What is Mwi: Definition and 129 Discussions

In Caroll and Seben's paper, Many Worlds, the Born Rule, and Self-Locating Uncertainty, they present a derivation of the Born rule. For the equal probability case their derivation is based on the following principles. Self Locating Uncertainty - "the condition of an observer who knows that the...

In a different thread, hungrybear asks, Are the implications of MWI really this horrifying? The argument being that every conceivable world must happen to some extent, so that includes worlds so horrific that the mere possibility of their existing makes life intolerable here. Of course there...

The "worlds" of MWI do not actually appear in the theory behind it. They are, so to speak, an interpretation of the interpretation. But what exactly are worlds? The picture begins with an interaction. In general this results in an entanglement. If we decompose it into product terms, each of...

If we take the wave function Ψ of a particle X that gets measured in a basis with a finite countable number of eigenvectors N, then according to MWI and myself, the interpretation suggests that we can write Ψ as the sum of projections of Ψ on the eigenvectors the following way: Ψ= Σn |e(n)> ⊗...

I can't find the anwer on this anywhere, so I hope I may ask it here. My question: In a standard double slit experiment, according to the Many Worlds Interpretation, does the photon create different worlds with different impact locations of the photon? So, without measuring which way...

Sorry for derailing that discussion even further. My reference to Dieter Zeh's German book was unlucky, not just because it is not a peer reviewed paper, but also because I did not remember the exact place with the remark. Since this has bothered me since a long time anyway, I now searched the...

Please excuse my massive ignorance but I find this really troubling and I would hugely appreciate some input from people who know more than me. The implications of the many-worlds interpretation of quantum mechanics seem to be awful for individuals. Am I getting something wrong? As I...

I was wondering, if we have a measurement of, say, spin of an electron, which can yield spin-up and spin-down in the context of MWI, then the electron gets entangled with the measurement device, yielding the wave function ##|Measurement_{spin-up}, Value_{spin-up} \rangle +...

If we have binary decoherence at spacetime location X, as far as I understand, we almost instantly have a splitting into two worlds. Now if we have a different location Y, about a lightyear apart from X, then the decoherence hasn't reached Y before a year has passed. So for Y, the split hasn't...

Is it correct to say: Under the Many Worlds Interpretation: If we rerun the universe repeatedly from the same state S(0), it winds down the same way each time, which is determinism; Under the Copenhagen Interpretation: If we rerun the universe repeatedly from the same state S(0), it may well...

If I consider the MWI, one of the notions for what happens during measurement is that the initial wavefunction, if I use Dirac notation and two dimensions, ##|A\rangle+|B\rangle## undergoes the transformation ##(|A\rangle+|B\rangle)|E_{before}\rangle \rightarrow...

Hi Really interesting thread today on MWI @PeterDonis and another poster- nipped out came back and I can't find it "world" featured a lot what it is and is not mathematically Peter referred to "branch" not actual world If I am being a bit senior apologies tks

I've read from various sources that Everett's original version of the MWI is different than the current popular account of MWI which I believe is more due to DeWitt. Specifically, Everett's initial interpretation placed less emphasis on the reality of the branching universes. I haven't found a...

Hello, and thank you for any input. This forum is a wonderful venue for gathering information and clarity on otherwise quite abstruse topics. I have had an enduring interest in QM interpretations for some time(and quantum mechanics generally), and find their diverse ontological and...

Hello. There is the idea that Many Worlds interpretations could imply subjective immortality (known as Quantum Immortality). However, could this work even if MWI is not true? If the universe is infinite in space or time, or there are an infinite number of universes like ours (several...

I think I have a rough idea about it, but I am not sure whether it is correct. At least I feel that my understanding is a bit vague. Here it is: Globally (I mean across all worlds), the energy is conserved because the universal wavefunction evolves strictly according to Schrodinger equation...

I am in my self-driving car and approaching an intersection, where I can either drive to the right or left. I choose to drive to the right. There are two buttons on the instrument panel, R (ight) and L (eft). I press R, and a QM random number generator is activated. My car drives to the right...

I hope my thread won't be closed (too soon) and some forummers can shed their light over my question. Let's suppose a deterministic universe. I assume all events have a cause, that everything is cause and effect. Then, given that the state of the universe at some instant is X, and this leads to...

Suppose that in Copenhagen, we measure one of the eigenvectors/eigenvalues ##e_x##, the outcome being ##M_x##. Now, in MWI, micro-outcome ##e_x## gets entangled with macro-outcome ##M_x##, right? So, what does that mean in this case? If all outcomes are realized, should outcomes ##e_n## resp...

Suppose we have an operator with three eigenvectors/eigenvalues ##e_1##, ##e_2## and ##e_3##. The operator measures wavefunction ##\psi##. Could we say that we find outcome ##e_x## with probability ##P(\psi,e_x)##, and could we extend this to an infinite dimensional operator as a spectrum of...

I may have misunderstood the expectation value, but if not then with the Copenhagen Interpretation it is easy to understand the expectation value for a wave function. It is just based on the probability of each event. If there were 4 possible events, and the probability of the event having a...

The question seems similar to the one asked here, https://www.physicsforums.com/threads/energy-in-everetts-many-worlds-interpretation.966266/ but since there didn't seem to be an answer I am asking it again in a slightly different form. I was watching a youtube video where Sean Carroll...

If we have a spin measurement with P(up)=0.5 en P(down)=0.5, this is equivalent to tossing a coin P(heads)=0.5 and P(tails)=0.5. The probability of having five heads and five tails out of ten tosses is the binomial: ##\binom{10}{5}(0.5)^5(0.5)^5##. So the same would hold for the spin...

Can MWI account for the probabilities of outcomes? If MWI says all outcomes are realized, is the probability that an outcome occurs then not 100%? How is this explained with the entanglement of the measured object and the measurement apparatus?

In MWI, would you say that a measurement puts the observer in superposition of being in the various worldlines? If I said "yes" to that, would I be correct?

Does MWI just say that everyone agrees about what the pointer of the measurement apparatus shows?

So I consider a measurement on a superposition, in MWI, leads to another superposition: ##(|A\rangle+|B\rangle)|Observer\rangle \rightarrow |A\rangle|Observer{A}\rangle+|B\rangle|Observer{B}\rangle## If we come to the latter situation, a superposition of branches, why does that not mean that...

Summary: Are there worlds where MWI does not hold? (I made a comment on this but I lost track of it). I hope this makes sense: Does MWI allow for worlds were MWI itself does not apply? Where rules of Physics as we know, understand, don't apply? If so, is our world one of these?

I couldn't match this question with another topic, so I made a new topic. Suppose we have past H and present P at a certain moment. In present P a measurement is made. For matter of speaking we adopt MWI, so we have the two measurement outcomes A and B diverging in two realities A and B in...

Summary: Counterfactual Definitiveness and Many World's Interpretation Sorry for all these threads, my noetic fluids and bursting. Wiki states the following: In quantum mechanics, counterfactual definiteness (CFD) is the ability to speak "meaningfully" of the definiteness of the results of...

I was recommended by another mentor to purchase a good book on MWI, which I think should be a thread or poll of its own. Anyway, I might have debased myself too much in that other topic, as I understand on an abstract level how QM works. In my own words, I feel as though possible worlds are...

If MWI and collapse-theory are both possible interpretations of QM, then both of them are not a fact, right? If MWI is a fact then collapse isn't and vice versa, you could say the least. So, shut up and calculate, i.e. the minimal interpretation, makes no inference about the realness of these...

Is QM causal? Specifically, is it time reversable? Does that equate determinism? Specifically, in the case of MWI? Edit: Is QM deterministic? Specifically, in the case of MWI? Is it time reversable?

Could MWI signify that there are not necessarily a (near) infinite number of real worlds, but rather that officially we can't tell if, or to what degree, the world we are in is real?

Quantum theory shows that every and all posibile states exist. As we get better at measuring our visible and detectable universe, it becomes ever clearer that we are missing so much. My question is: If infinity is infinite, then that must apply to scale, could you have infinite multiverses in...

Summary: Could MWI (Many Worlds Interpretation) create universes with fundamentally different physical laws? Physicist John Wheeler proposed along with Hugh Everett and Bryce DeWitt the 'Many Worlds' Interpretation of Quantum Mechanics (although he expressed some doubts about its validity) I...

While the now infamous Frauchiger and Renner publication generated a lot of buzz, it was largely concluded that they drew way too premature conclusions with a too wide brush. Especially the topic of its implication that "Single Universe" interpretations were mostly ruled out garnered quite a lot...

I don't know how to understand this: Suppose we measure the spin of an electron with apparatus M. M can yield spin-up or spin-down. According to MWI, M briefly becomes in superposition of measuring spin up and spin down. Extremely quick however, M gets split by the splitting into two universes...

Would this be correct: in MWI, if a binary measurement is made, the world splits, say in world A and B. Is it then correct to say that you experience both A and B, but that the experiences of A and B become separated?

If we would, for sake of argument, adopt the MWI interpretation, then are there wavefunctions (like for instance position) that have a continuous probability spectrum, and will MWI then propose that there are an infinite number of actual universes that each represent a position in that...

Suppose we have a quantum object in superposition to some measurement basis, given by: ##\frac{\sqrt{2}}{\sqrt{3}}|a \rangle + \frac{1}{\sqrt{3}}|b \rangle##. (1) Suppose the measurement is made, and the system evolves, according to MWI, into ##\frac{\sqrt{2}}{\sqrt{3}}|a \rangle|W_a \rangle +...

Can we suppose that a quantum property (like spin, polarisation, velocity, position) becomes a potential, a probability, when we are going to measure it? Can we say that this property does not exist while remaining unmeasured, and that when measured takes on a value that depends on both the...

In a Mach-Zehnder interferometer the light arrives independent on the path at one the two detectors because of complete constructive resp. destructive interference at the final beam splitter. Is it possible to modify the device such that dependent on the path either detector A or Detector B will...

I'd like to learn about the MWI. I know undergraduate level QM (Copenhagen) and can, within reason, cope with a mathematical formulation of it. What's the best reference for learning the MWI? Thanks

Is MWI equivalent to a superposition of possible Collapse-worlds? That is, is it equal to a superposition of the possible scenario's given by Collapse Interpretation? Is it imparative that the "worlds" given by MWI all ontologically exist?

Suppose we have a pair of spin entangled electrons, measured by resp. Alice and Bob. The basises of Alice and Bob make an angle of α=10°. If Alice and Bob wind up in a joint world where Alice measures ##|u\rangle##, then the probability that, in that world, Bob measures ##|d\rangle## is...

Because I understand that for unitary evolution, MWI is required, which suggests that for different interpretations, there may not be unitary evolution?

Hello all, I have only seen this paper brought up here once before based on the search function 2 years ago, and the thread devolved into something off topic within the first page. I am asking in reference to this paper: https://arxiv.org/pdf/1604.07422.pdf Which claims to show that single...

Please restrict your answers to criticisms of derivations of the Born Rule that are generally accepted by proponents of MWI. Please provide a verbal description of the issue where possible so that people like myself who are certainly graduate-plus* but rusty as hell have a chance of seeing what...

From another thread: I see this claim made fairly often, but it does not seem correct to me. According to the MWI, the dynamics of the wave function is always unitary (there is no collapse), and a unitary process cannot "create" or "destroy" anything. All it can do is entangle things. So, for...