# Hypothetical entanglement question

• Molecule
In summary, the conversation discusses the concept of entanglement and its implications for time and distance. It is suggested that entangled particles do not react to changes in the other particle's state, but rather remain in a superposition of states until measured. An experiment has been conducted to test this phenomenon, and it aligns with standard quantum theory that suggests instantaneous collapse of the wave function.
Molecule
Hey guys,

I'm new to to this Physics Forum. In fact, this is my first post ever. So I hope this question hasn't been asked and answered a billion times already.

Suppose that you have an experiment set up where two particles that are in a vacuum with each other become entangled and then one is sent rocketing off at near light-speeds. If you measured the stationary particle, would the other one, who is flying around near the speed of light, react instantly or would it take longer to react (from the spectator's view point) because it is moving through time slower? Or is an experiment like this even possible?

Thanks. This has been keeping me up at night!

1. Distance and speed do not matter
2. "react" is not the right word. You won't be able to detect any CHANGES in a second particle: you have only 1 change to measure it, and when you get information about the measurement you confirm the entanglements. You can use it to send information FTL

Hmm maybe I should rephrase my question then. I'm talking about the difference in time between the two particles. Would you detect the changes immediately even if they were on drastically different 'internal clocks'?

No, your vision of entanglement is incorrect.

Say, I have 2 balls: white and black. I put them randomly into 2 boxes and then send one of them to you. After a while I open my box and I find while ball. Aha, then you have a black one! I say.

What is a time difference between I open the box and your ball becomes black? Nonsense, right?

So in fact entanglement has some mysterious components, so my example with the balls is not 100% correct (because it is realistic while Bells shows that it is not), but there is no change.

You think about second particle in state A then 'changing' into state B. No, this is not how it works.

Yes, they're in superposition. However,

Molecule said:
Would you detect the changes immediately even if they were on drastically different 'internal clocks'?

To detect the change, there has to be some kind of a detector on the rocket. It turns out that, unless you tell the detector the expected result beforehand, the outcome in the rocket appears random to the detector. So we can't detect "the change" at all because nothing actually changes, as Dmitry67 said.

Edit: I want to clarify what I said a bit more. Two particles together are in a superposition of correlated states, but each particle is in a mixed state.

Last edited:
Molecule said:
Do the particles not go into a 'superposition' (http://en.wikipedia.org/wiki/Quantum_superposition)
state where it is undecided whether the particle is 'black' or 'white' until it is measured?

Welcome to PhysicsForums!

There has in fact been an experiment intended to probe this particular phenomenon to a degree. This used particles moving parallel and perpendicular to the Earth's velocity. The result was that there was no difference in the outcomes regardless of the movement of the entangled particles. Because of the speeds involved, the result is not absolutely certain but clearly there were no observable differences.

http://arxiv.org/abs/0808.3316

This is completely in keeping with standard quantum theory, in which collapse (whatever that is physically, if anything) of the wave function is considered to be instantaneous. This is sometimes called quantum non-locality. Quantum nonlocality should be considered separate and distinct from conventional nonlocality, as quantum nonlocality does not involve faster than light communication or the propagation of forces or causes instantaneously.

## 1. What is a hypothetical entanglement question?

A hypothetical entanglement question is a thought experiment in which two or more particles become connected or "entangled" in such a way that their states are correlated, even when they are separated by large distances.

## 2. How does entanglement occur?

Entanglement occurs when two or more particles interact or are created together in a way that their properties become correlated. This means that the state of one particle cannot be fully described without taking into account the state of the other particle(s).

## 3. What is the significance of entanglement in physics?

Entanglement is significant because it challenges our understanding of the classical laws of physics and has implications for the development of quantum technologies such as quantum computing and quantum communication. It also plays a role in various phenomena, such as quantum teleportation and quantum cryptography.

## 4. Can entanglement be observed in the real world?

Yes, entanglement has been observed in numerous experiments, including the famous "EPR paradox" experiment and more recent experiments using quantum entanglement for quantum communication and teleportation.

## 5. How is entanglement related to quantum mechanics?

Entanglement is a fundamental aspect of quantum mechanics and is often described as one of its most mysterious and counterintuitive features. It is a key concept in understanding the behavior of quantum systems and has been confirmed by numerous experiments.

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