# Thread: Expansion of Universe and Lunar Distance

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Originally Posted by cjameshuff
The friction has nothing to do with the "equilibrium gravitational point". If you mean the point where gravitation from both the Earth and the Moon are equal, that's way out near the Earth-Moon L1 point, closer to the moon than the Earth and certainly not inside Earth.
No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.

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Originally Posted by Relative
No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.
The term is the barycenter of the system. And no, the mere fact that the earth orbits the barycenter doesn't induce any stresses, just like the mere fact that the earth orbits the sun doesn't induce them. The stresses are there because of tidal effects, irrespective of where the barycenter is.

3. Originally Posted by Relative
Well a clockhand, whether it is one cm long or one kilometer has the same orbital speed. To make a statement about the radius in the way I guess what you mean is: we need the correct masses. And here is, where it begins: Neither earth's nor moon's mass are determined within the accuracy needed. Even more, these are estimated due to their angular momentum behavivour, and not vice versa.
...what?
If the distance is increasing, so is the orbital period. Measuring changes in one is equivalent to measuring changes in the other. You don't even care about the masses...those don't change by any meaningful amount, they're a constant factor.

Originally Posted by Relative
I never did. If my last answer didn't show this, I'm afraid I will be unable.
Um, it's right there in post #18...

You know, rather than arguing you didn't say what you did, you could just explain the orbit of Phobos. And while you're at it, other oddball terms you've thrown around like "equilibrium orbit".

Originally Posted by Relative
At least my math mixing nanosconds was "less wrong" than yours, mixing seconds with years. And I didn't know, we were able to measure within 10^-14 to 10-15 meters within an accuracy of more than one number before the decimal point.
My math wasn't wrong, and I didn't mix seconds with years.

As for the measurement precision...well, I stated the precision and instrument in my first post on the subject. I did mistakenly quote the wrong number, though...LIGO can detect a strain of one part in 10^21, which given the 4 km arm length is actually more sensitive than the quantity I gave.

Originally Posted by Relative
No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.
That's the barycentre...it's got nothing to do with any equilibrium point and nothing to do with tidal forces.

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The barycenter, yes. Thank you both.
(sometimes I hate missing vocabulary in English)
Or mistaking like "orbital speed". I misunderstood "angular speed", sorry!! for it, cjameshuff.
And the last one:
"There are always phenomena like this" was mistaken as exceptions. (So I used "exceptions", when replying) No, there are a lot of them ("always" rather to be pronounced as in "always and everywhere")

PS. The word "Equilibrum" can mean a barycenter (I guess, it is derivated from it?). I didn't state that this has an influence on the tidal forces between earth-moon. I just wondered whether this is unconsidered in terms of slowing down earth's rotation and the effect is only seen as tidal influence

PPS. I read the Wiki article about LIGO (in my native language :-)) ). Interesting project, but it works (or should work) very differently from what I've understood after you mentioned it, starting with 75 times passing the 4 kilometers, two observatories 3000 km apart and so on. I need more time for it...
Last edited by Relative; 2012-Apr-28 at 09:11 PM.

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So, I have voted myself to this interesting project.
As far as I can figure out they make laser runtime comparisions between the two 4 km long legs. This is the reason for their „incredible“ accuracy in the order of 10^-22 meters.
It is like comparing the ratio of 1/x to x, (which becomes 1/x^2 then), therefore, their „accuracy gets squared“ in comparison to the accuracy of what can be measured by atomic clocks when it comes to absolute values.
The problem is: IF (I want to state this as BIG if), c changes in terms of OP, these people won‘t notice, because it would effect both legs, so the relative diifference would be zero.
So what about each leg itself, will they notice that differnce ?
I guess they put their pants on the same way as you, so using the newest atomic clocks which have a relative accurcy of 10^-16 seconds. What does this mean: The longer a laser experiment is or the greater the distance we will get a more precise absolute value.
For a laser experiment of duration one second, our current atomic clock time measurement will be precise to the order of 3x10^-8 meters. If we use an experiment whichs is 8000 meters (back and forth the leg lenght of LIGO), we get a precision of 7.5x10^-12 meters (note: square of this is 5.6x10^-23m, so the above mentioned LIGO accuracy) per second of duration. The changing value of OP per second and 8000 meters is 1.84x10^-14. So only after about 7 minutes a change in the last digit!! (15 behind the decimal point that this atomic clock shows) should be noticed.
Im just afraid, that those more than 30 parameters of LIGO (as stated on their homepage) have already been „adjusted“ meanwhile...
I hope, I didn‘t make too much „miscalculation“ this thime. On this platform you must watch like a hawk.

But, as always, you are welcomed to show me we're I failed
Last edited by Relative; 2012-Apr-29 at 06:26 AM.

6. They might not measure the second-to-second difference if that measurement precision is purely of the difference in strain between arms, but that's not the only example of things that would be influenced by changes in c. A great many pieces of high precision instrumentation depend on it being constant, it is part of what determines the spectral lines emitted and absorbed by atoms, which we can observe across intergalactic distances and time spans of a good part of the age of the universe, and so on.

And you keep avoiding answering this...what about Phobos? What about the tidal locking of every large moon in the solar system, including Triton, which appears to be a recently captured Kuiper belt object? That's not coincidence. Each of those moons is an example of transfer of angular momentum between an object's rotation and its orbit through tidal drag effects, and those effects work on the planet's end too. This is why the moon, which orbits much slower than Earth rotates, is being pulled into a higher orbit, and why Phobos (which orbits faster than Mars rotates) and Triton (which orbits in the opposite direction of the rotation of Neptune) are being dragged down into lower orbits.

7. Originally Posted by Relative
As far as I can figure out they make laser runtime comparisions between the two 4 km long legs. This is the reason for their „incredible“ accuracy in the order of 10^-22 meters.
If I understand it correctly, LIGO doesn't exactly use "runtime comparisons," that is, it does not use atomic clocks to measure the times and compare them. It uses light wave interferometry. When the laser beams are brought back together, any slight shift in the phase of one wavelength compared to the other can be detected, indicating a slight change in distance for one of the legs. After all, LIGO is short for Laser Interferometer Gravitational-Wave Observatory.

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Originally Posted by cjameshuff
They might not measure the second-to-second difference if that measurement precision is purely of the difference in strain between arms, but that's not the only example of things that would be influenced by changes in c. A great many pieces of high precision instrumentation depend on it being constant, it is part of what determines the spectral lines emitted and absorbed by atoms, which we can observe across intergalactic distances and time spans of a good part of the age of the universe, and so on.

And you keep avoiding answering this...what about Phobos? What about the tidal locking of every large moon in the solar system, including Triton, which appears to be a recently captured Kuiper belt object? That's not coincidence. Each of those moons is an example of transfer of angular momentum between an object's rotation and its orbit through tidal drag effects, and those effects work on the planet's end too. This is why the moon, which orbits much slower than Earth rotates, is being pulled into a higher orbit, and why Phobos (which orbits faster than Mars rotates) and Triton (which orbits in the opposite direction of the rotation of Neptune) are being dragged down into lower orbits.
Well yes, I guess the determination of the spectral lines would be effected. A peak, for example at 1000nm, would shift in the order of 7.27x10^-17m per year. Even at cosmic scale (let‘s say 13 billion years) this would mean a difference of only 55 nm, whereas about 7960nm are observed (redshift). So the first could still be „a part“ of the latter.

Same with Phobos and all the moons which are dragged to lower orbits. One question of OP was, if that value could be „a PART of it“. Even if the net amount is negative, it still could contain a positive other value: 3 + 1= 4 vs. -3 + 1 = -2. Looking at this simple example, the spiraling away thing just should be relatively faster than the lowering orbit stuff. Unfortunately, I don't know whether or not this is observed...

9. Originally Posted by Relative
Well yes, I guess the determination of the spectral lines would be effected. A peak, for example at 1000nm, would shift in the order of 7.27x10^-17m per year. Even at cosmic scale (let‘s say 13 billion years) this would mean a difference of only 55 nm, whereas about 7960nm are observed (redshift). So the first could still be „a part“ of the latter.
That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.

Originally Posted by Relative
Same with Phobos and all the moons which are dragged to lower orbits. One question of OP was, if that value could be „a PART of it“. Even if the net amount is negative, it still could contain a positive other value: 3 + 1= 4 vs. -3 + 1 = -2. Looking at this simple example, the spiraling away thing just should be relatively faster than the lowering orbit stuff. Unfortunately, I don't know whether or not this is observed...
Well, with the numbers you were throwing around, you were considering it to be most if not all of the moon's recession.

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Originally Posted by cjameshuff
That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.
Like how much so?

Originally Posted by cjameshuff
Well, with the numbers you were throwing around, you were considering it to be most if not all of the moon's recession.
I would be "satisfied with less than the half" :-)
In this context, and as promised in post #17, the LATEST scientific article (published 20th April 2012) concerning the moon's recession anomaly:
http://www.planetary-science.com/con...1-2521-1-1.pdf
Note that the author also considers "several possible explanations", and focusses on speed of light decreases.
At least, I'm not alone :-)

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Actually Louise Riofrio's GM = tc^3 speculation has been around for at least 6 years so it is not that new. The physics that she uses in this speculation is simplistic and wrong based on her Recent GM=tc^3 Paper (2006!). She states that the "relative" (to what?) radius of the universe (R) is R = ct where c is the speed of light and t is the age of the universe. This ignores General Relativity and so is wrong.

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Originally Posted by Reality Check
Actually Louise Riofrio's GM = tc^3 speculation has been around for at least 6 years so it is not that new. The physics that she uses in this speculation is simplistic and wrong based on her Recent GM=tc^3 Paper (2006!). She states that the "relative" (to what?) radius of the universe (R) is R = ct where c is the speed of light and t is the age of the universe. This ignores General Relativity and so is wrong.
In the above mentioned post you statet that „we do not expect any effect of the expansion of the universe on the Earth-Moon system because they are gravitaionally bound“.
Gravitaion is the weakest of all fundamental forces to be in the order of 10^-34 compared to stronge force. BUT: It STILL claims its rights, as you can see when your pencil is dropping.
So, you may call the value of OP negligalbe, but it still would have its influence, even if „gravitational bounding“ of two bodies seem to overpower it. Otherwise, if this influence would totally be gone (so, zero as you conclude) our seek of a „theory of everything“ must be questioned. Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.

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Originally Posted by cjameshuff
That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.
I suppose we could let c vary if we let the other constants vary accordingly such that the physical results would be the same. But then it is of course hardly meaningful to say that c varies.

14. Originally Posted by Relative
In the above mentioned post you statet that „we do not expect any effect of the expansion of the universe on the Earth-Moon system because they are gravitaionally bound“.
Gravitaion is the weakest of all fundamental forces to be in the order of 10^-34 compared to stronge force. BUT: It STILL claims its rights, as you can see when your pencil is dropping.
So, you may call the value of OP negligalbe, but it still would have its influence, even if „gravitational bounding“ of two bodies seem to overpower it. Otherwise, if this influence would totally be gone (so, zero as you conclude) our seek of a „theory of everything“ must be questioned. Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.
For a reasonably circular orbit, the only result would be a slight mis-estimation of the primary body's mass. The presence of expansion means the moon orbits very slightly closer to Earth, where gravity balances the sum of centrifugal force and expansion (which appears as an outward force directly proportional to distance, and is thus constant for circular orbits). It might make a major difference in large, highly eccentric orbits that are barely bound, but the moon is not in such an orbit...and I think the major effect would be precession or a gradual increase in eccentricity, not spiraling outward.

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Originally Posted by cjameshuff
For a reasonably circular orbit, the only result would be a slight mis-estimation of the primary body's mass. The presence of expansion means the moon orbits very slightly closer to Earth, where gravity balances the sum of centrifugal force and expansion (which appears as an outward force directly proportional to distance, and is thus constant for circular orbits). It might make a major difference in large, highly eccentric orbits that are barely bound, but the moon is not in such an orbit...and I think the major effect would be precession or a gradual increase in eccentricity, not spiraling outward.
That's not quite correct. Expansion per se will not have an influence even if we factor it in. The change in equilibrium is from the acceleration of expansion, which would not depend on distance[*], but more importantly can be negative. If the expansion is decelerating (which it has been doing for a good part of the history of the universe) the result will be an extra inward force. Which is incidentally one of the reasons it really doesn't even make much sense to factor in expansion in non-homogeneous backgrounds (even if we could).

*ETA: erratum: it does depend linearly on the distance
Last edited by caveman1917; 2012-May-01 at 02:16 AM.

16. Originally Posted by caveman1917
That's not quite correct. Expansion per se will not have an influence even if we factor it in. The change in equilibrium is from the acceleration of expansion, which would not depend on distance, but more importantly can be negative. If the expansion is decelerating (which it has been doing for a good part of the history of the universe) the result will be an extra inward force. Which is incidentally one of the reasons it really doesn't even make much sense to factor in expansion in non-homogeneous backgrounds (even if we could).
In general, sure. But we're talking about human observations of the moon's orbit. Expansion is currently accelerating, but not at a particularly high rate, and for this purpose and timespan it seems reasonable to consider it to be constant.

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Originally Posted by cjameshuff
In general, sure. But we're talking about human observations of the moon's orbit. Expansion is currently accelerating, but not at a particularly high rate, and for this purpose and timespan it seems reasonable to consider it to be constant.
True, it just seemed to me that Relative is thinking of the effect of the "base" expansion (at least that's how he calculates it) and i'm not sure the distinction has been made clear in the discussion.

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Relative, consider the following:

I throw a ball away from me (in empty space). When it has reached a certain distance, i grab it with my hand. From that moment i and the ball form a bound system. Would you consider the ball to keep "pushing away" in my hand? I (hopefully) presume not. Then why would you consider the moon to keep "pushing away" from the earth even when they are a gravitationally bound system?

Think of it this way: why was the ball moving away from me before i grabbed onto it? Because it was doing so a moment before. Once i grabbed onto it, it lost that tendency to move away from me. The reason we see galaxies move away from us is likewise because they were doing so in the past and nothing ever "grabbed onto them", however because the moon is gravitationally bound to the earth it simply does not have that tendency anymore (assuming it ever had that in the first place).

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Originally Posted by caveman1917
Relative, consider the following:

I throw a ball away from me (in empty space). When it has reached a certain distance, i grab it with my hand. From that moment i and the ball form a bound system. Would you consider the ball to keep "pushing away" in my hand? I (hopefully) presume not. Then why would you consider the moon to keep "pushing away" from the earth even when they are a gravitationally bound system?

Think of it this way: why was the ball moving away from me before i grabbed onto it? Because it was doing so a moment before. Once i grabbed onto it, it lost that tendency to move away from me. The reason we see galaxies move away from us is likewise because they were doing so in the past and nothing ever "grabbed onto them", however because the moon is gravitationally bound to the earth it simply does not have that tendency anymore (assuming it ever had that in the first place).
Hm, well if you consider that in terms of c "grabing" the ball would make no difference to the fact that you wouldn't have grabed it, what next?

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Originally Posted by Relative
Hm, well if you consider that in terms of c "grabing" the ball would make no difference to the fact that you wouldn't have grabed it, what next?
I'm not sure what you mean by "in terms of c", but what i'm trying to say is to look at it the other way. Rather than say that galaxies recede because space expands, space expands because galaxies recede. I can frame my example of throwing the ball away in terms of an expanding space between me and the ball. But that picture only works in so far as nothing intervenes in the ball moving away from me. There is no universal law saying that the ball must constantly try to move away from me, it just happens to do so because it was doing so in the past. Neither is there some law saying that the moon must try to move away from the earth.

Once something intervenes, me grabbing onto the ball, or likewise the moon being gravitationally bound to the earth, the picture of expanding space simply fails. Grabbing onto it or not makes all the difference. In a sense, expanding space is nothing more than the statement that nothing has intervened in something moving away because it was doing so in the past. Those galaxies we see receding aren't constantly being coerced into receding, no more than the ball needs constant coercion to keep moving away from me, as long as nothing intervenes they just keep doing what they're doing and we find it convenient to frame that behaviour in terms of an expanding space. Expanding space is not a cause, it's a way of picturing a situation. The ultimate cause lies in what made those galaxies start moving away in the first place, not in what happens afterwards.

After that you get into the effects of acceleration of expansion, but that's quite another story. But i think that is not where the main misunderstanding lies.

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Originally Posted by caveman1917
I'm not sure what you mean by "in terms of c", but what i'm trying to say is to look at it the other way. Rather than say that galaxies recede because space expands, space expands because galaxies recede. I can frame my example of throwing the ball away in terms of an expanding space between me and the ball. But that picture only works in so far as nothing intervenes in the ball moving away from me. There is no universal law saying that the ball must constantly try to move away from me, it just happens to do so because it was doing so in the past. Neither is there some law saying that the moon must try to move away from the earth.

Once something intervenes, me grabbing onto the ball, or likewise the moon being gravitationally bound to the earth, the picture of expanding space simply fails. Grabbing onto it or not makes all the difference. In a sense, expanding space is nothing more than the statement that nothing has intervened in something moving away because it was doing so in the past. Those galaxies we see receding aren't constantly being coerced into receding, no more than the ball needs constant coercion to keep moving away from me, as long as nothing intervenes they just keep doing what they're doing and we find it convenient to frame that behaviour in terms of an expanding space. Expanding space is not a cause, it's a way of picturing a situation. The ultimate cause lies in what made those galaxies start moving away in the first place, not in what happens afterwards.

After that you get into the effects of acceleration of expansion, but that's quite another story. But i think that is not where the main misunderstanding lies.
OK, I know comparisions flaw. But, since you have used the "grabbing ball metaphor":
What about grabing the ball on your 6th birthday. And, then growing up to an adult, still holding the ball in your hand?

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Originally Posted by Relative
OK, I know comparisions flaw. But, since you have used the "grabbing ball metaphor":
What about grabing the ball on your 6th birthday. And, then growing up to an adult, still holding the ball in your hand?
During none of that time would the ball have had any tendency to move away from me, it just rested in my hand the entire time, which is kind of my point. Any such tendency it may have had before would have been lost the moment i first grabbed onto it. Or to frame it in different terms, even if everything else had been moving away from me during that time (the space around me "expanded"), the ball has during that time not participated in the expansion of space, and has never "tried" to do so. So why would you consider an equally bound system (earth-moon) to behave differently?

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Ed Wright is a good resource for cosmology questions:
Why doesn't the Solar System expand if the whole Universe is expanding?
This question is best answered in the coordinate system where the galaxies change their positions. The galaxies are receding from us because they started out receding from us, and the force of gravity just causes an acceleration that causes them to slow down, or speed up in the case of an accelerating expansion. Planets are going around the Sun in fixed size orbits because they are bound to the Sun. Everything is just moving under the influence of Newton's laws (with very slight modifications due to relativity). [Illustration] For the technically minded, Cooperstock et al. computes that the influence of the cosmological expansion on the Earth's orbit around the Sun amounts to a growth by only one part in a septillion over the age of the Solar System. This effect is caused by the cosmological background density within the Solar System going down as the Universe expands, which may or may not happen depending on the nature of the dark matter. The mass loss of the Sun due to its luminosity and the Solar wind leads to a much larger [but still tiny] growth of the Earth's orbit which has nothing to do with the expansion of the Universe. Even on the much larger (million light year) scale of clusters of galaxies, the effect of the expansion of the Universe is 10 million times smaller than the gravitational binding of the cluster.

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Originally Posted by caveman1917
During none of that time would the ball have had any tendency to move away from me, it just rested in my hand the entire time
It's the arm length, to stay in this picture, that would have grown from childhood to adult, too.

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Originally Posted by Relative
It's the arm length, to stay in this picture, that would have grown from childhood to adult, too.
Then you have the picture wrong because if the arm length grew accordingly with the distance to say some other guy, then that other guy would be staying at the same amount of arm-lengths and you'd see no expansion. If the ruler with which you are measuring the distance to some other galaxy grows along with the distance to that galaxy there would be no discernable expansion. Expansion isn't something a local object does, it's what happens to the distance between two different objects.

Even so, if the arm length grew than the distance between you and the ball only grew because you pushed the ball away (your growing arm exerted an outward force on the ball). That's obviously not the right picture for the earth-moon system, gravity does a lot of things but it doesn't "push"

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Originally Posted by Relative
My last post does not mention your estimation at all.
Post #15 states that your estimation is wrong.

Originally Posted by Relative
Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.
You are right: It does have a very little influence on galaxies, the earth-moon-system or even the earth-sun system.
That effect on the the earth-sun system is 1 part in a septillion (1,000,000,000,000,000,000,000,000) over 4.6 billion years. So your estimate is really, really wrong because you do not include that the earth and moon are gravitationally bound.
Why doesn't the Solar System expand if the whole Universe is expanding?
This question is best answered in the coordinate system where the galaxies change their positions. The galaxies are receding from us because they started out receding from us, and the force of gravity just causes an acceleration that causes them to slow down, or speed up in the case of an accelerating expansion. Planets are going around the Sun in fixed size orbits because they are bound to the Sun. Everything is just moving under the influence of Newton's laws (with very slight modifications due to relativity). [Illustration] For the technically minded, Cooperstock et al. computes that the influence of the cosmological expansion on the Earth's orbit around the Sun amounts to a growth by only one part in a septillion over the age of the Solar System. This effect is caused by the cosmological background density within the Solar System going down as the Universe expands, which may or may not happen depending on the nature of the dark matter. The mass loss of the Sun due to its luminosity and the Solar wind leads to a much larger [but still tiny] growth of the Earth's orbit which has nothing to do with the expansion of the Universe. Even on the much larger (million light year) scale of clusters of galaxies, the effect of the expansion of the Universe is 10 million times smaller than the gravitational binding of the cluster.

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Originally Posted by Reality Check
That effect on the the earth-sun system is 1 part in a septillion (1,000,000,000,000,000,000,000,000) over 4.6 billion years. So your estimate is really, really wrong because you do not include that the earth and moon are gravitationally bound.
Why doesn't the Solar System expand if the whole Universe is expanding?
I am afraid that these are arguments like this:
is raining now, because the swallows were flying low before.

We simply observe the redshift of distant galaxies.
Why? Probably because the cosmos is not empty. After all dissipation of energy is a completely natural phenomenon, and perhaps even inevitable according to thermodynamics - entropy increases.

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Originally Posted by Hetman
I am afraid that these are arguments like this:
...snipped trivial stuff and a bit of gibberish...
I am afraid that these are arguments actually like this: Gravity exists. We know how it works. Over scales of millions of lightyears the acceleration it causes dominates any acceleration caused by the observed expansion of the universe. The science is explained in Why doesn't the Solar System expand if the whole Universe is expanding?

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Standard non-empty universe and standard thermodynamics is not negotiable - neither here nor in the ATM.

In the given link are factual errors, unfortunately - in particular:
definition of the curvature of space is only one, not two alternatives.

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Starting with post #21, all the posters that invoke gravitational binding are correct. The expansion of the universe in gravitationally bound systems, and this includes structures as large as galaxy clusters (galaxy -> group -> cluster), is negligible. Myself or others must type this out at least once a week in some part of the forum. Expansion is not a local phenomenon.

Say it to yourself over and over. 'Not local. Not local. Not . . . .'

Regards, John M.

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