Is the Old Model of the Universe Still Valid?

[binbots]

Back when we thought the Earth was in the middle of the universe we came up with a mathematical model that predicted the movements of the planets with great accuracy. Then after we put the sun at the center of our solar system the model changed and became much easier to understand. But more recently we discovered that there are no special places in the universe. No universal time, no universal middles and starting points. So my question is: is that early model of the universe still valid? Both models are right but the sun in the middle just makes the math easier?

 

[russ_watters]

The early model using the Earth at the center was not accurate and did not include have an operating mechanism or the predictive power of current theory.

 

[Fewmet]

Back when we thought the Earth was in the middle of the universe we came up with a mathematical model that predicted the movements of the planets with great accuracy. Then after we put the sun at the center of our solar system the model changed and became much easier to understand. But more recently we discovered that there are no special places in the universe. No universal time, no universal middles and starting points. So my question is: is that early model of the universe still valid? Both models are right but the sun in the middle just makes the math easier?

I prefer to think of model selection as a matter of convenience rather than validity. I usually sketch atoms using the Dalton model. While atoms are clearly not little balls of uniform composition, it is far easier to work with than one with all the overlapping orbitals drawn in. But the Dalton atom is useless when calculating, say, molecular shapes.

In the case of the geocentric and heliocentric models, I cannot think of many cases in astronomy where the former is more convenient to use. I have heard that the Navy teaches navigation calculations in the geocentric model because they are simpler than those in the heliocentric model and nearly as a accurate. I once read that it was historically hard to differentiate between the two because their predictions of planetary positions were the same within about one percent.

 

[AstrophysicsX]

As we gain more and more information our answers change. When we thought the Earth was the center of everything we tried to base our answers on that, but now that we know we aren't the center we must change our old concepts and knowledge.

 

[binbots]

But then we found out that the sun is not in the middle of the universe. In fact there are no middles of anything in the universe, only places with more mass. So now that we know how our solar system works, can’t we pick any spot and make accurate predictions from anywhere?

 

[ideasrule]

But more recently we discovered that there are no special places in the universe. No universal time, no universal middles and starting points. So my question is: is that early model of the universe still valid? Both models are right but the sun in the middle just makes the math easier?

What does the fact that there's no universal time, middle, starting point, etc. have to do with whether the Sun's gravity dominates Earth's? General relativity clearly predicts that the metric tensor is more strongly affected by large masses like the Sun, so Earth orbits the Sun, not the other way round.

 

[russ_watters]

But then we found out that the sun is not in the middle of the universe. In fact there are no middles of anything in the universe, only places with more mass. So now that we know how our solar system works, can’t we pick any spot and make accurate predictions from anywhere?

Sure, but the easiest way to do that is to use General Relativity and a sun-centered reference frame* and then translate the results into another coordinate system.

There is big difference between the usefulness of the three reference frames you listed and the way you do the calculations taking each into account. In each case, you set the little object to be orbiting the big object and if you want to model three objects, you do two sets of calcs, ie Earth moving around the sun, then the sun moving around the center of the galaxy. And both calcs can be accurately made using gravity.

But with epicycles, in order to set the small object as the center, you need highly convoluted calculations that as far as I know have never been successfully accomplished to anywhere close to the accuracy of GR.

Moreover, AFAIK, the concept of epicycles was never put into a predictive model, meaning it was always developed ad-hoc to explain past observations and refined as new observations came in that it didn't fit. Contrast that with a theory of gravity where all you need is a starting position and speed (or two points and a time) and the mass of the larger object and you can accurately predict the entire orbit.

Gravity isn't merely simpler to use than the epicycles model, it's more accurate and more predictive.

*Caveat: for best accuracy, you need to use the center of mass of the system as the reference.

 

[phinds]

is that early model of the universe still valid?

That early model had little to nothing to do with that thing that we now mean by the word "universe". They THOUGHT it did, but that was seriously mistaken. It only predicted the movement of the planets which compared to the currently understood size of the universe is essentially nothing.

If you mean does the early model still work to predict the movement of the planets, I don't believe the movement of the planets has changed significantly in the last few hundred years so it should still be as accurate as it ever was. And, yes, when you create a more rational model, the math is WAY easier. Those epicycles were murderously wicked.

 

[binbots]

So if we use general relativity and place Earth back in the middle would it still work? I guess I am just stuck on the words that we use to describe our universe. Words like middle. What is right and wrong?

 

[phinds]

So if we use general relativity and place Earth back in the middle would it still work? I guess I am just stuck on the words that we use to describe our universe. Words like middle. What is right and wrong?

The epicycle math models PUT us in the center and our being in the center is a requirement for them to work. That was their POINT ... to work under the assumption (strong belief at the time) that we are ARE at the center of the U. Again, taken as an internally consistent system, they work as well as they ever worked (or maybe not quite as well ... I don't know what change there may have been in planetary motions in the last couple hundred years ... I'm assuming not much) but they are just a math construct that works in the solar system, but not as well as the elliptical-orbit model and way more ugly to use.

 

[russ_watters]

So if we use general relativity and place Earth back in the middle would it still work?

It would be convoluted and ugly and reducible to putting the center of gravity in the middle, but it could be made to work.