Magnetism and Gravity Discussion/Questions

[Sterkx]

TL;DR Summary

Questions and discussion on magnetism and gravity.

Hi all,

I've recently become transfixed with the idea of magnetism and gravity.
I have two main questions I'd like to see discussed more.

1. Would it be possible to harness magnetic fields for energy on earth/for acceleration between planets?
1a. Has this been studied at all?

2. Why do we understand so little about a fundamental force like gravity and are there any good resources for learning more about what we do know?

Any answers/discussion on these questions from anyone at all would be awesome to see because as I said I have become very intrigued by the idea of using magnetism more/wanting to understand gravity more.
Thanks

 

[FactChecker]

1) It is not clear what you are asking. Are you asking about using the magnetic field of one planet to attract or repel another planet?
2) Gravity is a subject of Einstein's General Relativity. There is a great deal known about it, but it is a very advanced subject. Essentially, mass and energy warp space-time which causes the effect of gravity. With the warped space-time, gravity is only the tendency of a body to continue in a straight (geodesic) path.

 

[Sterkx]

1) It is not clear what you are asking. Are you asking about using the magnetic field of one planet to attract or repel another planet?
2) Gravity is a subject of Einstein's General Relativity. There is a great deal known about it, but it is a very advanced subject.

1. No, I'm more asking if it's possible to accelerate a craft by repelling it from a planet/object that exerts a magnetic field.
2. It seems like anything I find online says it's based on observations, I'm more asking what causes gravity and how I can learn more about that.
Edit:
2a. So theoretically would Earth have an effect on every other object in the universe (albeit a small one)

 

[FactChecker]

1. No, I'm more asking if it's possible to accelerate a craft by repelling it from a planet/object that exerts a magnetic field.
2. It seems like anything I find online says it's based on observations, I'm more asking what causes gravity and how I can learn more about that.

Essentially, mass and energy warp space-time which causes the effect of gravity. With the warped space-time, gravity is only the tendency of a body to continue in a straight (geodesic) path.

 

[Orodruin]

No, I'm more asking if it's possible to accelerate a craft by repelling it from a planet/object that exerts a magnetic field.

Do you mean like this?

 

[Sterkx]

Do you mean like this?

Sort of, that just seems to replace the wheels of a train with magnets and work that way, it doesn't seem to use the Earth's magnetic field itself.

 

[Orodruin]

The Earth’s magnetic field is way too weak to do anything similar.

 

[Sterkx]

The Earth’s magnetic field is way too weak to do anything similar.

I mean as another means to have constant acceleration. No matter how small. Constant acceleration is constant acceleration.

 

[Ibix]

I mean as another means to have constant acceleration. No matter how small. Constant acceleration is constant acceleration.

The intensity of the field drops off rapidly with distance, and is tiny near the Earth's surface anyway. Think about a compass - look how light and carefully balanced the needle has to be to be any use. You can knock it out of line with almost no effort, and you couldn't do much to a rocket with similar effort. And the force would be weaker in orbit and utterly negligible long before you get to the Moon, let alone another planet.

Regarding gravity, what do you want to do? If you want to learn facts about it, something like Kip Thorne's Black Holes and Time Warps is pretty good, although it's from 1994 so doesn't cover the most recent developments like Gravity Probe B and LIGO.

If you want to be able to actually use the theory you need a proper textbook. You'll need to learn Special Relativity first, much of which is in reach with high school maths. You'll need to be very confident with calculus to move on to General Relativity, which is our current theory of gravity, but there are a lot of resources online to help. For SR, I'd recommend Taylor and Wheeler's Spacetime Physics, now a free download from Taylor's website if you don't want a paper copy. Others here prefer Morin's Relativity for the Enthusiastic Beginner.

 

[FactChecker]

I mean as another means to have constant acceleration. No matter how small. Constant acceleration is constant acceleration.

The next question would be whether the extra weight, cost, and maintenance are worth the "no matter how small" acceleration.

 

[Vanadium 50]

Given that there's not even constant acceleration, probably not. This thread is based on a lot of assumptions that are untrue.

 

[Ibix]

What if there is no gravity in earth?

That question translates to "what if physics were completely different?" It doesn't work that way - you can't just say how things aren't, you have to say how they are. You need to define a self consistent mathematical model of physics that doesn't include gravity but does give some reason for why, when I let go of a ball, it falls.

Note that actually providing such a model would be against the rules here - we only discuss mainstream physics here.

 

[berkeman]

What if there is no gravity in earth?

There is one place "in Earth" where it is zero. Can you guess where that is?

 

[Ibix]

There is one place "in Earth" where it is zero. Can you guess where that is?

...but note that the gravitational potential there is not the same as at infinity, and this has detectable effects. So (depending on what you mean by "gravity") one could make the case that there is gravity there even if the force is zero.

But maybe you are right and the question does have an interpretation that is answerable - let's see what @JOYDIKOSTA says.

 

[Orodruin]

If there was no gravity the Earth would not exist in the first place.

 

[Ibix]

No structures like galaxies, stars and planets would have formed since that was all driven by gravity. It isn't even obvious that you can have a universe without gravity, since it's the geometry of spacetime and without spacetime it's not clear anything else can exist.

As I noted before, you can't really remove one bit of physics and ask how the rest would behave. It's all interconnected and it isn't clear what arbitrarily removing one bit of it does.