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 07-15-2012, 11:57 PM #16 Pooh-Bah   Join Date: Jun 2009 Posts: 5,832 Re: If gravity is warpage of space, how can it effect objects at rest? Using a frame of reference where the Earth is stationary isn't very useful , as it means distant galaxies are moving at jillions of times the speed of light in order to complete a full orbit of the universe every 12 months, etc. etc. Basically Occam's razor, it's much simpler to say the earth and the other planets go in ellipses around the sun and the theory of gravity is as Einstein presented it; than it is that the Sun goes in an ellipse around the Earth, the other planets all follow these bizarre trajectories around the Earth, and the distant galaxies exceed the speed of light in our frame, and modify all the equations of relativity to be valid in this frame.
07-16-2012, 12:04 AM   #17
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by Kittens Using a frame of reference where the Earth is stationary isn't very useful , as it means distant galaxies are moving at jillions of times the speed of light in order to complete a full orbit of the universe every 12 months, etc. etc.
And if you spin around on your chair, the moon goes around your head faster than the speed of light.

07-16-2012, 12:14 AM   #18
old hand

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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by Kittens Using a frame of reference where the Earth is stationary isn't very useful , as it means distant galaxies are moving at jillions of times the speed of light in order to complete a full orbit of the universe every 12 months, etc. etc. Basically Occam's razor, it's much simpler to say the earth and the other planets go in ellipses around the sun and the theory of gravity is as Einstein presented it; than it is that the Sun goes in an ellipse around the Earth, the other planets all follow these bizarre trajectories around the Earth, and the distant galaxies exceed the speed of light in our frame, and modify all the equations of relativity to be valid in this frame.
Seriously? and you still don't think this is correct? http://forumserver.twoplustwo.com/47...69/?highlight=

okay you didn't talk about decimal ones, like what if we put the reference somewhere uniform, or in a negative spot?

so the earth doesn't necessarily revolve around the sun, and the sun does in a sense revolved around the earth. Don't we feel lied to? Shouldn't we change the school curriculum?

Quote:
 Originally Posted by BruceZ And if you spin around on your chair, the moon goes around your head faster than the speed of light.
And you seriously can't infer time travel from this?

 07-16-2012, 12:29 AM #19 Pooh-Bah   Join Date: Jun 2009 Posts: 5,832 Re: If gravity is warpage of space, how can it effect objects at rest? ^ not sure what point you are trying to make
07-16-2012, 12:32 AM   #20
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by Kittens ^ not sure what point you are trying to make
well just that we spend our time thinking people were silly for thinking that the sun revolved around the earth, but really they were right and there math would work for it?

And also that the world is flat depending on the perspective, but if you drive to the edge you come out the other side.

07-16-2012, 02:52 AM   #21
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by newguy1234 well just that we spend our time thinking people were silly for thinking that the sun revolved around the earth, but really they were right and there math would work for it? And also that the world is flat depending on the perspective, but if you drive to the edge you come out the other side.
Classic example of brilliantly making the easy hard and being proud of being wrong without knowing it and yet still correct in describing observations for the wrong reasons (a lesson for today?), what an irony of the greatness of ancient Greeks. But they had it right too by some other astronomers well in advance of Copernicus. So they did it both wrong and complicated and phenomenologically interesting and also correct but not globally embraced by the majority. However indeed embraced by those that counted like Archimedes.

Wrong and elegant (but not in an Einstein way of doing things)

http://en.wikipedia.org/wiki/Ptolema...olemaic_system

http://en.wikipedia.org/wiki/Deferent_and_epicycle

but also right and ahead of its time;

http://en.wikipedia.org/wiki/Heliocentric_system

Archimedes' reference of Aristarchus' work 23 centuries ago;

"You King Gelon are aware the 'universe' is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the 'universe' just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface."

Impressive isnt it?

And the ultimate!

http://en.wikipedia.org/wiki/Antikythera_mechanism

Last edited by masque de Z; 07-16-2012 at 03:01 AM.

07-16-2012, 03:05 AM   #22
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by masque de Z Impressive isnt it?
no not the least bit, because now we would need to move to a thread that discusses the relationship between our thinking now, the dark ages, the bibles history counts, past civilizations, and antiquity. Also we would have get into the knowledge the ancients had when they built there great temples. And we'd have to get into the genocide of the 'natives' and the wiping out of there texts and histories.

Also we can get into hilter, Atlantis, Nazism, Aryans, the Indus valley etc.

I think once you do then you don't think its impressive I think it can be argued our knowledge was suppressed at one point and still is.

So have we decided there is no centre of an atom or whatever ? Obviously there is a centre that something spins around, but also the centre actually spins around the something. they are also spinning around each other at the same time, and they are also not. They are also spinning around each other in fractional viewpoint. They also don't move everything just goes berserk around them. Also certain fraction of each happening.

That we can infer from the sun moon thing right? or does science not say that yet?

07-16-2012, 03:23 AM   #23

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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by BruceZ The earth and the moon revolve around their center of mass which is between the earth and the moon, closer to the earth since its bigger. The earth and the sun do the same thing, but since the sun is so much bigger, the center of mass is inside the sun.
If by this you mean to imply that the CoM of the earth/moon system is not inside the earth, that's not true.

ME = 5.9742 e24 kg
Mm = 7.36 e22 kg

distance between centers ≈ 384,400 km
distance from CE to CoM = (384,400 km x 7.36 e22 kg)/(5.9742 e24 kg + 7.36 e22 kg) = 4,678 km

So, about 73% of the way out from the center of the earth (RE ≈ 6,371 km average, 6,384 at equator)

Some billions of years from now when the moon has drifted out far enough such that the CoM is now outside the earth, we can call the two a double planetary system, but for now, we're just a planet and the moon is just a moon.

Last edited by atakdog; 07-16-2012 at 03:29 AM.

07-16-2012, 03:54 AM   #24
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by atakdog If by this you mean to imply that the CoM of the earth/moon system is not inside the earth, that's not true. ME = 5.9742 e24 kg Mm = 7.36 e22 kg distance between centers ≈ 384,400 km distance from CE to CoM = (384,400 km x 7.36 e22 kg)/(5.9742 e24 kg + 7.36 e22 kg) = 4,678 km So, about 73% of the way out from the center of the earth (RE ≈ 6,371 km average, 6,384 at equator) Some billions of years from now when the moon has drifted out far enough such that the CoM is now outside the earth, we can call the two a double planetary system, but for now, we're just a planet and the moon is just a moon.
Hmmm, I didn't realize that the earth was over 80 times more massive, but it turns out that the moon's density is only 60% that of earth, and of course its volume goes down as the cube of its radius which is 0.273 times that of earth. So I guess the moon goes around the earth after all, part of it anyway.

Last edited by BruceZ; 07-16-2012 at 04:21 AM.

07-16-2012, 06:37 PM   #25
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by newguy1234 This made me wonder, not sure if its on topic. We imagine the earth orbits the sun and the sun doesn't move. But thats perspective, really they both move in relation to each. What does the perspective look like if we use the earth as the stationary object?
Well, we know that our solar system(including the sun) is moving as well, but we like to work with a stationary sun because it makes things easier without causing errors in nearly anything we'd do. Also, when analyzing our solar system, working with a stationary sun allows for a simple yet accurate explanation for the movement of the planets. Trying to draw the Earth in the middle instead makes for some complicated orbits for the other planets.

07-16-2012, 09:30 PM   #26
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by newguy1234 well just that we spend our time thinking people were silly for thinking that the sun revolved around the earth, but really they were right and there math would work for it?
The simplicity of Kepler's laws were one of the key arguments Galileo used in trying to convert everyone to heliocentrism; although why Kepler's laws worked wasn't fully explained until Newton developed calculus about 70 years later.

07-16-2012, 09:41 PM   #27
Pooh-Bah

Join Date: Jun 2009
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by BruceZ Hmmm, I didn't realize that the earth was over 80 times more massive, but it turns out that the moon's density is only 60% that of earth, and of course its volume goes down as the cube of its radius which is 0.273 times that of earth. So I guess the moon goes around the earth after all, part of it anyway.
You can actually measure the density of the Sun by using the moon's density and a stick on the beach

We observe that the effect of the Moon on tides is about 2.1x that of the Sun; but the two have approximate the same angular diameter as viewed from Earth.

So the density of the Moon is about 2.1x that of the Sun

07-17-2012, 02:02 AM   #28
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Re: If gravity is warpage of space, how can it effect objects at rest?

Quote:
 Originally Posted by FoldnDark Are there any objects at rest in the universe? If so, how would we know?
Everything that isn't accelerating is at rest in its own reference frame.

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