Tag Info

New answers tagged

0

Yes, Bell's theorem (together with the Einstein-Podolsky-Rosen argument) necessarily implies that causality is nonlocal, i.e. causal connections outside the past light cone exist. So the past light cone is not sufficient to determine all measurements. Note that this is regardless of whether hidden variables exist or not. This is an often-misunderstood ...


0

The pure states are extremal in the (convex) set of quantum states, i.e. the set of linear positive functionals of norm one in a unital $C^*$ algebra. They are thought to be the states that carry the maximal information about the system. In addition, the complete set of states can be obtained from the set of pure states taking the convex hull. In this sense ...


0

According to the Pusey-Barrett-Rudolph theorem, if scientists Alice and Bob disagree about their beliefs of the wave function, at least one of them has to be wrong. By your definition of objectivity, this makes the wave function "objective". Note the PBR theorem doesn't apply to mixed density states, as in Wigner's friend scenarios. This kind of implies ...


0

Most papers on quantum mechanics don't explain issues like interpretation clearly and non-locality clearly. The most notable exceptions to this are David Deutsch and to a lesser extent David Wallace. "The Fabric of Reality" by David Deutsch is a popular book that explains quantum mechanics, see especially chapter 2. See also "The Beginning of Infinity" by ...


0

Lectures on Quantum Theory: Mathematical and Structural Foundations by Chris Isham is a thin, easy to read book. The first 6 or so chapters are a simple introduction to quantum mechanics, but from about chapter 7 or 8 he goes into the Quantum Measurement problem and various interpretations and their associated difficulties. He also discusses Bell's Theorem, ...


0

First of all, I'm not a physics specialist. In my opinion, the reason why I'm typing this text at this second and the next one is that we are working inside another parameter. In other words, we are dealing with a "computer" object that is made up of other quantum objects, but that molecules are working as a computer. Once we catch computer, it is always ...


0

In mathematical terms, the PBR theorem shows that the relation between the states of a more fundamental theory and the states of quantum mechanics (wave functions) is functional (i.e., to every state of the more fundamental theory, there belongs at most one wave function; the relation does of course not have to be onto or one-to-one). If this is enough for ...


0

Your linked article ('How do probabilities emerge…') only seems to explain why each universe is internally consistent and acts according to what we would statistically expect. The argument pretty much goes that it is of course entirely possible to get weird behavior, but it is precisely as likely to occur as in a single universe obeying the known physical ...


0

The answer I give here is the result of many discussions with experts, and I heard many opinions in all the directions. So, I write here what is known to me by the time that I give this answer. 1. There are three interpretations known as the most elaborated, most investigated: a) The standard (or Copenhagen) interpretation + the von Neumann's reduction ...


0

People have strong opinions about the interpretations of quantum mechanics. As alanf points out, quantum mechanics already implies many worlds, provided that you think that quantum mechanics should hold for arbitrarily large closed systems. We have no evidence for that, but we haven't found any counterexamples yet, and neutron stars are pretty big. I suppose ...


1

Yes, as long as you're assuming a local hidden variables theory it can be shown that even allowing the outcome to be determined by any arbitrary amount of prior events in the past light cone will not allow for violations of Bell inequalities. Bell demonstrates this for example in his paper "La nouvelle cuisine" which is reprinted in the collection Speakable ...


62

I'm not a quantum cosmologist, but I am an early-universe cosmologist, so I can give you my opinion after having read this paper. The article claims that Bohmian trajectories is a valid replacement for geodesics. This was claimed in the very beginning of the paper and not much is offered in the way of defense for this assumption. That's not to say that it's ...


8

There are a number of models for the universe over the years. The Big Bang as you show it in the figure has become the "standard model" for the creation of the observed universe as we know it because it fits observations, i.e. data, using known theories and behaviors from elementary particle theories. This model has been evolving as data are added in our ...


3

The debate over evidence for the many worlds interpretation is largely misconceived. Suppose that you take quantum mechanical equations of motion seriously and apply them to all physical systems, including macroscopic systems like detectors. When you do this, you find that it implies the existence of multiple versions of all those systems. Those multiple ...


26

While this work certainly investigates an interesting point, I think simply replacing geodesics in GR with similarly looking quantum trajectories does not solve the issues here. Finding the Friedmann equations while assuming large-scale homogeneity and isotropy is no surprise to me. There are a number of people working on so-called Big-Bounce Cosmologies. ...


6

The question is whether quantum computing necessarily implies that the many worlds interpretation of quantum mechanics is correct. This issue is dealt with in the question How much is quantum computation changing the interpretation of quantum theory, and, if at all, how?, though I suspect the discussion there is too deep for non-physicists. The simple ...


2

The view that wave function is only a mathematical object rather than a real object is, unfortunately, only a (probably) majority view but it is not agreed upon universally. This is in part because not all people agree that mathematical object is not a real object. There are people who prefer to think mathematical objects can be real objects. This is partly ...


0

I post this answer to check my understanding. Imagine a wavefunction in 1 dimensions with a known energy and momentum it's wavefunction will be: $$\Psi(x, t) = e^{i(kx-\omega t)} = e^{i(px-E t)/\hbar}$$ With some calculus and algebra you can derive the momentum operator and get this: $$-i\hbar \partial_x \Psi = p \Psi$$ There $-i\hbar \partial_x$ is ...


2

This is not a "real" answer to your question but rather points you should consider while making a mental picture of the wavefunction. "as every respectable physics professor I've ever encountered has treated the wavefunction as an indisputably non-real mathematical tool" Quantum Mechanics, as taught in undergrad and early graduate courses, deals ...


1

I will expand on my comment, answering the title: “Reality” of EM waves vs. wavefunction of individual photons - why not treat the wave function as equally “Real”? What does Real mean in physics It is instructive to look at the definition of fields for physics: "A field is a physical quantity that has a value for each point in space and time." ...


0

There are many issues. Firstly, in nonrelativistic quantum mechanics, there is a wavefunction that is a function not of spacetime, but of time plus configuration space. That is the true sense in which it is not real, because it's not a thing that has a value at every point in space. Secondly, there is an actual quantum field, that only some very ...


2

To me, the whole subject feels somewhat like a comedy of errors, and your question reveals some misconceptions. Hopefully, I'll be able to clear up some of them without just spreading my own misconceptions ;) Let's start off with de Broglie, who wanted to represent matter as physical waves. But when quantum mechanics emerged, we did not end up with matter ...


14

When dealing with a single quantum mechanical particle, both the wavefunction and the electric field appear to belong to the familiar class of "fields", both $\mathbf{E}(x)$ or $\psi(x)$. This analogy completely breaks down when you consider multiple particles, in which case the wavefunction depends on all of the particle coordinates, i.e. ...


3

There is no correct criticism of treating the wave function as real if by that you mean treating the equations of motion of quantum systems as if they describe how those systems actually work. There are many criticisms of treating the wave function as real that are no good: some examples follow. If quantum mechanics is a correct description of how ...


3

If the wave-function is a real thing or not, that doesn't depend on how many particles you put in a single wave-packet. If the wave-packet is of very low intensity, you should produce many copies of it. If the wave-function is a real thing, so it is for a thousand particles in a wave-packet, or for a single one particle. If the wave-function is a real-thing ...


10

You can, in principle, measure the electric and magnetic field strength at every point in space and time. Thus, the EM field is real in the the sense that its value can be determined uniquely by measurements, and thus, also excitations of it - the EM waves - are real. You cannot, in principle, measure the wavefunction at any point. The true quantum state ...



Top 50 recent answers are included