# Gravity

whodey
Science 22 Dec '15 18:30
1. 22 Dec '15 18:30
I still don't get it.

How can space be bent when there is seemingly nothing to bend?
2. 22 Dec '15 19:015 edits
"seemingly nothing to bend"? You do understand that 'space', even if and where it is completely empty of any matter or radiation, is not the same thing as 'nothing', right? -just checking because its pretty important not to equate the two else you are going extremely wrong.
3. sonhouse
Fast and Curious
22 Dec '15 19:083 edits
Originally posted by whodey
I still don't get it.

How can space be bent when there is seemingly nothing to bend?
There is one thing you can use to tell how much space is bent: Light. (or any frequency RF). Light and RF follows the curves of space. That is what proved relativity in 1917 I think. The experiment waited till a full eclipse of the sun when stars that would have been totally drowned out in light from the sun, can during a total eclipse, be seen. So they knew the position of the target star if the sun had not been there and then showed it was not in the right place, because of the mass of the sun.

The gravity or bending of space/time caused the light from the star to deflect a bit inwards, a tiny angle of 1.75 arc seconds of bending to be exact. 1 arc second is one part in 1,296,000 so call it 2 arc seconds and you see it bends about one part in 700,000 ish. That is 360 degrees of the circle divided by 700000, a rather small bending but they were able to measure it pretty accurately a hundred years ago.

Space/time is kind of like a multidimensional fabric. You can see some examples where they take a thin rubber sheet and stretch it out over a circular frame and then drop small iron ball on it. That ball goes to the center and stays there making a curve in the rubber, but if you take a smaller steel ball and roll it in at the right angle and speed it will go in circles around the bigger ball which is a demonstration of moons orbiting around planets or planets orbiting around stars.

What bends space and time is mass. The bigger the mass in a certain volume, the more space and time get stretched. So if you spend time a thousand miles above Earth, you live a shorter life than if you spend time on the surface of Earth. Time goes a tiny bit slower close to the ground than it does away from Earth.

So what we think of as gravity, Einstein showed it not to be so much a force like we think of it, but as a bending of space, so like you are on a skateboard on flat land, you get on, nothing happens which represents space trillions of miles from any mass.

If you are facing downhill, you accelerate. That is what is going on with the bending of space, except the bend is towards the middle of the mass in question and the bending is 360 degrees around in all directions so no matter what the angle you approach earth from you are going to be going downhill till you hit dirt.
4. 22 Dec '15 19:27
Originally posted by whodey
I still don't get it.

How can space be bent when there is seemingly nothing to bend?
The "bending" of space is an analogy used to visualize what the formulae tell us. This picture make some sense because we can, for instance, see the "bending" of light through gravitational lensing.

If you want to understand gravity, study general relativity.
5. 22 Dec '15 20:17
Originally posted by sonhouse
There is one thing you can use to tell how much space is bent: Light.
As I think KazetNagorra is implying space isn't quite technically 'bent'. Light always travels in a straight line in free space. (OK, I am simplifying a little bit, but lets leave all the wave stuff out of this for now). So where ever light goes is 'straight' not 'bent'. We say space is bent because two parallel lines may meet up.
6. 22 Dec '15 21:356 edits
Originally posted by KazetNagorra
...

If you want to understand gravity, study general relativity.
I don't think there is much hope of him (and most theists) understanding general relatively, which is harder than special relativity because general relativity deals with accelerating frames of reference. Even I barely half understand only a very few of its concepts and none of the equations and at least I have reasonable understanding of basic Newtonian physics + some respectable partial understanding of special relativity and of some of its equations. I doubt he even has that.
7. joe shmo
Strange Egg
23 Dec '15 00:52
Originally posted by humy
I don't think there is much hope of him (and most theists) understanding general relatively, which is harder than special relativity because general relativity deals with accelerating frames of reference. Even I barely half understand only a very few of its concepts and none of the equations and at least I have reasonable understanding of basic Newtonian ...[text shortened]... tial understanding of special relativity and of some of its equations. I doubt he even has that.
You do realize that Einstien himself held partially theistic views?
8. joe shmo
Strange Egg
23 Dec '15 01:041 edit
Originally posted by humy
I don't think there is much hope of him (and most theists) understanding general relatively, which is harder than special relativity because general relativity deals with accelerating frames of reference. Even I barely half understand only a very few of its concepts and none of the equations and at least I have reasonable understanding of basic Newtonian ...[text shortened]... tial understanding of special relativity and of some of its equations. I doubt he even has that.
If we are going to be insulting people here with honest inquiries...

1) I doubt many here are shocked that you only barely half understand general relativity concepts and none of the equations...so I don't know why you brought it up.

2) You can't have a respectable partial understanding of special relativity with only a reasonable understanding of basic Newtonian physics.
9. 23 Dec '15 08:042 edits
Originally posted by joe shmo
You do realize that Einstien himself held partially theistic views?
As far as I am aware, he was an agnostic. When he spoke of "God", he didn't mean some kind of supernatural human-like being but merely "everything" or "the universe and its natural laws" and he protested bitterly when people kept saying he meant a supernatural and/or human-like God.
10. 23 Dec '15 08:126 edits
Originally posted by joe shmo
If we are going to be insulting people here with honest inquiries...

1) I doubt many here are shocked that you only barely half understand general relativity concepts and none of the equations...so I don't know why you brought it up.

2) You can't have a respectable partial understanding of special relativity with only a reasonable understanding of basic Newtonian physics.
I had no intent to offend. But most modern scientists are atheist/agnostic and tend to be the most intelligently people in society. Not intending to offend, I will leave it to you to figure out why that is rather than tell you explicitly. I don't think that is mere statistical coincidence, do you?

And my response to your two assertions are;

1) where did I say/imply you should be "shocked"? I clearly implied we should be surprised if he could understand it, not that we should be surprised if I couldn't.

2) False inference. Don't know where you got that from. You can, in theory, directly learn relativity first before formally learning Newtonian physics, by learning these Newtonian principles that happen to be implicitly inclusive in relativity as you go along, although I think that wouldn't be the best way of doing it.
11. divegeester
the altruistic one
23 Dec '15 08:27
Originally posted by whodey
I still don't get it.

How can space be bent when there is seemingly nothing to bend?
Watch the movie, it's all in there.
12. divegeester
the altruistic one
23 Dec '15 08:31
Originally posted by humy
I don't think there is much hope of him (and most theists) understanding general relatively, which is harder than special relativity because general relativity deals with accelerating frames of reference. Even I barely half understand only a very few of its concepts and none of the equations and at least I have reasonable understanding of basic Newtonian ...[text shortened]... tial understanding of special relativity and of some of its equations. I doubt he even has that.
That's a pretty biggoted and ignorant thing to say (about theists). The religious world is admittedly populated with high degree of craziness but there is absolutely no reason (at least not in Christian theism) why cosmic science is incompatable with faith.
13. 23 Dec '15 08:577 edits
Originally posted by divegeester
That's a pretty biggoted and ignorant thing to say (about theists). The religious world is admittedly populated with high degree of craziness but there is absolutely no reason (at least not in Christian theism) why cosmic science is incompatable with faith.
I just like to point out that any religious faith, Christian or not, is logically inconsistent with scientific method, which is a fundamental principle behind all the sciences including cosmic science. The only sense in which the two are 'comparable' is in the very narrow psychological sense that some people can sometimes mentally apply one 'logic' (scientific method) to one thing but then, logically inconsistently, apply a different 'logic' (religious faith) to another thing, even though that second 'logic' is logically inconsistent with the first logic (and, as a result, they have a logically inconsistent belief-forming process) so that the two are only 'compatible' in the very narrow sense that they can maintain the two logically incompatible things in their heads without the two seeming mentally incompatible to them.
But the fact remains that the two are not 'comparable' logically.
14. 23 Dec '15 08:59
Originally posted by humy
I don't think there is much hope of him (and most theists) understanding general relatively, which is harder than special relativity because general relativity deals with accelerating frames of reference. Even I barely half understand only a very few of its concepts and none of the equations and at least I have reasonable understanding of basic Newtonian ...[text shortened]... tial understanding of special relativity and of some of its equations. I doubt he even has that.
Well, I have a PhD in physics and at best a fleeting understanding of general relativity. My point is mainly that one should not expect the compact - but beyond the grasp of laymen - mathematical formulation to be fully explained with a few lines of text suited for the layman. If the analogy of the "bending of space-time" is not good enough for whodey, tough luck.
15. 23 Dec '15 09:11
Originally posted by KazetNagorra
Well, I have a PhD in physics and at best a fleeting understanding of general relativity. My point is mainly that one should not expect the compact - but beyond the grasp of laymen - mathematical formulation to be fully explained with a few lines of text suited for the layman. If the analogy of the "bending of space-time" is not good enough for whodey, tough luck.
Agreed. I didn't mean to imply you were implying that he could really understand general relativity if only he tried (just in case you thought I was implying this )