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Author Topic: Spacetime - reality, model, or fabrication? What is it exactly....  (Read 9443 times)

Offline old guy

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the big bang theory is a good one in all , but how does something just explode and create a universe?
what was it that exploded?
where did it come from?
whats it made of?
what is the fabric of space made of?
These are such good questions! I'm suprized the discussion has not taken serious flight.
Can we not assume that "what exploded" were the raw materials for what cooled down and evolved into today's observable (and beyond) cosmos?

"Where did it come from?" is my favorite cosmological question... and I've been an amateur cosmologist for a long time.
Positing "something out of nothing" is no different than the "creationist" belief that "god' pulled it all out of his magic hat as "creator," i.e., that it just magically appeared ( sans the "deity" as an agent for non-religious cosmologists.)

My best (speculative) answer is the oscillating, "Bang/Crunch" model. We just need to find enough of the "missing matter" to reverse the expansion... eventually... if it ever quits accelerating in rate of expansion and slows down.
Anyway, we are finding more ordinary matter all the time, not even counting whatever "dark matter" is supposed to be.

So I think the Bang/Crunch model is the only one which can explain where it all came from... an eternally existing cycle with no beginning or ending. Entropy is not a factor on cosmic scale, as nothing is created or destroyed. It just gets re-distributed... way out... but eventually comes back for another Bang.
"What is the fabric of space made of?" is an excellent question. General relativity is always introduced by "explaining" that "mass curves spacetime," but there is never a supporting ontological discussion of what those component parts are! What IS space besides 3-D volume? Who said that it is "made of" anything?... let alone "What is time?" or "What is the 'fabric' of both 'woven together'?"
I would really like to see some serious discussion of these questions.
« Last Edit: 23/11/2012 14:17:33 by imatfaal »


 

Online yor_on

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #1 on: 01/11/2012 21:05:58 »
Is there a 'fabric of space'?
Gravity?
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #2 on: 02/11/2012 19:37:09 »
Is there a 'fabric of space'?
Gravity?
Gravity: Mass attracts mass. What "fabric?"
 

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #3 on: 11/11/2012 16:04:57 »
Nah, that's my point too, but I've seen it used and think I've used it too at times, sloppy but? It's so easy to say, the 'fabric of space' :) but gravity is just a metric, shaping that space into whatever forms (geodesics) we find matter to take, and the shape defined by the mass taking them.

Maybe the 'fabric' could be seen as all dimensions together? Then also including the observer describing it and mass/energy and relative speed & acceleration (observer dependencies). That as you can't have any definition of a universe without a detector observing it. And if you want to take it to its limit also assume that you need consciousness to know that you actually are observing.

Seems too need a lot of stuff before becoming any fabric I would say :)
 

Offline JP

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #4 on: 11/11/2012 21:36:08 »
Well, space-time does have structure (due to gravity), and fabric implies a structure.  But fabric also implies a sheet of physical matter, and space-time is decidedly not that.

So yeah--I also agree that it's a confusing term.
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #5 on: 12/11/2012 18:48:30 »
JP:
Quote
So yeah--I also agree that it's a confusing term.

Indeed. Why can we not dispense with the term based on Occam's razor.*

yor_on:
Quote
... but gravity is just a metric, shaping that space into whatever forms (geodesics) we find matter to take, and the shape defined by the mass taking them.


I  think the confusion results from  phrases like "shaping space" without an ontology of what space is. If space is simply 3-D volume, the void in which all things and forces exist, what is there to "shape?" Same for "time"... what more than the concept of event duration?... not "something" to be woven together with another non-entity. That is why Brown and Pooley wrote a paper, presented at a conference of the International Society for the Advanced Study of Spacetime: Minkowski's Spacetime: a glorious non-entity.
We observe the curved paths of masses orbiting other masses, but we do not observe a maleable curved medium guiding them...* so what does the concept add to our understanding of gravity?
 

Offline JP

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #6 on: 12/11/2012 19:08:39 »
Well, training physicists comes down to teaching equations at the end of the day and hopefully also imparting a degree of physical intuition, so they don't waste time computing obvious results.

Einstein's field equations and the geodesic equation are fine mathematics by themselves, but pretty complex and hard to get an intuition for.  The geometrical formulation of those equations makes things much more intuitive and has streamlined research because of that.  Plus, a lot of work had been done prior to GR on complex geometries, so much of that could be immediately applied to GR when people realized that it's equations were geometrical in nature, speeding the theory along.

On the other hand, for laypeople the description can be confusing and misleading, since space-time is not physical matter, whereas the analogies used refer to fabric or rubber sheets, or ants running on the surface of a balloon, etc., which all are physical surfaces in a 3D space.  Still, if you're careful, a lot can be gained by thinking geometrically.
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #7 on: 14/11/2012 19:18:15 »
JP,
This is the best explanation I've seen yet of "spacetime curvature" as just a coordinate system, a sort of conceptual geometry for the math by which GR is a clear improvement over Newton's gravity.

Yet every intro to GR refers to mass curving spacetime as if it is an entity that "guides",for instance, planets in their elliptical orbits around the sun.

It seems that the "complex geometries" of the non-Euclidean transition made up "shapes of space" that have no referents in the physical cosmos. (Flat, spherical, parabolic, etc.) If space is 3-D volume, how did it become a malleable medium, except in imagination?
How did Euclid's fifth postulate on parallel lines get debunked, for openers? How is it that the new "complex (non-Euclidean) geometry" has parallel lines intersecting? How did the shortest distance between two points become a curved line on the 'curved surface' of "spherical space?" Two points on a sphere can still be connected by a straight line through the sphere without restriction to an imaginary surface.

I have studied the transition from Euclidean to non-Euclidean geometry (the model for GR's cosmology) in depth for many years, and these questions just "scratch the surface" of ontological study of "what spacetime is supposed to be."
If I started a thread on that, would it need to be in "New Theories?" It is, after all a question of cosmology... what spacetime actually is.
« Last Edit: 14/11/2012 19:20:40 by old guy »
 

Offline JP

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #8 on: 14/11/2012 20:08:59 »
JP,
This is the best explanation I've seen yet of "spacetime curvature" as just a coordinate system, a sort of conceptual geometry for the math by which GR is a clear improvement over Newton's gravity.

Yet every intro to GR refers to mass curving spacetime as if it is an entity that "guides",for instance, planets in their elliptical orbits around the sun.
Well, every theory is a model.  Anyone that tells you that a scientific theory tells you what something really is is lying to you.  We don't have a theory that describes what everything really is yet, and there's debate over whether such a theory is even possible. 

What GR does tell you is that as a model, it describes space-time as a 4D geometrical construct, and that:

1) energy and momentum curves this 4D structure,
2) objects moving through space-time follow paths influenced by this curvature.

What is space-time made up of so that this geometrical model works for GR?  Science doesn't know.

Quote
It seems that the "complex geometries" of the non-Euclidean transition made up "shapes of space" that have no referents in the physical cosmos. (Flat, spherical, parabolic, etc.) If space is 3-D volume, how did it become a malleable medium, except in imagination?
How did Euclid's fifth postulate on parallel lines get debunked, for openers? How is it that the new "complex (non-Euclidean) geometry" has parallel lines intersecting? How did the shortest distance between two points become a curved line on the 'curved surface' of "spherical space?" Two points on a sphere can still be connected by a straight line through the sphere without restriction to an imaginary surface.

I have studied the transition from Euclidean to non-Euclidean geometry (the model for GR's cosmology) in depth for many years, and these questions just "scratch the surface" of ontological study of "what spacetime is supposed to be."
Confusion over what geometry in general relativity (and other non-Euclidean geometries) means is usually due to trying to interpret these geometries by using familiar objects that live within our 3D Euclidean space.  A lot of non-Euclidean geometry is mathematics, which obviously has no problems describing all sorts of surfaces in any number of dimensions which can display non-Euclidean properties such as parallel lines not existing or shortest paths being curved lines. 

Just what these geometries mean in physics requires a model.  General relativity uses non-Euclidean geometry in one way, while trying to draw maps on the surface of the earth uses it in another way.  In the case of the earth's surface, we know that the model requires non-Euclidean geometry because we've intentionally restricted ourselves to the surface (if we could tunnel through the earth, we'd be back to Euclidean geometry).  In general relativity, we don't have a deeper model explaining how this 4D Euclidean geometry arises, though it is an active area of research (whoever figures it out will probably get a free ticket to Stockholm).

Quote
If I started a thread on that, would it need to be in "New Theories?" It is, after all a question of cosmology... what spacetime actually is.
I think you've been around long enough to have a good idea of what's acceptable, Old Guy.  If it's mainstream science, or close to it, then a mainstream forum is a good place for it.  If you're going to propose or promote ideas that aren't testable, then it probably belongs in New Theories. 
« Last Edit: 14/11/2012 20:11:15 by JP »
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #9 on: 16/11/2012 20:00:25 »
JP:
Quote
Well, every theory is a model.  Anyone that tells you that a scientific theory tells you what something really is is lying to you.  We don't have a theory that describes what everything really is yet, and there's debate over whether such a theory is even possible. 

What GR does tell you is that as a model, it describes space-time as a 4D geometrical construct, and that:

1) energy and momentum curves this 4D structure,
2) objects moving through space-time follow paths influenced by this curvature.

What is space-time made up of so that this geometrical model works for GR?  Science doesn't know.

Of course "every theory is a model." And every model is the theoretician's version of the "real world" he is modeling. So it is legitimate to ask, "what is the nature of the world he is modeling?" Is it not disengenuous to state, as a matter of fact, as GR theory does, that "mass curves spacetime" and then "spacetime guides masses in curved paths"... without first defining what is being curved by mass?
A simple graph is a model of an actual event, say stock market fluctuations. The above claim that mass curves our coordinate system model is the same as saying that a sharp upturn in the market makes the graph spike. Yes, but the spike is just a graphic record, after the fact, on paper or a screen. No one would claim that it is an entity directly effected by the market.

The International Society for the Advanced Study of Spacetime has been holding conferences and presenting papers for many years delving into the claim that presents spacetime as an actual entity effecting and effected by masses.
So when you say:
"1) energy and momentum curves this 4D structure,
2) objects moving through space-time follow paths influenced by this curvature."...
It falsely presents the 4-D coordinate system as *something* that is directly effected by energy and momentum. It also falsely makes spacetime into an agent which influences or "guides" objects in their curved paths.

You say:
Quote
A lot of non-Euclidean geometry is mathematics, which obviously has no problems describing all sorts of surfaces in any number of dimensions which can display non-Euclidean properties such as parallel lines not existing or shortest paths being curved lines.
 

How can math make parallel lines not exist? Does it matter at all that the many "manifolds" and imaginary 'shapes and surfaces of space' are imaginary?
Doesn't imagining space as the curved surface of a sphere "make something of it" conceptually that is not there as simple 3-D volume? Do we not then just arbitraily say that the shortest distance between two points on its surface is the curved arc on the surface, restricting as off limits the straight line through the imaginary sphere?

I'm still not sure that these questions would survive in this section as a new thread, but I must ask them. 
 

Online yor_on

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #10 on: 19/11/2012 13:46:16 »
The one about parallel lines is one I'm wondering about too JP. You have a postulate that two paralell lines never will cross each other in the same plane. And that one should hold in a 4-D reality too, as I think? I've seen people referring to it as imagining lines on a sphere (Earth and meridians) or a ellipse, but whenever those lines cross they shouldn't be in the same plane, as it seems to me? Because if they do the postulate is wrong, at least for us. If I assume this then wherever those parallel lines cross must be something 'folding in' on itself as they must have a point meeting where they no longer are possible to differentiate? And that seems as a fold to me?
 

Offline JP

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #11 on: 19/11/2012 15:12:07 »
Well, yor_on, I think your confusion is coming from trying to imagine curved surfaces in our everyday 3D world.  Obviously if you put a sphere in a 3D space and ask "draw me a parallel line on the sphere," you can point out that parallel lines do exist in this world, but you need to take your pen off the sphere (or cut through the sphere) to draw them.  But if you're dealing purely mathematically, you can imagine geometries that don't behave like our own familiar world, in which the entire universe consists of a spherical surface, and there is no such thing as "going off the surface."  In this universe, how would you draw parallel lines?

Since this is a physics forum, not a mathematics forum, the important question is when these mathematical models are useful for physicists.  In many cases, you can model a process taking place within our everyday world by assuming you're stuck to some curved surface.  For example, travel on the earth's surface is pretty well modeled by assuming we're stuck to the surface of a sphere.  Obviously we know this model has limits because we could go off the earth or through the earth if we wanted.

The unique thing about general relativity is that we weren't looking at a problem and asking "how can we model this geometrically?"  Einstein came up with the equations by making some simple postulates and those equations happened to perfectly describe objects moving through a curved 4D structure, space-time.  However, because we don't have a deeper "theory of everything" that places general relativity in the context of some deeper theory, we don't know if this 4D structure is somehow a simplification of a deeper structure.  So the idea of "lifting our pencil off the paper" when tracing out lines in space-time doesn't make scientific sense.  It's possible that advances towards a theory of everything might illuminate this, but right now we just don't know.
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #12 on: 19/11/2012 20:08:31 »
JP:
Quote
But if you're dealing purely mathematically, you can imagine geometries that don't behave like our own familiar world, in which the entire universe consists of a spherical surface, and there is no such thing as "going off the surface."  In this universe, how would you draw parallel lines?
We can imagine anything we fancy, but doesn't even math require referents in the world which our models are modeling?
If the "entire universe consists of a spherical surface" what is the nature of this surface if not just imaginary and what is beyond and within the sphere? This is the classical challenge to a finite universe with a particular shape. First, of what does the boundary consist, and then what is beyond that boundary?
Meanwhile, back in the real world, not imaginary, if "parallel lines" are said to intersect, they are not parallel lines. And a curved line is still not the shortest distance between two points, disregarding (or going straight through) imaginary curved surfaces. So, does non-Euclidean geometry and cosmology simply re-define the terms to create an imaginary model to suit the math?
 

Offline imatfaal

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #13 on: 20/11/2012 16:14:25 »
Let's not have this thread devolve into another debate about realism.  If you wish to debate matters of philosophy, ontology and epistemology - please do it in chat or new theories.  The main boards are not the place for metaphysical musings.

Thanks
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #14 on: 20/11/2012 19:58:51 »
Let's not have this thread devolve into another debate about realism.  If you wish to debate matters of philosophy, ontology and epistemology - please do it in chat or new theories.  The main boards are not the place for metaphysical musings.

Thanks
I'm sorry if that is how you read my intent. JP said:
Quote
...you can imagine geometries that don't behave like our own familiar world, in which the entire universe consists of a spherical surface, and there is no such thing as "going off the surface."  In this universe, how would you draw parallel lines?
How is this "imagined geometry" not a "metaphysical musing?"
I was asking about the physical and geometric referents to which the model of curved spacetime (and a spherical universe) refers (the opposite of metaphysical), as per the original post. ("What is the fabric of space made of?") The transition from Euclidean to non-Euclidean geometry and cosmology is of central relevance to the understanding "spacetime" and its theoretical properties.
« Last Edit: 20/11/2012 20:02:48 by old guy »
 

Offline JP

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #15 on: 21/11/2012 19:06:32 »
In the post you quote above, yor_on asked how geometry can render the idea of non-intersecting parallel lines impossible.  I explained how it could, and that it was pure mathematics.  I haven't made any attempts to shoehorn metaphysics into this discussion.
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #16 on: 21/11/2012 20:16:48 »
thedoc (admin.) introduced the question in the OP:
"What is the fabric of space made of?"
JP,
You said in reply 23:
"What is space-time made up of so that this geometrical model works for GR?  Science doesn't know."

How then can GR theorists say, as a matter of fact in every intro to GR, that mass curves spacetime and in turn curved spacetime guides masses in their curved paths? Yet we are not allowed to ask the ontological questions, "What is it that is curved by mass" and "What then guides masses (as above)?" If science doesn't know what it is... well, what curves after all... besides the obvious... the paths of masses influenced by gravitational attraction?

Btw, how do parallel lines intersect again, debunking Euclid's fifth postulate and laying the groundwork for all non-Euclidean geometry and resulting cosmology? Please explain the "pure mathmatics" of it as applied to the geometry. I'll try to follow as best I can. This is not sarcastic. It could be the key to the Euclid-to-non-Euclid transition for me... That and the curved line being the shortest distance between two points. Does that depend on sticking to imaginary curved surfaces too?
 

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #17 on: 22/11/2012 12:43:04 »
If science doesn't know what it is... well, what curves after all... besides the obvious... the paths of masses influenced by gravitational attraction?

I may have the wrong end of the stick here, do you mean newtonian gravitation? if so, given that Newton never described a mechanism by which his postulated attracting force worked, can you tell us ? Am i still holding the wrong end of the stick?
 

Offline old guy

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #18 on: 23/11/2012 05:43:52 »
If science doesn't know what it is... well, what curves after all... besides the obvious... the paths of masses influenced by gravitational attraction?

I may have the wrong end of the stick here, do you mean newtonian gravitation? if so, given that Newton never described a mechanism by which his postulated attracting force worked, can you tell us ? Am i still holding the wrong end of the stick?
No, I can't tell you.
Please start a new thread for this question in "New Theories." It will not be tolerated here by the mods. No one knows how gravity works. We observe that mass attracts mass. Quantum physics posits "gravitons" between masses somehow conveying attractive force. GR posits a *metaphysical* medium, entity, model called but unexplained, "spacetime."
The meaning of that compound concept would require an ontology of what space is, what time is, and what the coalescense of the two into a unified "fabric" is concieved to be. Not allowed in this forum's version of physics and cosmology.
And there is no philosophy of science in this forum. Sorry.
 

Offline imatfaal

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Re: Re: What was the Big Bang, and where did it come from?
« Reply #19 on: 23/11/2012 14:10:06 »
Exactly - this is a physics Question and Answer forum, and not a fitting location for a discussion of philosophical points that are not answered by modern physics.  I have pointed out on numerous occasions that discussions of metaphysics, ontology, epistemology are more than welcome in the chat forum and in new theories - but we do like to keep the main fora clear and dedicated to questions that can be answered without recourse to non-scientific methods.

What space time geometry actually is?  This is a fine question - and may well be answered by physicists in the future when we see a convergence between quantum field theory and gravitation; but at present it is either a wild speculation that must go into New Theories, or non-scientific and belongs in Chat or New Theories.  How we use the stress-energy-momentum tensor and other tensors to calculate the local curvature and thus the geodesic that an body will follow through 4d space time; that is modern physics.  It is clear that you do not appreciate or agree with the arbitrary line that we have drawn - that is your prerogative in your own dealings, but on this site we must ask that you abide by the rules and guidelines we have laid down. 

I am going to move this and the preceding posts on this topic to New Theories.


Stop Press

I changed my mind on the move and split the recent section into this newly named thread
« Last Edit: 23/11/2012 14:14:50 by imatfaal »
 

Offline Phractality

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I would love to explain exactly what the fabric of space-time is, but I can't do so in this mainstream forum without having my account suspended. The last time I came close to doing so I was booted off for three weeks. So I must confine my answer to mainstream concepts, and there is no mainstream concept of what the fabric of space time really is, except that it has no existence apart from mathematics, which is a concept that I detest.

I think I can get away with stating the following: Space-time is warped because of the way we define the units of distance and time. The second and meter are defined in terms of the constancy of the speed of light and the wavelength and frequency of a particular emission from the cesium atom, and it doesn't matter where that cesium atom is located. It can be located at the maximum gravitational potential in the universe (the middle of a cosmic void) or at the event horizon of a black hole. As long as meters and seconds are defined that way, it is necessary for a metric divided into equal 4-cubes of meter-seconds to be warped.

I am no mathematician, but I suspect it would be possible to define space-time as being a flat (Euclidian) metric; but then, the units of distance and time relative to the cesium atom emissions would have to be variable, depending on the gravitational potential where the cesium atom is located. It might also be necessary to define the speed of light as variable in such a metric.
We use Minkowski space-time because, to the best of our knowledge, it works and because it is consistent with how we believe an observer would measure his own environment, regardless of where his is.
 

Online yor_on

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Thanks JP, I see how you define it and that way it makes sense. The problem for me is that I sometimes see it as something expected to be inside SpaceTime, and I fail to see where that is possible? If it is possible then wouldn't that point where those lines cross become something of a enigma physically? Maybe one could imagine it as a black holes center possibly? There is the argument that you indeed can draw parallel lines on a ball though? I think I only need a marker, keeping a same distance between those lines at all times, to call those two lines parallel? Or is that to simplistic?
==

You can argue that if we fold out the ball those lines won't be parallel any longer, but that is assuming that a plane is the only correct way to define those lines as being parallel? But maybe that is a argument for it? after all, we all need some ground to stand on. And btw? If I would fold it out and then draw two parallel lines, would they then intersect as I form it into a ball anew?
« Last Edit: 23/11/2012 19:50:01 by yor_on »
 

Online yor_on

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OG, as for the questions of why a curved line is the 'shortest path' in SpaceTime that's just because it is, in SpaceTime :) As long as gravity distort those ideal 'straight' paths we otherwise imagine. I would call it a practical approach to what we have, as a 'straight' path would need to consume/expend energy to be straight.

Sometimes I think of it as invisible onions out there, every 'leaf/shell' defining a geodesic :) But I guess you would need a infinite amount of onions as those geodesics must exist in all directions, at all and any point. And you need the onions to 'melt' into each other too to make it work, as I think. Gravity and geodesics are strange in that I'm not sure how they can express themselves as 'no resistance' if all points can be said to represent a indefinite amount of possible directions simultaneously. You can imagine it as a infinite amount of balls, all moving uniformly, simultaneously, in all directions possible, through and in, and out of, each point of SpaceTime. And doing it that way the question becomes what this 'no resistance' means?
==

the point being, ahem, that I think all directions are possible geodesics if you allow mass to pass at a point in 'normal' space although a black hole then becomes something of a opposite, as it only allows for one ultimate direction (after passing the event horizon).
=

One point more, if gravity and mass goes together, then gravity must be dynamically updated at all points, as all mass are in motion relative all other mass. Now think of a light beam, or a 'photon' propagating and try to see how it moves :) and here the question also becomes one of 'fluidity' relative 'quanta/jumps' because if I assume that all points inside SpaceTime finds a equilibrium relative all other points 'gravity', each point representing one gradient/slope or 'direction of gravity'. would those points gradients be quantized, or would they smoothly pass into each other?
« Last Edit: 23/11/2012 20:12:03 by yor_on »
 

Offline old guy

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imatfaal:
Quote
What space time geometry actually is?  This is a fine question - and may well be answered by physicists in the future when we see a convergence between quantum field theory and gravitation; but at present it is either a wild speculation that must go into New Theories, or non-scientific and belongs in Chat or New Theories....

I changed my mind on the move and split the recent section into this newly named thread

This leaves me thoroughly confused as to what is and is not acceptable discussion of the ontology of spacetime in this thread.
I will do my best to avoid "wild (and non-scientific) speculation" and state as clearly and succinctly as I can what I think space, time, and spacetime are. Please assume "I think" in front of each statement as a given.

Space is the 3-D volume in which everything exists and moves. "It" is nothing by itself... just the void, on all scales, with no limit, boundary, or "shape." Beyond any proposed "shape of space" is... more space. What boundary? What beyond a proposed boundary. Infinite space.

Time is the concept of event duration. All movement can be said to require time, but it is an ontological error to reify time, "making something of it." When clocks slow down in rate of "ticking" (as when velocity increases relative to a "stationary" control clock), it is called "time dilation." This is a misnomer, an example of reification as above, misleading physicists to believe that it is an entity which is "woven together" with space as "spacetime."

Since neither space nor time is an entity, neither is "spacetime." There is nothing to be "curved by mass." It remains a convenient tool, a coordinate system, an abstract geometry, a conceptual "scaffolding" for the math, which demonstrates significant improvement over Newtonian theory in predicting the movement of mass and light effected by other masses.
GR's insistence that "mass curves spacetime" is therefore false and misleading, and shoould be corrected. All that can be honestly said is that mass attracts mass (and light, with momentum equalling mass) and that the paths of masses and light are curved around other masses.
That is my answer to the last question in the original OP.
 

Online yor_on

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Well OG, we know that light bend to mass. The reason is gravity and there you have physical experiments proving it. What gravity is, and space, is another thing though and not settled yet. It depends on what you find the best explanation, and also depending on where you stand relating to Relativity, Quantum physics, or anchored in the classical version of what we see. As for if they are entities? (That which is perceived or known or inferred to have its own distinct existence (living or nonliving)) space surely exist, and so do time.
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If you think of it then what Einstein did to time and space was just to put them together, as responding to each other, relative 'motion' acceleration and mass. What one have to remember there is that it all is relative a observer, meaning that whatever shape one find the universe to have it must always be relative ones (relative) motion, acceleration and mass. Objectivity can only be reached conceptually in Einsteins SpaceTime, as long as we assume a undivided homogeneous universe, same for us all. Another thing worth noticing there is that simultaneity, as in us being able to define the exact same 'time', also becomes a conceptual definition depending on the observer.
« Last Edit: 23/11/2012 21:30:48 by yor_on »
 

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