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Author Topic:   Debunking the Creationist Earth-Moon separation nonsense.
Eta_Carinae
Member (Idle past 4375 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 1 of 30 (101241)
04-20-2004 3:10 PM


I posted this calculation on another forum to counter a poster called 'evolutionbuster' who was trotting out the supposed problems of the Earth-Moon separation in the past leading to high tides etc etc.
I apologise in advance for the lack of typesetting for equations and the fact I do leave a couple of pages of the algebra out.
I went to way too much trouble for this! (Earth-Moon separation vs. time)
Earlier today on another thread our newest post and run Creationist 'evolutionbuster' trotted out the time honoured Hovindism about the Moon having been too close to the Earth in the past thus producing huge tides making life on the Earth presumably impossible. I challenged him to produce calculations supporting this nonsense. Of course (and at least he admitted this) he could not do so. But of course he was confident that his sources had this capability and thus the statement was legit.
So I, being bored this evening, decided to calculate this myself from first principles. Especially since he asked if I could provide calculations. Well here goes. (this does get a little involved and so I'm sure it will turn people off this thread but what the heck!)
The problem of calculating the Earth Moon separation as a function of time is not a trivial problem - as I discovered trying to calculate the bugger. Also let me state that this calculation I shall present is really only an approximation - a somewhat sophisticated one but an approximation nonetheless.
In fact the true Earth Moon separation history will forever remain unknown in an accurate manner. Any calculation of this has some fundamental limitations which I shall mention below. But a plausible calculation is possible.
Calculation
The aim is to derive a function describing the rate of change of the semi-major axis of the Moon's orbit as a function of time. The tides raised on the Earth by the Moon dissipate energy (from friction) due to tidal oscillations caused by the fact the Moon orbits in a different period than the Earth rotates. A corresponding phase shift of the Earth's tidal response thus ensues.
The simplest (on a Saturday evening) method of tackling this problem is to model the Earth's response as forced harmonic oscillator.
After about a page of algebra (omitted here because of the lack of typesetting for equations) the key result I get is that
sin(phase shift) = -1/Q.
Q is the dissipation function of the oscillator which should be recognised by physics undergrads.
Now the mean motion of the moon (denoted by n) is less than the Earth's angular velocity (W) therefore the tidal bulge is ahead of the Moon by an angle I = 2 x (phase shift).
Therefore (as I think most people know) the tidal bulge is not aligned with the Earth-Moon direction. This means a tidal torque exists and thus a transfer of energy and angular momentum exists between the Earth and the Moon.
We determine the torque T on the Moon by the usual
T=r X F where the X is the vector cross product.
And the Force F is determined by the gradient of the Earth's external potential V at the Moon's position.
Now only the component of the force orthogonal to the Earth-Moon direction contributes to the torque and only the second order dipole term of the Earth's potential contributes to the force component.
Now the work done by the torque increases the orbital energy of the system at the rate = T x n. By Newton's 3rd Law an equal and opposite torque acts at a rate T x W to decrease the rotational energy of the Earth. Since W > n then these rates are NOT equal and therefore the total mechanical energy of the Earth Moon system decreases at the rate = -T(W-n).
This energy goes into heating the Earth and of course determines the evolution of the Moon's orbit over time. This is what we want.
Thus by now applying an energy argument I can calculate the separation as a function of time.
Total Earth-Moon mechanical energy is :
E = (1/2 * I * W^2) + (-G M m/2 a) I= Earth moment of inertia M = Earth mass
m= Moon mass and a = semi major axis of Moon's orbit.
Therefore differentiating with respect to time:
E(dot) = I W W(dot) + 1/2 * (M * m /(M + m)) * n^2 * a * a(dot)
where (dot) means the time derivative. I used Kepler's 3rd law above.
Looking at the total system angular momentum we get:
L = I W + (M m /(M +m))* a^2 *n (and is conserved of course)
L(dot)=0 which implies I W(dot) = -1/2 * (M *m/(M+m)) *n a a(dot)
Putting this in the E(dot) expression gives us:
E(dot) = -1/2 * (M*m/(M+m)) * n a a(dot) (W-n).
Thus a increases while W decreases. As we observe currently for the Earth Moon system.
Now putting all this together and using the standard Newtonian tidal potential V = -3/5 R^4 (constant) g (1/r)^3 * P2(cos H).
R=Earth radius P2=second order Legendre polynomial r=Earth-Moon distance
we finally get that the a(dot) - which is our goal is:
(I have omitted quite a bit of algebra here and above in the V expression)
a(dot) = 3 (Love #) * (m/M) * R^5 *(a^-4) * n/Q and n=(G*M/a^3)^0.5
Now the Love # is a number based upon the elasticity of the Earth and I cheated (because I don't know how to calculate it) and found it's value is 0.3.
But the real problem for any calculation to proceed is the tidal dissipation function Q.
The current value is approx. 12. But this value depends on the position of the continents and the fact that the Earth's oceans are in near resonance with the Moon. That is the phase shift I mentioned at the start is a small angle. In the past when the Earth was rotating faster the value would have been higher.
This is where uncertainty crops up and I found a reference Webb (1982) paper in Geophysical Review of Royal Astron. Society that a mean value for the entire Earth's history is approx. 34.
Thus we can integrate the above a(dot) expression and find the a as a function of time.
This gives us (finally !!!!!!!!)
a(final)^6.5 - a(initial)^6.5 = 39*(0.3)*(G/M)^0.5 * R^5 * m * (Time)
where G=Newton Grav. constant.
Results
I wrote a quick C program to calculate this and some numbers kicked out are:
Current Moon a = 3.844 X 10^10 cm
Going back 1 billion years I get a = 3.698 X 10^10 cm
Going back 4 billion years I get a = 2.731 X 10^10 cm.
As we can see the Moon is nowhere near the Earth. Closer yes - but not that close. I have seen Creationists say that the Moon a billion years ago would be so close as to break up at the Roche limit which is only some 2 X 10^9 cm - what a joke!!!!
As for the height of the tides - I used the standard equlibrium calculation in any udergrad mechanics text.
Currently the Moon on average raises a tide of approx. 35 cm on the Earth. The Sun raises about 15 cm for comparison. So the current total is about 50 cm.
According to my calculations, 4 billion years ago the tide from the Moon would have been about (3.844/2.731)^3 = 2.78 times greater.
Thus the Moon would have produced a tide of about 100 cm (2.78*35) and the Sun's would have been the same as above for a total of 115 cm.
So this supposed doom of HUGE tides is typical Creationist bs. The total is just over twice the current level. Annoying for coastal areas but not Earth threatening.
All in all - another example of Creationst nonsense.
I realise this is way too much effort for a message board but heck it was kind of fun.

  
Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 2 of 30 (101243)
04-20-2004 3:15 PM


Thread moved here from the Proposed New Topics forum.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 3 of 30 (101322)
04-20-2004 6:04 PM
Reply to: Message 2 by Adminnemooseus
04-20-2004 3:15 PM


Thank you, Eta
Thanks for that Eta. It is, among other things, an example for some who need a good example of the kind of thing you have to do to actually have an argument.
Can you tell me where the weakest (most iffy, most sensitive) parts of the calculation are? What would be your error bars on the calculated values?
Have you ever received any kind of literalist response? Let me guess: No! Or if you have it would amount to (in a lot of words ) "Huh?"

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Replies to this message:
 Message 4 by Eta_Carinae, posted 04-20-2004 8:38 PM NosyNed has replied
 Message 6 by RingoKid, posted 04-21-2004 1:44 AM NosyNed has replied

  
Eta_Carinae
Member (Idle past 4375 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 4 of 30 (101345)
04-20-2004 8:38 PM
Reply to: Message 3 by NosyNed
04-20-2004 6:04 PM


Reply
The biggest unknown as I alluded to in the OP is the value for the tidal dissipation function Q.
This value is known currently to be about 12. But the exact value in the past is difficult to calculate. It depends on the position of the continents and ocean depths. Obviously plate tectonics only allows us to go back a few hundred million years at the most. Before that we have no knowledge of their positions.
However, this is alleviated somewhat by the fact the value is somewhat dominated by the Earth's rotation rate. The Q value would have been greater in the past due to the fact the tidal bulges would have led the Earth-Moon axis by more and more due to the faster rotation of the Earth - and thus been further from resonance than now. So to some extent you can give reasonable values for the Q based on this fact and the continents positions is of lesser importance in the determination of Q.
All in all I would say the average value of 34 I took above is probably accurate to 50% or so.
But since I am taking the 2/13 th power of this leads to about a 8% error in the answer.
You can also account for any errors due to variations in G this way. If G varied it wouldn't have too much effect - and of course there is ample reason to believe it hasn't varied from other astrophysical phenomena.
Of course many 2nd order effects have been neglected. I took no account of the eccentricity of the Moon's orbit, shapes of the Moon and Earth, apsidal motions, nodal precessions etc etc.
All in all I would guess this simple model would be accurate to about plus or minus 15%. Which is not bad at all. And certainly enough to debunk the Creationist nonsense which would need me to be off by over an order of magnitude or more.
I might post some of the responses I got. They are kind of sad really.
One of them was basically
Well if that is how physics is - I want no part of it - I'm glad I never studied it!

This message is a reply to:
 Message 3 by NosyNed, posted 04-20-2004 6:04 PM NosyNed has replied

Replies to this message:
 Message 5 by NosyNed, posted 04-20-2004 10:07 PM Eta_Carinae has not replied

  
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 5 of 30 (101374)
04-20-2004 10:07 PM
Reply to: Message 4 by Eta_Carinae
04-20-2004 8:38 PM


The Sad Reply
quote:
One of them was basically:
Well if that is how physics is - I want no part of it - I'm glad I never studied it!
Somehow that is about what I would expect. And these are the people who think they have a place in the science classroom.
For the literalists who might have gotten past the OP. You should note that an attitude like the example given is some of the source of irritation with those who think they have any right to make statements on scientific subjects.
For those who are somewhat less dogmatic, you might note that this is a very, very, very, very simple example of real physics. Untill the creation "scientists" of ICR (and others) are prepared to deal with it all at this level they have no right at all to be expected to be taken seriously.

This message is a reply to:
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RingoKid
Inactive Member


Message 6 of 30 (101423)
04-21-2004 1:44 AM
Reply to: Message 3 by NosyNed
04-20-2004 6:04 PM


Re: Thank you, Eta
quote:
Thanks for that Eta. It is, among other things, an example for some who need a good example of the kind of thing you have to do to actually have an argument.
uh no, I don't actually need any of that to have an argument all I need is another opinion as for settling arguments if you can't blind them with brilliance baffle them with bullshit..."Huh?"
I am definitely in the second category...
...so it must really piss you off Eta and others when you get dumasses like me who think they have their defined realities all sorted but in your reality we don't have any case for even thinking we have the right to be thinking about stuff like that let alone expressing it in such a forthright manner ???
oh well back to the deafening silence...
...as you were

This message is a reply to:
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Replies to this message:
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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 7 of 30 (101428)
04-21-2004 2:03 AM
Reply to: Message 6 by RingoKid
04-21-2004 1:44 AM


BS and Bafflement
There are some issues which require a detailed analysis. This often involves actual quantitative work. Full details of the calculations are required. If someone is unable to handle the math involved then they have no valid opinion on the correctness of the result.
In this case, if a literalist wants to use the moon distance argument they must point out the flaws in Eta's calculations.
It is the responibility of anyone attempting to use this argument to be honest about it. Those who continue to use it when they can't answer the analysis given are not being honest.
Some here have noticed that there are posters who attempt to baffle with bullshit. It doesn't seem to be working very well.

This message is a reply to:
 Message 6 by RingoKid, posted 04-21-2004 1:44 AM RingoKid has not replied

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jar
Member (Idle past 394 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004


Message 8 of 30 (101569)
04-21-2004 1:32 PM


I'm not sure I understand what the issue is...
but then again, that is often the case.
It would seem to me that a reasonable question related to the Earth Moon relationship would be, "Would a close moon producing super high tides make life on earth impossible?"
If for example, there was a time when the norm really was super high tides (pick any size tides that you want. Make them monsters if desired.), would that say anything about the prospects of life?
Well, a significant portion of the biomass of this planet happens to be in the sea. There is lots of evidence that there was life in the seas about as far back as we can imagine.
Would super high tides exclude sea life? Not in anyway that I can imagine.
So even if all of the assumptions regarding a moon so close to the earth creating super high tides were absolutely true, it would not in anyway preclude life.

Replies to this message:
 Message 9 by RAZD, posted 04-21-2004 1:54 PM jar has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 9 of 30 (101573)
04-21-2004 1:54 PM
Reply to: Message 8 by jar
04-21-2004 1:32 PM


Re: I'm not sure I understand what the issue is...
You could even argue that super high tides makes for more mixing, not just of the water\silt\etc\soup but of water with varying levels of intertidal environments subject to UV and solar energy action, all amounting to more variety of places for life to start.

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

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SRO2 
Inactive Member


Message 10 of 30 (101611)
04-21-2004 5:06 PM
Reply to: Message 7 by NosyNed
04-21-2004 2:03 AM


Re: BS and Bafflement
Try standing in front of an Engineering Change Board and giving an "opinion" of a fluid mechanics math model...thats why they call call it science, because it's NOT an opinion.

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 Message 7 by NosyNed, posted 04-21-2004 2:03 AM NosyNed has not replied

Replies to this message:
 Message 11 by RingoKid, posted 04-21-2004 8:42 PM SRO2 has replied

  
RingoKid
Inactive Member


Message 11 of 30 (101684)
04-21-2004 8:42 PM
Reply to: Message 10 by SRO2
04-21-2004 5:06 PM


Re: BS and Bafflement
cosmology theories are somewhat different to engineering don't you think...???
...differing "opinions" abound
choose what you wish to believe or make your own up...

This message is a reply to:
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Replies to this message:
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 Message 13 by NosyNed, posted 04-21-2004 9:28 PM RingoKid has not replied

  
SRO2 
Inactive Member


Message 12 of 30 (101696)
04-21-2004 9:18 PM
Reply to: Message 11 by RingoKid
04-21-2004 8:42 PM


Re: BS and Bafflement
You constue theory from raw data here. Theory is a postulation of reason(s) for why a thing(s) "might" be. Typically, it is where raw data points subside that "theory" begins. Science by it's nature doesn't draw conclusions from speculation, nor does it stagnate on raw data points...it lies somewhere in between, it's the gray area..."it's finite probabilities drawn from a possibility of infinite data points"....is somebody writing this down?

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 13 of 30 (101697)
04-21-2004 9:28 PM
Reply to: Message 11 by RingoKid
04-21-2004 8:42 PM


Cosmology
We aren't talking about cosmology here. We are talking about the earth-moon classical, celestial mechanics.
As far as cosmology goes: Until someone can do a lot more good math on the "opinions" they will remain speculative just as you say. The state of these ideas is understood to be somewhat (or a lot) speculative. They are not, however, just whatever anyone wants to make up.
My third year math-physics prof used to do "cosmology" for fun. He said that was because no one could prove you wrong. That, however, was a long time ago. Now a lot can be proved wrong. You don't get to make up your own anymore. We know way too much.

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 Message 11 by RingoKid, posted 04-21-2004 8:42 PM RingoKid has not replied

  
RingoKid
Inactive Member


Message 14 of 30 (102382)
04-24-2004 8:26 AM


and just what is it that we think we know...
...that dark matter and energy exists and has more to do with everything than any other thing in our universe but that it originates from a time and space beyond our universe and is often mistaken for nothing...hmmmmm
I'd say we know way too little and the rest is grasping at straws of course there is a simple answer but it's not very scientific...
I'm not really interested in proving what is already known so what would it take to disprove all cosmology theories in favour of a new paradigm ???
go on get off that fence, get way out on that limb and speculate til the cows come home, you know you want to...

Replies to this message:
 Message 15 by AdminNosy, posted 04-24-2004 11:54 AM RingoKid has not replied

  
AdminNosy
Administrator
Posts: 4754
From: Vancouver, BC, Canada
Joined: 11-11-2003


Message 15 of 30 (102396)
04-24-2004 11:54 AM
Reply to: Message 14 by RingoKid
04-24-2004 8:26 AM


Topic
RingoKid, please read the topic title again. This is not a cosmology topic. It is discussing some particular, peculiar ideas about the orbital mechanics of the earth-moon system.
Stay on topic, please.

This message is a reply to:
 Message 14 by RingoKid, posted 04-24-2004 8:26 AM RingoKid has not replied

  
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