Q: Most cosmologists believe that the vast majority of the universe’s mass—something on the order of ninety-six percent of all the material of which the universe is made—is actually invisible, consisting of two mysterious quantities they call “dark matter” and “dark energy.” The question is: What could they possibly be?

Neil de Grasse Tyson: Consider all we’ve learned about the size, age, and contents of the universe—from its fiery birth in the big bang through fourteen billion years of expansion that has followed. Even better, consider the powerful laws of physics we’ve discovered that account for it all.

Kind of makes you stand with pride for being human. But before you stand too tall, consider that, at the moment, we can account for only fifteen percent of all the gravity we’ve ever measured in the universe. We’re simply clueless about what’s causing the rest. Not only that, if you add up all the matter and energy in the universe, it comes to just four percent of all that drives cosmic expansion. So we’re clueless about that one, too, with no idea about what occupies the remaining ninety-six percent of the universe.

We call these invisible entities “dark matter” and “dark energy.”

What are they? Maybe they’re exotic, never-before-seen forms of matter and energy. Or maybe they reveal a hidden flaw in our understanding of how the universe works. But really, the two terms are placeholders for our abject ignorance. We could just as easily have labeled them “Bert” and “Ernie” or “Without-a-Clue A” and “Without-a-Clue B.”

So we are left in a curious situation. What we know of the universe, we know well. Yet a larger cosmic truth lies undiscovered before us—a humbling, yet thrilling, prospect for the scientist—driven not only by the search for answers but by the love of questions themselves.

Neil deGrasse Tyson, an astrophysicist, is director of New York City’s Hayden Planetarium at the American Museum of Natural History and the author of The Sky Is Not the Limit (2000), Origins (2004), and Death by Black Hole (2007).

Reprinted with permission from “The Cosmic Perspective”
©2008 Neil deGrasse Tyson, NOVA scienceNOW, WGBH Boston

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Paul Davies: When it comes to dark matter, it’s been known for quite a long time that there is a lot of invisible substance tugging on the visible stuff in the universe. What you see is not what you get. The stars move in such a way that if there wasn’t a lot of invisible gravitational material, then galaxies like the Milky Way would unravel like an exploding flywheel. The question is, what is this stuff? But it’s never been hard to think up possible objects or particles that it could be.

People have tended to divide these possibilities into two categories, which have been whimsically called “MACHOs” and “WIMPs.” MACHO stands for massive compact halo objects. These could be anything from black holes to dim stars to objects like asteroids and so on. The idea is that any galaxy that we see is embedded in a much larger, roughly spherical halo of such nonluminous objects, and that a lot of a galaxy’s mass is distributed there. Yet people have looked for MACHOs, and they found things, but nowhere near enough of them to account for the gravitational mass of dark matter.

The other category, WIMP, stands for weakly interacting massive particles. Now, we know plenty of weakly interacting particles, such as neutrinos, which interact so weakly with ordinary matter that billions of neutrinos from the sun, for example, are passing straight through you all the time without you noticing. Neutrinos are filling the whole universe, but they just don’t have enough mass to account for dark matter. So the WIMP would mean a particle like a neutrino but massive.

There is some hope that one of these particles will be produced in a few months when the Large Hadron Collider at CERN, the European particle accelerator lab, gets switched on. For my money, I think that’s probably what we’re dealing with. We will find one or a collection of these WIMPs, and that will satisfactorily account for this dark matter.

WIE: So what do you think dark energy is?

Davies: Well, here I’m a little bit out of fashion with some cosmologists who love to say, “It’s a great mystery what this dark energy is. It’s a crisis in physics.” We have a perfectly good explanation for what it is, and we’ve had it for decades and decades. The original idea for what we now call dark energy was dreamt up in 1917 by none other than Albert Einstein. In those days nobody knew that the universe was expanding, and Einstein assumed it was static. So he introduced what he called a cosmological repulsion term in his equations to counteract the force of gravity—to explain why, in a static universe, all the stars and galaxies can just hang out there in space when there is this universal force of attraction wanting to pull them together. But in 1930 we learned that the universe isn’t static—it’s actually expanding. The galaxies are flying apart. When Einstein learned this, he abandoned his cosmological repulsion term—which he’d put in purely by hand just to fix up his model of a static universe—and said it was his greatest mistake.

But about ten years ago astronomers discovered that there does indeed seem to be something like Einstein’s cosmological repulsion force at work in the universe, which got dubbed “dark energy.” In my view, it is none other than what Einstein introduced in 1917. So his greatest mistake might actually turn out to be one of his greatest triumphs.

Paul Davies, a cosmologist, is director of BEYOND, a research institute at Arizona State University dedicated to cutting-edge fields of science. His many books include The Mind of God (1992) and Cosmic Jackpot (2007, reprinted in paperback as The Goldilocks Enigma, 2008).

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Janna Levin: It’s really hard to conjecture what dark matter and dark energy might be. I’ve worked on some crazy ideas; other people have worked on some crazy ideas.

One of the things I’ve been interested in personally is whether or not the dark energy could come from extra spatial dimensions, dimensions that are so small and curled up that we don’t notice them, where a kind of vibration in those multidimensional spaces creates this energy that’s felt everywhere in the universe. That could be responsible for the dark energy. And there’s been several other ideas totally unrelated to that.

Now with dark matter it would be nice if it connected to dark energy in some way, and it wasn’t just a completely separate, random piece of information about the universe. It would be nice if it were somehow a different side of the same coin as dark energy, perhaps related to vibrations in extra dimensions, just like dark energy might be. But until we have more data and more information, that’s really all we’re going to be doing—exploring possibilities and comparing them to the few observations we do have.

WIE: Some physicists are highly critical of dark matter and dark energy, claiming they’re merely theoretical concepts that are so inextricably tied to Einstein’s particular model of the universe that if that model were somehow disproved, they’d be disproved along with it. Would you agree with that?

Levin: Well, I should state that these are new observations, and so it only seems to be the case that there is dark energy and dark matter. It is becoming very convincing, but these are still early days. There are many cosmological observations that seem much more absolute and concrete than these.

So I would agree that there is another possibility, which is that in terms of Einstein’s theory, it’s not that the whole paradigm is wrong, but that the theory might need to mutate into a slightly modified theory of gravity that’s a little bit different from his original one. As we look at vaster scales of the cosmos or higher energy scales, it’s possible that an unexpected distortion of gravity begins to appear, which we’re misinterpreting to be the existence of dark energy and dark matter, when all that it really is is a modification of gravity on large scales and high energies. And we cannot yet disentangle which one of those things is right.

Janna Levin, a theoretical cosmologist, is professor of physics and astronomy at Barnard College of Columbia University. She is the author of How the Universe Got Its Spots (2002) and the historical novel, A Madman Dreams of Turing Machines (2006).

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Deno Kazanis: When I first heard about dark matter I was impressed by the quantity of it, making up most of the universe. Although I never really took the mystical view of the physical universe very seriously when they talked about different “planes” of matter, when I read about dark matter, I began to realize that it fit in pretty well with what the mystics have been talking about. Mystics in all parts of the world have tended to see the universe as actually being composed of different layers of matter, different types of matter, most of which were said to be invisible to our usual narrow vision. But in mystical states of consciousness, these other forms of matter would become visible to them.

Now when the mystics talk about the “subtle bodies” of man, such as the etheric, astral, mental, soul, and spirit bodies, they describe how they interpenetrate each other and interpenetrate with our visible body as well. A hundred years ago, interpenetration would have been something of a taboo, but thanks to quantum mechanics, we now know that matter isn’t solid. Atoms aren’t solid things. Our ability to see, touch, taste, smell, and hear the world is really only due to atoms’ electric charge. And because objects on the atomic level interact through electric forces, if there’s no such force present, then objects can literally pass right through each other. The reason we can hold an apple in our hand and it doesn’t fall through is because the apple is made of charged atoms and our hand is made of charged atoms, so they can’t interpenetrate. But if an object were actually made of uncharged atoms held together by some other unknown force, it could literally pass right through you.

What intrigued me was that dark matter, being as invisible as they say it is and not able to produce light or any type of electromagnetic waves, meant that this was a substance that was not composed of any electric charge. That’s what the invisibility tells you about it—it has no charge whatsoever. Its presence is determined by its gravity, which is an enormous amount, yet the material itself is totally invisible. So it occurred to me that when the mystics were talking about subtle bodies interpenetrating with our visible body, the only way that could be possible would be if these bodies were made up of something other than charged matter. And dark matter would fit that category quite well.

WIE: So you’re envisioning dark matter as a subtler form of matter, but which somehow coexists in the same space as regular matter, in layers stacked atop one another?

Kazanis: Yes, you could picture these different types of atoms on a three-dimensional periodic table. Our ordinary periodic table is a chart of charged atoms. Then layered above that would be a periodic table of atoms that are made up of, say, pranic, or etheric, matter—which in India would correspond to what they call the pranamaya kosha. Above that might be a layer of atoms that have a manomaya kosha type of matter, or mental matter, and above that would be a layer of vijnanamaya matter, or soul matter, and anandamaya matter, or spirit matter, depending on how you wanted to look at it. You can break the gradations up into many different levels, as different cultures have.

Deno Kazanis, a biophysicist, was formerly head of the Orlando Branch Laboratory. He has been a research associate at Duke University, has studied both Tibetan Buddhism and Taoism, and is the author of The Reintegration of Science and Spirituality (2002).

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Bernard Haisch: The concept of dark matter is needed to provide an additional gravitational force to explain some of the things that we see in the cosmos, such as the rotation curves of galaxies. Dark energy, however, might as well be called antigravity, because it’s something we invoke in order to explain the accelerating expansion of the cosmos or why things are being pushed farther apart. So they’re exact opposites. But as to what these things are, I don’t know.

WIE: In your work, you’ve attempted to create a synthesis of physics, cosmology, and consciousness. How do dark matter and dark energy fit into that? Are they related to consciousness?

HAISCH: Well, I wouldn’t necessarily assume that because ninety-six percent of the universe is unknown stuff, there’s something profoundly spiritual lurking there. It may not be. It may have nothing at all to do with spiritual stuff. What I propose in my book is that consciousness plays a central role in the origin of the universe, that the universe is the product of consciousness, the product of a conscious intelligence. You’ll find some startling evidence for this if you look at quantum physics today, because a lot of research—such as the University of Vienna’s experiment last year expanding on the Bell Inequality—is really pointing to the idea that consciousness is necessary to resolve quantum events, that consciousness acts at a fundamental level to basically create reality.

WIE: Is this the idea that the universe somehow didn’t fully exist until humans came on the scene to observe it, to collapse quantum probabilities into concrete reality with our consciousness?

HAISCH: No, I wouldn’t say that because I attribute the origin of the universe, not to human beings, but to a preexisting intelligence. I think this intelligence is both beyond space and time and beyond the universe, but also lives deeply in it, entering into all the life forms in that universe such as you and me, such as the plants and animals on this planet, such as the alien civilizations that probably exist elsewhere. It’s the entering of consciousness into all of these forms that, I think, is the purpose behind the universe—for God to experience reality, to experience physicality, to experience some of its infinite potential—and that ultimately the consciousness in all of us will return to the fountain of intelligence that made the universe in the first place. We are simply sparks of a huge bonfire of consciousness, and ultimately we return to the source.

Bernard Haisch, an astrophysicist, was formerly editor in chief of the Journal of Scientific Exploration. He has worked at the Lockheed Martin Solar and Astrophysics Laboratory, among other research institutions, and is the author of The God Theory (2006).