What is "spacetime" really?

[modest]

I found the 58 or so pages a bit more than I could reasonably handle, give that so many posts were just capricious, witty, opinionated... not actually scientifically astute dialogue on what "time" is. Granted, any such contributions (or all of them) were lost in the pile of less-than-serious-or intelligent replies.

 

You make a good point. People have varied interpretations and objections to time and a good chunk of previous discussion on the topic is not going to speak to your particular concerns no matter how often they are continually discussed.

 

First, I an left wondering whether anyone here understood my brief comments on time. Seems it is only an artifact of the human mind in that the *duration of a selected event* is arbitrarily dependent on the observer's selection of "an event" and how "long" the intended observation lasts... i.e., a nano-second, a millennium (based on number of Earth orbits) or a full ""Bang/Crunch" cosmological cycle, if one were to subscribe to that model

 

<...>

 

Time is clearly the concept of "event duration" arbitrarily designated as above. "It" (same "it" as in "It is raining", i.e., no agent or entity involved) is always *now* everywhere... transcending local observation of light as limited by its speed limit. This is a "cosmic perspective"... a mental exercise much like Einstein's exercises but not limited to local perspective.

 

Anyway, since time is not actual but a nominal human artifact ( observed, conceptual seconds, minutes, days, years, millennia, etc) and space remains the emptiness between observable phenomena *in space*, my question stands unanswered.

 

The crux of your post centers around units of time being arbitrary. I agree with you that such units are the creation of the human mind and are arbitrary. From that you conclude that time is "not actual, but a nominal human artifact". This is a non sequitur that shows some misunderstanding with units and measures that I can correct.

 

The fundamental units of time, space (distance), and mass are arbitrary. As you say, there are seconds, minutes, days, years, etc. Putting units of time and space together into a coordinate system gives you a mathematical model that we can call "spacetime". I refer here to the model of reality and not reality itself. On this coordinate system we can model things like kinematics or electrodynamics and they should work regardless of which units of measure we decided to start out with.

 

In other words, the predictions we make about reality should be the same regardless of which arbitrary coordinate system we choose. All good and correctly-formulated laws of physics are like this. You can put Maxwell's equations (for example) on any coordinate system you like and predict the same future. This idea is called "coordinate invariance" or "general covariance" and Einstein's general relativity is so formulated. It works the same regardless of the chosen coordinate system (regardless of the units of time and space).

 

Whatever philosophical implications general relativity makes about mass affecting space and time are then meaningful regardless of your objection about arbitrary units of measure. The fact is, clocks run faster on the top of a building than they do at the bottom—if we mean seconds, minutes, or hours.

 

An aside:

(What other model accounts for the origin of cosmos... if "something out of nothing" is taken to be as absurd as religious "creation-ism"... where it all came out of "God's magic hat... a myth without scientific credibility?)

 

Big bang theory doesn’t describe “something out of nothing”. The theory doesn't make any claims regarding what (if anything or nothing) there was before (if there was a before) the big bang. Neither does the big bang theory “account for the origin of the cosmos”. Other theories such as loop quantum cosmology are attempting to answer these questions, but they are beyond the scope of the current big bang theory.

 

What is "Spacetime" supposed to be?

 

Spacetime is supposed to be a mathematical representation of the geometry and happenings of our universe.

 

All physical laws used to be modeled on three-dimensional Euclidean space with universal time. In the beginning of the last century, Einstein demonstrated that time (as is measured by clocks) and space (as is measured by rods) was not universal, but depended on the relative motion of the clocks and rods.

 

Hermann Minkowski shortly thereafter created a 4-dimensional space appropriate (and very useful) to the new observations and physics. This is Minkowski space, or as we might now call it: "spacetime". It treats time very much like another dimension of space. When Minkowski introduced the idea, he said:

The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.

 

-

source

Of course, this introduces very big philosophical questions regarding the world we live in. Namely, is the universe really four dimensional as relativity seems to imply? If so, why is time so different, and what makes it different? I don't have the answer to these questions.

 

Does not gravity, its agent and active force still a mystery, remain the mystery of the movement of massive objects being pulled together as per the old "universal law of gravitation" (directly with massiveness and indirectly with distance... no distance limit...?) Does gravity need a "fabric, spacetime" to explain the observed effects... including "bent light" (its momentum acting exactly like mass) without the superfluous concept of "spacetime?"

Seems a violation of "Occam's Razor" to me to posit an unnecessary "fabric" which still doesn't contibute an explanation of gravity's active agent, its "action-at-a-distance."

 

By directly and indirectly, I think you mean proportional and inversely proportional. General relativity is conceptually very different from Newtonian gravity. If we do treat space and time as a single construct or coordinate system as Minkowski shows, then it becomes possible to model gravity in this construct—not as a force or instantaneous action at a distance, but as changes in the geometry of the construct itself.

 

As odd as this seems, it correctly predicted many phenomenon involved with gravity such as gravitational time dilation, gravitational redshift, and the previously anomalous precession of Mercury. The strength of spacetime is that it simply and beautifully expresses physical laws. Theories of spacetime have made falsifiable predictions that have been confirmed, so there's certainly something to this idea.

 

But, "the fabric of spacetime" is just an analogy. Space and time are not a thing like fabric. They are not energy or matter. Whatever they are or whatever they represent is something very foreign from our human experiences. Space and time seem easier to model mathematically than to understand philosophically.

 

~modest

[Doctordick]

Space and time seem easier to model mathematically than to understand philosophically.

Isn't "understanding" the primary issue? Unless, of course, your only interest is regurgitating answers by plugging equations.

 

Personally, I find your post to be an exercise in obscuration.

 

Have fun -- Dick

[Essay]

Well, I sure learned a lot. Thanks, superlative Mod.

===

 

Isn't pretty much the same thing being said in many of these posts?

Spacetime is:

just an analogy... not a thing, a model, defined only in relation to matter/energy, an artifact, an illusion, space and time would disappear (without matter), ...not an "entity," spacetime (is not) a background, this word (aether) is not to denote a substance, and ...is a matter of semantics.

It may be easier to describe the models mathematically, but it's more fun to write creatively about the ontology of spacetime.

:hihi: ...and creativity abounds when the OP ends with an invitation such as, "Anyone?"

===

 

space and mass are energies of varying densities.

...and that conjures a familiar image too. :doh:

Interesting question about this is whether matter "pushes aside" space, or if matter "incorporates" the space it occupies, eh?

...and how do you define matter for this question, atomic or sub-atomic, or...?

...and what about energy: Does it travel through space, or generate space as it travels?

 

...although the more I think about it, "pushing aside" or "incorporating" space is probably just a semantic difference too.

 

~ :shrug:

[modest]

I read articles all the time which give “properties” to Einstein's aether: some say it's “foamy” on a small scale or, rotation tends to “twist it about the rotating object”...

 

Suppose no such thing exists! If that is the case, the whole theory (as it is commonly understood) just goes down the tubes.

I've been very busy lately hence the delayed response. I don't have a lot of time to formulate my thoughts which may come across as chaotic.

 

What you say is true of any field theory. If the field doesn't exist then either the theory is being misinterpreted or the theory is wrong.

 

On a fundamental level, it might be important to note that not every aspect of a theory can directly translate into something that really exists in isolation in nature. Numbers for example are not real and do not exist—yet they are to be found in many physical theories.

 

How about you give me a definition for that term which does not depend upon your definition of space or time: i.e., a definition which is not dependent upon your presumption of what “space and time” are supposed to be. The issue here is, “what comes first”. If you are going to define “space-time”, you need to tell me exactly what it is without invoking usage of concepts such as space and/or time.

 

I don’t believe it would be possible to define spacetime without invoking space and time. I also can’t imagine why you’d say I need to do so.

 

Space and time seem easier to model mathematically than to understand philosophically.

Isn't "understanding the primary issue? Unless, of course, your only interest is regurgitating answers by plugging equations.

Of course understanding is the primary issue. I remark only on the difficulty involved. Every scientific theory needs a conceptual interpretation that gives meaning to the mathematical expressions. Understanding the conceptual interpretation is what philosophy of science is all about—and it’s just as important as the math. I completely reject the commonly-held attitude that the math is the explanation.

 

Consider something that’s completely off-topic as an example. I can model a tesseract or a 3-sphere easily. The math is simple. But, no matter how hard I try, I cannot truly understand such shapes. My human brain just doesn’t seem made to understand higher dimensions. The same is true of some aspects of quantum theory. In these cases the math is unfortunately easier than the philosophical understanding. I find time and space similar in this respect.

 

Interesting question about this is whether matter "pushes aside" space, or if matter "incorporates" the space it occupies, eh?

Or matter and energy is all wave-like and point-like occupying no volume at all :shrug:

 

~modest

[watcher]

Interesting question about this is whether matter "pushes aside" space, or if matter "incorporates" the space it occupies, eh?

...and how do you define matter for this question, atomic or sub-atomic, or...?

i imagine space to be more solid that matter. matter is like bubbles in the oceans of space.

micro or macro matter behaves/ moves the same like waves. the crest of the wave seemed to travel horizontally but we know that the crest only goes up and down in sequence point by point so that it appears to move sideward.

 

...and what about energy: Does it travel through space, or generate space as it travels?

 

energy is the ability to do work. i don't believed that there actually a substance called energy.

 

...although the more I think about it, "pushing aside" or "incorporating" space is probably just a semantic difference too.

 

~ :(

 

could be. its always referred here that spacetime is just a model, a human artfact. this description smacks right to the nature of spacetime. that we cannot find any reality with it outside our mind. if i have to buy the aether theory, aether might just as well be consciousness. but i think that is too much for science to take. LOL

[Doctordick]

I don’t believe it would be possible to define spacetime without invoking space and time. I also can’t imagine why you’d say I need to do so.

Then you would have to at least define “space” and “time”; unless you just want to invoke the adage, “you either know what I am talking about or you don't”. I take mathematics as a well defined field as others have spent much time eliminating contradiction from their terms and I certainly don't wish to suggest that I know more than they do about their field; however, barring that exception, if you look over my work you will find that I do not use any term without first defining what I mean by it.

 

If you use terms you can not define, it truly means “you don't know what you are talking about!”

 

Have fun -- Dick

[modest]

I find nothing inherently wrong with Einstein's "definitions" of time and space being what clocks and rods measure.

 

If space and time are the fundamental entities they are believed to be then it should be impossible to define them with 'things' that are more fundamental.

I take mathematics as a well defined field as others have spent much time eliminating contradiction from their terms

 

In the language of mathematical logic, space and time are axioms of our system. It is by no means necessary to derive by principles of deduction everything in a system (by Godel's incompleteness theorem it's actually impossible). Consider the parallel postulate of Euclidean geometry. It is an axiom that cannot be deduced from the other axioms of that system. Why would our universe be different? Would you assume that every term we define is further defined by more fundamental and basic terms indefinitely?

 

~modest

[Doctordick]

I find nothing inherently wrong with Einstein's "definitions" of time and space being what clocks and rods measure.

That is clearly a circular mental construct! I don't think you have any comprehension of what I am talking about.

[modest]

I find nothing inherently wrong with Einstein's "definitions" of time and space being what clocks and rods measure.

That is clearly a circular mental construct!

 

Of course it’s circular.

 

A clock measures time and time is what a clock measures.

 

The same is true, Doctordick, with any fundamental property or entity of our universe. How would you define mass? Is it a measurable property of matter? You define it by its measurable effects and the effects are obtained by measuring them. If it can only be defined with things that it helps define then it’s quite possibly fundamental to the system.

 

You can only examine an axiom by the theorems that are built on the axiom and you can only build the theorems out of the axioms.

 

~modest

[watcher]

nothing has meaning outside a frame of reference.

everything is self-referencing. even logic.

and the point of reference is always arbitrary.

spacetime is the frame of reference we use to make sense of the world around u

[Rade]

But now you will have to define a "moment".

 

moment = that which connects the end of the before (past) with the beginning of the after (future).

 

And, in addition, you need to define "existence" and/or an object.

 

Existence is an axiomatic concept, all that can be said about it is that 'existence exists'. All philosophy begins with these two words.

 

object (thing) = an entity of a specific nature made of specific attributes.

 

In your philosophy Doctordick an object would be what you term a 'valid ontological entity'

 

entity = that which exists as distinquished from nothing of non-existence.

 

===

 

I do hope these definitions help you better understand my definition of OP question:

 

'spacetime' = that which is intermediate between two moments of existence.

[Michael Mooney]

First, I'm sorry that I don't have more frequent and prolonged opportunities to visit this forum. So far I have found the dialogue quite intelligent in presenting the background issues surrounding my question, though not actually directly responsive to the question, "What is it."

 

Since I last logged on there has been a lot of conversation, and it seems I can not respond to all of it as questions and comments spontaneously arose while dong the catch up reading.

 

So I will go "back to basics."

 

My question was labeled a philosophical one, specifically ontological, and the thread was moved to the "Humanities" section, "Philosophy of science."

 

Being a newbie, will someone please explain how the direct question, "What is spacetime" belongs in ontological debate.

 

Ontology is " the study of the nature of being, existence or reality in general."

(Wikipedia, for quick ref.)

My question was and is very specifically inquiring as to whatever it is that mainstream science now posits as something (whether or not an actual existential *entity*) that is consistently described as being bent or curved or spherically enclosing a point ("singularity") or a massive ball (black hole)... having an actual "geometry" as if it were a malleable (as above) medium.

 

If "spacetime" is, after all, only a mathematical construct... like a combination of distance and elapsed time for an observable phenomenon or phenomena transversing that distance with a certain describable vector, then *it* is not an "it" with properties as above at all.

Enter the concept of *reification*:

(Again from Wikipedia for easy common reference):

"Reification (fallacy), fallacy of treating an abstraction as if it were a real thing. "

 

For instance, Modest responded to Doctordick's challenge above with, among others, the following comment.

"On a fundamental level, it might be important to note that not every aspect of a theory can directly translate into something that really exists in isolation in nature. Numbers for example are not real and do not exist—yet they are to be found in many physical theories. "

 

I must ask you, Modest, if your previous posts (including the "geometry" of "spacetime" do not constitute a reification of the concepts of elapsed "time" (see my earlier post on "time") and distance into "something that really exists?"

*What* in all of this is being bent and curved and distorted my mass/gravity?

 

If space is actually *nothing* but the emptiness between observable (or in some way evidential) phenomena and time only the concept of event duration (event and its window of observation being arbitrarilly selected by the observer)...then how is "spactime" *not" a superfluous conceptual "fabric" which Occam's Razor must ultimately cut away for the irrelevance it is in the scientific discussion of the observable effects of masses on other masses and on (otherwise straight line) trajectory of light... the momentum of which acts exactly like mass? (Please forgive the run-on sentence style... difficult to "chop up" into smaller bits with periods.)

 

Gotta go again, but I'll be back tomorrow if not later tonight.

Thanks for all the comments so far. I'll try to address more of them and the links (my homework) when I get time for it.)

 

Still looking for a more definitive answer to "What is it?"

PS:

Numbers are not "real" either in the literal sense outside math jargon, i.e., in the objective world/cosmos. They too are "ontologically" merely tools of the human mind for quantification of actual "things" (in the broadest sense) in the "real" (objective) world.

Later.

Michael

[Michael Mooney]

MM, don't think my "fractals links" have any overt connection to explaining this stuff. They only serve to help break linear, 3-D type preconceptions (though imho, fractals need to be worked into our equations of horizons, fields, etc.).

 

I should probably read the time thread too, but let me just add a bit:

 

Time shouldn't be thought of as a line of measurement (which is simply how we conceptualize it);

Time should be thought of only as change.

Without space to change (w/ the flux of matter/energy), what sense would time make?

Without time, what sense would space make, with no movement, perception, or interaction?

 

You're pursuing different semantic paths in describing space and time. It should be the same path.

Thinking of the emptyness between objects as "space," we should think of "now" as the emptyness between events (changes).

Interestingly as you localize space, the now increases in duration; or as you expand the space measured, then the now between events get very quick. ...or something like that....

 

~ ;)

 

p.s. If you want to pin down the what, of 'what' is spacetime, I would go with:

Spacetime is an illusion. ;)

 

Now has no "duration", yet "it" is *always now.*

 

Essay,

I'm trying to catch up but too much to address... so I'll back track to my understanding of time, which you clearly misunderstood in my post above.

 

Time is the *concept* of event duration, but the present is always the present... everywhere.

Everything is always changing. An observer can take whatever sized bite of perpetual change, always now he wants and call it "time", but there is no time between past and future no bits or slices of now, just artifacts of our clocks or designations of natural cycles or parts thereof.

 

What do you think space is besides emptiness... no-thing-ness? Space does not change. (If it is emptiness, what changes? Only *things in space* change.

 

How do you see the above as "... pursuing different semantic paths in describing space and time"?

 

I am not the one making these two concepts, emptiness and event duration into some *thing* that is *malleable* as in bendable by masses. Gravity does not need the concept "spacetime" to act, one mass upon another or upon the trajectory of light, the momentum of which gives it the property of mass in that it is attracted toward masses that "pull" on it.

 

You wrote that " we should think of "now" as the emptyness between events (changes)." As I said, now is the ongoing present. this means that *all events are happening now. There is only, always the ongoing present.

Past is only history and future is not yet real and present, and there is no time between the not-still present past and the not-yet-present future.

 

I agree that "spacetime is an illusion."

 

But mainstream science (Wikepedia on "spacetime) asserts the following:

 

In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space, because the rate at which time passes depends on an object's velocity relative to the speed of light and also the strength of intense gravitational fields which can slow the passage of time.

 

Relativity claims that "time" is an actual (whatever) which can speed up and slow down.... and, of course that no-thing-ness is actually some-thing that has geometry and curvature. (Yes it works well as a math model/construct.)

 

Universally, Now is always now everywhere. Who can see what and when is obviously a function of the speed of light and all relativity is limited to local perspectives and lightspeed's limit.

 

I do know that clocks sent into orbit slow down relative to control clocks on the ground. Same on jets and as mentioned, various heights above clocks on the ground. If time is not some-thing that can "dilate", then the explanation must lie in forces acting on the clocks themselves, like the change in inertial frame of reference from the stationary control clocks with the force of accelleration (change in inertia) actually slowing the rate of vibration of, for instance the rate of radioactive decay in cesium-powered atomic clocks.

Certainly no one will assert that time slows down under water just because a submerged wind up clock will "lose time" with the increased friction on the flywheel. The force on the higher speed clocks slows them down. "Time itself", being nothing other than what clocks measure, does not "slow down... (or) "speed up. Clocks "run" faster or slower under various conditions, subjected to various forces, changes in inertia.

A specific fraction of an earth-revolution remains a standardized second or minute or hour.

 

"Time dilation" is a mind game, same as "bent space."

 

It's late. Back tomorrow, briefly before I again lose net access.

 

Got the run-around trying to post. I was logged in but got this:

 

"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."

 

Did so and got the "redirecting" screen, "push backbutton to reload page... then back to "your submission..."

 

Sheesh. On another browser, from un-corrected notepad... then, I'll edit.

[watcher]

MM,

whatever this spacetime that the human mind constructs as a model representation out of "what is", there is no way to know because we rely in our mind to tell as what is real. this imply that what ever the true nature of existence of spacetime must be prior to the mind.

 

but to speak of "something that is prior to the mind" is an idea beyond the scope of scientific philosophy. i guess

[Essay]

Thanks MM, I still think this is mostly a semantic problem. At the very least we are limited by our reliance on the use of "concepts" and definitions.

 

I'm catching up too, and will respond more later to....

What do you think space is besides emptiness... no-thing-ness? Space does not change. (If it is emptiness, what changes? Only *things in space* change.

 

How do you see the above as "... pursuing different semantic paths in describing space and time"?

....and more. :doh:

===

 

...but for now, just a quick:

.

 

'spacetime' = that which is intermediate between two moments of existence." -rade

 

Very nice!

I think that sums up, and is entirely consistent with, each of the descriptions put forward, from Einstein to the rest of the rabble at the windows. :)

===

 

I hate to invoke the image of the expanding universe (and the nothing that spacetime is expanding into), but it's easier to....

 

Visualize matter/energy generating the spacetime it needs to travel through, like an arrow generating a fractal bow-shock and wake (eventually overlapping with other fractal wakes....).

 

~ :)

[Michael Mooney]

Lots of catch-up replies to get back to, but first I want to share a couple of quotes with which I agree.

 

"I hold that space cannot be curved, for the simple reason that it can have no properties. Of properties, we can only speak when dealing with matter filling the space. To say that in the presence of large bodies space becomes curved, is equivalent to stating that something can act upon nothing. I, for one, refuse to subscribe to such a view" -- Nikola Tesla

 

 

[Excerpt from T. Van Flandern (2002), "Does gravity have inertia?", Meta Research Bulletin 11, 49-53.]

 

... "Moreover, “space-time” is a mathematical concept, which amounts to a fancy way of referring to proper time in relativity (the time kept by perfect clocks), and does not involve any curvature of space. To show this, consider the following mathematical and physical arguments."

( Link not allowed... under 10 posts. )

 

Summary (T. Van Flanden):

" If the curved path of a body through space is not caused by a curvature of space, then space remains Euclidean (flat) and an external force is still required to produce and explain any deviation from straight line motion. Moreover, some explanation other than curved space is needed to understand the equivalence-principle-like property of gravity."

[Michael Mooney]

duplicate post... attempting to delete

****! It deleted both posts,,, had a good hour into a reply to Modest.

I give up.