|How small can a particle be?|
|Question Date: 2013-03-06|
Great question! To answer it, first we need
to talk about what a "particle" is. When it
comes to everyday objects (baseballs, rocks,
grains of sand, and so on) we usually think of
a "particle" as something with a sharp edge, a
definite location, and a definite speed.
It turns out that this picture changes a lot
when we start talking about subatomic particles
(like electrons, neutrons, and protons).
Quantum mechanics (which is the best theory of
subatomic particles we have) tells us
that "particles" aren't just particles; they're
also waves! And like waves, subatomic particles
don't have a definite location, speed, or size.
And here's the key point: the wavelength of a
wave can change depending on how much energy it
has (this of ripples on a pond: if you splash
your hand in the water really fast, you get lots
of ripples close together, but if you slowly bob
your hand up and down in the water, you get
waves that are spaced further apart). It turns
out that the wavelength of a subatomic particle
gets smaller and smaller as you give it more and
more energy. So, to answer your question: a
particle can be as small as you want! You just
need to be able to give it enough energy to make
it that small.
Typical size of an atom is 0.000000001 inch ,
but the atom itself is made of still smaller
bits called quarks. These have a size around
It depends what you consider a "particle." In
general, when we talk about particle, we mean
something with mass that's made of atoms.
Sometimes these particles are large (like dust
particles), and sometimes these particles are
small (like nanoparticles). In this common
definition, the smallest particle would be an
Good question. There are several possible
answers, but the reality is that really small
particles behave in some ways like particles and
in some ways like waves, which makes giving the
particles attributes such as size difficult.:
Particles do have something called a Compton
wavelength, which is the amount of space in
which a particle can be found, which in a sense
is like a size in that you can't cram a particle
into a volume smaller than its Compton
wavelength. However, it's not the same as size
the way we think of it, because more than one
particle can potentially occupy the same space,
which isn't true of normal objects (e.g. your
body cannot occupy the same space as somebody
else's). The more mass a particle has, the
smaller its Compton wavelength, and so the
smaller a volume it can be forced into
However, Einstein's theory of general
relativity, which is currently the best theory
of gravity that we have (it replaces Newton's
theory), predicts that a black hole should have
a point at the very center with zero volume
containing all of the mass of the black hole.
Quantum mechanics says that this is impossible.
Therefore, either relativity or quantum
mechanics as we understand them must be wrong.
Physicists are still working on this one, and I
guarantee whoever solves it is going to get the
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