• Choose a category
• All
• Classic-Fiction

By Root 935 0

cannot possibly go to a heavier thing because there is no energy being added, whereas there is always the chance it can shed some energy and become lighter. Of course, the third option is that it does nothing and stays the same, and sometimes that is the case. For the hydrogen atom this means that the heavier version will eventually shed some of its mass. It does so by emitting a single particle of light, the photon we met earlier. For example, a next-to-lightest hydrogen atom will at some point spontaneously convert into a lightest hydrogen atom as a consequence of a change in the orbit of the electron. The excess energy is carried away by a photon.8 The reverse process can occur too. A photon, if one just happens to be around, can be absorbed by the atom, which then jumps to a higher mass because the energy absorbed promotes the electron to a higher orbit.

Perhaps the most everyday way of getting energy into atoms is to heat them up. This causes the electrons to jump up into the higher orbits and subsequently drop back down again, emitting photons as they go (this is the physics behind a sodium vapor street lamp). These photons carry an energy that is exactly equal to the energy difference between the orbits, and if we could detect them, we would have a direct window into the structure of matter. Fortunately, we are detecting them all the time because our eyes are nothing more (or less) than photon detectors, and the energy of the photons is registered directly as color. The azure blue of an island-pitted tropical ocean, the jagged diamond yellow of Van Gogh’s stars, and the iron-red of your blood are a direct measurement by your eyes of the quantized structure of matter. The origin of the colors emitted by hot gases was one of the driving forces behind the discovery of quantum theory at the turn of the twentieth century. The years of careful observation of the light emitted from anything and everything by legions of diligent scientists are commemorated in our language by the name of the gas that fills party balloons. “Helium” is derived from the Greek word “helios,” which means “sun,” because the signature of this atom was first discovered by French astronomer Pierre Janssen in the light from a solar eclipse in 1868. In this way we discovered helium on our star before we found it on Earth. Today, astronomers search for signs of life on distant worlds by looking for the characteristic fingerprint of oxygen in the starlight shining through the atmospheres of planets as they pass across the face of their parent stars. Spectroscopy, as this branch of science is known, is a powerful tool for exploring the universe without and within.

All of the atoms in nature come in a tower of energies (or masses), depending on where the electrons are, and since there is more than a single electron in every atom except hydrogen, the light emitted from them spans all the colors of the rainbow and beyond, which is ultimately the reason why the world is so colorful. Chemistry is, very crudely, the area of science that is concerned with what happens when bunches of atoms come close together (but not too close). As two hydrogen atoms approach each other, the protons repel because they both carry positive electric charge, but that repulsion is overcome because the electron in one atom attracts the proton in the other. The result is that there is an optimal configuration where the two atoms are bound together to make a hydrogen molecule. The atoms are bound in the same sense that the electron is bound into orbit around a single hydrogen nucleus. Being bound means simply that it takes some effort to pull them apart and “it takes some effort” is a sloppy way of saying that we need to supply some energy. If we need to add energy just to break the molecule apart, then it follows that the molecule is less massive than the sum of the original two hydrogen atoms, just as the hydrogen atom is less massive than the sum of the masses of its constituents. In both cases, the binding energy comes about because of the force of electromagnetism that we