The Delayed Choice Experiment

  • Thread starter lmerriam
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Main Question or Discussion Point

Hello,

I'm uncomfortable with the usual description of this experiment and wonder if this is justified. In a nutshell, when (in the usual double-slit setup) detectors are placed between the barrier and the final screen -- such that an electron, say, has already passed the two-slits -- an interference pattern will still form as though the detection had been made earlier. It is then suggested that the electron knows it was watched and adjusts its behavior in the past to conform accordingly.

Here's my problem with this ...

Electrons travel at the speed of light where time either does not exist at all, or perhaps simply stops (I recall reading it is the former .. is this correct, btw??). Regardless ... although from our perspective the electron most certainly crossed the barrier before it reached the detector beyond, from the electron's point of view no time elapsed at all; hence, there was no delay to speak of.

Am I missing something?

thanks!
 

Answers and Replies

  • #2
3
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Hello,

I'm uncomfortable with the usual description of this experiment and wonder if this is justified. In a nutshell, when (in the usual double-slit setup) detectors are placed between the barrier and the final screen -- such that an electron, say, has already passed the two-slits -- an interference pattern will still form as though the detection had been made earlier. It is then suggested that the electron knows it was watched and adjusts its behavior in the past to conform accordingly.

Here's my problem with this ...

Electrons travel at the speed of light where time either does not exist at all, or perhaps simply stops (I recall reading it is the former .. is this correct, btw??). Regardless ... although from our perspective the electron most certainly crossed the barrier before it reached the detector beyond, from the electron's point of view no time elapsed at all; hence, there was no delay to speak of.

Am I missing something?

thanks!
---

Yes. Electrons do not travel at the speed of light. They may be at any velocity from standstill to almost light-speed, but they will never actually be at the speed of light. Hence, time may be shortened for them but it never actually stops per se.
 
  • #3
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Ouch! And thanks for correcting me. I should have said photons which, unlike electrons, are mass-less. In this case, there would be no delay at all, and the original argument survives ... no?

---

Yes. Electrons do not travel at the speed of light. They may be at any velocity from standstill to almost light-speed, but they will never actually be at the speed of light. Hence, time may be shortened for them but it never actually stops per se.
 
  • #4
There is a FAQ here, but I don't know where (sorry!) about how "light" might 'experience' time. I think it would be helpful... maybe an adviser or mentor can link?
 

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