bath said:
shadron said:
Beth, the current theory is that, yes, there is just as much subduction going on as there is sea floor spreading.
Yes, I'm aware of that. However, I don't think that the evidence supporting that is solid enough to preclude the hypothesis of expansion.
The preclusion of this expansion theory is not based on the results of some study of plate tectonics; the volumes and masses have not yet been sampled in sufficient amounts to make any but the roughest of computations about their magnitude. Rather, the expansion theory and plate tectonics both answer to general physics, which has not yet found any reason besides change in temperature or pressure for the density of any material to change over time. No one seriously proposes that measurements of volume in plate tectonics says that expansion is not occurring; rather they predict that such measurements will confirm that as much mass and volume goes down as comes up.
bath said:
shadron said:
If the size of the constituent molecules is constant, and we have no evidence otherwise, this thread to the contrary notwithstanding, then there has to be - roughly all the goes up must come down.
Actually, no. It's not just the size of the constituent molecules, but how they are positioned relative to one another. When I bake a cake, the volume of the batter going in is different than the volume after baking. The texture and density has changed over time due to heat.
Actually you're right (see, I can be reasonable!!) Some of the growth of your cake is strictly from heat - perhaps 1% of increase in linear measurement - that also explains some of why it shrinks marginally when it cools. But - and its a very big but here - your cake is mostly rising because of a completely different reason - it's rising from production of CO2 from either a chemical reaction (baking powder) or because of yeast growth. The easy tes of that is to bake a cake without either. You cannot use either of these to explain the huge increase in volume these expanding earth people are requiring; there's simply not enough baking powder or yeast in the world (and I'm only being a little bit facetious in making that point).
In general, chemical change will lead to density change, that is true. That's why iron can turn wholly to rust, unlike aluminum. However, the vast majority of the Earth's mass is elemental, not chemically molecular. Iron is probably the largest contributor. All the chemical changes that are possible on the surface will never change the density of the planet more than infinitesimally on the planetary scale.
bath said:
shadron said:
There are subduction zones off the Pacific coast of Washington and Oregon, that are responsible for the Klamath mountains and the volcanoes there. That subduction zone has even "come ashore" in California and is responsible for tearing the state apart along the San Andreas (and a host of other) faults.
I am aware of an understand these facts. They do not preclude the alternate hypothesis because we don't yet know with certainty whether or not the diameter of earth is actually expanding. At some point, our measurements will be accurate enough to make that determination.
No, there you are wrong. We have made measurements of the geodesy of the earth that are accurate enough to preclude expansion, at least in the magnitude these people claim. Among other ways, precise measurement of satellite orbits and measurements made by reflecting radar and laser light off of the moon (specifically, the reflectors left there by Apollo) have accuracies into the inches for supporting various other observations, such as the slow expansion of the moon's orbit size due to energy transfer from Earth's rotational momentum to the moon's orbital velocity.
bath said:
shadron said:
As I said above, there is no convincing evidence that matter in general is changing in volume or density over time.
You're right, there isn't. On the other hand, we've only been measuring things for a few hundred years at best. I don't have the faith you do that such changes might not ever occur. The news about Mercury shows both that planets can be dynamic, changing size over time. It also shows that we can detect such changes. So I'll wait until more evidence comes in to make up my mind on the matter.
Ah, but what is the point to science if we don't take our observations and infer general rules about the way things work from them? If we never allow ourselves to extrapolate about things then observation buys us nothing.
For example, you point out that we've only been making measurements for a couple of hundred years. Depending on the accuracy you require, that might be 30 years, or 5 years, or only in the last 25 minutes. Certainly we've been observing animals, say, for at least 10,000 years, and I hear nothing about elephants having been less fragile due to falling in the past - indeed, we have archaeological evidence of large animal traps in which this fact about size was purposefully used against them, and the fossil evidence going back 100as of millions of years doesn't show any way to consider large animals being less fragile than they are today (this is, by the way the obverse side of one the the young Earth arguments). So, because we weren't here to measure their freshly gnawed femurs we must throw away all that evidence? No.
bath said:
Sometimes a new theory like this comes in and changes the way we view our world. The earth is a dynamic living planet.
Yes, but being dynamic and living doesn't say it followed different physics in the past than it does today. The physics is the same.
bath said:
shadron said:
There are a good many reasons to disbelieve it, as size is not a simple thing to scale. Think about why, for example, you can drop an ant any distance at all and it will survive, but an elephant would not easily suffer a fall of a couple of feet in height. That has to do with the scale of things, and why you cannot simply scale an ant to elephant size and have it work.
Yes, there are good reasons to doubt it, and doubt it I do. I don't think you've even scratched the surface of problems with the theory. But I gather there are problems with the current theory as well.
Oh? Such as? Perhaps there are other explanations for these anomalies or objections which can be brought forth without wrecking what we believe we know about the past. Occasionally (very occasionally) they can lead to a change in science theory. I don't believe the expansionists are there, though.
I enjoy the speculation. It gives me a reason to anxiously await new data to see what the results are.
As do I.