What is "spacetime" really?

[Michael Mooney]

The point is not that "clocks" slow down, but reality slows down.

 

Ummmm.... "Reality slows down"??

Say, just for a moment, that you took a flying leap out of the "relativity paradigm" and landed in what most folks *think* is impossible... a cosmic perspective on "Reality.

(Just for a moment... please... you can go back to relative perspective immediately after this little "thought experiment. But *please* "go with it" for this exercise.)

 

"Seeing" (or even Being!!... a thought experiment, remember!) Cosmos aa a whole... everything everywhere is all happening right now. The speed limit of light only limits what local perspectives can "see," and even the sunlight we see now left the sun over eight minutes ago. So, there is, of course, a time delay in what we can see... the farther away the event/lightsource, the longer the delay.

OK... back to "Reality" with a capital 'R'. Everything everywhere is moving... on all scales from subatomic to universal/cosmic. We all know about these cycles on all scales ('cept maybe the Big Cycle of a possible cyclic cosmos!) Earth spins in "real time*" "one rev a "day" and orbits sun once a "year." Etc., etc... Galaxies spin one rev every so many million "earth years"... etc. (*Real time* in this sense is "absolute* meaning natural cycles that have nothing to do with human (or other intelligent life form) "observation" or the limits of relative perspective.

 

Are you with me so far??

 

So... from this "cosmic perspective" what would be the meaning of your phrase, "Reality slows down?" It would lose its meaning outside the paradigm of relative perspective.

 

So then, what would the concept of gravitational slowing down of time mean? Absolutely nothing! It is just a myopic, relativistic paradigm... as if human perspective and our poor instruments of measurement... (like clocks that slow down under variable gravitational conditions) actually dictate that "Reality slows down!"

 

Is there anyone here who can see the anthropomorphic absurdity of this?

I think not, and I am sorry about that.

 

Now, granted, this was presented as a "thought experiment." But then so was the Minkowski/Einstein/relativity *theory* of "spacetime" and in particular "dilated time."

 

So... the above can be seen as just another thought experiment. It is in fact, the way I have "seen" Reality all my life. ... And It doesn't "slow down" just because our clocks can't keep absolute cosmic time under the stress of various gravitational and other inertial changes "relative to each other."

 

Just a little food for thought to sleep on.

Hope it doesn't give anyone nightmares!:)

 

Michael

 

Moderation note: this post and 91 responses to it and following posts have been move to thread 19450 , because they concern the assertion that an absolute “now” exists, while the original thread is excessively long, and a more general discussion of spacetime.

[modest]

Another viewpoint on Time:

GR tells us that time "runs slower" in a gravitational field. Yet (as we know from other threads) we do not have a good understanding of just what the gravitational "force" is.

 

...So, gravitational force derives from the Time Gradient. (?)

 

I like this question. It would be easy to interpret GR very rigidly and say: yes, the curvature of time is absolutely the reason objects follow an inertial path which accelerates them toward a massive body (i.e. gravitational force). But, I don’t think that interpretation (as valid as it is) needs to be considered the cause of the force.

 

Changing up the question a bit we could ask how clocks act in a rocket and apply the equivalence principle. If a rocket is accelerating in a straight line far from any gravitational field then a clock on the ceiling (toward the front or nose of the rocket) will run faster than an equivalent clock on the floor. If the clock on the ceiling emits x flashes of light per second then an observer on the floor will receive more than x flashes per second by Doppler shift alone.

 

The light transit time from the top of the accelerating rocket to the bottom is t=h/c. Change in velocity is acceleration times change in time (v=at). Putting these together gives v=a(h/c). Doppler shift is 1+v/c and subbing the difference in velocity gives 1+ah/c^2. So, the clock on the ceiling runs 1+ah/c^2 faster than an equivalent clock on the floor while the rocket is accelerating. The equation for gravitational time dilation is the same (1+gh/c^2) and so too the equivalence principle says these situations (a rocket accelerating and a person standing on a planet) are equivalent.

 

So why is a test particle on the ceiling of an accelerating rocket forced to the floor? Is it because of curved time (or alternatively stated: “the time gradient”)? While the inside of the rocket can be described with curved time such as with Rindler coordinates, I don’t think that would usually be said to cause the pseudo (or as they say now: "fictitious") force. More likely, we would say the rocket's engines are responsible or perhaps conservation of momentum or inertia.

 

I see no reason why we shouldn't look at gravity the same way. Curved time describes the situation that massive bodies present, but I don't think that should necessarily be considered the cause of the pseudo force. The cause would be the thing that makes the freefalling frame the inertial one—the thing that causes time to present as curved. I don't think GR explains what that cause is more than to say it is mass (or more properly: energy, momentum, and stress). But why does mass do that? In other words: what is the ontology of curved time?

 

Clearly there could be many ontological elements which could be said to be the cause and I'm sure many would be quite valid. I don't think GR constrains the ontology of the force of gravity as much as a lot of people tend to think. The "time gradient" can be considered a description of the pseudo force (in both the cases of the rocket and the planet) but it doesn't explain the cause of the pseudo force.

 

~modest

[lawcat]

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

 

 

 

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.

 

Beautifully said.

[Doctordick]

From what I have seen used when considering coordinate system representation is on a local scale and not global. In fact when considering the radius of curvature is dependent if at all on anything it would be "hidden variable" or parameter. One then uses a parametric representation (say that parameter is the local mass at that coordinate point) to define the curvature. Of course Cosmology does try to apply this on a global scale (with possible pitfalls).

What you are ignoring is the fact that any non-Euclidean geometry possesses fixed relationships between the coordinates in order to establish that geometry.

 

The only fixed relationship in a Euclidean geometry is the trivial issue of scale of the coordinates which, as a matter of fact, can be totally independent (all one need do is establish that scale in the measure [imath]dl=\sqrt{a_1dx_1^2+a_2dx_2^2+\cdots +a_ndx_n^2}[/imath]). Thus Euclidean geometry is the only geometry which can be used to display absolutely any geometric structure. Non-Euclidean geometries inherently limit the possibilities.

I don't see what I am doing is "bullying". I can not speak for others. After 750+ some posts to this thread, I have become to think of this more about the discussion between the "representation" of the "thing" vs the "thing" and how that can confuse people. Pointers definitely confuse any newbie programmer first attempt at using them.

I don't really argue with that. I think most all your posts seem quite rational but they are nonetheless not completely thought out.

 

A comment on "pointers"! They are essentially the information contained in a "goto" statement; and modern programmers always tell me that good programing does not use "goto" statements but every time I go to look at the actual machine language representation of most any modern program I find them salted throughout with long lists of "goto" instructions. Sometimes just long strings of "goto"s pointing to "goto"s. Of course, I am so old that most of my serious "programing" was in machine language; something nobody seems to do anymore.

 

The central issue of my Ph.D. thesis was "how to squeeze a complex nuclear computation into a machine where the core memory was 64K". That was back when you needed a pickup truck to carry a 300k disk drive and things were so slow that swapping out core was all but inconceivable. I once told my thesis advisor that the smartest approach to our problems would be to go drink beer and party until they built more powerful machines. He didn't appreciate it but, looking back, I think I was right. :lol: :lol:

 

Have fun -- Dick

 

PS before one can talk about space time one needs a good self consistent definition of both "space" and "time"; something totally lacking in this thread.

[lemit]

I've been sitting here listening to traffic outside my house.

 

Michael, how do you explain the difference in sound as each automobile passes? The space the sound travels through should be the same each direction. The time needed for the sound to arrive should be the same each direction. What is it that happens to the sound?

 

That's something I've wondered for a long time, since on the farm we could hear a car coming from a long distance and hear it leaving from a shorter distance. The difference in the tone and the duration of the sound wasn't explained in any of our antiquated science books.

 

We had antiquated schools and antique teachers too, so I was raised on the theory that atoms were the smallest, indivisible units of nature, even as split atoms proliferated around the world. I also had some trouble understanding that plasma rolling around after liightning strikes, too.

 

So, some childhood questions weren't resolved and I still enjoy thinking about them. I know about Doppler Shift now, but it seems to me that Doppler Shift is a slippery slope to a relativistic understanding of space and time. I'm open to a better explanation. Michael?

 

--lemit

[Michael Mooney]

Hi lemit,

I must be misunderstanding your question.

Here is the Wiki intro on the speed of sound:

Sound is a vibration that travels through an elastic medium as a wave. The speed of sound describes how much distance such a wave travels in a certain amount of time. In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s). This equates to 1,236 kilometers per hour (768 mph) or about one mile in five seconds.

 

Then, of course, the Doppler effect makes the sound more high pitched coming at you than going away after it passes. Just more compressed air waves in the former and more stretched out in the latter.

Michael

[lemit]

Thanks, Michael.

 

I thought I was really onto something, but I guess I wasn't. I really am here to learn, so I like being disabused of my thinking.

 

I've noticed you seem to treat me with some respect. I appreciate that. I would appreciate your opinions more if you were more respectful of the other people who disagree with you. I think I'm right in saying you were the one who started the name-calling. It would be nice to see you stop it.

 

Actually, since this is your thread, stopping the name-calling maybe should be your responsibility anyway. That's another thing I'm here to learn: how these forums work. Also, I've never in my life discussed science with scientists. I'm learning how scientists treat non-scientists and how they treat each other. I still have a lot to learn.

 

Again, thanks for the explanation. I'll keep looking for a spacetime definition in everyday life.

 

--lemit

[NomDePlume]

Over the last three/four hours I have read this thread, and decided it needs one more voice (i.e. mine ).

 

I have a lot of things I want to add but it looks like the conversation has moved on a bit from the earlier parts of the thread.

 

First, to everyone involved, maybe we ought to agree on a few things. In particular- ontology should effect epistemology. i.e. what is real/exists should effect what we can know (and what we know should effect our picture of what is real).

 

I propose the following- all ontological models of reality have some observable consequences. Do people agree with this?

 

I propose also- due to the limits of induction, an empirical model is NOT an ontological model.

 

And finally- observable consequences of valid ontological models should not contradict observational data. Valid ontological models CAN contradict empirical models IF no observations have yet been made of the contradicting events.

 

Do these propositions seem reasonable? Maybe they can put us all on the same page.

 

Finally, Michael, you said "Ontology 101" starts with the obvious fact that everything in the universe (the real stuff) did not magically appear "out of the Void of Space." It all actually had to always be in existence. None of "it" is created or destroyed. It just constantly changes form."

 

This isn't actually where introductory ontology courses start (or at least not the one I took last semester). The question of whether or not "something can come from nothing" has a long history, and not all thinkers agree. Start at the site plato.stanford.edu/entries/nothingness/

 

Also, how can we show that the "void of space" is actually nothing? Isn't the whole point of the Higgs field stuff (please, correct me if I'm wrong!!) that space isn't actually nothing, but instead full of a different sort of stuff?

[Pyrotex]

...First, to everyone involved, maybe we ought to agree on a few things. In particular- ontology should effect epistemology.

...Also, how can we show that the "void of space" is actually nothing? Isn't the whole point of the Higgs field ...that space isn't actually nothing...?

A NomDePlume (by any other name) would sound just as rational.

 

You have my total undivided attention, sir. Rave on! :)

[maddog]

Over the last three/four hours I have read this thread, and decided it needs one more voice (i.e. mine ).

I have a lot of things I want to add but it looks like the conversation has moved on a bit from the earlier parts of the thread.

First, to everyone involved, maybe we ought to agree on a few things. In particular- ontology should effect epistemology. i.e. what is real/exists should effect what we can know (and what we know should effect our picture of what is real).

Welcome to our Nightmare... ;-)

I propose the following- all ontological models of reality have some observable consequences. Do people agree with this?

Sounds good to me, though there may be a few exceptions.

I propose also- due to the limits of induction, an empirical model is NOT an ontological model.

I am ok with this, though I can not speak for others.

And finally- observable consequences of valid ontological models should not contradict observational data. Valid ontological models CAN contradict empirical models IF no observations have yet been made of the contradicting events.

I strongly agree, though I admit a direct contradiction may imply that some though not

part of a model is incorrectly configured.

Do these propositions seem reasonable? Maybe they can put us all on the same page.

So far, yes.

Finally, Michael, you said "Ontology 101" starts with the obvious fact that everything in the universe (the real stuff) did not magically appear "out of the Void of Space." It all actually had to always be in existence. None of "it" is created or destroyed. It just constantly changes form."

 

This isn't actually where introductory ontology courses start (or at least not the one I took last semester). The question of whether or not "something can come from nothing" has a long history, and not all thinkers agree. Start at the site plato.stanford.edu/entries/nothingness/

Interesting...

Also, how can we show that the "void of space" is actually nothing? Isn't the whole point of the Higgs field stuff (please, correct me if I'm wrong!!) that space isn't actually nothing, but instead full of a different sort of stuff?

Michael has this "thing" about Empty Space. You will have to get his clarification. I

was taking about a space of some size and consider the energy (lack of within). From

QM a space (of some size) when even no-thing is present can undergo Vacuum Fluctuations.

This is indicative that even in a "void" the energy density is not zero and can thus create

some-thing.

 

maddog

[maddog]

Maddog:

The Ontology of Spacetime, by Dennis Dieks (Editor)

Good find!

See Post# 637, p.64:

Thank You! I though you might like it. :)

See also other refs in that post on same subject and on Ontology in general.

(Seems I've been "talking in a vacuum"... and invisible too!)

I will go back and look. I put the book on my Google list as I especially plan to read that

second paper. It has proven difficult to just print the one paper.

 

maddog

[Michael Mooney]

Hi NonDePlume,

Welcome.

Responding one piece at a time...

 

First, to everyone involved, maybe we ought to agree on a few things. In particular- ontology should effect epistemology. i.e. what is real/exists should effect what we can know (and what we know should effect our picture of what is real).

 

Yes. And, of course, what exists is beyond the reach of what we know. But we keep reaching for it. ("But man's reach must exceed his grasp or what is heaven (or science!) for?")

 

I propose the following- all ontological models of reality have some observable consequences. Do people agree with this?

 

Emphatically, yes!

 

And finally- observable consequences of valid ontological models should not contradict observational data. Valid ontological models CAN contradict empirical models IF no observations have yet been made of the contradicting events

 

Agreed. This is the true interface between ontology and the empirical branch of epistemology.

 

Finally, Michael, you said "Ontology 101" starts with the obvious fact that everything in the universe (the real stuff) did not magically appear "out of the Void of Space." It all actually had to always be in existence. None of "it" is created or destroyed. It just constantly changes form."

 

This isn't actually where introductory ontology courses start (or at least not the one I took last semester). The question of whether or not "something can come from nothing" has a long history, and not all thinkers agree. Start at the site plato.stanford.edu/entries/nothingness/

 

I'll study the link asap. Meanwhile, can you explain how there was absolutely nothing...

And then... (what... "Presto!)... the cosmos appears??

 

What I have been calling "empty space" in this thread is merely the absence of things/stuff between and beyond them. This is not to deny that there are an abundance of "things in space"... rendering it 'not empty' where things "occupy space"... (obvious... but still a debate here!)...

 

Also, how can we show that the "void of space" is actually nothing? Isn't the whole point of the Higgs field stuff (please, correct me if I'm wrong!!) that space isn't actually nothing, but instead full of a different sort of stuff?

 

Well, "void" in common parlance means "nothing" in the space designated "void."

 

Perhaps the following distinction will be useful in regard to the Higgs field.

Space can "look" empty when as our senses... including their technological extensions... detect nothing. And then... whaddaya know!... stuff appears! Early on, the debate in quantum physics (and elswhere) was about the transition from "waves" (which are 'invisible'... now more like "virtual particles")... to "real boy" particles which 'collapse' from their "potential" state as waves or virtual particles into detectable particles.

 

So it's not so much that real particles appeared out of nothingness but rather that waves (energy potentials) travel undetected until an "antenna" (in the broadest metaphorical sense) "picks up the wave" and manifests its potential into... whatever... the "signal on the set."

 

Nice to have you aboard.

Michael

[Essay]

"So it's not so much that real particles appeared out of nothingness but rather that waves (energy potentials) travel undetected until an "antenna" (in the broadest metaphorical sense) "picks up the wave" and manifests its potential..." -MM

 

So would the question be something like:

Is that space, that is filled with only waves, empty space--just because the waves haven't yet collapsed?

[watcher]

Perhaps the following distinction will be useful in regard to the Higgs field.

Space can "look" empty when as our senses... including their technological extensions... detect nothing. And then... whaddaya know!... stuff appears!

 

so we can say that space is empty but full of potential.

 

Early on, the debate in quantum physics (and elswhere) was about the transition from "waves" (which are 'invisible'... now more like "virtual particles")... to "real boy" particles which 'collapse' from their "potential" state as waves or virtual particles into detectable particles.

 

So it's not so much that real particles appeared out of nothingness but rather that waves (energy potentials) travel undetected until an "antenna" (in the broadest metaphorical sense) "picks up the wave" and manifests its potential into... whatever... the "signal on the set."

 

so is space made of waves or waves propagate in space?

[watcher]

So would the question be something like:

Is that space, that is filled with only waves, empty space--just because the waves haven't yet collapsed?

 

 

 

if space is empty, waves cannot propagate in it. an alternate way of thinking should be to assume that space is resonant waves.

[Michael Mooney]

watcher:

so we can say that space is empty but full of potential.

 

Language can be tricky. "Space is empty ... but full." Do not be fooled by the language.

My thesis here is that space is emptiness. That is way different than "space is empty"... and I am frankly very tired of explaining the difference. Within all matter is a vast majority of emptiness. Likewise between all "objects"... even dust clouds or the occassional hydrogen atom is mostly empty space.

But...forces propagate through *empty space*... gravity... electromagnetic waves/fields. This is obvious and never should have become part of the argument that "spacetime is a real entity... with properties like malleability.

 

My signal is now going off for an upgrade out here on the land trust. Time's up.

Michael

[watcher]

watcher:Language can be tricky. "Space is empty ... but full." Do not be fooled by the language.

My thesis here is that space is emptiness. That is way different than "space is empty"... and I am frankly very tired of explaining the difference. Within all matter is a vast majority of emptiness. Likewise between all "objects"... even dust clouds or the occassional hydrogen atom is mostly empty space.

 

so do waves propagate in emptiness? and before you answer you might like to consider that we are talking about quantum waves here and not say tidal waves or sound waves.

 

But...forces propagate through *empty space*... gravity... electromagnetic waves/fields. This is obvious .

 

this is not obvious if your thoughtful.

forces are either attractive or repulsive.

now think hard how can they propagate? the idea is total nonsense.

not unless you reify force into a "something" that you called gravity.

its an ancient practice of give an attribution or name to something unknown.

but what are attracting and repulsing means?