Maybe … contrary to our theories, the universe is not uniform throughout, or not at all scales. Maybe gravity is not a constant at all scales but has different values at different scales.
We know that the force of gravity appears to be nonexistent at the subatomic scale, apparently playing no part in quantum mechanics. We can measure the force of gravity and use gravity equations at the planetary, solar, and interstellar scales, where it governs the attraction between bodies with which we are familiar. But we observe that, at the galactic scale, gravity is apparently not strong enough to produce the effects we can observe. That stars in a spiral galaxy spin in a manner—as if they were stuck to a platter instead of floating freely—which suggests each galaxy contains more matter than we can account for by the stars that shine and the planets, brown dwarfs, and black holes that we presume must accompany them.
Instead of considering variable gravity, we hypothesize that something else must be at work: a substance called “dark matter,” which does not react with normal matter or electromagnetism at all, but has a measurable effect on gravity—but only, apparently, at very large scales. The effect on galaxies is so apparent that we attribute this “dark matter” with comprising 85% of the substance of the universe and about 25% of its total energy density. All this for something we cannot see, touch, feel, or detect—only “observe its effects” at very large scales.
Perhaps we are wrong in our assumptions about the gravitational constant being fixed at all scales larger than that of quantum mechanics.
This kind of “wrong” thinking—if it is wrong, and perhaps “dark matter” actually does exist—has happened before. During the 19th century, geologists debated between “catastrophism” (the theory that geological changes in the Earth’s crust were created by sudden and violent events) and “gradualism” (the theory that profound change is the cumulative product of slow but continuous processes). Gradualism would be the slow accumulation of sediments to form rocks like sandstone and shale. Catastrophism would be sudden explosions like volcanos or events like the formation of the Snake River Canyon from the collapse of the earth- or ice-dam holding back Lake Bonneville about 15,000 years ago. What has since been resolved is that either theory on its own is too constricting, too reductive, and that both theories and systems played their part in the formation of the Earth’s surface.
This is probably not the case with gravity. A variable gravitational constant vs. the existence of dark matter is probably an either/or rather than a both/and situation. One kind of physics that explains the observations does not necessarily make room for a second kind to explain them. However, it wouldn’t surprise me if each galaxy contained more normal matter that we can’t see by either the ignition or the reflection of starlight—that is, black holes, brown dwarfs, and rogue planets—than we have habitually counted. And still there may be something going on with the effects of gravity at the very small and the extremely large scales that is out of whack with the gravitational constant we see at the planetary and stellar scale.
Time and distance are variables that we have only been seriously considering over the past hundred years or so—ever since Edwin Hubble exploded the idea that the local stars in the Milky Way galaxy were all that comprised the universe and instead introduced the idea that the fuzzy patches (“nebulae,” or clouds) on photographic plates were actually distant galaxies that are not much different from the Milky Way, and that they all were receding from us. In one conceptual leap, the universe, the cosmos, all of creation, became really, really—add a few exponents here—big.
But the universe did not become correspondingly old. We still had various measurements and computations putting the age of the oldest stars and the universe itself at approximately thirteen billion years. That’s about four generations of stars from the creation of matter itself to the Sun with its disk of gas and dust that contains elements which must have formed in the fusion processes and catastrophic collapse of older stars. By winding back the clock on the expansion, the scientific consensus came up with a universe that started in the explosion of, or expansion from, a single, tiny, incredibly hot, incredibly dense—add more exponents here, with negative signs—point. That singular point contained all the matter we can see in the billion or so galaxies within our view.
Because that view comprises a distance that the farthest galaxies could not have reached in thirteen billion years, even when receding from a common point at the speed of light, a scientific consensus originating with Alan Guth has formed around an “inflationary” universe. At some time, the story goes, at or near the very earliest stages of the expansion, the universe blew up or inflated far faster than lightspeed. Perhaps from a hot, dense thing the size of a proton to a cloud of unformed matter probably the size of a solar system, the whole shebang expanded in a blink—whereas a photon from the Sun’s surface now takes about five and a half hours to reach Pluto.
While I don’t exactly challenge the Big Bang and the inflationary universe, I think we are reaching for an easily understandable creation story here. We want to think that, because we know the universe is now expanding, and because our view of physics is that basic principles are the same in every place and at every scale, and that processes continue for all time unless some other observable force or process interferes with them, then the universe must have been expanding from the beginning: one long process, from the hot, dense subatomic pencil point that we can imagine to the vast spray of galaxies that we see—extending even farther in all directions than we can see—today. And with such thinking, we may be writing our imagination and our physics into a box.
The truth may lie somewhere in between. And I don’t think we’ve got our minds around it yet.