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# A debate (attempt) about Gravity, what we know (and don't know) and why Newtonian Gravity is 'wrong', and Blackholes.

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8 hours ago, OceanBreeze said:

If you still do not know the difference between G and g you should never be posting about gravity and arguing against current theory. I have more important things to do than spoon feed you theory. Learn to use Google or even better just read a physics book.

And when you post nonsense on this forum there is a very good chance you will get ridiculed for it.

Also, I do know what big G and little g means, and I know that is from Newtonian gravity where gravity is treated as a force, big G is 'unit force per unit mass', and is a constant. Little g is 'how much you weigh', or gravitational acceleration.

Now, you probably know that it is accepted that gravity is NOT a force and although it is close Newtonian gravity F = - Gm1m2/r2, is an approximation, at no scale at all does that equation yield an error of ZERO.

It is a close approximation, that is close but NEVER right.

Newtonian gravity is NOT how nature works, and it is not why things fall.

What that equation and model implies, is that as you increase r, your weight or rate of acceleration decreases, that is not correct.

HOWEVER, in our universe you can consider that in fact you do weigh less because there further you get away from the earth, the less influence of earths gravity you experience, and the more of the rest of the universes gravity.  So sure, if there were only two objects in the universe, the earth and the moon, as you moved towards the moon, you would weigh less on the earth, and more on the moon, get close enough such that the moons gravity is greater than the earths and you have a negative weight on the earth.

But if only the earth existed, and you built a massless tower out to the distance of the moon (static system, no movement), then even at the distance of the moon you would weigh the same, and you would fall towards the earth at 9.8m/s2.

At no distance from the earth (if only the earth existed) would you weight zero, or less than when you weigh at the surface of the earth.

This is why Newtonian gravity cannot be applied to making assumption about what a black hole is, it is a fundamental misunderstanding of gravity.

Also big G is 'amount of gravity per unit mass', considered as a force, although that amount of gravity (little g) is calculated at a 'force at distance' the density of the matter makes no difference, the big G value will never exceed the value based on mass, regardless of how small a value of r for little g.

You have a light source that radiates 100 watts of energy, say the light source if a globe (ball), the amount of light per unit area of that light will never exceed 100 watts, no if you create a shell around that light, the unit area of that shell will in total receive 100 watts, but as the shell is larger the unit area energy will be lower.  This is simple inverse square law.

You are thinking with that black hole model, that if you reduce the volume of that sphere, at some point you will exceed that 100watts (or big G).

But in reality, in the real world, no matter how small you make r, you will only ever get 100 watts.

So no, you do not get lighter the higher you go, the rate of acceleration will be the same in a single earth universe even if you are 10 billion light years away from the earth, you will still weigh 1g and you will still fall towards the earth at 9.8m/s2. It would not make any difference if the earth was the size of the sun or the size of a grain of sand either.

That is only one problem with the Schwarzschild radius, another problem is the limits of the density of matter, there is no indication at all that matter can get any more dense that neutrons or protons packed together with no space between them. Even black holes take up volume, if it is the case that this maximum density cannot exceed the Schwarzschild radius, the no event horizon can possibly occur.

I expect this is the case, you hear statements such as 'Mt Everest' would fit in a tea cup or tea spoon even in a black hole.

Another one, is if you just got all the matter from every human on earth it would be the size of a sugar cube, If you applied that to the entire mass of the earth the volume of that mass would be greater than the volume required for the earth to form a Schwarzschild black hole.

All humans make up enough mass to make a sugar cube, all the mass of the earth would make up millions of sugar cubes, the Schwarzschild radius of an earth mass black hole is about the size of a golf ball.

You therefore cannot create a Schwarzschild radius black hole, because there is a limit on the density of matter, and like speed and temperature it is a universal limit.

So Ocean, this is what a debate looks like, I make points and explain things, I don't insult or act like a child, these are my opinions and take on science, science is not a closed book.  But we do have to work with what we do know because we can speculate on what we do not.

Ocean how about you put this post in the Physics section, so we can debate, actual science, instead of putting this in some backwater that no one will see?

Edited by Mutex
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Newtonian Gravity is wrong: You need to get over it.

Newtonian Gravity is 'descriptive' but not explanatory, it states approximately what happens, but does not even attempt to explain HOW it works.

As such Newtonian Gravity is a good approximation, and perfectly useful for most 'human scale' purposes, but if you were to plot the error that Newtonian gravity has, that error never equals zero.

Newtonian Gravity is not a description of how nature creates what we observe as gravity. This is NOT a controversial issue in science, although having been in use for 300 or so years, it is still very ingrained in current thinking. But it HAS to be understood (if you want to try to understand what gravity actually is), that it is not a correct description of the nature of gravity.

Newtonian Gravity treats gravity as a FORCE, and that this force is created by matter with mass, and influences matter with mass.

When we measured the precession of the perihelion of Mercury, and we (science) determined that the Newtonian equations are wrong (but still a good approximation), science need to explain or develop a model that explains what we observe.

Science is about finding out how the world ACTUALLY works.

Enter Einstein:

Having observed that Newtonian Gravity is wrong (observed not assumed), that opened the door to a different model that explains the interaction of matter that we see as gravity.

Einstein with relativity considered the problem from a fundamentally different perspective, instead of gravity being a force that influences matter at a distance, relativity shows that matter (and gravity) is a process of mass changing some aspect of space, and as different masses share the same space we see an interaction between matter.

However it is a matter to space and space to matter interaction, not a direct matter to matter interaction as assumed by Newtonian Gravity.

Some misconceptions derived from Newtonian Gravity

There has been some discussion regarding 'big G' and 'little g' in another thread that was shut down:

Big G is the 'amount' of gravity a unit amount of mass produces (measured in Newton meter squared / kg squared), it is the 'force' in Newton meters per unit of mass.

Little g, is the 'gravitational force at distance r from the center of mass', little g is what you weigh and it's the 9.8m/s^2, gravitational acceleration.

Misconception 1. (for debate).

Based on this model little g decreases the further away from the earth you get, they you will weigh less, and you will fall slower than 9.8m/s2.

Although in our universe that is the case, we do feel lighter and accelerate slower as we leave the earth, because the further away from the earth we get the closer we are to all the other matter in the universe, and it's gravity.

Thought experiment time:

So can I justify the above claim? Yes I can.

In this thought experiment imagine that the earth is the only object in the universe, no other matter exists, just the earth with the same gravitational conditions that we have on earth today.

This lone earth is stationary and motionless, as will all observers, (no motion is necessary here).

We on this earth build a super tall tower using a massless material, this tower is so high that it would reach to the moon (if there was a moon).

Now according to Newtonian gravity, as you climb this tower your weight (little g) would reduce with the inverse square law, at some point you would be 'weightless'.

However, in the real world, no matter how high the tower and where you are at it, if you put down your scale you would weight exactly the same as on the surface of the earth. What's more, if you jumped off the tower you would fall to earth and accelerate at 9.8m/s2.

If your tower was 10,000 light years high, it would make NO difference, you would weight the same!

If you are at the top of this 10,000 light year high tower, it is immaterial to you what the diameter of the earth is, it makes no difference at all to you, and you would not detect ANY difference if it was the size of the earth or the size of a grain of sand.

Orbits:

All you need to do to achieve an orbit around this round earth is the achieve a sufficient horizontal speed such that by the time you fall directly down at 9.8m/s2, you move sideways enough to miss the earth.

That means the further you are away from the earth the slower you need to go horizontally to miss the earth, so if it takes you 10 hours to fall to the earth, and you have to miss the center point by 1000km, then you need a horizontal velocity of 100km/h to miss the earth, the higher you are the lower the horizontal velocity you need.

So with Newtonian gravity the higher the distance r you have the slower the horizontal velocity you require.

The confusion with black holes and the Schwarzschild radius is that by tying G or g with mass density you are effectively reducing distance r to zero and assuming that orbital velocity is infinite or at least exceeds c (the speed of light).

But if you compress the matter to a small volume, the distance you need to travel to go over the horizon is also much lower, so you see even the incorrect Newtonian model fails.

Nature has its limits:

Highest speed, lowest temperature, maximum density!

That is another problem with Schwarzschild black holes, is the maximum density of matter, you cannot get matter any more dense that protons, neutrons and electrons touching each other, with no space between them.

We know for a fact we cannot put matter in the same space as other matter, (CERN would not work, and/or would produce micro black holes in vast quantities, CERN works and does not produce black holes).

So if the maximum density of matter exceeds that required to achieve a Schwarzschild radius, than an event horizon black hole can never form.

Some rough 'rules of thumb' about the maximum density of matter, is done in examples, such as Mt Everest would fit in a tea spoon, or if you took all the matter of every human on earth and took out the space, it would have the volume of a sugar cube (1cm^3).

The Schwarzschild radius of the earth is about the size of a golf ball, if all the humans on earth make a sugar cube, then all the mass of the earth take a volume much greater than a sugar cube, or a golf ball.

Relativity: (general)

Relativity has the opposite problem to Newtonian Gravity, Newtonian Gravity treats gravity 'as if' it is a force, Relativity treats it like a modification of space and time.

Where Newtonian gravity is descriptive (it says what approxitemly happens) it does not describe how it happens.

Relativity is explanatory and not descriptive (clearly descriptive).

We cannot use geometrical relativity to explain WHY a rock you picked up falls to the ground when you let it go.

It often said by science we don't really know how gravity works!

I do have a model that agrees with relativity that does explain, using relativity, why a rock falls to earth and why we observe what we do about space and time (tests of relativity). But that will be the subject of another post, assuming this post prompts some mature debate

I hope I do not see replies alone the line of 'you are wrong, because we do it this way'.

Will this forum actually promote and contribute to reasoned debate, or fall into name calling, thread closing or banning?

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Moved to silly claims. Read a Physics book and stop posting complete nonsense on this forum.

For example this is total rubbish: "However, in the real world, no matter how high the tower and where you are at it, if you put down your scale you would weight exactly the same as on the surface of the earth. What's more, if you jumped off the tower you would fall to earth and accelerate at 9.8m/s2"

If you continue to post rubbish on this forum and then complain when it is justly ridiculed, you can expect to have your posting privilege taken away.

This is the last warning. The next offense will result in a ban.

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OK, I see there is no point at all in trying to make this a decent forum, at least as long as you are here as a moderator.

So, I also note you threaten your mod ban, again, as expected.

So be it, clearly you don't want this forum to go anywhere, it's shame too..

Ok, Good bye.

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