The Cosmos?

Papist

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stanley123 said:
Papist said:
stanley123 said:
Papist said:
...can you explain to me what a gravitational force is? We do not know that there are any such things. We only know that objects move in a uniform way according to the inverse square law. We come up with the idea of "forces" in order to explain that movement.
Gravity is an attractive interaction between massive bodies. We know that it exists since if you throw a basketball up in the air, it will come back down.
No, all we know is that if we throw a ball up in the air, it will come back down according to the inverse square rule. We have no idea why.
??
The modern post Einstein explanation for gravity is that it is curvature in space time caused by massive bodies. According to Newton, force is defined as Mass x acceleration, so even if you postulate that gravity is space time curvature, a basketball thrown up in the air will experience a force given by mg, where g is the acceleration due to gravity on the earth, excluding of course the lesser force of air resistance. 
That's the current view  based on the current model. But what happens when their is another paradigm shift in physics? Just because certain mathematical absractions are useful for making predictions, it does not follow that such models describe the inner workings of physical bodies as they truly are. There is always a danger of making metaphysics out of mathematics.
 

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stanley123 said:
Papist said:
That I am a geocentricist (I most certainly am not) but can you explain to me what a gravitational force is? We do not know that there are any such things.
I can prove to you that gravitational force exists. Simply come with me to the top of the empire state building and step forward. I won't try it, since I know that there is a force which will pull you down. I am just as certain that there is a gravitational force as I am sure that the sun will not shine all day long at the equator.
That proves no such thing. All it proves is that my body moves towards the earth according to the inverse squar law. It does not tell me why.
 

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Papist said:
stanley123 said:
Papist said:
stanley123 said:
Papist said:
...can you explain to me what a gravitational force is? We do not know that there are any such things. We only know that objects move in a uniform way according to the inverse square law. We come up with the idea of "forces" in order to explain that movement.
Gravity is an attractive interaction between massive bodies. We know that it exists since if you throw a basketball up in the air, it will come back down.
No, all we know is that if we throw a ball up in the air, it will come back down according to the inverse square rule. We have no idea why.
??
The modern post Einstein explanation for gravity is that it is curvature in space time caused by massive bodies. According to Newton, force is defined as Mass x acceleration, so even if you postulate that gravity is space time curvature, a basketball thrown up in the air will experience a force given by mg, where g is the acceleration due to gravity on the earth, excluding of course the lesser force of air resistance. 
That's the current view  based on the current model. But what happens when their is another paradigm shift in physics? Just because certain mathematical absractions are useful for making predictions, it does not follow that such models describe the inner workings of physical bodies as they truly are. There is always a danger of making metaphysics out of mathematics.
What is your description of the inner workings of physical bodies as they truly are? Do you have such a description, or is this just another meaningless and undefined ambiguous  concept that has no applications in the real world.
And a paradigm shift does not mean that there is no gravity. It simply means that the model which we are currently employing to describe the force is in need of some modification because of some change in outlook, such as a change in scale from the very large to the very small. Gravity continues to exist, regardless of what some deconstructionist philosopher might claim about either its existence or his own existence. If you are so keen on asking why, you might ask why do deconstructionist philosophers exist except to create confusion. Certainly not to further our understanding of what gravity is.
 

stanley123

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Papist said:
stanley123 said:
Papist said:
That I am a geocentricist (I most certainly am not) but can you explain to me what a gravitational force is? We do not know that there are any such things.
I can prove to you that gravitational force exists. Simply come with me to the top of the empire state building and step forward. I won't try it, since I know that there is a force which will pull you down. I am just as certain that there is a gravitational force as I am sure that the sun will not shine all day long at the equator.
That proves no such thing. All it proves is that my body moves towards the earth according to the inverse squar law. It does not tell me why.
This is what gravity is: the attraction of one massive body to another. It is a  contradiction to say on the one hand that gravity does not exist but on the other hand to say that a massive body moves toward the earth according to the inverse square law.
 

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davillas said:
Ebor said:
I mean no disrespect to you, and I know that you are new here on OC.net, but making assumptions about other posters' knowledge or abilities can come across as rather patronizing.  Perhaps it is the crossing of messages that led to you repeating yourself on the concept of research.

Have you read  A Brief History of Time ?  One short quote does not mean that Dr. Hawking ideas should be based on one short quote.  

And on the matter of evidence, there's the "Ulysses" Solar-Polar space probe that among other things was sent out to Jupiter so that the gravity field there could bend the path out of the ecliptic so that it could go around the Sun over its poles
http://en.wikipedia.org/wiki/Ulysses_%28spacecraft%29
No, i didn`t read it, i read The grand design and i was disappointed. I know that his idea is that the Earth has no special place, i am not interested in his idea but rather in what made them to follow this path. I am sure that today you can bring a lot of other ideas into play, you can say that dark matter doesn`t allow a geocentric universe or that dark energy or whatever. Or that there was no Earth in that thing that came into being 13.5 billions years ago.
But the problem is this is like having a train in A station. And we make a theory that the train came through B, C, D and E. Then i say : wait a minute, maybe the train came trough F, G, H, and E. No you say, that`s stupid, that will mean the train never passed through C and D and we already know that.
The thing is such a view can change a lot of what we know today ( or what we think we know ) about the universe. But somewhere in the past we had to choose the path. So why did we choosed this B, C, D and E path ? This is the question.
Well, if you haven't read it, then just taking the one clip out of the work is not workable as extrapolating what Dr. Hawking writes in the rest of it.

Ummm. I'm sorry, but your train illustration doesn't make sense. For one thing since trains systems are built by people and schedules are set up by people they would certainly have a good idea of how a particular train got to station A while suggesting other routes would show conflict with the time-tables. 

May one ask if you personally belief that the planet Earth is stationary in space with the Sun and other planets going around it?  (of course the Moon does so that is why I did not include that in the question.) 

Have you taken any classes or read many books on how Science is properly done? 

I do not mean this facetiously but ask because I am trying to understand where you are coming from, as it were.

Thank you.
 

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stanley123 said:
Papist said:
stanley123 said:
Papist said:
stanley123 said:
Papist said:
...can you explain to me what a gravitational force is? We do not know that there are any such things. We only know that objects move in a uniform way according to the inverse square law. We come up with the idea of "forces" in order to explain that movement.
Gravity is an attractive interaction between massive bodies. We know that it exists since if you throw a basketball up in the air, it will come back down.
No, all we know is that if we throw a ball up in the air, it will come back down according to the inverse square rule. We have no idea why.
??
The modern post Einstein explanation for gravity is that it is curvature in space time caused by massive bodies. According to Newton, force is defined as Mass x acceleration, so even if you postulate that gravity is space time curvature, a basketball thrown up in the air will experience a force given by mg, where g is the acceleration due to gravity on the earth, excluding of course the lesser force of air resistance. 
That's the current view  based on the current model. But what happens when their is another paradigm shift in physics? Just because certain mathematical absractions are useful for making predictions, it does not follow that such models describe the inner workings of physical bodies as they truly are. There is always a danger of making metaphysics out of mathematics.
What is your description of the inner workings of physical bodies as they truly are? Do you have such a description, or is this just another meaningless and undefined ambiguous  concept that has no applications in the real world.
And a paradigm shift does not mean that there is no gravity. It simply means that the model which we are currently employing to describe the force is in need of some modification because of some change in outlook, such as a change in scale from the very large to the very small. Gravity continues to exist, regardless of what some deconstructionist philosopher might claim about either its existence or his own existence. If you are so keen on asking why, you might ask why do deconstructionist philosophers exist except to create confusion. Certainly not to further our understanding of what gravity is.
You think I'm a deconstructionist philosopher? That's rich! :D It's much worse than that actually... I'm a Thomist.  :) As such, I don't think we should make a metaphysics out of our mathematics. We have no idea what gravity is, but we know how bodies move. What is deconstructionist about that? hmmmmmmm?
 

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"In Newton's time and for two hundred years afterwards, physicists spoke of the action of gravity as 'action at a distance,' a  phrase that was accepted as a substitute for explaining the physical mechanism, much as we speak of spirits or ghosts to explain unseen phenomena. The inability to comprehend the mechanism of gravity accentuates the power of mathematics, for Newton's work was, as the title of his Mathematical Principles indicates, entirely mathematical. His work and the additions made by his successors not only provided the calculation of the planetary motions that transcended observations but also enabled astronomers to predict phenomena such as eclipses of the sun and moon to a fraction of a second...

"Contrary to popular belief, no one has ever explained the physical reality of the force of gravitation. It is a fiction suggested by the human ability to exert force. The greatest science fiction stories are in the science of physics. However, mathematical deductions from the quantitative law proved so effective that this procedure has been accepted as an integral part of physical science. What science has done, then, is to sacrifice physical intelligibility for the sake of mathematical description and mathematical prediction..." (Morris Kline, Mathematics and the Search for Knowledge (NY: Oxford), pp. 122-123).

I'm with Papist on this one. And yet we are confident enough of Newton's equations to slingshot ourselves to the moon using mathematical equations of classical mechanics alone. Why does mind mirror nature to such a degree? (cf. Fr. Stanley Jaki's works, and Nobel Prize winner Eugene Wigner's essay (online) "The Unreasonable Effectiveness of Mathematics in the Natural Sciences" http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html )



 

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Ebor said:
Well, if you haven't read it, then just taking the one clip out of the work is not workable as extrapolating what Dr. Hawking writes in the rest of it.

Ummm. I'm sorry, but your train illustration doesn't make sense. For one thing since trains systems are built by people and schedules are set up by people they would certainly have a good idea of how a particular train got to station A while suggesting other routes would show conflict with the time-tables. 

May one ask if you personally belief that the planet Earth is stationary in space with the Sun and other planets going around it?  (of course the Moon does so that is why I did not include that in the question.) 

Have you taken any classes or read many books on how Science is properly done? 

I do not mean this facetiously but ask because I am trying to understand where you are coming from, as it were.

Thank you.
The example with the train : The problem is that you chose B from the start. From there you go to C, D and E, because it is the only way you can come to A. But if the train started from F then it never passed through C,D and E so you can`t bring them on to disprove the theory. Which is what is happening in this topic but i am not that sophisticated, and it was not my intention to talk about that.
The problem i wanted to ask was this : Two good astronomers are telling us that there is no reason not to consider the Earth as the center of our universe. One of them ( Sir Fred Hoyle ) is saying that there is no good reason for why the geocentric model is wrong and the heliocentric model is right. The other one is saying that he can build such a model with the Earth in the centre .
And we have the third telling us how they chosed B back then, based on philosophical assumptions. I don`t understad why i have to read the whole book when it is written pretty clear " we have no evidence for or against it ". And i don`t understand why i have to understand what is C, D, and E and to argue about them when these people are telling us that there is no evidence that the Earth is not in the center of the universe ( or let`s say close to the center ).

The problem i have with the actual model is that even from my poor educated point of view i can`t agree with a model that uses notions like dark "something". When you postulate invisible mass and an invisible force to keep your model alive it means you put 2 big variables in the system. So for example, in the future you can say the dark energy is only .5 of what it is today or 2 times what it is today.

From my poor understanding science should work like this : You make a hypothesis and then you look for the evidence for and against it. So for example if according with your hypothesis the entire mass of the universe should be 100 and you look at the sky and you only find 4 you throw your bad papers to the garbage.  Or if let`s say the rate of expansion should decay in time and you look in the sky and you see that the rate of expansion is accelerating you do the same thing. You don`t start to create exotic invisible notions to fill the gaps of your theory.  But who am i to say how the science should work ?

 

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xariskai said:
"In Newton's time and for two hundred years afterwards, physicists spoke of the action of gravity as 'action at a distance,' a  phrase that was accepted as a substitute for explaining the physical mechanism, much as we speak of spirits or ghosts to explain unseen phenomena. The inability to comprehend the mechanism of gravity accentuates the power of mathematics, for Newton's work was, as the title of his Mathematical Principles indicates, entirely mathematical. His work and the additions made by his successors not only provided the calculation of the planetary motions that transcended observations but also enabled astronomers to predict phenomena such as eclipses of the sun and moon to a fraction of a second...

"Contrary to popular belief, no one has ever explained the physical reality of the force of gravitation. It is a fiction suggested by the human ability to exert force. The greatest science fiction stories are in the science of physics. However, mathematical deductions from the quantitative law proved so effective that this procedure has been accepted as an integral part of physical science. What science has done, then, is to sacrifice physical intelligibility for the sake of mathematical description and mathematical prediction..." (Morris Kline, Mathematics and the Search for Knowledge (NY: Oxford), pp. 122-123).

I'm with Papist on this one. And yet we are confident enough of Newton's equations to slingshot ourselves to the moon using mathematical equations of classical mechanics alone. Why does mind mirror nature to such a degree? (cf. Fr. Stanley Jaki's works, and Nobel Prize winner Eugene Wigner's essay (online) "The Unreasonable Effectiveness of Mathematics in the Natural Sciences" http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html )
If gravity is a fiction, what causes a ball thrown up in the air to drop and not fly away?
 

Opus118

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davillas said:
Ebor said:
Well, if you haven't read it, then just taking the one clip out of the work is not workable as extrapolating what Dr. Hawking writes in the rest of it.

Ummm. I'm sorry, but your train illustration doesn't make sense. For one thing since trains systems are built by people and schedules are set up by people they would certainly have a good idea of how a particular train got to station A while suggesting other routes would show conflict with the time-tables. 

May one ask if you personally belief that the planet Earth is stationary in space with the Sun and other planets going around it?  (of course the Moon does so that is why I did not include that in the question.) 

Have you taken any classes or read many books on how Science is properly done? 

I do not mean this facetiously but ask because I am trying to understand where you are coming from, as it were.

Thank you.
The example with the train : The problem is that you chose B from the start. From there you go to C, D and E, because it is the only way you can come to A. But if the train started from F then it never passed through C,D and E so you can`t bring them on to disprove the theory. Which is what is happening in this topic but i am not that sophisticated, and it was not my intention to talk about that.
The problem i wanted to ask was this : Two good astronomers are telling us that there is no reason not to consider the Earth as the center of our universe. One of them ( Sir Fred Hoyle ) is saying that there is no good reason for why the geocentric model is wrong and the heliocentric model is right. The other one is saying that he can build such a model with the Earth in the centre .
And we have the third telling us how they chosed B back then, based on philosophical assumptions. I don`t understad why i have to read the whole book when it is written pretty clear " we have no evidence for or against it ". And i don`t understand why i have to understand what is C, D, and E and to argue about them when these people are telling us that there is no evidence that the Earth is not in the center of the universe ( or let`s say close to the center ).

The problem i have with the actual model is that even from my poor educated point of view i can`t agree with a model that uses notions like dark "something". When you postulate invisible mass and an invisible force to keep your model alive it means you put 2 big variables in the system. So for example, in the future you can say the dark energy is only .5 of what it is today or 2 times what it is today.

From my poor understanding science should work like this : You make a hypothesis and then you look for the evidence for and against it. So for example if according with your hypothesis the entire mass of the universe should be 100 and you look at the sky and you only find 4 you throw your bad papers to the garbage.  Or if let`s say the rate of expansion should decay in time and you look in the sky and you see that the rate of expansion is accelerating you do the same thing. You don`t start to create exotic invisible notions to fill the gaps of your theory.  But who am i to say how the science should work ?
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct? That the question is not meaningless?

You already answered your question about the dark matter hypothesis. It is based on evidence that can be explained by non-light emitting matter that we cannot see from the planet earth. Do you really believe we should understand how the universe works at this point of time in our history?
 

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davillas said:
Is the ball coming down or is the Earth moving up ? 
A point on the ball will experience large gravitational forces up and down because of the acceleration of the ball. A point on the earth will experience close to zero forces due to the movement of the ball. What is your reference frame for this two body problem?
 

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Opus118 said:
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct?
You need to have absolute space, if you are going to talk about the center of the universe, and this is where Newton's laws will apply. But if you are talking about Newtonian mechanics, then the earth cannot be geostationary because its rotation is proven by the oblate earth, the Foucault pendulum, and the reason why satellites are launched close to the equator and to the east.  On the other hand, if you say that there is no center in the universe, then it is a contradiction to say that the earth is the center of the universe.  So there really is no basis for geocentrism.
 

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stanley123 said:
Opus118 said:
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct?
You need to have absolute space, if you are going to talk about the center of the universe, and this is where Newton's laws will apply. But if you are talking about Newtonian mechanics, then the earth cannot be geostationary because its rotation is proven by the oblate earth, the Foucault pendulum, and the reason why satellites are launched close to the equator and to the east.  On the other hand, if you say that there is no center in the universe, then it is a contradiction to say that the earth is the center of the universe.  So there really is no basis for geocentrism.
The oblate earth and Foucault pendulum are also explained in a geocentric model. There are some circumstances where the geocentric model is useful. I suspect it is easier to calculate a flight from Earth to Pluto from Earth rather than from the view point of the Sun. There is a basis for centrism, which is utility. I do not happen to know where the center of the universe is. Presumably it will be proximal to where the Big Bang occurred, depending on whether there was a bias in the ejection of mass and energy during this event. The terms geocentric and heliocentric are simply used to specify the frame of reference. The situation would be the same if we picked a spot at the edge of the universe somewhere.
 

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Opus118 said:
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct? That the question is not meaningless?

You already answered your question about the dark matter hypothesis. It is based on evidence that can be explained by non-light emitting matter that we cannot see from the planet earth. Do you really believe we should understand how the universe works at this point of time in our history?
The thing is even Hawking is saying that they picked a certain path based only on "modesty ". For me it doesn`t matter if the Earth is in the center of the universe or not, it is not so important from a religious perspective because i have the example of Thomas, i don`t need to put my hand in Christ`s wounds to believe in Him. But from a naturalistic point of view, such a thing will mean that someone created the universe. There is no other explanation. So based on observation one can say : From what we see it looks like: A -  we are in the center on the universe, or B : every point in the universe can be a center. So if you are honest you can`t chose a certain path saying that B must be true. You need to make different models based on A and B, put the both ideas into competition and compare them with the evidence.
Of course we need to understand how the universe works. But when we exclude A from the beginning based only on our antitheism, the least a religious person can do is to have doubts about their model of universe.
 

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Opus118 said:
The oblate earth and Foucault pendulum are also explained in a geocentric model.
A proof by assertion which I don't believe.

There are some circumstances where the geocentric model is useful. I suspect it is easier to calculate a flight from Earth to Pluto from Earth rather than from the view point of the Sun.
You are incorrect. The vast majority of such a flight is going to consist of a partial orbit of the sun, or a series of such partial orbits, with (given the current way we do these things) a set of slingshot maneuvers around some of the major planets. It's going to be a lot harder to model this by superimposing the earth's orbital motion on the sun, the planets, and the vehicle as an epicycle; since doing this involves solving the three body problem (which can't be done, at least not yet) the simplest solution is simulation, and a simulation where the center of the system is the sun has the simplest mathematics.
 

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davillas said:
The thing is even Hawking is saying that they picked a certain path based only on "modesty ".
Regardless of what (you think) Hawking said, the fact is that this isn't true. There are really three key figures in this: Copernicus, Tycho, and Kepler. The first is important as the originator of the idea, but it is the third who is the most important figure in cementing the heliocentric model as superior, because he's the one who worked out elliptical orbits. You have to understand how the Ptolemaic model worked to appreciate the development. Ptolemy, being a man of his time, insisted that the motion had to be circular; but astronomers could already see that simple circles around the earth didn't give accurate predictions of position (especially the phenomenon of retrograde motion). So they imposed secondary circles called epicycles, so that (for instance) Mars orbited around around a point on Mars's primary circular orbit. This got them closer, but it was still imprecise, and led to adding more epicycles on the epicycles. So along came Tycho, who was a very good astronomer with a commitment to the Ptolemaic model. And he started messing with the epicycles, and eventually heads off to a model where the primary epicycle for each planet is a duplicate of the sun's principle orbit, with each planet's location on those epicycles in correspondence to the sun's position. In other words, he's simply taken the Copernican model and put the fixed point at the earth instead of the sun.

That is really the only point at which there is still something of an arbitrary choice between the two models, because Kepler's observation gets rid of the epicycles and the circular motion which were the chief cause of the difficulty. He instead not only worked out elliptical orbits, but came up with a very simple formula for the motion along those orbits. Each such ellipse has two foci, and the body being orbited sits at the one of those foci. For the moon, that point is where the earth rests; for the planets, it is where the sun sits. You can of course make a hybrid model like Tycho's final version, but it's a model in which only the sun and the moon are geocentric, and all the other planets are heliocentric; in any case this model was so much more accurate and so much simpler that it killed the Ptolemaic model completely. The discovery of the Galilean moons of Jupiter pushed this further along since it was obvious that whatever model you came up with had to have them effectively orbiting Jupiter; a contrived orbit of earth was outlandishly complicated in comparison.

Newton's theories of gravitation and motion explained why Kepler's laws worked, as well as getting rid of almost all the rest of the error (there's another small correction arising from relativistic effects). You cannot make geocentrism work in Newton's system; you have to come with an extremely contrived mess in which the earth's motion, and only that motion, follows a different set of rules. The math quickly becomes too complicated to take seriously, so nobody bothers; it's a lot easier to work from the observation that things work just fine if you assume that the earth follows the same laws as everything else. Throwing the relativistic effects into the mix only make it that much worse.

It's not just that a geocentric model is more elegant; it's that, in the solar system observed in isolation, a relativistic model based on Newtonian mechanics is far and away the simplest, and that alternate versions either don't work (e.g. the Ptolemaic system) or are simply Newtonian models with an exception for the earth. All the stuff Hawking is talking about is at a larger scale, galactic in the case of dark matter and intergalactic in the case of dark energy. They are being introduced because the apparent deviation from Newtonian/relativistic motion is most readily explained by keeping the model as is and introducing unseen objects and substances which act within that model to produce the observed deviations. Personally I think dark matter has a better chance of long-term survival as a real phenomenon, but in any case the whole thing is still something of a theoretical kluge that wants more verification. The expansion of the universe is a phenomenon which also needs explanation, but again things are pretty speculative; the notion that we have some idea of what set off the big bang can be rejected out of hand as the purest of speculation.

 

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Keble said:
Opus118 said:
The oblate earth and Foucault pendulum are also explained in a geocentric model.
A proof by assertion which I don't believe.

There are some circumstances where the geocentric model is useful. I suspect it is easier to calculate a flight from Earth to Pluto from Earth rather than from the view point of the Sun.
You are incorrect. The vast majority of such a flight is going to consist of a partial orbit of the sun, or a series of such partial orbits, with (given the current way we do these things) a set of slingshot maneuvers around some of the major planets. It's going to be a lot harder to model this by superimposing the earth's orbital motion on the sun, the planets, and the vehicle as an epicycle; since doing this involves solving the three body problem (which can't be done, at least not yet) the simplest solution is simulation, and a simulation where the center of the system is the sun has the simplest mathematics.
In retrospect that wasn't a good example. I was writing from an 1950's SciFi movie space flight perspective and we do not have an inertia-less drive yet.

In regard to proof by assertion. I can provide links, but they are, more or less, dinner table-type discussions amongst physicists. And given the topic, this discussion is only justified as a source of amusement.

Let me know and I will hunt some of them down.

If earth were the sole entity in the universe, then there is no frame of reference to rotate against. Does it become an oblate spheroid? I am still seeking answers in regard to relativity.
 

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Opus118 said:
stanley123 said:
Opus118 said:
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct?
You need to have absolute space, if you are going to talk about the center of the universe, and this is where Newton's laws will apply. But if you are talking about Newtonian mechanics, then the earth cannot be geostationary because its rotation is proven by the oblate earth, the Foucault pendulum, and the reason why satellites are launched close to the equator and to the east.  On the other hand, if you say that there is no center in the universe, then it is a contradiction to say that the earth is the center of the universe.  So there really is no basis for geocentrism.
The oblate earth and Foucault pendulum are also explained in a geocentric model. There are some circumstances where the geocentric model is useful. I suspect it is easier to calculate a flight from Earth to Pluto from Earth rather than from the view point of the Sun. There is a basis for centrism, which is utility. I do not happen to know where the center of the universe is. Presumably it will be proximal to where the Big Bang occurred, depending on whether there was a bias in the ejection of mass and energy during this event. The terms geocentric and heliocentric are simply used to specify the frame of reference. The situation would be the same if we picked a spot at the edge of the universe somewhere.
The rotation of the earth changes measurably during an earthquake. An earthquake is relatively minor when compared to activity in the whole universe. If the earth were stationary, it would mean that this type of relatively minor activity on the small planet earth would influence the rotational motion of millions of other stars and galaxies.
 

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Keble said:
davillas said:
The thing is even Hawking is saying that they picked a certain path based only on "modesty ".
Regardless of what (you think) Hawking said, the fact is that this isn't true. There are really three key figures in this: Copernicus, Tycho, and Kepler. The first is important as the originator of the idea, but it is the third who is the most important figure in cementing the heliocentric model as superior, because he's the one who worked out elliptical orbits. You have to understand how the Ptolemaic model worked to appreciate the development. Ptolemy, being a man of his time, insisted that the motion had to be circular; but astronomers could already see that simple circles around the earth didn't give accurate predictions of position (especially the phenomenon of retrograde motion). So they imposed secondary circles called epicycles, so that (for instance) Mars orbited around around a point on Mars's primary circular orbit. This got them closer, but it was still imprecise, and led to adding more epicycles on the epicycles. So along came Tycho, who was a very good astronomer with a commitment to the Ptolemaic model. And he started messing with the epicycles, and eventually heads off to a model where the primary epicycle for each planet is a duplicate of the sun's principle orbit, with each planet's location on those epicycles in correspondence to the sun's position. In other words, he's simply taken the Copernican model and put the fixed point at the earth instead of the sun.

That is really the only point at which there is still something of an arbitrary choice between the two models, because Kepler's observation gets rid of the epicycles and the circular motion which were the chief cause of the difficulty. He instead not only worked out elliptical orbits, but came up with a very simple formula for the motion along those orbits. Each such ellipse has two foci, and the body being orbited sits at the one of those foci. For the moon, that point is where the earth rests; for the planets, it is where the sun sits. You can of course make a hybrid model like Tycho's final version, but it's a model in which only the sun and the moon are geocentric, and all the other planets are heliocentric; in any case this model was so much more accurate and so much simpler that it killed the Ptolemaic model completely. The discovery of the Galilean moons of Jupiter pushed this further along since it was obvious that whatever model you came up with had to have them effectively orbiting Jupiter; a contrived orbit of earth was outlandishly complicated in comparison.

Newton's theories of gravitation and motion explained why Kepler's laws worked, as well as getting rid of almost all the rest of the error (there's another small correction arising from relativistic effects). You cannot make geocentrism work in Newton's system; you have to come with an extremely contrived mess in which the earth's motion, and only that motion, follows a different set of rules. The math quickly becomes too complicated to take seriously, so nobody bothers; it's a lot easier to work from the observation that things work just fine if you assume that the earth follows the same laws as everything else. Throwing the relativistic effects into the mix only make it that much worse.

It's not just that a geocentric model is more elegant; it's that, in the solar system observed in isolation, a relativistic model based on Newtonian mechanics is far and away the simplest, and that alternate versions either don't work (e.g. the Ptolemaic system) or are simply Newtonian models with an exception for the earth. All the stuff Hawking is talking about is at a larger scale, galactic in the case of dark matter and intergalactic in the case of dark energy. They are being introduced because the apparent deviation from Newtonian/relativistic motion is most readily explained by keeping the model as is and introducing unseen objects and substances which act within that model to produce the observed deviations. Personally I think dark matter has a better chance of long-term survival as a real phenomenon, but in any case the whole thing is still something of a theoretical kluge that wants more verification. The expansion of the universe is a phenomenon which also needs explanation, but again things are pretty speculative; the notion that we have some idea of what set off the big bang can be rejected out of hand as the purest of speculation.
Why do you write such a thing that " i think " Hawking said something ? You have the quote and probably have the book. What does it mean " We have no evidence for or against it " ? It can only mean that our model of universe is based on the assumption that any point of the universe can be considered the center. How can you understand something different ?
Most likely from what he writes it doesn`t mean that the other option is a geostationary earth. I don`t think even Ellis talked about this. At the scale of the universe, even if we consider the solar system or the Milky Way to be in the center it will mean the Earth is in the center. The fact remains, the model we have is based on the assumption that every point in the universe can be considered to be the center.
 

Opus118

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stanley123 said:
Opus118 said:
stanley123 said:
Opus118 said:
Is there a good scientist that claims that the geocentric and heliocentric models are not both correct?
You need to have absolute space, if you are going to talk about the center of the universe, and this is where Newton's laws will apply. But if you are talking about Newtonian mechanics, then the earth cannot be geostationary because its rotation is proven by the oblate earth, the Foucault pendulum, and the reason why satellites are launched close to the equator and to the east.  On the other hand, if you say that there is no center in the universe, then it is a contradiction to say that the earth is the center of the universe.  So there really is no basis for geocentrism.
The oblate earth and Foucault pendulum are also explained in a geocentric model. There are some circumstances where the geocentric model is useful. I suspect it is easier to calculate a flight from Earth to Pluto from Earth rather than from the view point of the Sun. There is a basis for centrism, which is utility. I do not happen to know where the center of the universe is. Presumably it will be proximal to where the Big Bang occurred, depending on whether there was a bias in the ejection of mass and energy during this event. The terms geocentric and heliocentric are simply used to specify the frame of reference. The situation would be the same if we picked a spot at the edge of the universe somewhere.
The rotation of the earth changes measurably during an earthquake. An earthquake is relatively minor when compared to activity in the whole universe. If the earth were stationary, it would mean that this type of relatively minor activity on the small planet earth would influence the rotational motion of millions of other stars and galaxies.
This is similar to the merry-go-round story attributed to Albert Einstein. I think it applies here as well or I cannot figure out the distinction.

Hans Reichenbach, The Philosophy of Space and Time (1928):

"According to the general relativity of rotation, we can consider not only the earth but also any given rotating system, e.g., a merry-go-round, as the rest system. This conception, however, has absurd consequences. The horse, which in the usual interpretation pulls the merry-go-round, must in the second interpretation be able to put the earth, even the universe, in motion by means of treading, since now the merry-go-round remains at rest. How can the horse have the strength to do so?  This objection overlooks the fact that, in the relativistic conception, the rotation of the stars is due to a gravitational rotational field, and not to the horse. The latter has an entirely different task; it prevents the merry-go-round from following the rotational field and taking part in the general rotation. We see that even according to the relativistic interpretation, the horse has to perform a task determined by the mass of the merry-go-round and not by the mass of the stars. If an elevator glides down slowly and a fly inside crawls upward so that it remains at the same level relative to the building, it has to transport only its own mass – it does not have to “push down” the elevator."

 
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