The Life of Super-Earths by Dimitar Sasselov Read Free Book Online Page B

vagaries of the scale of the atoms—the world of quantum physics. At the same time, life benefits from the richness of chemical bonds that is the hallmark of the atomic scale. From my point of view, the complex molecules and chemical networks of life avoid the violent destructiveness of the very large Universe by inhabiting a scale small enough to allow for many stable environments.
    So, it seems that the scale inhabited by life has some special qualities. We can observe curious things if we take a swift tour through the space scales of the Universe. The galaxies move slowly like giant turtles, the stars inside them buzz around like bees, the planets orbiting the stars move faster still, and so on until we reach the scale of the microworld—the quantum world of atoms and electrons. The smaller the scale, the crazier the world seems to appear. In fact, it is crazy , and modern physics has a good explanation for it. To oversimplify it a bit, big things move slowly, small things move faster. Just think of the truck and the motorcycle at the stoplight when the light turns green. Remember that mass and speed combine to give you energy, and energy is conserved. If mass goes up, speed must go down. There is order to all this, after all.
    There is more to the scale of life, though, than simply the profusion of stable environments. To understand the special qualities that the scale of life has, one needs to know nonliving matter first.
    The atomic scale and the atoms are the basic building blocks of ordinary matter, as the ancient Greeks surmised. We still think of this as true, at least for the pure elements of the chemical table, such as carbon, iron, or gold, although
we recognize most ordinary matter as being made of compounds of atoms. What the twentieth century revealed, however, is that ordinary matter is really composed of smaller particles. These are called fundamental or elementary particles and fall into three families of four particles (and four antiparticles) each. Most common and familiar among them to us are the light particles of the first family: the electron, the up quark and down quark, and the tiny electron neutrino.
    You and I, our planet, our star, are all made up entirely of them, particularly electrons, up quarks, and down quarks. The two types of quarks make the protons (two up plus one down) and neutrons (two down and one up) that combine to form the nucleus of an atom and thus the chemical identity of a given element. The lighter electrons orbit the nucleus and give atoms the ability to bond together into molecules. The nucleus of the atom is where the mass is; the electrons around it are insignificantly light, but they make chemistry possible. When you cook in your kitchen, you are playing with the electrons—breaking and reforming chemical bonds. If eating results in your gaining weight, it is because you have added more quarks to your body.
    This is not yet the whole story. We can’t forget about the fundamental forces. One particle can affect another; for example, the positive proton of a hydrogen atom keeps a negative electron in orbit. One piece of matter can influence another piece of matter by means of these forces. There are four fundamental forces—the gravitational force, the electromagnetic force, the strong force, and the weak force. Our
daily lives are, for almost all purposes, exclusively affected by the first two forces. Gravity keeps us on the ground (which we experience as weight) and electromagnetism allows us to move around (via friction), among other things. A common feature to all forces is that they can be represented by an associated particle (usually of no mass at rest) which contains the smallest quantum (or “packet”) of force. The electromagnetic force particle is called a photon. We experience photons as light or radiant heat, for example, or we use them to broadcast our cell phone conversations. The gravitational force particle is called a graviton.