The unbearable lightness of being... Gravity.

[Gene Vincent]

moreflaps said:

Err, bit of a physics slip there eh GV?

Only for the purposes of illustration, the full paragraph was designed to convey an image of how a photon conveys its information without corruption from others looking right across their line of sight.

If you can think of a better way to explain that then please do so.

moreflaps said:

Isn't a simpler explanation that gravity is the projection of a higher order dimension onto the dimensions of Minkowski space time resulting in it not being flat ...

We've not got to explanations, we are still at the 'conditions' stage... and there are other hypotheses.

Plus, you don't need further dimensions for Minkowski spacetime to incorporate gravity.

Just placing a planet in Minkowski spacetime as per SR results in the trajectories of inertial observers not bending towards that planet, so any falling observer will not be inertial!

You need another spacetime not a dimension, the inertial trajectories of which are falling trajectories.

You need a different spacetime for each and every arrangement of matter.

Falling into the planet will then just be following an inertial path, and that needs no force to be present.

This is why gravity is not a force, but rather the result of following the contours of spacetime and the shape of spacetime depends on the matter present.

No dimensions added or needed.

But we will get to explanations that do have them.

(edit... syntax!)

Edited by Gene Vincent on Thursday 13th September 12:05

[MiseryStreak]

I've often disliked the rubber sheet analogy in describing the curvature of spacetime created by gravity. OK, massive objects will fall towards each other, but how are they falling? In a zero gravity environment, the rubber sheet will be flat as pancake. As an analogy it is miserably self referential and inadequate.

Please, please, please find the Graviton soon. We really need to know which tree to bark up, and help smash this list down:
http://en.wikipedia.org/wiki/List_of_quantum_field...

[Gene Vincent]

MiseryStreak said:

Oh no, he's back. GV - your theory about a thread degrading rapidly at 250 posts has been supplanted, 40 seems nearer the mark.

How does the inflaton field come into this?

We are for the purposes of this thread not going to deal with how gravity was during the inflationary period, the reason is that we experience gravity today, as it is, we don't experience anything today that can be related in any real sense to what things were like during the inflationary period.

[Gene Vincent]

MiseryStreak said:

I've often disliked the rubber sheet analogy in describing the curvature of spacetime created by gravity. OK, massive objects will fall towards each other, but how are they falling? In a zero gravity environment, the rubber sheet will be flat as pancake. As an analogy it is miserably self referential and inadequate.

Please, please, please find the Graviton soon. We really need to know which tree to bark up, and help smash this list down:
http://en.wikipedia.org/wiki/List_of_quantum_field...

All explanations and analogies that are not pure maths are limited or truncated and faulty in some way.

Even my explanation to moreflaps above is limited and could be more comprehensive, Minkowski spacetime is a small distance spacetime and only works at that scale because it is the spacetime of SR, once we get to the huge scale of the Cosmos Minkowski fails mathematically.

In much the same way that Euclidean geometry works on the earth over small distances because locally the earth is effectively flat, be we live on a sphere.

This cheese-paring can continue ad nauseum, it is the remit of anyone trying to give a non-mathematical explanation to something that is pure maths is to convey as much of the image as you can.

[mattnunn]

Gene Vincent said:

All explanations and analogies that are not pure maths are limited or truncated and faulty in some way.

Even my explanation to moreflaps above is limited and could be more comprehensive, Minkowski spacetime is a small distance spacetime and only works at that scale because it is the spacetime of SR, once we get to the huge scale of the Cosmos Minkowski fails mathematically.

In much the same way that Euclidean geometry works on the earth over small distances because locally the earth is effectively flat, be we live on a sphere.

This cheese-paring can continue ad nauseum, it is the remit of anyone trying to give a non-mathematical explanation to something that is pure maths is to convey as much of the image as you can.

Well Gene, in this case aren't you just better to show us your maths, most likely we (I mean I) won't understand it but at least give the ignorrant masses a chance.

[Gene Vincent]

mattnunn said:

Well Gene, in this case aren't you just better to show us your maths, most likely we (I mean I) won't understand it but at least give the ignorrant masses a chance.

Thus destroying any idea of greater inclusion to insight.

But perhaps you're right and I'm wasting my time here.

[MiseryStreak]

No, you're not, and including the maths on a motoring forum would be more of a waste of your time. If everyone really wanted to get into the maths and can understand it then this thread serves no purpose, all the maths is out there to read in publicly viewable documents, and indeed on the physics forums and blogs.

The trouble with the analogies and mental models that I was trying to convey is that most of them fall down because of their translation to lesser dimensioned models. I haven't yet seen or heard a decent visual or verbal representation of how any higher dimensional concept works, such as how gravity is primarily exerted in a 'curled up' fifth dimension. It's always shown as little loops extending into the three or even two spatial dimensions. I'm sure it can be done, probably through an CG animation, but I've yet to see one.

Anyway, I'm keeping up so far, carry on...

[Gene Vincent]

I won't be stopping, I've started so I'll finish.

But it would be so much better if anyone can convey anything in a better way than I can, to do so, thereby adding to the threads strength.

I think I'm a bit disappointed that my attempt to explain how 'crossed lines' of clear vision are accommodated by QFT didn't hit the spot, I thought it was quite good! I haven't ever seen one before set out in laymans terms and was quite pleased with my first attempt.

Perhaps moreflaps might want to give it a go, he may have a better visualisation.

I'll then steal it...

[IainT]

Gene Vincent said:

I think I'm a bit disappointed that my attempt to explain how 'crossed lines' of clear vision are accommodated by QFT didn't hit the spot, I thought it was quite good!

The silent masses might be silent for two reasons:

1) lack of understanding and not wanting to say so
2) Some level of understanding from your analogy.

For what it's worth I'd never even contemplated the question of why photons from one source don't disrupt photons form another...

[EliseNick]

Gene Vincent said:

mattnunn said:

Well Gene, in this case aren't you just better to show us your maths, most likely we (I mean I) won't understand it but at least give the ignorrant masses a chance.

Thus destroying any idea of greater inclusion to insight.

But perhaps you're right and I'm wasting my time here.

Why not just include a link to some of your recent publications on the topic for the professionals, then the thread can concentrate on your explanations?

Nick

[FarmyardPants]

IainT said:

For what it's worth I'd never even contemplated the question of why photons from one source don't disrupt photons form another...

Me neither. And yet two beams of light can interfere with one another (diffraction grating experiment). Perhaps we can have a thread on photons

edited to add quote

Edited by FarmyardPants on Friday 14th September 09:54

[Gene Vincent]

This Science! forum started in January and I watched... and waited.

I was waiting for some big contributions from people here, pithy up to date stuff, none was really forthcoming other than bad interpretations of the badly reported 'news'.

In the end I decided that if no-one was going to put forward 'where we are today' types of thread, I'd give it a go.

So, after this post I'll back off for a while and let others, who obviously have something of value to say, do so.

Over to you...

ETA

Just to give all a fair wind and a free hand won't even look in this section of the forum for a couple of weeks.

Cheers

Gene.

Edited by Gene Vincent on Thursday 13th September 21:48

[Piersman2]

Bye.

[moreflaps]

Gene Vincent said:

moreflaps said:

Err, bit of a physics slip there eh GV?

Only for the purposes of illustration, the full paragraph was designed to convey an image of how a photon conveys its information without corruption from others looking right across their line of sight.

If you can think of a better way to explain that then please do so.

moreflaps said:

Isn't a simpler explanation that gravity is the projection of a higher order dimension onto the dimensions of Minkowski space time resulting in it not being flat ...

We've not got to explanations, we are still at the 'conditions' stage... and there are other hypotheses.

Plus, you don't need further dimensions for Minkowski spacetime to incorporate gravity.

Just placing a planet in Minkowski spacetime as per SR results in the trajectories of inertial observers not bending towards that planet, so any falling observer will not be inertial!

You need another spacetime not a dimension, the inertial trajectories of which are falling trajectories.

You need a different spacetime for each and every arrangement of matter.

Falling into the planet will then just be following an inertial path, and that needs no force to be present.

This is why gravity is not a force, but rather the result of following the contours of spacetime and the shape of spacetime depends on the matter present.

No dimensions added or needed.

But we will get to explanations that do have them.

(edit... syntax!)

Edited by Gene Vincent on Thursday 13th September 12:05

There is no need for waves to interfere with the direction of propagation of other waves. You don't have to invoke photons like particles with discrete trajectories -just look at waves in the ocean! The key is that the propagation of a wave is self sustaining...

As for the distortion of space time to explain gravity that is fine and what I was alluding to, the question is, how is space time bent? Is the bending explained by our experiencing the projection of higher dimensions (that we, as 3D beings cannot ever perceive) so that real space is (say) 4 dimensional but that we experience/see only 3 dimensions. Thus we think we travel intertially in geodesics in 3D but which are actually geodesics in 4 dimensions so that our path in 3D becomes distorted... The distortion we call gravity and we then make equations to describe a 'force' that may not exist at all...

By analogy, what about how a 2D being would experience interaction with a 3D object that distorts the 2D space they live in...

Cheers

[AJI]

Gene Vincent said:

This Science! forum started in January and I watched... and waited.

I was waiting for some big contributions from people here, pithy up to date stuff, none was really forthcoming other than bad interpretations of the badly reported 'news'.

In the end I decided that if no-one was going to put forward 'where we are today' types of thread, I'd give it a go.

So, after this post I'll back off for a while and let others, who obviously have something of value to say, do so.

Over to you...

ETA

Just to give all a fair wind and a free hand won't even look in this section of the forum for a couple of weeks.

Cheers

Gene.

Edited by Gene Vincent on Thursday 13th September 21:48

For what its worth I will thank you for your contributions to the Science section of the forum.
I would also say that a number of people who post negatively in this forum are only doing so because they (a) do not have the depth of knowledge on a particular subject and (b) feel embarrassed about the fact that what they think they know may not be what it may be.

I would also say to GV that there will be many people taking a peek at your threads/posts (even if they don't comment) and maybe taking a step further in their knowledge and the way they think about/approach science. And that is a good thing.

I am benefitting a lot by laymen explainations of various aspects of the subjects that have been dicussed so far. I like maths and I would even say that I am competant at a lot of it, but still much of the maths used in explaining many of the topics within the Science! section is way beyond my 'level'. So with the likes of GV using layman language and being prepared to discus the finer points when people come in trying to 'find holes' per say, then it provides an enjoyable and interesting read.

I would say to GV to ignore the few that only bother to post in a -ve manner, because there are many more that read and digest the positive stuff.

[IainT]

AJI said:

stuff

Well said. I think there are a lot of us who find GV's posts both interesting and useful - even if it does highlight one's own limitations in understanding from time to time.

[FarmyardPants]

mattnunn said:

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

I think it depends how you treat the rotation of the Earth.

If we can ignore it - ie say that the same bit of Earth always faces a distant star, then if you draw a line through the centre of the sun and Earth at the time it vanishes, you'll see that some people are closer to the sun than others, but everyone is following the natural orbit of the combined Earth/people mass. At the moment of disappearance, everyone is travelling in the same direction, but this direction may not be a sustainable orbit for each person's distance from the sun. Those who happen to be on the path of the original orbit will continue to orbit the sun as the Earth had. People closer to the sun aren't travelling fast enough for their nearer orbit and would probably spiral into the sun, whilst those further from the sun are travelling too fast for their orbit height and would (I think) enter an elliptical orbit.

If we say that 1 day == 1 year (period of rotation of Earth is equal to the time taken to orbit the sun - like the moon's relationship with Earth), then I think everyone is in the right place for their orbit distance and would continue to orbit the sun as the Earth had.

I think that for the 'real world' case (365 rotations/year), people would continue to follow their individual trajectories tangential to the former Earth surface, hence some would burn up, others would form orbits of various shapes.

Those who continue to follow Earth's orbit would gradually drift together to form a clump, although this would be considerably complicated by the uneven distribution of people and collisions that occur before meeting in the middle, which might have some people orbiting (slowly) an irregular rotating clump of people at the centre.

Edited by FarmyardPants on Friday 14th September 10:49

[R300will]

FarmyardPants said:

mattnunn said:

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

I think it depends how you treat the rotation of the Earth.

If we can ignore it - ie say that the same bit of Earth always faces a distant star, then if you draw a line through the centre of the sun and Earth at the time it vanishes, you'll see that some people are closer to the sun than others, but everyone is following the natural orbit of the combined Earth/people mass. At the moment of disappearance, everyone is travelling in the same direction, but this direction may not be a sustainable orbit for each person's distance from the sun. Those who happen to be on the path of the original orbit will continue to orbit the sun as the Earth had. People closer to the sun aren't travelling fast enough for their nearer orbit and would probably spiral into the sun, whilst those further from the sun are travelling too fast for their orbit height and would (I think) enter an elliptical orbit.

If we say that 1 day == 1 year (period of rotation of Earth is equal to the time taken to orbit the sun - like the moon's relationship with Earth), then I think everyone is in the right place for their orbit distance and would continue to orbit the sun as the Earth had.

I think that for the 'real world' case (365 rotations/year), people would continue to follow their individual trajectories tangential to the former Earth surface, hence some would burn up, others would form orbits of various shapes.

Those who continue to follow Earth's orbit would gradually drift together to form a clump, although this would be considerably complicated by the uneven distribution of people and collisions that occur before meeting in the middle, which might have some people orbiting (slowly) an irregular rotating clump of people at the centre.

Edited by FarmyardPants on Friday 14th September 10:49

I think that because the mass of the people wouldn't be enough to sustain the orbit and they'd end up firing off into space

[FarmyardPants]

R300will said:

I think that because the mass of the people wouldn't be enough to sustain the orbit and they'd end up firing off into space

How do you mean "sustain the orbit"? Mass is irrelevant, assuming a vacuum (no drag).

If the earth were to be suddenly replaced by a billiard ball such that their centres of mass are the same, the ball would follow the path that the Earth would have done, more or less (the Earth's gravity makes the sun wobble, the two orbit their combined effective centre, but I don't think you're talking about that), but it wouldn't fire off into space. I'm assuming the moon doesn't exist of course.

[R300will]

Bedazzled said:

FarmyardPants said:

R300will said:

I think that because the mass of the people wouldn't be enough to sustain the orbit and they'd end up firing off into space

How do you mean "sustain the orbit"? Mass is irrelevant, assuming a vacuum (no drag).

If the earth were to be suddenly replaced by a billiard ball such that their centres of mass are the same, the ball would follow the path that the Earth would have done, more or less (the Earth's gravity makes the sun wobble, the two orbit their combined effective centre, but I don't think you're talking about that), but it wouldn't fire off into space. I'm assuming the moon doesn't exist of course.

Yes, the mass of the primary body (Sun) isn't changing so the orbital path just depends on velocity; the centripetal force from gravity would be less due to the reduction in mass, and there would be a corresponding reduction in inertia 'pushing' outwards, so it cancels out.

The mass of the sun may not have changed but the mass of the earth has if its vanished and been replaced by the people living on it. They will have much less mass than the earth therefore the Sun will have a different gravitational pull on them and since their velocity would be the earths orbiting velocity (assuming it just vanished) then their orbital path would change causing them to fly off.