What hold galaxies together?

Seems like we circle back to Newton and the description of gravity as an attraction.

 

Not sure what you need to add. The article says it all.
Nice one.

 

It needs dissection.

 

The article has needs?

 

Yup, but not just at low velocities either. That's why the acceleration due to gravity causes different masses to accelerate at the same rate.
If gravity was a force it would cause objects of different masses to fall at different speeds. Remember Galileo's experiment from his tower, and Scott's experiment on the moon?

 

Have you not learned about Newton's formulae? They pretty clearly explain that phenomenon.

 

Yes, that gravity is an acceleration.
If gravity was a force, then objects of different masses would accelerate at different rates. The fact that falling objects of different masses accelerate at the same rate demonstrates, in Newtonian mechanics, that gravity is an acceleration, not a force.

 

Newton's Law of Universal Gravitation:
F=G(M•m)/r²
where F is the gravitational force acting between two objects, M and m are the masses of the objects, r is the distance between the centers of their masses, and G is the gravitational constant.

You see, the smaller the mass, the smaller proportional force of attraction. Combine this with F=ma and it takes more force to accelerate a more massive object. The heavier object requires more force to achieve the same acceleration as the lighter object. Luckily, Gravity adjusts naturally to maintain an equal acceleration. You want math that proves it? Try it out. It works. Massive or small, acceleration is the same between two objects being influenced by the same large 'M' where M's inertia is so large as to not be influenced by the inertia of m. Where M is influenced by m, the closing acceleration would still be equal, just not m's acceleration taken alone.

You can call it an acceleration without a force, if you like, but the math works if you translate it into a force.

F/m2 = (G(M•m)/r²)/m = a

Note, 'a' is not constant here. 9.8 m/s² is only a reasonable rate when the change in r is insignificant. Within the atmosphere of the Earth, compared to the radius of the Earth, ∆r is small enough to ignore.

-Will

 

Okay, let me see if I understand what Cornell is saying.
#1 "It turns out that there are two cases where this description of the effect of gravity gives vastly different results compared to the concept of gravity as a force." There are two unique cases that don't fit Newtonian mechanics for gravity. Sounds easy enough. I just need to learn about these two cases.

As I understand it, the majority of scientists consider the photons massless. However, there is some debate and the mass of a photon has been measured based on its inertial influence on physical objects. Photons have inertia and can push on other objects.
I wonder about a phenomenon that is described as both a wave and a particle. Is the zero mass proven or is it theory to make General Relativity work?

Next is

From what I gather by this statement is that, classical mechanics did describe this phenomenon. The problem was that it involved the use of the law of conservation of energy to account for the loss of radio active particle energy. This is an aspect of light Newton wouldn't have known about, yet could be treated separately because it doesn't fit into the model of gravity as described by Newton. So... does the law of conservation of energy work with massless particles? Does it matter if the particle is massless? Why is it a problem to use a different physical law when it is discovered there was an unknown and unique property to a light particle? This is fine though. I can accept this, since I am being told that General Relativity accounts for this attribute and phenomenon. It's about the math, right?

Then there's,

Again with the massless particle. Add to that, the concept of black holes were a predicted construct from a theory and all we have for their evidence are observations of celestial movements around areas of space we can't see into. A theory supporting a theory that predicted the theoretical. And yet, it is also the case that Newtonian mechanics works too, as long as you were to consider light to have mass.

Hey, here's an idea. What if light did have mass? Would the amount of light in the Universe be enough to account for the same gravitational force we invented dark matter to hold galaxies together? But no. Mass is not what holds galaxies together because gravity is not a force. So why invent something that we then discount? As the lessons on GR states, mass is not included in GR Gravity (curved space/time).

I hope you can see why I'm hung up here. It doesn't make sense and seems to have conflicts and paradox built into the explanation. I will admit the the math works.

-Will

Stay tuned for my complaint about the rocket analogy.

 

I have needs.

-Will

 

Who has ever claimed that gravity is A force. It is proportional to the masses involved so the acceleration is the same for different masses.

What are your thoughts on Modified Newtonian dynamics?

 

I have been reading "The Janus Point" By:
(Julian Barbour) A theoretical physicist that argues the second law of thermodynamics has been misapplied and that the growth of order determines how we experience time/space.

We tend to look at the 2nd law as some atoms in a cylinder if instead we look at it as a Locomotive we see it is much more complex the same with gravity/time dial
The box is misleading and can throw one off the track.
Its about the (Locomotive Breath)
"God has stole the handle and the train won't stop going no it won’t slow down"
Jethro Tull

 

Why the concentration on the indefinite article?

What is "proportional to the masses"?

I'm not familiar with that.

 

Happy holidays all.
And, for all you here in the New World, Happy Thanksgiving.

-Will

 

Happy Thanksgiving to you and yours!