shape of our universe theory and questions..

The non amateur stuff. Hawking, black holes, that sort of thing

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joe
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Post by joe »

spodzone wrote:Oh, strange - I don't picture black holes that way at all. (It's only a schematic of a gravitational potential well, it doesn't mean you're going to see a rubber sheet with grid-lines from your space-ship window, after all.)
This is the problem, I think (not necessarily Moonstruck's) Often diagrams that show the properties of something are taken literally, especially visual representations of mathematical solutions (The dreaded extra dimensions being the perfect example). Both of the other representations that you and Dave picked are close to what I have in mind also.
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davep
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Post by davep »

spodzone wrote:
davep wrote:Like this impression for example.
Oh, strange - I don't picture black holes that way at all. (It's only a schematic of a gravitational potential well, it doesn't mean you're going to see a rubber sheet with grid-lines from your space-ship window, after all.)
Yes, the diagram I pointed at is a 2d representation of the gravity well.
spodzone wrote:http://sci.esa.int/science-e-media/img/f4/17316.jpg sort of works for me, except note that we don't see X-rays so that'd be mostly black, right?
From what I can gather the impression I pointed at (see link above) is more or less a representation of a black hole as if it wasn't obscured.
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Post by Moonstruck »

Joe,Davep,Spodzone,
After all your welcome tuition,I am happy to say there is now a glimmer of understanding.
So, would I be right in thinking that, a black hole is the result of an implosion of a star or galaxy of stars, which creates a gravitational force that defies the earthly rules of physics.
RIGHT, Think you've finished with me?
Next question.
Do I understand correctly, that where there are two stars revolving around one another, they have a common centre of gravity at a point in space between them?
Agian thank you all for your time and effort.
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Post by davep »

Moonstruck wrote:So, would I be right in thinking that, a black hole is the result of an implosion of a star or galaxy of stars
More a collapse than an implosion.
Moonstruck wrote:which creates a gravitational force that defies the earthly rules of physics.
Not quite. Black holes were predicted by physics (nothing "Earthly" about the "rules"). Where the "rules" are supposed to break down is at the singularity.
Moonstruck wrote:Do I understand correctly, that where there are two stars revolving around one another, they have a common centre of gravity at a point in space between them?
Yes, it's called a Barycenter. It's not just stars that this relates to, it relates to all bodies that orbit each other. The Earth and Moon orbit a Barycenter for example, the orbits can be thought of as looking something similar to this:

Image
joe
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Post by joe »

Nice little animation. Can you throw in a moon around the planet as well? :roll:
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Post by davep »

That is a planet and a moon, if you want it to be.

The image is from here. There's a few others there too.
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Post by joe »

Yes, but I was looking for a moon orbiting a planet orbiting a star and all their barycentres....while whistling dixie.
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Post by davep »

Joe's profile wrote:Occupation: illustrator
Interests: cosmology
The image is "copyright-free" (depending on where you live). Off you go... ;)
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Post by Moonstruck »

Thanks davep,
The next question. How on earth was the barycentre even thought of let alone worked out. Will do some searching on the net.
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Post by davep »

I've no idea who might have first thought of it but I wouldn't be the least bit surprised to find out that Newton figured it out when working on the Law of Universal Gravitation. Actually, thinking about it, I'd have thought that Kepler would have figured it out when creating the Laws of Planetary Motion.
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Post by spodzone »

Moonstruck wrote:Thanks davep,
The next question. How on earth was the barycentre even thought of let alone worked out. Will do some searching on the net.
Fairly simple, I would have thought. The equation for attraction between two bodies due to gravity is

F=-GMm/r^2

(M,m masses, r distance, G gravitational coefficient, - because it's attractive.)

So you can use this equation to work out the force on a test-object at varying distances from the earth, and at varying distances from the moon, set the two forces to be equal (so the force from the moon is as strong as that attracting to the earth) and solve for r accordingly. You'll find the mass of the test-object itself is irrelevant, as long as it's tiny compared to the other two bodies ;)

You might find http://en.wikipedia.org/wiki/Barycentre handy.
~Tim
joe
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Post by joe »

davep wrote:
Joe's profile wrote:Occupation: illustrator
Interests: cosmology
The image is "copyright-free" (depending on where you live). Off you go... ;)
Funny, I had a friend/colleague at a newspaper where we both worked who did (and probably still does) all of the graphics for Astronomy Now. I would give my eye teeth to do that. That's why I'm trying to learn the ins and outs of all the Photoshop programmes, in case such an opportunity should arise. Doesn't pay well though. If your reading Mark, drop me a line!

I digress....
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Moonstruck
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Post by Moonstruck »

Gee Spodzone,
Are you sure?
Simple it maybe.
I can only just work out what pocket money management will allow me from MY pension.
:shock:
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The Greek view..

Post by brian livesey »

The ancient Greeks realised that the part can never be greater than the whole. It seems that our actions must be restricted to knowing the "bits" that make up our universe. In attempting to find the "ultimate" origin of the universe itself,are we not being like a goldfish in an opaque bowl,trying to work out what's on the outside? Answers please. :shock:
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Re: The Greek view..

Post by spodzone »

brian livesey wrote:The ancient Greeks realised that the part can never be greater than the whole.
Sounds a bit of a cliché to me.
In attempting to find the "ultimate" origin of the universe itself,are we not being like a goldfish in an opaque bowl,trying to work out what's on the outside?
No.
~Tim
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