Two Slit Experiment

Question 1:

What is the outcome of the Two Slit Experiment in Test 10, if 1000 photons are considered ?

Question 2:

What is the outcome of the Two Slit Experiment in Test 10, if 1000 electrons are considered ?

Introduction and Purpose

Understanding is based on observations and experiments.
It is the opinion of the author that before you want to explain your experiments, you have to challenge and evaluate your experiments
This implies that your experiments have to be complete and should include all possibilities.
This also implies information about the difficulties, accuracy and errors in your experiments.
Specific this is true for the Two Slit Experiment.

Description

Test 1
Consider a pond which is divided by a wall in two parts. Drop a stone in the pond. What will happen behind the wall?
Answer
Before the wall there will be a disturbance in the form of waves. Those waves will spread out in circles, with as the centre, the place where the stone entered the pond.
Behind the wall there are no waves.

Test 2
The same as test 1, but now there is one small hole in the wall
Answer
Before the wall the same as in test 1.
Behind the wall there will be a disturbance in the form of waves. Those waves will spread out in circles, with as the centre, the hole in the wall.

Test 3
The same as test 1, but now there are two small holes in the wall
Answer
Before the wall the same as in test 1.
Behind the wall there will be a disturbance in the form of two wave patterns. Each wave pattern will spread out in circles, with as the centre, one of the holes in the wall. After a certain distance those two wave patterns will meet and will interfere with each other.
They will form what is called an interference pattern. This pattern does not move and depends about the length of each wave.

Test 4

Consider a ray of light which is projected on a wall.
Answer
Behind the wall no light will be detected.

Test 5
The same as test 4, but now one hole (slit) in the wall.
Behind the first wall there is a second screen.
Answer
At the second screen there will be a light pattern visible, centred around the hole. This light pattern (bell shaped) can be described with the following intensity pattern:
0 1 2 4 8 16 32 64 128 64 32 16 8 4 2 1 0

Test 6
The same as test 5 but now there are two holes in the wall.
Answer
At the second screen you will see a light pattern, centred around the middle between the two holes. This light pattern can be described with the following intensity pattern:
0 2 0 8 0 32 4 128 16 128 4 32 0 8 0 2 0

The explanation is that light behaves similar as (water) waves
At a distance were light from the two holes meet you will see an interference pattern very similar as in test 3

Test 7
This test is similar as test 4. The difference is that not a continuous light source is used, but 1000 single photons. Those individual single photons are sent to the wall at equal intervals. For example one photon each second.
Light consists of photon. One photon is one light particle.
Answer
The answer is the same as test 4.

Test 8
The same as test 7 but now there is one hole in the wall.
Answer
The answer is the same as test 5.

Test 9
The same as test 7 but now there are two holes in the wall.
Answer
The answer is the same as test 6.
This means that a single photon also behaves as a wave.
Now there are two possibilities:
  1. Each single photon goes through one hole.
  2. Each single photon goes through both holes.
The next test will be used to find the answer.

Test 10

This test describes Question 1. The test is subdivided in subset's or runs.
Three things are very important:
  1. During the whole test the position of photon source should not be modified. The source should transmit during each run the 1000 photons every time in exactly (?) the same way. The intensity should not be modified.
  2. The position of the first slit (hole) should be centred and every time the same.
  3. During each run , when the first hole is open, exactly 1000 photons should be detected.
Following are the five subset's or runs to perform:

Answer

The explanation is that, when there are two holes, (and the distance is small), that what is considered as one photon, physical goes through two holes.
This is detected as an interference pattern.

The twoslit.bas program is supplied which shows a possible outcome of question 10

Reflection

To perform the Two Slit Experiment as described in Test 10 is very difficult.
  1. In each part of the test exactly only one photon is involved. This means that the room in which the test is performed has to be completely dark.
  2. Because light is an electromagnetic phenomena, the room should be free of all electromagnetic signals and fields. That means the test has to be performed in a Cage of Faraday.
  3. Because only one photon is involved, the observer will not see anything during the test.
  4. The only thing that the observer detects during each test, is a regular pattern of the 1000 tics, as each individual photon hits the detector. At the end of the test, the photographic plate will give the only visible evidence.
  5. In many experiments that involve light beams, lenses and mirrors are involved. In order to show the path that the light beam follows, the experimenters blows smoke through those set-ups. Such a setup can not be used to explain the Two Slit Experiment with single photons.
  6. I would like to hear from people performed this tests, about actual problems encountered.

Feedback

None

Answer in case electrons are considered.

A special case is when instead of 1000 photons in each run 1000 individual electrons are used.
Also in that case interference patterns are detected.
The whole issue is the accuracy of the subset's or runs. The first hole should be exactly in the path of the electrons and the second hole can be slightly of centred.
The most probable answer is that:

Feedback in case electrons are considered

None

Other Interesting Sites

Sites which addresses the same or similar subjects are:
  1. Two Slit experiment Google Search
  2. Quantum Optics and Foundations of Physics - Research University Innsbruck "old"
  3. Quantum Optics and Foundations of Physics University Innsbruck "new"
  4. Quantum Optics and Foundations of Physics Google Search
  5. Paul Kwiat Google Search
  6. The Tao of Interaction-Free Measurements Google Search
  7. Interaction free measurements University Innsbruck Google Search

Last modified: 21 November 1996

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