How slow can Gedanken experiments be theoretically?

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Discussion Overview

The discussion revolves around the theoretical limits of slowing down Gedanken experiments, particularly in the context of delayed-choice experiments in quantum mechanics. Participants explore whether new techniques could extend the duration of these experiments significantly, potentially into seconds or longer, and discuss the implications of manipulating light's travel time within these frameworks.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that new techniques could theoretically slow down the duration of Gedanken experiments significantly.
  • Others argue that since Gedanken experiments are thought experiments, they can be conceptually slowed down as much as desired.
  • A participant clarifies that they are specifically asking about real experiments rather than thought experiments.
  • It is suggested that actual delayed-choice experiments can be conducted without needing to slow light, as the causal connections can be maintained regardless of light speed.
  • One participant questions whether it is feasible to drastically slow down the experiment by using time instead of space, such as by having light bounce off mirrors for a set duration.
  • Another participant notes that adding delays does not slow light itself but increases the distance traveled, thus extending travel time.
  • There is a discussion about the implications of measuring entangled partners after observing an interference pattern, with some speculation on how uncertainty might affect the results.
  • A later reply challenges the feasibility of certain setups involving entangled photons and their correlation with interference patterns.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and implications of slowing down experiments. While some agree on the theoretical flexibility of Gedanken experiments, others emphasize practical limitations and the nature of real experiments. The discussion remains unresolved regarding the best approach to manipulating the duration of these experiments.

Contextual Notes

Participants highlight limitations related to the alignment of experimental components when adding delays, as well as the potential loss of photons affecting results. There are also unresolved questions about the relationship between interference patterns and measurements of entangled partners.

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New techniques are slowing down light. Spacial separation is used in Wheeler’s delayed-choice Gedanken experiments to increase the time between aspects of the experiments. Potentially, could new techniques slow the experiments down much further, and, if so, within reason how much slower could the experiments be? Are there hypothetical strategies that could extend such experiments into seconds or longer?
 
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Given that a "Gedanken experiment" is just a fancy word for a thought experiment, I imagine they can be about as slow as you'd like them to be.
 
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Agree w/ Dewgale. NTHstars, are you asking about thought experiments, or about real experiments?
 
The real experiments, thanks!
 
Actual delayed-choice experiments have been done. You can keep the interesting steps without causal connection and it still works. You don't need to slow light for that.
 
I guess another way to ask the question is...theoretically, is it feasible to slow the experiment down drastically by using time instead of space? I don't mean in some sci-fi way, I mean by purposefully "holding up" the light by perhaps having it bounce off mirrors (or whatever) for a set duration of time before it was allowed to "complete" the experiment. What I'm looking for is...from the time the light first enters the experiment, until the experiment is complete and the total results are known, could you theoretically purposefully drastically "slow" or delay the passage of the photons to the extend the duration of the experiment?
 
You can add delays for the light as much as you want, it doesn't matter. It just makes the experiment more challenging in terms of alignment of the components and so on.
 
NTHstars said:
perhaps having it bounce off mirrors (or whatever) for a set duration of time before it was allowed to "complete" the experiment.
That doesn't slow the light, it just makes it go a longer distance which of course increases the travel time. This is a common experimental technique (although it's generally more practical to do "whatever" using optical fiber instead of mirrors - easier to route around obstacles, less attenuation).
 
mfb said:
You can add delays for the light as much as you want, it doesn't matter. It just makes the experiment more challenging in terms of alignment of the components and so on.

If you tried to set up an experiment where one set so results (let's say an interference pattern - or not) was recorded and then you tried to force the entangled partners to do something uncorrelated, is there any thinking on what would happen? I can think of a few ways that nature might get out of it (*), but I wonder what the best theory is at present?

(*) For example, if we definitely have a double-slit interference pattern and we then look at the entangled partners - assuming the photons are confined in some way and so the second measurement apparatus is not too far away - then perhaps too much uncertainty in each photons path has built up - or too many get absorbed by the apparatus and are lost to the experiment. So that the more certain the interfence pattern, then the more photons that go missing from the second half of the experiment?
 
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PeroK said:
but I wonder what the best theory is at present?
Quantum mechanics. The Wikipedia article describes the experiment in more detail.
PeroK said:
For example, if we definitely have a double-slit interference pattern and we then look at the entangled partners
You can't do that (unless the entanglement is in something irrelevant).
 

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