# Many Worlds, Many Treats

I’m sitting at the computer typing, when the dog bumps up against my legs. I look down, and she’s sniffing the floor around my feet intently.

“What are you doing down there?”

“I’m looking for steak!” she says, wagging her tail hopefully.

“I’m pretty certain that there’s no steak down there,” I say. “I’ve never eaten steak at the computer, and I’ve certainly never dropped any on the floor.”

“You did in some universe,” she says, still sniffing.

I sigh. “I’m going to move the quantum physics books to a higher shelf, so you can’t reach them.”

“It won’t matter. I’ve got Wikipedia.”

“All right, what ridiculous theory has your silly little doggy brain come up with?”

“Well, it’s possible that you would eat steak at the computer, yes?”

“I do eat steak, yes, and I sometimes eat at the computer, so sure.”

“And if you were to eat steak at the computer, you’d probably drop some on the floor.”

“Dude, I’ve seen you eat.” Yes, the dog calls me “dude.” There may be obedience classes in her future.

“All right, we’ll allow the possibility.”

“Therefore, it’s possible that you dropped steak on the floor. And according to Everett’s Many Worlds Interpretation of quantum mechanics, that means that you did drop steak on the floor. Which means I just need to find it.”

“Well, technically, what the Many Worlds interpreation says is that there’s some branch of the unitarily evolving wavefunction of the universe in which I dropped steak on the floor.”

“Right, so I just need to find the unitary whatsis.”

“The thing is, though, we can only perceive one branch of the wavefunction.”

“Maybe you can only perceive one branch. I have a very good nose. I can sniff into extra dimensions.”

“That would explain some of your mystery barking fits, but extra dimensions are a completely different thing. In this case, once there has been sufficient decoherence between the branches of the wavefunction that there’s no possibility of interference between the different parts, they’re effectively separate and inaccessible universes.”

“What do you mean, decoherence?”

“Well, say I did have a piece of steak here– stop wagging your tail, it’s a hypothetical– quantum mechanics says that if I dropped it on the floor, then picked it back up, there could be an interference between the wavefunction describing the bit of steak that fell and the wavefunction describing the bit of steak that didn’t fall. Because, of course, there’s only a probability that I’d drop it, so you need both bits.”

“What would that mean?”

“Well, the steak would probably produce some sort of interference pattern. I’m not really sure what that would look like. The point is, though, it doesn’t really matter. The steak is constantly interacting with its environment– the air, the desk, the floor–“

“The dog!”

“Whatever. Those interactions are essentially random, and unmeasured. These interactions lead to shifts in the wavefunctions of the different bits of steak, and those shifts make it so the wavefunctions don’t interfere cleanly any more. That process is called ‘decoherence,’ and it happens very fast.”

“How fast?” she asks, looking hopeful.

“It depends on the exact situation, but as a rough guess, I’d say about the same time as the lifetime of a bunny made of cheese. 10-30 seconds or less.”

“Oh.” She deflates a little. “That’s fast.” She still hasn’t caught a bunny made of cheese.

“Yeah. And once that decoherence has happened, the different branches of the wavefunction can’t really interact with each other any more. Which means, essentially, that the different branches become separate universes that are completely inaccessible to one another. Things that happen in these other ‘universes’ have absolutely no effect on what happens in our universe.”

“Why do we only see one branch of the whatchamacallit?”

“Ah, now that’s the big question. Nobody knows. A lot of people think this means that quantum mechanics is fundamentally incomplete, and there’s a whole community of scientists doing research into the fundamentals of quantum theory, and the various interpretations. Matt Leifer has a whole blog talking about this stuff.”

“We don’t like him. He said mean things about me.”

“It wasn’t so much mean, as dismissive. But that’s not the point. The point is, there’s no way you’re going to find steak under my desk, so please get out of there.”

“Oh. OK.” She mopes out from under the desk, head down and tail drooping.

“Hey, look on the bright side,” I say. “In the universe where a version of me dropped a piece of steak on the floor, there’s also a version of you.”

“Yeah. And you’re a mighty hunter, so you probbaly got to the steak before I could pick it up.”

“Yeah?” Her tail starts wagging.

“Yeah. So, in the universe where I dropped steak, you got to eat steak.”

“Oooh!” The tail wags furiously. “I like steak!”

“I know you do.” I save what I was working on. “Tell you what, how about we go for a walk?”

“Ooooh! Good plan!” and she’s off, clattering down the stairs for the back door and the leash.

She’s really a very silly dog.

1. #1 Mark
May 10, 2007

Dogs know some very serious tricks.

2. #2 Stuart Coleman
May 10, 2007

I suppose you’ve changed that old Einstein quip about explaining things to your grandmother into explaining them to your dog. Your dog seems to have fantastic physics and speaking abilities, much greater than any other dog I’ve met.

3. #3 Ron Avitzur
May 10, 2007

I’ve been trying to teach Spike to program, but so far he’s more interested in going for runs.

4. #4 Jonathan Vos Post
May 10, 2007

On the walk, she barked at a Schrodinger’s Cat…

5. #5 rat-terrier
May 10, 2007

My dogs go around measuring “no-steak” in the hopes that they’re forcing “yes-steak” somewhere else in an entangled system.

6. #6 Matt Leifer
May 10, 2007

“We don’t like him. He said mean things about me.”

Well, that was before I knew she was an expert on quantum foundations, or at least had about as good a grip on them as the majority of physicists :)

To clarify, I have nothing against dogs in general, just the concept of writing posts about them when they are not either discussing physics or being captioned in an amusing way. In any case, they don’t allow pets in my apartment building, so my dog related posts would be rather boring.

7. #7 Kate Nepveu
May 10, 2007

Another human-dog conversation: less intellectual, but, and I’m sorry, dear, a whole lot funnier.

8. #8 Trent
May 10, 2007

Wow, that was the most entertaining excuse for posting a crotch shot on one’s blog that I think I’ve ever read….

9. #9 N. Johnson
May 10, 2007

Smart and cute. I’d hang on to her.

May 10, 2007

she barked at a Schrodinger’s Cat

You shouldn’t have open that box.

11. #11 Skwid
May 10, 2007

I dunno, Kate…I guess your link might be somewhat funnier, but I’d rate the two conversations roughly equivalent in entertainment value as Chad’s gets points for novelty.

12. #12 Trent
May 10, 2007

Oh, and Kate’s right..this was an entertaining dialogue, but the one she linked to was downright heelarious, on a par with dogs in elk when it comes to side-splitting doggie stories.

13. #13 Sarah
May 10, 2007

what a GORGEOUS dog!

14. #14 patches
May 10, 2007

F-ing hilarious, and I learned something about decoherance as well :)

15. #15 lisa
May 10, 2007

omg. well, the sweet potato story might get funny + simplicity points, but yours definitely gets funny + originality + educational points. i was a philosophy major and i learned something, for pete’s sake. yay you!

16. #16 Mike
May 10, 2007

Not only a great post, but also picked up by BoingBoing (by way of Making Light) as well….

17. #17 Craig
May 10, 2007

I got a question for the pup…

If these are truly physical universes that are created anytime something might happen, where does the matter come from? Doesn’t the Conservation of Matter still apply?

18. #18 CR McClain
May 10, 2007

Brilliant post!

19. #19 Laurie
May 10, 2007

ok, considering I was on my way to bed and considering I have had three glasses of wine, I was very amused. Enough to actually follow the text and the gist and not get brain farts or stare blankly into the ether nor did I lose track. I have to say, I loved this piece (coming from my interest in …wait now…brain fart..have to scroll up…right: quantum physics/mechanics..) and having my own menagerie of cats who like to knead private parts of the body and lay on the warm bits, I did not see anything weird about the crotch shot. Keep up the great writing. Laurie

20. #20 Ed Martz
May 11, 2007

I guess sweet potato particles don’t move as quite quickly as bunnies made of cheese.

You realize that this series of conversations would make for a terrific book on the current state of physics.

21. #21 Bee
May 11, 2007

:-) nice

I remember one of Lee Smolin’s book has quite an amusing passage about gender confused quantum pets (forgot which book. might have been 3 Roads to QG). best,

B.

22. #22 swine
May 11, 2007

I once tried to explain economics to my cat, but she just ignored me and kept on typing

23. #23 Ook
May 11, 2007

Dude,

The mystery barking fits are a psychological event not physical.

Dogs are pack animals. They are instinctively built for constant company, not to mention constant activity. Life among humans denies them this for the greater part of each day, causing them stress/distress. Barking is one method of relieving this stress. It is such a common symptom that we have come to expect it of dogs.

24. #24 Lissy
May 11, 2007

awww, so cute! my puppies make the same face, though they’re not as smart :P

25. #25 Kathaclysm
May 11, 2007

Absolutely wonderful! If text-books were written in this style, I’d have paid a lot more attention in school. I agree, conversations with the dog about physics would make a great book in general. :-)

26. #26 Kathaclysm
May 11, 2007

Absolutely wonderful! If text-books were written in this style, I’d have paid a lot more attention in school. I agree, conversations with the dog about physics would make a great book in general. :-)

27. #27 Zenny
May 11, 2007

I live in a universe where I always eat at my computer desk, I always have steak on Friday, I usually drop a bit of steak on the floor every Friday, and I don’t own a dog but the cat won’t eat anything but catfood… So it goes…

28. #28 Zenny
May 11, 2007

I live in a universe where I always eat at my computer desk, I always have steak on Friday, I usually drop a bit of steak on the floor every Friday, and I don’t own a dog but the cat won’t eat anything but catfood… So it goes…

29. #29 Mohan
May 11, 2007

Awesome post man!

Absolutely funny.

One question. Is Everett’s Multiverse hypothesis really true?

30. #30 Keith
May 11, 2007

Please Don’t tell the dog about the universe where you all of a sudden decide to cook her for dinner.

31. #31 themacthinker
May 11, 2007

Oh boy, you are killing me with these thoughts.
Yes dogs have some pretty nice reflex and intuitions.
But one should not over estimate dogs. After all they are pets.
———
http://www.mostofmymac.com

32. #32 Shaze
May 11, 2007

I can’t believe Matt thinks what you do is less informative than his boorish, self-indulgent ramblings. I know for a fact that you speak to a much great audience, because you use a relative medium.

Real men have websites! :D

33. #33 Opie
May 11, 2007

Picked up by Digg.

34. #34 Ivan Minic
May 11, 2007

Priceless

35. #35 Dexx
May 11, 2007

aw dude,

u have a gorgeous dog

*pat pat* for the dog that is =/

36. #36 Shaze
May 11, 2007

I can’t believe Matt thinks what you do is less informative than his boorish, self-indulgent ramblings. I know for a fact that you speak to a much great audience, because you use a relative medium.

Real men have websites! :D

37. #37 steak
May 11, 2007

In a universe with no steak the cat is a mans best friend.

38. #38 Grasshopper
May 11, 2007

I reside in a time warp with two rescued dogs of mix breeding who apparently not only know physics but in their own way, they’ve been trying to teach me…they lose patience with me as I’m too dumb to comprehend their teachings and the subject matter, and I’m sure they use this computer when I’m not around… so much for higher human education..dogs 1, human 0.

39. #39 Jonathan Vos Post
May 11, 2007

My Dog: {Howling]

Me: Why are you howling at the Moon?

Dog: Thanks for asking. Wag, wag! [howls some more]

Me: No, really, why are you howling at the Moon?

Dog: That’s what you call it. Well. LOOK at it. It’s big! It’s bright!

Dog: But it has NO SMELL! No smell at all! That’s weird. That’s an anomaly. That’s outside the paradigm. Might be dangerous. Right? Anyway, this is our territory! [Howls some more]

Me: Okay, I get it now. Let me know when you want to go back inside. The Moon: LOOK at it. It’s big! It’s bright!

Dog: Glad you finally understand. [wag, wag]. Glad you’re in my Pack.

40. #40 Chas
May 11, 2007

How do I get to that universe wherein I am the master and he is the dog. In this one, it seems the other way round.

41. #41 BJ
May 11, 2007

Does that dog give you pleasure once in awhile in that position?

42. #42 Paul Levinson
May 11, 2007

Kudos, accolades, plaudits – depending upon which world you’re in.

43. #43 300redbulls
May 11, 2007

Love this. Make me think of my brother in-law who is a true life quantum professor. But he’s also a vegetarian, and israeli… and like most tremendous science minds out there, doesn’t have much sense of humor. All that said, I laughed out loud reading this.

44. #44 Jonathan Vos Post
May 11, 2007

Kudos to the very clever Dr. George Hockney, quantum computing expert, who figured out my dialogue, and emailed me as below.

===========

Aha. That explains why this appeared today. I was wondering about that.
— George

> Is the moon there when nobody looks?
> (Submitted on 10 May 2007)
>
> Abstract: In 1981, David Mermin described a cleverly simplified version of Bell’s theorem. It pointed out in a straightforward way that interpreting entanglement from a local realist point of view can be problematic. We propose here an extended version of Mermin’s device that can actually be given a simple local realist interpretation, and we argue that we still have no scientific reason to believe that the moon could possibly not be there when nobody looks.
>
> 11 pages, 8 Figures, 1 Table
> Subjects:
> Quantum Physics (quant-ph)
> Cite as: arXiv:0705.1477v1 [quant-ph]

===========

45. #45 Justin
May 11, 2007

Hey Chad! Didn’t know you had a blog. I found it from the 2nd page under “Top stories in 24 hours.” I enjoyed the post, I’m taking Quantum Chemistry right now, so I have a light grasp on what you are talking about. I’ll be working with the chemistry and physics departments this summer for research so I’ll see you around.

46. #46 Paul Levinson
May 11, 2007

Jonathan Vos Post: greetings! everyone – I haven’t seen Jonathan’s posts in years!! Talk about alternate worlds!

47. #47 Theriomorph
May 12, 2007

Okay, that was so cute it hurt.

48. #48 Jacob Bechtel
May 13, 2007

You stole my dog, Ginger. And you’ve ruined all the work I’ve done in teachng him classical Neutonian physics. Next thing you know she’s going to want to know about spooky action at a distance.

Thanks for nothing.

On the serious side, very nice article. Think I’ll send the link to the wife. She likes dogs, maybe she’ll grab the science.

49. #49 miss puzzlebrain
May 13, 2007

I just LOVE your posts about your pet dog :-) And this one is especially educating :-)

themacthinker: you simply cannot overestimate dogs

50. #50 Buğra Gökalp Okçu
May 13, 2007

51. #51 Brook Monroe
May 13, 2007

I don’t want to be an alarmist, but if that were my dog I’d have her checked for cataracts.

52. #52 hikingprem
May 15, 2007

Expand this. Weave it into a kids’ story for 6-10 year olds. Second book on chemistry from the perspective of physics for the same age group. Then another on math. All can feature your dog. You won’t need tenure to have a career and you’ll do more good for a lot bigger audience than being a professor. You’re on to something. It’s highly needed.

53. #53 Motorcycle Guy
May 15, 2007

“Wow, that was the most entertaining excuse for posting a crotch shot on one’s blog that I think I’ve ever read….” lol

54. #54 Kate Nepveu
May 15, 2007

Brook Monroe: it’s the equivalent of red-eye from flash photography on humans. Her eyes are brown.

55. #55 Mara Brown
May 17, 2007

Greetings,

Nice Posted! Its so very informative and knowledgeable for your visitors or readers.
Thank You for sharing.. Keep up the good work..

More Power,
Mara Brown

56. #56 pie
May 24, 2007

She has a much more interesting (and intellectual) life than my hound, Oliver. [Check out A Day in the Life of Oliver Basset here: http://www.piefilling.net/permalink.php?id=1083 ]

Great blog, by the way.

57. #57 Don R.
July 19, 2007

Very interesting Chad and entertaining! Dogs do know this stuff, they just choose not to apply it! 8^) There are some interesting implications here: Those things at absolute zero either exist across all dimensions or none. One might also suppose that black holes do too, as, according to the latest thinking, no information is lost at the event horizon.

Don

58. #58 Richie Savant
May 5, 2008

Wow – a dog that mis/undertands the quantum world. That’s amazing!
I like reading about physics, although there’s a lot in quantum physics I distrust. This is an informative, and entertaining blog. Well done! The fun aspect makes the learning easier.
Although, thinking about it some more, most if not all pet owners talk to their pets, and there’s no doubt the pets try to communicate back with us. Maybe one day when they can talk, or relay their thoughts to as in another manner, they may actually be able to un-entangle all this quantum stuff for us.

May 5, 2008

Wow – a dog that mis/undertands the quantum world. That’s amazing!
I like reading about physics, although there’s a lot in quantum physics I distrust. This is an informative, and entertaining blog. Well done!

Thank you.
I should also drop a note here to say that this will be coming soon(ish) to fine bookstores everywhere

60. #60 Hakan
December 16, 2008

Hahaha…Ver sweet ! I like dogs.

61. #61 Smoshing
November 17, 2010

“Wow, that was the most entertaining excuse for posting a crotch shot on one’s blog that I think I’ve ever read….” lol