|
One contender for the smallest thing in the universe is the
singularity at the center of a black hole. (Shown here, an artist's
drawing of a black hole pulling gas away from a companion star.
CREDIT: NASA E/PO, Sonoma State University, Aurore Simonnet
|
The answer to the enduring question of the smallest thing in the
universe has evolved along with humanity. People once thought grains of
sand were the building blocks of what we see around us. Then the atom
was discovered, and it was thought indivisible, until it was split to
reveal protons, neutrons and electrons inside. These too, seemed like
fundamental particles, before scientists discovered that protons and
neutrons are made of three quarks each.
"This time we haven't been able to see any evidence at all that there's
anything inside quarks," said physicist Andy Parker. "Have we reached
the most fundamental layer of matter?"
And even if quarks and electrons are indivisible, Parker said,
scientists don't know if they are the smallest bits of matter in
existence, or if the universe contains objects that are even more
minute. [
Graphic: Nature's Tiniest Particles]
Parker, a professor of high-energy physics at England's Cambridge
University, recently hosted a television special on the U.K.'s BBC Two
channel called "
Horizon: How Small is the Universe?"
Strings or points?
In experiments, teensy, tiny particles like quarks and electrons seem
to act like single points of matter with no spatial distribution. But
point-like objects complicate the laws of physics. Because you can get
infinitely close to a point, the forces acting on it can become
infinitely large, and scientists hate infinities.
An idea called
superstring theory
could solve this issue. The theory posits that all particles, instead
of being point-like, are actually little loops of string. Nothing can
get infinitely close to a loop of string, because it will always be
slightly closer to one part than another. That "loophole" appears to
solve some of these problems of infinities, making the idea appealing to
physicists. Yet scientists still have no experimental evidence that
string theory is correct.
Another way of solving the point problem is to say that space itself
isn't continuous and smooth, but is actually made of discrete pixels, or
grains, sometimes referred to as
space-time foam.
In that case, two particles wouldn't be able to come infinitely close
to each other because they would always have to be separated by the
minimum size of a grain of space.
A singularity
Another contender for the title of smallest thing in the universe is the singularity at the center of a black hole.
Black holes are formed
when matter is condensed in a small enough space that gravity takes
over, causing the matter to pull inward and inward, ultimately
condensing into a single point of infinite density. At least, according
to the current laws of physics.
But most experts don't think
black holes are really infinitely dense. They think this infinity is the product of an inherent conflict between two reigning theories — general relativity and
quantum mechanics — and that when a theory of
quantum gravity can be formulated, the true nature of black holes will be revealed.
"My guess is that [black hole singularities] are quite a lot smaller
than a quark, but I don't believe they're of infinite density," Parker
told LiveScience. "Most likely they are maybe a million million times or
even more than that smaller than the distances we've seen so far."
That would make singularities roughly the size of superstrings, if they exist.
The Planck length
Superstrings, singularities, and even grains of the universe could all turn out to be about the size of the "Planck length." [
Tiny Grandeur: Stunning Photos of the Very Small]
A Planck length is 1.6 x 10^-35 meters (the number 16 preceded by 34
zeroes and a decimal point) — an incomprehensibly small scale that is
implicated in various aspects of physics.
The Planck length is far and away too small for any instrument to
measure, but beyond that, it is thought to represent the theoretical
limit of the shortest measureable length. According to the uncertainty
principle, no instrument should ever be able to measure anything
smaller, because at that range, the universe is probabilistic and
indeterminate.
This scale is also thought to be the demarcating line between general relativity and quantum mechanics.
"It corresponds to the distance where the gravitational field is so
strong that it can start to do things like make black holes out of the
energy of the field," Parker said. "At the Planck length we expect
quantum gravity takes over."
Perhaps all of the universe's smallest things are roughly the size of the Planck length.
Follow Clara Moskowitz on Twitter @ClaraMoskowitz or LiveScience @livescience. We're also on Facebook & Google+.
“Philosophy
is merely thought that has been thought out. It is often a great bore.
But man has no alternative, except between being influenced by thought
that has been thought out and being influenced by thought that has not
been thought out. The latter is what we commonly call culture and
enlightenment today. But man is always influenced by thought of some
kind, his own or somebody else’s; that of somebody he trusts or that of
somebody he never heard of, thought at first, second or third hand;
thought from exploded legends or unverified rumours; but always
something with the shadow of a system of values and a reason for
preference. A man does test everything by something. The question here
is whether he has ever tested the test.”
