Newtonian Gravity

Quote from: markjo on September 16, 2009, 07:27:31 PM

Quote from: Roundy the Truthinessist on September 16, 2009, 06:52:08 PM

Quote from: markjo on September 16, 2009, 06:43:18 PM

So Newton's gravity can't predict the trajectory of a bomb dropped from 10,000 feet at 600 mph?

I can't imagine it could do so exactly.

How exact would it need to be?  Feet, inches, microns?

No one has dropped a bomb at 10,000 feet in a vacuum. The fact is, Newton is always wrong, because relativity always applies.

Wow, I never realized that you could use relativity to compensate for wind resistance. 

Quote from: Kathleen Wilcox on September 17, 2009, 03:06:18 PM

Quote from: markjo on September 16, 2009, 07:27:31 PM

Quote from: Roundy the Truthinessist on September 16, 2009, 06:52:08 PM

Quote from: markjo on September 16, 2009, 06:43:18 PM

So Newton's gravity can't predict the trajectory of a bomb dropped from 10,000 feet at 600 mph?

I can't imagine it could do so exactly.

How exact would it need to be?  Feet, inches, microns?

No one has dropped a bomb at 10,000 feet in a vacuum. The fact is, Newton is always wrong, because relativity always applies.

Wow, I never realized that you could use relativity to compensate for wind resistance.  

I never realized that one can calculate the effects of drag over a 10,000 feet in variable gases so easily. But then again I am a chemistry major. 

I never realized that one can calculate the effects of drag over a 10,000 feet in variable gases so easily. But then again I am a chemistry major. 

  What does atmospheric drag have to do with Newtonian gravity?

No. He provided laws which govern the observation of the effects of gravity, not the possible underlying cause(s). You still don't understand this. It's not too hard but we'll have to leave it be. Drop me a PM if it still troubles you.

Uh, he was also wrong about the effects of gravity...

You may be shocked by what I'm about to say, but 'reality' involves all circumtances, not just the majority. Newton's theories do not reflect reality, end of story. A theory about how the universe works, which is incorrect in that regard, is wrong.

I may be shocked by what I am about to say but I agree totally. However, as reality involves all circumstances and not just the majority, the earth cannot be flat. There are many things that are observed that could not or cannot happen on a flat earth therefore the earth cannot be flat.

when dismissing newton's law of gravity because it isn't an exact representation of reality you could as well dismiss all other physical laws as there are none that aren't aproximations to observations.

Again, thank you to FEers for taking an isolated conclusion and applying it in a blanket and overgeneralised way.

Yes, Newton was wrong. But Newton being wrong doesn't mean the truth has to be the complete opposite. Newton's laws were a refinement on the work of Galileo. Similarly, Newton's work was refined by General relativity, which will no doubt be refined again whenever quantum gravity is more accurately formulated.

The point is, these are steps of refinement, each progressively more accurate than the last. Newton's laws of motion are still used today because they are accurate enough for most purposes. Newton being "wrong" is true only in the sense that his laws are not infinitely accurate.

Similarly, in mathematics, you can argue that Pi = 3.14159 is wrong because it's not infinitely accurate. However, unless you're measuring photons orbiting around the edge of the universe, you won't need a value of pi more accurate than that. Plus, it would be ludicrous to suggest that, because this value is not infinitely accurate, then Pi must be equal to something around five hundred thousand.

He called it his "Universal" Law of Gravitation.  He was attempting to solve it as a universally.

So ignoring that it is wrong in the first place, it is also obvious that he was trying to solve the problem for everything.

So what does Newton being wrong about gravity have to do with the accuracy of his predictions where they are applicable?  Or are you guys saying that Newton's gravity is never applicable to any situation?

So what does Newton being wrong about gravity have to do with the accuracy of his predictions where they are applicable?  Or are you guys saying that Newton's gravity is never applicable to any situation?

No one said that.  The discussion was on whether it was correct, not a useful tool.

Quote from: markjo on September 18, 2009, 05:10:02 AM

So what does Newton being wrong about gravity have to do with the accuracy of his predictions where they are applicable?  Or are you guys saying that Newton's gravity is never applicable to any situation?

No one said that.  The discussion was on whether it was correct, not a useful tool.

How can it be useful if it's wrong?

I think what nobody has pointed out here is that yes, Newton was wrong, but for most real world systems and events occurring in our day to day experiences his laws are so close to what is observable as to be indistinguishable from being correct.
If one cannot distinguish the difference between what is predicted by Einstein and what is predicted by Newton in a given situation, without measurements that are more precise than are needed or capable of being obtained, then one set of laws is as good as another.

Did you bother to read this, Markjo?

Quote from: John Davis on September 18, 2009, 05:40:24 AM

Quote from: markjo on September 18, 2009, 05:10:02 AM

So what does Newton being wrong about gravity have to do with the accuracy of his predictions where they are applicable?  Or are you guys saying that Newton's gravity is never applicable to any situation?

No one said that.  The discussion was on whether it was correct, not a useful tool.

How can it be useful if it's wrong?

Approximations are wrong, but they are often close enough to be useful in calculations.

Euler's method is flat out wrong, but it is still useful because it somewhat estimates the rest of a function.

Newton's law of gravitation has no basis in reality however, unlike Euler's method.

Quote from: Kathleen Wilcox on September 17, 2009, 09:31:29 PM

I never realized that one can calculate the effects of drag over a 10,000 feet in variable gases so easily. But then again I am a chemistry major. 

  What does atmospheric drag have to do with Newtonian gravity?

You are the one making the claim that Newtons law for universal gravitation can accurately predict where a 10,000 foot high bomb will drop.

Quote from: markjo on September 17, 2009, 09:44:01 PM

Quote from: Kathleen Wilcox on September 17, 2009, 09:31:29 PM

I never realized that one can calculate the effects of drag over a 10,000 feet in variable gases so easily. But then again I am a chemistry major. 

  What does atmospheric drag have to do with Newtonian gravity?

You are the one making the claim that Newtons law for universal gravitation can accurately predict where a 10,000 foot high bomb will drop.

And it can.  Just as accurately as relativity can.

The real issue here is that RE'ers so consistently get defensive over Newton. Someone says 'Newton was wonrg', and each time we have to watch RE'ers defend him, and then slowly give ground, and eventually admit that yes, he was wrong.


Can we shorten this process somehow?

if we agree that exact mathematical representations of nature are very rare (more or less not possible) and that usefulness and quality of a theory (assuming you apply it correctly) are not necessarily dependant on overall correctness the case is settled.
(i don't want to speak for other re'ers, that's my point of view)
  

The real issue here is that RE'ers so consistently get defensive over Newton. Someone says 'Newton was wonrg', and each time we have to watch RE'ers defend him, and then slowly give ground, and eventually admit that yes, he was wrong.

Can we shorten this process somehow?

Yes, you can stop making it sound like Newton being wrong about gravity has the slightest thing to do with the shape of the earth. 

Quote from: John Davis on September 18, 2009, 05:40:24 AM

Quote from: markjo on September 18, 2009, 05:10:02 AM

So what does Newton being wrong about gravity have to do with the accuracy of his predictions where they are applicable?  Or are you guys saying that Newton's gravity is never applicable to any situation?

No one said that.  The discussion was on whether it was correct, not a useful tool.

How can it be useful if it's wrong?

Whats a Gaussian surface or a circle or a triangle or a point in reality?

There is no such thing - they are concepts that are false as far as the physical goes but have useful applications. 

There are two kinds of people in the world: those that believe Newton was wrong and those that do not.

There are two kinds of people in the world: those that believe Newton was wrong and those that do not.

Please keep this sort of low content posting out of the sensible forums.

There are two kinds of people in this site: those that believe Newton being wrong matters and those that do not.

Fixed.

Quote from: Jack on September 19, 2009, 02:36:01 AM

There are two kinds of people in the world: those that believe Newton was wrong and those that do not.

Please keep this sort of low content posting out of the sensible forums.

Perhaps you should refrain from telling a moderator what to do, as you have no power to do so; the best you can do is file a complaint. My statement pretty much summarizes the debate here, and it is nowhere near low content because it is not spam and it is on-topic. A low content post would contain nothing but "lol", "yeah ur right", "hi!", etc.

Einstein never "proved him wrong" because Isaac Newton "wasn't" wrong in the "first place". Newton is only "wrong" in a few "exceptional" circumstances, such "as" high speed, or large "gravitational" fields. These were "not" scenarios Newton was aware, nor "ones" that he claimed to "solve".

Newton was also wrong about space and time. He believed that space and time were absolute, and that they are distinct. It seems that he believed in a absolute reference frame, where space and time remain constant and are independent to any observers. Thus, time travel will be impossible. However, relativity corrected these mistakes. According to special relativity, there is no such thing as a preferred, absolute reference frame, and space and time are dependent to observers. One example is time dilation. In other words, space and time are relative. Perhaps the only thing that is absolute is the speed of light in a vacuum, as it is always constant relative to any inertial observers.

So yes, Einstein did prove Newton wrong.

Quote from: Thermal Detonator on September 19, 2009, 04:19:33 AM

Quote from: Jack on September 19, 2009, 02:36:01 AM

There are two kinds of people in the world: those that believe Newton was wrong and those that do not.

Please keep this sort of low content posting out of the sensible forums.

Perhaps you should refrain from telling a moderator what to do, as you have no power to do so; the best you can do is file a complaint. My statement pretty much summarizes the debate here, and it is nowhere near low content because it is not spam and it is on-topic. A low content post would contain nothing but "lol", "yeah ur right", "hi!", etc.

Moderators are all, of course infallible. 

Whilst your comment was on topic, I disagree that it adds anything whatsoever to the debate. Any fule kno that in this thread, some think Newton was right, and some think Newton was wrong. It's so obvious that it does not need summarizing. Because what you posted is patently obvious to anyone who has read the thread, and because it adds nothing whatsoever outside that one platitude, it is almost by definition low content - there are no ingredients in it.
Just because I have no power doesn't mean I'm wrong.

Newton was wrong! His theory of Universal Gravitation, applied to the whole Universe, does not allow for a stable finiite universe. If the Universe is infinite with approximately constant density of stars around, then we arrive at the so called Olber's paradox.

I have just copied this from my post in the other new gravity thread. Its a quick proof that for low mass and velocities Newtons theory of gravitation if perfectly accurate. For any object much lighter than a star and slower than a good fraction of the speed of light unless your doing very precise calculations (GPS is the only thing that springs to mind) then Newtons calculations are perfectly accurate. Philosophically what Newton and Einsein tried to do was very different. Newton did not know why masses appeared to attract but he noted that they did and described their behavior well. He did not have access to precise data from space to see deviations between reality and his predicitions. Einstein, managed to come with a theory that partly explained how gravitation works.

In Newtonian gravitation this is MODELED by F = GMm/r^2 in general relativity the field is caused by the Riemann curvature tensor. If this is true then Einsteins gravitation should approximate to Newtons gravitation in the classical limit. We can easily show that GR corresponds to Newtons description in the classical limit, firstly v << 1.
(Apologies for the next bit I have no idea how to do tensor algebra in this forum so if theres random sups and subs I failed at covariance an contra-variance.)
As the particle must be traveling slowly compared to the speed of light so Tmn / T00 = Tmn/p << 1.
i.e. stresses are small relative to mass-energy
One finds the world lines in general relativity approach those for Newtonian mechanics if g00 = -1 -2V
One then finds that Rn0n0 = d2V / dxn dyn
Again some messing around with G = 8piT gives R00 = 4pi X p
Contracting with above gives R00 = d2V / dxn dyn
so d2V / dxn dyn = 4pi * p.

So we see that Newtons equations are simply the classical limit of Einsteins equations - this is gravitation.
At this point we note that even in Newton's theory the Force is very much like a fictitious force.
F = ma - inertial acceleration
F = mg - gravitational acceleration
Its even easier to see than for Einsteins equations. To complicate matters further in GR a photon feels the effects of gravity despite being massless.

i think this is where the FET view of Gravitation disparts with GR. Namely, in FET mass does not curve space-time.

i think this is where the FET view of Gravitation disparts with GR. Namely, in FET mass does not curve space-time.

Then not only was Newton wrong, but obviously Einstein was too.

Please give a list of bodies for which it was experimentaly proven that create a gravitational field (a.k.a curve space-time).

Please give a list of bodies for which it was experimentaly proven that create a gravitational field (a.k.a curve space-time).

The Sun
Some galaxies