How the Universe got its Spots...

[FreakBoy]

I'm reading the book "How the Universe got its Spots" by Janna Levin right now. Its an interesting read and she put forth an analogy I hadn't encountered before.

She suggests, using General Relativity, that matter and gravity are similar to electricity and the electric field. Her analogy says that just as electricity creates the surrounding electric field proportional to the charge(?), that matter creates gravity proportional to its mass (as its charge in the aformentioned meaning).

Is this an accurate description? If it is an accurate description then it provides a question. As electricity flows it creates a magnetic field perpendicular to the electrical field. Would matter, creating it gravitational field, then create a perpendicular expression of time?

I understand that gravitation/acceleration creates dilations of time, and we experience time in all points where we could be to have a clock to measure intervals of time.

We can only experience and measure intervals of time in any place where we have matter that gives us a method of measuring time. Quantum mechanics suggests that the constant creation and annihilation of virtual particles would mean that there is always "some" matter everywhere which would affect the intervals of time measured... so if there was hypothetically no matter in a specific area and we had a way of measuring time without placing matter in this void, would there be no time?

hrmmmm trees falling making no sound?

 

[Stimpson J. Cat]

FreakBoy,

Is this an accurate description? If it is an accurate description then it provides a question. As electricity flows it creates a magnetic field perpendicular to the electrical field. Would matter, creating it gravitational field, then create a perpendicular expression of time?

Sort of.

One thing you should keep in mind is that there really is no distinct electric and magnetic fields. There is only the electromagnetic field.

When charges are not moving, the field is just given by the ordinary inverse-square law for electric fields which we learn about in basic physics. When they start moving, the equation gets more complicated (thanks to special relativity).

At small velocities (compared to the speed of light), we can easily approximate this as having the ordinary electric force, plus an additional small force perpendicular to it, which we call the magnetic force. At higher velocities, we can no longer use this approximation, and must switch to the full relativistic equation for electromagnetism.

Similarly, when masses are not moving, gravity conforms to the well-known inverse-square law. Again, for low velocities, the perturbations can be conveniently regarded as an additional small force perpendicular to the normal force. This has to be taken into account, for example, when looking at the orbit of Mercury.

At higher velocities, this no longer works, and you have to switch over to General Relativity.

Also, both electromagnetism and gravity become more complicated at high energy densities.


The main difference is that with gravity there is only one charge. This makes the analog of magnetism much harder to detect. Magnetism is usually orders of magnitude weaker than the electric force, but we can cancel out the electric field by combining positive and negative charges. This cannot be done with gravity. The only way I can think of would be to build a gigantic hollow sphere, and then spin it. The gravitational force inside the sphere would completely cancel out according to the inverse-square law, so all that would remain would be the relativistic perturbation (gravitational magnetism).


Dr. Stupid

 

[BillyJoe]

Stimpy,

Looooooooong time! Howdy.

Similarly, when masses are not moving, gravity conforms to the well-known inverse-square law. Again, for low velocities, the perturbations can be conveniently regarded as an additional small force perpendicular to the normal force. This has to be taken into account, for example, when looking at the orbit of Mercury.

I have heard about the perturbation in the orbit of murcury confirming Einstein's General Relativity. But what is this "small force perpendicular to the normal force" and what is it an approximation of in General Relativity?

The only way I can think of would be to build a gigantic hollow sphere, and then spin it. The gravitational force inside the sphere would completely cancel out according to the inverse-square law, so all that would remain would be the relativistic perturbation (gravitational magnetism).

Why do you need to spin the hollow sphere? If it wasn't spinning, would there be a "relativistic perturbation"?

thanks,
BillyJoe

PS: It could be relevant in a UFO/anti-gravity discussion I am having elsewhere.

 

[Iamme]

The moon does not spin on it's axis. Don't ask me what that means. Just trying to help.

 

[Dorian Gray]

The moon does not spin on it's axis. Don't ask me what that means. Just trying to help.

Yes, it does. The Lord helps those who help themselves - so go help yourself to a textbook.

 

[BillyJoe]

Yes, it does. The Lord helps those who help themselves - so go help yourself to a textbook.

Yes, it does. One rotation for each revolution around the Earth, which is why we see only the one face of the Moon from Earth.

(Perhaps the mental picture is too much for Iamme )

BJ

 

[Tez]

FreakBoy,

This cannot be done with gravity. The only way I can think of would be to build a gigantic hollow sphere, and then spin it. The gravitational force inside the sphere would completely cancel out according to the inverse-square law, so all that would remain would be the relativistic perturbation (gravitational magnetism).


Dr. Stupid

I think gravity probe B is meant to be looking for this "gravitomagnetic" effect from the earth's rotation. Though as you say its gotta be very, very small...

 

[FreakBoy]

Thank you for the responses. As I understand from the responses, gravity is the perpendicular portion of the matter/gravity relationship.

What about the effect of virtual particle pairs being created and anihilated on time dilation? Would there conceivably be a measurable difference between standard "empty" space and a hypothetical area of space where there was no matter and no virtual particle pairs doing their standard thing?

 

[FreakBoy]

Nothing?

Virtual Particles or not, I would have expected that even their very temporary status would have some type of gravitational effect. Is this considered to be so?

 

[DrMatt]

Nothing?

Virtual Particles or not, I would have expected that even their very temporary status would have some type of gravitational effect. Is this considered to be so?

Um, they exist within limits set forth by Heisenberg. Off the top of my head I believe that means they can't exchange particles with anything--unless you peel one off using a black hole. So, most of the time, nothing.