The Fundamentals of Gravity: Examining its Place in Nature

[2keyla]

Why is gravity considered a fundamental force and not the production of electromagnetism and weak/strong nuclear forces?

 

[Danger]

Welcome to PF 2keyla.
Gravity is a result of mass, regardless of any other forces. While it is far and away the weakest of all forces, it's the only one that doesn't have an opposing counterpart. That's why it 'governs' the universe. That's just my layman's take on it, though. Wait for an expert to respond with something more tangible.

 

[negitron]

The strong and weak nuclear forces are also only attractive forces, but they operate over very short distances, less than the diamater of an atomic nucleus.

 

[Vanadium 50]

The strong and weak nuclear forces are also only attractive forces, but they operate over very short distances, less than the diamater of an atomic nucleus.

The first part of your statement is not so. The strong and weak forces can be either attractive or repulsive.

 

[negitron]

The first part of your statement is not so.

Strike the weak force, then. I see it is only repulsive. It is true for the strong force, however:

http://www.vias.org/physics/bk4_03_04.html

This force, called the strong nuclear force, is always attractive, and acts between neutrons and neutrons, neutrons and protons, and protons and protons with roughly equal strength.

 

[Vanadium 50]

That site is wrong. The force between nuclei has a repulsive component. This is why nuclei don't get infinitely close to each other, and you can get a hint that the force has a repulsive component because the two neutrons don't stick together.

 

[Gear300]

Why is gravity considered a fundamental force and not the production of electromagnetism and weak/strong nuclear forces?

I'm not sure what experiments were done to exclude gravity from the other fundamental forces, but it might be noteworthy to point out that it is an attraction between masses - meaning that the theory works for measurements of mass. Unless some subtle relation between mass and charge is made, the argument tends to close around gravity being its own force. For a more in depth relation between gravity and the other forces, you'd have to look into higher level theories.

 

[TheDestroyer]

That site is wrong. The force between nuclei has a repulsive component. This is why nuclei don't get infinitely close to each other, and you can get a hint that the force has a repulsive component because the two neutrons don't stick together.

The repulsive nature of strong force at very close distances can be discussed only with quantum mechanics using second quantisation, a fact that those sites can't share. We simply tell you guys that it has such a repulsing component at very short distances, this is (as a simplification) due to the fact that this force is due to the exchange of bosons between those particles, and when the flux of those bosons becomes very high (at small distances) it turns to be repulsive to conserve energy and stability of the matter. I hope this simplifies the matter.

About the gravity being a fundamental force, I can tell you that in General relativity, the only force that bends (curves) the time over space is the gravity and it accepts the equivalence principle, and there is not a reason to consider it as other forces. Actually since it has been discovered that the universe is expanding and accelerating in the expansion, scientists think that the universe should be expanding in constant speed due to the big bang, and because of a repulsion component of gravity (dark energy which is proportional to the cosmological constant) the universe is accelerating. The topic is still under debate.

I hope this answers :), if you look for more details, just ask :)

Good luck :)

 

[Andru10]

Isn't the repulsive nature of the strong nuclear force just a manifestation of the Pauli exclusion principle ? At least that explains why 2 neutrons can't stick together.

 

[TheDestroyer]

Pauli principle applies on energy and momentum spaces, since they are quantised, I don't think it can be applied that way on space.

I forgot to say that strong forces where studied in the idea of exchanging bosons classically by the scientist "Yukawa", he created the potential of the form V(r)=1/r exp(-r/r0). This form is totally classical and doesn't support repulsion.

 

[Vanadium 50]

Isn't the repulsive nature of the strong nuclear force just a manifestation of the Pauli exclusion principle ?

No. I can have two neutrons with opposite spins. Indeed, if there were no strong force, the dineutron would be electromagnetically bound, so the fact that it is unbound indicates that the strong force must have a repulsive component.

 

[2keyla]

This is great. Thanks everyone for your input. I have another related question.

So does gravity have a minimum threshold? That is, does gravity affect atoms?

KG

 

[Andru10]

Gravity is produced and affects anything with mass, so yes, atoms too. In General Relativity gravity isn't regarded as a force but as the geometry of space-time itself. Mass and energy (which are equivalent) curve space-time, and this curvature is gravity.

 

[2keyla]

Then gravity would also exist between an electron's orbit and its nucleus, yes?

 

[Andru10]

Yes, but it's so weak, it's negligible compared to the electromagnetic force. It's negligible compared to all of the other forces. Even the weak nuclear force is 10^25 times stronger. The EM force is 10^36 times stronger than gravity.

 

[nirax]

Why is gravity considered a fundamental force and not the production of electromagnetism and weak/strong nuclear forces?

we believe in evidences. and so far there is no evidence of gravity being a result of smallish electrons ... but all evidence of it being a handiwork of giant galaxies. the day we see that gravity actually is a conspiracy of electrons and protons, we would abandon Newtons /einstiens theory.

 

[Danger]

we believe in evidences. and so far there is no evidence of gravity being a result of smallish electrons ... but all evidence of it being a handiwork of giant galaxies. the day we see that gravity actually is a conspiracy of electrons and protons, we would abandon Newtons /einstiens theory.

 

[emilio_l]

I have a question to:

Why does everybody keeps seeing space as distance?
If you would see space as something that belongs to matter you can solve everything.

The big bang as well as the excellerating expanding of the universe

Space has nothing to do with distance, time has something to do with distance.

 

[Vanadium 50]

Space has nothing to do with distance,

That's nonsense. Distance is how we measure space.

 

[Danger]

That's nonsense. Distance is how we measure space.

Quite right. Space is generally considered to be the 'nothing' between two 'things', although technically those two 'things' occupy the space. I tend to think of it as a lake. If there are two boats, one is inclined to comment about there being a lot of water between them. In fact, though, both of them are in the water. That's a pretty lame analogy, but the best that I can come up with on short notice.

 

[emilio_l]

And that is why you can't explain the growing speed in the expanding of the universe.
And you can't explain what's going on in the very first moment of our universe.

I have a theory that explains everything but you need to let go of the idea that space is distance.

I will show you the mistake that we have been making since the first human looked up in the sky and saw some objects. If you want to ...
This mistake is so fundamental that science people can't see it but children do!

 

[Vanadium 50]

You might want to take a look at the PF Guidelines on overly speculative posts.

 

[emilio_l]

Oops, I saw it and you are right, I am sorry.

 

[2keyla]

OKay... back to my original question as to why gravity is a fundamental force.

I have another question. Let's say I have a box and I fill this box with space-time, the stuff that makes space, and nothing else. There would be no fundamental forces present in this box. Outside the box, I have an electron or proton or neutron. By themselves anyone of these would have a fundamental force associated with them (weak/strong nuclear or EM) BUT alone there would be no gravity. Only when I take the electron/proton/neutron, whichever, and drop it into the box of space-time would there be gravity.

My question is, why isn't space-time it's self a fundamental force and gravity is when gravity requires space-time to exist?

 

[Vanadium 50]

Let's say I have a box and I fill this box with space-time,

That makes no sense. How do you do this? What was in the box before? Imagining a simpler case, how do you fill a box with time? If you have two boxes, which has more time in it?

 

[2keyla]

It's a theoretical box. It could be any size you like. What was in the box prior doesn't change the idea that there's nothing but space-time in the box now.

The idea is that gravity can't exist unless matter and space-time interact.