I thought about putting this in GD, but it fits better here.
In times past, humanity believed the Earth was the center of the Universe. In modern times, we have all been taught that the Earth revolves around the sun. But what we have been taught is simply not true. And I can prove it.
We tend to think in Newtonian physics, but Einstein pointed out that the Universe is far stranger than an apple falling on some dead English guy’s head. There is only one way to measure motion - by measuring it relative to something else. What is it the something else? Isn’t that pretty arbitrary?
So I posit the seemingly insane idea that the Earth does NOT move around the Sun, but it is, in fact, vice versa. There is no center of anything, so you have to pick an arbitrarily “fixed” point. I choose Earth. Shoot, I choose me.
If the Earth is stationary, then the stars go round it about once a day. That means that they are all travelling much faster than the speed of light (the Sun excepted, because it’s so close to us). How does relativity cope with that, together with the enormous accelerations the stars are going through?
Isn’t the point of this motion relativity thing that you can CHOOSE the fixed point depending on context?
So in the context of our solar system the planets revolve around the sun. In the context of Earth the moon revolves around it. In the context of Earth’s surface cars travel relative to the road surface, in the context of the Universe the whole galaxy is travelling away from the source of the big bang.
Seems to be begging the question. If motion is relative, why isn’t the OP’s thesis reasonable and why isn’t it a problem for the thesis that stars can’t be whirling around us at greater than the speed of light?
If you have a hypothetical empty universe and drop one object into it, I assume you cannot consider it to be spinning. (Relative to WHAT?). Drop another a couple hundred meters away and you could now say that either object A is rotating or else object B is revolving around object A, but you can’t pin one down as “the” correct interp, right?
If you can, in fact, via the accepted laws of physics, define what portion of relative motion is “owned” by object A as opposed to object B, does that have implications for identifying a reference point (occupied by an object or not) as “non-moving”? If not, why not? Is radial motion somehow different from linear with regards to relative versus absolute considerations of whether or not object X is moving?
It’s true that all linear motion is relative. It’s not true for rotational motion, such as the Earth going around the Sun, or you rotating with the Earth. To be technical, the fixed-Earth coordinate system (for some problems, at least) is a non-intertial frame of reference. That means you see stuff happening that is inconsistent with Newton’s laws.
The movement of air on large scales is an example. It behaves as if there is a force deflecting it from straight-line motion (this makes hurricanes and other storms spin counterclockwise in the northern hemisphere and clockwise in the southern). That violates Newton’s first law- objects in motion don’t continue in a straight line, they deflect.
If you want to do some physics problems in a non-inertial reference frame, you have to introduce fictitious forces- centrifugal force and the Coriolis force for a uniformly rotating frame. If you’re going to argue that your frame really is an inertial frame (as it would be if the earth were not moving around the sun), you have to come up with some explanation of those fictitious forces. You’d have to come up with some explanation for stellar parallax, for example, if you were going to use this coordinate system for a problem in which stellar parallax matters.
Wrong. If the object is spinning, things on its surface will experience the Coriolis force. If it isn’t, they won’t. That’s true regardless of what else is in the universe. If a Foucault pendulum were set up on the surface of the object, it will precess if the object is spinning, regardless of whatever else might or might not be in the universe.
Surely you can pick any random point in the universe and call it the center.
But in the Earth-Sun system, you don’t have that convenience. True, the Sun revolves around the Earth, AND the Earth Revolves around the Sun. Actually, they both revolve around the center of gravity created by both. Since that center of gravity is far closer to the Sun – in fact, inside of it – then it’s fair to say that the Sun is the center. An even better model is to take into account all of the planets, moons, asteroids, comets, dust, and whatever else is in our solar system. The center of gravity is still going to be in the Sun.
But it could be done, right? Ficticious forces, Mars revolving on some weird massless stick, and complex explanations for parallax aside, is there anything for which there is no inordinately-complex workaround?
Yeah, it could be done. In fact, it is done for doing certain physics problems (though probably not ones involving Mars or stellar parallax). If you’re trying to solve a physics problem that involves you throwing an object at a specified velocity and angle, you’d probably want to make yourself the center of the coordinate system because that will make the problem easier to solve. You can probably ignore the fictitious forces in this example (unless you’re throwing something a really long distance).
But if you wanted to argue that the earth really isn’t moving (as opposed to assuming it isn’t moving to solve a particular problem), you would have to come up with a physical explanation for those forces that was more convincing than the theory that the Earth is moving.
If you’re the center of the universe, that means that the rest of the observable universe is moving away from you at close to the speed of light.
You might want to ask yourself why that is. What is it about you that drives others away? Why are whole galaxies in such a hurry to get as far away from you as possible?
Weather systems, for example. I was an earth science minor in college, and remember having to calculate the Rossby number of certain weather systems to see whether certain forces could be ignored.
The sun does revolve around the Earth (and vice versa). But as a matter of convenience, we give preference to the object within which the center of revolution lies.
But actually given relativity, how does one explain the bit about stars revolving around the Earth at greater than light speed?
It’s an apparent violation of the laws of physics that shows up because you’re assuming a non-inertial reference frame is inertial. Just like how a Foucault pendulum appears to violate the laws of physics by changing direction when no force is applied to it.
You can get around this by making up a force that makes the Foucault pendulum do what it does. That’s exactly what we are doing when we talk about centrifugal force or the Coriolis force.
But arguing that these forces are real (rather than being an artifact of a non-inertial frame of reference) and the earth really isn’t moving is something else entirely. That gets into philosophy of science, more than physics. The problem is, there are a lot of observed effects, such as stellar parallax, that have a simple explanation if the earth is rotating around the sun, but that don’t have a simple explanation if it isn’t (Occam’s Razor means that simple explanations are favored over complex ones, all else being equal). And there are no observed effects that can be explained by a non-moving Earth at the center of the universe, but can’t be explained by a more standard model of the universe. There have been effects that looked that way (gravity is a simple example), but were later explained by other theories.
It’s obvious- he’s a monkey with a gun! I’d run away from a monkey with a gun at as close to the speed of light as I could manage…
If you’re not a monkey with a gun, or something similarly dangerous, and find yourself in this situation, you might want to try changing brands of deodorant and see if that helps.
In the context of my living room, whenever I sit down I eventually end up with two cats and a dog in my lap, or as close to it as they can get. In the context of my living room, my lap is the center of the universe.
As to the galaxies retreating. What can I say. I’m shy and asked politely for a little more space. I appreciate the consideration that most of them are showing. :dubious:
I was an earth science minor in college, and remember having to calculate the