Thread: The Double Slit Experiment

Hi All,

I am new to this forum and I am by no means a scientist, I just have a very active interest in science and hope to learn more.

I have a potentially silly question regarding the double slit experiment, but one i hope you can answer.

Firstly, I understand in very broad terms how this experiment works, an un-observed electron will take all possible routes to the back screen, and hence interfere with itself as it travels through both slits. and an observed electron will travel trough only one of the slits (even if it is observed after it has traveled through the slits).

What i don't understand is..........
How does the double slit experiment show electrons acting like waves when i presume (dangerous i know) that this experiment is carried out in an enviroment where it will contantly be observed by background and / or solar radiation.

Am I missing something quite important here?

Thanks in advance....

I don't get the experiment how does an unobserved electron get through and the observed one doesn't.

This site explains it a lot better than i ever could! The video on this site is also very helpful, althought very simplified.

http://www.doubleslitexperiment.com/

Again, what i don't understand is how can you get results stating that the electron is un-observed when we live in a world full of electromagnetic interference, which would surely act as the observer?

Originally Posted by Andy Swainson

Hi All,

I am new to this forum and I am by no means a scientist, I just have a very active interest in science and hope to learn more.

I have a potentially silly question regarding the double slit experiment, but one i hope you can answer.

Firstly, I understand in very broad terms how this experiment works, an un-observed electron will take all possible routes to the back screen, and hence interfere with itself as it travels through both slits. and an observed electron will travel trough only one of the slits (even if it is observed after it has traveled through the slits).

What i don't understand is..........
How does the double slit experiment show electrons acting like waves when i presume (dangerous i know) that this experiment is carried out in an enviroment where it will contantly be observed by background and / or solar radiation.

Am I missing something quite important here?

Thanks in advance....

Observe means:
First gain info, then don't forget the info.

If a photon was guarding slit A, this photon might observe an electron. But that photon
would likely drift into being at slit A and at slit B ...

Originally Posted by jartsa

Observe means:
First gain info, then don't forget the info.

If a photon was guarding slit A, this photon might observe an electron. But that photon
would likely drift into being at slit A and at slit B ...

right ok, but how does the electron know it is being observed? (using the definition of observe that you have provided) and by what means is the information being retained or remembered.

I have seen articles which state that the observer needs to be conscious, however i have seen equally many stating the opposite. Personally i don't think consciousness has anything to do with it, as that would imply we are significant in some way to the structure of the universe - which is absurd.

Originally Posted by Andy Swainson

right ok, but how does the electron know it is being observed? (using the definition of observe that you have provided) and by what means is the information being retained or remembered.

There's a bump when light hits you.

Does an electron remember that "there was a bump". No it remembers that "I am now here, where I am" .

Like: "I'm in slit A and I'm in slit B, but I'm more on the left side of the slit B "
(because in slit B there was a photon hit from the right )
(this would cause just a little bit distortion in the interference pattern)
(unless the photon remembers that "it was in the slit B where the collision happened")

This isn't so terribly mysterious. (Well maybe a little.) Here's a real-world analog to the double-slit experiment.

Suppose you're trying to measure with radar both the position and velocity of an aircraft. You have complete control over what type of signal to send.

If you send a single short pulse, you will have excellent information about the aircraft's position by measuring the time the pulse takes to get back to you. However, you won't know anything about its velocity.

You could then send multiple pulses to see how the position changes with time. But if you send the pulses too rapidly, you will lose track of which return echo corresponds with which pulse that you sent, and you will gradually lose your ability to estimate its position.

The other extreme would be to send a continuous wave to the aircraft and measure the reflected Doppler shift to very accurately determine its velocity. But then you would have no idea what its position was.

No matter what you do, you cannot simultaneously measure both the velocity and position of the aircraft -- you can only trade one for the other.

It's the same way with electrons. By detecting its presence with a photo-multiplier tube, you are nailing down its position, in effect by zapping it with a single short-burst radar pulse. But then you have no way to determine its velocity (or Doppler-shifted frequency). Alternatively, you can pass it though double slits. Better yet, make it pass through a multiple-slit diffraction grating. Then you can very accurately measure its Doppler frequency and hence its speed. (This is analogous to the continuous wave radar.) But then you can have no idea where it is.

Disregard EVERYTHING jartsa says. His command of physics is equivalent to my command of the Chinese Language.

Originally Posted by Arcane_Mathematician

Disregard EVERYTHING jartsa says. His command of physics is equivalent to my command of the Chinese Language.

Photon's bad eye sight and crappy memory are reasons why electron interference experiment
can be done in daylight.