Expert: Carlo Segre - 4/2/2011

Question
QUESTION: Is there a part of the atom that doesn't have energy such as the empty space, even if it is affected by the energy of the atom? Thanks.

ANSWER: Hi Gena:

Again this is a nuanced answer because if you speak with a theoretical physicist and ask this, she/he would say that there is energy in the vacuum too!  Let me answer it in a very simplistic way though.

Let's consider the simplest atom, hydrogen.  It is composed of a proton and an electron.  If you have a proton and an electron separated from each other by an infinite distance, with nothing else existing in the universe (of course this is not possible but we are doing what is called in physics a "thought experiment" to understand the physical situation).  The energy of the system is just the sum of the masses of the two particles times the speed of light squared (E=mc^2).  As you bring these two particles closer together, they are attracted to each other by the Coulomb force.  This can be understood as a negative potential energy of the system which reduces the total energy of the system.  When the atom is formed, this energy is reflected in a reduction of mass of the hydrogen atom compared to the two particles alone.  It is all a question of interactions between the two particles.

The electron will not fall into the proton for quantum mechanical reasons but will have stable orbitals in which it can reside.  These are the states that we know from chemistry and the periodic table as 1s, 2s, 2p, etc.

Cheers,

Carlo

---------- FOLLOW-UP ----------

QUESTION: Hi Carlo,

Thanks so much for trying to help me understand
how things work. I am not a student but am someone who wants
to understand this in a basic sense.
Are particles, mass, and matter made up of only energy
without having any other substance to them or are they
more than just energy? It is overwhelming
to me to think of the world of matter around me
and living things as just energy. It feels more balanced
to say that matter and mass (not sure if they are the same)
Is both energy and more than this, perhaps with elements or substance
that can't be fully defined.
Also, were you saying that everything originally has come
from energy and if so could this be contained in everything while not being only this?
Perhaps energy is more than what I think
of it as also. It is hard to describe with words just what something is.
Could you please answer this question as simply as possible?
It's okay to not use a lot of technical terms. Thanks so much.

Answer
Hi Gena,

Mass is just one manifestation of energy.  This is what E=mc^2 tells us.   Matter is nothing more than this.  It is a stable form of energy but if you take a particle and accelerate it to very high energies, such as in the Large Hadron Collider, and you smash it into another particle, you can create new particles, lots of them!  Some particles are unstable and the energy stored in their mass can be released as they decay.  Basically everything in the universe is about energy, period, end of story.

If you read a book about the origins of the universe, something like "The First Three Minutes" by Steven Weinberg, you can get an idea of how this happens.

What you are having a hard time understanding is why something as material as matter is equivalent to other forms which seem more disorganized, like motion or heat.  This is because of a second important physical quantity which is called entropy.  Entropy is a measure of how energy is organized.  In some sense, a particle is a more organized form of energy.

Hope this helps...

Carlo