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- Thread starter stglyde
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For instance, you can find some discussion of quantum determinism on wiki,

http://en.wikipedia.org/w/index.php...60792599#Other_matters_of_quantum_determinism

I wouldn't go so far as to say that the wave function is reality (as the wiki article on quantum determinism discusses), I take the position that it could be and it wouldn't matter. In short, I don't think determinism is a testable theory, it's a non-testable philosohpical issue.

It's really hard to say if this is a "consensus" position or not, but it's mine, and I don'tthink it's terribly uncommon.

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ghwellsjr

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Isn't there an oxymoron going on here?Block Time in relativity wherepast, present and future exist all the timeseems to be in conflict with quantum indeterminism where the latter states the future is uncertain. So why do physicists still competely believe in Block Time? What is the consensus about this in the physics communityat the present time?

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I don't believe that special relativity necessarily implies block time.

But the lorentz frames and the way they are boosted and lorentz transformation automatically create block time. Block time is the heart and meat of special relativity. How can you create SR without implying block time?

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ghwellsjr

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That's a new one on me. That's like saying that since my cell phone has a calendar in it the goes up to the year 2069, then the next 58 years already exist. Maybe you could explain how you arrived at this conclusion because I don't see anything that would suggest block time. Also, maybe you should expand on what you mean by block time, just to make sure we're all on the same page.But the lorentz frames and the way they are boosted and lorentz transformation automatically create block time. Block time is the heart and meat of special relativity. How can you create SR without implying block time?

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That's a new one on me. That's like saying that since my cell phone has a calendar in it the goes up to the year 2069, then the next 58 years already exist. Maybe you could explain how you arrived at this conclusion because I don't see anything that would suggest block time. Also, maybe you should expand on what you mean by block time, just to make sure we're all on the same page.

Block time means the past, present and future are just worldlines which don't flow but already exist. This is how physicists can contemplate how making spacetime loop (like rotating black holes or universe) can entail time travel because you can visit the past.

This is in contrast to old views of space and time where the present exist, the past has happened, and the future is still to come.

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That's a new one on me. That's like saying that since my cell phone has a calendar in it the goes up to the year 2069, then the next 58 years already exist. Maybe you could explain how you arrived at this conclusion because I don't see anything that would suggest block time. Also, maybe you should expand on what you mean by block time, just to make sure we're all on the same page.

In addition to the above. Look at the illustration of Block Time by Paul Davies here:

http://www.nikhef.nl/pub/services/biblio/bib_KR/sciam14327034.pdf

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I find block time a useful concept but I don't believe the world is actually like that.

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ghwellsjr

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Thanks for that link. At least now I can see why they call it Block Time.In addition to the above. Look at the illustration of Block Time by Paul Davies here:

http://www.nikhef.nl/pub/services/biblio/bib_KR/sciam14327034.pdf

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But the lorentz frames and the way they are boosted and lorentz transformation automatically create block time. Block time is the heart and meat of special relativity. How can you create SR without implying block time?

Well said, stglyde. I think many physicists recoil at the thought of a block universe because some of the implications are quite unwelcome to our thinking. Subjectively, I don't like the implications, but at the same time I have never found a way to objectively discount what you have just stated.

On determinism, one should consider that the 4-dimensional filaments making up the fabric of the 4-dimensional universe do not necesarily have to obey laws of physics at the sub-microscale. In the block universe, filaments are woven into the fabric of the universe (to borrow Brian Greene's language) in a way that manifest physical laws to us observers. The filaments are not positioned along the world lines in response to forces, etc., rather the illusion of forces, masses, etc., are a result of the filament configurations. For whatever reason these filaments are layed out along the 4th dimension in a very special and precise way.

Then there is conscousness and time, about which physics has little to say.

And by the way, ghwellsjr was quite incorrect in implying there was an oxymoron in your earlier statement. A more natural characterization of time than what he probably had in mind is correctly implied in your comments.

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I find block time a useful concept but I don't believe the world is actually like that.

I agree with you.

Doesn't block time come up because we can convert time into the same unit of measure as the other 3Ds? And graphically it's typically represented as time in meters to distance in meters. So graphically how long is a meter?; Very little time.

But in 4D, spacial xyz coordinates already account for position, I don't think time can still be considered a forth distance measurement with 4D space time.

Is the block universe concept considered 2D + 1 time dimension? Otherwise in what sense is a "right now" slice of space 3D?

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And by the way, ghwellsjr was quite incorrect in implying there was an oxymoron in your earlier statement. A more natural characterization of time than what he probably had in mind is correctly implied in your comments.

Yea that was funny.

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In addition to the above. Look at the illustration of Block Time by Paul Davies here:

http://www.nikhef.nl/pub/services/biblio/bib_KR/sciam14327034.pdf

I see Davies uses the term "block time", but I'm not sure it means what he seems to think it means.

Consider this quote:

For example, during a future manned expedition to Mars, mission controllers back on Earth might say, "I wonder what Commander Jones is doing at Alpha Base now." Looking at their clock and seeing that it was 12:00 P.M. on Mars, their answer might be “Eating lunch.” But an astronaut zooming past Earth at near the speed of light at the same moment could, on looking at his clock, say that the time on Mars was earlier or later than 12:00, depending on his direction of motion. That astronaut’s answer to the question about Commander Jones’s activities would be "Cooking lunch" or "Washing dishes" [see illustration on page 46]. Such mismatches make a mockery of any attempt to confer special status on the present moment, for whose "now" does that moment refer to? If you and I were in relative motion, an event that I might judge to be in the as yet undecided future might for you already exist in the ﬁxed past.

To me, this does not suggest that my "future" already exists; all it suggests is that the question "I wonder what Commander Jones is doing at Alpha Base now" is not well-defined, even though our intuitions suggest that it should be. I can change which event on Commander Jones' worldline corresponds to my "now" by changing my state of motion, but no matter how I change it, I can't bring what Commander Jones is doing "now" into my *causal* future, which is what would be required to say that my future must already exist. No matter how I change my state of motion, whatever Commander Jones is doing "now" will be outside my future light cone. So what he is doing "now" can have no causal effect on what *I* am doing "now", and vice versa. So the question "what is Commander Jones doing now?" is physically meaningless; I can label any event on Jones' worldline that is spacelike separated from me as "what Jones is doing now" and it will make no difference at all to the results of any observation I make or any experiment I run.

However, Davies does bring up a different issue that strikes deeper:

Although we ﬁnd it convenient to refer to time’s passage in everyday affairs, the notion imparts no new information that cannot be conveyed without it. Consider the following scenario: Alice was hoping for a white Christmas, but when the day came she was disappointed that it only rained; however, she was happy that it snowed the following day. Although this description is replete with tenses and references to time's passage, exactly the same information is conveyed by simply correlating Alice's mental states with dates, in a manner that omits all reference to time passing or the world changing. Thus, the following cumbersome and rather dry catalogue of facts sufﬁces:

December 24: Alice hopes for a white Christmas.

December 25: There is rain. Alice is disappointed.

December 26: There is snow. Alice is happy.

In this description, nothing happens or changes. There are simply states of the world at different dates and associated mental states for Alice.

Julian Barbour has written a number of papers expanding on this kind of thinking:

http://platonia.com/papers.html

However, even this view does not imply that my future "already exists" in the sense of being fixed. All it implies is that time is not something that "flows"; it's just a dimension along which we can assign coordinates to events. It does not require that events with coordinates that we, at this particular point on Earth's worldline, would label as "future" must be "determined" from our viewpoint "now". There can still be quantum indeterminacy; it just shows up as a statistical variation in relationships between types of events, looked at over the entire 4-dimensional continuum.

For example, there might be lots of events, at various different coordinate "locations", that can be described as "spin-up electron going into spin-measuring device oriented left-right", and lots of events at coordinate "locations" very close to the first set that can be described as "electron coming out of the spin-left side of the spin-measuring device" or "electron coming out of the spin-right side of the spin-measuring device". Quantum indeterminacy just means that the two types of "electron coming out" events are randomly associated with the single type of "electron going in" event, with 50-50 odds, if we look at the entire collection of such event pairs over the entire spacetime.

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The block universe requires the 4th dimension actually be a spatial dimension. You could not have various 3-D cross-sections required by special relativity without that. The 4th dimension is identified with time because time seems to flow as the observer's consciousness appears to move along his world line (along his rest 4th dimension) at the speed of light.

Let's say everyone is required to move along the interstate from point A to point B at exactly 60 mph. Then, at every mile from point A there is a time marker on the side of the road, i.e., a clock, that reads out the time lapsed from point A. And instead of looking at an odometer, you look at your watch to keep track of time lapsed from point A (no distances are displayed). Now, you've turned the highway (your 3D world line, so to speak) into a time dimension in exactly the same sense that the 4th dimension is regarded as a time dimension.

So, the 4th dimension is a time dimension only in that sense. But, more fundamentally, the 4th dimension is a spatial dimension.

All of the 4-dimensional filaments strung along the 4th dimension that make up objects are just all there. On a macroscale the pattern posses unique forms that allow a description in terms of laws of physics. And from these laws you can predict the future 3-D cross-section organization of the objects. However, you cannot rely on these overall patterns to predict the future 3-D cross-section organization of objects down to the level of individual quark filaments, electron filaments, and photon filaments.

So, the 4-dimensional filaments are all there. You could say that the future is determined, but the rules we physicists have only work for predicting the future on a macro scale. We do not have rules capable of predicting the future of individual elementary particles. We can only predict statistically what to expect of a sizeable group of 4-D elementary particle filaments. And that's not because the filaments have not extended far enough along the 4th dimension; it's just because the filaments down at the sub-micro scale are not layed out with a fixed pattern reflecting the rules recognized at the macro level.

We have the wave functions, but a wave function is not, in this view, an actual object--it is a mathematical description which, when complex conjugate squared, allows you to make statistical predictions about the configuration of some 3-D cross-section of 4-D filaments at some point in the future.

One of the mysteries of the sub-micro patterns is that, even though we don't recognize a specific pattern conforming to specific laws of physicis, the wave functions have a very detailed and specific phase in it's description of the individual 4-D filament shape in 4-dimensional space.

Thus, we have two major mysteries of physics: 1) The many different cross-section views of 4-dimensional space (attended by the constant speed of light) and 2) The double-slit experiment of QM.

Let's say everyone is required to move along the interstate from point A to point B at exactly 60 mph. Then, at every mile from point A there is a time marker on the side of the road, i.e., a clock, that reads out the time lapsed from point A. And instead of looking at an odometer, you look at your watch to keep track of time lapsed from point A (no distances are displayed). Now, you've turned the highway (your 3D world line, so to speak) into a time dimension in exactly the same sense that the 4th dimension is regarded as a time dimension.

So, the 4th dimension is a time dimension only in that sense. But, more fundamentally, the 4th dimension is a spatial dimension.

All of the 4-dimensional filaments strung along the 4th dimension that make up objects are just all there. On a macroscale the pattern posses unique forms that allow a description in terms of laws of physics. And from these laws you can predict the future 3-D cross-section organization of the objects. However, you cannot rely on these overall patterns to predict the future 3-D cross-section organization of objects down to the level of individual quark filaments, electron filaments, and photon filaments.

So, the 4-dimensional filaments are all there. You could say that the future is determined, but the rules we physicists have only work for predicting the future on a macro scale. We do not have rules capable of predicting the future of individual elementary particles. We can only predict statistically what to expect of a sizeable group of 4-D elementary particle filaments. And that's not because the filaments have not extended far enough along the 4th dimension; it's just because the filaments down at the sub-micro scale are not layed out with a fixed pattern reflecting the rules recognized at the macro level.

We have the wave functions, but a wave function is not, in this view, an actual object--it is a mathematical description which, when complex conjugate squared, allows you to make statistical predictions about the configuration of some 3-D cross-section of 4-D filaments at some point in the future.

One of the mysteries of the sub-micro patterns is that, even though we don't recognize a specific pattern conforming to specific laws of physicis, the wave functions have a very detailed and specific phase in it's description of the individual 4-D filament shape in 4-dimensional space.

Thus, we have two major mysteries of physics: 1) The many different cross-section views of 4-dimensional space (attended by the constant speed of light) and 2) The double-slit experiment of QM.

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The block universe requires the 4th dimension actually be a spatial dimension. You could not have various 3-D cross-sections required by special relativity without that.

The fact that the time dimension has the opposite sign in the metric to the three space dimensions indicates that it is not quite the same as a spatial dimension. It is *like* a spatial dimension in some respects (for example, it can be measured in the same units as spatial dimensions by using the speed of light as a conversion factor), but it is not a spatial dimension. It is a dimension of the overall 4-D manifold of spacetime, topologically speaking, which is sufficient to allow 3-D cross-sections to be cut as you describe; cutting those cross sections does not require that the time dimension be exactly like the space dimensions.

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The fact that the time dimension has the opposite sign in the metric to the three space dimensions indicates that it is not quite the same as a spatial dimension. It is *like* a spatial dimension in some respects (for example, it can be measured in the same units as spatial dimensions by using the speed of light as a conversion factor), but it is not a spatial dimension. It is a dimension of the overall 4-D manifold of spacetime, topologically speaking, which is sufficient to allow 3-D cross-sections to be cut as you describe; cutting those cross sections does not require that the time dimension be exactly like the space dimensions.

Hi, Peter. I think you've made very good points with that analysis. The other way to look at it may be seen with the sketches below. First, the left sketch symbolizes red and blue rockets moving away from each other with the same speeds relative to the black "rest" system. We have the usual time dilation. Red, when at his world line station 9, "sees" blue in red's simultaneous space at blue's world line station 8. But, blue, when at his station 9, "sees" red in blue's simultaneous space at red's world line station 8.

The 4-D metric, from which the Lorentz transformation time dilation equation follows is derived directly from 4 spatial dimensions. The selection of coordinates in the 4-space is simply selected based on orientations of 4-D world lines in the space. So, we have a right triangle with the blue X4 axis as the hypotenuse. The negative sign in the metric does not arise as a result of some mysterious role of time. It is just related to the orientation of world lines. It just results from the red X4 and blue X1 axes in the position of legs of the triangle. So, when we solve for the red X4 we're just solving for a leg of a right triangle instead of a hypotenuse. Some physicists refer to the red leg of the triangle as "Einstein's Hypotenuse."

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The 4-D metric, from which the Lorentz transformation time dilation equation follows is derived directly from 4 spatial dimensions.

No, it isn't, because the sign of the "time" term is opposite from the sign of the "space" term. In 4 spatial dimensions, the sign of all the terms would be the same and the metric would be positive definite. In 4-D spacetime, the metric is not positive definite. That makes a big difference.

The selection of coordinates in the 4-space is simply selected based on orientations of 4-D world lines in the space. So, we have a right triangle with the blue X4 axis as the hypotenuse.

Yes, the labeling of events by coordinates respects a standard R4 topology; coordinate 4-tuples that are almost the same represent points that are "close together" topologically, meaning they lie in small open neighborhoods of each other.

The negative sign in the metric does not arise as a result of some mysterious role of time. It is just related to the orientation of world lines. It just results from the red X4 and blue X1 axes in the position of legs of the triangle.

And look at how the axes are tilted relative to the black axes. If both dimensions were "spatial", so the metric was Euclidean, the red and blue sets of axes would each be perpendicular to each other, as the black axes are. But they're not. Minkowski spacetime is not Euclidean space. It's a different geometric object.

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So, when we solve for the red X4 we're just solving for a leg of a right triangle instead of a hypotenuse.

Also, I can play the same trick with Euclidean space, to make it look like the "metric" has a minus sign for one dimension. But that requires me to mix coordinates from two different frames on one side of the equation, which means it isn't a metric any more; it's just an equation that's been rearranged. A valid metric expression involves coordinates that are all from the same frame. For example, write the equation for the blue X4 in terms of the black X4 and X1; it will have a minus sign. *That* is the metric. I can rearrange that equation to move the negative term to the other side, but all that shows is that I can do algebra; it doesn't change the intrinsic geometry of the manifold.

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Also, I can play the same trick with Euclidean space, to make it look like the "metric" has a minus sign for one dimension. But that requires me to mix coordinates from two different frames on one side of the equation, which means it isn't a metric any more; it's just an equation that's been rearranged. A valid metric expression involves coordinates that are all from the same frame. For example, write the equation for the blue X4 in terms of the black X4 and X1; it will have a minus sign. *That* is the metric. I can rearrange that equation to move the negative term to the other side, but all that shows is that I can do algebra; it doesn't change the intrinsic geometry of the manifold.

That's not the way the block universe works. We begin with a Euclidean R4 manifold and freely select an initial set of coordinates using blue X1 and red X4 (blue and red X2 and X3 are the same). Do not regard the blue and red as belonging to two different coordinate systems at this stage.

Using these coordinates we have a distance along the blue X4 direction using Pythagorean theorem. Having these relationships we can now freely select a new set of coordinates, i.e., the blue coordinates X1, X2, X3 and X4. The Minkowski metric follows.

We have had no need to make any reference to time. It is all spatial. Now, if you wish to introduce a concept of time as an observer's consciousness moving along his X4 world line at the speed of light, you are free to postulate that and then investigate the implications and the consistency with special relativity theory.

Again, I don't like the concept at a subjective level. I'm just trying to do the best job I can at explaining the 4-D spatial universe concept. There are probably others on the forum who can make it more clear (and perhaps present it more accurately) than I. The link to Paul Davies's article given in the earlier post is good. I visited Davies's place at Arizona State University and hoped to meet him, but he was out of town on that day.

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Surely you meant "our eternally static worldtubes had such and such a 4D spatial separation at that region of eternally existent Platonia"?:rofl:...I visited Davies's place at Arizona State University and hoped to meet him, but he was out of town on that day.

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Surely you meant "our eternally static worldtubes had such and such a 4D spatial separation at that region of eternally existent Platonia"?:rofl:

Hey, that's a good one, Q-reeus. I'm definitely not into Julian Barbour's platonia stuff. He should have stopped once he built the case for the 4-D spatial universe. However, there's something to be said for investigating the configuration space of 4-D objects. Penrose takes a better approach.

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Just for fun looked at a YouTube video by Barbour 'Killing Time'. He starts off with 'time and motion don't really exist'. Oh well, at least he said it, plain and clear. But not 5 minutes in and there is a distinct shifting of ground going on. Now we are being told time is a relational thing - the comparison between a huge number of fundamental clocks. Time is suddenly real after all - just redefined. Sort of weasely to me. Set up and then knock down a straw man - 'everyone believes wrongly that time flows'. About as much as folks these days believe 'the sun rises and sets'. Never read any of his books but actually like his Machian relational ideas in general (sans 'Platonia'), but definitely not the shifty approach demonstrated imo in that video. From the sidelines have looked at various arguments for 'presentism' vs 'eternalism' and conclude it best to spend my time on other topics. So much gets down to subtleHey, that's a good one, Q-reeus. I'm definitely not into Julian Barbour's platonia stuff. He should have stopped once he built the case for the 4-D spatial universe. However, there's something to be said for investigating the configuration space of 4-D objects. Penrose takes a better approach.

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Just for fun looked at a YouTube video by Barbour 'Killing Time'. He starts off with 'time and motion don't really exist'. Oh well, at least he said it, plain and clear. But not 5 minutes in and there is a distinct shifting of ground going on. Now we are being told time is a relational thing - the comparison between a huge number of fundamental clocks. Time is suddenly real after all - just redefined. Sort of weasely to me. Set up and then knock down a straw man - 'everyone believes wrongly that time flows'. About as much as folks these days believe 'the sun rises and sets'. Never read any of his books but actually like his Machian relational ideas in general (sans 'Platonia'), but definitely not the shifty approach demonstrated imo in that video. From the sidelines have looked at various arguments for 'presentism' vs 'eternalism' and conclude it best to spend my time on other topics. So much gets down to subtledefinitions.

I can certainly appreciate where you are coming from, Q-reeus. And thanks for the link. I've read Barbour's book a couple of times (and Davies's and a couple of others). I don't know why, since youth, I've been dogged by this compulsion to comprehend some kind of external reality. It must be genetic. I just can't shake it. I don't talk physics around family and friends--they would think I'm nuts (or rather, discover that I'm nuts). At least I'm a kind of recovering physicist--not anywhere near the condition of poor Kurt Godel.

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That's not the way the block universe works. We begin with a Euclidean R4 manifold

R4, yes. Euclidean, no, not if the metric ends up being Minkowski. "Euclidean" refers to a metric, not just a topology. Or at least, it does the way I am used to seeing the term used. If "Eucldiean" is just supposed to refer to the topology, then I have no problem with what's quoted above, but I would still object to the term "spatial" since it, too, implies a Euclidean, positive definite metric, at least as I am used to seeing the term used. The key is that there is a fundamental geometric difference between a Euclidean metric and a Minkowski metric, which is there no matter how you rearrange terms in equations. See below.

We have had no need to make any reference to time. It is all spatial. Now, if you wish to introduce a concept of time as an observer's consciousness moving along his X4 world line at the speed of light, you are free to postulate that and then investigate the implications and the consistency with special relativity theory.

I don't need to introduce that to introduce a concept of "time". As soon as I have the Minkowski metric, I have one "direction" which is singled out from the others as being fundamentally different, because of the opposite sign in the metric.

I understand how the "block universe" concept *derives* temporal relationships instead of treating them as fundamental. Basically, some portions of the universe contain "records" of other portions, and you can use the "records" to create a temporal ordering on the entire block universe. That still doesn't change the fact that once you've created the temporal ordering, it is not a Euclidean ordering; the metric on the "block universe" is Minkowski and is not positive definite, so there is a fundamental physical difference between "temporal" relationships (a portion of the universe containing a "record" of another portion must be in the future light cone of the portion it contains a record of) and "spatial" relationships (between portions of the block universe that are spacelike separated, so neither portion can contain a "record" of the other).

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R4, yes. Euclidean, no, not if the metric ends up being Minkowski. "Euclidean" refers to a metric, not just a topology. Or at least, it does the way I am used to seeing the term used. If "Eucldiean" is just supposed to refer to the topology, then I have no problem with what's quoted above, but I would still object to the term "spatial" since it, too, implies a Euclidean, positive definite metric, at least as I am used to seeing the term used. The key is that there is a fundamental geometric difference between a Euclidean metric and a Minkowski metric, which is there no matter how you rearrange terms in equations.

But, I'm just establishing the Euclidean R4 with the blue X1 and red X4, then using the one-to-one correspondence between the Affine space (a generalization of Euclidean) and the orthonormal Euclidean space, S. So, we have the fundamental space, S, associated with the positive definite metric, then any point in the Affine space, A, can be reached with 4-tuples of a S vector using the basis vectors defining A.

I can understand your preference for not referring to a metric for the A space. You may wish to restrict the language to Affine coordinates associated with the S space (the S space having the positive definite metric). The 4-dimensional description of special relativity remains intact in this context.

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