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"Why do we assume particles are spherical?" Topic


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215 hits since 25 May 2017
©1994-2017 Bill Armintrout
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Personal logo Bowman Supporting Member of TMP25 May 2017 2:12 p.m. PST

From Quora (hopefully of some interest to some):

Why do we assume particles to be spherical?

"Short answer: We don't.

Longer answer: In the best theory that we have, quantum field theory, particles are neither spherical nor do they have any other shape. Rather, they are excitations of the underlying field. For instance, there is the one-and-only electron field; each electron is a unit excitation of this field. These excitations may be localized or may be "spread out", depending on the circumstances, but we do not assume any particular shape.

Now it is true that we don't always need the full machinery of quantum field theory. Simple problems can be used using quantum mechanics, i.e., quantum particle physics. But no, even in quantum particle physics we do not assume that the particle has a particular shape. Such an assumption would be grossly misleading; for starters, it would make us visualize a particle as a miniature bullet or cannonball, but a quantum particle does not have such classical existence. For instance, when an electron goes through both slits at once in a two-slit experiment, it is not very helpful to think of the electron as a small sphere. Rather, it has a disembodied existence; it only acquires an actual location when it is measured.

Last but not least, however: especially when a particle is localized, it makes sense to ask if it interacts the same way in all directions, or if it has a preferred direction. If it interacts the same way in all directions, it is spherically symmetric. But most particles aren't. For instance, an electron has a spin and a corresponding magnetic moment, so the way it interacts with other particles is dependent on its orientation. So no, it is not spherically symmetric."

More answers here:

link

Ed Mohrmann Supporting Member of TMP25 May 2017 2:40 p.m. PST

Certainly not 'intuitively obvious to the casual observer'
I'd guess…

Winston Smith Supporting Member of TMP25 May 2017 5:53 p.m. PST

I was informed by Wise Men, who should know, that many atomic nuclei are NOT spherical, but …. oddly shaped.
In fact, this may be what made them unstable.
Because of past posts, you may think that my believing them is odd.
Au contraire! I am perfectly prepared to believe counter intuitive things! grin

Now sometimes I have to force myself to believe these counter intuitive things. Like 95% of my quantum mechanics courses…

I am like the King of Sapodilla, in Avram Davidson's magnificent two part Peregrine trilogy. He was being grilled by 4th Century bishops on whether the Son proceeds THROUGH the father or FROM the Father.
He agreeably replied "Whatever your Worships say!" And he was puzzled when he was attacked for Heresy.
So if you wish me to believe that particles need not be spherical, I'll go along with it.

Winston Smith Supporting Member of TMP25 May 2017 5:54 p.m. PST

And whenever my professors brought up stuff like the two slit stuff, I would just nod my head.

JSchutt25 May 2017 6:46 p.m. PST

"…..disembodied existence." Sounds like my dead mother-in-law….

Personal logo Bowman Supporting Member of TMP26 May 2017 5:13 a.m. PST

So if you wish me to believe that particles……

I don't. I was simply hoping others would find the discussion interesting.

As for the double slit experiment:

link

Personal logo Bowman Supporting Member of TMP26 May 2017 5:18 a.m. PST

From a previous topic:

TMP link

Personal logo Great War Ace Supporting Member of TMP26 May 2017 6:19 a.m. PST

Out of my depth. But I can assert this much: fractals answer all esoterica. Fractals allow endless expansion and reduction. Therefore, on any given "scale" of observation, fractals demonstrate a response to gravity that causes spherical bodies. The stuff that makes up such bodies is inarguably not spherical. We animals, and plants, and even rocks (whether "grounded" as part of a planet, or tumbling through space as asteroid "junk"), are not spherical. But reduced to our elements, we find spherical shapes again, if observed on the reduced scale. And "God" describes himself and his purpose as "one eternal round"………….

Martin from Canada26 May 2017 8:42 a.m. PST

Fractal wrogness: the ability shown by some people to be off at all scale levels.
link

Personal logo Andrew Walters Supporting Member of TMP26 May 2017 8:59 a.m. PST

I've seen hundreds of drawings, animations, schematics, models, and diagrams, trust me, they're spherical.

Personal logo Bowman Supporting Member of TMP28 May 2017 3:39 p.m. PST

Fractal wrongness! Love it!

You can be wrong, totally wrong and then fractally wrong.

But reduced to our elements, we find spherical shapes again, if observed on the reduced scale.

Actually, we find spheres and spheroidal shapes every time we have the conjoining of two different and opposing environments. You will get a sphere in order to minimize the surface area for the volume given. Hilbert's Rule #7:

"Of all the solids having a given volume, the sphere is the one with the smallest surface area; of all solids having a given surface area, the sphere is the one having the greatest volume."

Hilbert, David; Cohn-Vossen, Stephan (1952). Geometry and the Imagination (2nd ed.). Chelsea. ISBN 0-8284-1087-9.

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