Was Newton wrong?

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Was Newton wrong?

#1  Postby zaybu » May 29, 2013 10:25 am

Often you get on a forum and some people are claiming that Einstein proved Newton wrong. Well, not exactly. Einstein Field Equations reduces to Newton's law of gravity at low gravity and low velocity. I've made the calculations available. So any time you get to meet those people, you can refer to it.

Is Newtonian Gravitational Fields Valid Within General Relativity?
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Re: Was Newton wrong?

#2  Postby DavidMcC » May 29, 2013 6:32 pm

This is already well known, zaybu.
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Re: Was Newton wrong?

#3  Postby iamthereforeithink » May 29, 2013 7:15 pm

DavidMcC wrote:This is already well known, zaybu.


Indeed, but there are a surprising number of people who still pose this question. So for the relatively ill-informed layman this is still a good reference to see how exactly general relativity reduces to Newton's equations as a special case. Yeah, the thread title is a little sensationalist, but I probably wouldn't have clicked on it if it said "Newton's equations as a special case of general relativity".
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Re: Was Newton wrong?

#4  Postby Calilasseia » May 29, 2013 11:32 pm

Quite simply, Newton was working in an era when the fastest form of transport was the horse. In that era, his equations appeared to work, and work extremely well, because when dealing with slow moving objects and weak gravity fields, his equations constitute an excellent first approximation. Indeed, the error involved doesn't show up unless you're able to work to 15 decimal places, and for physicists in Newton's era, this was way beyond their capabilities. Even today in the 21st century, physicists have to exert an enormous amount of effort in order to measure errors that small. Indeed, the errors involved remain tiny even when planning space missions.

Einstein alighted upon the reason for this, in the form of the Lorentz Gamma Factor, which appears in the transformation equations of Special Relativity, and which acts as a multiplier in equations involving velocity. The Lorentz Gamma Factor is extremely close to 1 for everyday velocities, and even when you're travelling at the speeds achievable by current spacecraft, the deviation of the Lorentz Gamma Factor from 1 is somewhere around the 8th or 9th decimal place. Only when velocities reach a significant fraction of the speed of light, does the Lorentz Gamma Factor start deviating significantly from 1. Indeed, the relativistic coordinate transformation equations reduce trivially to the Newtonian or Galilean transformations when the veloctiy equals zero.
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Re: Was Newton wrong?

#5  Postby zaybu » May 30, 2013 10:54 am

Calilasseia wrote: Indeed, the relativistic coordinate transformation equations reduce trivially to the Newtonian or Galilean transformations when the veloctiy equals zero.



My guess is that you didn't visit the link provided in the OP. One can go directly from Einstein's Field equations to Newton's Law of Gravity by making two approximations: low gravity, low velocity.
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Re: Was Newton wrong?

#6  Postby klazmon » May 30, 2013 11:59 am

I vaguely recall that this was given as a student excercise in the book Gravitation by MTW.
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Re: Was Newton wrong?

#7  Postby DavidMcC » May 30, 2013 12:20 pm

So, zaybu, were you just being "sensationalist", as iamthereforeithink implied above, or did you really think that no-one knew that Newtonian mechanics are the low speed /low gravity limit of the more generally applicable physics of relativity?
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Re: Was Newton wrong?

#8  Postby zaybu » May 30, 2013 5:11 pm

DavidMcC wrote:So, zaybu, were you just being "sensationalist", as iamthereforeithink implied above, or did you really think that no-one knew that Newtonian mechanics are the low speed /low gravity limit of the more generally applicable physics of relativity?


As I stated in the OP, and maybe I should emphasize it, there are too many on the internet who uses these arguments: Einstein proved Newton was wrong; scientific theory one day, gone tomorrow; you can't trust science, it's unreliable, but religion is forever; and so on. And one can't hardly debate that -- no, Newton's law is contained in Relativity. They'll ask, where's the proof. So I thought of putting the actual calculation on a blog so that if anyone encounters such a situation, then one can shut up these ignoramuses. Of course people in the know about physics don't need any convincing. I only used this title because this is how the debate is often framed by people who are trying to discredit science. So, if I implied otherwise, I apologise.
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Re: Was Newton wrong?

#9  Postby DavidMcC » May 30, 2013 5:35 pm

OK. That's fine. I'm no expert on creatinism.
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Re: Was Newton wrong?

#10  Postby lpetrich » Jun 07, 2013 1:56 pm

Isaac Asimov - The Relativity of Wrong has an excellent discussion of this issue. Some sorts of wrongness are not so much wrong but approximate, and that's the sort of wrongness that Newtonian mechanics has.
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Re: Was Newton wrong?

#11  Postby zaybu » Jun 11, 2013 10:21 am

lpetrich wrote:Isaac Asimov - The Relativity of Wrong has an excellent discussion of this issue. Some sorts of wrongness are not so much wrong but approximate, and that's the sort of wrongness that Newtonian mechanics has.


It couldn't possibly be completely wrong. If you follow Einstein, it basically went: g00 → φ→ρ→T00. And from that, Einstein deduced brilliantly:

Rμν - ½gμνR = 8ΠGTμν

That Newton is included in Relativity goes without saying.
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Re: Was Newton wrong?

#12  Postby DrWho » Jul 03, 2013 9:04 pm

zaybu wrote:
lpetrich wrote:Isaac Asimov - The Relativity of Wrong has an excellent discussion of this issue. Some sorts of wrongness are not so much wrong but approximate, and that's the sort of wrongness that Newtonian mechanics has.


It couldn't possibly be completely wrong. If you follow Einstein, it basically went: g00 → φ→ρ→T00. And from that, Einstein deduced brilliantly:

Rμν - ½gμνR = 8ΠGTμν

That Newton is included in Relativity goes without saying.


It follows that Newton was partially correct.
The skeptical writers are a set whose business it is to prick holes in the fabric of knowledge wherever it is weak and faulty; and when these places are properly repaired, the whole building becomes more firm and solid than it was before. - Thomas Reid
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Re: Was Newton wrong?

#13  Postby z8000783 » Jul 04, 2013 6:28 am

Didn't Newton propose that forces act between bodies according to his equations whereas Einstein demonstrated that no forces were necessary due to the topology of spacetime.

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Re: Was Newton wrong?

#14  Postby hackenslash » Jul 04, 2013 7:07 am

Newton WAS wrong. He asserted that space and time were absolute. That was what he was wrong about, And what Einstein demonstrated, overthrowing absolute space and time and replacing them with absolute spacetime.

Yes, it is correct that, in his treatment of gravity, he was substantially correct, and his equations reduce to a special case, in much the same way that a circle is a special case of an ellipse, but he was still wrong about space and time being independent and absolute.
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Re: Was Newton wrong?

#15  Postby hackenslash » Jul 04, 2013 7:11 am

zaybu wrote:
DavidMcC wrote:So, zaybu, were you just being "sensationalist", as iamthereforeithink implied above, or did you really think that no-one knew that Newtonian mechanics are the low speed /low gravity limit of the more generally applicable physics of relativity?


As I stated in the OP, and maybe I should emphasize it, there are too many on the internet who uses these arguments: Einstein proved Newton was wrong; scientific theory one day, gone tomorrow; you can't trust science, it's unreliable, but religion is forever; and so on. And one can't hardly debate that -- no, Newton's law is contained in Relativity. They'll ask, where's the proof. So I thought of putting the actual calculation on a blog so that if anyone encounters such a situation, then one can shut up these ignoramuses. Of course people in the know about physics don't need any convincing. I only used this title because this is how the debate is often framed by people who are trying to discredit science. So, if I implied otherwise, I apologise.


And this is an important point. That Newton was wrong in one of his assertions about the nature of space and time doesn't impact the fact that he formulated a correct working law that, although inaccurate at significant velocities and distances, was still correct enough that us equations are still in use today, owing to the fact that they accurately describe the workings of gravity under certain conditions.
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Re: Was Newton wrong?

#16  Postby surreptitious57 » Jul 04, 2013 7:34 am

Newton was wrong of course to assume time as eternal and absolute but General
Relativity
does not invalidate the Universal Law Of Gravitation rather adds to it

In the same way that a Theory Of Quantum Gravity shall not invalidate General Relativity
but add to that : Assuming as many physicists do that that is what needs to be modified

For in science one never has the complete puzzle : Some of the pieces do not fit though even those
that do may not be the right ones : For what looks right at the time may not actually be right at all
And then one gets more pieces : And those are put together but some of them have to be changed
too : And so on and so on and so on : For it is an infinite puzzle with infinite pieces : Which might
seem pointless : But is not as the point is to enjoy putting the pieces together : Since it is an end
in it self rather than a means towards an end and that is the point of science : No more or no less
A MIND IS LIKE A PARACHUTE : IT DOES NOT WORK UNLESS IT IS OPEN
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Re: Was Newton wrong?

#17  Postby DrWho » Jul 05, 2013 3:47 pm

Newton asserted many things. He was wrong about some things like an absolute time and space. He was right about other things such as his three laws of motion and understanding physical phenomena with the tools of mathematics. He was partially right about some things such as his calculations for mass at low velocities. But I think he was right about more things than wrong.
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Re: Was Newton wrong?

#18  Postby Matt_B » Jul 05, 2013 4:20 pm

Newton was very wrong about many things. Alchemy and his estimation of the age of the Earth spring to mind.

I'd think it obvious that Newtonian mechanics has to be the classical approximation of relativistic mechanics though, because we know it works in all the circumstances that it's been tested to work. And it's not going to stop working because someone's come along with a new theory. New science rarely overturns old science; it just encompasses it.
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Re: Was Newton wrong?

#19  Postby z8000783 » Jul 06, 2013 9:52 am

DrWho wrote:He was right about other things such as his three laws of motion and understanding physical phenomena with the tools of mathematics.

What is the source of the forces mentioned in Laws 2 & 3 and how is the influence exerted at a distance?

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Re: Was Newton wrong?

#20  Postby Timpe84 » Feb 19, 2015 10:37 am

Hello! I think i solved how the gravity works, using theory of gravitational waves. Unlike Einstein, i understood, that like light and electrons, matter is affected with same gravitational waves, only in different wavelenghts.
Here's my theory: http://gravitaatioaalto-teoria.blogspot.fi/
Can you help to tell me what's wrong with my theory? =)
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