# Double Slit

• B
I was wondering if the double slit experiment had been conducted in space away from interference from earths magnetic core/field. I know the scientific community would have considered all variables and would have set proper controls for this experiment but I am unable to find any notes on this. I am trying to figure out the magnetic/electrical field and gravity into this whole equation.

-Geronimo

JonathanCollins

Orodruin
Staff Emeritus
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Earth's magnetic field is far too small (and homogenous on the scale of a typical double slit experiment) to affect the double slit experiment significantly. Furthermore, you can perform the double slit experiment with photons, which do not have a coupling to the magnetic field.

Simon Clement and bhobba
Earth's magnetic field is far too small (and homogenous on the scale of a typical double slit experiment) to affect the double slit experiment significantly. Furthermore, you can perform the double slit experiment with photons, which do not have a coupling to the magnetic field.
Would you know what effect, if any, would gravity and solar winds have? I'll have to do the math on this one.

Thank you,

Geronimo

Nugatory
Mentor
I was wondering if the double slit experiment had been conducted in space away from interference from earths magnetic core/field. I know the scientific community would have considered all variables and would have set proper controls for this experiment but I am unable to find any notes on this. I am trying to figure out the magnetic/electrical field and gravity into this whole equation.
Every piece of electronic equipment in any modern satellite or space probe depends on quantum mechanics working the way we expect in the presence or absence of the earth's magnetic field. That's a lot of testing of the basic principles.

DrChinese
Gold Member
Do you get a interference pattern in a vacuum is a good question i have no idea =)
Yes, you get an interference pattern in a vacuum. In quantum versions of the double slit, the interference is always self-interference. Therefore the presence of air does not increase the interference effect.

Simon Clement
I was wondering if the double slit experiment had been conducted in space away from interference from earths magnetic core/field. I know the scientific community would have considered all variables and would have set proper controls for this experiment but I am unable to find any notes on this. I am trying to figure out the magnetic/electrical field and gravity into this whole equation.

-Geronimo
The same question occurred to me today and I was also unable to find any references for the 2 slits experiment having being carried out away from the influence of these fields. It would be fascinating to test for any variation in the results of the experiment were it to be carried out on the space station (perhaps this is not a practical option?). However Nugatory makes a good point to cast doubt on there being any variations when he says "Every piece of electronic equipment in any modern satellite or space probe depends on quantum mechanics working the way we expect in the presence or absence of the earth's magnetic field".

From my understanding wherever the experiment was conducted there would always be some field present (e.g. background radiation) which could potentially be a factor in the presence of interference patterns. One difficulty with considering the potential effect of the presence electromagnetic waves on an atom or molecule seems to me to be in first comprehending what constitutes the wave (i.e. what is actually waving?).

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DrChinese
Gold Member
From my understanding wherever the experiment was conducted there would always be some field present (e.g. background radiation) which could potentially be a factor in the presence of interference patterns.
Do you have a hypothesis as to how "background radiation" would affect the outcome of a double slit experiment? Because nothing from current theory would apply. And the experiment controls for that anyway, by removing the presence or absence of "background radiation" as a variable.

If you have a hypothesis, that could be separately tested - even on Earth perhaps. If you have no hypothesis, then this is purely speculation. You may as well ask if the results on Thursdays in Manila might be different than Tuesdays in Canada. I don't think that has been done either. Hopefully my point is clear.

Would you know what effect, if any, would gravity and solar winds have?
I almost missed where you were going, and was going to say gravity is negligible, and it should be commonly known what effect solar flares have on electrical systems, so I ask you to elaborate and confirm my suspicion, if you wouldn't mind.

Staff Emeritus
. It would be fascinating to test for any variation in the results of the experiment were it to be carried out on the space station
Why? The gravity on the space station is almost the same as it is on Earth.

Why? The gravity on the space station is almost the same as it is on Earth.
it is apparently about 89% of the effect on the surface of the earth so there is enough difference to potentially alter the results of an experiment.

Do you have a hypothesis as to how "background radiation" would affect the outcome of a double slit experiment? Because nothing from current theory would apply. And the experiment controls for that anyway, by removing the presence or absence of "background radiation" as a variable.

If you have a hypothesis, that could be separately tested - even on Earth perhaps. If you have no hypothesis, then this is purely speculation. You may as well ask if the results on Thursdays in Manila might be different than Tuesdays in Canada. I don't think that has been done either. Hopefully my point is clear.
How does the experiment remove the presence or absence of "background radiation" as a variable?

DrChinese
Gold Member
How does the experiment remove the presence or absence of "background radiation" as a variable?
Because it is present when there is an interference pattern, and it is present when there is no interference pattern. The purpose of the double slit experiment is to demonstrate there is particle interference when the path is unknown/unknowable. So obviously the demonstrated effect is independent of "background radiation".

On the other hand: if you had a hypothesis that "background radiation" could alter this experiment somehow, it would not be enough to change the standard predictions. But it might be detectable in a range of experiments that were designed to detect it.

But you would need to have a hypothesis. What is yours? And is this simply conjecture, or do you have a particular reason to associate it with the double slit experiment in particular?

Because it is present when there is an interference pattern, and it is present when there is no interference pattern. The purpose of the double slit experiment is to demonstrate there is particle interference when the path is unknown/unknowable. So obviously the demonstrated effect is independent of "background radiation".

On the other hand: if you had a hypothesis that "background radiation" could alter this experiment somehow, it would not be enough to change the standard predictions. But it might be detectable in a range of experiments that were designed to detect it.

But you would need to have a hypothesis. What is yours? And is this simply conjecture, or do you have a particular reason to associate it with the double slit experiment in particular?
Thank you for this explanation. I do not currently have any coherent hypothesis.

What would preclude the individual atom during its journey through the slits from actually consisting of both a particle and a wave?

DrChinese
Gold Member
Thank you for this explanation. I do not currently have any coherent hypothesis.

What would preclude the individual atom during its journey through the slits from actually consisting of both a particle and a wave?
Nothing in particular. This is something of a philosophical question, as there are interpretations (Bohmian Mechanics for example) in which there is both a point particle and something called a pilot wave. There is no known experiment (on Earth or otherwise) however which would identify this concretely, and it is actually axiomatic that there cannot be such (that doesn't stop folks from trying however).

...One difficulty with considering the potential effect of the presence electromagnetic waves on an atom or molecule seems to me to be in first comprehending what constitutes the wave (i.e. what is actually waving?).
The background fields are not the only problem. When the experimenters put a sensor at one of the slits, the interference pattern disappears. The sensor must have an effect on the wave/particles going through the slit. How can they do that without invalidating the test. Also the particles that go close to the sides of the slit would be influenced by the Casmir effect. I am looking for a intuitive interpretation of the double slit experiment that takes into account these fields, sensors, and Casmir issues.

the double slit experiment that takes into account these fields, sensors, and Casimir issues.
The magnetic and gravitational fields are all very well understood besides the double slit, the only near miss is gravitational collapse, but that is way off topic for a standard double-slit interference pattern, which is simply intended to display destructive and constructive interference. Sensing the path the quantum objects take, as you mentioned has not just a lack of interference, but the introduction of "particle behavior" as well. The Casimir effect would just scatter the edges.

DrChinese
Gold Member
The sensor must have an effect on the wave/particles going through the slit. How can they do that without invalidating the test.
Actually you can have the same "sensors" on both slits and get interference, or not get interference. So no, it's not the presence of sensors that do it. You should review the double slit fundamentals so you understand why this and the other things you mentioned are not factors. If they are held constant, they do not explain the results.

Nugatory
Mentor
The sensor must have an effect on the wave/particles going through the slit. How can they do that without invalidating the test.
Of course the detector has an effect - it makes the interference pattern disappear. That doesn't "invalidate" the test, it confirms the quantum mechanical prediction that there will be no interference pattern if there is a macroscopically significant interaction at either slit.

bhobba
I hear a lot about detector's interfering with the pattern but no explanation ever telling me what detector's there actually using that causes it. Other than polarization filters what detectors are used ??

Of course the detector has an effect - it makes the interference pattern disappear. That doesn't "invalidate" the test, it confirms the quantum mechanical prediction that there will be no interference pattern if there is a macroscopically significant interaction at either slit.
Let me sum things up: Conventional wisdom: if there is a "macroscopically significant interaction at either slit" the wave collapses down to a particle which appears to go through only one or the other slit and the interference pattern disappears. I have no trouble with the wave itself anymore because particles cannot be made of still finer particles indefinitely. I used to find the wave-collapse concept as very mysterious but now I see it more intuitively: Any attempt to measure a wave must steal energy from it, and at the quantum level that might easily be half or all of the energy, so it disrupts the wave. It flips the attribute bits in a probabilistic way (based on probability, but perhaps jittered by real world chaos rather than true randomness).

Nugatory
Mentor
Let me sum things up: Conventional wisdom: if there is a "macroscopically significant interaction at either slit" the wave collapses down to a particle which appears to go through only one or the other slit and the interference pattern disappears.
That's not so much the "conventional wisdom" as it is a very common misstatement of a particular interpretation of QM. This notion that there's a wave that "collapses down to a particle" doesn't appear in the mathematical formalism at all - it dates back to the early 20th century when we were still trying to make sense of the newly discovered quantum phenomena, and was largely abandoned after the modern theory of QM was developed. At some point in your study of QM you have to let go of this notion, stop thinking in terms of waves and particles and start thinking in terms of quantum systems.

It flips the attribute bits in a probabilistic way (based on probability, but perhaps jittered by real world chaos rather than true randomness).
Bell's theorem shows that "jittered by real world chaos" is not a viable explanation, at least as the term is generally used to describe the apparent randomness that appears when we're observing a complex system whose inner workings are deterministic but we don't know enough to predict the outcome in advance.

bhobba
Nugatory
Mentor
I hear a lot about detector's interfering with the pattern but no explanation ever telling me what detector's there actually using that causes it. Other than polarization filters what detectors are used ??
It depends on what type of particle we're using for the experiment. Photons are used most often because they're easy to produce and manipulate with relatively inexpensive equipment. (For example, photons travel freely through air; electrons don't, so if you're going to do anything with them you first have to consider how to enclose your entire experiment in a vacuum chamber. Because of this and other practical considerations the double-slit experiment was done with photons decades before it was done with electrons).

But with that said... Photons are detected with photomultiplier devices, photographic film, careful use of polarizing filters as DrChinese mentioned, and if you google for "single photon detector" you'll find more. Kim's version of the delayed choice quantum eraser experiment used a particularly clever technique for detecting which slit a photon went through without disturbing the photon as passed through the slits; wikipedia has a good description.

However, the simplest "detector" of all is to block one slit or the other - if the particle reaches the screen we have a detection at the unblocked slit. This may look like cheating ("Huh? - if you block one slit it's not a double-slit experiment at all, it's a one-slit experiment!") but that's missing the point - the quantum mechanical prediction we're testing is that even when we're sending single particles an interference pattern appears or doesn't appear according to whether there are two paths or one.

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DrChinese
Gold Member
Conventional wisdom: if there is a "macroscopically significant interaction at either slit" the wave collapses down to a particle which appears to go through only one or the other slit and the interference pattern disappears. ... Any attempt to measure a wave must steal energy from it, and at the quantum level that might easily be half or all of the energy, so it disrupts the wave. It flips the attribute bits in a probabilistic way (based on probability, but perhaps jittered by real world chaos rather than true randomness).
First of all, when polarizers are present as the potential mechanism to learn which-path information: the determining factor for whether there is interference is ONLY the relative orientation of the polarizers. If a particle only goes through 1 slit, that should make NO difference.

Secondly: What are you saying when you refer to "attribute bits" and "real world chaos" and this experiment? How does that explain ANYTHING about an interference pattern?

Guys, as I understand all double slit experiments performed are not what is described, but rater there is a physical devices like mirrors, filters and etc. used for detecting which path the particle takes. I am wondering, how we know that with this physical devices we are not disturbing the experiment in a way we do not understand. So I am wondering is there a real double slit experiment performed by pure eye observation and recording the paths of the particles without any, let me repeat ANY physical interventions - just a particle source, slits and a screen.

DrChinese