hard to get more new ones with no bookshop presence :( you have to rely on word of mouth.

(But then, this is a typical computer-assisted writer destruction method: each print run gets a smaller number of copies because the previous run sold badly because it didn't get enough copies printed because of a previous historical estimate that the run would be bad: it only takes one round of lower-than-predicted sales to get you into the cycle, and once in you can't get out. Countless authors have by now been driven out of professional publication by this cycle of self-reinforcing doom, and several authors have had to adopt pseudonyms just to escape it: one that springs to mind is Sarah Monette, and as we know the automated sales predictions were quite right and her next book,*The Goblin Emperor*, sold terribly, nobody bought it at all!)29w - Getting back to the science, there's been discussion of
*Dichronauts*on Reddit printSF. Calicocobber commented ( https://www.reddit.com/r/printSF/comments/639ai6/spoilers_if_anyone_else_finished_dichronauts_lets/dk8jez9/ ) "I'd never stopped to give thanks for living in a universe with a sane spacetime metric until I read this book".

Though I'm not so convinced that rotation behaves sanely even in our own universe. There's a remark in the art book*Sketching Without a Master*( https://archive.org/details/sketchingwithout00brow ) by J. Hullah Brown, that when drawing a tree, the branches that point left or right give the general outline, while those pointing toward and away affect how you draw the mass and tone of the foliage. Such a radical change just because of a bit of rotation? Life would be much simpler if everything looked the same from every point of view.28w

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