# Modifying Newton's First Law of Motion

Discussion in 'Alternative Theories' started by hansda, Jun 8, 2017.

1. ### DaveC426913Valued Senior Member

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And if one were to come up such a fictional force to explain length contraction, one would be completely and utterly contradicted by observations.

You see, you and I and everyone on Earth are right now moving at a large fraction of the speed of light with respect to a number of reference points. Do you feel squashed?
Which reference point would you feel squashed with respect to? The one to the West of us? Or the one to the North of us? How can we be squashed along two different axes at the same time? Do we shrink??

The Newtonian model can not - and does not - explain observed phenomena resulting from relative velocities approaching the speed of light. Now that we can observe such things in detail, the Newtonian model must be replaced, because it is actually wrong on many things. Full stop.

I'm sorry to say, you are demonstrating a lack of knowledge of 20th century physics. If there were any question whether your papers on physics were in error, that doubt has been erased.

Last edited: Sep 1, 2017

3. ### exchemistValued Senior Member

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Don't be an idiot.

If a force were acting to squash things, it would be observable. Forces can be felt and measured.

Even worse, it would need to be a force that both acted and didn't act, at the same time, in order to account for the perception of length depending on the relative velocity between the observed object and several observers moving at different speeds with respect to it.

There is thus no possible way in hell for a compressive force to reproduce the predictions of relativity.

5. ### DaveC426913Valued Senior Member

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He's not an idiot; he's simply a young man of the 19th century, thrown headlong into the 21st century.
He can't be blamed for not having access to 20th century physics.

7. ### exchemistValued Senior Member

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You mean....we are dealing with Jacob Rees-Mogg?!!

But I find you very charitable. There is little excuse today for not reading at least about Special Relativity, if you are interested in physics, and none at all for making assertions that Newtonian mechanics can model its predictions.

8. ### DaveC426913Valued Senior Member

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His words "... you are not able to come out of your GR obsession" are very telling.

He is aware of obsessive behavior. He probably realizes his own obsession with Newtonian Physics, but has gone one step further down the rabbit hole in trying to rationalize that it can explain modern observations.

I wonder how he rationalizes other areas that Newton never addressed, such as time dilation (time is universal in Newton's model) and the speed of gravity propagation (gravity travels at infinite speed in Newton's model). Both these have been debunked with 20th century observations.

9. ### exchemistValued Senior Member

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I'm not sure gravity travels at all in Newton's model. He only deals with static fields. Though in a way it's a moot point as you only need the idea of it travelling if it propagates at finite speed!

Our friend has no worked out scheme at all, I don't think. He's just yet another anti-relativity crank, proceeding as they all do from ignorance.

10. ### DaveC426913Valued Senior Member

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That's where I was going to go next.
The Newtonian model does not address length contraction at all, since relativistic effects were not observed in Newton's time. So he will likely invent a force - but he will have no explanation for it.

Unfortunately, it is doomed from the get-go, for the reasons I mention: it will be self-contradictory.

11. ### James RJust this guy, you know?Staff Member

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hansda:

That's not quite right. In GR, gravity is not a force, but all the other forces are still forces. In particular, all electromagnetic forces between atoms are still forces in GR.

Notice that we never directly feel any "gravitational force". As you sit in your chair, you're only aware of what you call your "weight" because the chair is pushing up on you. That is, there is an electromagnetic repulsive force between the atoms in the chair and the atoms in your backside, which you can feel. If you're in free fall, you have no perception of "weight" any more.

There was no explanation of length contraction prior to Einstein. It is fundamentally a relativistic effect. Newton wasn't even aware of it. And it can't be explained using Galilean/Newtonian relativity.

No. There is no measurable force on length-contracted objects. The contraction is entirely a feature of observing the object from a different frame of reference.

hansda likes this.
12. ### Michael 345Next mythical choc bunnies for mystic who diedValued Senior Member

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I don't think that's right

Your weight is the gravitational attraction between you and the Earth. You are also gravitationally attracted to the chair (as it is to you)

While electromagnetic repulsive forces only keep the atoms of your backside from a truely physical touching and melding with the atoms of the chair

13. ### James RJust this guy, you know?Staff Member

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Michael345:

That's the Newtonian picture, in which gravity is an attractive force between masses.

In General Relativity, you'd be in free-fall towards the centre of the Earth if the ground (or your chair) wasn't there to stop you. That is, free-fall motion is the "natural" motion of objects, and it doesn't require a force. In GR, when you stand still on the ground, you're in an accelerating frame of reference - the ground is literally accelerating you upwards. However, this is occurring in a curved spacetime (caused by the Earth's mass), so you don't move further away from the centre of the Earth, despite the fact that you're accelerating.

14. ### exchemistValued Senior Member

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James, this intrigues me. I know little about relativity but I read recently that in SR one replaces the Newtonian concept of force with something called a Four Force, which is a vector in spacetime rather than just in space. Is this right and does it make any practical difference, or is it just a mathematical technique for handling the concept of force in the 4D mathematics encountered in relativity?

15. ### hansdaValued Senior Member

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Say a particle is subjected to all the four forces of nature. The particle's movement will change as per the resultant of these four forces. The resultant of these four forces can be calculated if gravity is considered as a force. If gravity is considered as GR, can this resultant force be calculated?

I thought this is due action-reaction as per Newton's Third Law.

In this case, there is no action-reaction. So we dont feel any weight.

May be at the time of Newton or prior to Einstein, it was a hidden variable or hidden force.

Solar system can be explained in Newtonian Model. Solar system also can be explained in Einsteinian Model. So, length contraction also can be explained in other models of gravity.

This compressive force can be tested with a force-meter. The way Time-Dilation is tested with a clock; in a similar fashion, this force can be tested with a force-meter.

16. ### originTrump is the best argument against a democracy.Valued Senior Member

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I am going to give you some good advice. Try to shut up and listen for a change, you will end up learning something if you do.

Now you go on ignore. Bye.

17. ### NotEinsteinRegistered Senior Member

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So you have a TOE based on the Newtonian model, but you don't even understand the Newtonian model. That's... special.

18. ### hansdaValued Senior Member

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Yes. You are correct.

Where do you think, my understanding of Newtonian Model is wrong? Can you explain this?

What is special?

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People have been explaining this! You posit "hidden forces" which cannot or have not been measured, where no such forces can exist. You posit an 'instantaneous force' which would require a quantized time vector, which is contrary to all observations ever made.

Can you not seek attention some other way?

20. ### NotEinsteinRegistered Senior Member

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Please note that by responding to a partial quote, pulling it out of context, you are dangerously close to quote-mining. I did not confirm that what you have is a TOE.

The sentence I quoted seems to show you doubting your interpretation of the third law of Newton. How can somebody who's build a TOE on top of a Newtonian model be uncertain about the third law of it?

Read the first two parts of the sentence. That is special.

21. ### The GodValued Senior Member

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This has no meaning.
There is nothing like "all other forces" in GR. GR is a theory of gravity, curvature of spacetime. There is no treatment of EM "in GR". Electromagnetism cannot also be defined as curvature of something, simply because neutral particles (chargeless) are not influenced in EM while massless (photons) particles are influenced in GR.

22. ### James RJust this guy, you know?Staff Member

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exchemist:

Four-vectors in GR are objects that transform in a particular way (using the Lorentz transformations) when you change reference frames. They are constructed so as to maintain the form of familiar definitions of quantities like $\vec{p}=m\vec{v}$. To run with the example of momentum, the problem is that the Newtonian 3-momentum is not conserved in collisions when you change reference frames. Therefore, we need to find some kind of similar quantity that is properly conserved when we change frames. What we end up with is 4-momentum, which happens to be $(c, v_x, v_y, v_z)$.

4-force is defined as $\bf{F}=\frac{d\bf{P}}{d\tau}$, that is the rate of change of the 4-momentum with respect to the proper time. In GR, the derivative is actually a covariant derivative.

23. ### James RJust this guy, you know?Staff Member

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hansda:

Yes. In GR there is no force of gravity, so you just add the effects of the other three forces together and determine the resulting motion against the background of the local spacetime.

No. The reaction force to the electromagnetic force of the chair pushing up on your body is not a gravitational force - it is the electromagnetic force of your body pushing down on the chair. Action and reaction forces always act on two different objects. The force on your body due to the chair cannot be a reaction to the gravitational force on your body, because both forces are acting on your body. That is true even in Newtonian physics.

My point is that we never feel "weight", as such, even in Newtonian physics. We only feel those "reaction" forces you're talking about.

I have no idea what you mean.

No, it can't. Take the advance of the perihelion of Mercury, for example. That's quite a famous example of where Newton fails and Einstein succeeds.

Newtonian physics cannot explain length contraction. It's an effect of the invariance of the speed of light - a postulate of Einstein's relativity.

Yes, in principle. And if it was tested, it would be found that no such compressive force exists.

Do you feel a compressive force on your body right now? You're whirling around the centre of the galaxy at a speed of about 200 kilometers per second as we speak.