Hi, I'm John Skieswanne, and this post is part 6 of a series on physics. In this series I will explain a few pillars of modern physics. I won't be
using any complex maths. It is my hope that this series will introduce some of you brilliant, curious-minded laymen out there to the inner circles of
So, sit back and enjoy.
The Four Forces of the Universe
The Strong Force:
Imagine you are in a forest and you find a 4-feet stick from a tree. I ask you to split the stick in two (with no tools). So you hold both ends of the
stick with your hands, and with your knee you apply a force that eventually breaks the stick in its center. Now imagine that I ask you to break one of
these new, 2-feet long halves of stick. You do the same but the stick is smaller, more leverage is needed, and it takes a bit more time. Then I tell
you to the same with the new 1-foot long piece. Difficulty increases. When the stick reaches to a few inches, the task is almost impossible - the
leverage is so bad, you'd need more energy than any humans have just to compensate. The more you break the stick into its parts, the more energy it
takes to split the parts into even smaller parts, and the more energy-concentrating tools are needed.
Similarily, the strong force, responsible for the structural integrity of the atom's nucleus, is the strongest force in the known universe - a
whopping 1000000000000000000000000000000000000000 times stronger than gravitation. In fact, the force has to be strong enough to hold protons together
in a nucleus, despite the protons' mutually repulsive electric charges of +1.
But most of all, the strong force is responsible for binding quarks themselves (the very building blocks of protons and neutrons) together to form
hadrons or mesons. The force (also called colour force) is being mediated by gluons, which were named this way for obvious reason. It is also the only
force to actually strenghten with the distance (but then fall off after a certain point) - this is caused by a complex mechanism.
The Weak Force:
We all heard about radioactive substances, such as carbon-14. Some particles, such as neutrons, cannot survive long if not bonded properly. In atoms
with more neutrinos than protons, such as carbon-14 (which has 8 neutrons and 6 protons - that is, it has an over of 2 neutrons), one of the extra
neutrons will eventually decay. According to the Standard Model of Physics, neutrons decay as such: the neutron turns into a proton, emitting at the
same time a W- boson (carrier of the Weak force), which in turn splits into an electron and an electron antineutrino. So, in a carbon-14 atom, one of
the two extra neutrons will turn into a proton, emitting a W- boson which will provide a new electron (and antineutrino).
The atom now has 7 neutrons, 7 protons, and 7 electrons - this is why carbon-14 eventually turn into nitrogen, which happen to be made of 7 neutrons,
7 protons, and 7 electrons.
The Weak force is pretty much the "force of decay". Quite unusual for a force, it is carried by three particles instead of only one. The W- boson is
but one of three particles that carry the force of decay; the two others being the W+ boson, and the Z boson. They all carry their own decay modes.
Another unusual thing for a force is the fact that the Weak interactions only affects left-handed particles, whereas all three other forces affect
both left- and right-handed particles. Furthermore, all three weak bosons are heavily massive, whereas all other force bosons are massless. And, it is
the only force that transforms a particle into another. All this coupled with the practical impossibility to actually observe W-, W+ and Z bosons
(according to the Standard Model of Physics their half-life is around 0.0000000000000000000000003 second - their life is so short that they can be
considered virtual particles) make the weak force the oddest of all four forces.
The Gravitational Force:
This is the force with the less strenght. Yet it is the most familiar of all four forces. Most (if not all) everyday objects are subject to Gravity.
From planets to grains of sand.
Yes, it is true that two object with different weights will actually fall at the same speed to the ground. This is because objects have inertia.
"Inertia" is resistance to acceleration - it is the reason why it takes far more energy to push a car than a shopping cart. Sure, the graviational
force excerces a greater pull on the 10-pound weight than upon the 1-pound weight. But, the gravitational force also needs to accelerate 10 pounds of
resistance to movement instead of only one pound.
So in the end, both objects really end up falling at the exact same rate.
Einstein suggested that gravity was the result of mass as it bends space-time, whereas quantum theorists theorize that gravitation is carried by a
particle called the graviton.
Gravitation is posing a problem for the current Standard Model of Physics, for although quantum theorists can give an accurate model for gravitation
on macroscopic scales, their model represents not reality at the Planck lenght scale. Furthermore, mass (which gravitation interacts with) is giving
trouble to the Standard Model - the latter gives no mass for neutrinos, whereas in reality these particles are known to have (albeit a small) mass.
Newton gives a way to determine the graviational force (F) between two object (object A and object B) with mass A and mass B:
F = G*((massA*massB)/distance^2)
where G is equal to 0.00000000006674. In astronomy, the velocity (V) a body needs to achieve so to stay in orbit (with mass A) around another body
(with mass B) is equal to:
V = sqrt((G*(massA+massB))/distance)
With Einstein's theory of General Relativity, though, a few adjustements are made - but Newton's orginal equation is still a rather precise
approximation for most calculations.