What is gravity....exactly?

I have thought on multiple occasions about gravity. What exactly is gravity. Is gravity a simple effect of the mass of an object creating a a "gravity well" that affects other objects by simply creating a a depression in the fabric of space time? Is gravity an effect of the multiple atoms of a masses electrical charges interacting with another body's atoms electrical charges? Does this include the lighter elements of a planets atmosphere? Why is it that an astronaut experiences weightlessness when they leave a planets atmosphere, obviously the atmosphere has an effect on the gravitational pull of the planet. Does rotation of a body such as Earth increase or decrease its gravitational force?

I have seen so many different explanations of gravity that I am confused as to the source of its effects. What are "your" thoughts?

[edit on 20-4-2010 by nonnez]

This is a really good question and one I've wondered about myself a lot. Not being a physicist, there is only so far I can go in my conjectures, but it seems to me the answers fall into two general camps. Those who favor a more Einstienian view see gravity as the very shape of spacetime; a kind of topographical contour if you will. Those who are more quantum-mechanics-oriented would like to explain it through particle interactions involving "gravitrons" or the like, like any other force.

I do think its interesting that of all the major forces (electromagnetic, strong force, weak force, etc.) they have been able to find a unified force...except for gravity. This may imply that gravity is deeply different from other forces. Or it may simply imply that we haven't found the connnection with other forces yet.

One angle that interests me... the universe seems to be expanding, yet gravity is a "drawing together," i.e., the opposite of general expansion. I've wondered about the relationship between expansion and gravity. I've also wondered about the connection between entropy/neg-entropy and gravity-versus-expansion. But as stated I'm certainly far from a pro in these areas so who knows.

Here is a good place to start.

en.wikipedia.org...

They were having problems with accuracy and stopped in 2008, but there may be some algorithm they can use to cancel out the errors and still get some meaningful data.

My personal belief is that someday they will be able to explain gravity as a geometric aspect of space time with a model simple enough for grade school kids to understand.

[edit on 20-4-2010 by Bordon81]

Gravitational effects are present in space.

The reason an astronaut "appears" weightless is that he is travelling at the proper speed to produce a "falling arc" that matches that of the Earth's own curvature.

Think of this: when you throw a rock, it forms a short arc as it falls to the ground. Fire a rifle, and because the speed is greater, the arc of fall is lessened, though it still falls to the Earth. if you fire a cannon, the speed is even greater, and the cannon shell falls a greater distance away.

Now imagine a tower 105 miles high. this is the lowest stable orbit of the space shuttle. If you could fire your cannon at a speed over 17,000 MPH, the cannon shell would speed out of the barrel, and begin an arc, bending down toward the Earth as it fell. However, this particular arc is going to match the very curvature of the Earth, so that the distance between the projectile and the Earth remains constant. Thus, when the cannon projectile returns, it is still 105 miles in altitude.

For the astronaut, the sensation is like the floor of an elevator falling out from under you at the moment of MECO, or main engine cut-off. You start to fall, but at the same speed the orbiter is falling. If your mission is for fourteen days, you continue your free-fall for 14 days. Just like two sky-divers who jump out of an aircraft at the same time, if all you look at is the other diver, you seem to be stable, with a very strong wind in your face. But if you look up at the aircraft you jumped from, you immediately realize how fast you are falling.

This is why we call being on-orbit being in micro-gravity, rather than weightlessness.

Originally posted by Truth1000
Gravitational effects are present in space.

The reason an astronaut "appears" weightless is that he is travelling at the proper speed to produce a "falling arc" that matches that of the Earth's own curvature.

That being said, if a spacecraft were to change course in the opposite direction towards, lets say an asteroid (in the Asteroid Belt), they would still experience "weightlessness" regardless of the lack of matched orbit or velocity of the closest massive body. Correct?

reply to post by nonnez


Thats how alien ships travel great distances through space time, essentially they are always free falling into a black hole that they induce from a parallel universe.

Not really, Nonnez.

During the Apollo missions to the moon, the gravitational pull of the Earth continued to slow the spacecraft until they reached the point where the gravitational forces of the moon took over, speeding up the spacecraft as they fell toward the moon. There was gravity acting on the astronauts as well, but it was micro-gravity.

Remember, it is the gravitational force of the Sun that keeps a massive planet like Saturn revolving around the solar system, even at the tremendous distance it is from the Sun.

Edited to clarify to whom my response was directed, to avoid confustion with the post above me.

[edit on 20-4-2010 by Truth1000]

reply to post by nonnez


No one knows exactly what gravity is right now and it certainly is not akin to dropping a bowling ball on a rubber sheet as Einstein would have you believe. Matter does not bend space and this supposed phenomena has never been proven and rightly so as we can't even describe what space itself is or what it's made of. Don't let anyone fool you into thinking they have the answers, because they don't.

Gravity, like magnetism, is directly effected by heat.

www.newscientist.com...

They aren't the same thing but it's interesting to see that it's effected by it.


[edit on 20-4-2010 by sremmos]

A really good program I saw on TV a couple of nights ago by physicist Brian Cox - What On Earth Is Wrong With Gravity.

Here's a link to a video of it online:
video.google.com...#

And here's a link to the BBC page about it.
www.bbc.co.uk...

Hope this helps!

Originally posted by sremmos
Gravity, like magnetism, is directly effected by heat.

www.newscientist.com...

They aren't the same thing but it's interesting to see that it's effected by it.


[edit on 20-4-2010 by sremmos]

Interesting! What does heat do to atoms? It speeds them up just as cold slows them down which in turn (cold) would decrease their electrical charge, wouldn't it? I wonder if density also has a direct effect upon the electrical charge emitted by matter? In the case of a black hole it would seem that its forces are increased.



[edit on 20-4-2010 by nonnez]

Originally posted by sremmos
Gravity, like magnetism, is directly effected by heat.

www.newscientist.com...

They aren't the same thing but it's interesting to see that it's effected by it.


[edit on 20-4-2010 by sremmos]

That is extremely interesting and only goes to show how little we don't know about this mysterious force. In my opinion, something like that should only be proof enough that Einstein was wrong on how he thought of gravity.

Quite a while ago I created a thread where I basically asked a very simple question ... to which I really didn't receive a satisfactory answer at that time. Perhaps it's worth re-asking in the context of this new thread.

The question was directly pertinent to the question asked by the OP and is ...

"At what speed does gravity propagate through space ?"

The reason I asked this question was that I had been thinking about the solar system in general and the fact that the Earth is held in solar orbit due to the suns gravitational attraction.
But then it occurred to me that I had no idea whatsoever what the resulting effect would be on the Earths orbit if somehow (I know it's highly unlikely but bear with me) the sun was to instantaneously disappear completely.

We know that even so, we would still 'think we see' the sun because it would take a further 8 mins approx for the last photons to travel the intervening distance to Earth, and our eyes. So for 8 mins after the sun actually disappeared, we'd still have the illusion that it still existed.

But what about the suns gravitational pull on Earth ? What would happen to that if the sun completely and entirely disappeared instantaneously ?

Would the Earth still experience a gravitational pull for a certain amount of time without the sun being there physically, and therefore continue in it's orbit for a little bit longer ... or would the gravitational pull caused by the sun disappear completely and instantaneously when the sun disappears ?

In other words, one could ask what the speed of gravity really is.

One can imagine that if the Earth remained in orbit for a little while longer after the sun had disappeared, that would therefore imply that the speed of gravity must be less than OR equal to light speed.

BUT ... if gravity was seen to disappear completely and immediately when the sun disappeared, this would therefore indicate that gravity has a speed in excess of light ... which would violate known physics.

To the OP:

Nobody knows what causes gravity, per say.. All anyone knows is that it can be found wherever matter is found, and its effects are fairly well understood on the macro scale -- although not necessarily on the micro scale.


Somebody else explained how astronauts orbit the earth, so I guess that's all there is to say on the topic ^_^

Speculate away..


Oh, but one more thing: Spacetime definitely "curves" in the presence of massive objects -- like stars. This has been proven many times.

reply to post by tauristercus


I'm fairly sure there's some experimental evidence to suggest it propagates at the speed of light.. but you'll have to find it on your own, cause I'm not looking through google to confirm this -- as I don't really care what the answer may be. But if you find it, let us know

reply to post by tauristercus


Well that is a good question and one I need to ponder for a bit. I am thinking on similar lines of thought but with possible other solutions than your line of thought. I do think though that we would experience the effect of gravity longer than the period that it takes the light to finally fade. I will get to that idea later.

Originally posted by Kaytagg
To the OP:


Oh, but one more thing: Spacetime definitely "curves" in the presence of massive objects -- like stars. This has been proven many times.

Yeah, which still begs the question.........why it curves? Space time effect? Electrical effect? "

Your" thoughts.
I realize you said speculate away.

Great thread. QUESTION: do all things have gravity? If we land on a small asteroid, woulkd it have gravity because of its matter or would we just fall off because there is no gravity..

I know, it's a stupid question, but I am curious

Some time back I posted a thread about my own hypotheses on space, time, and gravity. You can read it here.

It may not be complete, but I believe it is a good start on understanding the phenomenon.

TheRedneck

Gravity is a property of matter which creates an attractive force with other matter.

Isac Newton figured out how it behaves in our "normal" world but not what the source of that force is. Einstein figured out that the force is a result of matter increasing the curvature of spacetime. He also figured out that that bending would also cause light to appear to bend (and a lot of other stuff). He also figured out that when you have a whole lot of matter gravity behaves a bit differently than what Newton came up with.

We know very well how gravity behaves and why. We don't know why matter has gravity but it does.

[edit on 4/20/2010 by Phage]