# Thread: Double slit experiment and CERN

1. Originally Posted by Jeff Root
The "bullets" need to be very small to create an interference
pattern with detectable banding. Atom-size "bullets" can work.
Photon-size "bullets" definitely work.
I think gzhpcu was taking about bullet bullets.

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You might need a specially-made "gun" to fire such tiny bullets,
but being tiny doesn't mean they aren't real bullets. The bigger
the bullet, the less obvious the interference pattern will be, until
you get the problem Grant pointed out that the bullets are larger
than the slits, messing up the experiment.

-- Jeff, in Minneapolis

3. Originally Posted by Jeff Root
You might need a specially-made "gun" to fire such tiny bullets,
but being tiny doesn't mean they aren't real bullets.
It kind of does, when the word is used without qualification or scare quotes.

Grant Hutchison

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Is there a minimum size a bullet can be?

-- Jeff, in Minneapolis

5. Originally Posted by Jeff Root
Is there a minimum size a bullet can be?

-- Jeff, in Minneapolis
You seem to be missing the point. The distinction was being made between macroscopic object (e.g. a real bullety-bullet) and waves. Trying to make the macroscopic object behave like a quantum object destroys the distinction being made.

(Not that I think characterising the difference as "wave" vs "particle" is useful, but that is the point that was being made.)

6. Originally Posted by Jeff Root
Is there a minimum size a bullet can be?
Corresponding to the minimum size of functioning cartridge, and the minimum size of gun to fire that cartridge. Currently around 2mm calibre.
Could go smaller, but the cartridge design is the tricky bit, and the exercise increasingly pointless.

But as Richard Feynman said, the purpose of language is communication. If you use a word that creates a confusing impression in someone else's head, it's the wrong word.

Grant Hutchison

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Yes, if there is no lowest size intended in the meaning of the word "bullet", then one can simply use the term "particle," which clearly has no lower limit, and is the word usually used for talking about quantum effects. So it's always strange when people say things like "bullets do this too, you just don't notice because they are too big to notice," because science is what we can notice by trying hard. So if something is too big to notice it doing something, no matter how hard we try, then one cannot say it does that at all. We should really say, bullets don't do what quantum particles do, but only because they are so big. Indeed, I think saying that particles that are thought to be behaving particlelike are really behaving wavelike is muddling the insight-- the insight should be that waves do both what we call wavelike, and what we call particlelike, behavior. It's clear that waves can have any wavelength, so said that way, there's no confusion. It's not that particles always have a bit of wavelike properties, it is that wavelike properties are more general than we realized, and include particlelike behavior-- even behavior that is so particlelike we cannot notice anything wavelike beyond the fact that waves can do that too.
Last edited by Ken G; 2018-Feb-12 at 09:17 PM.

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Originally Posted by Ken G
Yes, if there is no lowest size intended in the meaning of
the word "bullet", then one can simply use the term "particle,"
which clearly has no lower limit, and is the word usually
used for talking about quantum effects.
That was my point. A bullet is an example of a particle.
There are no specific size limits on particles, and no specific
size limits on bullets. And there is is no specific limit at which
the wave properties of particles disappear. They just become
more and more difficult to detect, until they are lost in the
grass, and you can't be sure they are detectible anymore.

-- Jeff, in Minneapolis

9. But of course there is a size limit to both particles and bullets, in common usage, and the overlap in size is effectively zero. We do not anticipate "particles" being bigger than our heads, or "bullets" being too small to see, so if we use either of those words in senses outside the usual, we create confusion.

Grant Hutchison

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The "particle" term is a bit broader than that, as physicists treat cannon balls, or even planets, as particles sometimes. Language is always so intentionally vague, we are forever stuck between the rock and the hard place of wanting precision but also not wanting to learn a million different terms! Often, "particle" is not a question of size, it's a question of not caring about the internal dimensions (and even that has exceptions but such is the nature of language!). I've even seen simulations where entire galaxies were treated as "particles"! It really just means, the object in question is small compared to the size scale of interest. We can call a particle a "bullet" if we expressly want to say we are ignoring quantum effects, but the converse is not the case-- calling a bullet, cannon ball, or planet, a particle does not mean we are interested in quantum effects, it means we are not treating them any different from each other and are not interested in their sizes. For example, there is a computational device called "smooth particle hydrodynamics" where chunks of fluid are treated as "particles," and their "smallness" is only related to the grid in question, not quantum effects. The grid could be the observable universe! That's a technical meaning of "particle," but even in common usage, the key element is smallness in some relative scale, not an absolute scale.
Last edited by Ken G; 2018-Feb-13 at 02:54 AM.

11. Originally Posted by Ken G
The "particle" term is a bit broader than that, as physicists treat cannon balls, or even planets, as particles sometimes.
Oh yes - terms of art do all sorts of violence to the common meaning of words that you find in the dictionary. My point was about general usage, though - a conscientious physicist speaking to a lay audience would define "particle" in context, or avoid the term all together.

Grant Hutchison

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In this case, both the term "particle impact pattern" and the term
"wave interference pattern" were introduced by the original poster
in the second sentence of the original post.

Part of what I was trying to do was push the idea that those are
not two different things.

as anyone. In this particular case, conflating bullets and particles
seems natural and not at all confusing to me. But I can, if I try,
imagine it being totally confusing to all sorts of other people.
But I'm not sure I would do anything different. From my point
of view, bullets are particles as the original poster used both of
those terms. It seems to me that the original poster used the
term "bullets" as an obvious example of particles, as contrasted
with waves.

Also from my point of view - which is strongly shaped by my
understanding of theory, and which appears to conflict with some
aspects of Ken's point of view - bullets have wave properties every
bit as much as any other particle, even if bullets are too big for
those wave properties to be detected.

-- Jeff, in Minneapolis

13. Originally Posted by Jeff Root
... bullets have wave properties every
bit as much as any other particle, even if bullets are too big for
those wave properties to be detected.
So now you're talking about bullets of the conventional kind?
Can you see how this confusing?

Grant Hutchison

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I think you read something into my use of the word "bullets" that
does not exist. My assertion that you quoted applies whether the
bullet is a single proton or an entire planet, so it certainly applies
to the entire range of actual bullets.

-- Jeff, in Minneapolis

15. Originally Posted by Jeff Root
I think you read something into my use of the word "bullets" that
does not exist. My assertion that you quoted applies whether the
bullet is a single proton or an entire planet, so it certainly applies
to the entire range of actual bullets.
You might want to review the grammar then, since your statement was a conditional on "bullets are too big for those wave properties to be detected". If you'd written "some bullets" or "bullets may be" you'd have allowed for a subset of bullets for which wave properties could be detected (like a proton). As it was, your phrase applies to all bullets being too big, and therefore excludes bullets on the scale of a proton.

Grant Hutchison

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Originally Posted by Jeff Root

Also from my point of view - which is strongly shaped by my
understanding of theory, and which appears to conflict with some
aspects of Ken's point of view - bullets have wave properties every
bit as much as any other particle, even if bullets are too big for
those wave properties to be detected.
Let me clarify my point. Physics is an empirical science. Hence, we should never say that anything has any property that has never been detected and has no prospect of ever being detected. So we should not say that bullets "have wave properties," by which one assumes you mean "do things only waves do like diffract," because that would be to claim we know things about them that we do not in fact know. But much more to the central issue of "wave/particle duality," though, I feel what is so often missed by language like "wavelike properties" is this:
It is not that bullets have some strange properties we could never detect, it is that waves can do everything that bullets are actually found to do. See the difference?
Last edited by Ken G; 2018-Feb-13 at 05:02 PM.

17. Originally Posted by Ken G
Let me clarify my point. Physics is an empirical science. Hence, we should never say that anything has any property that has never been detected and has no prospect of ever being detected. So we should not say that bullets "have wave properties." More to the point, though, I feel what is so often missed by this language is that it is not that bullets have some strange properties we could never detect, it is that waves can do everything that bullets (and I mean real bullets) are found to do. See the difference?
I think this is what motivates the people who say: "There are no waves and no particles, only fields." But then they have to explain that the field does wave-like stuff, and interacts via excitations that look like particles. So it's back to waves manifesting themselves through "particulate" interactions.

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Originally Posted by grant hutchison
I think this is what motivates the people who say: "There are no waves and no particles, only fields." But then they have to explain that the field does wave-like stuff, and interacts via excitations that look like particles. So it's back to waves manifesting themselves through "particulate" interactions.
There is certainly no more slippery issue in physics than ontology! For example, in another thread I am being told that gravity is actually a curvature of spacetime, so any model that doesn't treat it like that is null and void. That reasoning is wrong on so many levels I hardly know where to start.

19. Originally Posted by Ken G
There is certainly no more slippery issue in physics than ontology! For example, in another thread I am being told that gravity is actually a curvature of spacetime, so any model that doesn't treat it like that is null and void. That reasoning is wrong on so many levels I hardly know where to start.
Yeah. My feeling over there was that if someone thinks of mathematical theories as defining ontological entities, then they're going to have trouble following the reasoning when someone treats them as part of an epistemological toolkit.

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Originally Posted by Ken G
For example, in another thread I am being told that gravity is actually a curvature of spacetime, ...
This is that thread where I stated 10 days ago the textbook physics that in general relativity the source of (I used "caused by") gravity is curved spacetime which excludes gravity as in GR from being included in QM..
Specifically: Gravity is caused by curved space-time. QM is has no curved space-time. The operators in QM are only defined in a flat space-time. (imprecise but the gist is clear: QM cannot include GR).

On the other hand, Newtonian gravity can be included in QM but is normally not because its effects are generally negligible, e.g. people who learned the hydrogen atom solution to Schrodinger's equation can quickly calculate the Bohr radius for a gravitationally system (say an electron and neutron) and see that it is several magnitudes greater than the radius of the universe. That trivial calculation is a reason why QM textbooks with a chapter on gravity in QM are rare. I had to do at least 10 minutes research to find one!

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Originally Posted by grant hutchison
My feeling over there was that if someone thinks of mathematical theories as defining ontological entities, then they're going to have trouble following the reasoning when someone treats them as part of an epistemological toolkit.
No one in that thread (a link so people can actually look at the thread in question) has stated that mathematical theories defined ontological entities. For example I stated that the theory of and the evidence for GR makes it the best current theory of gravity.

ETA: But this seems a derail from both threads so perhaps we should stop here.
Last edited by Reality Check; 2018-Feb-13 at 11:06 PM.

22. Actually, my comment has relevance here, too. Which was why I made it here.

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Originally Posted by Ken G
Originally Posted by Jeff Root
Also from my point of view - which is strongly shaped by my
understanding of theory, and which appears to conflict with some
aspects of Ken's point of view - bullets have wave properties every
bit as much as any other particle, even if bullets are too big for
those wave properties to be detected.
Let me clarify my point. Physics is an empirical science. Hence,
we should never say that anything has any property that has never
been detected and has no prospect of ever being detected.
I'll say it.

All fundamental particles have wave properties. All matter
consists of fundamental particles. Therefore, all matter has
wave properties.

Originally Posted by Ken G
So we should not say that bullets "have wave properties," by which
one assumes you mean "do things only waves do, like diffract," ...
I would definitely leave out the "only". I'm saying that particles
do things that waves do. I'm saying that everything does things
that waves do.

Wasn't it you who recently referred to "the wavefunction" of macro
objects? I'm not sure you ever asserted that such a wavefunction
actually "exists", and I'm almost certain you didn't claim it could
actually be known, but I think you were talking about it.

In my view, this "wavefunction" is a step (or possibly more) beyond
the concept of "wave properties" when applied to macroscopic
objects.

Originally Posted by Ken G
... because that would be to claim we know things about them that
we do not in fact know.
I can't define what it means for me to "know" something, but I'm
quite satisfied that I know that all matter has wave properties,
whether those wave properties can be observed or not. I know
lots of things that nobody has ever observed, usually by a
combination of inductive and deductive logic applied to a
large range of things I *have* observed.

Originally Posted by Ken G
But much more to the central issue of "wave/particle duality,"
though, I feel what is so often missed by language like
"wavelike properties" is this:
It is not that bullets have some strange properties we could
never detect, it is that waves can do everything that bullets
are actually found to do.
See the difference?
Waves by themselves can't do anything. Waves are a set of
behaviors of matter. "Waving" in various ways is something
all matter does, including bullets.

-- Jeff, in Minneapolis
Last edited by Jeff Root; 2018-Feb-14 at 12:25 AM.

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Originally Posted by grant hutchison
Actually, my comment has relevance here, too. Which was why I made it here.
No evidence given that the thread you are commenting on has relevant posts = seemingly a derail of this thread. If you or Ken G had inked to specific posts and those poste contained what you stated then those poste would be relevant. Then we perhaps could have fun looking at every other post in every other thread to see if they are relevant !

The thread is how does 'particle in a box' relate to compact bodies?. I can find no posts that match the comments in your posts here as I pointed out in my 2 posts

25. Originally Posted by Reality Check
No evidence given that the thread you are commenting on has relevant posts = seemingly a derail of this thread. If you or Ken G had inked to specific posts and those poste contained what you stated then those poste would be relevant. Then we perhaps could have fun looking at every other post in every other thread to see if they are relevant !

The thread is how does 'particle in a box' relate to compact bodies?. I can find no posts that match the comments in your posts here as I pointed out in my 2 posts
As I said already, the ontological/epistemological divide occurred to me on the thread you're referencing, for reasons that I've already stated on the thread you're referencing.
I mentioned it here, too, because it's relevant on this thread, and Ken reminded me of the thought. Synchronicity.

Grant Hutchison
Last edited by grant hutchison; 2018-Feb-14 at 03:07 AM.

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Originally Posted by grant hutchison
As in the post you replied to, you give no evidence for your assertion - not even the posts that you are commenting on from the other thread. So:
grant hutchison: Please supply links to the posts where "someone thinks of mathematical theories as defining ontological entities"
It was not my posts as far as I can see.
ETA:
There is my post I agree: A set of equations alone cannot cause anything. which is close to "mathematical theories do not define ontological entities".
There is a discussion of "cause of" versus "best described by".
That leaves your posts, Ken G's posts, or someone else's posts.

ETA2: A very tiny possibility of "caused by" big interpreted as "defined"? That GR is the best model that we have currently for gravity so using "caused by" means GR math defines gravity?
Last edited by Reality Check; 2018-Feb-14 at 03:52 AM.

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## Link to the posts(s) stating that gravity is actually a curvature of spacetime

Originally Posted by Ken G
For example, in another thread I am being told that gravity is actually a curvature of spacetime, so any model that doesn't treat it like that is null and void.
Ken G: Please give a link to the specific posts(s) that state that gravity is actually a curvature of spacetime.
Gravity is a force. Curvature of spacetime is a geometric property. Their definitions make "actually" wrong. In GR the curvature of spacetime best describes/causes gravity. A bit simply put and I am sure you know this: mass curves spacetime, objects thus follow curved paths relative to a flat spacetime, a curved path = changes in direction, a change in direction is a change in velocity, a change in velocity is an acceleration, F=ma so there is a force, thus F is the force of gravity. That GR reduces to Newtonian gravitation in the appropriate limit is also a big hint that it describes the force of gravity !

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Sticking to what is relevant here, and avoiding the usual semantic whirlpools, ontology to the physicist is like hats to a Vaudeville actor. You put them on when you need them. The question is never "what is our most accurate model in every situation," instead it is always "what is the simplest model that meets our needs." So when one talks about bullet dynamics, classical mechanics is the answer, not quantum mechanics. It is interesting that quantum mechanics works too, as per Bohr's correspondence principle, but it doesn't mean classical mechanics is wrong and quantum mechanics is right. Both are likely wrong at some level, so we pick the one we need. But as I keep stressing, the takeaway message is not that bullets act like waves and we have no way to see that they do, it is that waves are perfectly capable of acting like bullets. It's that latter point that gets overlooked.

29. Originally Posted by Ken G
Sticking to what is relevant here, and avoiding the usual semantic whirlpools, ontology to the physicist is like hats to a Vaudeville actor. You put them on when you need them.
It would be better, I think, if physicists thought of this as swapping epistemologies - that the nature of the thing being investigated doesn't change when you change your hat, it's the best route to knowledge that changes. It's why I find the statement, "It's not a particle or a wave, it's a field," at best unhelpful and at worst counterproductive.

Grant Hutchison

30. Originally Posted by Reality Check
As in the post you replied to, you give no evidence for your assertion - not even the posts that you are commenting on from the other thread. So:
grant hutchison: Please supply links to the posts where "someone thinks of mathematical theories as defining ontological entities"
It was not my posts as far as I can see.
ETA:
There is my post I agree: A set of equations alone cannot cause anything. which is close to "mathematical theories do not define ontological entities".
There is a discussion of "cause of" versus "best described by".
That leaves your posts, Ken G's posts, or someone else's posts.

ETA2: A very tiny possibility of "caused by" big interpreted as "defined"? That GR is the best model that we have currently for gravity so using "caused by" means GR math defines gravity?
You know you're not in ATM?

Really, I don't need to defend a post in which I describe a "feeling" I had on another thread. Either I did have that feeling, and my statement is accurate, or for seem deep nefarious reason I'm lying about having had that feeling. My posts on the thread in question actually show me sharing that feeling publicly, so it seems I'm not actually lying.

I suggest you move on.

Grant Hutchison

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