> Remember that everything is relative and perspective is key.
This has always bothered me a bit, everything being relative. You can validly say that we're the ones moving at near light speed and those stars we're talking about are actually the stationary objects; there's literally no way to tell the difference.
Couldn't you say the same thing about the earth and the sun? Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Well I understand the reason actually, and it seems that there is good reason to believe one interpretation of relative motion is the correct one, conforming to physics.. and the other view of relative motion isn't actually what's happening in reality.
It actually annoys me that we still teach kids that the Earth revolves around the Sun and the ancients with their silly earth-centric system were wrong. Just the math is (kinda [1]) simpler, thats all.
First, its a lie. And second it breeds contempt for the ancients that said and discovered many great things. I dont mind telling them that heliocentism is a great (amazing) approximation. But I really dont appreciate how from K-University previous work that has been outdone is dismissed [2]
[1] the higher order terms are sill there in the heliocentric system, they're just smaller in magnitude.
[2] Another example is atomism and how the physicists who rejected it are mocked in undergrad classes. Those guys were bloody titans and their models and methods are the cornerstone of modern engineering (try designing a bridge w/out continuum mechanics but using MD)
>Why do we insist that we are moving around the sun, and not the other way around if everything is relative?
Try to express the trajectories relative to earth of other planets in our solar system and you will quickly understand why we use a heliocentric model.
> A planet orbiting the sun is accelerating toward the sun.
How do we know that the sun isn't orbiting the fixed earth, and accelerating toward the earth? Everything would look _exactly_ the same to everyone.
Yes, the math works out much easier and more neatly, so that is likely what is happening in reality. But from a purely relativistic framework.. you can consider any point in space the frame of reference, and all motion relative to that "fixed" point.
It makes me think that relativity is actually describing a more subjective experience, rather than the objective reality where we "know" the earth orbits around the sun.
> How do we know that the sun isn't orbiting the fixed earth, and accelerating toward the earth? Everything would look _exactly_ the same to everyone.
That wouldn't work out. You can take the earth as a fixed point and describe the Sun's motion relative to it, and it would be perfectly valid, but it wouldn't look as the Sun orbiting the Earth in any kind of almost constant speed elliptical orbit, it would look like a very different kind of motion.
Well, maybe, but I think you're mixing the everyday definition of "relativity" (i.e., things are relative) with what physicists mean by "relativity" (i.e., the Theory of Special or General Relativity, both theorized by Einstein).
> but I think you're mixing the everyday definition of "relativity"
Well, yes.. because Einstein's theory beautifully makes all the math work out, explaining one interpretation of motion as the real one. But what it did at the same time was show that there is no "fixed grid" of space independent of the objects themselves. Which is what leads to my uneasy feeling of how we ever can say one interpretation is more real than another -- i admit it may just be a nonsensical perspective.
As for what all physicists mean by relativity in general... I can highly recommend this old series from the National Science Foundation:
I was confused about this too, until a physicist friend pointed out that you can always tell which of the bodies actually did the acceleration to get up near light speed.
> Why do we insist that we are moving around the sun, and not the other way around if everything is relative?
Because it makes the math easier - that's all. If you fix your frame of reference to the Sun, the orbits of all other bodies become almost perfectly elliptical. If you try to pin the reference frame to any other body, you end up with complicated curves. But they model the same thing[0]. So the whole thing about "Earth orbits the Sun" is that it gives same results, but is much easier to work with.
Technically, for the easy math, the point you're after is the barycenter[1] of the Solar System - the center of mass, which, per Newton's First Law, can be used to center the reference frame, because it's not accelerating[3]. As it turns out, the barycenter of the Solar System spends most of the time within the volume of the Sun[2], and otherwise is very close to it. So for most calculations, you may just as well pin the reference frame to the Sun.
And then, when you fix your sights at the barycenter, you'll notice the movement of celestial bodies fall out pretty much straight from joining Newton's Second Law with the Law of Universal Gravitation - m₁a₁ = Gm₁m₂/r². Your model simplifies - you now realize the movement of celestial bodies is governed by the same laws movement on Earth is, and all the complexity of geocentric model was caused by needless coordinate transformation, due to a bad choice of the reference frame.
Also worth noting that historically, humans have developed the geocentric model to a very impressive level of precision - to the point that the "upstart" heliocentric model initially was worse at predicting movement of planets. It took some extra insights for the heliocentric model to beat the old ones[5] - and only then Newton came along, and people connected the effect with the cause.
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[0] - If I recall correctly, if you were to take the path of a planet in a geocentric model and do a Fourier transform on it - that mathematical operation which represents a function of time as a possibly infinite sum of sine waves - you'd notice that the path of your planet is essentially a sum of two periodic functions. One would correspond to the movement of Earth around the Sun, the other to the movement of the planet around the Sun. This would give you a strong hint that your model is needlessly complicated, and can be recreated using much simpler curves.
[3] - Only forces from outside the considered system could cause it to move, which we're by definition not considering when talking about our system in isolation. And besides, they add up to negligible amounts anyway. Nice thing about forces in our reality scaling like 1/r^2 or worse[4] is that they very quickly add up to nothing with distance, which makes it easy for us to treat systems as isolated in calculations, and have the results match up to reality with extreme accuracy.
[5] - Like using ellipses instead of circles as the fundamental curve, because your competition that used circles moving on circles could just keep adding circles - they were doing a Fourier transform without knowing it, and each circle added a frequency component, increasing the accuracy of approximating the actual ellipse.
No, it absolutely isn't valid to say the earth is stationary while the sun rotates around it, you end up with crazy nonsense.
Technically, the earth doesn't rotate around the sun either -- they both rotate around the center of mass of the solar system, which happens to be very close the the center of the sun, so it looks like everything rotates around the sun.
Thanks. Still unsettling that while both perspectives are equally valid, Newtonian physics is so much more convincing than what came before (clockwork/earth at the center of the universe).
So while both relative views are equally true, the laws of physics (or at least mathematics) don't seem to hold both those views with equal esteem.
In Newtonian physics the sun is the preferred frame of reference.
However with the introduction of the mathematics of general relativity by einstein in 1915; we can prefer whatever reference frame we like and we get the same correct predictions. Predictions that are more accurate than Newton's.
This has always bothered me a bit, everything being relative. You can validly say that we're the ones moving at near light speed and those stars we're talking about are actually the stationary objects; there's literally no way to tell the difference.
Couldn't you say the same thing about the earth and the sun? Why do we insist that we are moving around the sun, and not the other way around if everything is relative? Well I understand the reason actually, and it seems that there is good reason to believe one interpretation of relative motion is the correct one, conforming to physics.. and the other view of relative motion isn't actually what's happening in reality.