This is what I understand about spacetime. Please tell me if I understand it wrong.

[FayeKane]

Educate me. Here's what I think I know about SR. Please tear my understanding of it to pieces if it's wrong. I want to be humiliated now rather than someday.

 

Thanx,

 

--flk

Okay, consider an "event". In particular, consider an (almost) point mass, stationary in space. Call it event A.

 

 

The same point mass still sitting in the same place, but one nanosecond later, we will call "event B".

 

Now consider the nexus (set of points in spacetime) which have a four-dimensional distance (a spacetime interval) from event A which equals zero.

 

The point mass called "event A" is in that set by definition. But because the interval is a pseudometric (specifically, a Lorentzian metric), two events in different places, if they also exist at different times, can have zero distance between them.

 

This happens when the time displacement expressed as space (the "ct" term in the interval equation) exactly equals the spatial displacement. This is because the time displacement is SUBTRACTED from the metric when the spatial displacement is ADDED.

 

Thus a stationary pointlike mass at time 0 has a zero interval (4-D distance) from many other points. In particular, it has zero distance from all points on a sphere 12 inches in radius but existing one nanosecond later.

 

 

 

The critical thing to note is that this sphere is NOT identical to "event B". Why? Because it has a nonzero interval from event B. Event B is a pointlike mass sitting in the same spatial location as event A, but one nanosecond later.

 

The pointlike mass which sits there immobile, has persistance in time. It is not moving through space. It is, however moving through TIME.

 

And what is the rate of its motion through time? Well, after a time of 1 nanosecond, the spatial distance between event A and event B is 12 inches.

 

Because we ourselves are moving through time too, we really have no choice but to see the pointlike mass as stationary. "It was sitting there, and it's still sitting there. It hasn't moved", a situation similar to looking at an object on a table when you're in a moving train.

 

But the mass/energy which moved from event A to event B IS moving: through time. We just don't notice that because we're moving through time at the same rate.

 

And what is that rate? 12 inches per nanosecond, or "c".

 

Another interesting curiosity which I believe is hugely important in understanding what's going on but which has recieved little attention is:

 

Event A is NOT the same event as B because they are separated by a nonzero interval. You can chose to interpret it as we always do, as no spatial displacement over an interval of one nanosecond, BUT it is equally valid to view the situation "from the ground, outside the moving train". That is, it is equally correct to think of A and B as existing at the same time, but spatially displaced by 12 inches (spherically). Either reference frame is equally valid. The peculiar nature of pseudometrics makes this arbitrary choice necessary.

 

I won't go into the utility of viewing the spacetime metric in this way (it really helps understand gravitation), but it is important to note that nothing I have said is "news". It's all just simple, direct, and probably even obvious consequences of the fact that 4-dimensional distances are Lorentzian, that is, that "time distance" is the same thing as spatial distance, but with the sign inverted.

 

When you read what others have written about it, this last point is usually phrased as "time is imaginary space", in the sense of "multiplied by the square root of minus one."

 

 

While all of the above is just a restatement of things that every physicist knows, the following is just my opinion about the implications of the above.

 

> Okay, fine. But what does all this have to do with gravity?

 

Well, if you see a coin sitting on a table, the above discussion states that you can view the situation in two ways:

 

View One: the coin is sitting in space, motionless. This is what an observer thinks when she fails to notice that she is moving through time at the same rate as the coin. It's as if the coin, the table, and the observer were both on a moving train.

 

View Two, which is more general (from the ground outside the train): The coin is observed to be moving. A moment ago it was one foot away from it's present location; a minute ago it was a mile away, and yesterday it was in Philadelphia.

 

What this means for us is that at any given moment, event A exists both as a point source, AND as a sphere centered on that point.

 

So why can we only detect (see) the point as a point, and not as a spherically expanding shell?

 

I believe we do, and that the gravitational attraction we feel from the mass at event A is the expanding shell that existed as a point (event A) in the past.

 

Think about it. From the above discussion, we already know, as a FACT, that at any particular moment, a coin on a table exists both as the coin we see, AND as an expanding sphere surrounding the coin.

 

Whatever a "gravity wave" is, it is spatially identical to the mass of an object in the past.

 

Also note that the denser the object (like a coin) is, the denser the expanding shell will be when it hits you. And since the surface of a sphere expands as the square of it's radius, when the expanding sphere hits you, it does so with an impact that is proportional to the inverse of the square of your spatial distance from it when it was a point mass.

 

That's exactly the same way a gravitational field propagates. It's called the "inverse square law". Not all fields propagate this way; magnetic field strength varies with the CUBE of the distance.

 

So it seems that if a gravity wave emitted from an object is NOT, literally, the physical object from the past, then it is, by coincidence, something else which:

 

1) spatially overlays in three dimensions the mass of an object in the past

 

2) propagates through space at the same speed as an object in the past

 

3) propagates through space in the same direction as an object in the past (spherically outward)

 

4) The strength of the gravitational field just happens to vary with distance exactly the same as the density of expanding mass from the past does.

 

If the object in question were two stars rotating around each other, the density of their combined mass reaching out from the past just happens to vary exactly in the same complex way that gravity waves emitted from the system do.

 

The moon is a quarter-million miles away, which is one light-second. If it were to suddenly disappear from existence, then on Earth, the moons' gravity would stop one second after the moon disappeared. Coincidentally exactly the same time that the mass sphere expanding from the past stops.

 

When you feel the tug of the earth's gravity, I believe it is literally the earth -- the whole thing, even the melted iron ball at the center -- reaching up from the past and dragging you down.

 

But again, that's just my opinion. It could just be a coincidence that the gravity emitted from an object is in the same physical locations at the same densities as the object in the past is.

 

In the unlikely case that anyone understands that, I'm waiting for them to say "well, the distance (interval) to an object in the future is also zero if you're the correct distance from it, so why don't we feel gravitation from objects in the future?"

 

Feynman and Wheeler answered that about 50 years ago when they asked the same question about EM radiation. They observed that Maxwell's equations SEEM to say that we should be able to see light from the future as well as light emitted by an object in the past, and they explained very elegantly why we can't.

 

Details HERE.

 

Note that if the above is correct, it doesn't imply anything new or even important. It's just interesting to know what gravity really is.

 

In the last chapter of Six Not-So-Easy Pieces: Einstein's Relativity, Symmetry, And Space-Time, Feynman pointed out that while distortion of the geometry of spacetime is a good way to look at gravitation, an equally valid way is to think of empty space somehow being "denser" near a massive object.

 

In another book, called QED (for "quantum electrodynamics"), he explained that refraction occurs because glass is denser than air, and light moves more slowly through matter than it does through air (or a vacuum).

 

I suspect that space is "denser" near massive objects because anything on a free-fall path (a geodesic) that gets close to the massive object must pass through this continual, spherical wave of mass from the object's past which is described above.

 

That would imply that gravitation is actually the same phenomenon as refraction.

 

We actually have a way to check this conjecture. If it were true, then one would expect the deflection of light by glass to vary with the glass density in exactly the same way that a geodesic is deflected by when passing near mass.

 

We could test this by making a lens (actually just a chunk of glass or other transparent material) which varies in density as the square of the distance to some point inside it.

 

If light bends when passing through such a material in the same way that the path of a spacecraft bends when it passes a planet, then I believe that would be strong evidence that refraction and gravitational deflection are the same phenomenon.

 

My personal opinion is that since this conclusion can be reached by just thinking about it while lying on the sofa drinking beer and smoking cigarettes in one's underpants, then if is true, it has probably been known for a century, and I'm merely the ten-thousandth person to stumble upon it.

 

Unfortunately, while I can calculate the trajectory of an object near a planet, I am too stupid to calculate the path light takes when it passes through a material of a continually-changing refractive index.

 

Oh well.

 

If someone smarter than me knows how to do this, and the trajectories turn out to be identical, and that fact turns out to be important, please "steal" this whole idea and publish it as part of your Master's thesis. It isn't necessary to give me "credit" for it; I just want understanding to increase.

 

We already have a model of gravitation: curved spacetime. I suppose that thinking about another model of gravitation just uses time and attention that people could spend thinking about the first one.

 

The thing is, if this way of looking at it is valid, then maybe it's a description of what's actually happening, and that "curved spacetime" turns out to just be an analogy that returns the same mathematical predictions. It would certainly be easier, at least for ME, to not have to think about empty space curving in three dimensions if the much simpler and more factually accurate model of refraction were available.

Edited September 8, 2008 by FayeKane

[Pete]

Educate me. Here's what I think I know about SR. Please tear my understanding of it to pieces if it's wrong. I want to be humiliated now rather than someday.

If you don't get any/many responses its probably because your post was too long to read.

 

Pete

[FayeKane]

Yeah, I figured.

 

Oh well.

[Dennisg]

None of this make any sense to me. So where does one start.

1. Reads more like a poem than an explanation.

2. I feel somehow degraded just reading it.

3. I think FayeKane may be headed for a low and feel sorry.

[Cap'n Refsmmat]

Whoa, no need to be derogatory. FayeKane is just trying to learn here, and this is the first time I've ever seen a speculation on SFN with an actual section on how to see if it's correct.

 

I'll try to read through this when I have more time to see if it makes sense to me.

[Dennisg]

Whoa, no need to be derogatory. FayeKane is just trying to learn here, and this is the first time I've ever seen a speculation on SFN with an actual section on how to see if it's correct.

 

I'll try to read through this when I have more time to see if it makes sense to me.

 

My apologies. I did not mean to sound derogatory- because I don't feel that way. No offence intended to anyone. Just giving feedback on something that only made sense me on those levels.

 

Everything considered it looks like a case of "bull shxt baffles brains"

Edited September 8, 2008 by Dennisg
add a thought

[FayeKane]

> My apologies. I did not mean to sound derogatory

 

God, what is it with you non-autistics? You inject personal ego-battles into EVERYTHING! It's like watching a little-kids' slap fight.

 

And your governments are even worse!

 

> No offence intended to anyone.

 

It seems at every turn, you people are either offended, or apologizing for "making" someone else feel offended.

 

> None of this make any sense to me.

 

That's perfectly okay!! The reason I posted it was specifically to find out if it made sense.

 

> 1. Reads more like a poem than an explanation.

 

Well unless that's an insult (I can't usually tell), thank you. That's beautiful.

 

2. I feel somehow degraded just reading it.

 

WTF? Unless that was a joke (and again, I usually can't tell), why would not understanding something make you feel that someone who does understand it is degrading you?

 

Wait, it's injection of the normal-people ego-pecking-order thing again.

 

Never mind.

 

3. I think FayeKane may be headed for a low

 

What do you mean "a low"? My guesses, in descending order of reliability:

 

1) a "low" in my online reputation because I posted something either subsequently proved incorrect, or that you deem silly

 

2) depressed because you believe I want people to tell me how smart I am and that didn't happen, or

 

3) sad because not everyone agrees with what I wrote, or

 

4) you insulted me, I didn't perceive that, and you think it makes make me feel "low" which, presumably, would have been your intention.

 

Evaluations rejected for being too improbable:

 

5) It's a clever pun involving the extremely low (air) pressure of the hurricane which is about to hit where I live.

 

In any case, I don't feel "low". I hope that is a good thing to you. What I feel is "curious".

 

> and feel sorry.

 

Why should I feel sorry? Did I do something wrong? I often do, you know, without knowing it. If so, I apologize. It seems I have to do that a lot. But would you tell me what it was so I don't make the same "politeness mistake" again?

 

I'll never understand normal people!!

 

You'd think I'd be used to that by now.

 

Oh well.

 

--flk

 

PS

Can we return this thread to a discussion of spacetime? It's a subject I feel much more comfortable with than the evaluation of other people's "feelings".

Edited September 8, 2008 by FayeKane

[Dennisg]

Can we return this thread to a discussion of spacetime? It's a subject I feel much more comfortable with than the evaluation of other people's "feelings".

 

Maybe start with a general statement of what it is that you want to explain about space time. Try to keep is as simple as possible for people like me.

[swansont]

My first reaction is that objects are not events. A point object does not become a sphere; what would be spherical is the region of potential causality — if an event happened at t=0 at the location of the point particle, then any event outside that sphere at t=1 nanosecond could not have been caused by that event.

[FayeKane]

> My first reaction is that objects are not events.

 

In SR they are called that, for the same reason that distances are called "intervals", that is, there is really no fundamental distinction between space and time other than their sign in the metric.

 

> A point object does not become a sphere;

 

I believe the interval equation says does, because the spacetime distance between the sphere and the original "point" object is zero. It looks like a point or it looks like a sphere, depending on where in spacetime you observe it from.

 

Furthermore, it slows light passing through it, indicating it's presence.

 

I don't think the pseudometric is "pseudo"; I think it's a legitimate metric. "An event occurring at two places at the same time?" It's just something people have chosen to ignore because it's embarrassing, like so many other things.

 

But it clearly shows mass as being a wave (in spacetime), as opposed to something of a completely different type: an "object" which just sits there.

 

> what would be spherical is the region of potential causality

 

Yes, of course. But the physical object also exists as a sphere, though a "defocused" one.

 

You might as well say that if your wife saw you through the window at your girlfriend's house, it only means you COULD have touched her, it doesn't mean you were actually there.

 

I think the interval equation clearly implies that the energy of every mass point physically exists at it's null cone. Of course, one could object: "where is it then?"

 

That would be problematical, were it not for gravitation. The gravity waves emitted from an object in the past are like a smoking gun in all of this.

 

--flk

Edited September 8, 2008 by FayeKane

[ajb]

You seem to be "throwing out" the right words, but honestly I don't understand what you are trying to say.

 

An "event" is simply a point in space-time.

 

It is called "pseudo" as it does not satisfy all the requirements of a metric. Namely the positive definite property. Thus we can have zero and negative "lengths" or "intervals" as is often the nomenclature.

 

Apart from these comments I am a bit lost.

 

Special relativity is honestly not a very deep theory once you get to grips with some modern geometry. Carroll's lecture notes on general relativity deal with special relativity from a modern view point. I recommend it.

Edited September 8, 2008 by ajb

[Baby Astronaut]

Here is how I understood FayeKane's post.

 

Gravity isn't really a tug by objects themselves in space, but a tug caused by their movement through time away from us. Perhaps like a "time wind" created by the more dense objects that drags along less dense objects towards them as they move through time, rather than space.

 

Except the objects aren't moving away from us, it's their past existence that is moving away. Thus an object's existence a nano second ago will tug on objects existing in this nanosecond.

 

And the time landscape is comparable to space, where one can measure it in inches or centimeters, to approximate how near you are to an object in time distance (rather than space distance).

 

Of course I might be totally off. Regardless, I like the basis of your idea, FayeKane. Did I get close?

[FayeKane]

> Gravity isn't really a tug by objects themselves in space

 

well yes, everyone believes that. Specifically, that it's not the objects "tugging", but a distortion in spacetime.

 

I suspect that's just another way of looking at what's going on, but not really understanding GR, I can't say very much about it. I only made it to page 26 of "The Feynman Lectures in Gravitation", when he started doing calculus on 4D tensors.

 

> but a tug caused by their movement through time away from us.

 

not a tug really, but the same thing that makes light bend when it goes through water or glass (or anything denser than air). It's called "refraction", and why it happens is so bizarre that for sure you'd think I was making up a crackpot theory. Feynman explains it much more eloquently than I could in his "six not so easy pieces" and in QED.

 

But the bottom line is that waves in "free fall" (i.e. following a geodesic) behave very strangely when they interact with matter before they continue on their merry way. In particular, light is bent when it goes through a lens.

 

All I suggested was that matter (which, at the quantum level, is really a lot of little waves, like light) does this too., and pointed out that things we already know that everyone agrees with would explain why.

 

It's not a big deal, really, it's just that if this is NOT the case I desperately want to know that fact. Not because I care about looking foolish for proposing it, as I couldn't care less about that. But because I really, REALLY have this fear that I'll believe something that turns out not to be true.

 

And all I really want to do before I die is understand what the hell is going on around me, because I don't.

 

And "what's going on around me" is the universe.

 

--flk

Edited September 9, 2008 by FayeKane

[patm]

Maybe none of this is new to professional physicists, but Faye's description and supposition seem much clearer than what I've read in other books espousing various unification theories. I look forward to a healthy discussion from any real guru's on this board.

 

What I got from Faye's descriptions is that what we perceive as gravity could actually be the effects of matter being impacted by the wave effects/interferance of other matter moving through time. Cool is an understatement.

 

Faye, when you say gravitation is like refraction... I wonder... what is being bent? Is it a particle'ss position in 3D space or actually... the particles movement through time itself?

 

Just as gas particles all bounce off each other in three dimensions and jostle about while being seen as smooth at a macro level of general pressure, etc. -- what I'm now wondering about is whether a particle always moves through time at a constant speed. Could the physical acceleration force effect we perceive as 'g' be a side-effect of the time 'pressure waves' an object moves through? Could it be possible that A going through the expanding time waves of other matter could affect A's own speed in in time? With the imparted difference in how A is affected in it's movement through time making A *appear* to accelerate/decelerate in our normal 3D space. (See, my crackpot ideas are WAY crazier than yours!!)

 

-Pat M

[ajb]

What I got from Faye's descriptions is that what we perceive as gravity could actually be the effects of matter being impacted by the wave effects/interferance of other matter moving through time. Cool is an understatement.

 

Faye, when you say gravitation is like refraction... I wonder... what is being bent? Is it a particle'ss position in 3D space or actually... the particles movement through time itself?

 

Classical gravity is already well understood in general relativity. Why not start there as we have nearly 100 years of experience with it.

[FayeKane]

> Faye, when you say gravitation is like refraction... I wonder... what is being bent? Is it a particle's position in 3D space or actually... the particles movement through time itself?

 

> Could the physical acceleration force effect we perceive as 'g' be a side-effect of the time 'pressure waves' an object moves through?

 

Mmm... possibly, but I don't think so. It wouldn't be like running into water which slows you down through the mechanical effect of pushing water molecules out of the way (even though that effect is ultimately due to the electrical bonds between atoms). It would be from whatever causes light to slow in glass, which is a completely different mechanism involving wave interference, so I *guess* that the slowdown is due to the quantum waves of mass interacting with and interfering with each other.

 

You may be right, though.

 

> Could it be possible that A going through the expanding time waves of other matter could affect A's own speed in in time?

 

Again, I would imagine that's gravitational time dilation.

 

--flk

 

> Classical gravity is already well understood in general relativity. Why not start there as we have nearly 100 years of experience with it.

 

We already HAVE started there. I'm just observing something I though was curious and which doesn't involve believing anything new. If you don't find it a strange coincidence that the expanding mass is coincident with the gravity wave in both position, intensity, and rate of dispersion, that's okay with me. I just wanted to point it out in case other people think it's interesting.

 

I'm not trying to change what people believe; I'm just trying to figure out what's going on.

 

What I personally believe is that ultimately, "bending spacetime", "space is denser near mass", and "interference with expanding mass waves" are three ways of saying the same thing.

 

--flk

[ajb]

I don't know what this expanding mass is.

[FayeKane]

> I don't know what this expanding mass is.

 

Well never mind, then.

[ajb]

No problem FayeKane, I'll just let you blabber on. Never mind me.

[Pete]

Whoa, no need to be derogatory.

Who was being derogatory? I most certainly wasn't. Not at all. I was merely saying that long posts like that will often be ignored because readers often don't want to take the time to read long posts like that. I certainly never mean to be derogatory by any means.

 

FayeKane - I hope you understand that I was by no means trying to be derogatory. Far from it in fact. I appreciate people who check their views with others for feedback. That is highly commendable and I compliment you on your effort. I just wanted to let you know that if you didn't get many responses that it wasn't due to your question per se. It may just be that the reader may be very lazy, like me.

 

I'll try to read it later when I have the time and patience. Good luck.

 

Pete

[swansont]

Who was being derogatory? I most certainly wasn't. Not at all. I was merely saying that long posts like that will often be ignored because readers often don't want to take the time to read long posts like that. I certainly never mean to be derogatory by any means.

 

I don't believe the remark was directed at you.

[Pete]

> Gravity isn't really a tug by objects themselves in space

 

well yes, everyone believes that. Specifically, that it's not the objects "tugging", but a distortion in spacetime.

I don't believe that myself. A gravitational field, at least as it was defined by Einstein, has a relative existance and does not require that the spacetime be curved (what you called distorted). Spacetime curvature refers to the presence of tidal forces. Its quite feasable to have a gravitational field with no tidal forces. A uniform gravitational field is just such an example. In fact that's what the weak equivalence principle depends on. I.e. the weak equivalence principle states

A uniform gravitational field is is equivalent to a uniformly accelerating frame of reference.

Einstein viewed the gravitational force to be quite real, i.e. that there is a gravitational force acting on objects which are in the field. His general theory of relativity states that the force is frame dependant and thus is an inertial force and as such inertial forces, like the Coriolis force, are real forces too, contrary to what Newtonian mechanics holds to be true.

 

Pete

[throng]

> I don't know what this expanding mass is.

 

Well never mind, then.

 

 

I do actually get the drift. It is a good visual challenge. I've got a notion on moving points which I think may represent the radius of what you see as a sphere. I'm a bit iffy in the physics but the visual image has exact proportions.

 

It starts with an infinitely small elementary solitary primary point which is the actual source of future movement, so it is moving, and the observer, whos point of reference is the point. He has observed nothing and doesn't know time or anything.

 

The point is called (e1). Observation nothing. Nothing can be deduced.

 

The point splits (we assume that now but confirm it later) and (e1) and (e2) move away from eacthother. (which is akin to your radius). You see that the observer on (e1) has a perception problem at the time of the split.

 

The observer is strictly restricted to (e1). The observer is fairly intergral in this.

 

If you are interested in discussion I would love to pick it appart a bit. The disparity is at the "time" of the split I have one dimention and you have three. (In loose terms.) I'd have no use for Pi, in one dimention.

[phyti]

Faye:

You might want to review SR.

1. Events are in essence photon emissions and absorptions, and because light speed is independent of the source, the interval between events is invariant/fixed. Objects (excepting structureless particles) would be multiple events.

2. The imaginary "i" is used as a mathematical device for purposes of symmetry. This supposedly makes time an orthogonal and thus independent dimension, but, with four variables, only three can be independent and will decide the fourth. It's a only a model for the universe.

3. The idea of all things moving through time has a serious problem. Light/photons are timeless, i.e., experience no time, call it maximum time dilation, so they can only move in a spatial dimension, within the framework of this type of theory. The problem then is, how do they communicate between objects that are moving through time?

That's it for now

It's wise to ask questions.