- #1

Cobalt101

- 27

- 0

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Cobalt101
- Start date

In summary: There are several things in quantum mechanics that could be called "measurements", but many of them are not relevant for your question.In summary, the conversation discusses the key mystery of the double slit experiment and whether it is the observation or the interference of interaction that causes the collapse of the wave function. It is suggested that the current view is that collapse is caused by interaction with the environment, such as air molecules or thermal radiation. Decoherence is also mentioned as a factor in apparent collapse, but it does not fully solve the measurement problem. The ancient and modern points of view on collapse are also discussed, with the modern view incorporating decoherence. The concept of "measure and throw away" is also mentioned, but its exact

- #1

Cobalt101

- 27

- 0

Physics news on Phys.org

- #2

StevieTNZ

- 1,934

- 883

The answer to your experimental question: we would see two hidden interference patterns on the back-screen. I say hidden, because if you conduct quantum eraser of which way information you correlate the data with the points and two interference patterns emerge. The combination of those interference patterns looks like the back-screen you would get if the system went through one slit or the other.

- #3

atyy

Science Advisor

- 15,168

- 3,378

Cobalt101 said:

If the result is made unobservable, then there is only apparent collapse.

Collapse occurs when one observes the result and retains the result.

- #4

ShayanJ

Gold Member

- 2,810

- 605

The current view is that its not caused by observation, but by interaction with the environment. Also this is not an abrupt process, but a continuous one, although it happens very very fast.Cobalt101 said:

For example in the double slit experiment, it is observed that in the vacuum, the result is a interference pattern. As they increased the density of air, the interference pattern gradually disappeared.

But its not just scattering from air molecules. Even photons bouncing off the objects can cause decoherence. And even in the darkest room you can find, the thermal radiation from the walls and also the CMB is enough to induce decoherence in a very efficient way.

I suggest you read this book, of course if you have a good knowledge of QM.

At the end, I should mention that it doesn't solve the measurement problem completely, but only some parts of it.

- #5

atyy

Science Advisor

- 15,168

- 3,378

Shyan said:The current view is that its not caused by observation, but by interaction with the environment. Also this is not an abrupt process, but a continuous one, although it happens very very fast.

For example in the double slit experiment, it is observed that in the vacuum, the result is a interference pattern. As they increased the density of air, the interference pattern gradually disappeared.

But its not just scattering from air molecules. Even photons bouncing off the objects can cause decoherence. And even in the darkest room you can find, the thermal radiation from the walls and also the CMB is enough to induce decoherence in a very efficient way.

I suggest you read this book, of course if you have a good knowledge of QM.

At the end, I should mention that it doesn't solve the measurement problem completely, but only some parts of it.

The modern point of view is the same as the ancient point of view: collapse occurs when an observation is made and the result is known. Decoherence only causes apparent collapse.

- #6

ShayanJ

Gold Member

- 2,810

- 605

Yes, I wasn't careful. But it doesn't mean the two viewpoints are the same. In the "ancient" point of view, the collapse is a blackbox. The "modern" point of view opens up the blackbox and explains some parts of it but encounters a smaller blackbox(the problem of outcomes).atyy said:The modern point of view is the same as the ancient point of view: collapse occurs when an observation is made and the result is known. Decoherence only causes apparent collapse.

- #7

atyy

Science Advisor

- 15,168

- 3,378

Shyan said:Yes, I wasn't careful. But it doesn't mean the two viewpoints are the same. In the "ancient" point of view, the collapse is a blackbox. The "modern" point of view opens up the blackbox and explains some parts of it but encounters a smaller blackbox(the problem of outcomes).

Yes, people say that and I'm not sure whether I agree. But what is nice about the modern point of view for the ancient point of view is that decoherence is implicit in the ancient point of view, even if the ancients perhaps didn't understand it so well (though I wouldn't put it past von Neumann to have seen it and Bohm sketches it out for Bohmian Mechanics). Decoherence ensures the consistency of the ancient point of view - if we measure and throw away the results, then we can just have decoherence and apparent collapse - so collapse is really dependent on keeping the information from the measurement.

- #8

Swamp Thing

- 920

- 623

atyy said:if we measure and throw away the results, then we can just have decoherence and apparent collapse - so collapse is really dependent on keeping the information from the measurement.

The exact meaning of "measure and throw away" is sometimes not clear to someone who is new to this subject. This leads to questions like, "what if I burn the printout without anyone ever looking at it"?

- #9

atyy

Science Advisor

- 15,168

- 3,378

Swamp Thing said:The exact meaning of "measure and throw away" is sometimes not clear to someone who is new to this subject. This leads to questions like, "what if I burn the printout without anyone ever looking at it"?

If you burn the printout without anyone ever looking at it, then you don't need collapse, you only need decoherence and apparent collapse. Of course if you want to say it collapsed and you threw away the results, it's fine too. But you have the option of saying it only decohered with apparent collapse, but no true collapse.

Remember, the wave function and collapse are not necessarily real, so this subjectivity is fine. We only care that we make correct predictions.

The wave function collapse is a phenomenon in quantum mechanics where a particle's wave-like behavior collapses into a single definite state when it is observed or measured.

The exact cause of wave function collapse is still a topic of debate among scientists. Some theories suggest that it is caused by the interaction between the particle and the measuring device, while others propose that it is a result of the consciousness of the observer.

No, the wave function collapse is a random event and cannot be predicted with certainty. However, the probability of a particle collapsing to a certain state can be calculated using mathematical equations.

Yes, the wave function collapse occurs every time a measurement is made, regardless of the measuring device or the observer. However, the effect of the collapse may be negligible for macroscopic objects due to their large number of particles and interactions.

The wave function collapse is considered to be an irreversible process. Once the particle's state is collapsed, it cannot return to its previous probabilistic state. However, some interpretations of quantum mechanics suggest that the collapse may be reversible in certain scenarios.

- Replies
- 23

- Views
- 3K

- Replies
- 59

- Views
- 4K

- Replies
- 11

- Views
- 487

- Replies
- 18

- Views
- 2K

- Replies
- 7

- Views
- 1K

- Replies
- 36

- Views
- 4K

- Replies
- 28

- Views
- 5K

- Replies
- 14

- Views
- 2K

- Replies
- 6

- Views
- 2K

- Replies
- 4

- Views
- 944

Share: