Native said:
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Why would Einstein make his own gravity ideas if Newtons were OK?
No, Newton was´nt technological limited regarding the planetary motions, as these were known by earlier philosophers/scientists - and even known by ancient cultures.
You keep saying this, but it is false historically. The ancient cultures simply did NOT have anything close to the accuracy of what newton produced.
Here is the progression:
The ancient Babylonian astronomers took fairly careful observations of the sky, keeping track of the positions of the planets in the sky over long periods of time.
From these, certain cycles were noticed. But the cycles were far from perfect. it was not uncommon for the position of a planet to be tens of degrees off from where those cycles predicted.
Then Ptolemy came along. he gave a detailed system based on the Babylonian observations, but added some more cycles in to fit the data better.
Nonetheless, during the middle ages, there was widespread acknowledgement that Ptolemy's model, while much better than the ancient one, was still deficient in many ways. It was still very common for the actual positions of the planets in the sky to be many degrees off from where the model said they would be.
In particular, the motion of Mars was very poorly explained. With improved observations from Tycho, Kepler was able to find much more accurate laws of motion that were able to predict where the planets would be in the sky to an accuracy as good as observation without a telescope could give. There were still serious inaccuracies in the position of the moon, though.
Newton came along and proposed his laws of motion, including his law of gravity. From them, he was able to derive Kepler's laws (and vice versa, by the way). But Kepler's laws only applied when gravity from the sun was the only force taken into account. With Newton's laws, the gravity from other planets could be included, which greatly increased the accuracy of the results.
In particular, with Newton's descriptions, the positions of the planets could be calculated ahead of time and give accuracy over the course of a century in the seconds of arc realm. This didn't only include the planets, but the moons circling those planets, comets, asteroids, etc.
In particular, when the planet Uranus was discovered (by accident), the motions did not exactly agree with Newton's laws. What happened next is a good lesson. Some people said that Newton's laws needed to be discarded, saying they didn't apply that far from the sun. others used Newton's laws and proposed an unseen planet whose gravity affected the motion of Uranus.
That planet was actually discovered where Newton's laws predicted. it is now called Neptune.
Nonetheless, Newton's laws did not *precisely* predict the motion of Mercury. It was off by 43 seconds of arc in its orbit per century.
You should ponder that. The ancient cycles were frequently off by tens of degrees. Now, Newton's laws were being challenged because they were off by 43 seconds in a century.
His mechanical planetary calculations were OK, but his gravitational assumptions was so bad that Einstein stated Newtons idea as "not being a two-body-force" at all, hence Einsteins attempt to hypothezise another way of explaining the phenomenon as a "field force" - which was just as speculative spooky as Newtons superstitious invention.
And, what happened is that Einstein's modification explained the already minuscule deviations of the motions from Newton's laws. In particular, the largest deviation was in the orbit of Mercury and Einstein's laws showed exactly why the 43 seconds of arc came about.
It should be emphasized that the differences between the results of Newton's calculations and those of Einstein are incredibly small. That 43 seconds of arc over the course of a century is a very, very small difference. That is why Newton's laws can still be used to aim probes to other planets. Except for those situations requiring extreme levels of accuracy, Newton's laws work well within the solar system. Einstein's work even better.
Any *new* theory will have to be able to make predictions even more accurate than those from Einstein's equations.
Furthermore, Newton's laws have been validated for other star systems. Binary stars, stars with planets, globular clusters, open clusters. In ALL of them, the observed motions agree with the calculations based on Newton's laws. For more intense environments, like those around neutron stars and black holes, Einstein's equations become more relevant because the differences between Einstein's and Newton's results become important.
Once you´ve explained the substance of Newtons "gravity", you can begin to get cocky and patronizing.
You keep asking for this, but fail to explain why it is necessary given the extreme levels of accuracy these theories provide.
I'll go further and say that asking to 'explain the substance' is missing the whole point. If the description WORKS (which it does), then no further explanation is required.
Yes, I know of the Scientific Method - and of the many occasions, where this method simply is ignored just by adding more assumptions to the one wich was contradicted, Adding ad hoc assuptions and new epicycles, brings you nowhere very quickly.
On the contrary, when observations don't agree with a very accurate theory (like Newton's or Einstein's), the first thing to do is to ask what was missed. And, that worked for finding Neptune (as described above). It has also worked in a variety of other situations, postulating the existence of things that were later verified by other methods.
And, as always, there are those who propose other explanations. And that is well and good. But the demands for those other explanations are extreme: they have to agree with the observed motions within the solar system while ALSO agreeing with the motions at the galactic level. Furthermore, they have to get agreement that surpasses those given by the results of Newton's or Einstein's theories. That is a very high bar to pass.
As with Newtons "Universal law of gravitational celestial motions", which was contradicted in the galactic realms and the "scientists" just invented yeat another superstitious "dark matter-force" to the initial one.
Yes, that was one proposal. Another was MOND, which modified the laws of gravity. BOTH were tried *as they should be*.
You like to focus on the galactic motions 'contradicting' Newton's law, but I would also point to the question of *how much*. How badly off were the results of Newton's laws? Were they as bad as the cycles of the ancient astronomers in describing the motions of the planets? Nowhere close! Even in failure, Newton's laws were more accurate than those.
And, just like the proposal that another planet was affecting things (which was verified by finding Neptune), the proposal of dark matter has *other* consequences that can be used to test it. And it has passed those other tests.
Completely irrelevant to me.
And my points are that modern science would be much better of by ignoring these speculative and superstitious guys. Even space craft launching and slingshot effects can be calculated and made without the superstitious "gravity".
No, they cannot. Those calculations use the inverse square law of gravity at essentially every step! Again, this is simply a blatant falsehood. It is impossible to calculate the motion of a probe without using gravity.
