Gravity Bends spacetime

[ryan2006]

Why is energy balanced because in all things harmony is essential. What would alter the balance of the end result of your equations?

[Boerseun]

Why is energy balanced because in all things harmony is essential. What would alter the balance of the end result of your equations?

Wrong thread... I think :beer:

[IDMclean]

I ask simply, what then is a blackhole? Such that it pulls an apparently "massless" object into it. A photon is only massless when it is at rest, a photon is never at rest so therefore a photon has mass and curves spacetime. This is basic GR and SR. Einstein himself describes the curviture of spacetime in terms of charge. GR and SR arise out of Maxwell's equations and Lorentzian laws. Tell you what I'll back this up as soon as I can find the GR and SR papers.

 

What I know (only in that I don't know everything) is that mass in GR and SR is described in terms of charge. that though the dimensions cancel out, the photon in it's basic definition is a charged body. Neutral yes, without absolute charge? No.

[Erasmus00]

Einstein himself describes the curviture of spacetime in terms of charge.

 

No he doesn't. In Einstein's field equations the sourcing term is the stress-energy tensor which doesn't require charge at all. Yes, SR was originally derived in the context of electrodynamics, but there is no need to develop it as such, considering it is essentially a theory of mechanics.

 

What I know (only in that I don't know everything) is that mass in GR and SR is described in terms of charge. that though the dimensions cancel out, the photon in it's basic definition is a charged body. Neutral yes, without absolute charge? No.

 

What then is the difference between having charge and having "absolute charge"? What is this distinction you are making? Rest mass in GR and SR is not defined in terms of charge, but is a parameter that has to be put in by hand.

-Will

[IDMclean]

It goes like this:

If I have charge and it relates in such a way as to additive then the relation will show like this:

1 + 1.

If I have charge and it relates in such a way as to be subtractive then the relation will show like this:

1 - 1.

If I have charge and it relates in such a way as to be equal but opposite, then the relation will show like this:

1/1.

 

Opposite in physicallity in my particular interpitation. That is that the Earth is opposite to the sun, or the moon opposite to the earth.

 

in the [math]c^2 = \frac{1}{\epsilon_0\mu_0}[/math] equation the units of charge are related in such a way as to suggest EQUAL but OPPOSITE relationship. This to me, according to Newtons Laws of Motion, Maxwell's Equations (All of them Laws) and Lorentzian Force Law, suggest that we have a two body system defining an apparent single body system. I could be absolutely wrong, I will admit, but I basis my assumetions out of the physical laws.

 

Therefore if we can express through Lorentz Force Law:

[math]F = q(E + \frac{v}{c}B)[/math]

and

[math]\sum F = ma[/math]

then

[math]\sum F = q(E + \frac{v}{c}B) = ma[/math]

 

This is just my two cents, and my interpitation of the given set of laws.

[Jay-qu]

photons dont need mass to be affected by gravity, because gravity is the curvature of space time, and they are affected by the curve.

[IDMclean]

Mostly correct jay-qu. Except that you forget Einstein's tensor. Spacetime tells energy how to move and energy tells Spacetime how to bend. if you have zero energy then you have zero spacetime ripples, and zero anything. Quantum mechanics precludes this, as such Photons have energy and bend spacetime.

[dagaz]

just for clarification, gravity doesnt cause spacetime to curve, gravity is the curving of spacetime :lol:

 

OK, in my head I can allow for this explanation of gravity causing circular (elliptical) orbits of bodies around stars, planets, etc. What I find hard is using this explanation to explain how when I drop my pen it falls straight to the ground. I know how Newtonian mechanics can make sense of this but have trouble applying relativistic gravity to a small, localised effect.

[Jay-qu]

It may be helpful to think of space having an extra dimension that this curving happens in, although not entirely correct, it may help you wrap your head around it a little more.

[Qfwfq]

A photon is only massless when it is at rest, a photon is never at rest so therefore a photon has mass and curves spacetime.

Remeber that, in modern (Lorentz-covariant) terms, only rest energy is called mass and not kinetic energy. A photon has only kinetic energy and no rest energy, hence it is massless.

[EWright]

OK, in my head I can allow for this explanation of gravity causing circular (elliptical) orbits of bodies around stars, planets, etc. What I find hard is using this explanation to explain how when I drop my pen it falls straight to the ground. I know how Newtonian mechanics can make sense of this but have trouble applying relativistic gravity to a small, localised effect.

 

It may be helpful to think of space having an extra dimension that this curving happens in, although not entirely correct, it may help you wrap your head around it a little more.

 

Additionally, try not to relate this curvature to the planetary orbits you are familiar with. Instead, think of gravitational attraction being toward a sort of point toward the center of the gravitational source. In this way the closer to the soarce you are the more direct the direction will be.

 

Why then aren't planets attracted directly toward the sun, or sattelites toward earth? They are. However, they are caught in a sort of balance balance between this inward attraction and the outward pull of their force of motion. In essence, they are continually falling around the source of gravity. This is why the objects must be in motion or orbits. If you dropped the pen you mention from the right height, in the right direction and with the right speed, its path would curve and it would orbit the earth (but you'd need a really high stool to accomplish that).

[Jay-qu]

yeah I get all that yadda yadda - whats interesting is talking about why gravity does what it does! and the implications of some of its said properties!

[sebbysteiny]

suggest EQUAL but OPPOSITE relationship. This to me, according to Newtons Laws of Motion, Maxwell's Equations (All of them Laws) and Lorentzian Force Law, suggest that we have a two body system defining an apparent single body system. I could be absolutely wrong, I will admit, but I basis my assumetions out of the physical laws.

 

Therefore if we can express through Lorentz Force Law:

 

and

 

then

 

 

This is just my two cents, and my interpitation of the given set of laws.

 

You have misunderstood the equation, sorry.

 

Magnetism (ie the B field) is the effect caused by a current (ie it goes around a wire of electricity). However, a current is just a FLOW of charge, ie it is charge moving. It stands to reason therefore that if you move in the same frame as the moving charges ie at the same velocity, the magnetic field will decrease to zero and you will be left with just a stationary electric field.

 

Basically, magnetism IS an electric field, but just the effects one sees in a different frame of reference. Travel at a volocity of 0.99c and you will get a completely different magnetic and electric field value.

 

The equation you have quoted is just the general relation between magnetic fields and electric charge that holds in all frames. It is just special reletivity applied to E and B fields and has zero to do with gravity.

 

 

 

 

As for 4 dimensional curviture of spacetime causing things to appear as if they are falling towards us, I'll try and explain it the way I see it.

 

When things fall, it is actually just staying in a 4d straight line (ie a geodesic). It is US, the observers that are accellerating towards it. Every second we push ourselves up from the ground with our legs is one seconds worth of accelaration we do from one geodesic to the next. So things don't fall towards us, we accelerate towards them. Everything, if no forces act on it, simply follow a geodesic in space time. Although it looks like things stay in a straight line once in motion (which is true) when you bend the universe in space and time, that straight line appears to be an orbit to people thinking in 3 dimensions.

 

As for the question about whether light can escape from this universe. No. Neither can we. Just like if you keep walking from the any point on the earth in an apparently straight line (a geodisic), you arive back where you started, if you travel far enough along a geodisic anywhere in the universe you return back to your initial position.

[IDMclean]

Magnetism (ie the B field) is the effect caused by a current (ie it goes around a wire of electricity). However, a current is just a FLOW of charge, ie it is charge moving. It stands to reason therefore that if you move in the same frame as the moving charges ie at the same velocity, the magnetic field will decrease to zero and you will be left with just a stationary electric field.

 

Quite Clever my friend, but you miss a few parts. I use the set of Maxwell's equations which are setup for monopoles.

 

 

 

Gauss's law:[math]\nabla \cdot \mathbf{E} = \frac{\rho_e}{\epsilon_0} [/math]

 

Gauss' law for magnetism: [math]\nabla \cdot \mathbf{B} = 0[/math]

 

Faraday's law of induction: [math]\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t}[/math]

 

Ampère's law

(with Maxwell's extension): [math]\nabla \times \mathbf{B} = \frac{1}{c^2} \frac{\partial \mathbf{E}} {\partial t} + \mu_0 \mathbf{J}_e[/math]

 

Gauss's law:[math]\nabla \cdot \mathbf{E} = \frac{\rho_e}{\epsilon_0}[/math]

 

Gauss' law for magnetism: [math]\nabla \cdot \mathbf{B} = \mu_0 c \rho_m[/math]

 

Faraday's law of induction: [math]\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t} - \mu_0 c \mathbf{J}_m[/math]

 

Ampère's law

(with Maxwell's extension): [math]\nabla \times \mathbf{B} = \frac{1}{c^2} \frac{\partial \mathbf{E}} {\partial t} + \mu_0 \mathbf{J}_e[/math]

 

You'll notice something subtle. Take a look at the B portion of that all.

[sebbysteiny]

Seriously, Maxwells equations are not relativistic equations. They work but only in one frame. In another frame, the E and B field changes. The equation you gave is just Maxwells equations for special relativity, if I remember right. It still has nothing to do with general relativity and the explanation of gravity.

 

I can't quite work out what you mean by "You'll notice something subtle. Take a look at the B portion of that all."

 

I've used those equations left right and centre so I should understand them quite well. I doubt I've missed anything 'subtle'. Please, oh wise one. I have subjected my ideas to scrutiny, and I invite you to do the same.

[IDMclean]

I did not present the text book equations.

 

You'll notice that B does not equal zero.

[sebbysteiny]

I did not present the text book equations.

 

You'll notice that B does not equal zero.

 

Yes you did. The text books name is Electricty and Magnitism by Bleany and Bleany.

 

And what do you mean "B does not equal zero"???? That makes no sense. If there is a B field, B will be non zero. Where there is no B field, the above equations give zero. Further, these are differential vector equations only. The solution is not as simple as you are making out and will depend entirely on the variables of the particular problem. Lastly, there is a good reason that magnetic monopole equations are ignored generally: they have never ever ever been observed. And even if they did, special relativity will not break down like you are trying to suggest. Magnetism and electric fields are and forever will be one and the same effect.

 

I do wish you would actually make an effort to understand the equations you quote before patronising those that have a thorough grasp of the subject.

 

If you actually have a point that is supported by the equations, make it.