Skip to comments.Is Dark Matter a Glimpse of a Deeper Level of Reality?
Posted on 06/13/2012 11:11:54 AM PDT by 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 dont think Ive ever been so flummoxed by physicists reactions to a paper. Mathematically it could hardly have been simplerthe level of middle-school algebra for the most part. Logically and physically, it was a head-hurter. I couldnt decide whether it was profound or trite. The theorists we consulted said they couldnt 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 hasnt changed. One told me: There are a lot of ideas hes bringing together in an interesting way, but its a little hard for us to decipher, so Im 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 Einsteins 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 doesnt 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 universes degrees of freedomall that its most fundamental building blocks are capable ofare 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 possibilitiesin the jargon, a phase space commensurate with their almost unimaginably rich repertoire of behaviors.
Verlindes 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 forcea 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 theres much more phase space than we usually assumemuch moreyou 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 dont do anything truly wackyit 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 floorboardsthe 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 freedomspecifically, 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. Im 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 doesnt 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 matterordinary as well as darkconsists 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 doesnt 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?
My head hurts.
The argument can be (and is being) made that gravity does not pull. It pushes. Problem is, to push it depends on some sort of as-yet undetected “ether”. But it solves some of the paradoxes, like light slowing down in water and then speeding back up when it exits it.
That’s good! It means you’re smart. :-)
I could tell my cat about this and it wouldn’t hurt his head. Dumb cat.
My cat is heavy into string theory.
My head hurts.
My eyes also. I think they must be paid by the word. creative writing has gone too far and must be stopped.
Scientists: Dark matter exists
New observations of a great big cosmic collision provide the best evidence yet that invisible and mysterious dark matter really does exist.
The collision, between two huge clusters of galaxies, is the "most energetic cosmic event, besides the Big Bang, that we know about," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
The impact split normal matter and dark matter apart, rendering the dark matter's gravitational presence observable.
Scientists announced the discovery today in a teleconference with reporters.
The normal matter in the cosmos -- atoms that make up stars, planets, air and life -- accounts for only a small fraction of what must exist, based on the fact that without an additional source of gravity, galaxies would fly apart and galaxy clusters could not hold together as they do.
Nobody knows where all that gravity comes from, so scientists say there must be some invisible stuff out there, which they call dark matter. Its presence is indirectly supported by many observations. Given what's known, this is the makeup of the universe:
5 percent normal matter
25 percent dark matter
70 percent dark energy
Dark energy is an even more mysterious phenomenon, a force of some sort that beats out gravity and is causing the universe to expand at an ever-faster pace.
Some theorists have suggested that rather than invoking dark matter, perhaps existing ideas about gravity might be wrong. Maybe gravity is stronger on intergalactic scales than what is predicted by Newton and Einstein.
And all astronomers agree that dark matter is such an exotic idea as to border on the crazy. "A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."
Clowe and colleagues used NASA's Chandra X-ray Observatory to study the galaxy cluster 1E0657-556, which contains a bullet-shaped cloud of superheated gas. X-rays show the shape was produced by cosmic winds created in a high-speed collision of two clusters of galaxies.
Other telescopes were used to locate and quantify the mass in the clusters. They actually measured the effect of gravitational lensing, in which gravity from the clusters distorts light from thousands of background galaxies, as predicted by Einstein's theory of general relativity.
The dark matter is not seen, but its gravity has a predictable effect on the observations. The resulting blue color in a new image represents the gravity fields observed by noting how the light from each background galaxy is distorted. Here's what the image reveals:
The hot gas -- normal matter -- was slowed by a drag force described as the cosmic equivalent of air resistance. But the dark matter was not slowed by this effect, presumably because it does not interact with normal matter, as theory had predicted.
So the normal matter and dark matter became separated.
"This proves in a simple and direct way that dark matter exists." Markevitch said in the teleconference.
Other theories must cope
The finding provides further evidence that standard Newtonian gravity, which keeps planets in orbit around the sun, is the glue that makes things stick on the largest scales, too.
It is still possible there is some modification of gravity going on, but these findings make it less necessary to have such theories, said Sean Carroll, a cosmologist at the University of Chicago who was not involved with the study. "No matter what you do [in devising new theories] you're going to have to believe in dark matter."
"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said. "This is the first time we've had a direct detection of dark matter" in which you can't explain the results with any altered-gravity theory, he said.
The findings will be detailed in an upcoming issue of the Astrophysical Journal Letters.
God, who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son, whom He has appointed heir of all things, through whom also He made the worlds; who being the brightness of His glory and the express image of His person, and upholding all things by the word of His power, when He had by Himself purged our sins, sat down at the right hand of the Majesty on high, having become so much better than the angels, as He has by inheritance obtained a more excellent name than they. Hebrews 1:1-4 (NKJV)
We’re all just living in one form of our universe a multiverse.
Michael Crichton said so in Timeline.
Much easier to understand when written as fiction.
They why are gravity wells like dimples in the fabric of space time? Or maybe they aren't?
We’re not even close to understanding the nature of our existence. And that’s not necessarily a bad thing.
“My cat is heavy into string theory.”
Hopefully it wasn’t the cat you found in the box behind Schrodinger’s house.
In other words:
There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.
Most of this is over my head, except the string theory. My theory is if you see a loose string on your cargo shorts .... don’t pull it because if you do your pants might fall off.
me not understand
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