Is Dark Matter a Glimpse of a Deeper Level of Reality?

Scientific American ^ | 6/11/12 | George Musser

[LibWhacker]

Two years ago several of my Sci Am colleagues and I had an intense email exchange over a period of weeks, trying to figure out what to make of a new paper by string theorist Erik Verlinde. I don’t think I’ve ever been so flummoxed by physicists’ reactions to a paper. Mathematically it could hardly have been simpler—the level of middle-school algebra for the most part. Logically and physically, it was a head-hurter. I couldn’t decide whether it was profound or trite. The theorists we consulted said they couldn’t follow it, which we took as a polite way of saying that their colleague had gone off the deep end. Some physics bloggers came out and called Verlinde a crackpot.

For those who know Verlinde, that label hardly fits. He is a brilliant theorist, and the amount of discussion his paper provoked suggested that most of his colleagues saw something in it. The whole story caught the eye of New Scientist and the New York Times, but ultimately we at Sci Am opted for watchful waiting. I caught up with Verlinde this spring during a workshop at the Kavli Institute for Theoretical Physics. He has doubled-down on his original paper, and his colleagues’ reaction hasn’t changed. One told me: “There are a lot of ideas he’s bringing together in an interesting way, but it’s a little hard for us to decipher, so I’m withholding judgment.” All he has really done, though, is take a general sentiment among string theorists and follow it to its logical conclusion.

String theorists and other would-be unifiers of physics face a basic problem. The theories they seek to unify, quantum field theory and Einstein’s general theory of relativity, are well-grounded and well-tested, yet mutually incompatible. Reconciling them will demand that some deeply held intuition must give way. One such intuition is that the world exists within space and time. Participants at the Kavli workshop were inclined to think that space and time are not fundamental, but emergent. The universe we seeing playing out in space and time may be just the surface level, where we float like little boats while leviathans stir in the deep.

Black holes provide the strongest argument for this point of view. The laws of gravity predict that these cosmic vacuum cleaners obey versions of the laws of thermodynamics, which is strange, because thermodynamics is the branch of physics that describes composite systems, such as gases made up of molecules. A black hole sure doesn’t look like a composite system. It just looks like a warped region of space that you would do well to stay away from. For it to be composite, space itself must be.

In that case, black holes represent a new phase of matter. Outside the hole, the universe’s “degrees of freedom”—all that its most fundamental building blocks are capable of—are in a low-energy state, forming what you might think of as a crystal, with a fixed, regular arrangement we perceive as the spacetime continuum. But inside the hole, conditions become so extreme that the continuum breaks apart. “You can make spacetime melt,” Verlinde told me. “This is really where spacetime ends. To understand what goes on, you need to use these underlying degrees of freedom.” Those degrees of freedom cannot be thought of as existing in one place or another. They transcend space. Their true venue is a ginormous abstract realm of possibilities—in the jargon, a “phase space” commensurate with their almost unimaginably rich repertoire of behaviors.

Verlinde’s 2010 paper applied this reasoning to the laws of gravity themselves. Instead of being a fundamental force of nature, as almost all physicists since Newton have thought, gravity may be an “entropic force”—a product of some finer-scale dynamics, much as the pressure force in a gas arises from collective molecular motions. At Kavli he went further and argued that the notion of emergent spacetime transforms our entire conception of the universe. “If you realize there’s much more phase space than we usually assume—much more—you will think about cosmology differently,” he argued.

For starters, dark matter may be a glimpse into the depths. To account for anomalous motions within galaxies and larger systems, astronomers think our universe must be filled with some invisible material that outweighs ordinary matter by a factor of five to one. They have never detected the material directly, though, and for something that is supposed to be so overwhelmingly dominant, dark matter has a puzzlingly subtle effect. The anomalous motions occur only in the unfashionable outskirts of galaxies. Stars and gas clouds out there move faster than they should, but don’t do anything truly wacky—it is as if the gravitational field of the visible galaxy were simply being amplified.

Consequently, some astronomers and physicists suspect there may be no dark matter after all. If you notice the floorboards in your house are sagging, as if there is too much weight on them, you might conclude there is an 800-pound gorilla in the room with you. You see no gorilla, so it must be invisible. You hear no gorilla, so it must be silent. You smell no gorilla, so it must be odorless. After a while, the gorilla seems so improbably stealthy that you begin to think there must be some other explanation for the sagging floorboards—the house has settled, say. Likewise, perhaps the laws of gravity and motion which led astronomers to deduce dark matter are wrong. “I think dark matter will be a sign of another type of physics,” Verlinde said.

The leading alternative to dark matter is known as MOND, for Modified Newtonian Dynamics. Verlinde has reinterpreted MOND not just as a tweak to the laws of physics, but as evidence for a vast substratum. He derived the MOND formula by assuming dark matter is not a novel type of particle but the vibrations of some underlying degrees of freedom—specifically, vibrations produced by random thermal fluctuations. Such fluctuations are muted and become conspicuous only where the average thermal energy is low, such as in the outskirts of galaxies. Astoundingly, Verlinde even derived the five-to-one ratio. “I started seeing this as a manifestation of this larger phase space,” he said.

MOND is super-iffy, as cosmologist Sean Carroll has detailed in a series of blog posts over the years, most recently this one. I’m inclined to agree, but one thing gives me pause. MOND manages to account for a wide range of anomalous galactic motions with one simple formula. Even if MOND doesn’t overturn the laws of physics, it has shown that dark matter behaves in a simple way. All the complicated dynamics of dark matter must somehow settle down into a very regular pattern. Dark-matter modelers tell me they have yet to explain this.

Verlinde bucks conventional wisdom not only on dark matter, but also on much of the rest of cosmology. For instance, he has reintroduced elements of the steady-state theory that most cosmologists thought they had ruled out in the 1960s. In his model, all matter—ordinary as well as dark—consists of vibrations of the underlying degrees of freedom and so is being created and destroyed all the time. In fact, the same degrees of freedom also explain dark energy, thereby unifying all the components of the universe. What differentiates these components is how fast they respond: ordinary matter is the surface chop, dark matter the languid but powerful deep currents, and dark energy the quiet bulk of the sea. As for another leading cosmological theory, cosmic inflation, he doesn’t think much of that, either.

The grander his claims become, the less plausible they seem. Still, Verlinde has captured theorists’ sense that cosmological mysteries signal a new era of physics. The impulse to explain dark matter and dark energy as signatures of a deeper reality, rather than a bolt-on to current theories, arises not only in string theory but also in alternatives such as loop quantum gravity and causal set theory. And if Verlinde is wrong and spacetime really is a root-level feature of our world, what other intuition will have to give way? What other thing that we thought we knew for sure is wrong?

[OldNavyVet]

What other thing that we thought we knew for sure is wrong?

Well, since the world ain't flat, there's probably a whole lot more to be discovered.

[Bloody Sam Roberts]

I have learned a few years ago that one scientists admits you need to have faith that it exists even though they have no evidence it does.

For my money, Dark Matter is a label for a mathematical construct that theoretical physicists must use to make all their other equations work out. That way they do not have to admit they are wrong about anything.

"Well, it's the Dark Matter you see. We have no evidence it exists but we know it's there. Our equations say so."

[muir_redwoods]

At a time when “queer” still meant strange, JBS Haldane In the 1920’s observed,

“I have no doubt that in reality the future will be vastly more surprising than anything I can imagine. Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.”

[OneVike]

"Well, it's the Dark Matter you see. We have no evidence it exists but we know it's there. Our equations say so."

You are right, they cannot admit He exists, so they make up reasons to explain that which they cannot understand.

Remember, many of these individuals have been educated beyond their intelligence.

[Little Ray]

Nice. I wish I understood what he was trying to say better. How it be tested? Better yet, how can it be exploited?

[LibWhacker]

me not understand

Mean Tonto not need peyote see Happy Hunting Grounds. ;-)

[GreenOgre]

Does this mean that Dark Energy is comprised of 800 lb Ninja Gorillas

[Errant]

Problem is, to push it depends on some sort of as-yet undetected “ether”.

I don't know.

It seems electromagnet force does, but not gravity, for its effect is not affected by the accumulation of itself... :)

[The Cajun]

Our space/time reality floating around on and the results of a more basic reality with not necessarily the same laws of physics..........I could go for that.

[BrandtMichaels]

Ping for later...

[BipolarBob]

Hopefully it wasn’t the cat you found in the box behind Schrodinger’s house.

No, but it was a dead ringer.

[newheart]

Scientists say dark matter is the cosmic glue that holds things together, well that is a secularists way of describing christ, they are just too ignorant to accept the truth.

I completely agree that it is Christ who holds all things together as the author of Hebrews clearly points out. I do NOT agree that dark matter = Christ. That would, in my opinion, confuse the identity of the Lord of the universe with part of the created universe. A position that is, shall we say, strongly advised agains in Romans 1:25. It opens the door to pantheism.

[ctdonath2]

MOND manages to account for a wide range of anomalous galactic motions with one simple formula.

Worth repeating.

If it is simple, and there are no demonstrable counterexamples, then we may presume it is correct.

[Retired Greyhound]

That’s deep, man

[762X51]

Some of what we know is mind boggling. What we don’t know is incomprehensible.

[UCANSEE2]

Christ is who keeps us all from becoming cosmic dust. Without Christ to hold us together, we would be gone. He is the same thing they call dark matter.

The law of attraction. The force that causes cells to unite for the common good. The force that causes floating particulates in a confined liquid weightless environment to form clumps (this was a discovery by a scientist aboard the space station, who merely was curious about what would happen if...?).

The force of gravity is the force of attraction.

Love creates attraction. God is LOVE. Jesus was conveying the word 'love' and the principals of it's workings, to man.

Regardless to how we 'imagine' it, or express it, we know about as much about love as we do about gravity.

One day, we will probably wonder why robots, left in the dark, huddle together.

[wxgesr]

I firmly believe that when my soul is released from this earth that God will make all things known. While I may have the potential for massive amounts of knowledge, my psyche cannot handle it. I would go crazy if God allowed me to know everthing that is knowable in the universe. Some insanity is just a glimpse to what can be known after I pass on. Sometimes you just have to step back from the edge.

[cuban leaf]

—They why are gravity wells like dimples in the fabric of space time? Or maybe they aren’t?—

I’m no expert on the subject but there is actully a lot of interesting information on the web. Here is one: http://www.amazon.com/Pushing-Gravity-Perspectives-Theory-Gravitation/dp/0968368972

[baddog 219]

Dark matter.... matter with no photons?

[cuban leaf]

—We’re not even close to understanding the nature of our existence. And that’s not necessarily a bad thing.—

At least we’ve discovered that the more we know, the more we know we don’t know. Evolution was so simple and made a lot of sense in some ways. Then we discovered DNA. Then we discovered how it works. Then we discovered ways in which parts can be used differently by some cells than in others.

Suddenly the simplest cell seems complex beyond human understanding - still.