Why are we are essentially empty?

I know that I've talked about this before, but it needs some clarification. The truth is that what we see as solid matter is an illusion. This is a difficult idea to grasp because what we see is a result of our size. There are approximately 10 to the 27 power atoms in a human body. That's a bunch.

Atoms are very tiny things, but they are immense compared to subatomic particles. By definition an atom is the smallest constituent of ordinary matter. Ordinary matter is the kind of matter that you and I see in the world.

Atoms range in size from 62 to 520 pm. A pm (picometre) is a ten-billionth of a meter or ten to the -12 power meters. That's very tiny. So, a typical atom is 10 to the -10 power meters in size.

If you think that's small, the nucleus of an atom is ridiculously small in comparison. The typical nucleus is in the fm (femtometre) range. A fm is ten to the -15 power meters. That's crazy tiny. This means that an atom is approximately 100,000 times the size of its nucleus.

You can think of this in the following way. If a pea represents a nucleus of an atom and you hold the pea in the center of a football stadium. The electron cloud that is around your pretend nucleus would be out at the peripheral of the stadium.

The funny thing about this is that 99.94% of the mass of atom is in the nucleus, which means that the electrons are very light in weight. An electron is 9.109 times ten to the -31 power kilograms. The nucleus of an atom is in the range of 10 to -25 to ten to the -27 power kilograms. Volume wise, an atom is mostly empty.

So, if this is the case, why do things that we see look perfectly solid? The reason is simple. The electron cloud around the nucleus is moving so fast it appears to be solid, and since electrons are negatively charged, the electron cloud of an atom repels the electron cloud of another atom. This is why things feel solid.

You might ask the question: how do atoms form molecules? The answer is that atoms can form bonds, which involve sharing electrons. It's a like a marriage of sorts, and in some cases these marriages are polygamist in nature. One atom can have many partners attached to it. How scandalous!

You might wonder why I am fascinated with this apparent illusion of matter. The reason is because it shows how things are not what they seem. We humans are programmed to visualize things in order to function in our world. However, there are things that we can't see, and that's where it gets crazy. The atom and its nucleus fall into the realm of the quantum world where things are strange and very crazy.

One of the properties of atoms is that they are in constant motion as long as they're above the temperature of absolute zero. Atoms vibrate, shake and oscillate constantly. It's the way that quantum stuff works. This constant motion is why gas molecules exert pressure. The molecules are in constant motion banging into one another and the walls of whatever container they're in. This motion is constant and increases in velocity and frequency when the temperature goes up.

Why don't molecules of water at room temperature and normal pressure fly away like a gas? The reason is that water molecules are attracted to one another because they have polarity. In other words the two oxygen atoms are more electronegative then the hydrogen atom (the shared electros stay more around the oxygen atoms). This causes water molecules to be attracted to one another (the hydrogen ends attract to the oxygen ends), and they form a liquid at normal temperatures and pressures. If you heat water, the molecules increase their motion and can break free and form a vapor, which is like a gas. And, if you lower the temperature, the molecules clump together to form a solid, which is ice. Actually, some of the water molecules in liquid water do fly off as vapor. This is called evaporation. The same can happen to ice when it sublimates without melting. These changes of physical state are called phase transitions.

What's really strange about atoms is that some subatomic particles pass through them without interaction. What I mean by this is that a tiny particle may pass through an atom without hitting the nucleus where if it did it could cause damage and at the least cause the release of energy. Think of it this way. Let's say that you're trying to shoot a tiny pea placed somewhere in bails of hay. You could end up shooting many rounds of ammo without hitting it. This is why a particle easily misses hitting an atom's nucleus. Millions of neutrinos from the Sun pass through our bodies every day but we never feel any effect from them. They have very small masses and no charge. Even thought they travel at near the speed of light they pass through atoms without causing any harm.

Some scientists believe that dark matter is doing the same thing. Although neutrinos have been detected the particle associated with dark matter has not. Despite the fact that dark matter makes up 26.8 % of matter in the universe, we have no idea what it is. Some scientists believe that it's a WIMP, or a weakly interactive massive particle. The reason why they believe this is because of astronomical observations that have proven that dark matter exists.

The solar system planets orbit the Sun as predicted by Newton's laws of motion. Planets that are further away from the Sun move slower and take longer to orbit than those closest to the Sun. The Milky Way doesn't follow these laws. Stars out further from the center travel at the same velocity as those near the center. The reason this happens is because of dark matter. It's all around the galaxy. In fact if it weren't for dark matter the stars in our galaxy would fly off.

The other main reason that scientists know that dark matter exists is gravitational lensing. Hubble telescope images of galaxy clusters show distorted images of more distant galaxies because dark matter in the nearby galaxy cluster is acting to bend the light rays from these distant galaxies and act to focus them, thus acting like a lens. Remember Einstein showed that light is bent when it passes through a massive object. Large galaxy clusters have lots of dark matter around them.

So, why is this important? If dark matter is around us, it's passing through our bodies constantly. Even though a WIMP is massive (it needs to be to affect gravitation), it still doesn't cause damage to our atoms. Thank God that we're mostly empty!

Thanks for reading.