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spark802
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Okay i want to stir something up...do we Earth dwellers move around the sun in a roughly circular path (ellipse) OR are we moving in a straight line in a curved space?
Dave
Dave
Chronos said:It's merely a coordinate system thing. Gravity is the curvature of spacetime in the presence of matter so a straight line in GR is a circle/ellipse in a cartesian coordinate system.
spark802 said:Chronos, when you say "GR" are you referring to General Relativity?
We are following a geodesic in curved space time. A geodesic is an extension of the concept of a "straight line" to curved space time. And you can't leave time out of the equation.spark802 said:Okay i want to stir something up...do we Earth dwellers move around the sun in a roughly circular path (ellipse) OR are we moving in a straight line in a curved space?
e^(i Pi)+1=0 said:Scientifically, you would use whichever theory is more helpful to your calculations / prediction making at the time. Which one is really true is a question for a philosopher, not a physicist.
mfb said:While Newton is not right (and only an approximation), you cannot say that GR is "right" and "describes how the universe is". Maybe GR is just a better approximation? This is the usual opinion by the way, as it does not include quantum effects. But even if GR is exact, it does not tell you that there is a curved spacetime somewhere. The curved spacetime is a model. It gives the right predictions (at least up to now). But that is all we can get from a theory.
Pengwuino said:Nonsense. GR is the correct theory and the Newtonian approximation is just that, an approximation. No philosophy required.
Acker said:Could you please show or say how much difference the 'correct theory' shows versus the
'approximation' with regards to, say, the orbital period and velocity of the earth?
And what new information does this give us that pertains to earthly dwelling?
The realm of philosophy may be called upon to determine where we should stop our
decimal places.
D H said:We are following a geodesic in curved space time. A geodesic is an extension of the concept of a "straight line" to curved space time. And you can't leave time out of the equation.
It might help you understand by looking at a different non-Euclidean geometry, the geometry of the surface of the Earth. Ignoring the little bumps from mountains, dips from ocean trenches, is the equator a "straight line"? The equator is a circle. How could it possibly be a "straight line"?
The answer is that it is a straight line in the sense that a "straight line" between points A and B is the shortest of all possible paths between A and B. (Better said as "one of the shortest paths". The shortest path is not necessarily unique once you through out the parallel postulate). Consider the problem of going from point A to point B on the surface of the Earth. No tunneling is allowed. Each possible path from A and B must lie entirely on the surface of the Earth. In this sense, the equator is a "straight line" in the non-Euclidean geometry of a spherical surface.
The Earth's orbit around the sun is an elliptical path, meaning it is not a perfect circle. The sun's gravitational force keeps the Earth in its orbit, while the Earth's velocity and inertia prevent it from falling into the sun.
The Earth's tilt on its axis is what causes different seasons. As the Earth orbits around the sun, the tilt changes, causing different parts of the Earth to receive more or less direct sunlight. This results in the different seasons we experience.
Gravity is the force that keeps all planets in orbit around the sun. The sun's massive gravitational pull keeps the planets in their respective orbits, while the planets' own gravitational forces keep their moons in orbit around them.
The Earth takes approximately 365.24 days, or one year, to complete one orbit around the sun. This is why we have leap years every four years to account for the extra .24 days in our calendar.
The Earth's orbit is not a perfect circle, and it is constantly changing in shape and orientation. This is due to the gravitational pull of other planets and objects in our solar system. However, these changes are very small and do not significantly affect the Earth's orbit around the sun.