The double slit experiment

[Ouroboros]

26 minutes ago, ollypenrice said:

If no conscious observer looks at the consequences of the double slit experiment when detectors are fitted, does the diffraction pattern appear or not? How would we know?

Olly

We’re in Schrödinger’s cat territory there.  

[Ags]

What if the conscious observer is only aware of one of the slits?

[Albir phil]

On 19/10/2024 at 19:49, saac said:

Regarding time, I'm pretty sure there is mainstream acceptance now within the physicist community that our biological experience of time certainly obscures a deeper and altogether non intuitive nature. But perhaps that peculiar experience of time is the very thing that brings meaning to life and what it means to live. I for one am glad to experience fleeting moments, the sense of memories from yesterdays I can no longer visit and the promise and hopes of things to come. Have I a need for eternity? I don't know.

Jim 

Time is really a human invention in order to make sense of things,if we were not here would time still exist, probably,but with no one to measure it.

[Moonshed]

8 hours ago, ollypenrice said:

If no conscious observer looks at the consequences of the double slit experiment when detectors are fitted, does the diffraction pattern appear or not? How would we know?

Olly

Good question. The detectors, because they can detect which slit a photon goes through, will cause the photon to collapse into a particle and pass through one slit or another,  thus creating the two clusters in line with the slits. The detectors prevent the photons acting as a wave and passing though both slits simultaneously. At this stage no conscious observer has witnessed this so we can only assume that is the pattern that has built up on the screen, but as you say how can we tell? It may be that there will be an interference pattern until the moment our conscious observer looks at it. As far as I am aware we have no way of knowing if the detectors independently of observers can cause the collapse of the wave function. 

Edited October 21 by Moonshed

[Moonshed]

7 hours ago, Albir phil said:

Time is really a human invention in order to make sense of things,if we were not here would time still exist, probably,but with no one to measure it.

My understanding of time is that it was created at the time of the Big Bang along with the three space dimensions we are aware of to create the space time continuum. You could ask if the universe itself could exist without us humans to observe it. Right, that’s it, I’m going back to finish my cup of tea, that’s something I can understand, and I’m pretty certain that it stays there even when I’m not looking at it. I think. 

[iantaylor2uk]

12 hours ago, ollypenrice said:

If no conscious observer looks at the consequences of the double slit experiment when detectors are fitted, does the diffraction pattern appear or not? How would we know?

Olly

A conscious observer at the other side of the double slits will see a diffraction pattern. So will an automatic detector (such as a camera or photoelectric device). If the automatic device recorded something different, then when a conscious observer looks at the picture, there would be a disagreement, which can't happen physically.

The diffraction pattern only collapses if you try to observe which slit the photon passes through.

In practice, a single photon will go through BOTH slits.  

[Mr Spock]

Light is a particle (or wave) which interacts with other particles. That's where the 'until observed' comment comes from. 

When you look at a star, the light from that star travels through a relatively empty space, it is then either dispersed by the atmosphere or hits your optic nerve (or other object). Only at that point does it become visible.

The question then becomes, can you prove the particle exists before it is observed? 

[saac]

10 hours ago, Albir phil said:

Time is really a human invention in order to make sense of things,if we were not here would time still exist, probably,but with no one to measure it.

There is apparently no variable known as time "t" in any of our equations which describe the fundamental nature of the universe. Our experience of time isn't so much something that we have invented rather the result of life's interaction with the universe. Time (as we experience it) is likely an emergent property; if it is fundamental then an association with thermal time (directionality of entropy) may be where it emerges. Certainly on a large scale, the universe seems to have no use nor care for time; neither here (now), past, present or future have any meaning or influence. 

One of the more enjoyable reads on the nature of time is by Carlo Rovelli "The Order Of Time". It really is an enjoyable read and follows in Rovelli's beautifully poetic and imaginative style as found in his earlier "Seven Brief Lessons". A commendable read for those interested in this profound mystery of time.  

Jim 

 

[JOC]

I have always loved the double slit demonstration/light as waves and photons and have never seen it demonstrated better than on an ancient TV programme, possibly by the OU being done by people that I recall being dressed in very 1970's outfits.  I've searched the internet many times for the clip, but have always failed to find it.  They set it up, show the interference pattern on a flat surface then remove that and run a photon counter detector over the pattern and you can hear the photons increasing and decreasing in numbers at the detector as the diffusion pattern is passed through.  It was a brilliant demo and I do wish I could watch it again.

[Moonshed]

8 hours ago, JOC said:

I have always loved the double slit demonstration/light as waves and photons and have never seen it demonstrated better than on an ancient TV programme, possibly by the OU being done by people that I recall being dressed in very 1970's outfits.  I've searched the internet many times for the clip, but have always failed to find it.  They set it up, show the interference pattern on a flat surface then remove that and run a photon counter detector over the pattern and you can hear the photons increasing and decreasing in numbers at the detector as the diffusion pattern is passed through.  It was a brilliant demo and I do wish I could watch it again.

I don’t know about the program you mention but I went onto YouTube and typed double slit experiment into the search engine and was impressed with the number of videos on the subject. I was especially impressed with Veritasium’s take on it, he took a fridge sized cardboard box onto a beach and did the experiment with sunlight with interesting results. I managed to spend a lot of time looking at the various demonstrations and explanations, most enjoyable. 

[globular]

I’m not really qualified / equipped to contribute to this thread, but I do have a question.

9 hours ago, saac said:

There is apparently no variable known as time "t" in any of our equations which describe the fundamental nature of the universe.

What does the speed of light c mean if there is no time?

[saac]

21 minutes ago, globular said:

I’m not really qualified / equipped to contribute to this thread, but I do have a question.

What does the speed of light c mean if there is no time?

The t which appears in the relationship for speed = distance over time does not represent a fundamental property. Speed (potentially distance) is similarly an emergent property. It does not mean that there is no variable time, it just means that, as far as we know, time is not a fundamental property of the universe. 

ps edited   - In classical physics it would be appropriate to consider time  as fundamental or foundational.

Jim

Edited October 21 by saac

[robin_astro]

On 19/10/2024 at 22:22, iantaylor2uk said:

The double slit experiment works even if only one photon is sent through the double slits. It is important to note that a photon only ever interferes with itself, not with other photons. If you send through single photons at a time the interference pattern will build up.

Also with the multiple slits that make a diffraction grating. In these spectra of faint quasars, the photons are landing on any one pixel of my camera sensor at the rate of ~ 1  per minute (so spaced  ~18 million km apart) and end up landing on the right pixel depending on wavelength to form the spectrum.  The individual photons when they arrive at the grating must be spread over  the 3000 slits which make up the  5mm width of the grating.

https://britastro.org/observations/observation.php?id=20210411_134753_85f4b3ebf4faaefe

Robin

Edited October 21 by robin_astro
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