Archive for the ‘Many-worlds Interpretation’ Category

I liked this post so much (from Sean Carroll at CalTech) I couldn’t help sharing:



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The big news of late is the discovery of gravitational waves from the very earliest time after the Big Bang.  What hasn’t been widely reported is that this represents a huge bit of indirect evidence that multiple universes really do exist.

Here’s more:

Big Bang Discovery Opens Doors to the “Multiverse”.


(Harvard University / EPA)

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The conventional wisdom among people who know a little bit of quantum mechanics is that quantum mechanics is weird.

The conventional wisdom is wrong.  Quantum mechanics is not weird.  Interpretations of quantum mechanics are weird.

My thinking on this has changed over the years.  In high school I read everything I could about the “weirdness” of our universe: Schrödinger’s cat, wave-particle duality, the collapse of the wave function, many-worlds theory, the Heisenberg uncertainty principle.

Then a strange thing happened: I went to college.  I studied physics.  And guess what?  None of that stuff gets more than the briefest mention in the physics classroom.  Why?

Because those things are beside the point.  Quantum mechanics works.  How you interpret quantum mechanics is your problem.

There’s a dichotomy here which is the source of most people’s confusion.  Theories are different from interpretations of theories.  A theory is a mathematical model that allows us to make predictions.  An interpretation is a philosophical construct that allows us to sleep at night; it is a squishy heuristic that helps us unimaginative humans make sense of the math before us.  Theories get things done.  Interpretations never helped anybody, not really.


An abandoned shack.

Let’s say that in an abandoned shack you discovered a notebook with the word “PHYSICS” written by hand over and over, thousands of times, apparently filling every page.  You haven’t looked at the last few pages, but your theory is that these pages will also have the word “PHYSICS” written out.  Each time you turn a page, your theory is validated: “PHYSICS” is there, as predicted.

Next to this notebook is another that looks just like it.  You open the first page, and are not surprised to see “PHYSICS PHYSICS PHYSICS” again.  What’s going on?  Did some crazy person live in this shack?  Such speculation doesn’t really matter, since you can still hypothesize that “PHYSICS” fills this notebook as well.  In fact, you have a stronger theory: every notebook in this shack is filled with “PHYSICS”.

You perform an experiment: you turn the page.  “PHYSICS PHYSICS PHYSICS”.  The experiment supports your theory.  You find more notebooks; same results.  Every notebook in the shack is filled, apparently, with “PHYSICS”.  But guess what?  There are dozens of possible interpretations.  And in the absence of further data, you can never know which one is “correct”.

Maybe the shack was once inhabited by a crazy person, who wrote “PHYSICS” precisely 250,001 times in a futile attempt at summoning Cthulhu from his ancient slumber.

Maybe a student misspelled “physics” on a test, and her cruel teacher punished her in the most depraved way possible.

Maybe Matt Damon filled the notebooks, in a method-acting attempt to get into the mindset of an OCD scientist.

Which of these interpretations is the “truth”?  Without further data you cannot really say.  Arguing about which is right and which is wrong is futile at best, and annoying at worst.

Of course, new data may turn up.  We might find out that the notebooks are 75 years old, ruling out our Matt Damon interpretation.  That interpretation is no longer a valid interpretation of the data.

Which brings me to my next point: there is no official arbiter of what constitutes a theory versus what constitutes an interpretation.  Different philosophers and scientists have used the words differently at different times.  All you can hope for is that a particular author is consistent in his/her use of the terms.  I personally use the word “interpretation” to describe competing theories that cannot currently be differentiated by any known scientific experiment.  If two different interpretations make different, testable predictions, then they are promoted to being totally different theories.  (Caveat: others use the words slightly differently.  Deal with it.)

So what does this have to do with quantum mechanics?

Quantum mechanics is an entirely mathematical theory.  Its postulates are logical, concise, and powerful.  We can use quantum mechanics to invent cell phones, computers, lasers, and iPods.  Quantum mechanics doesn’t care if you “understand what it really means”, or not.  It is arguably the most successful and powerful theory to come out of the 20th century.

Now, the mathematics of quantum mechanics are abstract and hard to visualize.  Nevertheless, people insist on trying to visualize anyway.  And the result is all kinds of weirdness: Schrödinger’s cat, wave-particle duality, the collapse of the wave function, many-worlds theory, the Heisenberg uncertainty principle.  These ideas are all mental hoops that people have jumped through to explain some unambiguous, concrete, abstract linear algebra.  The math is just math, and it works; what it means is anyone’s guess.

There’s no crying in baseball, and there’s no philosophy in quantum mechanics.


There’s no philosophy in quantum mechanics!

Don’t like the many-worlds interpretation?  Fine.  Be a Copenhagenist.  Don’t like pilot waves?  Great.  Stick to your pet idea about superluminal communication.  Just remember that all of these competing interpretations make the exact same predictions, so for all practical purposes they are the same.  Some people go so far as to say, just shut up and calculate.  [Note added 3-19-14: there are problems with pilot wave theories that in my view rule them out as being a valid interpretations of quantum mechanics.  But there are hoops people can jump through to try and “force” pilot wave theories to be consistent with, say, Bell’s theorem.  My broader point is that there are multiple interpretations of QM and that all have followers to this day, but that none of the interpretations really have any distinct implications for our lives.]

I don’t usually go that far.  I actually think that the many-worlds interpretation is a testable theory, not an interpretation (hence the name of this blog).  I think many-worlds is falsifiable.  (If we ever observe a wave function collapsing, then many-worlds will have to be discarded.)  But I don’t think that will happen: many-worlds is too elegant, and too powerful, to not be true.

But we’ll see.

If you think it’s absurd that a cat can be alive and dead at the same time…if you think that it’s crazy to hypothesize other universes…if you think that God does not play dice with the universe…don’t blame quantum mechanics.  Blame the philosophers who try to interpret it.

Quantum mechanics works.  Otherwise, you’d be reading this on an actual piece of paper.

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WARNING: Spoilers abound!

Do not read further if you haven’t seen the wonderful, awesome The Lego Movie!

There are two kinds of good movies.  The first kind is a movie you enjoy while watching; you appreciate the acting, the writing, the set design.  You come out of the theater thinking, that was good.  I’d recommend that.  In the past six months, I’ve seen many of these so-called Good Movies of the 1st Kind.  Examples include The Dallas Buyer’s Club, Rush, Captain Phillips, the second Hobbit movie, and the second Hunger Games movie.  I liked them all.


A metaphor for the everyman

But then there is a Good Movie of the 2nd Kind—a movie which leaves you jacked up on adrenaline, with a big goofy smile on your face, and ideas buzzing around the inside of your head.  A movie where you come out of the theater thinking, when am I going to go see that again?  I need to see that again.  What just happened?

Don’t get me wrong; a GM2ndK is not necessarily a happy, fun movie.  Saving Private Ryan was for me a GM2ndK; for weeks I could not get the first half hour (Omaha Beach) out of my head.  Schindler’s List was also a GM2ndK.  So was A Clockwork Orange, and Magnolia, and Paths of Glory.

So, too, The Lego Movie.

Unless you’ve seen the movie, you won’t believe it.  You won’t have the context, the conceptual framework, the raw materials from which to grasp the idea: that The Lego Movie is as profound and philosophical as any movie you’ve (probably) ever seen.

Oh sure, the movie is beautiful to look at.  The animation is unique and charmingly quantized and pixilated.  The pace is frenetic, action packed.  The worlds depicted are stunning, goofy and marvelous.  The jokes are non-stop: I laughed out loud two or three times a minute for 100 straight minutes.

So, I liked the movie.  But this post wasn’t meant to be a movie review.

My broader point is that the movie resonated with me, personally, philosophically, because it so closely matches my own world view.


The message of the movie is that there are two (seemingly) diametrically opposed ways of playing with Legos.  In the first camp are the conformists, who follow instructions to the letter, never have an original thought, and prefer a world of rigidity and order.  The head conformist is Lord Business, who wants to spray Krazy Glue on every Lego in the universe so that nothing ever changes.

To me, Lord Business represents the Abrahamic God, the God of the Old Testament.  The God of one single, rigid construction, exactly the way He designed it.  Don’t go against God’s plan (or the plan of Lord Business).  There is only one way the world (or worlds) can be, and if you oppose that plan—if you don’t follow the instructions—then you have committed heresy.  You will be melted.  There’s no place for you in such a conformist world.


The God of Abraham

The other way of playing with Legos is the way children play with them: with unbridled imagination.  Sure, you can buy a Millennium Falcon Lego set and construct it as the instructions describe.  But you can ignore the instructions, too, and your play is just as valid.  Want to put Batman on the Millennium Falcon?  Sure; go for it.  Want to have Superman and Gandalf team up to battle a robot pirate?  Why not?  If you can imagine it, then you can do it, just as long as some adult doesn’t come down and spray the pieces with glue.

That’s what organized religion does: it sprays us with glue.

To me the world of organized religion is limiting, stifling.  The idea that there’s an omnipotent being that controls every aspect of everything is not comforting to me; it is horrifying.  Theologians mumble about free will and wave their hands reassuringly, but what good is free will if you’re still constricted by God’s plan?  If God has everything worked out, then you’re stuck to the world with Krazy Glue; your life is supposed to be lived in a single way and you’ll never be able to ignore the instructions.  You’ll never get to ride Unikitty into Middle Zealand and have tea with the Green Lantern.  Sorry, but you’re an average, run-of-the-mill Lego piece and that’s all you’ll ever be.

But imagine: suppose that there are an infinite number of universes, each with its own parameters, its own structure.  In such a multiverse, anything you can imagine is true.  There are still rules (each universe obeys its own laws of physics, just as Legos cannot escape their own block-like, quantized nature) but beyond those rules, anything goes.  And imagine there is no Lord Business that commands you to think in a certain way.  Imagine if you had the freedom to do as you will.

Here’s a table, to make the metaphor(s) more explicit:

In the movie… …is a metaphor for
A Lego person a human
The Lego world you’re in the universe you’re in
All of the possible Lego Worlds the multiverse
Quantized nature of Lego blocks the laws of physics
Krazy Glue God’s plan
Lord Builder (the Father) a rigid conformist deity
The Child the deity that any of us could be, using imagination
Instructions Rigid moral codes
“Everything is awesome” “Everything is awesome”

We are indeed trapped in the universe that we find ourselves in (we can’t get away from our quantized nature, alas) but we can at least imagine the other worlds, and dream, and find inspiration from them.  We can live our lives the way we like.  This isn’t anarchy; it’s freedom.  This world view doesn’t preclude morality; we shouldn’t put our hands into other people’s Lego Worlds, and mess the pieces up, and break their Lego constructions.  But we should be able to look at other people’s constructions, and value them, even love them.  If you want to have Batman marry Han Solo, and have them ride off into the Old West sunset (riding on Unikitty, no doubt) then I shouldn’t judge.  There is no Lord Business.  There is only what you can build, and what I can build, and what you can imagine, and what I can imagine.  We should not judge each other but embrace each other’s constructions.  Everyone’s trapped by the laws of physics, but no one’s trapped in their own minds; there are no laws that can ever force our imaginations to conform.

If God exists, then he’s a child, and wants us to play in all the worlds, and be free.  He wouldn’t even own a tube of Krazy Glue.

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One of the most common criticisms of the many-worlds interpretation (MWI) of quantum mechanics is that it is absurdly complicated, and therefore violates Occam’s razor.  Most people’s first reaction, on hearing of MWI, think that the theory is (to quote Martin Gardner) “bizarre”, “monstrous”, “fantastic”, “radical”, “appalling”, “nonsense”, “frivolous”, and “low”.  And many people seem to think that theorists who ascribe to MWI have their heads in the clouds to believe such nonsense.  MWI seems to be taken, in fact, as evidence that physics has lost its way—as if (supposedly) blind belief in such frivolity is indicative of a philosophical rot that pervades theorists like me.


Theoretical physics today, to some

There are so many refutations of such criticisms that I don’t know where to start.  First of all, although MWI is popular, it is by no means canon, and I daresay that a majority of physicists reject it still.  So there!  We’re not all sheep.  Still, MWI has become almost mainstream (especially with cosmologists) so maybe it’s the cosmologists and the ivory-tower theorists who should be singled out for criticism?

People who think this have probably never met a theoretical physicist before in their life.  Getting such people to agree is like herding cats; every theory one puts forth (in a journal article or in a conference talk) is debated, criticized—dare I say, attacked.  And that is as it should be.  There is not, contrary to popular belief, some holy scripture that every theorist quotes verbatim.  We are all different, and have basically come to interpret quantum mechanics in our own personal way…not at the behest of some lord on high.

How do I know this?  Because I was never taught about interpretations of quantum mechanics.  Ever.  Everything I know about such things, I learned on my own since graduation.  Thinking of taking a quantum mechanics class at your local university?  Guess what: they will probably not talk about MWI, or the Copenhagen interpretation, or Schrodinger’s f***ing cat.  Why not?  Because those are philosophy topics, not physics.  You can do quantum mechanics without ever interpreting a single thing.  There’s no crying in baseball, and there’s no philosophy in quantum mechanics.  It is a purely mathematical theory, that undeniably works, and most people just leave it at that.  The idea that thousands of physicists subscribe to one particular world-view just because they constitute a single monolithic conformist society is ludicrous.  Invite a physicist to lunch if you don’t believe me.

But I still haven’t addressed the idea that MWI is obviously absurd.  It is absurd, right?  I mean, come on!

But wait.  Let’s think back to the Copernican revolution.  It’s obvious that the Earth is stationary, no?  I bet people thought that Copernicus and Galileo and their ilk were bizarre, monstrous, fantastic, radical, appalling, nonsensical, frivolous, and low.

And what about the idea that there are billions and billions of galaxies, each with billions and billions of stars?  We forget now, but this idea was radical when first presented and wasn’t settled until the 1920’s.  Why are we OK with a multiplicity of stars, but not a multiplicity of universes?  Why aren’t people complaining about the absurd notion (fact) that there are more stars in the observable universe than there are grains of sand on Earth’s beaches?



So, Occam’s razor.  MWI just seems to have too much baggage, right?  For a lot of people MWI is too high a cost to bear to have a mathematically simple interpretation of quantum mechanics.  And let’s be clear: MWI is a simpler theory than (say) the Copenhagen interpretation (CI).  For you can start with three postulates, and add a fourth about wave-function collapse, and you get CI.  Or you can start with just three, and say nothing of wave-function collapse, and you get MWI.  Which interpretation seems simpler now?  MWI is a consequence of accepting the three basic postulates of quantum mechanics.  If you don’t like that, then you must introduce a fourth postulate ex nihilo to make yourself feel better.

But wait! you say.  10100 universes doesn’t seem simpler.  It’s a huge number!  It’s ridiculous!

OK.  You wanna go there?  I’ll turn the argument around.  By that rationale, you probably believe that there are only a finite number of integers, because any finite number is simpler than infinity.  There.  That makes sense, right?

The truth is that an infinite set is often simpler than a single member of that set.  Take the natural numbers.  I can write a computer program in BASIC that writes every natural number.  Here it is:

10           x=1

20           PRINT x

30           x=x+1

40           GOTO 20

On the other hand, if I want to print out the number


then my computer program is longer:

10           PRINT “5679200359662711389685023885761799”

Count the keystrokes.  The second program requires more typing.  And note that the first (simpler) program will eventually print this number—the long arbitrary program is “contained” within the first.

In information theory, the information “content” of something is related to its algorithmic complexity—roughly speaking, how easy it is to write a computer program that “specifies” the object.  By that measure, “all the natural numbers” is a simpler concept than the number


Similarly, “all possible universes” is a much simpler concept than one specific arbitrary universe.  You want to recreate this universe?  Good luck…you’ll have to specify the position and momentum of every particle in the universe.  That’s a long computer program.  However, if you just say “create all possible universes” then eventually this one will pop up…

Do I believe in the MWI?  Yes.  Why?  It’s not because I was indoctrinated into such belief; I don’t think a single professor in graduate school ever mentioned MWI.  It’s because I’ve looked at the evidence over a number of years, and (tentatively) decided that it fits the data best.  That is the only reason to ever believe something, ever.  It fits the data best.  But I stress that my conclusion is tentative because, hey, it’s science.  There is no dogma.  There is just stuff that we are 99.44% sure of.

Like evolution by natural selection, or heliocentrism, or the existence of ghosts.  I mean, seeing’s believing, right?

               [Note: more Americans believe in ghosts than evolution.  Sigh.]

If you enjoyed this post, you may also enjoy my book Why Is There Anything? which is available for the Kindle on Amazon.com.


I am also currently collaborating on a multi-volume novel of speculative hard science fiction and futuristic deep-space horror called Sargasso Nova.  Publication of the first installment will be January 2015; further details will be released on Facebook, Twitter, or via email: SargassoNova (at) gmail.com.

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I thought I would re-post this excellent discussion of the many-worlds interpretation by David Yerle:

Why I Believe in the Many-Worlds Interpretation

I agree with him 100%, and he says it better than I ever could.  The crux of the argument is this: it depends on the book you’re reading, but as a practical matter there are typically 4 postulates of quantum mechanics (about the primacy of the wavefunction, Schrödinger’s equation, measurements being Hermitian operators, and wave function collapse).  Many worlds is what you get when you reject the unmotivated “wave function collapse” postulate.  It is a simpler theory in terms of axioms, so obeys Occam’s razor.  If multiple universes bother you, think of how much it bothered people in the 1600’s to contemplate multiple suns (much less multiple galaxies!)


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When I was young, I once looked at a box of cereal and had an epiphany.  “Why is that cereal there?”  A universe of unfathomable complexity, with 100,000,000,000 galaxies, each with 100,000,000,000 stars, making 10,000,000,000,000,000,000,000 possible solar systems with planets around them—all that, and I’m sitting across from a box of Vanilly Crunch?


Since that existential crisis, I’ve always wondered why there was something instead of nothing.  Why isn’t the universe just one big empty set?  “Emptiness” and “nothingness” have always seemed so perfect to me, so symmetric, that our very existence seems at once both arbitrary and ugly.  And no theologian or philosopher ever gave me an answer I thought was satisfying.  For a while, I thought physicists were on the right track: Hawking and Mlodinow, for example, in The Grand Design, describe how universes can spontaneously appear (from nothing) according to the laws of quantum mechanics.

I have no problem with quantum mechanics: it is arguably the most successful theory devised by mankind.  And I agree that particles can spontaneously create themselves out of a vacuum.  But here’s where I think Hawking and Mlodinow are wrong: the rules of physics themselves do not constitute “nothing”.  The rules are something.  “Nothing” to me implies no space, no time, no Platonic forms, no rules, no physics, no quantum mechanics, no cereal at my breakfast table.  Why isn’t the universe like that?  And if the universe were like that, how could our current universe create itself without any rules for creation?

But wait—don’t look so smug, theologians.  Saying that an omnipotent God created the universe doesn’t help in any way.  That just passes the buck; shifts the stack by one.  For even if you could prove to me that a God existed, I would still feel a sense of existential befuddlement.  Why does God herself exist?  Nothingness still seems more plausible.

Heidegger called “why is there anything?” the fundamental question of philosophy.  Being a physicist, and consequently being full of confidence and hubris, I set out to answer the question myself.  I’d love to blog my conclusions, but the argument runs about 50,000 words…longer than The Great Gatsby.  Luckily for you, however, my book Why Is There Anything? is now available for the Kindle on Amazon.com:

rave book

You can download the book here.

You might wonder if my belief in the many-worlds interpretation (MWI) of quantum mechanics affected my thinking on this matter.  Well, the opposite is true.  In my journey to answer the question “why is there anything?” I became convinced of MWI, in part because of the ability of MWI to partially answer the ultimate question.  My book Why Is There Anything? is a sort of chronicle of my intellectual journey, one that I hope you will find entertaining, enlightening, and challenging.

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