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Relativity of Motion discussion from “What is Time”


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#137 jedaisoul

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Posted 02 November 2009 - 02:20 AM

But you refer to space as "emptiness, void, infinite volume". That's a problem for me. To be emptiness or a void, there would have to be a space that is empty. A space with metric properties: position, size and orientation. You seem to agree with that because you give it a size: "infinite volume". Are we still in agreement: Yes/no?

No. What is the problem for you in "a space that is empty" being "emptiness" or "void" devoid of "properties" assigned by scientific metrics like "position, size, and orientation," ... all "properties" of things/stuff/bodies/etc existing *in* space as defined above?
[snip]
To be clear, space is that emptiness in which nothing exists, as between and beyond things that do exist.

Then your beliefs are mutually contradictory. That's not unusual in intuitive beliefs. They are held separately, and its only when you analyse them critically that such flaws become apparent.

So what is the flaw in what you say? Well, I'm NOT saying that its wrong to see space as "emptiness in which nothing exists, as between and beyond things that do exist". I broadly agree with that. But if, as I do, you believe that space truly is nothing, then it follows that space does not exist in and of itself. It only exists to the extent there are things to be between and beyond. Hence if everything that does exist in and of itself were taken away, there would be no space, because there is nothing for it to be between and beyond. That is logical.

To claim that space can be both nothing, AND exist separately from the objects that it is between and beyond is not logical. Either of those statements could be true, but not both.

So think on this. Your beliefs are contradictory.

#138 HydrogenBond

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Posted 02 November 2009 - 07:38 AM

The motion of the comet in the empty universe runs into a relative reference problem, which in this case has no reference. The work around the lack of space-time reference has to do with energy, since energy can propagate through empty space. If there was a way to measure kinetic energy, from that energy we could tell its velocity.

Special Relativity has three equations, one for distance, one for time and one for relativistic mass. Relativistic mass is how you do your energy balance even in empty space. If we leave that out, and only use space-time, we are left blind in empty space.

If we could place the comet on a special scale, that can measure relativistic mass, we can know its absolute speed without needing a space-time reference. The scale will move with the comet. We then measure what happens to the scale, i.e., how its relativistic mass has changed by keeping up with the comet.

#139 modest

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Posted 02 November 2009 - 10:31 AM

If there was a way to measure kinetic energy, from that energy we could tell its velocity.


Kinetic energy is just as frame-dependent as velocity. The kinetic energy of a body depends on the frame from which it is considered.

Relativistic mass is how you do your energy balance even in empty space.


Relativistic mass is just as frame-dependent as velocity. The relativistic mass of a body depends on the frame from which it is considered.

If we could place the comet on a special scale, that can measure relativistic mass


A scale doesn't measure mass in empty space. To measure the mass of the body you would have to push on it and measure its acceleration. This would obviously require a second point from which to push and measure acceleration. and wouldn't work anyway if Mach's principle is valid.

You can't meaningfully give "relativistic mass" without giving some frame from which it is meaningful. In the object's rest frame the relativistic mass is relative to the object's rest frame and is the "rest mass" or "invariant mass" which doesn't tell you a velocity (except for zero).

we can know its absolute speed without needing a space-time reference.


You would not and could not. "Absolute speed" is a contradiction in term.

~modest

#140 modest

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Posted 02 November 2009 - 10:34 AM

But if, as I do, you believe that space truly is nothing, then it follows that space does not exist in and of itself. It only exists to the extent there are things to be between and beyond. Hence if everything that does exist in and of itself were taken away, there would be no space, because there is nothing for it to be between and beyond. That is logical.


:eek:

Einstein believed that the hole argument implies that the only meaningful definition of location and time is through matter. A point in spacetime is meaningless in itself, because the label which one gives to such a point is undetermined. Spacetime points only acquire their physical significance because matter is moving through them. In his words:

"All our spacetime verifications invariably amount to a determination of spacetime coincidences. If, for example, events consisted merely in the motion of material points, then ultimately nothing would be observable but the meeting of two or more of these points." (Einstein, 1916, p.117)


He considered this the deepest insight of general relativity. When asked by reporters to summarize his theory, he said:


"People before me believed that if all the matter in the universe were removed, only space and time would exist. My theory proves that space and time would disappear along with matter."


Hole argument - Wikipedia, the free encyclopedia

~modest

#141 modest

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Posted 02 November 2009 - 10:35 AM

Motion requires two points.


checkmate.


:eek: :(

~modest

#142 Michael Mooney

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Posted 02 November 2009 - 02:43 PM

Buffy:

Do you understand the difference between the words "temporally" and "temporarily?"


Yes. Sorry, I mis-read "temporally."

The use of the word "temporally" is extremely significant here because it points out changes in position that are in spacetime, not just space. When you realize that your argument is still based on the notion of movement relative to the now "missing" sun, you have--very ironically--continued to base the definition of the term "motion" on "change in relative distance."


I consider "spacetime" a "fabrication" in service to the metric or matrix overlaid or imposed on the real cosmos by relativity... a very useful fabrication at that, but not *ontologically* an existing entity, medium, etc. (As per the whole long tedius "spacetime" thread.)

No! My comet exercise was not "still based on the notion of movement relative to the now "missing" sun. It was intended to remove everything but the comet from the universe to illustrate that with nothing to stop it, the comet would continue to move through empty space, relative to nothing... intrinsic motion... as I have called it in disagreement with the common notion, as quoted from Wiki (twice now) as follows:

...Motion is always observed and measured relative to a frame of reference. As there is no absolute reference frame, absolute motion cannot be determined;


First, my exercise has no observer and no "frame of reference." If you accept the terms of the exercise, there is no force acting upon the comet anymore, so it would continue to move at the same speed, with the same inertia/momentum as it had with the universe intact. The straight line trajectory was just an aside, as, obviously it would no longer be in orbit around the non-existing sun. Simple as that!

In none of your posts so far have you really defined motion without reference to another point in any critical way...


I agreed with Wiki that:

Motion involves change in position...
In physics, motion means a change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, displacement, and time.[1] An object's velocity cannot change unless it is acted upon by a force, as described by Newton's first law also known as Inertia. An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in a closed system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum.


One can assign a virtual point *in now empty space* marking the locus of the comet at the time everything else disappeared (leaving only empty space... not an "entity" btw) and then "measure" its continued velocity from that virtual point as it continues to move through empty space... But, its continued motion is not dependent on this measurement!... which is why I call it intrinsic motion, not "relative" (necessarily) to anything else.

The above references to inertia and momentum apply to my argument that the comet's motion continues as it was ( but without an orbit.)

Unless you understand the above, we are going nowhere... fast!:eek:

...which as I pointed out in my previous post--but which you chose to ignore--is making motion an axiom of your system. That is, it is definitional, and does not constitute an observable ontological property.


I have defined motion as above as independent of measurement, tho measurement is still possible, as from its virtual locus before the disappearing act.
Btw, ontology is not only about categories and relationships of things that exist.
Quoting Wiki, it is also the

philosophical study of the nature of being, existence or reality in general, as well as of the basic categories of being and their relations.


Ontologically, the comet, now the only thing in the universe, still exists and is still moving... through empty space, relative to nothing... tho the virtual point of departure, as above is optional for relativity theorists who simply must measure things and have "two points" to even allow "movement."

More importantly though, by saying that there are no entities that have the state "not in motion," you make the entire notion of "motion" ontologically uninteresting, because ontology is only interested in the properties of things that distinguish one set of entities from another.


Ontologically, the comet, as the only thing left still exists and is still moving. (Am I repeating myself... very well... I'll skip most of the rest rather than continue such repetition.) Philosophically, I think the existence of only one thing is still existence, and it is still moving... if you accept the exercise on the terms it was presented.

But I may be reading too much into your statement, so please try to clarify if you can.


I hope the above does so.

Note however that if you are not simply saying "everything is in motion, therefore the comet is moving" you do indeed need to have a definition for "motion" in order to make any discussion of it as an ontological property because it must be possible to perceive it in some way, shape or form.


There it is, in the mind's eye only... still a lonely little ball of ice and dirt still moving through empty space... now without a tail, poor thing!:(

This is where your understanding of the notion of "observe" gets contradictory: I have in my previous posts even granted several ways for there to be a way to measure motion that is not dependent on a in-Universe observer with a reference frame. Oddly enough, the one that is most supportable is to use ether as an effective Cartesian Coordinate system for the Universe, however you have insisted that you do not accept the existence of ether--something that most of the rest of us would agree with.


If you get what I said above, you will see that the only contradiction is in your misunderstanding of my basic philosophy, stated here many times. The cosmos and all its moving parts exist and move around totally independently of measurement. The latter is the job of science, but measurement does not create that which is measured, including motion. And each "part" is moving regardless of the consideration "relative to what?"

The other key mechanism is to literally be "outside the system": that is, to be able to see all points simultaneously as if the Universe were a big disk drive that would let you be anywhere you wanted to be at anytime.


Yes! This is the perspective I have presented many times as transcending the locality arena of relativity... which is *cosmos as a whole* for which "it is always now, everywhere" transcending measurement of selected events being clocked for specific durations.
Also this perspective doesn't give a hoot about the constant speed of light and what local perspectives can see what and when relative to each other.

But the weakness of this is that it still requires either a coordinate system or other objects to compare the motion to to determine "if it's really moving."


Cosmos exists all by itself whether a coordinate system and measurements are applied or not.
And, yes, the lonely comet is still moving through empty space... velocity to be measured from virtual point of "departure" (from orbit) or not.

You need to explain motion without anything else being there to compare it to.


That was the whole point of the exercise, all references to inertia and momentum, etc... *through empty space* with nothing else left!

The comet exercise is simply using the *formerly existing point* represented by the Sun as the comparison point. It does not matter whether it was "there a minute ago and we were moving relative to it then, so we're moving relative to it now." You're still using it as a point of reference.


No. The sun disappeared. It's locus could still be used as a *reference point* for its continued motion, as could its point of departure from orbit, but non of this is required for the comet to continue to exist and move all by its lonely self.

Gotta go. back soon to see what I've not yet addressed.

Michael

#143 modest

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Posted 02 November 2009 - 04:39 PM

...so it would continue to move at the same speed, with the same inertia/momentum as it had with the universe intact.


Momentum is just as frame-dependent as velocity. The momentum of a body depends on the frame from which it is considered.

Momentum is mass times velocity. Saying "comet has momentum" is no more meaningful than saying "comet has velocity" or "point has distance". The comet has momentum and velocity and relativistic mass, and kinetic energy... relative to what? The point has a distance relative to what?

If you say "relative to a point which no longer exists" or "relative to space which doesn't exist" then you are still saying "relative to... something..." You can't leave the "relative to" part off of a frame-dependent quantity. You can't say that the comet has a million kilogram meters per second momentum in and of itself. That makes no sense. You have to say that it has that much momentum relative to something.

Velocity, momentum and kinetic energy are not intrinsic properties. If we could get past that then we could explore why/how duration and distance are likewise not intrinsic properties. But, we can't even get past the idea that a line needs two points... that velocity needs at least a line. :shrug:

~modest

#144 watcher

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Posted 02 November 2009 - 08:14 PM

Velocity, momentum and kinetic energy are not intrinsic properties. If we could get past that then we could explore why/how duration and distance are likewise not intrinsic properties. But, we can't even get past the idea that a line needs two points... that velocity needs at least a line


you have neglected to mention the inertial mass of the comet. it has potential energy equivalent to square the speed of light. now c is a constant, it is not relative to the velocity of the comet. so whether the comet has relative motion is irrelevant now to discussion.

now what you need to ask your self is ... does the existence of the inertial mass of the comet depends on some kind of motion (intrinsic/absolute , distinct from relative motion) or not?

,

#145 modest

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Posted 02 November 2009 - 08:43 PM

you have neglected to mention the inertial mass of the comet. it has potential energy equivalent to square the speed of light. now c is a constant, it is not relative to the velocity of the comet. so whether the comet has relative motion is irrelevant now to discussion.


I have certainly not neglected "inertial mass". I just addressed it in post 139. Energy is proportional to relativistic mass *not* invariant mass (ie rest mass). The equation E = mc2 only makes sense if m is the relativistic mass (which is contingent on velocity) or if m is the invariant mass *and* it is held in respect to the rest frame.

In other words: in no way does the invariant mass tell you the intrinsic velocity of a particle. It tells you the mass of the particle at rest.

Mass in special relativity - Wikipedia, the free encyclopedia

now what you need to ask your self is ... does the existence of the inertial mass of the comet depends on some kind of motion (intrinsic/absolute , distinct from relative motion) or not?


No—what you need to ask yourself is how in the universe you are going to measure the inertial mass of a single object. It can't be done. Not to mention, if Mach's principle is valid then "inertia" itself is relative. "Inertial mass" truly loses all meaning for a single object in and of itself.

~modest
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#146 Buffy

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Posted 02 November 2009 - 10:05 PM

I consider "spacetime" a "fabrication" in service to the metric or matrix overlaid or imposed on the real cosmos by relativity...

Do you understand that Relativity eschews ether? That it's big breakthrough is actually *not* requiring a "matrix overlaid...on the real cosmos?"

One can assign a virtual point *in now empty space* marking the locus of the comet at the time everything else disappeared (leaving only empty space... not an "entity" btw) and then "measure" its continued velocity from that virtual point as it continues to move through empty space...

Whew! All that effort! I'm glad you now agree with the rest of us that motion is based on a measurement between two points!

Now on to the remaining issue:

But, its continued motion is not dependent on this measurement!... which is why I call it intrinsic motion, not "relative" (necessarily) to anything else.

There's a question I've asked you repeatedly through the thread that you've yet to answer (so I'm forced to emphasize it):

How can you tell it's in motion?


You've just agreed that the only way to tell that it's in motion is to reference another--now "virtual"--point in space. But ontology requires a way to actually perceive its intrinsic qualities, and if in the Universe at that instant that its empty, motion ceases to be perceivable, it ceases to be an intrinsic quality.

You avoided that line from my last post, and although I bolded it there, you somehow missed that it is the essential hole in your argument.

It's easy to say:

I have defined motion as above as independent of measurement, tho measurement is still possible, as from its virtual locus before the disappearing act.

But by continually referring back to the actual measurement, you seem to have no way of defining an intrinsic quality of movement without that measurement.

That's the point we've been trying to get across here, and it has nothing to do with Relativity, pro or con.

So unless you respond to that, I'll agree with you:

Unless you understand the above, we are going nowhere... fast!:)


So to make it clear:

Philosophically, I think the existence of only one thing is still existence, and it is still moving...

In the empty universe, the comet has substance, it has width, it has mass, it has color, it has many properties, but one thing it cannot be shown to have is motion.

Thus motion in the empty universe is not an intrinsic property because it cannot be demonstrated.

That is unless you want to bring ether back in...but that is really ontologically equivalent to any other fixing of points, virtual or physical...

...and what that's all about comes down to this statement:

If you get what I said above, you will see that the only contradiction is in your misunderstanding of my basic philosophy, stated here many times. The cosmos and all its moving parts exist and move around totally independently of measurement. The latter is the job of science, but measurement does not create that which is measured, including motion.

This is fundamentally wrong: Ontology does indeed require measurement in order to define the intrinsic qualities!

From an ontological standpoint, a property is irrelevant if an entity cannot be defined as having it or not having it.

As you said:

Unless you understand the above, we are going nowhere... fast!:hihi:

-----------------------------------
I think it's important to recognize that what you really seem to dislike is Relativity:

Also this perspective doesn't give a hoot about the constant speed of light and what local perspectives can see what and when relative to each other.

...and this hostility has clouded your ability to deal with the purely ontological arguments against your theory.

I and others here have tried to explain the fault in your argument without reference to Relativity, and yet ultimately you accuse us of being blind Relativity-zealots.

That's unfortunate, but more importantly, to most reading this, it's become pretty apparent.

You're welcome to try some more to define how motion can be perceived in a Universe with no other points of reference, but you have to realize that without a way to define the possession of an intrinsic quality, an entity cannot be said to possess it.

Sorry, that's ontology...

The subspace W inherits the other 8 properties of V. And there aren't even any property taxes, :shrug:
Buffy
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#147 watcher

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Posted 03 November 2009 - 12:42 AM

I have certainly not neglected "inertial mass". I just addressed it in post 139. Energy is proportional to relativistic mass *not* invariant mass (ie rest mass). The equation E = mc2 only makes sense if m is the relativistic mass (which is contingent on velocity) or if m is the invariant mass *and* it is held in respect to the rest frame.

In other words: in no way does the invariant mass tell you the intrinsic velocity of a particle. It tells you the mass of the particle at rest.

Mass in special relativity - Wikipedia, the free encyclopedia


yes that is why i am asking you to consider the origin of mass. do you really think that a mass at rest has no intrinsic motion? that it is dead static?

if so, why did an object in space moves endlessly without any visible enrgy or force acting upon it.? or why the arrow continue to move long before the string force is spent? where is the impetus of motion coming from in both cases?

No—what you need to ask yourself is how in the universe you are going to measure the inertial mass of a single object. It can't be done.


you are confusing something undetectable or unmeasurable is equal and the same to non-existence.

Not to mention, if Mach's principle is valid then "inertia" itself is relative. "Inertial mass" truly loses all meaning for a single object in and of itself.

~modest


the inertial mass of a single object can be known as a ratio of its mass over the total mass of the universe. this can be done using natural units. the calculation requires super computer ability but the concept is sound.

#148 jedaisoul

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Posted 03 November 2009 - 02:48 AM

Michael, think about what Buffy has said:

You're welcome to try some more to define how motion can be perceived in a Universe with no other points of reference, but you have to realize that without a way to define the possession of an intrinsic quality, an entity cannot be said to possess it.

With reference to your "comet in an empty universe" example, she has shown that you can't define motion in a one body universe. Think also about my point:

I'm NOT saying that its wrong to see space as "emptiness in which nothing exists, as between and beyond things that do exist". I broadly agree with that. But if, as I do, you believe that space truly is nothing, then it follows that space does not exist in and of itself. It only exists to the extent there are things to be between and beyond. Hence if everything that does exist in and of itself were taken away, there would be no space, because there is nothing for it to be between and beyond. That is logical.

To claim that space can be both nothing, AND exist separately from the objects that it is between and beyond is not logical. Either of those statements could be true, but not both.

I have shown, using an example where there are no physical bodies, that space cannot both be nothing AND continue to exist if everthing else is taken away. These are two important flaws in your argument. Forget the pro's and con's of relativity; your argument simply does not make sense when you analyse it critically.

#149 AnssiH

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Posted 03 November 2009 - 04:21 PM

I find this philosophically satisfying because it allows us to describe wildly different perspectives with exactly the same physics giving exactly the same answers—describing the same underlying situation regardless of something that I don't think should matter: coordinate choice.

Coordinates aren't real so choosing them shouldn't affect the answers.


Yes and since you bring that up, I would like to comment that DD's analysis is very much revolving around that notion; some aspects of your worldview aren't "real" by themselves, and shouldn't affect the answers.

The symmetry constraints (that are succintly expressed as a single "fundamental equation") exist as "aspects of your explanation that cannot affect the answers". They cannot affect the answer because they arise as necessary symmetries during the transformation process from "unknown patterns" to "set of persistent entities".

E.g. the "origin of the universe" can be defined in our heads, but it is an unknowable aspect of universe (it is ontologically moot idea), and devoid of undefendable assumptions, our answers must be invariant when you shift the "origin of the universe". That is the same thing as "shift symmetry" (to prediction function), which is the same thing as conservation of momentum. I.e. it constraints you to define persistent entities as those features in the raw data that can be seen as conserving momentum (via some transformation process, of which a definition of space is an important aspect).

Things get complicated for intuitive thought very quickly, but I hope you can see the idea. Especially how this has got nothing to do with ontology, but it is still central to any definitions (human comprehension) about reality. The expectations for relativistic time relationships are yielded via the definitions behind electromagnetism (which arise from the symmetries too), and their expression in a specific form which just must be valid because of those underlying epistemological symmetries.

Another thing, about not being able to ignore the rest of the universe in case of rotation (of the lab frame), I think there's something to think about there in the fact that, linear momentum must vanish over the entire universe, and that that also sets the null rotation for the entire universe does it not? (If you choose an arbitrary rotation to your coordinate system over the entire universe, the linear momentum does not vanish) Foucault's pendulum and other coriolis type effects are of course easily understood as manifestations of linear momentum. So, with a definition of angular momentum, you get coriolis effect simply because you already had linear momentum.

I see the existence of the kind of symmetry as is expressed as Mach's principle as a little bit different issue. Although perhaps I am overlooking something and there are some interesting connections there (who knows, rotational things are goddamn complicated when you get into relativistic effects and whatnot :hihi:)

And a third thing... Remember my rant about that bad mainstream science publication and its silly article about how "time does not exist" (arguing that relativity indicates that spacetime exists, and being completely clueless about how they publish articles all the time that argue entirely from within spacetime ontology). I read a bit of another issue of the same magazine (hey, I wanted to be amused), and sure enough they had an article about "how did universe begin" or something. Obviously they made the argument that "time and space started from a singularity". Is that not an argument made entirely from within the spacetime paradigm?

The whole big bang model is just so deep into its own definitions of time and space that I just can't take it more seriously than any other creation myth. I think it's one thing to take the current state of affairs as an indication that the known universe has been a singularity in the past (which is a complex matter already), and another thing entirely to take that as a creation story (which is just naive beyond belief and I'm sorry if that offends anyone's beliefs).

It is also interesting that the definition of space and time must be accepted in very specific form for the model to be sensical. Those forms are not ontological forms any more than any other equally valid form, and personally I just feel that I could just as well say that the universe started from an "egg" that "hatched" and is still "spouting its contents all over the place". Given appropriate definitions for what I mean by those words, I'm sure it would be possible to build exactly as valid creation myth.

Now perhaps that example also is pointing out how these arguments tend to turn into completely pointless bickering about what things supposedly are "in-themselves". A primordial "egg" is not an "egg" unless you say it's an "egg", and same goes for anything you can think of; you had to define it first didn't you? "Whatever you say it is, it isn't", everyone remembers what that means? How many out there feel like asking "what is time?" and suppose to find ontologically valid answer?

Ahhh [/rant]

-Anssi

#150 modest

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Posted 07 November 2009 - 03:53 PM

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Moderation Note: The replies to the above post and subsequent discussion have been moved to: "Unknowable Ontology?".

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