# Basic gravity theories

1. Sep 17, 2015

### Kev.

Hello all,
i would like to start at the beginning please, am i right in thinking that gravity is created by the Mass of an object and has nothing to do with its actual size?

2. Sep 17, 2015

### rootone

Yes.
If the Sun somehow transformed into a small black hole (it won't), the Earth would still experience the same gravity and remain in the same orbit.

Last edited: Sep 17, 2015
3. Sep 17, 2015

### Kev.

is this unless the black hole was able to get extra matter?

4. Sep 17, 2015

### rootone

Yes, I'm assuming nothing other than the Sun is involved, but the fact that it has now hypothetically turned into a black hole won't magically cause additional matter to appear in the solar system which could increase it's mass.

5. Sep 17, 2015

### Kev.

so most black holes should really just sit there, can they close up or would they just go on and on?

6. Sep 17, 2015

### mathman

What do you mean by "sit there", "close up", "go on and on"?

7. Sep 17, 2015

### Kev.

sorry I'm very new to this, would the black hole hold its position in space like the sun does? close up as in the event horizon close of and disappear or would the back hole just remain open all the time, i thought i read somewhere that a black hole could run out of steam and fade away

8. Sep 17, 2015

### rootone

I'll answer this, but first a tip about posting on forums in general.
You are now wandering off of the original topic which is generally considered to be a 'bad thing' because it can easily get to the point where the topic title no longer relates to the discussion.
It's always best to start a new topic if you want to talk about something not directly related to the original post.

Anyway so ...black holes over a period of time manage to clear out the region of space close to them and stop growing.
After this they only grow in occasional stages when a chance encounter occurs with an other object, but most the time they would indeed 'just sit there'.
Stephen Hawkins has proposed that they can eventually start to actually lose mass (evaporate is the term used) through a form of radiation, but this has not yet been been verified by observation.
It's quite an exotic form of radiation resulting from quantum mechanical effects, and probably it can't be verified since the process would take billions of years.

9. Sep 17, 2015

### Kev.

your right about wondering off, I've never been on forums before i'm just full of questions and i do have a tendency to say random things,
back to the gravity stuff, are we any closer to creating artificial gravity or is that just a pipe dream?

10. Sep 17, 2015

### rootone

Gravity is equivalent to acceleration.
A pilot of a fast jet experiences 'g' forces when maneuvering for this reason.
G forces can also be experienced by a person placed in a centrifuge, and it's part of astronaut training.
We can also fake an absence of gravity, wieghtlessness, by flying an aircraft in a particular way.

However there are no gravity or antigravity boots or similar, gravity is a fundamental property of matter.
There is nothing I know of other than matter which can produce a true gravitational field (as opposed to the variations of simulated gravity which I mentioned.)
The field is entirely a result of the mass and nothing else.
There may be exotic forms of matter which are different to the normal matter we know of, but for now anyway no such stuff exists except as abstract mathematical conjectures.
Everything with mass that we know of interacts gravitationally, and everything which does so does it in exactly the same way.

Last edited: Sep 17, 2015