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Author Topic:   What is "the fabric" of space-time?
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 106 of 327 (459103)
03-03-2008 10:23 PM


the gravity of general relativity
Looking for people to cure a bit of my own ignorance. As with the original poster, I (mis?)understood General Relativity (GR) to say that mass tells spacetime how to curve, and spacetime tells mass how to move. That creates an image of mass acting on spacetime, or let's say the "fabric" of spacetime.

I'm not so hung up on what that fabric is, as I get the idea of fields. But I am very curious about GR's actual tenets regarding mass v spacetime, what they mean, and why I am unable to make sense of (or accept) them so readily.

So first off, is my understanding correct or not? Does GR state or imply that mass acts on spacetime? I thought the idea was that GR replaced the concept of gravity as a force between objects, with gravity as a force between an object and spacetime.

If this is true so far, then what is the difference (mathematically and experientially) of a force acting between objects and one of a force acting on spacetime (such that it then effects the motion of other bodies). Wouldn't Occam's razor come in to play if there is no difference (beyond the math), and remove ST as a metaphysical intermediary?

I imagine issues such as changing time rates at different distances from an object's surface might be a measurable experiential effect.

There has been mention that physicists are seeking a "graviton" which would be the gravitational equivalent of the "photon". This confused me as it seems to inherently dismiss GR's implications for gravity, and reasserts the idea of gravity being a force between two objects. Where have I messed up, or is there a disconnect between gravitons and GR theory?

That's probably enough mistakes for now. I hope people understand I am not questioning the utility of ST as a mathematical tool for understanding observed phenomena, just that I'm having problems with understanding it as an actual "thing" which gets acted upon by objects and then acts upon other objects.

Edited by Silent H, : +by,actual

Edited by Silent H, : a/an


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

Replies to this message:
 Message 108 by cavediver, posted 03-04-2008 4:35 AM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 115 of 327 (459174)
03-04-2008 1:51 PM
Reply to: Message 108 by cavediver
03-04-2008 4:35 AM


Re: the gravity of general relativity
Man, you are awesome... and that's before we introduce the underwater cavediving aspect. The world could use more physicists like yourself in public arenas, carefully (and patiently) explaining how this works.

I have been explaining the unified picture, where GR and matter are both aspects of some super-fundemental master field. It is the search for the consistent physical theory of this unification that is at the heart of much of modern theoretical physics.

I think that was a critical element that I was missing in trying to understand the current discussion. Let me repeat what I am getting out of this and see if I have it right. GR replaced gravity (force at distance) with mass effecting another entity space-time, however physicists are now trying to merge both entities (mass and space-time) into specific operations of a singular entity which would be a "master field".

If this is correct, then I want to ask if this work is a mathematical exercise, that is to say the creation of the simplest mathematical tool (aka model) possible, or is it attempting to describe the "real" nature of natural phenomena? There is a huge difference between convenience and actual understanding.

If it is the latter, how are distinctions made between model and underlying reality, beyond calculations fitting results?

'Forces' concern action-at-a-distance. Mass at a point acts on space-time at that point. The wider-area effect on space-time has nothing to do with the mass, but the properties of space-time. In the usual ball-bearing on rubber sheet, the ball creates the displacement in the sheet at the point of contact, but the surrounding depression is a result purely of that local displacement and the elastic properties of the sheet - it is nothing to do with the mass itself.

Yes, I did understand this point already, which was a major difference between the two conceptually. But this does lead me to more questions.

As I understand it, if a mass were to suddenly "appear" (let's say an enormously massive particle falls out of an accelerator experiment), then it effects space-time at its what? Surface? Interior? And then the space-time "field" begins to effect other masses (and massless objects too right?) as its warping spreads out at the speed of light?

If this is so, how is gravity represented on that new object? Normally gravity is represented as a function of two masses, but if a new mass has just appeared, during a certain period of time its effect on space-time will not have reached another object. So is the measured gravitational effect different? And does that new mass still act as if it is effected by the other mass which already existed (and so who's space-time effects have already reached that location)?

A graviton is simply the smallest possible fluctuation in space-time, a result of applying standard quantum thinking to GR. In terms of the rubber sheet, it is essentially the quantum of displacement. This not so much brings GR 'down' to the level of force, as brings electromagnetism 'up' from a simple 'force' picture, to the level of a geometric theory. And this must happen as we expect all of the fields (space-time, electromagnetism, strong, weak, matter) to be different aspects of the one unified field.

This addresses another question I had waiting in the wings. If I understand your explanation correctly, this means that all forces would start to go the way of gravity, in that we would stop discussing them as actions at a distance between objects but rather as different phenomena within a single entity, which appear to us as two objects effecting each other at a distance? For example, we would not discuss em attraction as a result of exchanging photons, but as general field effects?

If this is correct, then (mirroring my earlier question) what is the evidential difference between the two ways of thinking? Also, could you describe the difference between a photon and a graviton in that theory?

I was originally thinking that discovering the "graviton" would undercut GR in some way, but now I am wondering if the opposite is true given attempts to move GR into the singular field theory as you have suggested. If we cannot find a graviton, would that pose a problem?

AbE:
I've decided to end this on a revelation of sheer stupidity. One thing which I never conceptually understood in GR, is what the space-time distortion is supposed to be, and so how it acts on masses. The rubber sheet analogy always worked for me on moving masses, so moving objects would have their motion bent by the distortion, perhaps so great as to circle into the mass creating the distortion.

However, I don't understand what is happening on an object which is not in motion. For example I pick up a stone and then let it go. What is space-time doing that makes the originally motionless stone start moving toward the surface? Why does it keep moving? For the purpose of this hypothetical we can imagine the earth does not spin or move in any other way (which would mean the stone is in motion). Force at a distance makes more sense to me at that point than motion of a motionless object across a curved space.

Edited by Silent H, : revealing underlying ignorance

Edited by Silent H, : quick fix


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 108 by cavediver, posted 03-04-2008 4:35 AM cavediver has replied

Replies to this message:
 Message 135 by cavediver, posted 03-05-2008 4:20 PM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 146 of 327 (459307)
03-05-2008 7:20 PM
Reply to: Message 135 by cavediver
03-05-2008 4:20 PM


Re: the gravity of general relativity
I appear to prefer my physics as I do my Coke... classic! But preference means nothing and I must press on to understand something.

You mentioned Wheeler's work and it raised a question for me about quantum electrodynamics (QED). Am I wrong in thinking that much of Feynman's work (or at least QED's explanatory power) would be undercut by the current direction of physics? He seemed to have a purely statistical concept driven by particle behavior (or theoretical behaviors) rather than fields.

we started to notice that it was no longer the parameters of some physical object that was being described mathematically - it was the object itself. An electron is not some 'ball' that has such and such properties. *only* the properties exist. Once we have decribed the properties mathematically, there is nothing left over to say 'and that's the thing we are modelling'.

That sounds like a metaphysical philosophy I once read, objects as nothing but their properties. I'm pretty sure I get what you are saying on this, but I want to be more sure with another example.

We could for example model vibrations of atoms in a molecule using the same type of equation for balls attached to each with a spring. As accurate as that might be, there is no real "spring" between th atoms, which are not themselves balls (or even ball-like). This is where convenience is not the same as understanding what it really occurring.

While I understand that we can get mathematical models which accurately depict a property, I am wondering how we discern the difference between that being the reality of the property, versus being functionally identical for use in calculations. Does that make sense? I realize you answered that such distinctions would be "unparsimonious", isn't such a distinction important to make regarding the limits of what science is discussing?

In a Feynman lecture, he analogized physicists to being like ancient aztec priests using bean-counting to determine when certain celestial phenomena would occur. In the end, whatever they said was the reason for these phenomena to occur is besides the point. All they were actually doing is coming up with a system to predict the occurrence, not describe what was going on. I thought that was an important distinction for him to make, because it undercuts illusions regarding what we actually know. Is it just accurate mathematical models (bean counts) or is it an actual description of the phenomena?

If this is not important to your mind, I guess I'd like to know why you feel that way. Heheheh... debate Feynman's point!

Mass cannot 'appear'. So I cannot describe how space-time would respond because its occurance demonstrates that what we know of space-time is wrong! Mass is simply a measure of the energy in a volume.

Ahhhh all my trips to Fermi were for naught! In my defense, my hypothetical simply paraphrased something I saw by a physicist. In his example he imagined that the sun (its mass) suddenly disappeared. In my case I made something massive appear.

I did believe that mass and energy can be converted, and so where once you had no mass, suddenly you would have it. I did think that was happening in high energy collision experiments. Even if mass is energy in a volume, isn't there a point where energy in an area moves from something that does not exert a gravitational force (aka warps space-time) to something that does? Perhaps an explanation of how mass -energy conversion occurs as it relates to "gravity" would be the best bet.

What we call 'motion' is a rotation of this vector out of the pure time direction, so that there is a (very small) component in the spatial directions. Thus it is now clear why there is a limit to 3-velocity - it is simply a projection of a rotating 4-vector of fixed magnitude. Now, in curved space-time, what you think of as your time direction *here*, may well not appear to be the same direction over *there*. So you may well see someone else 'moving' but as far as they are concerned, they are 'still'.

You first discussed these vectors with me a while ago, and they are a fantastic tool to get my head around things. However, I am not quite sure I follow how this is working in curved space-time. I guess I'd like you to unpack the explanation of why a pure time directional arrow would be different from one place to another. This may be a good place to literally draw me a diagram.

As a follow on to that, why does mass create a situation where a fully time directed vector sets two masses in physical motion towards each other. I guess this is to ask, why does my natural path through time always point toward the center of something else? And why am I increasingly moving toward that center, rather than uniformly moving (I'd assume that's due to the nature of a curve rather than a straight line)?

This all gets wackier for me when I consider natural phenomena like tides. So the sea is not pulled up by the moon, but rather its motion through time is towards the moon and the earth at the same time, and the visible result is that it gains potential energy? The curvature of time itself is creating the visible changes of the sea and the energy we can harness?

Aaaaaaaagh!

Really though, if this is reality I need to wrap my head around it, rather than sticking same head in the sand.

It is very difficult to convey just how astounding this is - to reach the bedrock of existence to find that we have run out of 'blobs' to describe.

Well that really is astounding, and I feel sort of privileged to be in a time where we are reaching such points in physics and somewhat analogously in genetics and neuroscience (when looking at the concept of consciousness, the brain parts are it).


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 135 by cavediver, posted 03-05-2008 4:20 PM cavediver has replied

Replies to this message:
 Message 165 by fallacycop, posted 03-07-2008 10:11 AM Silent H has taken no action
 Message 166 by cavediver, posted 03-07-2008 1:49 PM Silent H has replied
 Message 168 by Son Goku, posted 03-08-2008 4:51 PM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 163 of 327 (459332)
03-05-2008 10:06 PM
Reply to: Message 160 by Percy
03-05-2008 9:38 PM


The great irony in randman's statement...

The way I look at this discussion is I am trying to get you guys to abandon your old worldview and accept the implications and facts of QM.

...is that the very same could be said by the scientists studying QM. Classic mechanics is the old world view and it is hard to shake in order to accept the implications and facts of QM (and also relativity). And Classic mechanics was a replacement for the rather ancient world view of action by supernatural agency.

It appears we have come full circle.

Edited by Silent H, : -re


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

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Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 174 of 327 (459746)
03-09-2008 5:47 PM
Reply to: Message 166 by cavediver
03-07-2008 1:49 PM


Re: the gravity of general relativity
Sorry, was busy... also a thank you to fallacycop for policing my earlier post. The mnemonic description of Feynman's work was useful which I will address in my reply to SonGoku.

The mathematical models are becoming entire bodies of mathematics that we are seeing replicated in nature - it's no longer a bunch of useful mathematical methods and tools patched together to make a good model of reality. The phsyics isn't just remaining ameniable to the mathematics as we descend through the layers, it appears solely as mathematics. Why should it tie in so closely?

Would I be wrong in taking this as a suggestion of "math is the language of God" or more secularly "math is the language of the Universe"? If so, I might have an argument against that position. Of course, you might beat me to a bloody pulp after the first swing.

Hmmm, he was obviously no relativist Mass cannot disappear either...

If you want, I can try to find the video. I believe it was from a PBS type documentary posted on YouTube. The physicist was purportedly trying to show an issue Einstein had with Newtonian physics, which would have all bodies immediately be effected by such a sudden loss of mass. His claim (and he had computer graphics to support it!) was that the sudden mass loss would result in a wave of change in gravity spreading out at the speed of light to effect each other body in turn.

You cannot change the mass in a volume without moving that mass out of that volume. You could annihilate every fermion in the Earth until it was just a cloud of photons, and as long as you could constrain those photons within a volume, the moon would never notice! The mass of the particles created in a particle accelerator was measurable as mass before in the energy of the power generation.

Okay, I think I get this idea. Let me repeat to make sure. Energy can be diffuse, or compact. When compacted in a location it exhibits the properties we ascribe to mass. If that compaction is of a self-sustaining nature it is what we'd call a particle with mass?

Take my classic space-time picture of a closed FRW universe - the globe. T=0 is the North Pole, with time flowing south. Care to suggest where the time directions of two separated particles would be parallel?

If I understand your description my guess would be the south pole (parallel but opposite direction)?


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 166 by cavediver, posted 03-07-2008 1:49 PM cavediver has replied

Replies to this message:
 Message 222 by cavediver, posted 03-29-2008 10:47 AM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 175 of 327 (459749)
03-09-2008 6:07 PM
Reply to: Message 168 by Son Goku
03-08-2008 4:51 PM


Re: A bit of history.
Sorry, was busy... I was going to ask some questions of both fallacycop and cavediver, but you have successfully answered them already. Thank you.

However, this appears to emphasize the issue I was talking about with cavediver. I've been asking about whether our current math is a model of the underlying reality, or just a useful tool.

Feynman seemed to suggest it was a tool. And the history you outline appears to substantiate his own commentary. His math was a tool.

Now what reason do we have to believe the more fully developed QFT is more than just a better tool?

Although I have not studied Einstein's math, and some limited amount of QM math, I did read Einstein's discussions and some of the QM pioneers of their work. I always got the feeling they had come up with interesting ways of conceptualizing reality (how phenomena function), based on the mathematical models which we needed to fit the observations (or make accurate predictions). All that logically entails (to my mind) is that the math is a useful tool, and that the conceptualizations help us understand the math... not what is actually happening.

The history you provided of Feynman's work would seem to support my feelings on the subject as the concepts were different, and so why can't there be still different concepts (especially when we haven't unified everything mathematically yet)? Cavediver is doing a nice job trying to dispel my unease, but maybe you'd like to take a shot.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 168 by Son Goku, posted 03-08-2008 4:51 PM Son Goku has replied

Replies to this message:
 Message 176 by Chiroptera, posted 03-09-2008 6:16 PM Silent H has replied
 Message 182 by Son Goku, posted 03-10-2008 8:52 AM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 177 of 327 (459767)
03-09-2008 6:59 PM
Reply to: Message 176 by Chiroptera
03-09-2008 6:16 PM


Re: A bit of history.
Yeah, I should probably define my terms better. I think I may have switched usage throughout my posts as well. I should have said "accurate depiction of the underlying reality", rather than "model of the underlying reality". Clearly mathematical models can be tools.

Earlier I gave the description of atomic vibrational calculations using a "model" of two balls connected by a spring. While a wonderful tool, it would not describe the underlying reality.

For the purpose of this thread, is curved space-time a description of reality, or an extremely useful tool? For example are objects really following the topology of space and time, or do they simply behave in a way such that if we want to do our best calculations we (so far) ought to use that conception?

Cavediver appears to be making a case that the math has become so particular in its definition of phenomena, that there is often nothing left to mathematically address. One theoretical question I keep trying to get at (though hopefully not ad nauseum) is whether it might be possible for a different mathematical approach to be found based on totally different conceptions for how the phenomena function, or even different concepts using relatively the same math?

If so, then I'd say that we are dealing in mathematical models which are tools, and not mathematical models that describe underlying reality. As an aside, I believe that it is possible to reach a point where all we can know are abstract rules for prediction based on observation, without getting further at what is actually occurring. Perhaps we have reached that stage in some areas. This does not reduce such knowledge in importance, it only clarifies its boundaries.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 176 by Chiroptera, posted 03-09-2008 6:16 PM Chiroptera has replied

Replies to this message:
 Message 178 by Chiroptera, posted 03-09-2008 7:08 PM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 179 of 327 (459793)
03-09-2008 9:18 PM
Reply to: Message 178 by Chiroptera
03-09-2008 7:08 PM


Re: A bit of history.
Although I have direct physics issues as well (where I want more info), you have correctly described my theoretical issue with mathematical "realism".

Obviously, from a logical standpoint, neither scenario you mentioned would prove any specific mathematical model true or false, but the former (aliens using different models) would undercut arguments that useful (or seemingly comprehensive) math proves a model true.

I have the feeling my skepticism runs so deep that if every alien species we ran into had the exact same math as we did, and conceptual underpinning, I'd still make my same argument. However, I'd keep a tighter lid on it.

It is nice to find someone with a stronger math background holding a similar issue with what I was taking cavediver to be advancing.

(on names... I am never consistent with capitalizing or even with spelling out the full name, so I'm not the guy to answer your quandry)

Edited by Silent H, : -also


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 178 by Chiroptera, posted 03-09-2008 7:08 PM Chiroptera has taken no action

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 188 of 327 (459978)
03-11-2008 6:48 PM
Reply to: Message 182 by Son Goku
03-10-2008 8:52 AM


Re: A bit of history.
Oh, that was a very nice progressive argument.

Let me see where I am getting things wrong by bringing up another set of measurements. I can record heights of people. I can also record time. If plotted for any person they will tend to show a curved structure. Does that mean that time is shaping people's height? Or maybe that height effects time?

That things can be plotted, and the plot useful, does not mean there is a direct interaction, rather only a solid correlation. It may be eminently useful to produce calculations based on a space-time model, but couldn't that simply be a correlation, rather than a causative structure?

See it starts getting iffy to my mind when we speak of mass and time interacting, given that they are simply measurable quantities. We can speak of how we measure their relation, but their direct connection?

If you reply to this post, as an addition can you unpack what a tensor is? That is a bit of ignorance on my part. I've heard the term and seen some discussions which were too vague for me to understand.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 182 by Son Goku, posted 03-10-2008 8:52 AM Son Goku has replied

Replies to this message:
 Message 189 by Son Goku, posted 03-13-2008 7:49 AM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 190 of 327 (460381)
03-14-2008 3:26 PM
Reply to: Message 189 by Son Goku
03-13-2008 7:49 AM


Re: A bit of history.
So, on a statistical, logical and observational front we have very good reason to conclude that mass causes spacetime to curve.

Well what the hell kind of reasons are those????

Heheheh. Your last few replies to me have been very useful for me and I'm quite thankful.

I apologize for the height-age example. I came up with it off the top of my head (a correlation involving time) but you adequately pointed out where it was not the same type of measurement-connection under discussion. I didn't reply immediately because I've been trying to think of a better example, but perhaps in the glare of your explanation of various independent quantities bearing out the same relationship I can't seem to find anything worthy.

I can't remember who told me about the GPS satellite time differential issue first, but that always struck me as a very strong indicator GR concepts were on the money. Still the maverick in me wants to make sure I'm not jumping on an apparent causative connection. Maybe something else (some other explanatory concept) ties them all together, though with similar mathematical results. I guess one could analogize this to the way Newton's laws are a subset of GR's results, which has a completely different explanatory concept).

I hope that makes sense.

One remaining question for now. Why is it with the success of GR in the realm of physics, that gravity is still discussed (and even taught) as a force between objects? I understand that the classical equations and concepts are easy, but shouldn't science be making a stronger push to flip the conceptual understanding to the correct model... from the beginning?


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 189 by Son Goku, posted 03-13-2008 7:49 AM Son Goku has replied

Replies to this message:
 Message 193 by Son Goku, posted 03-17-2008 9:11 AM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 191 of 327 (460525)
03-16-2008 1:20 AM


gravity and disappearing matter, (esp for cavediver, but all welcome)
Up thread I gave a hypothetical of some mass appearing and asking about resulting gravitational effects. Cavediver pointed out that this cannot happen. I mentioned that I had seen a similar hypothetical made by a physicist (though it was disappearing matter), and cavediver said that too cannot happen.

I'm not disputing anything said by cavediver, but I did find the video where I saw the hypothetical. It is from Brian Greene's Elegant Universe and the hypothetical starts about 3 minutes into the vid clip.

Perhaps someone can tell me what I got wrong, or if he was wrong.

Also to cavediver, can you finish explaining the sphere example related to time and motion. I think I got it wrong (after seeing an example by Chiro elsewhere). I'm still trying to get down (in a way I can explain to others) how/why objects at rest will be drawn into motion by a curvature of time toward another body.

Why does a body continue accelerating vs simply moving to a constant speed? Also, both bodies in a 2 body system actually start into motion toward each other, right? This raises the question of why there is a difference based on unequal mass as to which body is shifted more out of its original position, if it is simply an issue of following the curvature of time? Does each body's imposed space-time curve effect the other body separately, rather than creating a singular curve between them? Or does the time curve effect different size masses differently?

Also, if it is the curving of space-time which causes the motion of A toward B, why does it create momentum as if a force were acting on A, rather than both simply moving closer as if space were disappearing between the objects (sort of a reverse of space increasing between them due to cosmic expansion)?

Anyone can answer of course.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

Replies to this message:
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Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 204 of 327 (460802)
03-19-2008 1:10 AM
Reply to: Message 193 by Son Goku
03-17-2008 9:11 AM


Re: A bit of history.
I should have said thank you earlier, instead of letting fulton take the floor.

As a side note, I was aware that the GPS thingy was not designed as a test, but that is what appealed to my mind even more. When something is incidental, and at the same time shows complete practicality, that is very cool.

Your explanations have been very useful, and I appreciate the work you've put into the descriptions.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 193 by Son Goku, posted 03-17-2008 9:11 AM Son Goku has taken no action

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 227 of 327 (462045)
03-29-2008 7:41 PM
Reply to: Message 222 by cavediver
03-29-2008 10:47 AM


Re: the gravity of general relativity
As ever, helpful yet adding further points of inquiry. But then again that is essentially the defining characteristic of science, right?

I'd possibly swing it around and say the Universe is simply how our perception sees the mathematics. It always sounds like a copout, but you really do need to get down and dirty with the fundementals to get so strong an impression.

Not to start the debate here, but as an explanation of my current thinking. I tend to view math as a prosthetic for the human mind to grasp what it cannot understand intuitively. Thus math is not the reality which our perception sees as the universe, but what we strap on to our perception to in some way see the universe as it is.

But like I said, we don't have to debate that here...

consider distance - distance is merely a field that gives values assigned to pairs of points. So the distance say the Andromeda galaxy is away from you compared with your keyboard, is merely a case of a difference in a couple of values. There's no 'real' sense that Andromeda is way off in the Universe and the keyboard is next to you.

Okay, now you have to stop fucking with my mind (pardon the scientific jargon). Values do have meaning, right? How is there not a practical reality that my keyboard is next to me and Andromeda is far away, especially with the concept of a limited speed of light? Or is this to suggest that there is a difference between the universe and practical reality?

this is far beyond GR and definitely for another thread if you want to explore this further.

Yes, I would like to explore this further. Probably more than anything else at EvC, I would like to understand these concepts. However, I realize this puts a burden on you. If you feel you have the time and interest to walk me through it I will open a thread (probably Is it Science?). You can drop in as you can, and I will not expect immediate answers to any of my posts. But if this will likely strain your time in general, or our relationship as I suck knowledge from you like a very hungry intellect devourer, please let me know and I won't open that thread of worms.

except that even when energy is 'diffuse' it still has an associated mass.

Would I be correct in assuming an associated mass as if mass (equal in quantity with that energy) were spread "diffusely" over that same volume?

The masses in isolation experience no accelerations and simply trace out their path through time, following their purely time directed vectors. But near each other, their vectors are tipped by the space-time curvature generated by each other.

Let me try to restate... So two bodies start by simply moving through time, but when close to one another the c length vector each follow gets turned slightly (by the warping of space-time) from pure time, to both space and time. In this way a velocity is observed to begin in both bodies. As the curvature increases the vector turns more (aka vector follows curvature), and the resulting changes in velocity are the observed acceleration.

I realize that there are no initial forces at a distance, however isn't it true that this activity of simply "following a vector" creates real momentum, which once those bodies meet gets converted into a real force, which then perhaps accelerates one or both bodies in a way that is real?

It doesn't - in orbit, your path winds around the centre.

In orbit, I get. But in the example of two bodies initially at rest, the path of acceleration is towards the center of the other, right?

This next question is going to sound weird, but given your description of how this works, is it possible to create "isochronal" charts of space? This would be somewhat like weather maps or geologic maps with isobars and the like for elevation. These latter can be used to map out flows of air currents or water based on the difference between the high and low areas. In other words we get a good visual descriptions that allow accurate predictions of what will happen, without having to run mathematical equations.

If movement is associated with mass, which is directly linked to different rates of time (so high and low "time pressure"), this would seem to be possible.

Also, as rate of time does change, is there a minimum change in that rate which cannot be crossed? That is to say is rate of time change quantized?

If this all sounds like gibberish, it may be a combo of ignorance or lack of adequate vocabulary. I'll take whatever spanking I deserve.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 222 by cavediver, posted 03-29-2008 10:47 AM cavediver has replied

Replies to this message:
 Message 232 by Son Goku, posted 03-30-2008 4:05 PM Silent H has replied
 Message 233 by cavediver, posted 03-30-2008 5:10 PM Silent H has replied

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 236 of 327 (462240)
04-01-2008 6:51 PM
Reply to: Message 232 by Son Goku
03-30-2008 4:05 PM


Re: the gravity of general relativity
Thank you SG...

It's also fairly easy to teach somebody how to read them, even if they haven't too much mathematical experience with GR.

That's what I figured could be done. It makes life much easier in geology/hydrology/meteorology. Less calculations produce many predictions which make it easy to understand what is happening, and most people can get it just by looking.'

You mentioned the word "Isochronal". Just as isobars are surfaces of constant pressure, I'd imagine these would be surfaces of constant time, yes? If so, they're usually known as "spacelike hypersurfaces".

I meant constant rates of time. I'm not sure if that is exactly the same as constant time. An example I could describe would be a line showing the time rate for those at the surface of the earth, and another at a level above the earth where satellites are at a different rate. From descriptions of how matter moves, one could "see" that something would naturally want to "flow" down the gradient from where the satellite was, to the earth.

If that is like a spacelike hypersurface, while that is a cool name, isochronal is a bit shorter.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 232 by Son Goku, posted 03-30-2008 4:05 PM Son Goku has taken no action

  
Silent H
Member (Idle past 5090 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 237 of 327 (462243)
04-01-2008 7:08 PM
Reply to: Message 233 by cavediver
03-30-2008 5:10 PM


Re: the gravity of general relativity
Even without going beyond basic relativity, this 'practical reality' is seriously screwed. Along the path taken by a photon leaving a star's surface in Andromeda and entering your cornea, there is literally zero space-time distance. However, we perceive that distance to be 2.2 million light years as we are not travelling with the photon.

Ok, for photons I totally see your point. But for massive me, there really is a practical reality isn't there? I would never realistically reach the point of instantaneous travel, and for all practical reality distance is and distance seems... or at least it will take me a hell of a long time to reach Andromeda compared to this keyboard.

On this idea. Is light then somewhat of a wormhole for photons? I know we want space-like wormholes, which is an instantaneous jump between locations in the same moment. But what you describe seems to be instantaneous jumps to a different time and location. The idea that there is no real distance rings to my ear like the description of movement through a wormhole.

However, when you say isochronal (and SG says spatial hypersurfaces), this is not a universally agreed surface of equal time, as there is no simultaneity in relativity - different observers will argue different spatial hypersurfaces of equal time.

I want to make sure to get something straight, while there would always be debates on when something occurred, or within how large a volume/area, everyone would agree on (measure the same) rate of time proceeding at any location, correct?

For example if we have three ships zooming around at different angles and speeds to one another (some close to c, some not) When A and C look at B nearing a planet, while they would disagree on when B entered the planet's gravity, as well as how large B and the planet are, they would both predict the same rate of time going on within B as well as on the planet's surface, right? Or is there super-relativity?

I'll look to start a new thread soon, so thanks in advance.


h
"Civilized men are more discourteous than savages because they know they can be impolite without having their skulls split, as a general thing." - Robert E. Howard

This message is a reply to:
 Message 233 by cavediver, posted 03-30-2008 5:10 PM cavediver has taken no action

  
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