# Is the earth travelling in a straight line?

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Einstein's general relativity says that all the planets

and our earth actually travel in a "straight line"

within a curved space-time.

Put another way....GR can show that the earth is not orbiting the sun, rather the earth is travelling a straight path and space/time is wrapped/curved around the sun.

So gravity = space-time curvature.

What are some good non-mathematical ways to conceptualize "space/time" curvature around an large "mass/energy" like the sun? (other than the bowling ball and trampoline analogy that I keep running into when googling the subject)

Thanks,

Eon.

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From the point of view of the Earth, it *is* travelling in a straight line, it just so happens that from *our* perspective that straight line is curved around the sun because of gravity.

It must be confusing the the Earth though, to be constantly moving forward and to always have that big sun in the same place... shouldn't we have gone past it a few millenia ago?

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It must be confusing the the Earth though' date=' to be constantly moving forward and to always have that big sun in the same place... shouldn't we have gone past it a few millenia ago?[/quote'] lol...yea that would be confusing for the Earth but because space curves we don't have to worry about going past the sun.

I just can't visualize traveling along a straight line but through a curvature.

I can if one talks about flying a plane in a straight line as it actually curves around the earth, but does that translate into an analogy of the earth traveling (in a straight line within curved space/time) around the sun? I'm not sure.

(E.G. one visualizes the earth's orbit as a straight flight around the perimeter of a big planet with a radius spanning from its center (the sun) to its surface (the earth.)

I'm not sure if that's the same thing however, and I'm not sure if my analogy is clear?

So...I guess I'm stuck on the space/time curvature visualization part.

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I can if one talks about flying a plane in a straight line as it actually curves around the earth, but does that translate into an analogy of the earth traveling (in a straight line within curved space/time) around the sun? I'm not sure.

Yeah, I'd say so - because the plane is travelling in a straight line over the surface of the Earth. It it didn't travel in a curve it would break orbit and fly off into space.

Which I think to us, would appear to fly off in an upward curve iteslf?

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Visualizing 4 dimensions is a tad tricky. The bowling ball on trampoline is the only way I know how to visualize such a thing.

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I don't quite understand this bowling ball and trampoline anology

you talk about. But it was proven a long time ago that the sun

and earth are defined as the heliocentric model (earth moves

around the sun).

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I don't quite understand this bowling ball and trampoline anology you talk about. But it was proven a long time ago that the sun and earth are defined as the heliocentric model (earth moves

around the sun).

Ridiculous.

Machian Relativity

Both heliocentric and Earth-centric views are 'incorrect' if one accepts Machian relativity. From the Earth's point of view it is better to view the sun as travelling around the Earth. Only if one were standing on the Sun would it be reasonable to view the Earth as travelling around the sun.

Solar System-Centric View

It is only when all the other eight (+) planets are considered that the Heliocentric view becomes preferred' date=' since from this view the orbits of the [i']other [/i]planets are simplified and easily drawn. This is a pragmatic choice.

Absolute Space

From the view of Newton's postulate of Absolute Space, the Earth appears not to be accelerating significantly from that inertial frame, or else it is moving at a constant speed relative to Absolute Space. This is deduced by the relative effectiveness of Newton's Laws for inertial frames. This discussion ignores angular momentum however: from the Newtonian view it appears that the Earth is in fact rotating absolutely, since the equator bulges. This gives no true indication of translational (linear) motion however, or orbital frames. The only thing that can be said about the Earth absolutely is that it is spinning (independant of motion of itself re: sun).

Newton's 3rd Law

Now from the point of view of Action - Reaction, one could with reasonable assumptions presume the Sun as the heavier mass (based upon Solar system behaviour), and from this deduce that the Earth must move *more* than the sun for the preservation of momentum and exchange of energy between the two bodies. That is, the earth must be moving more because of the sun's greater inertia. Yet both bodies must definitely move according to this law.

Galileo was Wrong, not the Church

If by 'proven long ago' you mean in Galileo's time, this is just nonsense. Newton had not formulated the Laws of Motion or deduced the force behind Kepler's observations, and so Galileo could not have 'proven' that the Earth revolved around the Sun. In any case, the idea that the Sun did not move was wrong before and after Galileo's time. The fight between Galileo and the Church over Heliocentric versus Earth-centric was an exaggerated 'Black n White' argument similar to the ridiculous dispute between Catholics and Protestants over 'free-will' versus 'predestination'. Both sides were idiots.

Elegant but Impractical

All Galileo had to make his case more attractive was the simplification of the orbits of the other planets. This would be an argument similar to the superiority of Special Relativity over Newtonian mechanics. For ordinary masses and non-light speeds, Newton remains simpler and more useful. Special Relativity is really an Electromagnetic theory. Likewise, for the ordinary man on the ground, it was better to continue to view the orbits of the planets as giant 'curly-cues' across the sky, and let astronomers work out the horrible details of converting 'orbits' between views.

General Relativity?

Finally, Einstein stepped in with his gravity theory, only to surprise everyone by showing that there was indeed 'absolute motion' relative to the gravitational field or 'curvature of space' which was itself influenced by the distribution and motion of mass in spacetime. What this meant for Galileo's argument versus the Church is still really rather complex. Again, as with Newton's laws of action-reaction, General Relativity predicts that *both* the Earth and Sun move. A bit disappointing for extreme Heliocentrics.

The best we can hope for when all the dust settles is that the sun moves *less* than the Earth.

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123 oops delete this. My message was entered twice.

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Sure the sun travels around the Earth. The only problem is mixing up absolutes and relatives. That always leads to trouble if you're not perfectly clear on what you're using...

It's like mixing up metric and imperial units when designing a robot to go to Mars...

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