michaels@cornell.UUCP (Michael I. Schwartzbach) (09/11/85)
With considerable amusement I have been following the Ted Holden vs.
The World debate, and if I understand his postings (which may not be
the case) he claims that the gravity on earth in ancient time was
felt to be lower, since Saturn was hanging somewhere in the sky and
causing tremendous tidal-effects. Now, on the hemisphere closest to
Saturn gravity would indeed be lower, but on the far side gravity
would in the same manner be much higher (right?). So unless Saturn
was in a geosynchronous orbit the poor dinosaurs would we squashed
periodically, and hence succumb. If on the other hand Saturn was
fixed relatively to earth's position, then only one hemisphere would
be inhabited by dinosaurs; in fact, the far hemisphere would be
totally void of life except for turtles perhaps. Is that the case?
And would any astronomers care to comment on the stability of a
system as described above. While I'm at it, let me try to preempt
Ted's response to the fact that dinosaurs are found all over the
globe: "Saturn's gravity sucked the continents upwards to the
low-gravity hemisphere, and when Saturn disappeared they returned
to their orginal positions". I think I got the style of reasoning
right. I can't wait to hear Ted's response to this, but it will
probably be based on an understanding of the universe far exceeding
my own and any other mortal man's.
Michael I. Schwartzbach
CS dept. Cornell Univ.
"Everything is possible, but very few things can actually happen!"bill@utastro.UUCP (William H. Jefferys) (09/13/85)
> With considerable amusement I have been following the Ted Holden vs. > The World debate, and if I understand his postings (which may not be > the case) he claims that the gravity on earth in ancient time was > felt to be lower, since Saturn was hanging somewhere in the sky and > causing tremendous tidal-effects. Now, on the hemisphere closest to > Saturn gravity would indeed be lower, but on the far side gravity > would in the same manner be much higher (right?). So unless Saturn > was in a geosynchronous orbit the poor dinosaurs would we squashed > periodically, and hence succumb. Actually, no. (Too bad, this was an ingenious argument). There are *two* high tides per day, not one; one occurs when the Moon is on the same side of the Earth as we are, and the other when it is on the opposite side. During each high tide, the local gravity is reduced. Consult any elementary astronomy text for the reasons (which are best explained with pictures). However, there would be no relief from the full gravity of the Earth in the +/- 30 degree band midway between the subsaturn point and its opposite pole. And if the Earth turned with respect to Saturn the poor dinosaur would, as you point out, be alternately squashed and relieved even without any addition to the Earth's gravity, since as Ted avers, these particular dinosaurs were too heavy to have survived Earth-normal gravity. I have already pointed out that there are good physical reasons to disbelieve Ted's assertion that the pole of the Earth pointed towards Saturn (and I don't believe that Ted has told us - yet - how stupid I was to make that remark :-) -- Glend. I can call spirits from the vasty deep. Hot. Why, so can I, or so can any man; But will they come when you do call for them? -- Henry IV Pt. I, III, i, 53 Bill Jefferys 8-% Astronomy Dept, University of Texas, Austin TX 78712 (USnail) {allegra,ihnp4}!{ut-sally,noao}!utastro!bill (UUCP) bill@astro.UTEXAS.EDU. (Internet)
gordon@uw-june (Gordon Davisson) (09/14/85)
>[Michael I. Schwartzbach] > [Ted Holden] claims that the gravity on earth in ancient time was > felt to be lower, since Saturn was hanging somewhere in the sky and > causing tremendous tidal-effects. Now, on the hemisphere closest to > Saturn gravity would indeed be lower, but on the far side gravity > would in the same manner be much higher (right?). Nope. You're forgetting that up is the opposite direction on the far side of the earth, so the 'felt effect' of gravity is low at both the near and far ends, and normal on the great circle halfway between them. (actually, there are some nonlinearities, but a first approxamation is close enough for this). > So unless Saturn > was in a geosynchronous orbit the poor dinosaurs would we squashed > periodically, and hence succumb. If on the other hand Saturn was > fixed relatively to earth's position, then only one hemisphere would > be inhabited by dinosaurs; in fact, the far hemisphere would be > totally void of life except for turtles perhaps. Is that the case? Ted seems to think the earth's north pole always pointed toward Saturn, presumably with the earth's axis rotating once per orbit. This, of course, violates conservation of angular momentum, but Ted seems to be very good at ignoring problems like that. From this and Ted's theory that Ultrasaurs couldn't support themselves in normal gravity, we would expect to find them at both poles (or just one. They'd have a hard time spreading...), but not near the equator. Funny, I seem to reember some excitement a while back about dinosaur fossils being found quite a ways off the equator, implying that this was rare. (can anyone back me up on this, or is my memory flaking out again?) > And would any astronomers care to comment on the stability of a > system as described above. Stability? Like I said above, it's not unstable, it's impossible! (Thou shalt not violate conservation of angular momentum, and all that) -- Human: Gordon Davisson ARPA: gordon@uw-june.ARPA UUCP: {ihnp4,decvax,tektronix}!uw-beaver!uw-june!gordon Bitnet: gordon@uwaphast or gordon@phastvax or something like that.
throopw@rtp47.UUCP (Wayne Throop) (09/14/85)
> ... if I understand his postings (which may not be the case) he claims > that the gravity on earth in ancient time was felt to be lower, since > Saturn was hanging somewhere in the sky and causing tremendous > tidal-effects. Now, on the hemisphere closest to Saturn gravity would > indeed be lower, but on the far side gravity would in the same manner be > much higher (right?). Wrong. Tides don't work that way. Consider a primary P with satellite S, and on S are observers 1, 2, 3, and 4, as shown below. We are looking down on the north poles of P and S. 1 P 4S2 3 Now then, what would these observers see, apparent-gravity-wise. 1 and 3 would see "normal" gravity, and 4 and 2 would see reduced gravity. (Note that observers 5 and 6, on the poles of S but not shown, see normal gravity also.) (Also note that I am ignoring some minor tidal effects, and am only considering the major ones.) This is a little surprising at first, but becomes "obvious" when one thinks of where tidal effects "come from". The center of mass of S is in free fall about P. Our 4 intrepid observers are constrained to orbit at the same speed as S, but note that 4 is in a lower orbit, and 2 is in a higher orbit. Thus, 4 is going "too slow" to be in free fall with respect to P, and thus feels a net force towards P. 2, on the other hand, is going "too fast" to be in free fall with respect to P, and thus feels a net force away from P. Another way to think of it is this. 4 feels reduced gravity because P is pulling 4 away from S. 2 also feels reduced gravity, because (dramatic pause) P is pulling *S* away from *2*!!! > So unless Saturn was in a geosynchronous orbit the poor dinosaurs would > we squashed periodically, and hence succumb. Well, no. You apparently mean "unless Earth was either tide-locked, or had it's pole oriented toward Saturn." Anyway, it is correct that tidal effects could not have created a low-gravity environment earthwide. I think the major problem with such tidally-created reduced-gravity zones is not one of why dinosaur distributions don't show such patterns, but rather why Earth survived the experience at all. If Earth orbited Saturn close enough to reduce gravity by, say, 1/2 due to tidal effects, the crust would be "rent asunder", and "reduced to a state of candecence", if I have my catastrophic idiom correct. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
csdf@mit-vax.UUCP (Charles Forsythe) (09/17/85)
In article <241@uw-june> gordon@uw-june (Gordon Davisson) writes: >>[Michael I. Schwartzbach] >> Now, on the hemisphere closest to >> Saturn gravity would indeed be lower, but on the far side gravity >> would in the same manner be much higher (right?). > >Nope. You're forgetting that up is the opposite direction on the far >side of the earth, so the 'felt effect' of gravity is low at both the >near and far ends, and normal on the great circle halfway between them. >(actually, there are some nonlinearities, but a first approxamation is >close enough for this). I think you made a mistake. "Up" is in the OPPOSITE direction, but the gravity vectors from Saturns gravitational feild are in the SAME direction, so that feild would ADD to gravity rather than SUBTRACTING from it. (Or do gravity feild-line passing through a sphere of mass reverse? :-) This makes this statement wrong: >From this and Ted's theory that Ultrasaurs couldn't support themselves >in normal gravity, we would expect to find them at both poles (or just >one. I think it would only be one. (I really hate to correct someone who's correcting Ted...) -- Charles Forsythe CSDF@MIT-VAX "What? With her?" -Adam from _The_Book_of_Genesis_
gordon@uw-june (Gordon Davisson) (09/20/85)
>>>[Michael I. Schwartzbach] >>> Now, on the hemisphere closest to >>> Saturn gravity would indeed be lower, but on the far side gravity >>> would in the same manner be much higher (right?). >>[Gordon Davisson] >>Nope. You're forgetting that up is the opposite direction on the far >>side of the earth, so the 'felt effect' of gravity is low at both the >>near and far ends, and normal on the great circle halfway between them. >[Charles Forsythe] >I think you made a mistake. "Up" is in the OPPOSITE direction, but the >gravity vectors from Saturns gravitational feild are in the SAME >direction, so that feild would ADD to gravity rather than SUBTRACTING >from it. (Or do gravity feild-line passing through a sphere of mass >reverse? :-) Tides are caused by the difference in the sun/moon/saturn/Tide-Causing- Body's gravitational field: it's stronger the nearer you are to the TCB, so I assumed Michael had thought (as I had, before someone corrected me) that it was in one direction on one side of the earth and the other way on the other side. This is in fact correct: things on the near side of the planet see a tidal 'force' toward the TCB, and things on the far side see a 'force' away from the TCB. But since up is also opposite for opposite sides of the planet, both sides see the tidal 'force' as up. It having been pointed out that the other mistake (thinking the tidal 'force' was always toward the TCB) is actually more reasonable (and maybe even more likely), I can see how my comments might easily have confused someone. Sorry about that... I guess I like Wayne Throop's description best: when you're on the near end, you fall toward the TCB; when you're on the far end, the planet falls toward the TCB (and thus away from you). >(I really hate to correct someone who's correcting Ted...) I, on the other hand, just *love* correcting people who're correcting me. :-) -- Human: Gordon Davisson ARPA: gordon@uw-june.ARPA UUCP: {ihnp4,decvax,tektronix}!uw-beaver!uw-june!gordon Bitnet: gordon@uwaphast
king@kestrel.ARPA (09/21/85)
In article <369@cornell.UUCP>, michaels@cornell.UUCP (Michael I. Schwartzbach) writes: > With considerable amusement I have been following the Ted Holden vs. > The World debate, and if I understand his postings (which may not be > the case) he claims that the gravity on earth in ancient time was > felt to be lower, since Saturn was hanging somewhere in the sky and > causing tremendous tidal-effects. Now, on the hemisphere closest to > Saturn gravity would indeed be lower, but on the far side gravity > would in the same manner be much higher (right?). Actually, not quite. In a tidal situation the point under Saturn AND ITS ANTIPODES would have light gravitation; the points midway in between would have the heaviest. Think of the situation as the point under Saturn being pulled away from the main mass, but the main mass of Earth being pulled away from objects on Earth's far side. The midway points (which see Saturn on the horizon) are pulled towards Saturn with the same force as the Earth itself, but in a direction with an inward vector. -dick