john_c_mather's picture
Nobel Prize in Physics; Senior Astrophysicist, Observational Cosmology Laboratory, NASA's Goddard Space Flight Center; Coauthor (with John Boslough), The Very First Light
"The Big Bang"

The name “Big Bang” has been misleading scientists, philosophers, and the general public since Sir Fred Hoyle said it on radio in 1949. It conjures up the image of a giant firecracker, an ordinary explosion happening at a place and a time, a collection of material suddenly beginning to expand into the surrounding empty space. But this is so exactly opposite to what astronomers have observed that it is shocking we still use the name, and it is not the least bit surprising that some people object to it. Einstein didn’t like it at first but became convinced. Hoyle never liked it at all. People might like it better if they knew what it meant.

What astronomers actually have observed is that distant galaxies all appear to be receding from us, with a speed roughly proportional to their distance. We’ve known this since 1929, when Edwin Hubble drew his famous plot. From this we conclude a few simple things. First, we can get the approximate age of the universe by dividing the distance by the speed; the current value is around 14 billion years. The second and more striking conclusion is that there is no center of this expansion, even though we seem to be at the center. We can imagine what an astronomer would see living in another distant galaxy, and she would also conclude that the universe appears to be receding from her own location. The upshot is that there is no sign of a center of the universe. So much for the “giant firecracker.” A third conclusion is that there is no sign of an edge of the universe, no place where we run out of either matter or space. This is what the ancient Greeks recognized as infinite, unbounded, without limits. This is also the exact opposite of a giant firecracker, for which there is a moving boundary between the space filled with debris, and the space outside that. The actual universe appears to be infinite now, and if so it has probably always been infinite. It’s often said that the whole universe we can now observe was once compressed into a volume the size of a golf ball, but we should imagine that the golf ball is only a tiny piece of a universe that was infinite even then. The unending infinite universe is expanding into itself.

There’s another way in which the giant firecracker idea misleads us, because even scientists often talk about the “universe springing into existence.” Well, it didn’t, as far as we can tell. The opposite is true. There is no first moment of time, just as there is no smallest positive number. In physics we have equations and laws of nature that describe how one situation changes into another, but we have no equations that show how true nothingness turns into somethingness. So, since the universe did not spring into existence, it has always existed, though perhaps not in its current form. That’s true, even though the apparent age of the universe is not infinite, but only very large. And, even though there’s no first moment of time, we can still measure the age.

There’s still plenty of mystery to go around. What are those equations of the early universe which might describe what came before the atoms we see today? We’re pretty confident that we can imagine times in the early universe when temperatures and pressures were so high that atoms would have been ripped apart into the particles we have manufactured at our Large Hadron Collider. We have a Standard Model of cosmology and we have a Standard Model of particles. But the mysteries include: Why is there an asymmetry between matter and antimatter, such that the whole observable universe is made of matter? What is dark matter? What is dark energy? What came before the expansion and made it happen, if anything did? We’ve got the idea of cosmic inflation, which might be right. What are space and time themselves? Einstein’s general relativity tells us how they are curved but scientists suspect that this is not the whole story, because of quantum mechanics and especially quantum entanglement.

Stay tuned! There are some more Nobel prizes to be earned.