# Gravity - Electric Force questions

1. Mar 28, 2005

### StirlingA

I apologize if this question has been asked before. Also, please bear in mind that I'm a sophmore Mechanical Engineering major. So, I was thinking that the equations for Electric Force and Gravity are so similar, there must be something to that. Is it possible that there is no such thing as gravity? Perhaps atoms are not EXACTLY nuetral. Could it be theorized that there is only Electric force which attracts all bodies, be it electrons and protons, to planetary objects... What makes me think all of what I just wrote is complete hogwash is that there is no repulsive force of gravity, that I know about.

In any case, I would like to hear your opinions, and knowledge on this matter.

Thank you,
Stirling

2. Mar 29, 2005

### whozum

If you are theorizing the electromagnetic force and gravitation force are one forth then you are getting into "Theory of Everything" domain. There are theories that propose this.

The inverse square law, which is what Im assuming you are basing off of, runs in many other aspects of physics also. However, gravity and electromagnetics operate on two different physical entities, charge and mass. To say they are the same force is to say that charge and mass are the same.

3. Mar 29, 2005

### Aki

Gravity can actually be repulsive. Gravity doesn't just depend on mass and distance, but it also depends on pressure. If the pressure is negative, then gravity then becomes repulsive, and that's basically what contributed to the early expansion of our universe according to the inflation cosmoslogy.

4. Mar 29, 2005

### rbj

they're not the same the thing and the most fundamental eqs. describing gravity is General Relativity (Einstein's field Eq. etc.) whereas the equations describing E&M are Maxwell's Eqs. but there are a couple of papers that have shown that in reasonably flat space-time that derive a set of Gravito-Electromagnetic equations that look exactly like Maxwell's Equations except that charge density is replaced by mass density and $\epsilon_0$ is replaced by $$1/(4 \pi G)$$. both have the same speed of propagation, $c$.

r b-j

5. Mar 29, 2005

### Crosson

Gravity accelerates all massive bodies at the same rate.

The acceleration due to an electric field is proportional to charge/mass.

This is not explainable using your (original, but incomplete) theory.

6. Mar 29, 2005

### dextercioby

Electromagnetism is quantized by spin 1 particles,while gravity by spin 2 particles...That is a major difference,where it matters,namely at quantum level.

At classical one,sure,u can draw some paralles between the 2 theories (see em waves vs gravitational waves),but at quantum level,things are different.

Daniel.

7. Mar 29, 2005

### StirlingA

The equations I was reffering to was $$F = G (m_1*m_2) / (d^2)$$ and $$F = k_e (q*Q) / (d^2)$$. Thank you all for your responses, while I don't quite understand half of your responses... we haven't reached the quantum level in our class yet. All I know about quantum mechanics is from The Elegant Universe PBS special. Anyhow, thank you for taking it seriously, even if it does prove to be completely unfounded.

8. Mar 29, 2005

### p53ud0 dr34m5

i could not agree more. the only way i deviate from your perception is that i view gravity as a whole to be a pressure gradient. it just makes more sense to me that way. with it being a pressure gradient, density would be the main factor, but that's just how IIIIII think.

arent gravitational waves just theory. they have yet to be proven, right? i doubt their existance, but oh well. yea, in theory they are quite comparable. and in theory, doesnt em waves and gravitational waves travel at the same speed?

9. Mar 29, 2005

### dextercioby

They do travel at "c",and i think there have been built a lotta of detectors worldwide.
Incidentally,the theory predicts there existence since 1916 (an article of A.Einstein on linearized GR).

Daniel.

Last edited: Mar 29, 2005
10. Mar 29, 2005

### p53ud0 dr34m5

any "success" in detecting these gravitational waves?

11. Mar 29, 2005

### dextercioby

12. Mar 29, 2005

### dextercioby

Nope,nothing so far.U can browse the internet for "gravitational waves detection"...I did.

Daniel.

13. Mar 29, 2005

### roger

whats the difference between spin 1 and 2 ?

could you explain in detail please.

14. Mar 29, 2005

### dextercioby

Wrt the restricted Lorentz group,obviously tensor structure.However,both system are 1-st class.Both particles (the photon & the graviton) have 2 degrees of freedom,but the tensor structure & the gauge algebra determines their coupling to matter,implicitely their interactions.

Nice treatments are found in Ramond's book [1] and in Kleinert's book [2].

Daniel.

------------------------------------------------------
[1] Ramond,P. "Field Theory:A Modern Primer" (second ed.,1989).
[2] Kleinert,H. "Quantum Field Theory and Particle Physics (draft,2002).

15. Mar 29, 2005

### reilly

Both basic gravity and electric fields go as 1/R*R, but the analogy ends there, as people have already noted. The fancy folks say that these basic fields obey the Poisson Eq. When, however, you get into dynamics, gravity and electricity go in different diretions -- there's really nothing like a magnetic field in the realm of gravity.
Regards,
Reilly Atkinson

16. Mar 29, 2005

### p53ud0 dr34m5

the only similarity that i can think of is what reilly said. well, actually reilly was talking about fields. im pretty sure those differ from the force in concept. maybe im wrong. :rofl: but both forces do follow the inverse square law. the force that one particle or one charge exerts on another is spherical. this force loses intensity as you move away from the point source of the sphere. im sure thats obvious.

17. Mar 29, 2005

### dextercioby

It is,what Reilly said,is that classically,those static fields are almost the same.Once u consider time dependent em & gravity fields,they differ substantially.

However,i stated that em & gravitational waves share similar properties...Polarization states & speed of propagation.

Daniel.

18. Mar 30, 2005

### rbj

not true.

it is predicted with GR but it is (or will be) very hard to measure since, in the human scale of things, gravity is a very weak force.

just like magnetic effects can be describe solely in terms of electro-static forces and the effects of special relativilty, so the same thought experiment would predict gravito-magnetic effects from the static gravitational force with the effects of special relativity considered.

please google the term "gravitoelectromagnetism" or "gravitoelectromagnetic" and see what you get. would you like me to find and post references to the papers that derive (from GR) a corresponding set of Maxwell's Equations (called GEM equations) that have a "B" field for gravity?

r b-j