What is "spacetime" really?

[jedaisoul]

Sally doesn’t (and can't) measure AC. Why do her measurements of AB and BC invalidate AC? You skipped a few steps there—please explain.

 

Massive objects don't measure the length of a zero interval.

You have repeatedly mentioned measurement, and if you focus solely on what you can measure, of course, what you say is true. The metric is self-consistent. I agree with that.

 

I have expressed what Sally experiences. Sally does not experience the time-like and space-like intervals cancelling in a zero spacetime interval. To light the spatial and time intervls are zero anyway.Therefore a zero interval expresses what light experiences not what material objects experience in those circumstances.

 

I can't see how you can fault that logic.

 

What material objects experience is the time and spatial intervals separately. They do not cancel in a zero interval, so why should we assume that they do in a non-zero interval?

 

The fundamental philosophic question is whether zero intervals cancel for light, or are simply zero anyway. If the spacelike and timelike intervals are zero, there is no difference for light whether they add, subtract or multiply. They are still zero. The same is not necessarily true for material objects.

 

Anyway, I doubt we will make any progress. We've both repeated what we are saying without convincing the other that there is (in your case) no problem, or (in my case) a valid philosophic argument about the interpretation of zero intervals.

[modest]

You have repeatedly mentioned measurement, and if you focus solely on what you can measure, of course, what you say is true. The metric is self-consistent. I agree with that.

 

I have expressed what Sally experiences. Sally does not experience the time-like and space-like intervals cancelling in a zero spacetime interval. To light the spatial and time intervls are zero anyway.Therefore a zero interval expresses what light experiences not what material objects experience in those circumstances.

 

Let's call this an accord. ;)

 

~modest

[Michael Mooney]

jedaisoul,

For openers, you wrote:

This is where I have to (partially) agree with modest. Traveling at the veloity of light, time stops and all spatial distances are zero.

 

If you review my challenge to the standard error of reification of time in this thread you will find, stated as simply as I can: "The furture is not yet real and present, and the past is not still real and present, aqnd there is *no time* between future and past but only the perpetally ongoing now... everywhere, from cosmic perspective; i.e., transcending the local perspectives of relativity... what observer can see what light and when relative to sources and other observers.

So, "square one" of thgis threads inquire makes no assumption about what "time" is, but rather examinbes it outside the usual assumptions of relative perspectives and lightspeed.

So, If you understand the above, from the cosmic perspective of the absolute, eternally ongoing now, there is no "time dialation."

 

Secondly, if you understand what I've said in this thread about space, you will find that, contrary to relativity *dogma*, space is the emptiness between the "things" which occupy space,... in the linear sense, the actual distance between said objects, though space is infinite three dimensional volume. (Any posited boundary... made of what?... would have more space, in fact infinite space on "the other side" of the hypothetical boundary.

 

So, in *the real cosmos* there 93 million miles or so between sun and earth and it actually takes sunlight 8+ minutes to travel from sun to earth. Lightspeed remains constant in the actual cosmos at 186,000 mps.

You mathematicians can create "thought experiments" to suit your fancy and, in the process, imbue light with a reality all its "own"... i.e., "for a photon" there is no space between earth and sun and no "travel time" between them either. Problem is, it is false and irrelevant to the actual cosmos of objects and the space between them and the "time" it takes light to travel from its source to a destination which absorbes it.

Off to T-day dinner. Please address my post without negating the actual distance between things or the actual travel time of light between them.

(Does the light of our cosest neighboring star also travel instantaneously to earth, or does it still take 3 of 4 years, being so many lightyears away from earth in actual (relatively empty) space?

[Erasmus00]

"The furture is not yet real and present, and the past is not still real and present, aqnd there is *no time* between future and past but only the perpetally ongoing now... everywhere, from cosmic perspective; i.e., transcending the local perspectives of relativity... what observer can see what light and when relative to sources and other observers.

So, "square one" of thgis threads inquire makes no assumption about what "time" is, but rather examinbes it outside the usual assumptions of relative perspectives and lightspeed.

 

The problem is that special and general relativity make concrete, testable predictions, and those predictions have stood the test of time. Any interpretation of the theory has to square with the mathematics of the theory! "Now" in the theory is an observer dependent concept (the order of events is different observer to observer).

 

So, in *the real cosmos* there 93 million miles or so between sun and earth and it actually takes sunlight 8+ minutes to travel from sun to earth.

 

This is observer dependent, just like the concept of "now," in the theory of special relativity. Even if you try and reinterpret the spacetime metric, the predictions are the same. It could be argued that the frame of reference of light is completely meaningless. However, it cannot be argued that many different observers will measure different things for distance between the same two objects (and the time between two different events, etc).

 

If you deny these relationships, as you want to do for philosophical reasons, you need a new model to explain all the predictions.

-Will

[jedaisoul]

If you review my challenge to the standard error of reification of time in this thread you will find, stated as simply as I can: "The furture is not yet real and present, and the past is not still real and present, aqnd there is *no time* between future and past but only the perpetally ongoing now... everywhere, from cosmic perspective; i.e., transcending the local perspectives of relativity... what observer can see what light and when relative to sources and other observers.

So, "square one" of thgis threads inquire makes no assumption about what "time" is, but rather examinbes it outside the usual assumptions of relative perspectives and lightspeed.

So, If you understand the above, from the cosmic perspective of the absolute, eternally ongoing now, there is no "time dialation."

I would reply as follows:

• You state this philosophic interpretation of space and time as if it were fact. I would call it Presentism. There is an alternative philosophic view called Eternalism. Now I happen to prefer Presentism to Eternalism, but neither are fact.
  
• Spacetime is a specific interpretation of space and time that is part of Special and General Relativity. Neither Presentism nor Eternalism can account for relativity, so discussion of either, or both, would seem to be irrelevant to the question "what is spacetime really?".
  
• Spacetime is either an abstract mathematical model, or a description of reality. I have been pointing out where I think that spacetime fails to reflect reality, specifically in the interpretation of zero intervals. Hence I'm arguing, like you, that spacetime is really just a mathematical model.

 

Secondly, if you understand what I've said in this thread about space, you will find that, contrary to relativity *dogma*, space is the emptiness between the "things" which occupy space,... in the linear sense, the actual distance between said objects, though space is infinite three dimensional volume. (Any posited boundary... made of what?... would have more space, in fact infinite space on "the other side" of the hypothetical boundary.

I liked your argument against the reification of space and time. I regard neither as actual physical entities. However, here you seem to be reifying space yourself by saying "though space is infinite three dimensional volume...". In my opinion, space does not exist as an entity in and of itself. It is no more than the distance between material objects (which I think is what you are trying to say). Therefore it is neither finite nor infinite. It isn't, of itself, anything.

.

You mathematicians can create "thought experiments" to suit your fancy and, in the process, imbue light with a reality all its "own"... i.e., "for a photon" there is no space between earth and sun and no "travel time" between them either. Problem is, it is false and irrelevant to the actual cosmos of objects and the space between them and the "time" it takes light to travel from its source to a destination which absorbes it.

[snip]

Please address my post without negating the actual distance between things or the actual travel time of light between them.

It is my opinion that spacetime is not an accurate decription of reality, but the Galilean model you describe does not accommodate the fixed and finite velocity of light. That the velocity of light does not vary is generally regarded as a proven fact, albeit there is an alternative interpretation CICS. Setting CICS aside, you need to account for the known behaviour of light.

• If, like Einstein, you assume that the velocity of light is constant in every frame of reference, then you unavoidably arrive at the spacetime model.
  
• I regard the velocity of light as being constant with respect to the observer it is approaching. I therefore arrive at the "simultaneity-time" model discussed here:

  A Conceptual Alternative to Spacetime

• What is your answer to the fixed and finite velocity of light? You cannot simply claim that light "moves through space" in the same way as material objects do. It doesn't.

[Michael Mooney]

Will,

You wrote:

The problem is that special and general relativity make concrete, testable predictions, and those predictions have stood the test of time. Any interpretation of the theory has to square with the mathematics of the theory! "Now" in the theory is an observer dependent concept (the order of events is different observer to observer).

 

I agree with jediasoul that "spacetime" is a metaphorical math model, not a "real thing." I am not arguing with the improvement in testable predictions afforded by GR and SR, but that "spacetime" is not "something" which can be distorted, i.e., curved, expanded, contracted, etc. Rather that actual "things" have curved trajectories as effected by mutual attraction between masses (or light's momentum acting as if it had the property of mass), and that the observation of travel time between objects will vary dependent upon the position of the observer relative to the transit observed, not the actual travel time as observed from cosmic rather than local perspective.

 

You continue:

This is observer dependent, just like the concept of "now," in the theory of special relativity. Even if you try and reinterpret the spacetime metric, the predictions are the same. It could be argued that the frame of reference of light is completely meaningless. However, it cannot be argued that many different observers will measure different things for distance between the same two objects (and the time between two different events, etc).

 

If you deny these relationships, as you want to do for philosophical reasons, you need a new model to explain all the predictions.

 

What I am calling the cosmic perspective is independent of local-observer perspective. Philosophically I consider such a perspective, independent of the lightspeed limit and local perspective (who sees what and when), a supremely accurate view of actual distance between objects and the actual elapsed time of light traveling between them.

The GR and SR models work just fine for local perspectives. But cosmology has a broader scope than local perspective on light-travel. So I continue to challenge the assumption/reification of "spacetime" as something that is actually curved, expanded, contracted, etc., i.e., implicit in the title question: Is spacetime more than a metaphore and math model? I submit that it is not.

 

See my comments above on the dubious transition from Euclidean to non-Euclidean cosmology.

Michael

[Erasmus00]

but that "spacetime" is not "something" which can be distorted, i.e., curved, expanded, contracted, etc. Rather that actual "things" have curved trajectories as effected by mutual attraction between masses (or light's momentum acting as if it had the property of mass), and that the observation of travel time between objects will vary dependent upon the position of the observer relative to the transit observed, not the actual travel time as observed from cosmic rather than local perspective.

 

You cannot build the "cosmic observer" you want to build in GR, its simply not a possibility.

 

Further, as to spacetime having no reality of its own- what about gravitational waves? These exist independent of what generated them (in the same way light exists independent of the charges that generated the fields), and are nothing but energy carried by spacetime. If spacetime has no reality, as we normally understand it, how do you interpret a gravitational wave?

 

What I am calling the cosmic perspective is independent of local-observer perspective. Philosophically I consider such a perspective, independent of the lightspeed limit and local perspective (who sees what and when), a supremely accurate view of actual distance between objects and the actual elapsed time of light traveling between them.

The GR and SR models work just fine for local perspectives. But cosmology has a broader scope than local perspective on light-travel.

 

GR is, by definition, a global theory (not a local one). This is true whether you build the theory like Feynman did (virtual spin 2 particles) or like Einstein did (curvature of space). In the end, its the same theory. However it works out, there is no possibility of such a perspective. You cannot construct, in GR, just such a perspective.

 

The closest you can get are observers who co-move with the cosmological fluid (i.e. all the stars and galaxies), but these observers do not have all the properties you want to build in.

[Michael Mooney]

jediasoul,

You wrote:

You state this philosophic interpretation of space and time as if it were fact. I would call it Presentism. There is an alternative philosophic view called Eternalism. Now I happen to prefer Presentism to Eternalism, but neither are fact.

Spacetime is a specific interpretation of space and time that is part of Special and General Relativity. Neither Presentism nor Eternalism can account for relativity, so discussion of either, or both, would seem to be irrelevant to the question "what is spacetime really?".

Spacetime is either an abstract mathematical model, or a description of reality. I have been pointing out where I think that spacetime fails to reflect reality, specifically in the interpretation of zero intervals. Hence I'm arguing, like you, that spacetime is really just a mathematical model.

 

I could put "as I see it" in front of each statement, as I don't pretend that my critique of spacetime here is factual... only that the standard assumptions I have been criticizing are not factual either, i.e., that space and time can be distorted.

However, science has undeniable reified space and time and the blend "spacetime. "Presentism" is simply the recognition that time is an artifact of measurement/reckoning of specifically *selected event* duration or "elapsed time" from start to stop of the observer's "stopwatch." Actually the past is gone (not present) and the future is just potential (not present), and now is all there is... ever... always... everywhere.

This transcends the notion that science must focus only on local perspectives, as per relativity and its math analysis of vectors of light as viewed by individual observers in different locations.

 

So my critique goes beyond the latter perspective, as is appropriate for a philosophical discussion of the ontology of spacetime.

I totally agree with your last statement.

 

Do you think that the distance between sun and earth can be objectively stated as roughly 93 million miles regardless of a "photon's view" of it?

 

Do you think that, objectively speaking, we can say that there is an actual elapsed time of 8+ minutes for a photon to traverse the actual distance between the two actual objects?

 

You continued:

I liked your argument against the reification of space and time. I regard neither as actual physical entities. However, here you seem to be reifying space yourself by saying "though space is infinite three dimensional volume...". In my opinion, space does not exist as an entity in and of itself. It is no more than the distance between material objects (which I think is what you are trying to say). Therefore it is neither finite nor infinite. It isn't, of itself, anything.

 

Just to be clear, I am saying that space is *no-thing-ness*, the emptiness between "things." Reification is making something out of nothing, as per a concept into an actual fabric... or some-thing that can be described as curved, expanding. contracting, etc.

You agree that "It isn't, of itself, anything." Yet you have said that there must be "something" between masses to convey the force of gravitation. I said the forcefields themselves (electromagnetic, gravitational, quantum fields between entangled particles...) act across empty space... just like a magnet across a lab vacuum.

As to space being infinite as the empty volume in which "things take place"...

please posit how it can be otherwise. Can you posit a boundary "out there somewhere?" Made of what? What is beyond it? See what I mean?

 

You continue:

It is my opinion that spacetime is not an accurate decription of reality, but the Galilean model you describe does not accommodate the fixed and finite velocity of light. That the velocity of light does not vary is generally regarded as a proven fact, albeit there is an alternative interpretation CICS. Setting CICS aside, you need to account for the known behaviour of light.

See my post above to Will. I am not disputing that relativity has improved prediction of events including gravitation between masses and between mass and light, the momentum of which acts like mass. ( I find very interesting the experiments with light trapped in a box of mirrors... giving the box extra inertia as if it gained mass!)

 

Finally, you ask,

What is your answer to the fixed and finite velocity of light? You cannot simply claim that light "moves through space" in the same way as material objects do. It doesn't.

As I said, no argument here with relativity, including SR.

"In the same way? No, of course not. Mass becomes infinite as it approaches lightspeed, and no mass can ever reach lightspeed. That's different. But *at lightspeed* there is still an elapsed time of 8+ minutes for light as it travels from sun to earth. Zero space and zero time for this event "from the photon's perspective" is sheer nonsense.

(If a photon had eyes, what would it see forward and backward on this journey? Hmmmm... If pigs could fly.... no offense intended.)

 

Michael

[Michael Mooney]

ErasmusOO:

You cannot build the "cosmic observer" you want to build in GR, its simply not a possibility.

You really aren't hearing what I'm saying. I am not arguing against relativity. It has its "universe of discourse" being "local" (however far apart) perspectives on light travel and fine-tuned equations describing how masses and mass-light effect each. First point is that "spacetime" is metaphore, a math model, a visual aid to understanding the math. As per above, the ontological discussion of "spacetime" does not require mathematical expertise.

 

Just as Einsten proposed thought experiments to illustrate relativity, the "cosmic perspective" is a thought expetriment which transcends local perspectives, even in the broadest sense. In cosmic perspective "it" is always now everywhere. Time units belong in relativity, not in cosmic perspective. In the latter, for instance, there is no linear "time line" or "beginning of time" or creation of space. Space is infinite, eternal emptiness. All the "stuff" *in space* has always existed and will always exist... as seen from temporal perspective. I assume you have read my posts on the multiple Bang/Crunch in that regard.

So I have no intention of confining my cosmology or my view of space and time to the GR model.

 

Further, as to spacetime having no reality of its own- what about gravitational waves?

 

"Waves"... another word/concept like "spacetime." Masses still act on each other according to the universal law of gravitation whether or not you conceive of the force field as consisting of waves. Sun's and earth's mutual pull on each other is steady, just like the sunshine. It doesn't have crests of higher amplitude and troughs of lesser force. So how does the "wave" analogy help explain anything? Does positing "waves" , like "spacetime" give the illusion of understanding better what is not yet understood... how gravity works?

 

These exist independent of what generated them (in the same way light exists independent of the charges that generated the fields), and are nothing but energy carried by spacetime. If spacetime has no reality, as we normally understand it, how do you interpret a gravitational wave?

 

. If spacetime has no reality, as we normally understand it, how do you interpret a gravitational wave?

Oh, really? Without masses gravitational "waves" would exist anyway? Another thought experiment based on the impossible? Pardon me, but this is all in your mind. And light doesn't exist without a source either, whether you call it "the changes which generated the fields" or whatever. Then you glibly assert that it is nothing but the energy carried by spacetime, as if the latter were an established fact beyond question. It is not. In fact, questioning it is the subject of this thread.

 

Finally you say:

GR is, by definition, a global theory (not a local one). This is true whether you build the theory like Feynman did (virtual spin 2 particles) or like Einstein did (curvature of space). In the end, its the same theory. However it works out, there is no possibility of such a perspective. You cannot construct, in GR, just such a perspective.

 

The closest you can get are observers who co-move with the cosmological fluid (i.e. all the stars and galaxies), but these observers do not have all the properties you want to build in.

 

By whose definition? Is your "global" my cosmic? Where does GR transcend time-as-clocked-units-of-event-duration and space as a finite (whatever) which has shape and expandability, etc? I am not confining my perspective to the GR model.

How do you see the transition from Euclidean to non-Euclidean space/cosmology as reasonable and clear, making the former obsolete? You assume *way* too much, and have never answered my challenges in this regard. (Do you personally believe that the shortest distance between two points remains a straight line or not?)

 

Actually, the cosmic perspective I propose transcends " observers who co-move with the cosmological fluid (i.e. all the stars and galaxies)"...

 

The though experiment I propose is *one cosmic observer* observing the whole cosmos in "real time" *right now* as it expands, not this or that view of the parts thereof.

 

Gotta go.

Michael

[jedaisoul]

Do you think that the distance between sun and earth can be objectively stated as roughly 93 million miles regardless of a "photon's view" of it?

See below...

 

Do you think that, objectively speaking, we can say that there is an actual elapsed time of 8+ minutes for a photon to traverse the actual distance between the two actual objects?

I dislike the work objective, I don't think that it is precise. Tell me what you mean by "objective" and I'll reply to your question. Also, the subject of this thread is spacetime, not my opinions (which are quite different from spacetime).

 

Just to be clear, I am saying that space is *no-thing-ness*, the emptiness between "things."

[snip]

As to space being infinite as the empty volume in which "things take place"...

please posit how it can be otherwise. Can you posit a boundary "out there somewhere?" Made of what? What is beyond it? See what I mean?

My argument is with the idea that space is infinite. To be infinite (or finite) something has to exist. As space is "nothingness", it does not actually exist. So it cannot be either finite or infinite. It is nothing.

 

You continue:

It is my opinion that spacetime is not an accurate decription of reality, but the Galilean model you describe does not accommodate the fixed and finite velocity of light. That the velocity of light does not vary is generally regarded as a proven fact, albeit there is an alternative interpretation CICS. Setting CICS aside, you need to account for the known behaviour of light.

See my post above to Will. I am not disputing that relativity has improved prediction of events including gravitation between masses and between mass and light, the momentum of which acts like mass. ( I find very interesting the experiments with light trapped in a box of mirrors... giving the box extra inertia as if it gained mass!)

This does not answer my question. I'm talking about the very strange behaviour of light in that the velocity of the material objects does not add to its velocity. See below...

 

Finally, you ask,

]What is your answer to the fixed and finite velocity of light? You cannot simply claim that light "moves through space" in the same way as material objects do. It doesn't.

As I said, no argument here with relativity, including SR.

"In the same way? No, of course not. Mass becomes infinite as it approaches lightspeed, and no mass can ever reach lightspeed. That's different. But *at lightspeed* there is still an elapsed time of 8+ minutes for light as it travels from sun to earth. Zero space and zero time for this event "from the photon's perspective" is sheer nonsense.

(If a photon had eyes, what would it see forward and backward on this journey? Hmmmm... If pigs could fly.... no offense intended.)

This does not answer my question. If you take two aircraft flying towards each other at 500 mph each (with respect to the ground), the closing speed is 1,000mph. If one of the planes fires bullets at the other with a velocity (relative to his plane) of 700 mph, the velocity of the bullets (with respect to the ground) is 1,200 mph, and the closing speed between the bullets and the other plane is 1,700 mph. All the velocities add. But the flash of light from the plane's guns travel at the same velocity with respect to the plane it's leaving, the ground, and the other plane, even though they are moving with respect to each other. How do you explain that?

 

You can't just say, "I don't disagree with SR and GR on this", because you DO disagree. In SR and GR, distances and time lapses do not exist in the frame of reference of the photons. So the relative velocities are zero so far as light is concerned. Hence they do not affect the velocity of light. But you dispute that idea. So how come the velocities of the planes and the bullets do not affect the velocity of light with respect to them?

[Erasmus00]

You really aren't hearing what I'm saying. I am not arguing against relativity. It has its "universe of discourse" being "local" (however far apart) perspectives on light travel and fine-tuned equations describing how masses and mass-light effect each.

 

You misunderstand the theory! General relativity governs the global properties of the universe, if its a correct theory. Regardless of the ontological status of spacetime, general relativity makes predictions about the global structure of the universe. It is a global theory, not a local theory.

 

First point is that "spacetime" is metaphore, a math model, a visual aid to understanding the math. As per above, the ontological discussion of "spacetime" does not require mathematical expertise.

 

Except any interpretation of ontology MUST square with the predictions made by the theory! You want to divorce ontology from the theory completely, which is absurd.

 

the "cosmic perspective" is a thought expetriment which transcends local perspectives, even in the broadest sense...So I have no intention of confining my cosmology or my view of space and time to the GR model.

 

So, what you are defining is an ontological model with absolutely no testable predictions because its divorced from the physical theories? If it makes no new predictions, what does it matter?

 

Masses still act on each other according to the universal law of gravitation whether or not you conceive of the force field as consisting of waves....It doesn't have crests of higher amplitude and troughs of lesser force. So how does the "wave" analogy help explain anything? Does positing "waves" , like "spacetime" give the illusion of understanding better what is not yet understood... how gravity works?

 

A gravitational wave is divorced from the inverse square law of gravity. Again, actually learning some of the theory you are discussing would be helpful. If a system has a changing mass moment, it will give off gravitational radiation, the same way a wiggling charge gives off electromagnetic radiation (this is apart from the standard inverse square force fields).

 

A gravitational wave DOES have crests of higher amplitude, etc, just like electromagnetic waves (light), and it carries energy. The only way to make conservation of energy work is to have a "wave" (or whatever you want to call it) that actually carries energy. If I take a charge, jiggle it to create light, and then destroy the charge, the light keeps going. Once created, it exists on its own, independent of the source. The same is true for gravitational radiation.

 

I'll respond to the rest of this if I get time.

-Will

[Michael Mooney]

Originally Posted by Michael Mooney

Do you think that the distance between sun and earth can be objectively stated as roughly 93 million miles regardless of a "photon's view" of it?

 

J:"See below..."

 

'This does not answer my question.' I looked "below" and didn't find a "yes" or "no." You continue to evade this question. What I found was your objection to my use of the word "objectively." As I've said many times, my perspective and background for inquiry transcends the "frames of reference" essential to relativity.

If one actually engages in my "thought experiment" one will transcend the "frames of reference" baseline of observation and "see" from cosmic perspective. Without the limitation of "local frame of reference", the distance between sun and earth will remain about 93 million miles. Likewise the the well established distances to other planets, stars, galaxies, etc. This "cosmic perspective" is what I am calling "objective." It is also independent of lightspeed for event observation. As I've said, "it" is always now everywhere, and "realtime" observation will always remain "as now being observed from cosmic perspective."

 

Also, the subject of this thread is spacetime, not my opinions (which are quite different from spacetime).

This is a dialogue between persons in this forum on what spacetime is, not a library of links to the body of knowledge so far amassed by the scientific community in general on the subject.

 

My argument is with the idea that space is infinite. To be infinite (or finite) something has to exist. As space is "nothingness", it does not actually exist. So it cannot be either finite or infinite. It is nothing.

 

We are simply using the word infinite differently in this context. In my usage, though space is nothingness, this emptiness has no "end" or boundary, so is therefore infinite... i.e., not finite or bounded in "size" or "shape" as "timespace" is believed to be.

 

M:"...But *at lightspeed* there is still an elapsed time of 8+ minutes for light as it travels from sun to earth. Zero space and zero time for this event "from the photon's perspective" is sheer nonsense.

(If a photon had eyes, what would it see forward and backward on this journey? Hmmmm... If pigs could fly.... no offense intended.")

J:

"This does not answer my question. If you take two aircraft flying towards each other at 500 mph each (with respect to the ground), the closing speed is 1,000mph. If one of the planes fires bullets at the other with a velocity (relative to his plane) of 700 mph, the velocity of the bullets (with respect to the ground) is 1,200 mph, and the closing speed between the bullets and the other plane is 1,700 mph. All the velocities add. But the flash of light from the plane's guns travel at the same velocity with respect to the plane it's leaving, the ground, and the other plane, even though they are moving with respect to each other. How do you explain that?"

I do in fact understand that lightspeed is constant, as per SR and your example above. I am not disputing it as it is well documented. This does not mean that I understand the mystery of it. I do not... Nor the mystery of how gravitation travels through *empty space* (sans "spacetime") either.

 

I am familiar with the three classic tests of Einstein's theory of general relativity as well.*

(... the perihelion advance of Mercury,... the bending of starlight by the sun, and the slowing down of clocks by gravity.)

 

This doesn't imply that I follow the equations which explain the anomalies of Mercury's orbit. But the pull of gravity obviously alters light's trajectory/momentum even though it is massless. Making something out of nothing (curved spacetime) adds nothing to what we know about it. And since "time" is no "thing" either, "it" doesn't "dilate." Rather clocks are effected by gravity and changes in inertia, as I've said several times before.

 

As for SR: I get that " the time lapse between two events is not invariant from one observer to another, but is dependent on the relative speeds of the observers' reference frames." Calling this "time dilation" ads nothing to what we know about the phenomenon.

Likewise another tenant of SR: the " relativity of simultaneity... two events happening in two different locations that occur simultaneously to one observer, may occur at different times to another observer (lack of absolute simultaneity.)"

Again from a cosmic frame of reference, not one observer relative to another, there *is* absolute simultaneity... "objectively" speaking.

 

Likewise (quoting, as above, from a site on SR which I forgot to label):

 

This suggests what is in fact a profound theoretical insight as it shows that special relativity is simply a rotational symmetry of our space-time, very similar to rotational symmetry of Euclidean space. Just as Euclidean space uses a Euclidean metric, so space-time uses a Minkowski metric. Basically, SR can be stated in terms of the invariance of space-time interval (between any two events) as seen from any inertial reference frame.

 

Special relativity provides the transformation rules for how an electromagnetic field in one inertial frame appears in another inertial frame.

 

The Minkowski metric depends on curved space, which is a *concept* which reifies space and is unnecessary to the results... being the invariance of lightspeed independent of inertial reference frame.

 

You conclude:

You can't just say, "I don't disagree with SR and GR on this", because you DO disagree. In SR and GR, distances and time lapses do not exist in the frame of reference of the photons. So the relative velocities are zero so far as light is concerned. Hence they do not affect the velocity of light. But you dispute that idea. So how come the velocities of the planes and the bullets do not affect the velocity of light with respect to them?

 

As I said, your latter question remains, to me, a great mystery. I *suspect* that the extreme speed of light makes the relative speeds of the planes and bullets negligible, but I am not qualified to critique the experimental controls (in the original experiments) which are so well documented for this SR effect.

 

So I agree as above and also disagree as above. There is no "all or nothing" requirement in debate about relativity. I am free to pick it apart as I see fit, as above.

 

Wish I had time to reply to Erasmus00's post but I don't.

Later.

Michael

[Erasmus00]

More responses to above. I won't edit my above posts, rather just continue the discussion here.

 

How do you see the transition from Euclidean to non-Euclidean space/cosmology as reasonable and clear, making the former obsolete? You assume *way* too much, and have never answered my challenges in this regard. (Do you personally believe that the shortest distance between two points remains a straight line or not?)

 

I view the transition from Euclidean to non-Euclidean space the way most scientists do- as an empirical question. Spherical geometry, hyperbolic geometry, euclidean geometry,etc are all logically consistent ways of doing geometry, so why prefer one over the others? Euclidean geometry is easiest to visualize, but thats most likely an accident of psychology. If we were ants living on tennis balls we most likely would have developed spherical geometry rather then Euclidean. So the only way to settle the question is to make measurements.

 

In the weakest gravitational fields, the only curvature is of the temporal dimension into spatial dimensions (the Riemann tensor only has non zero components in temporal components).

 

In stronger gravitational fields, according to GR space is curved as well, and the straightest distance is a "straight line" but that line will appear curved to a higher dimensional observer (4d observing a 3d slice of spacetime). This is as yet an unverified prediction.

 

Observational astronomy has done a great job of showing that the observable universe is very close to flat.

 

But the pull of gravity obviously alters light's trajectory/momentum even though it is massless. Making something out of nothing (curved spacetime) adds nothing to what we know about it. And since "time" is no "thing" either, "it" doesn't "dilate." Rather clocks are effected by gravity and changes in inertia, as I've said several times before.

 

Curved spacetime allows us to CALCULATE THE EFFECT! The language of GR (no matter how it is formulated) is the language of Riemann curvature. Without this language, there is simply no way to calculate these effects! Without a predictive theory, we have to measure light bending in every new situation. Clearly, being able to predict light bending correctly is an advantage.

 

Further, as to clocks dilating- its hard to imagine something physical the effects all clocks the same, no matter their construction. Atomic clocks are different then clockwork, are different then human heart beats. Surely something that acts on all of these equally in the same way should be considered as acting on time.

-Will

[Michael Mooney]

"Your submission could not be processed because you have logged in since the previous page was loaded.

 

Please push the back button and reload the previous window."

(push button"... no post... "re-direct'... back to the above.

 

(I am so damn sick and tired of this **** that I am very nearly ready to quit this site. I log in... compose my post... the "preview" trick does not keep my post in tact... try to post, and get the above run around, having lost my editing on the "reply" screen.

I have learned to save it in phases on my notepad. However, I have not edited the notepad as I had the "reply" screen.

 

So, relflecting my impatience, here is the post as saved to "notepad" without editing.

(Expletive deleted!)

 

 

Erasmus00,

I'll start with a reply to your previous post and hopefully have time to also address your last.

You misunderstand the theory! General relativity governs the global properties of the universe, if its a correct theory. Regardless of the ontological status of spacetime, general relativity makes predictions about the global structure of the universe. It is a global theory, not a local theory.

 

You misunderstand my understanding of the theory because it is unconventional, and your understanding is quite conventional. GR "governs" nothing. It is a theory based on assumptions with which I, in part disagree. I refuse to disregard the ontological the ontological status of spacetime, as my challenge to it is the subject of this thread, and I have already acknowledged the math prediction improvement offered by both GR and SR without endorsing relativity's (as I see it!) erroneous reification of space, time, and spacetime. I'm still unclear about your usage of "global" as compared to my usage of "cosmic" regarding "local perspectives" dependent on lightspeed's limit

 

 

Except any interpretation of ontology MUST square with the predictions made by the theory! You want to divorce ontology from the theory completely, which is absurd.

Please adjust your "hearing aid." I have said repeatedly that I am not disputing the math but the ontological reification of "spacetime" as if it were an essential part of the prediction of actual observable events. (Incidentally, your telling me what I want, which I actually do not want, as above, is not only presumptuous but psychologically incorrect... and the absurdity lies in your apparently arrogant judgment of me.

 

So, what you are defining is an ontological model with absolutely no testable predictions because its divorced from the physical theories? If it makes no new predictions, what does it matter?

 

Are you at all familiar with the principles of theoretical science as contrasted with empirical science? My model and base of inquiry here is primarily theoretical/philosophical/ontological with an acknowledgment of the experimental evidence as stated consistently in this thread.

Are you familiar with string theory (now "M-theory) with its 11 "dimensions?" How does it rate in your book for "predictions?" Is "Bang/Crunch" cosmology "absurd" because the "missing matter" has not yet been found (though detection is improving) or that the fusion-explosion model can not work for all cosmic matter at once? (Have you read my multiple Bang/Crunch offering based on a maximized supernova model?

 

 

 

"What does it matter" if these cosmologies can not immediately satisfy your need for immediate evidential predictive gratification? I can not believe you are serious!

 

A gravitational wave is divorced from the inverse square law of gravity. Again, actually learning some of the theory you are discussing would be helpful.

 

Your latter statement above reflects the epitome of arrogance and presumption. Your assumption that, because I disagree with your textbook education, I have not studied the theories I am discussing is frankly disgusting and quite offensive.

 

Nothing is "divorced" from anything. Everything in the universe is interconnected, one way or another. Models of gravitation "divorced" from the masses which generated them are mental models without reality in the real cosmos. And, as I said, all light comes from actual sources. Sure, if you "turn off the light", the light already emitted keeps going, but your arguments for intermediate fields (and spacetime as a required energy medium) independent of mass as gravitational generator or light without a source are mind-games "divorced" from reality. (We can safely assume that the supernova of '87 has long since become a neutron star/black hole, even though we saw it explode.)

A gravitational wave DOES have crests of higher amplitude, etc, just like electromagnetic waves (light), and it carries energy. The only way to make conservation of energy work is to have a "wave" (or whatever you want to call it) that actually carries energy. If I take a charge, jiggle it to create light, and then destroy the charge, the light keeps going. Once created, it exists on its own, independent of the source. The same is true for gravitational radiation.

 

Do you seriously believe that gravitation fluctuates as "wave crests and troughs" reaching across space among all masses? Can you cite evidence of this fluctuation in any case? I know that "AM" radio transmission is based on amplitude modulation, as "FM" is based on frequency modulation, so please don't presume to lecture me on that! However, I am really interested in your reply to my request for evidence of gravitational fluctuations based on the wave model.

 

I hope you are familiar with the evidence that changes in gravitation travel at lightspeed conveying actual changes force in accord with mass alignments... as in Sirius B aligning with Sirius A relative to earth and changing our rotation speed in perfect synch with the observed alignment. This is a "real world" observable fluctuation in G-force as effecting earth.

 

BTW, your assertion that:

The only way to make conservation of energy work is to have a "wave" (or whatever you want to call it) that actually carries energy.

...

is a totally bogus reflection of your theoretical bias that spacetime is an actual medium of some sort rather than emptiness/nothingness.

You are in good company with Modest and Newton, who also could not conceive of "action at a distance" across empty space.

 

I suggest that it is time for mainstream science to "get over" this assumption, which is the intrinsic bias of scientific materialism.

 

Good night. Sorry I don't have time to reply to you last post.

 

Michael

[jedaisoul]

Originally Posted by Michael Mooney

Do you think that the distance between sun and earth can be objectively stated as roughly 93 million miles regardless of a "photon's view" of it?

 

J:"See below..."

 

'This does not answer my question.' I looked "below" and didn't find a "yes" or "no." You continue to evade this question. What I found was your objection to my use of the word "objectively."

I am not avoiding answering your question. I've noted that you are using words ideosyncratically, so I'm not sure what YOU mean by "objective". Perhaps it would help if I explain my dilemma:

 

Scientists use the word "objective" to mean "what our measurements are". They are objective in that, provided the experiments are conducted properly, it does not matter who makes the measurements. They are the same (within experimental error). Now, I suspect that you interpet "objectivity" differently. I.e. That by "objective" you mean reality. That would seem to fit in with your claim that scientists are reifying spacetime. That is only true if scientists believe that they are talking about reality. I believe that scientists, in general, are talking about a mathematical model which predicts what their instruments would measure (if the relevant experiments could be performed). Hence they are not reifying specetime, you are by misinterpreting their claims.

 

So, please, clarify what you mean by "objective", and I will answer.

 

As I've said many times, my perspective and background for inquiry transcends the "frames of reference" essential to relativity.

Then you are not talking about spacetime. Spacetime is a particular model of space and time that is relevant to the Minkowski metric.

 

We are simply using the word infinite differently in this context. In my usage, though space is nothingness, this emptiness has no "end" or boundary, so is therefore infinite... i.e., not finite or bounded in "size" or "shape" as "timespace" is believed to be.

Precisely. And I have pointed out that, by using the word "infinite" in this ideosyncratic manner, you are blurring the distinction between "not finite" and "infinite". Space is not finite because it does not exist, not because it is infinite. Infinite means something else. To describe space as "infinite" reifies it.

 

I do in fact understand that lightspeed is constant, as per SR and your example above. I am not disputing it as it is well documented. This does not mean that I understand the mystery of it. I do not... Nor the mystery of how gravitation travels through *empty space* (sans "spacetime") either.

Thank you. If you do not have an answer for how lightspeed is constant, nor how gravity works, what point is there in putting forward your ideas?

 

This doesn't imply that I follow the equations which explain the anomalies of Mercury's orbit. But the pull of gravity obviously alters light's trajectory/momentum even though it is massless. Making something out of nothing (curved spacetime) adds nothing to what we know about it. And since "time" is no "thing" either, "it" doesn't "dilate." Rather clocks are effected by gravity and changes in inertia, as I've said several times before.

I think that you are misinterpreting what scientists mean by curved spacetime. What scientists may consider as existing as real entities is not space but gravitational and electromagnetic field effects. That is the real nub of the question. Are field effects real, or do they just describe the way that physical entities interact?

 

Again from a cosmic frame of reference, not one observer relative to another, there *is* absolute simultaneity... "objectively" speaking.

How do you know this is true? If this is true, how can spacetime appear to be non-linear to us? How can you justify your claims, if you cannot provide basic mechanisms for how your version of the universe operates?

 

The Minkowski metric depends on curved space, which is a *concept* which reifies space and is unnecessary to the results... being the invariance of lightspeed independent of inertial reference frame.

No. I suggest that you reify it by misinterpreting it.

 

As I said, your latter question remains, to me, a great mystery. I *suspect* that the extreme speed of light makes the relative speeds of the planes and bullets negligible, but I am not qualified to critique the experimental controls (in the original experiments) which are so well documented for this SR effect.

The planes and the bullets were merely an example of velocities adding. There is a fundamental difference between the velocity of light being constant, and the fact that, in the example given, the relative velocities of the objects are insignificant.

[Michael Mooney]

Will:

I view the transition from Euclidean to non-Euclidean space the way most scientists do- as an empirical question. Spherical geometry, hyperbolic geometry, euclidean geometry,etc are all logically consistent ways of doing geometry, so why prefer one over the others? Euclidean geometry is easiest to visualize, but thats most likely an accident of psychology. If we were ants living on tennis balls we most likely would have developed spherical geometry rather then Euclidean. So the only way to settle the question is to make measurements.

Please review the paper/link on "The Ontology and Cosmology of Non-Euclidean Geometry" in this thread, and my commentaries on it. Seems I am repeating many times what I and others have already said about the nonsense, or the leap of faith into a model without referents in the "real cosmos."

Here is a short excerpt focused on how Riemann curved space and Lobachevskian hyperbolic space attemt to contradict Euclid's fifth postulate on straight and parallel lines:

 

Contradiction #1 above produces "positively" curved space ("spherical" or "elliptical" geometry, first described by Riemann himself), and contradiction #2 "negatively" curved space ("hyperbolic" or Lobachevskian geometry). To Euclid, this doubtlessly would seem to prove his point: the parallel postulate is about straight lines, so using curved lines hardly produces an honest non-Euclidean geometry. "Curvature" in this respect, however, is used in an unusual sense. "Intrinsic" curvature is distinguished from "extrinsic" curvature.

I maintain that empirical science requires validation of models by observation of real world events, which your merely "logically consistent ways of doing geometry..." do not.

 

You say:

In the weakest gravitational fields, the only curvature is of the temporal dimension into spatial dimensions ....

 

In stronger gravitational fields, according to GR space is curved as well, and the straightest distance is a "straight line" but that line will appear curved to a higher dimensional observer

 

So again you assert as existential realities "the temporal dimension" and "curved space" totally ignoring my extensive arguments in this thread that neither space nor time actually as having properties of spacial curvature or temporal dilation/contraction. Any cipher or symbol would do as well to take their place in the equations.

And from "cosmic perspective", the *highest* "dimension" of observation, there is no curvature of space. Space is emptiness without end and all cosmic material *in space* moves around as per common sense, easily accommodated by Euclidean geometry. Occams Razor cuts nonsense geometry right out of my favorite cosmology, and there is no real loss!

 

Observational astronomy has done a great job of showing that the observable universe is very close to flat.

 

The word "flat" not only gives empty space the *property* of shape, it implies a geometric plane, while in reality, non-finite (!) emptiness in endless volume.

 

Curved spacetime allows us to CALCULATE THE EFFECT! The language of GR (no matter how it is formulated) is the language of Riemann curvature. Without this language, there is simply no way to calculate these effects! Without a predictive theory, we have to measure light bending in every new situation. Clearly, being able to predict light bending correctly is an advantage.

Actual trajectories of actual massive bodies and light can be calculated without positing some-thing, "spacetime" which is actually no-thing.

(Am I repeating myself?) Call "it" The Great Mystery and signify it by "TGM."

Lets be honest about reification of space and time, making something out of nothing!

Finally:

Further, as to clocks dilating- its hard to imagine something physical the effects all clocks the same, no matter their construction. Atomic clocks are different then clockwork, are different then human heart beats. Surely something that acts on all of these equally in the same way should be considered as acting on time.

Obviously nothing I have said in this thread about time has registered with you.

There is no time between the not-yet-present "future" and the not-still-present "past." "It" is always "the present." Can you possibley "wrap your head around" this basic principle of "presentism."

Time is an artifact of (the concept of) event duration, of *selected events* not defined by nature but by man's "stopwatch."

 

Forces act on clocks and on human metabolism. The job of science is to explore the dynamics of the above, including the effect of change of inertia on the rate of radioactive decay of cesium.... whatever!... not to create some "thing"... time... and treat it like silly-putty.

 

I'm done here.

Michael

[Erasmus00]

I log in... compose my post... the "preview" trick does not keep my post in tact...

 

What browser are you using? I have no problems with firefox, but safari occasionally messes with me.

 

You misunderstand my understanding of the theory because it is unconventional, and your understanding is quite conventional. GR "governs" nothing.

 

GR makes consistently correct predictions. One of the predictions it makes is that your cosmic perspective cannot be well defined.

 

I'm still unclear about your usage of "global" as compared to my usage of "cosmic" regarding "local perspectives" dependent on lightspeed's limit

 

GR is not a theory regarding local perspectives depending on lightspeed (SR is).

 

Please adjust your "hearing aid." I have said repeatedly that I am not disputing the math but the ontological reification of "spacetime" as if it were an essential part of the prediction of actual observable events.

 

I'm sure you can make interpretations of GR that don't require the standard interpretation of spacetime. However, these must square with the math and the predictions.

 

You claim that you don't dispute the math, HOWEVER, the math makes the prediction that (for instance) there is no "correct" distance between the Sun and the Earth. You want to create a "cosmic" observer that the math predicts can't exist.

 

Are you at all familiar with the principles of theoretical science as contrasted with empirical science?

 

I am a theoretical scientist by trade. The problem with your model is that your construction is as follows "assume all the predictions of theory A are valid, BUT outside of the theory and ungoverned by the predictions of the theory there is a cosmic perspective." At that point its not science (you could replace cosmic perspective with practically anything).

 

Are you familiar with string theory (now "M-theory) with its 11 "dimensions?" How does it rate in your book for "predictions?"

 

It makes many predictions, they simply are NOT YET testable. In principle, if you could access arbitrarily high energy scales there would be predictions.

 

Is "Bang/Crunch" cosmology "absurd" because the "missing matter" has not yet been found (though detection is improving)

 

Big Bang + inflation makes many predictions (a largely flat universe, gaussian fluctuations in the CMB, etc). Dark matter hasn't been seen, but there are dozens of concrete models with testable predictions (thats what the LHC is for, among other things).

 

Your assumption that, because I disagree with your textbook education, I have not studied the theories I am discussing is frankly disgusting and quite offensive.

 

The assumption is that because you are largely unfamiliar with basic empirical consequences of the theory you haven't studied it. You seem to be completely unfamiliar with the idea of a gravity wave, for instance. This I will discuss below.

 

Sure, if you "turn off the light", the light already emitted keeps going

 

This is all I'm pointing out. If you turn off the source, the light keeps going. Light has some reality away from the source because it can exist on its own. This is because the light is carrying energy. Similarly, a gravitational wave keeps traveling away from the source, because it is carrying energy.

 

Do you seriously believe that gravitation fluctuates as "wave crests and troughs" reaching across space among all masses?

 

Consider the following analogy with electricity (ignoring boat loads of subtlety)- the standard electric force is 1/r^2, and similarly, the standard gravitational force is 1/r^2.

 

Now, if I wiggle the charge creating the force, in the case of electricity, ON TOP OF the 1/r^2 force a wave travels out, carrying the energy I put into the system with it. This is light. Again, this is distinct from the 1/r^2 squared force.

 

According to GR, if I wiggle the mass, a wave travels out, distinct from the 1/r^2 force. See, for instance, the wikipedia article on gravitational waves.

 

BTW, your assertion that (conservation of energy requires a wave)

is a totally bogus reflection of your theoretical bias that spacetime is an actual medium of some sort rather than emptiness/nothingness.

 

No it isn't. Either energy isn't conserved, or gravitational waves carry energy. If the energy of system A decreases, and then much later the energy of system B increases (in my "interpretation" the this is the time required for traveling of the wave), then energy was not conserved in between A and B. Either we give up exact energy conservation, or we put the energy into a wave. In Einstein's theory, this wave is a wave in components of a metric.

 

Now, as to geometry and cosmology, you say

 

I maintain that empirical science requires validation of models by observation of real world events, which your merely "logically consistent ways of doing geometry..." do not.

 

You missed my point- BECAUSE there is more then one logically consistent way of doing things, WE HAVE TO DO EXPERIMENTS TO DETERMINE WHICH IS THE RIGHT ONE. Hence, we have to validate the model! This is what experimental astrophysicists have done!

 

The word "flat" not only gives empty space the *property* of shape, it implies a geometric plane, while in reality, non-finite (!) emptiness in endless volume.

 

The word flat was being used in the technical sense, meaning "Euclidean." (Actually, in this case pseudo-Euclidean).

 

There is no time between the not-yet-present "future" and the not-still-present "past." "It" is always "the present." Can you possibley "wrap your head around" this basic principle of "presentism."

 

Except the best theories we have predict that there is no ONE present. Presentism works great when you can ascribe to the universe one time, and let it march forward. Unfortunately, our best theories seem to say that there are infinitely many possible vantage point, and each has its own timeline, and each forward march is different. Any interpretation of reality has to have room for these multiple timelines.