Dark Matter Is an Illusion, New Antigravity Theory Says • Hacker News Board

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#21

Post by philwelch » Sun, Sep 04, 2011, 6:24 PM UTC

splat wrote: post #20

philwelch wrote: post #19

This seems plausible to me. I'm not a physicist, but I think the case of dark matter can be compared to the case of the planet Vulcan. In the early 20th century, in the heyday of discovering planets by observing existing planets and realizing that classical mechanics didn't quite predict their orbits correctly, it was observed that Mercury's orbit didn't fit the classical model well enough. Reasonably enough, it was…

Either way our model of physics is off. Currently, the most reasonable explanation for dark matter is that it consists of some unknown, weakly-interacting particle. However, the standard model of physics predicts the existance of no such particle. Even this, the most mundane possibility, requires radical changes to our most fundamental physical theories.

That sounds even sillier. The most reasonable explanation is that there's some impossible matter around? At least the planet Vulcan was an ordinary planet that was just too close to the sun.

Again, I'm emphatically not a physicist. Stranger things have happened. It just smells funny to posit dark matter as a hypothesis.

The only thing that's not suspicious is the anomaly itself. Physics has always refined itself by looking at different scales. We were wrong about the quantum level the first time we looked at it, and we were wrong about even the planet Mercury, so it's to be expected that we're wrong about galaxy clusters.

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#22

Post by Confusion » Sun, Sep 04, 2011, 7:16 PM UTC

dedward wrote: post #17

Confusion wrote: post #12

Earlier quoted context omitted.

The whole 'virtual photons' thing is a physical interpretation of the mathematics, but it is a mistake to conclude that this is how it 'actually' is. There is a mathematical model that works. I don't think we know how it 'actually' is. There is every reason to doubt that this sea of 'virtual photons' has any physical reality in an independently verifiable way. Occam's razor doesn't favor solutions that involve multit…

In the end, all we have are our mental models and experiments to back them up.... we'll never know what anything 'actually' is - all we can do is model things to whatever degree of accuracy we can. A construction worker doesn't need to go around thinking about his hammer as being made up of mostly empty space, and of the electromagnetic forces that give it it's properties, it's a hammer! We all know what it "IS" righ…

Well, first and foremost: the existence of Hawking radiation hasn't been experimentally verified. There's no direct evidence (measuring radiation that could have no other source than the evaporation of the black hole) nor any indirect evidence (black holes losing mass at a rate that cannot be explained unless Hawking radiation is included). So although it seems to fit nicely into the picture, it may not exist at all.

A second type of answer is: I don't know and I admit that the physical picture of virtual particles hopping in and out of existence indeed nicely includes an explanation of Hawking radiation. However, I'm reminded of the texts that illustrate how many physical phenomena were considered to be satisfactorily 'explained' within, for instance, the aether model, even though it later turned out the model was fundamentally flawed and all of those physical interpretations were hogwash.

A third type of answer is: sometimes things simply aren't what they seem. For instance, we can describe phonons as if they're particles: they are described by the same statistics as 'real' particles are. However, they decidedly aren't particles. They aren't properties of individual particles either: they only exist in macroscopic, well-ordered, amounts of material. You could look at all individual atoms one by one and never arrive at phonons as partial explanations for their movements and properties. For that, you'd have to look at things at a different level.

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#23

Post by ppog » Sun, Sep 04, 2011, 9:51 PM UTC

philwelch wrote: post #21

splat wrote: post #20

Earlier quoted context omitted.

Either way our model of physics is off. Currently, the most reasonable explanation for dark matter is that it consists of some unknown, weakly-interacting particle. However, the standard model of physics predicts the existance of no such particle. Even this, the most mundane possibility, requires radical changes to our most fundamental physical theories.

That sounds even sillier. The most reasonable explanation is that there's some impossible matter around? At least the planet Vulcan was an ordinary planet that was just too close to the sun. Again, I'm emphatically not a physicist. Stranger things have happened. It just smells funny to posit dark matter as a hypothesis. The only thing that's not suspicious is the anomaly itself. Physics has always refined itself by l…

"Impossible matter"? What's "impossible" about it? That we don't know what it is, and that it isn't predicted by our current models, doesn't make it "impossible." It means we're going to need to extend our models, which we've been doing on a regular basis for hundreds of years. Rob Knop sums this up nicely:

"In the face of evidence otherwise, many still insist that most of the Universe must be made up of baryonic stuff that interacts with other baryons and our familiar photons. Is this not just as much hubris as insisting that the Earth, where we live, must be the center about which all the other Solar System bodies orbit?" (http://scientopia.org/blogs/galacticinteractions/2011/08/14/...)

The dark matter hypothesis seems to have a great deal of explanatory power. The antigravity hypothesis, like other MOND theories, has a good fit for the specific phenomenon it was designed to tackle, but doesn't explain a lot of the other things that dark matter does. Ethan Siegel has a good post on "What Dark Matter's Alternatives Must Do" (http://scienceblogs.com/startswithabang/2011/08/what_dark_ma...) which points out some of the stuff that dark matter explains and rival theories don't (e.g. temperature fluctuations, hydrogen/helium ratio). He does presciently note that 'antimatter has negative mass' could explain more than traditional MOND theories but claims that this impacts other well-tested assumptions such as conservation of energy.

He also has a specific article on the antigravity theory: http://scienceblogs.com/startswithabang/2011/09/dark_matter_... (and yes, he does acknowledge that "dark matter ... historically has problems for individual galaxies").

Of course, none of this is to say that the dark matter hypothesis won't eventually be disproved and go the way of Vulcan as you suggest. Ironically, though, it sounds to me like the MOND and antigravity theories are the Vulcans here: they solve only one specific problem, while dark matter fits with so much more.

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#24

Post by mparr4 » Mon, Sep 05, 2011, 12:13 AM UTC

hollerith wrote: post #15

127 wrote: post #9

Earlier quoted context omitted.

One thing I don't understand: wasn't there just discovered a ring of antimatter circling around the Earth? Wouldn't it just disperse into space if antimatter caused antigravity? Stupid question, I know, but just something that's beyond my comprehension.

Tiny amounts of antimatter were just discovered circling around Earth. The anti-grav effect on the antimatter particles is swamped by the effects of the Earth's gravity and magnetic field.

According to this theory, it would be the magnetic field alone--not the gravitational field--that is overwhelming the antigravity effect. After all, if these particles had an opposite "gravitational charge", then their experience of gravity wouldn't be attractive but would be equal in magnitude but opposite in orientation. Hence "anti"gravity.

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#25

Post by philwelch » Mon, Sep 05, 2011, 3:15 AM UTC

ppog wrote: post #23

philwelch wrote: post #21

Earlier quoted context omitted.

That sounds even sillier. The most reasonable explanation is that there's some impossible matter around? At least the planet Vulcan was an ordinary planet that was just too close to the sun. Again, I'm emphatically not a physicist. Stranger things have happened. It just smells funny to posit dark matter as a hypothesis. The only thing that's not suspicious is the anomaly itself. Physics has always refined itself by l…

"Impossible matter"? What's "impossible" about it? That we don't know what it is, and that it isn't predicted by our current models, doesn't make it "impossible." It means we're going to need to extend our models, which we've been doing on a regular basis for hundreds of years. Rob Knop sums this up nicely: "In the face of evidence otherwise, many still insist that most of the Universe must be made up of baryonic stu…

That we don't know what it is, and that it isn't predicted by our current models, doesn't make it "impossible."

I was indulging in a bit of poetic license with that one.

I'll agree that we don't currently have a good theoretical alternative to the dark matter hypothesis. Much smarter and more qualified people than me have tried and failed to come up with one. But it still seems unsatisfying to me.

Re: Dark Matter Is an Illusion, New Antigravity Theory Says

#26

Post by hollerith » Mon, Sep 05, 2011, 3:38 AM UTC

mparr4 wrote: post #24

hollerith wrote: post #15

Earlier quoted context omitted.

Tiny amounts of antimatter were just discovered circling around Earth. The anti-grav effect on the antimatter particles is swamped by the effects of the Earth's gravity and magnetic field.

According to this theory, it would be the magnetic field alone--not the gravitational field--that is overwhelming the antigravity effect. After all, if these particles had an opposite "gravitational charge", then their experience of gravity wouldn't be attractive but would be equal in magnitude but opposite in orientation. Hence "anti"gravity.

I accept the correction. Good one.