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FleaBagger (29.53)

Holiday weekend astrophysics

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July 04, 2008 – Comments (6)

I wrote this in an email to a friend a while back, after reading about astrophysics for several hours on the internet. I had been following rabbit trails in the course of researching theories of non-carbon biology for a sci-fi board game I'm making with said friend. Suddenly this thought occurred to me, in relation to the dark matter theory of anomalies in observed motion in the galaxy.

Isn't it awfully hubristic to assume that the difference between physical laws observed on Earth and physical motion observed in the rotation of a galaxy are due to some strange force acting upon the galaxy, and not due to:

A) a flaw in the observations/calculations of the rotation of galaxies
B) some unusual property on Earth, warping our understanding of physics (I like this explanation)
C) something beyond human comprehension or imagination

After all, why should the galaxy be ruled by laws we understand from an earthly perspective? Isn't it more likely that Earth is ruled by galactic laws of motion? Does that make any sense? Down with dark matter! Are you with me?

Maybe I'm the hubristic one, since I am a college drop-out (with an English major background, no less), but it seemed to me that there was a glaring logical flaw in the assumptions behind dark matter theory. If I am totally off base here, one of you astrophysics researchers that I know is on CAPS, come and tell me all about it. I'm curious how much of your response I'll understand. Happy Independence Day!

P.S. Even if you don't have a degree in astrophysics, feel free to leave a comment. 

6 Comments – Post Your Own

#1) On July 04, 2008 at 1:13 AM, hansthered0 (< 20) wrote:

I don't see whats so confusing about the way it moves. Whats wrong with the standard model?

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#2) On July 04, 2008 at 2:21 AM, DemonDoug (82.19) wrote:

flea, a major issue as i understand it in physics is gravity.  There has been no accepted general theory on why mass causes gravity.  We understand ionic and covalent bonds, and we understand that mass causes gravity - but we don't understand why mass causes gravity.  Theories abound on the subatomic nature of gravity, but then the question becomes what is happening with gravitational forces at the subatomic level?  The people trying to answer this question are none other than the highest theoretical physicists we have nowadays, and this is in large part with string theory is trying to figure out. 

So basically, what I'm saying is that it's not hubristic at all, because we as humans really don't know the nature of this very important universal force.  Without understand why we have gravity and where it comes from, we won't ever be able to understand the nature of dark matter, because dark matter and gravity don't get along really well when you test them either mathematically, in a model, or in the observable universe.  In another type of theory, some physicists believe that dark matter doesn't exist, only that our theory of gravity is wrong.

You are correct whe you say there are glaring flaws in the dark matter theory.  Here is a dense but at least palatable article on the matter (forgive the pun) http://physicsworld.com/cws/article/print/24991

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#3) On July 04, 2008 at 3:46 AM, AnomaLee (28.50) wrote:

We assume that the laws of physics are universal. If there were separate galatic laws of motion then they wouldn't..We "know" dark matter exists because of the displacement of visible matter throughout the observable universe. Dark matter is one of the least understood phenomenon in the universe. I'm not an astrophysicist, and this is only my third year majoring in physics. However, what you said has truth. There are gaping holes in the Standard Model. To this day we still don't understand the true nature of gravity(or time) at the elementary level. It's been theorized that there may exist a graviton which communicates gravity. The basis of science and understanding is repeatability. If a theory is true then it should hold up under repearted experimentation. We are hoping the Large Hadron Collider may show experimental data to prove several theories(reference Higgs particles), but its possible that the explainations may only be reachable at the Planck scale which is far beyond our possibility. Also, you can thank Congress for not developing the most power particle accelerator and leaving the U.S. and science community almost 20 years behind.

For your purpose it is completely possible that life as we know it could thrive as anti-matter and its possible life forms could be based on silicon. Also, the possibility that there are extra dimensions that we typically do not experience is growing support rapidly. We observe dark matter indirectly through its gravitational effects. Its assumed that dark matter is more abundant than matter. We don't fully understand the cause of the gravitational effects. String theory, m-theory, supergravity, and many other theories are all based on the concept of an n-dimentional universe which can attributed to Einstein. Personally, I think it is more than a possibility but its hard to think in these terms. It's hard enough to program and think in 3-Dimensions. Our observations, life as we know it, may be no different than the story of the controversial book, Flatland.

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#4) On July 04, 2008 at 9:19 PM, FoolishChemist (97.02) wrote:

You seem to be leaning toward Modified Newtonian Dynamics which says that gravity doesn't behave itself when the acceleration is really small.

Just so everyone is on the same page, dark matter is called dark because it doesn't interact with light.  Every charged particle (electron, proton) will couple to photons, but dark matter doesn't.  The only thing it does interact with is gravity and the only way it can be observed is if it bumps into something, but if the cross section is very small we can't observe it.  Dark matter has been backed up beyond the original galactic rotation rates. The WMAP probe has observed the microwave background

and the power spectrum (think of a 3D Fourier Transform) essentially tells you how much matter is present in what form.

I'm not saying the issue is closed, but unlike the unexplained famous 43 arcseconds/century of the perihelion of Mercury that was explained by General Relativity, it seems pretty likely that dark matter and not some other weird thing is going on.

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#5) On July 05, 2008 at 3:50 AM, FleaBagger (29.53) wrote:

FoolishChemist - I don't mean to be obtuse (and I do just want another excuse to use the word "hubristic"), yet allow me to hubristically ask: aren't we basing all of this on observations made from Earth (or at best our own solar system)? If dark matter exists, why shouldn't it completely skew every observation of distant galaxies and deep space? If it doesn't exist, mightn't each galaxy or even each solar system be subject to unknown, massless forces that distort our observations of things outside? (Regardless of whether we use light, heat, microwaves, toasters, or what have you to observe the outside universe.)

I guess what I'm trying to say is that if observed from intergalactic deep space, these things might look a whole lot different, and dark matter might seem pretty silly. But then again, you might ram right into dark matter on your way out to intergalactic deep space, and then you'd be sorry.

But seriously, part of me thinks that the more we need to deviate from the simpler theories to explain things, the less reliable ways we have of observing the phenomena we are seeking to explain. I know this sounds woefully simplistic, but how do we even know what's going on in distant galaxies? By indirect observation. Very indirect observation. We don't even know that distant stars aren't aliens in spaceships shining flashlights at us for late-night giggles (though I agree that idea offends both science and Occam). My point is, we don't know. There is a happy medium between thinking we know exactly what happened 2 billion ly away and how and why, on the one hand, and epistemological nihilism on the other. That very happy medium is, arbitrarily, belief in what can be observed within just a second or two of light. (Sorry, but it's 3:45 AM.)

While I've got all you smart people here, let me ask if it's plausible that an object (say, a superfast alien spaceship) might leave its galaxy of origin and enjoy some reduction in ambient galactic gravitation as it travels from one point to another in the same galaxy; say, an epigalactic scud effect. And don't be discouraged by my skepticism of your observations of the motion of distant galaxies. I really am interested in what you have to say.

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#6) On July 06, 2008 at 4:49 PM, FleaBagger (29.53) wrote:

To clarify: mightn't everything move faster intergalactically than intragalactically? Or perhaps everything would be slower? Maybe we'd just run into the dark matter and bounce off, like my dad's invisible wall of jello.

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