How does gravity work?

How does science work? And what's all this about quantum mechanics?

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PauloL
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Re: How does gravity work?

Post by PauloL »

uwot wrote: Thu Aug 31, 2017 1:29 pm
I think the Universe started expanding right on the Big Bang. Isn't that correct?

So why do you need a 'Dark force'?
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Re: How does gravity work?

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PauloL wrote: Thu Aug 31, 2017 1:59 pmI think the Universe started expanding right on the Big Bang. Isn't that correct?

So why do you need a 'Dark force'?
Well, the red-shift observed in galaxies beyond the local group, strongly suggests that the universe is expanding. The Big Bang hypothesis also accounts for why the universe isn't collapsing because of gravity. Until fairly recently, it was assumed that gravity would slow down the expansion, and possibly reverse it, so that all the matter would be pulled back into a Big Crunch. When the red-shift of distant galaxies was analysed, the results strongly suggested that, far from slowing down, the expansion of the universe is actually speeding up. Assuming Newton's first law of motion applies to galaxies, on the cosmic scale, some force is counteracting gravity. We don't know what it is, so we give it a fairy-tale name, but the red-shift, whatever the cause, is real.
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Re: How does gravity work?

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uwot wrote: Thu Aug 31, 2017 2:32 pm
That's interesting indeed. I don't read about it since some time.

Let's oversimplify that.

All the universe is a star and two planets orbiting it. So all gravity forces of the universe are withing the orbit of the farthest planet.

Now suppose the size of the universe doubles. Why should planets depart to orbits farther from the star?

If it happens, then new space interacts with gravity. Or the planets simply were already departing by action of a 'Dark force' and there's no need space expansion to be there. Or that 'Dark force' results from space and increased by space expansion.

Do I make myself clear?
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Re: How does gravity work?

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PauloL wrote: Thu Aug 31, 2017 2:59 pmAll the universe is a star and two planets orbiting it. So all gravity forces of the universe are withing the orbit of the farthest planet.

Now suppose the size of the universe doubles. Why should planets depart to orbits farther from the star?
You've highlighted one of the difficulties with the language used to describe the universe. If the universe is just the star and two planets, then in order that the universe gets bigger, the planets have to move to more distant orbits, because that would be what it meant for the universe to get bigger.
PauloL wrote: Thu Aug 31, 2017 2:59 pmIf it happens, then new space interacts with gravity.
This kind of gets to the heart of the problem. I think what you are assuming is that there is some stuff that would be the universe, even if there were nothing in it. In a way, that is what 'Dark Energy' appears to be, it is something that applies an apparently mechanical force on stars and planets; but on less than gargantuan scales, it's effect is swamped by gravity and we simply don't notice it on the scale of the solar system.
PauloL wrote: Thu Aug 31, 2017 2:59 pmOr the planets simply were already departing by action of a 'Dark force' and there's no need space expansion to be there.
If the simplified universe you are suggesting behaves the same way that 'our' universe appears to, then the gravity that binds the planets in orbit around the star would continue to do so, up to a point. The speed of orbit decreases the further out you go; so for example the Earth is going round the Sun at roughly 30km per second, whereas Jupiter is only going at 13km per second. Eventually dark energy would be pushing the planets away from the star, faster than they were going round it, so they would never complete an orbit, and effectively move away from the star in a straight line. I'm not sure that answers your question though.
PauloL wrote: Thu Aug 31, 2017 2:59 pmOr that 'Dark force' results from space and increased by space expansion.
Until the acceleration of the universe was discovered, it was common for physicists to dismiss Einstein's idea of 'spacetime' as a substance with mechanical properties and treat 'space' simply as the gap between objects. Most now accept that space really is some sort of stuff that can push galaxies apart.
PauloL wrote: Thu Aug 31, 2017 2:59 pmDo I make myself clear?
Better than some of the native English speakers.
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Re: How does gravity work?

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uwot wrote: Thu Aug 31, 2017 4:21 pm
Thanks for your comments and patience UWOT.

What I mean as universe here is space not bodies (of course universe contains bodies, otherwise it would be empty).

Let's suppose quite simplistically again that the universe is twice the orbit of the farthest planet. So if next time it's four times that size, universe expanded. If the planets depart to farther positions, but the universe size remain the same I wouldn't say universe expanded.

The main question here is expansion of universe in the first instance. I think that's 1) expanding it's dimensions and not just 2) expanding distances between bodies. Both things are accepted. The universe is expanding and there's a red shift (Doppler's effect from bodies changing relative positions). So expansion is 1) or 2) or both and there's a relation (interaction) between both?.

I hope I keep it clear again and appreciate your compliment.
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Re: How does gravity work?

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PauloL wrote: Thu Aug 31, 2017 4:45 pmLet's suppose quite simplistically again that the universe is twice the orbit of the farthest planet. So if next time it's four times that size, universe expanded. If the planets depart to farther positions, but the universe size remain the same I wouldn't say universe expanded.
The thing is, we simply don't know whether the universe we see is all there is. Lawrence Krauss wrote a book recently, A Universe from nothing, which basically argues that our universe began as a fluctuation in a pre-existing quantum field, which resulted in a chain reaction. Maybe so. It might also be the case that the same quantum field was created in the Big Bang, but as the evidence is beyond the visible universe, we may never know. Either way, the quantum field (or fields) do appear to have mechanical properties.
Part of the excitement around the 'discovery' of the Higgs boson was that a field with mechanical properties was predicted. One of the predictions was that if you hit this field hard enough, you will create a 'ripple' in it that is detectable. The LHC walloped the field, and lo and behold, there was a ripple that looked very like the one predicted.
So yes, empty space is not empty and it does exert a force. My personal hunch is that, regardless of whether the Big Bang started in a true vacuum, or some 'field', 'space' is expanding, and it exerts a push on the things we can see. In effect, it's like a cosmic wind (which is a very loose analogy).
PauloL wrote: Thu Aug 31, 2017 4:45 pmThe main question here is expansion of universe in the first instance. I think that's 1) expanding it's dimensions...
Personally, I think 'dimensions' are relational; I don't think there is any solid evidence that they exist as anything other than a means of locating events. If you just mean the universe is getting bigger, I would agree that is by far the best explanation of the data, but again, this is a subtlety of language that even native English speakers are confused by.
PauloL wrote: Thu Aug 31, 2017 4:45 pm...and not just 2) expanding distances between bodies. Both things are accepted. The universe is expanding and there's a red shift (Doppler's effect from bodies changing relative positions). So expansion is 1) or 2) or both and there's a relation (interaction) between both?
The theory is that space, as you suggest, is some sort of stuff. Matter is tiny blobs of this stuff, which have been warped and twisted into particular patterns, and squeezed together. As the stuff expands, it carries matter along with it; a (very) little bit like a sailing ship in the wind.
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Re: How does gravity work?

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uwot wrote: Thu Aug 31, 2017 8:46 pm
PauloL wrote: Thu Aug 31, 2017 4:45 pmLet's suppose quite simplistically again that the universe is twice the orbit of the farthest planet. So if next time it's four times that size, universe expanded. If the planets depart to farther positions, but the universe size remain the same I wouldn't say universe expanded.
The thing is, we simply don't know whether the universe we see is all there is. Lawrence Krauss wrote a book recently, A Universe from nothing, which basically argues that our universe began as a fluctuation in a pre-existing quantum field, which resulted in a chain reaction. Maybe so. It might also be the case that the same quantum field was created in the Big Bang, but as the evidence is beyond the visible universe, we may never know. Either way, the quantum field (or fields) do appear to have mechanical properties.
Part of the excitement around the 'discovery' of the Higgs boson was that a field with mechanical properties was predicted. One of the predictions was that if you hit this field hard enough, you will create a 'ripple' in it that is detectable. The LHC walloped the field, and lo and behold, there was a ripple that looked very like the one predicted.
So yes, empty space is not empty and it does exert a force. My personal hunch is that, regardless of whether the Big Bang started in a true vacuum, or some 'field', 'space' is expanding, and it exerts a push on the things we can see. In effect, it's like a cosmic wind (which is a very loose analogy).
PauloL wrote: Thu Aug 31, 2017 4:45 pmThe main question here is expansion of universe in the first instance. I think that's 1) expanding it's dimensions...
Personally, I think 'dimensions' are relational; I don't think there is any solid evidence that they exist as anything other than a means of locating events. If you just mean the universe is getting bigger, I would agree that is by far the best explanation of the data, but again, this is a subtlety of language that even native English speakers are confused by.
PauloL wrote: Thu Aug 31, 2017 4:45 pm...and not just 2) expanding distances between bodies. Both things are accepted. The universe is expanding and there's a red shift (Doppler's effect from bodies changing relative positions). So expansion is 1) or 2) or both and there's a relation (interaction) between both?
The theory is that space, as you suggest, is some sort of stuff. Matter is tiny blobs of this stuff, which have been warped and twisted into particular patterns, and squeezed together. As the stuff expands, it carries matter along with it; a (very) little bit like a sailing ship in the wind.
That's interesting indeed.

Well, 'dimensions' must exist for sure within universe. Outside universe you have nothing, and that means do dimensions and not even time. So if the universe is getting bigger, its dimensions must get bigger, I don't think this is a question of language.

How expansion of dimensions affect gravity in universe is a mystery to me. I think that shouldn't. I think this is the interpretation of red shift. Otherwise bodies were simply departing from each other.

I hope I made myself clear. This stuff is complex indeed and language confusions don't help.
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Re: How does gravity work?

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uwot wrote: Thu Aug 31, 2017 8:46 pm
That's interesting indeed.

Well, 'dimensions' must exist for sure within universe. Outside universe you have nothing, and that means no dimensions and not even time. So if the universe is getting bigger, its dimensions must get bigger, I don't think this is a question of language.

How expansion of dimensions affect gravity in universe is a mystery to me. I think that shouldn't. I think this is the interpretation of red shift. Otherwise bodies were simply departing from each other.

I hope I made myself clear. This stuff is complex indeed and language confusions don't help.
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Re: How does gravity work?

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Uwot, what do you think about the current definitions of dimensions? It seems illogical to me to posit height, width, depth and time and then jump to the notion of tiny, "curled up" dimensions (usually accompanied by a graphic of an ant crawling around a thin cylindrical surface).

It seems artificial to me to consider dimensions as, first, coordinates of what is essentially outwards observation in all directions. Then, the "next" dimension is time - the dynamism of outwards observation - and then start looking inwards to tiny "curled up" dimensions. It's hardly a "beautiful" model.

Further, the first three dimensions are completely theoretical constructs with no natural analogue - there is no Flatland (aside from, speculatively, at Planck scale?). It would make more sense to define dimensions at emergences, eg. universal scale is where dark energy rules, then the next dimension might be at the level of galactic superclusters where dark matter rules, and keep panning down to quantum or Planck scales.

Time strikes me to be less of a dimension in itself than a quality of all dimensions.
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Re: How does gravity work?

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PauloL wrote: Thu Aug 31, 2017 11:22 pmWell, 'dimensions' must exist for sure within universe. Outside universe you have nothing, and that means no dimensions and not even time. So if the universe is getting bigger, its dimensions must get bigger, I don't think this is a question of language.
I'm afraid 'dimensions' really can mean different things. Three spring to mind:
1. Size. You are quite right; the universe has physical dimensions, in that it has height, width and depth; x,y and z in Cartesian coordinates.
2. Location. On the surface of the Earth, we can get by using two dimensions; north/south or latitude, and east/west which is longitude; x and y in Cartesian coordinates. Once you leave the surface though, you need to state the height. Any place can be located using three coordinates. Events need to be located in time; I could invite you all to a party at my place and tell you where that is, but if I don't give a time and a date, there's no party. (It's all in How does time work? http://willijbouwman.blogspot.co.uk ) x,y,z and t are all relative to some arbitrary spot in space or time.
3. Hypothetical entities. This is where it gets really confusing. The problem is that although we can describe any location on Earth using two dimensions, the surface of the Earth isn't flat; the 'dimensions' are scrunched up by hills and valleys. In effect, that's what Einstein did to the three dimensions of space. The thing is, it's easy enough to think of two dimensions being scrunched up into a third, but what does it mean to scrunch three dimensions into a fourth? Turns out that you can do it mathematically and some people believe that, since extra dimensions exist as mathematical objects, they might exist as 'physical' objects. My suspicion is that they don't, but that hasn't stopped string theorists from positing ten or more such dimensions, which as Greta says, are rolled up or scrunched up so tightly that we can't see them. That may be so, but there is as yet no sound evidence.
PauloL wrote: Thu Aug 31, 2017 11:22 pmHow expansion of dimensions affect gravity in universe is a mystery to me. I think that shouldn't. I think this is the interpretation of red shift.
As far as I can tell, you are using 'dimension' in the third sense. Personally, I think it is plausible to think of 'space' as being a substance, Big Bang stuff in my blog, which expands, so that its dimensions in the first sense get bigger. But that is very different to saying that dimensions, in the third sense, expand.
PauloL wrote: Thu Aug 31, 2017 11:22 pmOtherwise bodies were simply departing from each other.
Which is dimensions in the second sense.
PauloL wrote: Thu Aug 31, 2017 11:22 pmI hope I made myself clear. This stuff is complex indeed and language confusions don't help.
Ain't that the truth.
Greta wrote: Fri Sep 01, 2017 1:31 amUwot, what do you think about the current definitions of dimensions?
Hi Greta. Hopefully what I've said above answers your questions. Short answer: Not much. But I could be wrong.
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Re: How does gravity work?

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uwot wrote: Fri Sep 01, 2017 7:24 am
Greta wrote: Fri Sep 01, 2017 1:31 amUwot, what do you think about the current definitions of dimensions?
Hi Greta. Hopefully what I've said above answers your questions. Short answer: Not much. But I could be wrong.
Actually, the post did not address the issues I raised at all :)
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Re: How does gravity work?

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Greta wrote: Fri Sep 01, 2017 8:09 amActually, the post did not address the issues I raised at all :)
Oh. Ok.
Greta wrote: Fri Sep 01, 2017 1:31 amUwot, what do you think about the current definitions of dimensions?
Well, of the three I suggested, I think it is reasonable to accept dimensions as a description of spatial extension. I also think it is reasonable to accepts dimensions as descriptions of spatial and temporal location.
Greta wrote: Fri Sep 01, 2017 1:31 amIt seems illogical to me to posit height, width, depth and time and then jump to the notion of tiny, "curled up" dimensions (usually accompanied by a graphic of an ant crawling around a thin cylindrical surface).
I don't think it's really illogical, insofar as there is no logical reason why you shouldn't, I just don't think it is a sound move.
Greta wrote: Fri Sep 01, 2017 1:31 amIt seems artificial to me to consider dimensions as, first, coordinates of what is essentially outwards observation in all directions. Then, the "next" dimension is time - the dynamism of outwards observation...
Time makes sense in terms of location. Like spatial dimensions, you start from some arbitrary point; the time now is 2017 and a bit years after some supposed event in the life of a man, who may or may not have existed for example.
Greta wrote: Fri Sep 01, 2017 1:31 am...and then start looking inwards to tiny "curled up" dimensions. It's hardly a "beautiful" model.
No, I don't much care for it myself. What I don't get is where these dimensions are supposed to be. If you went into space and brought back a bucketful of it, is there anywhere in the place you got the bucketful from that now isn't in the bucket? If not, then since you can describe any point within that bucket using 3 dimensions, who needs extra dimensions? If there is somewhere missing in the bucket, then the extra dimensions are not related to x, y and z and anything that exists in the extra dimensions isn't part of what we normally think of as the physical universe.
Greta wrote: Fri Sep 01, 2017 1:31 amFurther, the first three dimensions are completely theoretical constructs with no natural analogue - there is no Flatland (aside from, speculatively, at Planck scale?).
I've said before that the Planck scale is epistemological rather than ontological. It's the shortest distance, in space or in time, that we could physically measure. It doesn't follow that it is the smallest distance that exists. There could be all sorts of structure beyond the Planck scale; the point Planck was making is that we cannot see it, at least not using light.
Greta wrote: Fri Sep 01, 2017 1:31 amIt would make more sense to define dimensions at emergences, eg. universal scale is where dark energy rules, then the next dimension might be at the level of galactic superclusters where dark matter rules, and keep panning down to quantum or Planck scales.
I think you are introducing a different concept of dimension, and if it makes sense to you, go for it.
Greta wrote: Fri Sep 01, 2017 1:31 amTime strikes me to be less of a dimension in itself than a quality of all dimensions.
Well, again, time is in one sense simply the number of events, (orbits of Earth, swinging of pendulums, vibrations of caesium etc) either side of t=0. What seems to confuse mathematicians is that you can do the sums either way. So if you analyse a pool break, for instance, the sums are the same for the balls bouncing around the table, as they are for bringing them back into the triangle. Why then, wonder some mathematicians, can't we go back in time? The simple answer is that you are not going to get the universe back into its box.
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Re: How does gravity work?

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Greta wrote:
It seems illogical to me to posit height and width and depth and time and then jump to the notion of tiny
curled up dimensions ( usually accompanied by a graphic of an ant crawling around a thin cylindrical surface )
Height and width and depth are classical dimensions while the curled up ones are [ hypothetical ] quantum dimensions. But were
they real then there would be no incompatibility between the two. For the worlds happily co exist. There is of course the famous
incompatibility between GR and QM but that only pertains to the theories themselves rather than the actual phenomena. And it is
why one should never confuse the map with the terrain. Because one is only an approximation of the other. They are not the same
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Re: How does gravity work?

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surreptitious57 wrote: Fri Sep 01, 2017 9:53 pm
Greta wrote:
It seems illogical to me to posit height and width and depth and time and then jump to the notion of tiny
curled up dimensions ( usually accompanied by a graphic of an ant crawling around a thin cylindrical surface )
Height and width and depth are classical dimensions while the curled up ones are [ hypothetical ] quantum dimensions. But were they real then there would be no incompatibility between the two. For the worlds happily co exist. There is of course the famous incompatibility between GR and QM but that only pertains to the theories themselves rather than the actual phenomena. And it is why one should never confuse the map with the terrain. Because one is only an approximation of the other. They are not the same
Late ex-forum member and friend, Obvious Leo, said this about the map and territory:
Mistaking the map for the territory has been a subject dear to the heart of every philosopher in history because it is an aspect of human perception integral to our make-up and one which has meaning at a great many levels. Entire rainforests have been laid waste for the purpose of producing literature which explores the distinctions between subjective and objective reality, and thus the role of human consciousness in our understanding of the world around us.
I think that is what is happening now. The current models make no explanatory sense. Extend outwards in one direction - a line, dimension one. Move parallel to the line and we have 2D Flatland. Add depth and we have a 3D reality that is locked in stasis until "dimension 4", time, is added. None of these things would seem to exist in themselves in reality, only as approximate correlates and mathematical constructs.

What of the fact that everything in the universe (and seemingly the universe itself) turns inside out/outside over time? How do the current dimensional models express that aspect of reality? I don't ask this as a challenge, just wondering.
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Re: How does gravity work?

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We can consider the reality (3D+1 space) as a result of certain hyper darwinistic process. In more dimensional spaces the limited sources are not able generate (force) fields strong enough to such space keeps together (fields there fall too fast)...
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