Physicist: There is no new energy or matter (or even new universes), it’s just that how it’s distributed depends on who’s asking, and in what “world” they’re doing the asking. The important thing is: the universe doesn’t split or spawn new universes.
For those not familiar, here’s the crux of the problem. If you don’t interact with (measure) things they behave like waves and can be in many places and do many things. But when you do interact with a thing, it suddenly seems to only be in one state. The double slit experiment is the classic example. There are a couple of ways to explain this: the Copenhagen interpretation, psychic powers, Spaghetti Monsters, the Many World Interpretation, and a few others that are a little far-fetched.
If you go online (or read some kind of book or something) you generally find the Many Worlds Interpretation presented as the universe “splitting”. Something along the lines of “everything that can happen will, just in different universes”.
From howstuffworks.com: “When a physicist measures the object, the universe splits into two distinct universes to accommodate each of the possible outcomes.”
From about.com: “…every time a ‘random’ event takes place, the universe splits between the various options available. Each separate version of the universe contains a different outcome of that event. Instead of one continuous timeline, the universe under the many worlds interpretation looks more like a series of branches splitting off of a tree limb.”
Quick aside: I’m about to talk about why this is wrong, but don’t take that as a criticism. The “splitting/branching” thing is about the only narrative anyone ever hears, so I’m not knocking the fine and hard-working people of “about” and “howstuffworks” (or the authors of the hundreds of other examples out there). Much respect.
So, supposedly every time any kind of quantum event happens that could have one of several results (which is essentially every moment for every thing, which is plenty) the entire freaking universe splits into many universes. But, the universe contains a lot of energy. Like, even more than the U.S. uses in a year. So, whence does this energy come?
First off, in a not-really-explaining-anything nutshell: the universe doesn’t branch so much as it meanders and intertwines. This isn’t an answer to the energy question, but it’s worth mentioning.
If you want a picture to work with, rather than thinking about the universe as an ever-branching tree, think of it as an intertwining (albeit, very complex) rope.
The many (like: many, many) different versions of the universe branch apart, and come together all over the place. That is; one event can certainly lead to several outcomes, but in the same way, several causes can lead to the same event. Everything the could happen will happen (given the present) and everything that could have happened did happen (given the present). You can think of this as un-branching, or branching into the past. Either way. The Franson experiment, which demonstrates a single photon emitted at two different times in the past interfering with itself (isn’t that weird?), is one of the most beautiful examples of this “backward branching”.
That doesn’t answer the question, but it does sorta help set the stage for the universe being more complicated than just “splitting”.
The way that energy is conserved depends on the context of the question. Say you’ve got a particle and at some point, for whatever reason, it finds that it has to take one of two paths. There are a lot of reasons this could happen, but the particulars aren’t important. The cases to consider are: 1) you measure it taking one of the two paths and 2) you don’t.
Although the details change, the total amount of energy stays constant from all perspectives. Both from inside the system (left) where all the energy is concentrated on one of the possible paths, as well as when seen from outside (right) in which the particle and its associated energy can be distributed among the different paths.
If you’re “caught up” with the particle in question, maybe by observing it / interacting with it, you find that it only takes one path (More accurately, each of the different versions of you see each of the different versions of the particle taking one path). You’ll see the particle start out, “choose” between the upper and lower paths (a random choice), and continue on. From your perspective the total energy never changes. You may have a sneaking suspicion that there are other quantum worlds, but you never (none of your versions ever) actually see a problem. To have a problem you’d need to be able to see more than one of the particle’s “worlds”.
But that’s no problem! Seeing a particle in multiple states (each of which is a different “world” to the particle) is the oldest trick in the quantum book. This, by the way, is one of the great weakness of the language involved. You’d think that “worlds” and “universes” would have to be completely separate. But while the different states of the particle each see each other as being in different worlds, for something that sees the super-position of all those states (for example, something that sees the interference fringes in the double slit experiment) they seem to be in the same world.
When a particle (or whatever) is in multiple states its energy and matter is distributed among those various states. In the two-equally-probable-paths example above, half of particle’s existence takes one path and half takes the other. Likewise, its energy and matter are divided among the paths.
Although you can’t measure “half a particle” (a particle’s nature is to be indivisible), you can show that particles often need to be in multiple states (so their existence can be spread out), and you can even calculate and measure how much of each particle must be taking various paths. Again, the double slit experiment is an excellent example.
So, in the two-path example, a particle comes along with some amount of energy. When it has a choice of two paths it takes both. The energy of the particle is divided in proportion to the probability of the path taken. So, for example, 50% chance of each path means equal division of the energy and matter of the particle. Before the fork all of the energy is on one path, and afterwards, despite the fact that the particle is behaving as though it’s in two places, the same amount of energy is present, just spread out.
It may seem deeply weird to say that, but you could argue that no particle keeps all its matter/energy/existence in one place at a time. For example, if you look at an electron in an atom you find that it’s smeared out around the nucleus in the form of an “electron cloud”. Electrons don’t orbit atoms like planets around the Sun, they “wave” around the nucleus like vibrations in a ringing bell.
That, and other terrible similes, will be included in my upcoming book, “some thing are like these other things, but different, y’know?: a book that’s like a collection of similes”.
Each electron in an atom forms a "cloud" around the nucleus. Literally, it is in every possible position (some more than others). The nucleus itself takes the form of proton and neutron clouds, they're just much, much smaller.
For “uncertainty principle” type reasons, electrons (and everything else) always exist in a “cloud” of locations, all at once. You can say “there is an electron around this atom” and you can say “the energy and matter of the electron is around this atom”, but there’s nothing you can say past that. The existence of the electron, and everything else about it, is spread out.
Each different version of a thing, and every “parallel world” may see itself as holding all of its energy and matter, but from an outside perspective (where the “many-worldness” becomes important) it’s just part of a greater whole. Either way, energy is always conserved. So, while it’s fun to talk about “other quantum realities” and “different universes”, it’s more accurate to say that everything is happening in one universe. One, stunningly complex, weirdly put together, entirely counter-intuitive universe.
Reminds me of http://xkcd.com/895/
So, im curious. is there an infinite number of universes that exist? or simply an WHOLE LOT?
also, do universes split at every smallest increment of time? (there IS a smallest increment of time possible, right?) or just when one of those quantum experiment things happen (when an electron or whatever needs to choose what path to take)?
The point of the post is that there aren’t universes splitting off, so much as there’s just one that’s terribly complicated. Even the splitting, and whether a split even happens, depends on how related you are to the system in question (the particle, or Cat, or whatever).
If you’re asking about whether the total numbers of quantum states the universe can be in is finite, then there’s not much to say.
Some physicists say it’s finite, some some infinity, and some even argue about what kind of infinity!
Great post, but like string theory I only understand it enough to know that it is awesome, not enough to comprehend exactly what is going on. I get the gist of it though, and that’s what matters.
By the way, the sitcom Community recently did an episode based on the “many worlds” theory, comparing seven alternate timelines of the main characters. Not a lot of science, but definitely worth a watch:
http://www.hulu.com/watch/285095/community-remedial-chaos-theory
I was thinking about posting that exact link!
I’ve seen many references in documentaries about the MWI but, as it sometimes happens, the metaphors and examples in these ‘shows’ sometimes makes things even more difficult to understand, so here’s a short question: Does the MWI apply only to quantum particles or also to macroscopic objects? Is it actually true that for MWI proponents there’s ‘literally’ a copy of me that hasn’t read this article? Or one whole world of people that live “today” without electricity? One whole galaxy where non-human descendants of reptiles evolved here on earth are already traveling to the stars? And so on… By the way… Could there be a whole universe that “started” 10 billion years ago instead of 13.7?
The universe “splits” whenever there is a quantum interaction. But it is more accurate to describe it as the way the entanglement of particles spreads.
As crazy as it makes us sound: yes. If there’s some way for it to happen, then it does. Space dinosaurs and all.
It’s worth mentioning that it doesn’t matter. Whenever you want to figure out the probability of something happening, what you’re really doing is figuring out the probability of that thing given the way the world is now. So the probability of seeing space dinosaurs given the world we see is zero.
Similarly, for Captain Bigteeth of the star ship USS Notextinct, the probability of seeing us (given that the rise of mammals thing never happened) is also zero.
It’s an open question whether other quantum universes could have started at different times. I don’t think they could, but I can’t back that up.
The universe doesn’t split at all, it just supports a very complicated reality.
While there isn’t necessarily a smallest unit of time (although that is an open debate), time scales that are small enough are useless. Basically, there’s no way to distinguish order in any useful way when the time between two events is less than (around) the Planck time. But it’s not a hard and fast line.
It is absolutely better to describe “splitting” in terms of entanglement!
Hey, Physicist! Thanks a lot for answering!
Since the year I’ve been a physics “enthusiast”, this (MWI) is the one thing I don’t think I’ll EVER come to terms with. Paradoxically, many physicists seem to think it’s the best way to understand/explain many other quantum weird phenomena, if I understood your earlier post correctly. (http://www.askamathematician.com/2010/10/q-copenhagen-or-many-worlds). If ever the MWI is proven right, that would be an existential shock that would make previous such shocks (By Copernicus, Einstein, Hubble, Bohr, Heisenberg et al.) look like nothing in comparison.
Another short question/suggestion. Speaking of parallel things… did you ever thought of making a Youtube channel? I absolutely LOVE channels such as sixtysymbols, 1veritasium and others, but they rarely answer people’s questions or address problems as deep as those in this blog. Also (sadly) it’s a great way for approaching those people that see a few blocks of text and say “BBBOOOOOOOOOORING” and then run away.
Personally, I think the MWI is about as proven as it can get.
We do have a channel, but there isn’t just a heck of a lot in it.
http://www.youtube.com/user/AskAMathematician
Absolutely hilarious phony book title!
Additionally, I found this post useful but I certainly feel I read a lot more about MWI to come close to understanding it. I do know that Deustch supports it, but he also says that only 10% of professional physicists do. Are you able to clearly explain why this is the case? (if it is indeed the case)
Thank you!
Although (with a lot of pondering) MWI helps people understand quantum physics, it isn’t necessary or even useful when it comes to actually calculating stuff.
I suspect that most physicists, when pressed, wouldn’t be willing to say that they believe in any particular approach to quantum mech.
Since it’s seems you are not going to answer to my official question, I might aswell try to get an answer here in the comment section.
How can you claim that MWI is “Proved” when you can’t even make sense of the Born Rule (which is the entire reason to postulate unobservable nonscientific parallel universes to begin with?)
Wibbily-wobbily, timey-wimey stuff…. got it, thanks.
Many Worlds is just as ludicrous as metaphysics gets.
What seems to escape its proponents is we just so happen to live in the only coherent world?
You see, we dont live in a world where if I shoot a gun randomly in the sky it could get deflected by a Babe Ruth home run, skim off a birds beak, go through a crashing plane’s engine and get shot out the back to hit the President.
Yet these types of absurdities would be just old hat if everything that could happen happened and they would happen repeatedly in every single world.
We dont get to be in the world that makes sense.
We would see things like heads or tails coming up a thousand times in a row, Hitler naked on a pogo stick, and all probability would go out the window. How about the world where every single person got 2+2 wrong? There could be no truth is the many worlds philosophy–and thats what it is–a philosophy postulated by people who have no business straying out of the scientific world into the world of logic. Im sorry, but its just embarrassing, amateurish, philosophy.
The very point that Quantum theory can make predictions with excellent accuracy shows the many worlds view to be just another lame philosophy proposed by scientists to escape the fact that our will is our own, our choices are our own and we will be thoroughly responsible for them in the end.
While MWI does mean “everything that can happen does”, it doesn’t mean everywhere always. For example, say you give everyone in the world a different number from 1 to 7,000,000,000. You can definitely say “somebody out there has the number 10″, but you can’t say “everyone out there has the number 10″.
More than that, probabilities (and thus predictive powers) are maintained. You can definitely say “if I meet someone on the street, there’s a 10% chance their number will end with a 7″, but you can’t say “if I meet someone on the street, there’s a 100% chance that their number will be 1,023,675,899″.
MWI isn’t much more than the conclusions physicists have drawn from experiments over the years, and then applied generally. Basically, there doesn’t seem to be any limit, either theoretically or experimentally, to how big an object can be while still exhibiting super-positions (“many-ness”).