Post by: old guy on 29/10/2012 20:00:15
the big bang theory is a good one in all , but how does something just explode and create a universe?These are such good questions! I'm suprized the discussion has not taken serious flight.
what was it that exploded?
where did it come from?
whats it made of?
what is the fabric of space made of?
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.
Post by: yor_on on 01/11/2012 21:05:58
Gravity?
Post by: old guy on 02/11/2012 19:37:09
Is there a 'fabric of space'?Gravity: Mass attracts mass. What "fabric?"
Gravity?
Post by: yor_on on 11/11/2012 16:04:57
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 :)
Post by: JP on 11/11/2012 21:36:08
So yeah--I also agree that it's a confusing term.
Post by: old guy on 12/11/2012 18:48:30
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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:
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... 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?
Post by: JP on 12/11/2012 19:08:39
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.
Post by: old guy on 14/11/2012 19:18:15
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.
Post by: JP on 14/11/2012 20:08:59
JP,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.
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.
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.
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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?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.
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."
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).
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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.
Post by: old guy on 16/11/2012 20:00:25
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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:
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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.
Post by: yor_on on 19/11/2012 13:46:16
Post by: JP on 19/11/2012 15:12:07
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.
Post by: old guy on 19/11/2012 20:08:31
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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?
Post by: imatfaal on 20/11/2012 16:14:25
Thanks
Post by: old guy 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.I'm sorry if that is how you read my intent. JP said:
Thanks
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...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.
Post by: JP on 21/11/2012 19:06:32
Post by: old guy on 21/11/2012 20:16:48
"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?
Post by: lean bean 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?
Post by: old guy on 23/11/2012 05:43:52
No, I can't tell you.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?
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.
Post by: imatfaal on 23/11/2012 14:10:06
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
Post by: Phractality on 23/11/2012 18:07:02
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.
Post by: yor_on on 23/11/2012 19:14:26
==
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?
Post by: yor_on on 23/11/2012 19:30:37
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?
Post by: old guy on 23/11/2012 20:46:56
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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.
Post by: yor_on on 23/11/2012 21:18:32
==
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.
Post by: yor_on on 23/11/2012 22:48:32
A he* of a lot of energy it seems, creating a 3D 'place' for matter to come to be, having one dimension more that we call the arrow, making the processes from energy into matter we see logical (and so also linear), as found in the LHC. To us at least, macroscopically, but also microscopically as it is the outcomes we use to backtrack other possibilities. The ones most consistent seems to be what the universe use to give us what we have, but it also has to do with temperatures and symmetry breaks, assuming a hot Big Bang. Assuming a cold? Then it could be patterns, and how they evolve inside a arrow possibly?
But assuming a lot of energy seems to me to also assume a lot of 'heat', at least when it comes to those first particles of mass moving?
==
(Maybe it would be possible to argue that 'particles' create 'space' though? As in space and mass being some sort of symmetry where you can't have one without the other, including a arrow. Somehow it feels to me as if relativity's approach is this one. But then we also would need some mechanism for how the 'inflationary period' (FTL) slowed down to a accelerating expansion. All of it assuming that 'energy' isn't constricted geometrically, except when (transforming) inside our universe :)
Post by: JP on 24/11/2012 03:39:47
Post by: JP on 24/11/2012 03:49:38
So back on the question of what it really is--we know what models work for it, and our "deepest" tested model right now is one that describes a curved geometry, but we'll probably never be able to tell you with 100% confidence that any model is the absolute correct one and that there is nothing further to discover. At least no model in science so far has yielded absolute truth.
Post by: lean bean on 24/11/2012 15:12:33
that matter curves space-time because that's what our mathematical model describes. We do this because as scientists we understand that our model isn't a universal truth, but that it works for some range of problems. So when we say gravity curves space-time, we mean that no matter what space-time is on a deeper level, on some level it acts just like a 4D structure with curvature. If that's confusing or misleading, that's really a problem for the broader education system--there are a lot of people out there who don't understand how science works and don't understand the difference between a scientific model and metaphysical certitude.
Yes, I buy in to that big time.
Another mathematical model is the one that defines a particle as a wave or oscillation in a fundamental field. What’s that field made of? Sorry you have to start somewhere, the field just is.
Each type of particle having its own field. Even virtual particles may be thought of as ripples or disturbances in fields.
So, if you want your particles solid, that’s too bad.
Tin maybe malleable, but in the mathematical model of fundamental particle fields your just playing with fields all the way down.
And because the field is a mathematical entity or thing, then it can have the property of energy associated with its waves/particles, in other words, energy is a property of the field.
Post by: zordim on 25/11/2012 00:19:15
At least no model in science so far has yielded absolute truth.
What is - really, truly, scientifically - the space?
Well, it is the following:
- that is something that contains everything. And that "everything" is, essentially, the energy, packed in different ways/forms.
- that is something in which we can notice and measure that what we call "lengths". There can exist maximally three straight line segments which are mutually orthogonal (perpendicular) and which cross each other at one and the same point, and that is why we call it the 3D space.
- that is something that has the following two, detected, measured - that is - scientifically proven properties: the lengthwise capacitance
(a.k.a. electric permittivity), and the lengthwise inductance 
(a.k.a. magnetic permeability). Because of these two properties, electromagnetic properties, the space is an electromagnetic phenomenon.The elementary existence manifestation, the most elementary entity, which manifests its existence within the space, is the photon.
Photon's properties are: energy, EM-oscillation period, wavelength. It moves. "Moving" is the way it exists. There are no photons which do not move. And they move with the velocity which is determined with
and properties of space.Time is that what gives sense to existence. (Without it, we could not determine, we could not define the existence. Without it, some entity could pass some distance "in no time", so it could be throughout the space. So, that entity would be everywhere. Everything would be everywhere. So, space and that what has energy could not be distinguished. There is no need to continue this elaboration, since it is obviously absurd).
Time is the axiom of existence. How is it related to existence? Well, it is one of five axioms of existence, four of which are related in the following way:
. The fifth axiom of existence is energy. Its elementary manifestation is the photon. The time is related with energy in the following way: 
, and that directly follows from 
.
, , and are axiomatic properties of the space. Hence, due to the relation , 
is also an intrinsic, inherent property of the space. That is why the space is the spacetime.All of the five axioms of existence: lengths, time,
, , and energy, affect each other, and all of them change continually."We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes."Sir Isaac Newton
And, we do not need the Minkowski spacetime postulation to explain the reality. Minkowski's idea was right, but the model of that idea is wrong. With Minkowski spacetime postulation, and Einstein's postulated tensor equation, we can only approximately model the reality, and we cannot understand it in that way. It is just some nice, abstract mathematics, which produces approximate results, which model but do not explain anything. The goal of science is to understand, and not just to model. Ptolemy's helicoids described the movement of celestial bodies well. But that provided no understanding at all.
"A man may imagine things that are false, but he can only understand things that are true, for if the things be false, the apprehension of them is not understanding."Sir Isaac Newton
"The noblest pleasure is the joy of understanding."Leonardo da Vinci
The results, the final equations that Einstein-Minkowski postulates yield, are not in accordance with continuity principle, and with energy conservation principle. (And there are even worse consequences. And being worse than non-compliance with the continuity and energy conservation is really, really bad situation. And accepting that as science is extremely bad situation).
P.S.
"We can’t solve problems by using the same kind of thinking we used when we created them."Albert Einstein
"The important thing is not to stop questioning. Curiosity has its own reason for existing."Albert Einstein
Post by: old guy on 25/11/2012 19:56:35
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So when we say gravity curves space-time, we mean that no matter what space-time is on a deeper level, on some level it acts just like a 4D structure with curvature.
In other words science grants itself enough freedom to assert that mass curves something without saying what that something is. I understand the function of a model. As I said earlier, I also understand that a model models something. It is the "something" which is the issue here.
GR asserts that the "something" "acts like"... "a 4D structure with curvature." You totally ignored my post above asserting that space is the 3-D void* in which all things exist and move. (* A void is no-thing, not some-thing. A void has no "curvatgure.")
Likewise my ontology of time as a non-entity (which you ignored.) Yet you assert (GR asserts) that spacetime "acts like a structure" and you further describe it as curved. Surely a curved structure is an entity of some kind. I have mentioned the international society which strongly contests that universal assertion among GR theorists. Yet you speak of it as a given. That is not "discussion" but GR's version of dogma.
Post by: JP on 25/11/2012 22:10:07
I think we all know that no matter what your stance is on metaphysics, physics describes very precise properties for space-time. If you're unhappy with that description, New Theories is the place for it. :)
Post by: Phractality on 25/11/2012 23:00:05
You could define the units of distance and time in a flat metric to be equal to the meter and second at a point of maximum gravitational potential (like the middle of a cosmic void). For convenience, let's call the flat-metric units "fleters" and "fleconds". In the middle of a cosmic void, 1 fleeter = 1 meter, and 1 flecond = 1 second.
Measuring the cesium atom emission relative to those units, you would find that a meter stick at the bottom of a gravity well is shorter than one fleter, and an atomic clock ticking once per second would be ticking slower than one tick per flecond. (Someone please correct me if I got that bass ackwards.) I'm not sure, but it might also be necessary to let the speed of light, in fleters per flecond, to be different in and out of the gravity well. (Wanted: A mathematician to determine whether the speed of light, in fleters per flecond, is constant.)
It has been stated several times, in this thread, that gravity bends light. That is true in a flat metric, but it is not true in GR. In Minkowski space-time, the path of light in a vacuum is the definition of a straight line, so photons can't be bent by gravity. Light follows a straight line thru a gravity well, and comes out in a different direction. That's what a warped metric is all about.
I don't know for sure, but I strongly suspect that my own ontology for the fabric of space-time is uniform relative to a flat metric.
Post by: JP on 26/11/2012 02:38:22
Let me repeat myself, since no one seems to have heard me the first time. Meters and seconds are defined by the constancy of the speed of light and the wavelength and frequency of cesium atom emissions, regardless of where the cesium atom is. The space-time metric of GR is represented by a 4D grid of hypercubes, each measuring 1 meter cube by 1 second. That grid is what is warped, and it is warped because, in a flat space-time metric the cesium atom emission are not constant. By "flat space-time metric" I mean a metric represented by units of distance and time which, by definition, agree with Euclidean geometry. (I am not introducing new theory. Flat space-time is nothing more than a mathematical transformation of warped Minkowski space-time.)We can argue over definitions, but the basic assumption is that SR is correct and the speed of light is constant over small enough regions in a vacuum (i.e. over flat space-time). This allows us to define the "second" and "meter" in terms of EM radiation, either distance traveled in a fixed time or the length of time it takes for a given number of oscillations of a wave to pass us. So I think we basically agree, although we use slightly different terms. :)
I do disagree with the statement that the space-time metric is a grid of 1 meter x 1 second hypercubes. It's more correct to say that space-time is a geometric construct that can be represented in terms of a grid of those hypercubes (if it's flat) and in terms of some distorted grid (if it's curved).
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...General relativity assumes that space-time is continuous and is structured so that you can look at smaller and smaller regions without limit. Under those assumptions, if you look at a small enough region, it looks flat, and the speed of light over that flat region is constant (and equal to "c" if measured by a local observer). This is analogous to how if you look at the ground under your feet, it looks flat, even though the earth is (roughly) spherical. The curvature deals with how things move from 1 region to another.
Measuring the cesium atom emission relative to those units, you would find that a meter stick at the bottom of a gravity well is shorter than one fleter, and an atomic clock ticking once per second would be ticking slower than one tick per flecond. (Someone please correct me if I got that bass ackwards.) I'm not sure, but it might also be necessary to let the speed of light, in fleters per flecond, to be different in and out of the gravity well. (Wanted: A mathematician to determine whether the speed of light, in fleters per flecond, is constant.)
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It has been stated several times, in this thread, that gravity bends light. That is true in a flat metric, but it is not true in GR. In Minkowski space-time, the path of light in a vacuum is the definition of a straight line, so photons can't be bent by gravity. Light follows a straight line thru a gravity well, and comes out in a different direction. That's what a warped metric is all about.That's partway true. Light follows geodesics, which are a generalization of a straight line to curved geometries. They are not the same as straight lines because they can't always have all the properties of straight lines. What they are is the shortest path between two points (or longest path), which in flat space-time is a straight line. So it is correct to say that gravity bends light because it makes the shortest path between two points a curved trajectory.
Post by: old guy on 26/11/2012 07:41:12
Old Guy, I'm ignoring all your posts that try to shove realism into the discussion. That's why I haven't responded.JP,
I think we all know that no matter what your stance is on metaphysics, physics describes very precise properties for space-time. If you're unhappy with that description, New Theories is the place for it. :)
It is a misrepresentation of my intent to say that I am "trying to shove realism into the discussion." I hope it is not intentional. I am trying to bring realism into the discussion in a reasonable way for those who still understand that Earth does not change diameters with every possible frame from which it might be observed and measured. The same goes for distances between bodies in this solar system and between stars (and galaxies.)
Different observations of the same object or distance do not make the object or distance change. That is basic here, not "shoving" realism into the discussion. Earth's diameter is just under 8000 miles... not varying with the speed of a passing observer. Same for all the other examples.
A "physics" that describes that diameter as 4000 miles or whatever, depending on the relative velocity of the observer, is the metaphysics of Einstein, who said that there is no reality independent of differences in observation, and that all frames of observation are equally valid.
It is late and this may belong in my other thread, but Earth does have its shape independent of observation; and "spacetime" is still a metaphysical concept... a "model" or concept without observable referents ("time" and malleable space-as-an-entity.)
In other words, we do not " all know that physics describes very precise properties for space-time."
Non-entities have no "properties." "Spacetime" is not an entity. I can cite literally reams of arguments from the scientific commnunity which agree with that analysis. (I have already.)
Post by: JP on 26/11/2012 15:15:42
Old Guy, I'm ignoring all your posts that try to shove realism into the discussion. That's why I haven't responded.JP,
I think we all know that no matter what your stance is on metaphysics, physics describes very precise properties for space-time. If you're unhappy with that description, New Theories is the place for it. :)
It is a misrepresentation of my intent to say that I am "trying to shove realism into the discussion." I hope it is not intentional. I am trying to bring realism into the discussion in a reasonable way for those who still understand that Earth does not change diameters with every possible frame from which it might be observed and measured. The same goes for distances between bodies in this solar system and between stars (and galaxies.)
Different observations of the same object or distance do not make the object or distance change. That is basic here, not "shoving" realism into the discussion. Earth's diameter is just under 8000 miles... not varying with the speed of a passing observer. Same for all the other examples.
Sorry, you're just introducing it gently into the discussion despite being repeatedly asked by the moderators not to do so. :)
Going forward, I will shrink posts on realism in this thread, to keep it on track.
Post by: simplified on 27/11/2012 15:35:01
Some motion is speed,but some motion is time.Don't forget it!
Post by: old guy on 27/11/2012 18:58:13
JP,Old Guy, I'm ignoring all your posts that try to shove realism into the discussion. That's why I haven't responded.JP,
I think we all know that no matter what your stance is on metaphysics, physics describes very precise properties for space-time. If you're unhappy with that description, New Theories is the place for it. :)
It is a misrepresentation of my intent to say that I am "trying to shove realism into the discussion." I hope it is not intentional. I am trying to bring realism into the discussion in a reasonable way for those who still understand that Earth does not change diameters with every possible frame from which it might be observed and measured. The same goes for distances between bodies in this solar system and between stars (and galaxies.)
Different observations of the same object or distance do not make the object or distance change. That is basic here, not "shoving" realism into the discussion. Earth's diameter is just under 8000 miles... not varying with the speed of a passing observer. Same for all the other examples.
Sorry, you're just introducing it gently into the discussion despite being repeatedly asked by the moderators not to do so. :)
Going forward, I will shrink posts on realism in this thread, to keep it on track.
Imatfaal split this thread off from the "What was the big bang..." thread, gave it a title and called me the author.
Here is a breakdown of the questions raised in the title:
What is spacetime? That is an ontological question requiring discussion of the nature and "reality status" of space, time, and the combination "fabric." How can its "reality status" be discussed without referring to realism? Iow, "How real is spacetime?... Discuss without reference to what is real!"
"Is it a model?" Discuss without reference to what a model models or the difference between a model and that which is modeled (the real world)!
"Is it a fabrication?" Discuss how real the "fabric of spacetime" is without presenting the realist side of the argument!
So one moderator allows the ontological discussion (makes the title an ontological subject) while another forbids the argument from realism essential to such a discussion.
This leaves me totally confused about what is allowed here and challenged to a "fight" ("discussion") with both hands tied behind my back.
I think I need a 'referee' with a sense of fairness not forbidding realism in a discussion of what is real.
Post by: Phractality on 27/11/2012 21:39:28
As a member who has been disciplined for "proselytizing", myself, I caution you that you are skating on thin ice.
You are in good company when it comes to being beaten down for trying to bring ontology in the mainstream of science. Einstein, himself, was beaten down by his peers for the same thing. I think his Leyden Address (http://www.aetherometry.com/Electronic_Publications/Science/einstein_aether_and_relativity.php) may have been his last public mention of his conviction that the aether must be a ponderable medium. He reluctantly agreed that the reality of the aether, or lack thereof, is a moot point, given a purely mathematical space-time metric which correctly solves real-world problems.
I agree with you, and with Einstein, that a space-time metric with no ontological significance leads mainstream science up a blind alley. Without a sense of what the fabric of space time really is, there are limits to how far we can develop our theories. However, those of us who feel that way are, for the time being, outside the mainstream. We should consider ourselves lucky to have a New Theories forum in which we may discuss our heretical views.
Perhaps Imatfaal was wrong to place this thread in the mainstream forum. Several of the questions in the OP are not answerable without introducing new theory. These are cosmological questions, and in my opinion, cosmology has always been a matter of philosophy and religion, and it still is.
In my opinion, any theory which is not widely accepted by the mainstream is a new theory, regardless of whether it is championed by a mainstream scientist. Even some very old theories which are trying to make a comeback, like the Fatio/LeSage model, are not mainstream; so they belong in the "New Theories" forum. Maybe it should be called the "Renegade" forum, or the "Heresy" forum, instead.
Post by: old guy on 29/11/2012 03:10:53
Thank you for your support. I have been on thin ice here from the beginning. No one can challenge mainstream SR/GR (or parts thereof) without the threat of banishment. (I've participated on many science forums over the years.) I only challenge specific parts, as evident in all my posts.
And it is good that "The Lighter Side" section can still tolerate common sense, logical, reasoning and 'free thinking' as "New Theories"... though Euclid's postulates of geometry and implications for cosmology are not new theories but rather old theories not yet totally debunked by non-Euclidean imaginative revisions.
I hope for a reply to my last post clarifying the issue of what they accept in this section and what is still considered "wild speculation" and/or "the lighter side" not to be taken seriously... like asking what spacetime IS, and what the "fabric's" components are. The mods really need to find a consensus on this. Otherwise it is just a "bait and switch" situation. Like go ahead with your argument, and if that mentions or invokes realism, you will fall through the thin ice, by mod censorship.
Post by: grizelda on 29/11/2012 04:24:32