But what are the worlds?
My feeling is that Max Tegmark has it right. Everything is mathematics.
I wish I understood it better.
Me too but... It would still be some form of mathematics as soon as you tried to write it down in a neat, precise way for others to understand it. Maybe exotic math, but still math :p
Saying that sure, they evolve like ours, and sure they affect ours, but even so they are not real - that is I suppose one stance, but then you are getting pretty close to solipsism.
No, you'd get something like Bohmian mechanics, or Rovelli's relational interpretation. Which is my point: you can only take this as evidence of other worlds if you basically smuggle those assumptions in.
Is there any hope that one could actually do this? The article mentions that large systems may be self-observing (via gravity).
One location in the latent space of a latent diffusion model is a view into a universe that is as real as ours. That half cat, half dog monstrosity you accidentally created. It exists as a drawing, or as a physical mass of flesh, with every possible back story as to how it got there. And also every possible future.
edit- brain fart
Because we live in the macro world, it feels like a single unitary reality is simpler, but actually, the MWI makes fewer assumptions. So I would turn that around and put the burden on the other theories to show that collapse is real, the default position should be MWI.
This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. That is, the Schrodinger equation doesn't actually predict that a particle has some amplitude here and some other amplitude there, as is often presented; instead, it predicts that it is described by some vector which can be decomposed in many different ways. You can say it has some amplitude X here and some amplitude Y there, but with any 2 points in space-time (adjusting the amplitudes). Or, it can have some combination of position and spin with amplitude X, and some other combination of position and spin with amplitude Y. You can choose any basis you like for the measurement, and you will get the corresponding answer.
But, for MWI to actually predict experimental results (and the classical world we live in) you not only have to choose to look at a single element of that basis, but you also have to believe that the classical basis is somehow preferred.
It does predict it, this decomposition is called decoherence, where a classical state splits into a superposition of several different classical states.
No, that's not what decoherence is. Decoherence is the spread of entanglement over a very large number of untrackable degrees of freedom (usually referred to as the "environment"). This makes interference effects unobservable. But decoherence itself does not involve any "splitting"; the entanglement that decoherence spreads over a very large number of untrackable degrees of freedom has to already be there before decoherence can act on it.
And yes, spread of entanglement does mean splitting. Entangled state is not factorizable, because all states in it are split. This splitting is the result of splitting of the initial state.
No. The 100 atoms is the largest molecule that we can do experiments on without having decoherence happen and ruining our attempts to observe interference.
The number of degrees of freedom in the environment is many orders of magnitude larger, something like 10^30 or more for a typical experiment.
>The many-worlds interpretation implies that there are most likely an uncountably infinite number of universes.
The MWI says that there is one single universal wave function, which evolves in time by unitary evolution forever. That is one universe, not an infinity of them. It is just one universe that is nothing like what we think we perceive.
Wanna join? You can be number 2 thus have second dibs at the buffet.
What conditions are these?
Getting to that point can take several years. A quicker option seem to be drugs, based on conversations I had with friends, but I never wanted to artificially taint my perception, so I did it the hard way. My findings are that while there is no fate, there exist enough aspects in universes similar enough to yours, but perhaps chronically shifted, that you can learn from their mistakes. This is known as instinct, "guardian angels", premonition, deja-vue, etc. Good luck.
If you could travel between these many earths, you could even end up in one - let's call this mythical land "Australia" - where South was up!
Sounds a bit crazy but some people believe it could really exist.
The collapse amounts to just setting some terms to zero.
Title article is literally about trying to test those theories experimentally.
Here's the best poem ever written, or that will ever be written:
Roses are red
Violets are blue
MWI stinks
And so do you.
I hereby accept my position as God Poet of the Universe.
The MWI is a simpler theory than other interpretations because it does not require "collapse" to be a physical process. The "realness" of the other worlds is untestable, but also not part of the theory.
"unreal" MWI should be the null hypothesis given what we know to be true about quantum mechanics. If we find evidence that collapse is a physical process then we can reject it, but otherwise it makes the fewest leaps. At the moment the Copenhagen intepretation is taught instead, which is a problem. To quote wikipedia:
> There is no uniquely definitive statement of the Copenhagen interpretation
And
> the device used to observe a system must be described in classical language, while the system under observation is treated in quantum terms
In other words, it does allow you to predict the result of an experiment, but we know it can't be right because it's impossible to formalize without building this "classical observer" into the model. Attempting to build on this inevitably leads to metaphysical nonsense about consciousness.
In "unreal" MWI there is a universal wave function, and something is "real" to us if it is entangled with us. The "many worlds" terminology makes it easier to visualize but doesn't mean those other worlds are real because whether something is real is subjective in this interpretation. Subjective reality may be a problem for some people, but if you look at the evolution of physical theories, we consistently find that everything is more subjective than we thought it was (see also: relativity).
By making quantum computer, we are making us into Schrödinger’s Cat. Which entangles our destiny to a quantum possibility.
Such as a highly sophiscated military quantum computer which decides war and peace on quantum computing.
It must be very fun to observe us from a Alien Species's angle.
Such confidence ... I envy that.
You're right though, I very much doubt QFT as it stands is the bottom. However, that doesn't mean the current debate is stupid. Whatever underlies QM, you'd still expect the measurement effect to also be an emergent property. The debate about whether atoms existed is still meaningful even though we now know that "atom" isn't a perfectly natural category. Indeed there are protons and such underling the physics, but the protons do pretend to be atoms much of the time, and thus pretend to do all the things we use atoms to predict.
Similarly, MWI and collapse (as well as, if less so, weirder theories) can be good explanations as to why a quantum phenomenon occurs even if there's also a reason they happen.
lol
Until we find philosophically or experimentally distinguished ways to pare down its ontological cost, working with most general theory is just keeping an open mind.
It is a sign of the much greater maturity of the physical collapse models that their parameters can be constrained by experiment. The ability to be constrained is a good sign, not a bad one.
I love John Preskill’s standard nod to superdeterminism in his writings: without mentioning it by name he says “I leave it up to the reader to decide how seriously to take this possibility”
https://news.ycombinator.com/item?id=33223391
The idea is that the natural laws are fractal, which when mapped out trace many state space configurations. But with a fractal there are always gaps in state space that remain no matter how much you zoom in or out; fractals preserve certain structural invariants at all scales.
So the idea is that counterfactual reasoning sometimes fails in a fractal universe, because statistical independence no longer works as a general rule (your counterfactual could lie in one of those gaps). He first published this idea in 2009 under the name "invariant set postulate":
https://en.wikipedia.org/wiki/Invariant_set_postulate
His paper with Hossenfelder is also a good overview:
https://www.frontiersin.org/articles/10.3389/fphy.2020.00139...
Superdeterminism gets an unnecessarily bad rap.
If determinism is true, don't you mean "necessarily"? :)
Yes. That is a big reason why most physicists do not favor superdeterminism.
The game of life is perhaps a nice analogy here. On the 2d grid of the game of life, a glider seems moving in a certain direction when time moves forward. But in the 3d grid, where time is the third dimension, a glider is just a static volume of space.
The reason we experience time is that the evolution of the block universe does depend on the dimension you look at (e.g entropy generally increases in the positive time dimension), and because our consciousness is an emergent property of a self-sustaining structure within the block universe, it's plausible at least that we perceive movement in time different from movement in space. I realize this is very sloppy wording but I'm having trouble finding better words to describe my intuition here.
That's one way of interpreting it, but superdeterminism does not entail or require this. Superdeterminism can be formulated just fine for a universe that evolves in time from some initial state according to causal processes.
It’s not violated - it simply doesn’t apply because its predetermined that the measurements that are done work well together. The experimenters follow the script.
If you could refine what these words all mean, I guess we could understand it as something more than "Deutsch seems to think that yes", which can replace your sentence entirely, "yes" describing it all as precisely.
I am myself, in some ways, a general intelligence running on a quantum computer but I dont feel like I can observe myself existing in a novel special way. Let alone being able to then express it for you in a way that is novel as well.
And while you are indeed a general intelligence, I don’t think you’re running on a quantum computer.
If many-worlds is true, we are already observing ourselves in each of those universes in which we can observe, we just don't communicate with our replicas. And if the AGI can communicate with its other instances, the exponential replicas will quickly overload their channel.
I request further elaboration here, please. Examples would be great.
> than the fact that logic is not falsifiable
What?
Also, many worlds interpretation as it currently exists is already falsified by its incompatibility with gravitational nonlinearity.
"True" free will is ruled out by all existing physical theories, so that's not why it's controversial. The bigger problem with superdeterminism is that it wants to explain physics without assuming statistical independence, even for far away events.
“Proposed” - but as something that avoids the issue but it’s not worthy of much consideration.
- I was going to ask whether it is still possible to maintain, in the light of experimental experience, the idea of a deterministic universe?
You know, one of the ways of understanding this business is to say that the world is super-deterministic. That not only is inanimate nature deterministic, but we, the experimenters who imagine we can choose to do one experiment rather than another, are also determined. If so, the difficulty which this experimental result creates disappears.
- Free will is an illusion - that gets us out of the crisis, does it?
That's correct. In the analysis it is assumed that free will is genuine, and as a result of that one finds that the intervention of the experimenter at one point has to have consequences at a remote point, in a way that influences restricted by the finite velocity of light would not permit. If the experimenter is not free to make this intervention, if that also is determined in advance, the difficulty disappears.Uhh, no. Essentially all existing physical theories are devastating for any non-compatabilist account of free will.
The point, that many ignore, however is that, free will does not matter. It is irrelevant. Regardless of whether one has free will or not, one still has to make choices and support the consequences of said choices. Lack of free will was never the get out of jail free card some fear it to be.
If you bring in to the discussion sociology and psychology, free will makes even less sense.
That being said, in her latest book she has a pretty strong argument against free will that does not require superdeterminisim so if that sounds interesting check it out.
E.g., I am in some universe taking every possible action right now, but I'm only experiencing the actions which I "chose" to take.
Furthermore it still removes any actual willed choice of path within the context of our existence. I am not some meta-entity seeing all possible paths and choosing one for some unknown reason. That would be an existential alien "haunting" me and not "free will".
(Of course, you could also just say the feeling is an illusion.)
I don't know if you can ever answer it one way or the other, because while consciousness certainly exists (again a fact I believe just because I feel it), it can't in any way influence the universe, at least per current theories of physics.
On the other hand, if you're right that many-worlds is real and our consciousness persists in all of them, then we will, individually, come to realize that is the case, as find ourselves still alive, forever, ever more improbably (since, I think, the odds of dying would never be 1, so you'll always be alive in some lucky world).
I believe someone called that idea "quantum immortality" and I find it conceptually interesting if not somewhat terrifying. However it does seem like the inevitable conclusion of these ideas.
I'm not sure I'm following the argument. Let me phrase it this way: can you devise an experiment which will determine if a given entity is conscious?
> I believe someone called that idea "quantum immortality"
(Thanks for the term; I'd heared the idea expressed before, but not that phrase.)
Skimming the wikipedia page, I didn't find any of the counter-arguments to be particularly compelling.
So, while I'm not sure how deeply I believe it (simply because it feels very unintuitive -- and I'm definitely not about to try to kill myself to test it!†), I agree with you: it really does seem like the inevitable conclusion of these ideas; I also agree it's somewhat terrifying!
Especially when you consider that as time goes on, probably in the majority of the universes where you are alive, you are just barely alive, clinging onto life by a thread, in great pain. The only consolation is that, perhaps, you'll still have enough awareness to think to yourself, "incredible that I haven't died yet -- I guess many-worlds really is true!"
(† Even if you are knock-down 100% convinced in quantum immortality, you probably still don't want to engage in wildly risky behavior or try to kill yourself -- because you will be killing yourself off in a large number of universes, and causing a lot of pain to your loved ones in those universe. A similar argument could be applied to engaging in any sneaky behavior which would cause significant pain if discovered.)
No, without being able to define what consciousness is we can't make an experiment to test for it. The simplest explanation in my view is that qualia are a base "element" of the universe and information systems and our consciousness is a loosely drawn subset of qualia associated with our brain/body's information system. To be clear this is not dualism, the qualia are not some magical thing riding on top of physics and cannot change the path of particles from their physically determined routes.
Regarding quantum immortality I don't know if it necessarily demands a universe in which some form of every person lives forever by some unexpected chance of quantum improbability. At least in terms of a continuity of normal life it may be that the probability of a person living longer than a human body physically can is zero. However some have argued there is a non-zero chance that random quantum fluctuations could lead to brief instances of a person arising from "nothingness" anywhere and anytime in the universe, and some of those persons could by pure luck happen to match the mind of a person elsewhere. However this does start getting into the realm of silliness and quantum randomness and infinite universes allowing for literally every possible combination of particles.
Yeah, intuitively somehow it seems absurd to think that "everything possible is happening", somewhere, in some dimension. It almost feels like a modern version of Zenos paradox. Like, in the limit, there are no universes in which you're alive...
You can derive if from the MWI. We already know that the "worlds" separate and almost completely cease interacting. The interactions decrease to the order of "two to the power of Avogadro's number" almost immediately. The collapse interpretation rounds that to zero (at some arbitrary point).
To make that more concrete you have to add a term to the equations, making it theoretically testable, but it's remarkable that anybody could manage to test it in practice. It's clever to use a neutrino detector -- something designed to measure ludicrously small amounts of interactions.
I don't think anybody is surprised by the results, just that they could get any. The un-physical arbitrariness of the cutoff caused problems from the get-go.
I was going to say that it doesn't make MWI any more palatable, though I suppose it does. They've detected the other branches, albeit in a very indirect way. They're real. But they're just as inaccessible as they ever were.
You still need the concept of decoherence to make it work. The unstable equilibrium can't hold for large objects. That's both mathematically and physically sound.
Not as an actual physical process, no. "Collapse" in the MWI just means that, once the "worlds" have decohered, within each "world" the wave function can be collapsed to the one that describes the measurement result observed in that "world", for purposes of predicting future results. But in the MWI this is just a mathematical convenience and doesn't correspond to anything physically happening.
In the theories being tested by the experiments described in this article, though, collapse is an actual physical process: there is only one "world". This contradicts the MWI.
> They've detected the other branches, albeit in a very indirect way.
What experiments are you referring to here?
It corresponds to the inner product of the two branches of the wavefunction going to 0 due to physical phenomenon.
The dark matter halo looks like an invisible 3D ball around the thick 2D disk.
Something like https://www.google.com/search?q=dark+matter+halo&tbm=isch
(edit: to answer my own question, the rabbit hole starts here: https://physics.stackexchange.com/questions/485214/ -- basically, accretion happens because light matter can radiate and shed its (kinetic) energy that way. Dark matter does not radiate so it remains in a higher-energy state)
This was one of the more eye-catching statements in this thread. To be blunt, you're wrong. A straightforward and almost inevitable dynamical explanation has been available (and explored in ever greater detail) since at least the mid-1990s, driven in part by the Saskatoon experiment and subsequently supported by BOOMERanG's observation of the first acoustic peak, and many others lines of evidence since then (see [1] for a less-heavy explanation than what follows).
You may wish to check this chapter from a forthcoming graduate-level textbook in galactic dynamics from well-known galactic astrophysicist Jo Bovy <http://astro.utoronto.ca/~bovy/>, which you can read for free at his site: <https://galaxiesbook.org/chapters/IV-01.-Formation-DM-Halos....>.
There are of course other already-completed textbooks. For example, one can find an excellent pedagogic (if advanced) treatment of primordial Gaussian Random Fields[2] as applied to halo formation in chapter 7 of Mo, van den Bosch & White (2010) <https://www.cambridge.org/core/books/abs/galaxy-formation-an...> (you can find the chapter on scy hob via its DOI if you don't have institutional or otherwise affordable access).
- --
[1] https://lweb.cfa.harvard.edu/~deisenst/acousticpeak/acoustic... from <https://astronomy.fas.harvard.edu/people/daniel-eisenstein>
[2] If you're more visually inclined and can't find the illustrated version of Mo et al., see the diagrams on p.3-5 of this slide deck on GRFs <https://www.astro.rug.nl/~weygaert/tim1publication/lss2016/l...> from Rien van de Weijgaert of the Kapteyn Institute at the University of Groningen.
“What actually happens in an experiment with electrons is kind of interesting. Since photons are massless they are easy to excite if they have long wavelength and hence low energy. Whenever an electron gets accelerated many "soft" (i.e., long wavelength) photons get emitted. But if the acceleration is weak, the photons have such long wavelength that they provide little information concerning which path, and interference is possible.
It is the same with gravitons. Except the probability of emitting a "hard" graviton (with short enough wavelength to distinguish the paths) is far, far smaller than for photons, and therefore gravitational decoherence is extremely weak.”
So you’re saying… theres a chance…? :)
MWI also contradicts itself. Supposedly the universes are independent, but if their influence doesn't define the wave equation they do nothing to help explain it.
It's a very strong and exceptional claim with absolutely no evidence to support it. "Feeling" isn't enough.
Given the equations that describe quantum mechanics (ie Schrodinger equation) MWI is essentially the "null hypothesis". No equations that describe collapse have ever passed the rigor of experiment and all collapse theories require modifications to the mathematics of QM. The burden of proof here is on theorists that support collapse theories not proponents of MWI.
Null hypothesis in the sense of not producing any predicition? /joking
I agree with the grand-parent that substituting a "collapse" that we cannot understand with a "separation" that we cannot understand doesn't seem a big step forward.
MWI isn't just renaming the collapse. Copenhagen is fundamentally different in that exactly one outcome is somehow chosen / selected and all others cease to exist. In other words Copenhagen has to add / invent some information: Which world to pick and when to do so. MWI simply avoids having to pick by continuing every branch simultaneously and recursively.
Meaning that MWI is actually a simpler theory and shows that the selection is unnecessary and all problems that come with it can be avoided. In that sense, the burden of proof lies with Copenhagen IMO and it just gives handwavy answers that the selection process somehow involves a conscious observer, whatever that is ...
> MWI also contradicts itself. Supposedly the universes are independent, but if their influence doesn't define the wave equation they do nothing to help explain it.
In MWI the wave function IS the integral of all possible outcomes / worlds / branches. In that sense they don't just influence it, they define it. Not sure how that is contradictory.
Btw, the same goes for Copenhagen in the state of super position as well. So, they are identical up to the point where Copenhagen selects one (collapses) and MWI simply carries on.
In MWI exactly one outcome / branch is somehow what we see and all others cease to exist to us. MWI just gives handwavy answers about how it is so.
But, all the interpretations of quantum mechanics start with the axiomatic assumption that the universe is modal and that there are different possibilities / outcomes. They only differ in if they chose to turn hypothetical outcomes into real outcomes or simply let everything be equally real from the get-go.
And yes, even superdeterminism has to deal with / model hypothetical outcomes. It just says that some of them cancel out each other early on as they would lead to inconsistencies in the future otherwise.
Where the worlds come in is that it's impossible to do calculations on the wavefunction of the entire universe, so we need to come up with a way of dividing it up into manageable pieces. Not because the theory requires that it be divided into pieces, but because otherwise we couldn't handle the math. The worlds are one of the ways we do that: We break the wavefunction of the universe into approximately perpendicular components that don't interfere with each other very much and don't have too much entanglement making them hard to understand, and we call those worlds. We can further simplify things by just looking at a subsystem of the universe rather than the entire universe, which involves taking a partial trace (this tends to introduce randomness). As time goes on and entropy increases, the entanglement and complexity even within a "world" will continue to increase and at a certain point we may notice, "hey, this component is really complicated now, and it can itself be divided into subcomponents that are approximately orthogonal and don't really interact with each other much, I can simplify my calculations by treating those as separate worlds now". This is what we mean when we say that worlds tend to split apart, but since the worlds are only approximately orthogonal and independent, when you define splitting is really a matter of how much error you're willing to allow in your calculations. (Also, the process of splitting is driven by increasing entropy, so when (if?) the universe reaches a point of total heat death and entropy stops increasing, this will also imply that the worlds have stopped splitting.)
So I'm not sure what you mean by "strong and exceptional". It's just math, and can be compared with experiment just like any other piece of physics. Take the experiments done in the original article. If any kind of collapse had been observed, then that would have straight-up falsified the many worlds theory. Many worlds says that physical systems can become entangled with their environments, but their wavefunctions can never just collapse, and these two cases are distinguishable in a careful experiment. Since collapse wasn't observed when these tests were done, that provides a little bit of evidence in favour of many worlds.
Falsifiability is a little more complicated for collapse theories. People don't agree on the exact definition of a "measurement", and what level of interaction with the environment is required to trigger a collapse, but in order to have a falsifiable theory, it's important that we have a precise, mathematical definition of when a collapse should happen (this definition does not have to be deterministic, it could just give us a probability distribution). So various people have put forward different definitions, and it sounds like these experiments have ruled out a bunch of them, but obviously they haven't ruled out every collapse theory put forwards by every physicist ever. It's a bit like when the LCH failed to find any supersymmetry particles, and some physicists were like, "okay, but in my version of supersymmetry, the particles are heavier than the energies reachable by the LHC so of course we wouldn't expect to have seen them".
Separation that you are talking about boils down to different parts of wave function being uncorrelated with each other. If this is the case, then events in one "universe" can't have causal connection with another because that would imply correlation.
Worse than that, I'd say that "physical collapse" is usually presented to the general public as established scientific fact, even by prominent scientists that know better.
I've listened to enough Carroll to convince myself that I think MWI makes sense, but what I never got is that it doesn't seem to offer much in terms of explanation of how the entangled state ends up being what it is: We see a particular result of an experiment with many possible a priori outcomes, but is there a mechanism that determines which particular entangled state we end up in? Something like the phases of the wave functions on individual Hilbert space sectors conspiring to produce a certain outcome, so that an omnipotent observer with full access to both parts would be able to tell what happens a priori, no dice being rolled? Or is that just hidden variable theory?
According to MWI, all possible results of an experiment are manifest and real. You're asking "which particular entangled state we end up in?". You end up in all of them. For a 2-state superposition system, there are 2 versions of "you" that exist after the experiment, both of which are equally real. Subsequent measurements of the quantum system will appear to be "collapsed" for both versions of you but each will see a different different and opposing values.
Except that I've only ever experienced ending up in one of them, so exactly how did the "I" that is typing this right now wind up here, and not in some other branch?
There's an unexplained bifurcation of consciousness implied by MWI which it cannot explain (although I think it suggests the appeal of MWI since it gives enough wiggle room that people think that their free will could control which universe they wind up in, which appeals to everyone's inner Malcolm Gladwell).
Maybe your copy in another branch even posted the same comment.
Both are worthwhile if you like thinking about these kinds of things.
I've generally found nearly zero people who have read those books and of them most people poo-poo it all, and don't really engage with some of the issues presented in them.
He may be wrong. Einstein was also wrong about the EPR paper. But it seems like he's trying to engage with the problems and do science rather than just provide philosophical justification.
I don't see how that would allow or require seeing a cat in a complex linear superposition. You just have one set of frames which describe a live cat and another set of frames that describe a dead cat.
For simplicity, let’s say that all quantum interactions have two possible outcomes, 0 or 1.
The first point is that we can only talk about what interactions appear to have done in the past in our worldline/universe, which is randomly distribute themselves between 0 and 1. If we happened to be on a worldline where all interactions had always resulted in 0 for the whole history of the universe then that universe almost certainly wouldn’t support complex life. So perhaps there’s an observership bias here: if quantum interactions hadn’t decently distributed themselves between 0 and 1 then we wouldn’t be asking this question (just like the values of all the other fundamental constants).
As far as I can tell there’s nothing in current theories which would rule out all future interactions happening to result in a 0. Let’s hope our consciousness don’t end up on that worldline (unless you believe in quantum invulnerability).
Aa a function is a mathematical abstraction, I don't see how it could be real... unless you believe the world is made of math..
Some smart people have tried to make theories where wave function collapse is a real thing. These new experiments are working to rule out those ideas.
My feeling is that Everett's "many worlds" interpretation is the clear favorite: there is no wave function collapse.