This tag is for questions relating to what, if anything, the quantum mechanical formalism and experimental results say about the way the world works.

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Decoherence and interpretations

With quantum decoherence, are there still any "gaps" in our knowledge of quantum mechanics that hint (either in terms of the physics, philosophy, or otherwise) at the need for further interpretation? ...
3
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2answers
148 views

How does the Physics work for the Quantum Suicide thought experiment?

On page 5 of this paper written by Max Tegmark, Tegmark discusses a thought experiment called 'Quantum Suicide'. As far as I understand it, this experiment was created to show the experimental ...
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3answers
1k views

What is the physical interpretation of the density matrix in a double continuous basis $|\alpha\rangle$, $|\beta\rangle$?

(a) Any textbook gives the interpretation of the density matrix in a single continuous basis $|\alpha\rangle$: The diagonal elements $\rho(\alpha, \alpha) = \langle \alpha |\hat{\rho}| \alpha ...
2
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1answer
63 views

Many-worlds interpretation (MWI) and conservation of energy [duplicate]

I am not an expert of many-worlds interpretation (MWI), and what I say may be stated incorrectly. In that case i welcome corrections. If the MWI is true and it explains quantum theory and it splits ...
64
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6answers
28k views

Is the universe fundamentally deterministic?

I'm not sure if this is the right place to ask this question. I realise that this maybe a borderline philosophical question at this point in time, therefore feel free to close this question if you ...
3
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1answer
70 views

Does a particle “exist” between emission and detection?

In considering a simple Young's double slit setup: The classical idea that a particle must exist with defined position and momentum between the source and detection plate leads to philosophical ...
2
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2answers
212 views

Under what circumstances is observing a superposition possible?

According to Ian Stewart's 2013 Symmetry: A Very Short Introduction (pp. 119-120), Experiment and theory suggest that superposed states should not be observable as such; only individual ...
2
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1answer
145 views

References on De Broglie-Bohm pilot wave theory

Are there any good books related to the not much popular De Broglie-Bohm pilot wave theory and its application in hydrodynamics, walking droplets concepts?
6
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2answers
383 views

Has this experiment really demonstrated wave-function collapse?

My question is: why did the following experiment claim that it had demonstrated the wave-function collapse? Experimental proof of nonlocal wavefunction collapse for a single particle using ...
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0answers
64 views

How does one intrepret probabilites in the many-worlds interpretation?

Let's say I flip a coin, and don't look. From the copenhagen interpretation, the state of the coin is: $\frac1{\sqrt2}(i|\text{heads} \rangle - |\text{tails}\rangle)$ If I observe the coin, there is ...
2
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2answers
176 views

Can multiple timelines exist according to theoretical physics? [closed]

Multiple timelines is not a reality yet (as of 2016's science and technology), but exists only in Marvel/DC universe. It is something that is used to explain the paradox of time-travel. If you go back ...
0
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2answers
212 views

Many-world interpretation: simple physics explanation? [closed]

We went a little off topic in physics class today and my teacher was explaining how quantum physics explains the idea of parallel universes. She believes in a idea called many world interpretation ...
2
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3answers
147 views

Does valid interpretations of quantum mechanics always reduce to trivial arguments about the equations? [closed]

This is the editted 'short' version of the question :) Interpretation is very important in physics, but physics is governed by equations. With bare equations, physics would be just mathematics. ...
2
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0answers
90 views

What would be the abilities of a wave function collapsing oracle? [closed]

Although the Bell's theorem dismiss local hidden variables as an explanation of the quantum variability, there is nothing to prevent an observer to see the occurrence of a wave function collapse as ...
21
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2answers
748 views

What is the Copenhagen interpretation of quantum field theory?

I am most interested in interpretational differences due to the fact that quantum field theory is relativistic while quantum mechanics is not. By "Copenhagen interpretation" I mean a minimal ...
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1answer
68 views

Probabilistic realism

On consideration of Bell's inequalities and this Why is quantum entanglement considered to be an active link between particles?. Either localism or realism has to be given up. Can't we have a ...
0
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1answer
54 views

Does quantum mechanics separate ontology from gnoseology? [closed]

I mean this answer here. Laws present to us what we know (what we may know). But what we know cannot define what is real; it only defines our actions & assumptions. We may know only probabilities ...
11
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3answers
346 views

Can someone clarify whether the recent experiment closing all remaining loopholes to Bell's Theorem really shut the door on local realism for good?

I saw this recent article on Phys.org that purports to close all remaining loopholes that previous experiments on violations of Bell's inequality left open. My question is, does this really close the ...
5
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2answers
449 views

Is the many-worlds interpretation (MWI) of QM inconsistent with quantum field theory

I had recently posted a question on the Philosophy stack exchange about "true" randomness, and a lot of the discussion centered around Quantum Mechanics. One of the responders claimed: MWI has the ...
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2answers
87 views

Light interference single particle 4 slits experiment - what are interpretations apart from many-worlds interpretation?

Someone knowledgeable about physics advised me to read a book "David Deutsch: The Fabric of Reality, 1997". The book gives experiment like two-slit one, difference is that 2-slits compared to 4-slits ...
1
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1answer
99 views

Does “sum over all paths” in the path integral imply “sum over all paths” in momentum space when one Fourier-transforms?

How is the Fourier-transformed-field path integral interpreted? Is it still a "sum of all paths" in momentum space? Just that with another action? Consider for instance the (Euclidean) partition ...
1
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1answer
88 views

Many worlds probability of getting cancer [closed]

My understanding of probabilities in many worlds is following: If I would decide to start smoking and we know that 10% of smokers get cancer that means that in 10% of all worlds during my lifetime I ...
19
votes
3answers
887 views

Classical and quantum probabilities in density matrices

In textbooks, it is sometimes written that a mixed state can be represented as mixture of $N$ (I assume here $N<+\infty$) quantum pure states $|\psi_i\rangle$ with classical probabilities $p_i$: ...
2
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1answer
161 views

Double slit experiment and pilot waves [closed]

Why do almost all books on quantum start out with the double slit experiment and show how a single particle interferes with itself and say its a wave and particle when Yves Couder has shown on a ...
15
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1answer
646 views

Why is Copenhagen Interpretation the most used & popular interpretation of quantum mechanics? [closed]

It is well known that there are many interpretations of quantum mechanics. I'm wondering if there is a specific reason why the Copenhagen interpretation is the most popular. Why is it that the ...
1
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1answer
84 views

Bohmian trajectories vs. Feynman path integrals, continuous paths?

After reading some of the other posts online, I'm clear on the fact that Bohmian trajectories (of the de Broglie Bohm formulation) and the paths of the Feynman path integral formulation are very ...
4
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2answers
198 views

Does Bell's theorem rule out the possiblity that measurements are completely determined by events in the past light cone?

I'm studying Bell's theorem and the CHSH inequality for some time. Now it's clear to me that one cannot reproduce the correlations predicted by quantum mechanics by assuming that particles carry ...
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2answers
120 views

Physical quantities have definite values?

I don't really know if this question has an anwser but I thought it was worth to try asking. My point here is the following: in Quantum Mechanics, to describe the states of a system we use a Hilbert ...
6
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2answers
679 views

What's wrong with this experiment showing that either FTL communication is possible or complementarity doesn't hold?

The assumptions are: Alice and Bob have perfectly synchronized clocks Alice and Bob have successfully exchanged a pair of entangled photons The idea is simply to have Alice and Bob perform the ...
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3answers
155 views

Has the double-slit experiment been performed with animals as the observers?

As the title says, has the double-slit experiment been performed with animals (not humans) as the observers? If yes, which animal was used and what was the result?
1
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1answer
68 views

Is contemporary physics interpreted in an instrumentalist way? [closed]

I'm a master student in theoretical physics and the reason why I choose this career is far more related to the "philosophical beauty" of physics, than to my personal ability or skills. This, in some ...
2
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4answers
416 views

Is quantum physics truly random or does it just appear that way because of Heisenberg uncertainty principle

The behavior of an electron (and other tiny things) is said to be probabilistic because we can't say where an election will be when we measure it, but only where it will probably be. As I understand ...
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1answer
169 views

Do interaction-free measurements require a physical collapse or splitting in order to be truly interaction free?

Interaction-free quantum experiments like Renninger's experiment or the Elitzur-Vaidman bomb tester are often taken to be examples of interaction-free measurements of a system. Unfortunately, such ...
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6answers
1k views

Are coherent states of light 'classical' or 'quantum'?

Coherent states of light, defined as $$|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum_{n=0}^\infty \frac{\alpha^n}{\sqrt{n!}}|n\rangle $$ for a given complex number $\alpha$ and where $|n\rangle$ is a ...
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1answer
86 views

Does the uncertainity principle actually attack determinism? [closed]

It's not really clear to me how does QM attacks determinism. It sure attacks computability, which is a component of newtonian, naive determinism, but it's often claimed to destroy determinism itself ...
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2answers
221 views

Does the following experiment disprove the Copenhagen interpretation?

I have a question concerning the scientific experiment proposed in the following video, (25:00-29:00) titled the "EPR Thought Experiment", which bears resemblance to the quantum eraser experiment. ...
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2answers
71 views

Terminology for “measurable” and “hidden” realms in quantum physics

Please excuse if some of my terminology is vague, the whole point of this question is to clarify terminology. In quantum physics, one frequently encounters situations where there are some kind of two ...
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4answers
153 views

What limits causality in the many-worlds interpretation (MWI)?

It's widely held that it's either very difficult or impossible to affect the outcomes of experiments in other branches of the many-worlds. The reason given is usually something along the lines that ...
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2answers
78 views

In quantum mechanics does the truth/accuracy of a measurement really matter?

Once John Wheeler said "the past has no meaning or existence unless it exist as a record in the present". So, in a experiment of delayed choice entanglement swapping, if we used a faulty detector to ...
4
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1answer
111 views

In interpretations of QM where the wave function is real, what does that mean?

In a lot of interpretations of Quantum Mechanics they believe that the wave function is "real". But what does that mean? Are they saying that the wave function of an elementary particle ...
2
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3answers
203 views

Does the Copenhagen interpretation require Nature to solve NP problems instantaneously? [closed]

Let's say we have a quantum computer with two registers taking in $m$ and $n$ qubits respectively, with $m$, $n$ suitably large. Let $f:\{0,1\}^m \rightarrow \{0,1\}^n$ be a one-way function. Set up ...
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2answers
2k views

If the moon is not there when no one is looking, how does the moon know how to stay in orbit between observations? [closed]

Quantum Copenhagenists will tell you if there is a stop sign, it only manifests itself by the act of observation. When no one is looking, there is nothing there. This is like the cognitive process of ...
6
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3answers
333 views

How to understand the motion of a particle in Quantum Mechanics?

In Classical Mechanics when we talk about the motion of a particle it is the same as talking about the idea of trajectory. The fact is that in Classical Mechanics, a particle has a definite position ...
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2answers
2k views

Is the movement of electrons truly random?

The result of rolling dice is considered pseudo-random because it depends on an almost endless list of factors (how you roll it, the terrain it lands on, etc.), but it is not TRULY random. Is the ...
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0answers
58 views

A real 'two line' (non-interference pattern) when observed

I have seen many interference patterns from double slit experiments but I have never seen a real 'two line' pattern when observed. Does this actually exist or is it only a conclusion? if there is an ...
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0answers
109 views

Using the double slit experiment to prove or disprove the de Broglie-Bohm pilot wave theory

Probably a dumb question... If you have a double slit experiment with a second experiment (single or double slit) at 90 degrees intersecting the path of the first experiment, would the interference ...
4
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3answers
230 views

What is a measurement in MWI

I was reviewing the MWI, and couldn't figure what a measurement is in the MWI? Everett claims that split happens when you measure, but what is it for MWI (not for general QM)? Yes, I know about ...
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2answers
137 views

Does Bell's theorem exclude local hidden variables as explanation for radioactive decay?

Often it is said that Bell's theorem (and the observed violations thereof) rules out local hidden variable theories as the explanation for the seeming non-determinism found in quantum mechanics. I'm ...
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4answers
237 views

In Copenhagen, can this idea preserve locality for Bell inequalities?

Generate an entangled pair of qubits. Send to Alice and Bob far away from each other. Both measure along basis in one of two possible orientations. The result is sent to Charlie at some later time, ...
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0answers
58 views

Can string theory and the Penrose interpretation coexist?

Is it possible for string theory to coexist with the Penrose interpretation of quantum mechanics? Does string theory require the many worlds interpretation?