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Contents of the universe, according to the |
Recently a Facebook friend shared a graphic1 from the results of the NASA Wilkinson Microwave Anisotropy Probe, comparing the measured content of the universe as we see it today and as of just shortly—380,000 years—after the Big Bang.
According to the graphs, dark matter has always been a component of the universe, as have other components like atoms, photons, and neutrinos. Dark energy was also present in the early universe, but in such a tiny fraction as to go unnoticed. Then, as the universe expanded and cooled, the atoms of normal matter and the units of dark matter, in whatever form it takes, became less dense and so came to represent less of the universe’s total content. The early neutrinos and photons lost energy faster than the other visible matter, so they became just a tiny fraction of today’s universe. Meanwhile, the density of dark energy did not decrease at all—and so it grew in proportion, so that it dominates the universe today.
I cheerfully admit I'm not a degreed scientist, although I am a logical fellow with pretty good reasoning powers. Perhaps because I have not made a life-long study of this subject and immersed myself in the beauty of the mathematics that supports it, I can ask a few questions. Such as …
Since we can’t actually see, touch, taste, feel, or detect dark matter and dark energy, isn’t their part in the contents labeling of the Big Box of Universe® simply a supposition?
As I remember it, the only reason astrophysicists proposed dark matter at all—since it couldn’t be directly observed or detected—was to account for the motion of stars in galaxies. When you look at the galaxies that actually spin, their stars seem to orbit together, as if they were painted on a fixed disk, like a huge phonograph record, rather than chase each other at varying speeds around the center, like chips of wood floating on the surface of a whirlpool. When astronomers added up the mass of the stars, dust, and gas, they fell far short of the mass needed to create this painted-disk effect. And hence the need for something extra, some kind of matter whose nature we don’t yet understand and cannot see—and hence “dark”—to account for the computed mass requirement.2 Guesses about the nature of dark matter range from massive subatomic particles which don’t interact with the kind of matter we can see—weakly interacting massive particles, or WIMPs—to galaxies stuffed with the kinds of normal matter we might detect but normally can’t see at long range, like brown dwarf stars3 and rogue planets that might either have coalesced out of interstellar dust and gas or been thrown out of existing star systems.
Dark energy is a theoretical construct that accounts for the fact that the universe has not only been expanding since the time of the Big Bang, but that the expansion seems to be accelerating. The nature of the acceleration is such that instead of the universe eventually re-collapsing under gravity to start another Bang, astronomers now think the far future holds a Big Fadeout. First the galaxies will outrun the light they shine back at us, and so disappear.4 Then the stars in our Milky Way will grow dim and distant. Finally, even the Sun and planets, then the molecules of the Earth, and ultimately the molecules inside our own brains will become so distant from each other that they no longer interact. All activity in the universe eventually will cease. Guesses about the nature of dark energy range from some kind of negative pressure associated with vacuum, to some kind of gravitational repulsion that is currently unmeasured or unaccounted for, to the energy potential of a dynamic field called “quintessence.”5
Clearly, when we look out beyond the atmosphere of Earth, beyond the luminous bodies and simple orbits of our solar system, and try to take in the really big picture of the cosmos, we find complexities that pass our understanding. In our physics, which goes back to Newton and Einstein, the only way to get more mass is to add more stuff—even if it’s stuff you cannot see or detect, except by its effects. The only way to get more acceleration is to add more energy, even if you have to conjure it out of pure nothingness.
Our understanding of the nature of things breaks down in the realm of the very small. In Quantum Mechanics, which relies on mathematics and theory to help the human mind put order to what we can only marginally observe, we have constructed the Standard Model. It speaks of particles in terms of their trajectory, energy, and spin. And, for those bits that we cannot observe or corral directly, the Standard Model treats particles and fields interchangeably.
In the realm of the very big, dealing with scales of time and distance that are similarly outside of human experience, we use mathematics and theory to put order to observations that defy common sense. Cosmology has created an exploding universe that once expanded faster than light, has since slowed down, and now appears to be speeding up again, all to account for photons that lose energy for no otherwise apparent reason and a residual hiss of microwave radiation that appears to be the echo of the moment of creation. More mathematics and theory addresses galaxies that don’t spin as we would expect.
I sometimes think that when we venture outside the realm of the humanly observable, we're like an engineer trying to understand an internal combustion engine by riding on the face of the piston. All around us we see a lot of noise and activity, but we can only understand a fraction of what's going on and then theorize about the rest of it. From where we sit, we know nothing about the engine’s purpose, and we can only spin theories about things like gas tanks, carburetors, spark plugs, ignition coils, crankshafts, and wheels—all of which we've never actually seen and can only infer. All we really know and can observe is that we're inside a big, noisy space full of explosions and hot air.
I sometimes think the problem—both at the quantum and the cosmological levels—is one of viewpoint and perspective. We are trying to apply theories and metaphors from everyday experience to scales at which they may not apply. We believe in homogeneity and isotropy. That is, things should be pretty much the same everywhere and in every direction that we look.6 This is an assumption. To avoid excess theoretical baggage, in the manner of Occam’s razor, it makes sense to postulate that the physical reality we observe on Earth also operates on Mars or in the Andromeda galaxy, and that principles which operate at distances we can encompass with our two hands also operate at the span between two quarks or between two galaxies.
Our science is full of such assumptions. They let us think sanely, but they sometimes lead us to think wrongly. In geology, for example, the doctrine of uniformitarianism held sway for many years: that processes we can observe here and now have always operated at the same speed and intensity. Rivers wear away the riverbank at the same rate every year. Rain and runoff wear away mountains at the same rate over the millennia. That made for a gradually changing world, which is what we usually observe. As a doctrine, uniformitarianism made sense over catastrophism, which held that violent changes like Noah’s flood can suddenly create new landscapes. Of course, both processes—the quick and the slow—are at work. It took a while for geologists to accept that a great flood on the Snake River at the end of glaciation some 15,000 years ago carved canyons in a matter of days. But any of the old geologists who had seen a volcano explode would have had to admit that catastrophism sometimes happens.7
Perhaps our predilection for homogeneity and isotropy is leading us to wrong conclusions. As I’ve pointed out before,8 we use terms like “gravity,” “space,” and “time” in meaningful sentences; we measure their effects and can use those measurements in equations and calculations; but we don’t necessarily understand the mechanism that supports these effects. Perhaps to those three poorly understood effects, we should add huge masses, great distances, and great spans of time.
The universe is a strange place. I think we will need to adjust our thinking to different scales of time and distance. But then, our understanding of the physical space and other realities—like the nature of life—has always been the successive adoption of different ideas, models, frames of reference, and metaphors.
For example, most of us still live in a Euclidean world, where straight lines are straight forever, rooms have flat walls that meet in 90-degree corners, and clocks run at the same speed all over the world. But if you adopt the Einsteinian model, you know that the baseboards curve, however slightly, with gravity and that your watch slows down by a fraction of a second whenever you take a transcontinental flight.
In the same way, people living in pre-Darwinian times saw the animals and plants around them as separate, individually created beings—and certainly a different order of being from self-aware humans. But the new evolutionary model and the evidence of genetics now force us to see that all life on this planet is related at a molecular level and that the forms themselves are fluid because they change in response to the environment.
Think of these new models as “whacks to the head” which jar our understanding and lead to the “ah-ha!” moment of a new vision. But the universe is still an ultimate mystery. I believe we all have a dozen or more cycles of “whack” and “ah-ha!” before we figure out what's really going on out there. For now, the Big Bang in cosmology and the Standard Model in subatomic theory are useful metaphors and explainers of what’s going on—although each is now running into some bizarre complications. I believe either or both of these models will one day be overturned before we arrive at a more accurate—perhaps even a final—view of the Real State of Affairs.
1. Giving credit where due, my Facebook friend William Maness shared this chart from Mohan Sanjeevan’s Facebook page Sci-fi, Science and Space Geek, commenting, “The green and dark blue slices? Those are actually ‘we don’t know WTF, but we can quantify what we need to match our model with what we observe.’ ” He then tipped his hat to me for my recent blog post about scientific presumptions in the realm of cosmology, and wrote, “The more I think about it, the more I agree with him that the standard model has got a gaping hole in it.” The substance of this posting comes from my response to Maness.
Another commenter on that thread, a scientist with 30 years of experience teaching chemistry at the university level, observed that since he didn’t know the actual facts, it was best not to comment. I respect that. But I am not a scientist; I am a science fiction writer. It’s not my business to know but to question, wonder, and imagine. Without the froth of imagination, the soufflé of science just lies there like a pudding.
2. And yes, every galaxy is now believed to hide a supermassive black hole at its center, comprising the mass of hundreds of thousands or millions or billions of suns. And no, that’s still not enough mass to account for the orbital velocities we see.
3. Essentially solar fizzles, bigger than Jupiter but not big enough to ignite their own nuclear fusion or keep it going successfully for very long. If billions of solar masses tied up in a black hole are not enough to account for the missing mass, how many solar cinders lying around does it take to balance the equation?
4. Remember, this expansion is based on the observation that the light from distant objects like galaxies is red-shifted—that is, has a lower than expected energy level—which is thought to be due to the Doppler effect. This effect, in our everyday experience, accounts for the change in frequency of a sound wave that is either approaching or moving away from the hearer. Light waves are presumed to retain their energy over vast spans of time and distance, just as in Newton’s first law of motion an object once set in motion retains its inertia until it meets with a counteracting force like friction. So, if the photon is losing energy, it must be because the distance over which it travels is expanding and not because any other force is sapping its energy.
5. Quintessence, in its original meaning—from the Medieval Latin quinta and essentia, or “fifth essence”—was the purest and most concentrated form of a thing. Medieval philosophy accounted for four elements to make up everything in the realm below the celestial spheres: earth, air, fire, and water. The fifth element or essence supposedly permeated all of nature and was the material composing the celestial bodies. … See how far we have come?
6. Homogeneity is from the Greek homos, meaning “same,” and genos, meaning “kind”—or all of the same kind. Isotropy is from the Greek iso, meaning “equal,” and tropos, meaning “way”—or uniform in all orientations and directions.
7. In the same way, biologists once thought evolution took lots of time, that genetic mutations happened slowly, and their effects only accumulated over hundreds of generations. Then paleontologists Stephen Jay Gould and Niles Eldredge wrote about punctuated equilibrium: genetic mutations are happening all the time, but their effects only blossom into newly favored forms when the environment changes enough to make the old forms unworkable and the new forms advantageous. And then Peter and Rosemary Grant, as described in Jonathon Weiner’s The Beak of the Finch, showed how species of finches in the Galapagos Islands may change over a single generation to take advantage of environmental niches. Old scientific ideas die quickly under new evidence.
8. See the blog entries titled “Three Things We Don’t Know About Physics” from December 30, 2012 and January 6, 2013.