Prove that the earth goes around the sun

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  • #26
Nereid
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Originally posted by Canute
Does this mean that orbital motion is not relative?
To reinforce something which SelfAdjoint said, there are solid observations of the extent to which the Sun's mass 'bends' spacetime, and they match the predictions of GR to at least 1 part in 20,000.

Perhaps your question could be restated as "are there preferred frames of reference in GR?"
 
  • #27
Nereid
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Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.
Do you mean before stellar aberration and parallax? Do you mean 'in principle, using only the technology available in 1704'?

While not quite in the same class as parallax and stellar aberration, Olaus Roemer's observations of eclipses of the Jovian moon Io should also help convince skeptics.

If you want 'proof', why don't you build a telescope, a webcam system, buy an accurate clock, and do the observations of the light pulses from the Crab pulsar yourself? It won't be expensive, is well within the technical reach of an amateur astronomer, and the maths is straight-forward.
 
  • #28
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Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.
Hey, we love skeptics. Many of us are skeptics. But skepticism is not disbelief of everything until you obtain absolute proof. There are scales of certainty and granting "acceptance" of theories (scientific theories being the explanatory models that a consensus of the world's experts agree best fit the experimental evidence...and knowing that theories will continue to be tested and refined). Skepticism is a weighing the available evidence (critical thinking) and putting your best foot forward. With hyper-skepticism, you'll be stuck forever on the question of whether reality exists or not. :smile:

Several proofs have been described here. You could take the simple equations for stellar parallax to suit your maths, but you will need to dig up the databases of temporal telescopic measurements of nearby & distant stars to see that the data show that nearby stars show more motion relative to us than the distant stars do. Or you could take the equations from the laws of planetary motion/gravity to calculate that the center of mass is by the sun, not the Earth.

Hmm...sudden thought...what kind of gravitational torque would be placed on the Earth if it was the center of the universe? Would it tear the Earth apart?
 
  • #29
russ_watters
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Has anyone mentioned http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html [Broken]? Accepted or not, the Ptolemaic model was deeply flawed right from the start.

The problem of retrograde motion has been known for milenia and the explanation is elementary school simple. IMO, the main thing that kept people from figuring it out sooner was a blind following of Aristotle.
 
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  • #30
Nereid
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'proof'? this is science!

Originally posted by rattis
Ok. Is there any proof of this topic from a few hundred years ago? using just observations from earth and mathematics?

I am sorry to be a sceptic, but generally until i have proof i do not believe.
Forgot ... 'proof' works in mathematics; in science the paradigm (don't you just love that word?) is 'falsification'. The strongest statement you can make in science is something like: "all observations and experiments are consistent with X" (X is a theory), or "there are no repeatable observations or experimental results which are inconsistent with the predictions of X".

So, in the case of the Earth and the Sun, something like: all observations are consistent with {description of the Sun, including its mass}, {description of the Earth}, (etc, naming the planets and major moons) orbiting {description of the solar system barycentre} as predicted by GR.

rattis or Canute may make an observation tomorrow which is inconsistent with GR; bye-bye GR! (Of course, for such a dramatic consequence, there'd be dozens of folk who'd want to repeat the observations, to convince themselves).
 
  • #31
selfAdjoint
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Originally posted by russ_watters
Has anyone mentioned http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html [Broken]? Accepted or not, the Ptolemaic model was deeply flawed right from the start.

The problem of retrograde motion has been known for milenia and the explanation is elementary school simple. IMO, the main thing that kept people from figuring it out sooner was a blind following of Aristotle.
Eudoxos' homocentric spheres theory explained retrograde motion but didn't quantify it. Appolonios of Perga's deferents and epicycles explained retrograde motion and Hipparchos and eventually Ptolemy did quantify them/it. The only problem with the theory as Ptolemy left it was the motions in latitude. That plus the problem of the rate of motion. Ptolemy used a trick (arbitrary) called bisection of the equant to get a form of uniform motion to match the motion we now know to be governed by Kepler's second law.

The Ptolemaic theory could have been cleaned up (a la Tycho Brahe's model), but by the time Tycho died everybody but superskeptics and religious bigots had accepted heliocentrism.
 
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  • #32
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Originally posted by Nereid
So, in the case of the Earth and the Sun, something like: all observations are consistent with {description of the Sun, including its mass}, {description of the Earth}, (etc, naming the planets and major moons) orbiting {description of the solar system barycentre} as predicted by GR.
This is is the issue really. I'm not a sceptic, and certainly not suggesting that the earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the earth is at the centre, however mathematicallty strange that theory would have to be.
 
  • #33
Nereid
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Originally posted by Canute
This is is the issue really. I'm not a sceptic, and certainly not suggesting that the earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the earth is at the centre, however mathematicallty strange that theory would have to be.
It may well be fun to try to build a detailed mathematical model which accounts for parallax, stellar aberration, the Shapiro time delay (yes, that can be observed in a one-way observation, no need for spaceprobes), bending of light, semi-annual doppler shifts, etc, etc and explicitly starts with the Earth as the centre of the universe.

However, I doubt that it'd be very interesting. For a start, it would have to assume that little or none of the physics we observe in labs here on Earth applied to any of the things which our Heath Robinson model contained. Further, every time anything new was observed - gamma ray bursts, for example (yes, you can detect those from down here on the surface of the Earth, no satellites required) - you'd have to build new physics to handle it!

Oh, and you can forget such useful things as GPS and communications satellites - not only couldn't you launch them (unlikely rockets could make it out of the atmosphere, given that 'outside Earth' physics would be so different), but they wouldn't work (again because the physics would be too different).
 
  • #34
selfAdjoint
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Originally posted by Canute
This is is the issue really. I'm not a sceptic, and certainly not suggesting that the earth goes around the sun. (After all Nicole d'Oresme worked that, and 'Galilean' relativity, in the fourteenth century, pretty much by logic alone).

What you say here is true. But my question was whether all observations are also consistent with a description in which the earth is at the centre, however mathematicallty strange that theory would have to be.
Canute, have you got a site for Oresme and the earth going around the sun? I know he discussed a rotating model of the earth, but I never heard of the other.

My understanding of the discussion of the rotating earth in the 14th century is as follows: The philosopher Buridan had developed a concept of what we might call "naive momentum", which was sort of proportional to weight and speed, and sort of conserved (he described it in commentaries on Aristotle, so you have to read it carefully to see what he means). At any rate he gave the example, contra Ptolemy, of an object thrown up from the surface of a rotating earth.

Ptolemy had said it would fall behind the thrower, since he, attached to the earth, would be moving, while the object, freed from earth, would in accordance with Aristotle's physics, have no translational motion. But Buridan said that the object would still have his "impetus", which would keep it moving to fall in the same place as if the earth were at rest. So it was Buridan who introduced the basic Galilean relativity.

Oresme, who was basically a mathematician, then wrote a treatise observing that an object projected sufficiently high, even though it retained its impetus, would have the speed associated with that impetus less than the speed required of objects at that greater radius, to keep up with the rotating surface of the earth. So the object would too fall behind.

Assume the experiment takes place at the equator. Then the point of projection would move with whatever speed the rotating earth gave, v, during the time the object rose and fell, t, so a distance vt. And this would be at the distance R from the earth's axis, so the point of projection's path would subtend there an angle of arctan(vt/R). Meanwhile, the object's average height during its rise and fall would be h, and it would travel horizontally the same distance as the point of projection, vt. Thus its path would subtend the angle at earth's axis arctan(vt/(R+h)), which is obviously smaller than the first one, so the object would fall behind the point of projections's new position.
 
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  • #35
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Originally posted by Nereid

Perhaps your question could be restated as "are there preferred frames of reference in GR?" [/B]
Pehaps this is what I should have asked.
 
  • #36
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how can you say that the earth doesnt go around the sun?
the sun is as we have mathematically proven much much larger than the earth, and has a far greater mass. so if you believe gravity is directly a result of the presence of mass, and larger massed objects have greater gravitational pulls, then you could assume that the earth more or less goes around the sun.

In fact it isnt that the earth goes perfectly round the sun while the sun sits perfectly centered, the earth and the sun both rotate around their centre of gravity. But since the sun is so much bigger than earth it is easiest to say that the earth goes around.

for example think of two earths orbiting each other, each would view the other as going "around". It is all relative but there are ways to make the information more usefull. in this case, the earth is farther from the centre of the mass and so would be seen as the one orbiting. also the fact that there are other planets orbiting the sun makes it easier to say it is at the center of things, because the planets balance each other out, in a way so that the sun is more or less always in the middle.

So if you had a planet the size of earth, and put it in orbit around another planet that is twice as big, you would see both orbiting around a center of gravity, where the momentum of the mass on either side of the axis is equal, you could not say that the smaller planet is the one orbiting, because they both move around the same way. only the smaller one moves more, so it seems to be the one orbiting.

one distinction that can be made to clarify which one is orbiting, would be to trace the paths of the two objects aound there axis of motion. the one with the larger circle traced by its motion could then be labelled as orbiting around the other. I would have to assume that this is the case with the earth, although i dont have any proof, only logical reasoning.

If you want proof, i can give you proof but that requires you to assume that the sun is far more massive than the earth. for my proof i would tell you to do a simulation, take a basket-ball, make a wire come out from the ball and place a marble on the end. spin the ball and throw it in the air so it spins freely, then observe that the basket-ball does not spin around the marble. thats your proof.
 
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If you want proof, i can give you proof but that requires you to assume that the sun is far more massive than the earth. for my proof i would tell you to do a simulation, take a basket-ball, make a wire come out from the ball and place a marble on the end. spin the ball and throw it in the air so it spins freely, then observe that the basket-ball does not spin around the marble. thats your proof.
Ok, but all movement is relative isn't it? Although it might not be helpful or useful to do so, why can I not just take the marble as my static reference point and say that the basket ball is going round it and that myself, the earth and the entire universe are moving in a very inelegant and unnecessarily complex way relative to the marble?

Why can't I throw a one of those super bouncy balls around inside a hard walled room and say that the ball is still and the entire universe has this erratic bouncing in addition to its other natural movements until the ball (or universe) settles down?

Movement is relative isn't it? why can't one pick any item or point in the universe at random and call it "still"?
 
  • #38
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BAsically the thery ofrelativityproves gravity tobe true. GRavity casues ustorevolvearound the sun because the spacetime curvatureof thesunidgreater thanours and pullsusin intothesunsorbit
 
  • #39
russ_watters
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Ok, but all movement is relative isn't it? Although it might not be helpful or useful to do so, why can I not just take the marble as my static reference point and say that the basket ball is going round it and that myself, the earth and the entire universe are moving in a very inelegant and unnecessarily complex way relative to the marble?

Why can't I throw a one of those super bouncy balls around inside a hard walled room and say that the ball is still and the entire universe has this erratic bouncing in addition to its other natural movements until the ball (or universe) settles down?

Movement is relative isn't it? why can't one pick any item or point in the universe at random and call it "still"?
Motion is relative, acceleration is not. In order for the universe to bounce around a raquetball, an enormous force would need to be applied to it.
 
  • #40
DaveC426913
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how can you say that the earth doesnt go around the sun?
the sun is as we have mathematically proven much much larger than the earth, and has a far greater mass. so if you believe gravity is directly a result of the presence of mass, and larger massed objects have greater gravitational pulls, then you could assume that the earth more or less goes around the sun.

In fact it isnt that the earth goes perfectly round the sun while the sun sits perfectly centered, the earth and the sun both rotate around their centre of gravity. But since the sun is so much bigger than earth it is easiest to say that the earth goes around.

for example think of two earths orbiting each other, each would view the other as going "around". It is all relative but there are ways to make the information more usefull. in this case, the earth is farther from the centre of the mass and so would be seen as the one orbiting. also the fact that there are other planets orbiting the sun makes it easier to say it is at the center of things, because the planets balance each other out, in a way so that the sun is more or less always in the middle.

So if you had a planet the size of earth, and put it in orbit around another planet that is twice as big, you would see both orbiting around a center of gravity, where the momentum of the mass on either side of the axis is equal, you could not say that the smaller planet is the one orbiting, because they both move around the same way. only the smaller one moves more, so it seems to be the one orbiting.

one distinction that can be made to clarify which one is orbiting, would be to trace the paths of the two objects aound there axis of motion. the one with the larger circle traced by its motion could then be labelled as orbiting around the other. I would have to assume that this is the case with the earth, although i dont have any proof, only logical reasoning.

If you want proof, i can give you proof but that requires you to assume that the sun is far more massive than the earth. for my proof i would tell you to do a simulation, take a basket-ball, make a wire come out from the ball and place a marble on the end. spin the ball and throw it in the air so it spins freely, then observe that the basket-ball does not spin around the marble. thats your proof.
That's not proof. That's an analogy - and a weak one.

The OP is asking if there is empirical evidence that shows the Earth goes around the sun and not vice versa. He acknowledges that there are all sorts of inductive arguments that pile up why this is surely the case, but that's not observation. You cannot observe that the Sun IS hugely more massive than the Earth AND THAT the Earth must, logically orbit it. That is an interpretation.

You're asking a mathematician to accept that "but it just makes so much sense it's gotta be true!" - a mathematician.
 
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  • #41
tony873004
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The OP and revesz will probably never read your comment, Dave. This thread is 4 years old, and neither have posted in over 3 years.

It fooled me too. I was getting ready to reply before I realized it.
 
  • #42
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Ha aaaaa haaaaa haa ha haaaaaaa... That was so funny the thread is 4 years old & they havent posted here for last 3 years either...
I only saw that to now... Haaa ha haa haaa that was so funny...thanks!!..
 
  • #43
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Locking tp prevent any further resurrection.
 

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