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Squire

Registered: 12-2004
Location: falkirk
Posts: 596
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Is gravity constant?


Read this, wanted to share.

quote:

At St Andrews, Scotland’s most ancient university, a revolution is rumbling, and astronomers’ whole understanding of one of the fundamental forces of the universe is being called into question by a bold new theory. Isaac Newton changed the world forever when he tied the universe together with the invisible force of gravity, discovering that the same principle pulling a falling apple toward the ground is at work drawing out the sweeping arcs of planets and stars. Centuries later, Albert Einstein shocked the world again when he rethought Newton’s gravity in line with his general theory of relativity. There was one thing on which Einstein and Newton were unshakeable, though: the force of gravity is uniform throughout the universe. Now, though, St Andrews’ Dr Hong Sheng Zhao is assailing the constancy of gravity with a “simple” refinement, that could explain away one of astronomy’s biggest mysteries.

According to Newton and Einstein’s calculations of gravity, galaxies should, by rights, throw themselves apart as they rotate; there is not enough measurable mass to hold them together. Conventional astronomical theory deals with this conundrum by hypothesizing that up to ninety per cent of the mass of the universe is made up of mysterious “dark matter”, which cannot be detected from Earth, but according to Dr Zhao, a lecturer at the School of Physics and Astronomy and member of SUPA, the puzzle can be solved if the effects of gravity increase towards the edges of galaxies.

“There has always been a fair chance that astronomers might rewrite the law of gravity,” he says. “We have tested a new formula for gravity, which allows gravity to be boosted gradually from the Einstein/Newtonian prediction further away from the solar system. Our ‘simple formula’. . . is consistent with galaxy data so far, and if further verified for solar system and cosmology, it could solve the Dark Matter mystery. We may be able to answer common questions such as whether Einstein's theory of gravity is right and whether the so-called Dark Matter actually exists in galaxies.”

The new theory has been met with scepticism in some quarters, but is growing in popularity. Dr David Bacon, of Edinburgh Royal Observatory, has said “What Hong Sheng Zhao has done is . . . a good fit to some of the evidence – the evidence from the motion of stars. It is certainly very intriguing work.”




See, Scotland's better than NASA, haha.
No, seriously though, sounds... intriguing.

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6/17/2008, 2:25 pm Link to this post Email Blitzen   PM Blitzen
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Is gravity constant?


It's called MoND. Modified Newtonian Dynamics.

I learned about it in an astronomy class several years ago, and you can check out the theory on Wikipedia too (it had a pretty fair description when I looked a year or so ago). Actually, I posted a comment about this topic a year or so back on another board... Let me go dust it off:

quote:

Reythia wrote:
Anyone else out there heard of MoND? It's an unproven theory that suggests an alternative to Dark Matter. Basically, by altering the way we understand gravitational acceleration in this specific manner, you can model things on the edges of galaxies well (ie: they fit the data) without needing Dark Matter.

It's pretty cool and Wikipedia has a good description:
MoND Entry

I first heard about MoND in an astronomy class I was taking a couple of years back. The professor was... uh... well, a bit annoyed at me. (Apparently he wasn't too thrilled with having a bunch of aerospace engineering PhD students in his senior-year undergrad class. We had this habit of asking questions like "What sort of error bars does that plot have?" and he didn't much appreciate that...) But anyhow, he was sure we were all going to HATE this MoND theory because it refutes the engineer's favorite equation: F = ma. On the contrary, we were all intrigued and agreed that it was possible and certainly worth the effort of investigating. After all, we already ignore most relativistic effects when we do things, so we figure we can ignore this as well if it turns out to be true! emoticon (I think the prof was glad to get rid of us at the end of the semester.)



And, at least according to Wikipedia, the guy who first proposed MoND was Isreali, not American OR Scottish. emoticon Sorry, Blitzen!

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6/17/2008, 4:58 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
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Grand Master

Registered: 01-2005
Location: Maryland, USA
Posts: 492
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Re: Is gravity constant?


That is certainly AS plausible as dark matter. The only question then would be:

What causes the gravity to increase the further out you get?

It seems a little counter intuitive (not saying impossible, just not generally how we think about things.) after all the gravity of the earth does not increase the further away from it you go. So why would one gravity act in the reverse manner?

It definitely bears thinking about. The data would line up. I'd be interested in explanations on why it works though. emoticon

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6/17/2008, 5:49 pm Link to this post Email Loud G   PM Loud G AIM Blog
 
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Squire

Registered: 12-2004
Location: falkirk
Posts: 596
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Re: Is gravity constant?


According to the article I read the guy who proposed it wasn't Scottish, but he was based at a scottish research centre (in the university of St Andrews) but 90% of everything on the internet comes under Sturgeon's Law anyway. (90% of everything is rubbish).

But it's a cool theory. I can almost understand it. I'm happy.

Last edited by Blitzen, 6/17/2008, 6:15 pm


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6/17/2008, 6:15 pm Link to this post Email Blitzen   PM Blitzen
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Is gravity constant?


quote:

Loud G wrote:
It seems a little counter intuitive (not saying impossible, just not generally how we think about things.) after all the gravity of the earth does not increase the further away from it you go. So why would one gravity act in the reverse manner?


Actually, the MoND theory says that the gravitational pull of the Earth DOES increase after a certain point -- but it's so tiny that it doesn't affect much. (And if it does, we engineers would just measure it as a perturbation, not "gravity"). The reason the effect is visible in galaxies is because galaxies are so much more massive that even a tiny percentage change in their gravity is a large absolute change. Thus, we can see its effects.

For the record, I'm not 100% convinced MoND (or a similar construct) is the answer. But I am convinced that it's just as likely as the Dark Matter theory. Both theories fit the data approximately equally well, but both have very little in the way of certain evidence.

Isn't science FUN?!

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6/17/2008, 6:19 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
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Shepherd

Registered: 03-2006
Posts: 2138
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Re: Is gravity constant?


Well we never did quite figure out how gravity propagates, or for that matter what in hell it is. emoticon

Not that everyone hasn't tried of course, but as forces go gravity is very mysterious. Though we of course are making progress on it. emoticon

Anyway. the last I heard about a test for MOND was last year during a test for dark matter when they found two colliding star clusters (or was that galaxies?), I think NASA was hoping to get data that would rule out MOND, but instead it still seemed to match the current version which includes neutrino's. emoticon Still.... even if it was true, how could gravity reduce its dilution over distance like that?
Hmm, for a wild guess I'm going to guess odd space/time geometries in higher dimensions. emoticon

Ah well, great speculative possibilities for SF authors thus, less exacting rules after all.
6/17/2008, 7:33 pm Link to this post Email QS2   PM QS2
 


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