[Tom Bishop]

Where did Newton go to find no forces? Imagination land?

[AATW]

Where did Newton go to find no forces? Imagination land?

It was his hypothesis. I guess based on the observations that things require a force to make them move or change direction.
And given that his theories have got us to the moon and are still used in many fields to make calculations they seem to have been pretty accurate and stood the test of time.

[Tom Bishop]

So it is Imagination Land then. That just creates an assumption that there is a place where there are no forces.

Lets go into Imagination Land and try to get bodies to travel from Point A and Point B in a straight line.

Think of a rocket ship in space that blasts its engines for five seconds:



What makes you think it is possible to create an engine that fires perfectly evenly from all points? If the engine starts in the slightest manner from one side or gives off the slightest bit of more energy on one side then the rocket builds too much momentum on one side and goes spiraling off to one side, either quickly or slowly. It doesn't reach the Point B destination.

The only way to go straight is for the rocket to be constantly controlled and navigated. AKA, an artificial result.

Even in something as simple as the game of Pool, it is rather difficult to hit a ball to go straightly to the Point B hole:



You have to hit it in just the right spot to get it to go the way you want it to go. Luckily in pool you are only shooting a few feet.

What if you are shooting a ball at a Point B hole which is miles away? Ignoring the fact that you don't have the arm strength to do that, and ignoring everything about surface friction, to hit a pool ball perfectly for a distance ranging in miles and get into a hole is still very improbable. The ball is more likely to go off in some random direction.

So again, straight line trajectories between two points do not naturally occur in nature. They are highly unnatural.

[JSS]

So it is Imagination Land then. That just creates an assumption that there is a place that there are no forces.

Even if we go into Imagination Land and think of a rocket ship in space that blasts its engines for two seconds:



What makes you think it is possible to create an engine that fires perfectly evenly from all points? If the engine starts in the slightest manner from one side or gives off the slightest bit of energy on one side then the rocket builds too much momentum on one side and goes spiraling off to one side, either quickly or slowly.

The only way to go straight is for the rocket to be constantly controlled. AKA, an artificial result.

There is a very simple way to make the rocket go straight.

Shut off the engine.

Now it's continuing to move, but any flaws in the engine no longer matter as it's not providing thrust.

It is now going straight, until acted on by an external force like the pull of gravity from a planet, or hitting an asteroid.

Analogies have limitations. A particle like a photon is very different than an active rocket engine or a car with wheels driving along the road. There are lots of things cars can do that photons don't.

Long range communications between all the planets we have visited, plus all the space probes that have been and currently are exploring the solar system are very good evidence that light and radio waves do indeed naturally travel in straight lines.

[Tom Bishop]

Analogies have limitations. A particle like a photon is very different than an active rocket engine or a car with wheels driving along the road. There are lots of things cars can do that photons don't.

Light is pretty complex. There are several ways for light to bend. Here physicists bend light without applying any external force. Light bends on its own based on the properties of the phase of the beam.

https://physicsworld.com/a/light-bends-itself-round-corners/

Light bends itself round corners

Five years ago physicists showed that certain kinds of laser beam can follow curved trajectories in free space. Such counterintuitive behaviour could have a number of applications, from manipulating nanoparticles to destroying hard-to-reach tumours. But before this bizarre effect could be put to good use, researchers were faced with the challenge of how to bend the light through large enough angles to be useful. Now, two independent teams have solved this problem – and claim that the bending of sound and other kinds of waves could be next.

The concept of self-bending light was inspired by quantum mechanics and the realization in 1979 by Michael Berry and Nandor Balazs that the Schrödinger equation could support “Airy” wavepackets of particles, which accelerate without an external force. Then in 2007, Demetrios Christodoulides and colleagues at the University of Central Florida created the optical equivalent of an Airy wavepacket. This is possible because the equation describing paraxial beams – beams in which the constituent rays all travel almost parallel to the direction of the beam’s propagation – is mathematically identical to the Schrödinger equation once several parameters are interchanged, such as mass and refractive index.

The Florida team generated a specially shaped laser beam that could self-accelerate, or bend, sideways. The researchers did not bend the laser beam as a whole but rather the high-intensity regions within it. To do this they passed a centimetre-wide ordinary laser beam through a device known as a spatial light modulator that adjusted the phase of the beam at thousands of points across its width.

If light can do this, what makes you think that 'perfectly straight' would be the natural direction?

[JSS]

Analogies have limitations. A particle like a photon is very different than an active rocket engine or a car with wheels driving along the road. There are lots of things cars can do that photons don't.

Light is pretty complex. There are several ways for light to bend. Here physicists bend light without applying any external force. Light bends on its own based on the properties of the phase of the beam.

https://physicsworld.com/a/light-bends-itself-round-corners/

Light bends itself round corners

Five years ago physicists showed that certain kinds of laser beam can follow curved trajectories in free space. Such counterintuitive behaviour could have a number of applications, from manipulating nanoparticles to destroying hard-to-reach tumours. But before this bizarre effect could be put to good use, researchers were faced with the challenge of how to bend the light through large enough angles to be useful. Now, two independent teams have solved this problem – and claim that the bending of sound and other kinds of waves could be next.

The concept of self-bending light was inspired by quantum mechanics and the realization in 1979 by Michael Berry and Nandor Balazs that the Schrödinger equation could support “Airy” wavepackets of particles, which accelerate without an external force. Then in 2007, Demetrios Christodoulides and colleagues at the University of Central Florida created the optical equivalent of an Airy wavepacket. This is possible because the equation describing paraxial beams – beams in which the constituent rays all travel almost parallel to the direction of the beam’s propagation – is mathematically identical to the Schrödinger equation once several parameters are interchanged, such as mass and refractive index.

The Florida team generated a specially shaped laser beam that could self-accelerate, or bend, sideways. The researchers did not bend the laser beam as a whole but rather the high-intensity regions within it. To do this they passed a centimetre-wide ordinary laser beam through a device known as a spatial light modulator that adjusted the phase of the beam at thousands of points across its width.

If light can do this, what makes you think that 'perfectly straight' would be the natural direction?

I think perfectly straight is natural because that is what we observe in nature. We send light and radio waves into space across vast distances to space probes and planetary landers and they have never been observed to bend. When we point our light and radio telescopes where we expect Mars to be, it's always there, as is the signals from the Mars rovers. If light was bending, we would notice Mars not being where it should, or radio signals from the rovers coming from unexpected directions.

The article you linked is interesting, but there is a note at the end.

However, Michael Berry of Bristol University in the UK, is less so. He believes that the authors do not make it clear that in their experiments they are not bending light rays themselves but the rays’ envelopes, or “caustics”.

It's an interesting effect to be sure, but I don't understand the process enough to really comment further on it yet.  It certainly doesn't demonstrate 'natural' curving. I see no mention of this ever occurring in nature.

[Tumeni]

So it is Imagination Land then. That just creates an assumption that there is a place where there are no forces.

Lets go into Imagination Land and try to get bodies to travel from Point A and Point B in a straight line.

Think of a rocket ship in space that blasts its engines for two seconds:

(You've just applied a force, then....)

What makes you think it is possible to create an engine that fires perfectly evenly from all points? If the engine starts in the slightest manner from one side or gives off the slightest bit of energy on one side then the rocket builds too much momentum on one side and goes spiraling off to one side, either quickly or slowly. It doesn't reach the Point B destination.

(So you design the engine with a gimbal, to vary it's direction of thrust, or add smaller subsidiary engines to direct the craft. All applying forces, so we're no longer in "no-force" land)

The only way to go straight is for the rocket to be constantly controlled and navigated. AKA, an artificial result.

(Or, set it off in the general direction of point B, and modify course as you approach. There is no obligation to complete all thrust and direction control at the start of the flight)

Even in something as simple as the game of Pool, it is rather difficult to hit a ball to go straightly to the Point B hole:
You have to hit it in just the right spot to get it to go the way you want it to go. Luckily in pool you are only shooting a few feet.

What if you are shooting a ball at a Point B hole which is miles away? Ignoring the fact that you don't have the arm strength to do that, and ignoring everything about surface friction, to hit a pool ball perfectly for a distance ranging in miles and get into a hole is still very improbable. The ball is more likely to go off in some random direction.

(Only due to forces acting upon it. Variations in the texture of the cloth surface below it. Billiard cloth has a direction to the woven fibres, the "nap" of the cloth. This affects how the ball behaves. Variations in the slate bed below the cloth. The table not being perfectly level. Wind. All apply force to the ball once it is on its way to the pocket.

So again, straight line trajectories between two points do not naturally occur in nature. They are highly unnatural.

Execute the pool shot on a surface of glass, ice, sheet metal or similar, and it will be far easier to get it to go straight

[AATW]

What makes you think it is possible to create an engine that fires perfectly evenly from all points?

I don't think that. The craft that went to the moon did have to make occasional corrections.
In your analogy sure, if after the rocket fires the craft is not going along the line AB then the craft won't hit point B without correction.
That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.
You are basically asserting that the line AB is the only straight line which is obviously not correct.
Something going along a straight line - or let's put this in physics language, maintaining a constant velocity simply means the speed and direction of the rocket's path do not change without a force being applied.
This is an issue I have with your model of the sun's movements. It means a force will have to be constantly be applied to the sun to keep it moving in a circle and to keep changing the radius of the orbit. And to maintain a constant 24 hour circular period the sun would also have to keep increasing speed...and that increase in radius and speed would have to flip every 6 months so the radius and speed decrease. I don't believe any mechanism to make this happen has even been proposed.

What if you are shooting a ball at a Point B hole which is miles away? Ignoring the fact that you don't have the arm strength to do that, and ignoring everything about surface friction, to hit a pool ball perfectly for a distance ranging in miles and get into a hole is still very improbable. The ball is more likely to go off in some random direction.

Again, the fact the ball doesn't go in the pocket doesn't mean the ball isn't going straight. It just means it's going in the wrong direction.

[edby]

Interesting experiment for Tom's community proposal. What simple experiments would allow us to prove or disprove the hypothesis that light travels in straight lines (or nearly straight lines)?

[Tom Bishop]

That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.

The rocket deviated from the straight line that was defined in the text as Point A to Point B. Therefore it's not going on the straight line. It's just one example that shows that there are too many variables to plan for in order to declare any particular trajectory to be the natural one, even if we use your hypothetical universe without external forces where Newton's laws hold.

If you want to get more real than that, radiation pressure from the craft would cause it to deviate further.

For the Pool Ball, any irregularities in the mass distribution in the ball would also manifest when rolling over miles.

[Tumeni]

That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.

The rocket deviated from the straight line that was defined in the text as Point A to Point B. Therefore it's not going on the straight line.

It's going on a different straight line.

If the marksman aims rifle A at the bullseye B on the target, but someone nudges him as he pulls the trigger, the bullet still goes straight, but straight toward another point on the target, which we can call C.

The fact that the bullet misses B is not a proof of a bendy flight path, it's proof that the aim was adrift in the first place.

[Tom Bishop]

Sure, but I am talking about straight line trajectories between two points:

So again, straight line trajectories between two points do not naturally occur in nature. They are highly unnatural

The (deep space) marksman would have been trying to hit his target. But if he can't hit his target for some physical reason, then his bullet didn't travel on the straight line. If you are trying to shoot straight and narrow through your sights, and you can't, then you didn't shoot straight and narrow.

[AATW]

That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.

The rocket deviated from the straight line that was defined in the text as Point A to Point B. Therefore it's not going on the straight line.

Correct, it's going in a different straight line at a constant speed, just as Newton claimed.
It's not going along the line you defined but so what? You just defined an arbitrary line. There is no "the" straight line.
If the engine fires so the rocket is going along the line AB then when the engine stops the rocket will continue to point B at a constant speed unless any other forces act on it.
If the engine actually pushes the rocket in a slightly different direction then it will be going along a line AC instead, where C is some other arbitrary point.
In that case when the engine stops the rocket will continue to point C at a constant speed unless any other forces act on it.

That's all Newton's law claims.

[AATW]

The (deep space) marksman would have been trying to hit his target. But if he can't hit his target for some physical reason, then his bullet didn't travel on the straight line. If you are trying to shoot straight and narrow through your sights, and you can't, then you didn't shoot straight and narrow.

You understand that the sun isn't "aiming" photons at the earth or moon or anything else, right?
Photons just leave the sun in every direction. Some of those will hit the earth if they're going in the right direction. Some will hit the moon and so on.
You seem to be conflating the ability to aim things perfectly in a certain direction with the assertion that once something is going in a certain direction at a certain speed then it will continue to do so unless acted on by a force. The second of these things is what Newton claimed, the first is neither here nor there.

[Tom Bishop]

That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.

The rocket deviated from the straight line that was defined in the text as Point A to Point B. Therefore it's not going on the straight line.

Correct, it's going in a different straight line at a constant speed, just as Newton claimed.
It's not going along the line you defined but so what? You just defined an arbitrary line. There is no "the" straight line.
If the engine fires so the rocket is going along the line AB then when the engine stops the rocket will continue to point B at a constant speed unless any other forces act on it.
If the engine actually pushes the rocket in a slightly different direction then it will be going along a line AC instead, where C is some other arbitrary point.
In that case when the engine stops the rocket will continue to point C at a constant speed unless any other forces act on it.

That's all Newton's law claims.

My point is that Newton's assumptions are not really applicable in a real scenario. If the goal is to hit something to go to a destination we can't even rely on that.

From a Google Image Search on Newton's first law:



There are so many variables here. Angle of the hit, mass distribution in the puck, friction of the ice. It is more realistic to say that the more variables added into any scenario, the less Newton's laws alone applies. If we believe that the universe doesn't provide Newton's perfect environment and perfect assumptions, then we can't really rely on your statement about "Newton said..."

You understand that the sun isn't "aiming" photons at the earth or moon or anything else, right?
Photons just leave the sun in every direction. Some of those will hit the earth if they're going in the right direction. Some will hit the moon and so on.
You seem to be conflating the ability to aim things perfectly in a certain direction with the assertion that once something is going in a certain direction at a certain speed then it will continue to do so unless acted on by a force. The second of these things is what Newton claimed, the first is neither here nor there.

There are some problems with that:

- Newton was wrong about his straight line particle propagation theory of light (See: Double Slit Experiment). It propagates as a wave.

- It assumes that space is perfectly homogeneous:

https://web.archive.org/web/20200811195324/http://www.tedpavlic.com/post_phil101_uncertainty.php

Author: Dr. Theodore P. Pavlic - http://www.tedpavlic.com/facjobsearch/docs/tpavlic_cv.pdf

Now, the more modern view of quantum mechanics treats photons as particles which carry a probability with them which has both a magnitude and a phase. When photons with equivalent magnitudes and opposite phases "intersect," their probabilities subtract to zero and no photon is detected. Keeping this in mind, understand that light does not travel in straight lines from one point to another. Light travels in all directions through all possible curves and paths from one place to another. In the end, our observations are of where the probabilities "add up," which typically is along a path of a straight line. When light is forced through inhomogeneous space its probabilities cancel in such a way where the curved paths add up or perhaps multiple paths show up.

https://web.archive.org/web/20200811195321/http://www.wlym.com/archive/pedagogicals/light.html

Author: https://www.genealogy.math.ndsu.nodak.edu/id.php?id=43126

Let's try to take on a Newtonian with this:

"So you see, light does {not} travel in straight lines!"

"Yes it does, if you do not disturb it. But by interposing matter, an inhomogenous medium, you deflected the rays from their natural, straight-line paths."

"How do you know that straight-line paths are `natural`?"

"If a light ray were allowed to propagate unhindered, in a pure vacuum or perfectly homogeneous medium, then it would propagate precisely along a straight line. It is just like the motion of material bodies in space according to Newton's first law: `a material body remains in its state of rest or uniform motion along a straight line, unless compelled by forces acting upon it to change its state.` No one could deny that."

"Does a `pure vacuum` exist anywhere in nature? Does a `perfectly homogenous medium' exist in nature?"

"Well no, of course. There is always a bit of dirt around, or inhomogeneities that disturb the perfectly straight pathways."

"So the presence of what you call `dirt` is natural, right?"

"Yes."

"So then it is natural that light never travels in straight-line paths."

"Wait a minute. You are mixing everything up. I am talking about the natural propagation of light, quite apart from matter."

"What do you mean, `quite apart from matter`? Do you assume that the existence of light is something that can be separated from the existence of matter?"

"Yes, certainly. The natural state of light is that of light propagating in a Universe that is completely empty of matter."

"And a completely empty Universe is a natural thing? Do you claim such a thing could ever exist?"

"I could imagine one. Sometimes I get that feeling inside my head."

"Maybe that is because you are not thinking in the real world."

"Don't blame me for that. I am a professional physicist."

"Well then, fill the vacuum in your mind with the following thought: Light and matter do not exist as separate entities, nor does matter act to bend rays of light from what you imagine in your fantasy-universe to be perfectly straight-line rays."

[JSS]

That is not because it isn't going in a straight line, it's because it IS going in a straight line in the wrong direction.

The rocket deviated from the straight line that was defined in the text as Point A to Point B. Therefore it's not going on the straight line.

Correct, it's going in a different straight line at a constant speed, just as Newton claimed.
It's not going along the line you defined but so what? You just defined an arbitrary line. There is no "the" straight line.
If the engine fires so the rocket is going along the line AB then when the engine stops the rocket will continue to point B at a constant speed unless any other forces act on it.
If the engine actually pushes the rocket in a slightly different direction then it will be going along a line AC instead, where C is some other arbitrary point.
In that case when the engine stops the rocket will continue to point C at a constant speed unless any other forces act on it.

That's all Newton's law claims.

My point is that Newton's assumptions are not really applicable in a real scenario. If the goal is to hit something to go straight  to a destination we can't even rely on that.

From a Google Image Search on Newton's first law:



There are so many variables here. Angle of the hit, mass distribution in the puck, friction of the ice. It is more realistic to say that the more variables added into any scenario, the less Newton's laws alone applies. If we believe that the universe doesn't provide Newton's perfect environment and perfect assumptions, then we can't really rely on your statement about "Newton said..."

There is nothing wrong with Newton's laws applying to the real world. He says that without any external forces acting on an object it will continue it's current motion, which is true.

You are right that a hockey puck has plenty of external forces acting on it. Variations of friction on the ice, air currents, the hockey stick not being perfectly flat. But why are any of those a problem for Newton? In the end, we humans have intelligence and free will and can pick up that hockey puck at any time. So no laws could describe it's motion ever because we can always intervene. But Newton's laws still work and are useful, and in the case of picking it up, we still use them.

We can also still use Newton's laws to send spacecraft to Mars and Pluto. We can still send and receive radio signals that go straight from Earth to them. We can still see the planets they orbit or landed on with telescopes, again with straight lines.  If they were not straight they wouldn't match Newton's predictions of their locations. We rely on Newtons laws for a large number of things, including all the satellites in orbit. We very much rely on them, and very applicable in a real scenario.

The real world is complicated and has lots of variables, but if you account for enough variables you can get your predictions as accurate as you need. A hockey player doesn't need to worry about micro-air-currents when he's 10 feet in front of the goal and trying to get the puck past the goalie. There are a million small variables at play, but he doesn't need to know about most of them. He doesn't know the exact temperature of the puck or the ice, but he can still hit it where he wants.

[Tom Bishop]

Even if we only look at the internal variables, if the the mass distribution in a puck isn't perfect, then one side of it has more momentum than the other. That would cause a curved route.

Image:



In a hockey game the puck is likely always curving slightly by some internal or external variable. And manufacturers try to keep the mass in pucks as symmetrical as possible.

Hockey pucks are also unnatural artificial constructs. If we think of something natural like a rock, those are likely to have more mass distribution discrepancies.

[JSS]

Even if we only look at the internal variables, if the the mass distribution in a puck isn't perfect, then one side of it has more momentum than the other. That would cause a curved route.

Image:



In a hockey game the puck is likely always curving slightly by some internal or external variable. And manufacturers try to keep the mass in pucks as symmetrical as possible. Hockey pucks are unnatural artificial constructs. If we think of something natural like a rock, those are likely to have more mass distribution discrepancies.

I still don't see the problem here.

Nothing about hockey pucks not having perfect mass distribution invalidate Newton's laws, or make those laws impossible to use in the real world.

No matter what theory anyone comes up with, the real world will be messy and have lots of variables. A hockey puck is going to be imperfect on a round or flat Earth, imperfect using Newton's laws or any replacements.  Hockey players can still hit them into a net, and we can still use Newton's laws to land robots on Mars and send spacecraft to Pluto and beyond. Clearly all these discrepancies are not a problem or every hockey game would be 0-0 and we wouldn't have pictures of other planets from close up.

[Tom Bishop]

Hockey players can still hit them into a net

It takes practice and skill to become good at hockey. You are describing an intelligent process with your analogies, not nature.

Aiming, controlling, keeping something on course, are all artificial acts of man, and unrelated to whether straight line trajectories between points are or are not natural.

[edby]

Hockey players can still hit them into a net

It takes practice and skill to become good at hockey. You are describing an intelligent process with your analogies, not nature.

Aiming, controlling, keeping something on course, are all artificial acts of man, and unrelated to whether straight line trajectories between points are or are not natural.

Just so I understand, Tom, do you agree with the standard claim that momentum p is a vector quantity and equal to mv, where m is mass, and v is a vector, i.e. a speed in a specific direction? Obviously all objects have forces acting upon them, and so their momentum will change all the time. Is that your point?