Just need someone to clear something up for me

[iminhell]

I'm fascinated with space and all it's wonder but don't have much time to read about it. Recently taking some time to watch a few video's I've missed, and am enjoying them. But I'm coming up with questions that don't seem to mix well, or maybe it's just the analogies used that don't fit well?

The one that troubles me the most is this distorted space fabric theory, larger mass distorts fabric more and objects of less mass rotate about the higher mass ones ... marble in a funnel idea.
With that model I've seen people talk that nearing infinity the object of less mass will at some point prior to infinity hit the object it's orbiting around. But yes when I ask Google if the Earth is moving away from the Sun it tells me yes, and at an average rate of 15cm/year. source
- but how was this measurement taken? (3 points like GPS)
I assume one point, or maybe the only for all I know, was the Sun. So I ask Google, because I recall reading it years ago, is the Sun shrinking. It gives me a very good link that does not definitively say yes or no. source

But in my mind, the dark place that it is, one, the other or both have to be true for the marble in the funnel to be true, right?
If the Earth, according to General Relativity, should be moving closer to the Sun and someone's data says it isn't but someone else says that the Sun may be shrinking (at a rate faster than we're moving away I'd bet); then we would be moving closer to the Sun, right? (2 steps back, 1 forward sort of deal)


I'm just not sure what to search on at this point. So if someone could point me in the right direction would be great. Quite sure I'm not the only one who's been confused on these points, so there has to be something explaining the quandary.


-John

 

[NobodySpecial]

The one that troubles me the most is this distorted space fabric theory, larger mass distorts fabric more and objects of less mass rotate about the higher mass ones

That's Einsteins general theory of relativity's way of describing gravity.
It mostly gives the same answer as Newton's law - that the gravity force between two object is the two masses multiplied together divided by their distances squared.
There are some areas where Einstein's theory is better but mostly they are different ways of looking at the same thing.

nearing infinity the object of less mass will at some point prior to infinity hit the object it's orbiting around

Newton's law says that as objects get closer the gravity between them gets bigger and at 0 distance the force will be infinite. This is impossible but that's ok because you can't put two real objects zero distance apart.

But yes when I ask Google if the Earth is moving away from the Sun it tells me yes, and at an average rate of 15cm/year

.
That's completely different and not unexpected - the moon is moving away from the Earth for the same reason. It's a little difficult to really believe unless you know more about orbital mechanics - but the moon slows the Earth's rotation slightly and moves further as energy is lost. The same thing is happening between the Earth and the sun (goolge for tidal friction)

If the Earth, according to General Relativity, should be moving closer to the Sun

The Earth would move to toward and crash into the sun if it wasn't moving in an orbit around it. If the Earth somehow stopped it would fall straight into the sun!

 

[Chalnoth]

That's completely different and not unexpected - the moon is moving away from the Earth for the same reason. It's a little difficult to really believe unless you know more about orbital mechanics - but the moon slows the Earth's rotation slightly and moves further as energy is lost. The same thing is happening between the Earth and the sun (goolge for tidal friction)

I always thought tidal friction was very interesting (well, at least since I learned about it).

The basic idea here is that astronomical bodies aren't perfectly rigid (whether we're talking about moons, planets, stars, whatever). So when you have to bodies in a mutual orbit, they tend to pull one another into very slightly oblong shapes. This happens much more readily for fluids, which, for instance, is what causes the tides on Earth.

But the crucial thing here is that if the two bodies aren't rotating perfectly in sync, the distortion of the planet tends to get slightly out of sync with the body that caused it. For the tides our own moon causes, for instance, because the Earth rotates faster than the moon's orbital period, the tides are always pushed a little bit ahead of the Moon by this faster rotation.

In turn, the resulting elongated shape of the Earth results in a slightly different gravitational pull on the Moon. Because the elongated part of the Earth is slightly closer to the Moon, and because it remains ahead of the Moon in its orbital path, it tends to cause the Moon to speed up in its orbit. This has the effect of causing the Moon to go into a higher orbit, as well as slow the Earth's rotation. Eventually, the same side of the Earth will always face the Moon, just as the same side of the Moon currently always faces the Earth. This is known as "tidal locking".

Of course, the effect is small, but it large enough to make a significant difference over millions to billions of years (how long depends upon how close the bodies are and how massive they are), and very accurate measurements today are also able to measure the tiny changes in distances that it causes on shorter time scales.

The Earth would move to toward and crash into the sun if it wasn't moving in an orbit around it. If the Earth somehow stopped it would fall straight into the sun!

Well, that or it would move in a hyperbolic trajectory and escape the Sun's gravity entirely. But obviously the Earth formed from the same gas cloud that formed the Sun, so either situation is highly unlikely.