## S.R. Defining the present

This is not an everything goes forum, but rather a place to ask questions and request help for developing your ideas.

### Re: S.R. Defining the present

Maybe the answer is this: People who are the same age at different times will be different ages at the same time.
A guy is 40 in 1945 and another guy is 40 in 1965. Same age at different coordinate times. But at the same coordinate time of 1965, they are different ages; one is 60 and the other is 40.

Relativity throws in the wrinkle that they were both born the same day and aged at the same rate. Let's say one of the guys hibernated during the winter. He would live his normal human lifespan in a greater number of years. So both being born in 1905, they would have both aged 40 yrs in 1945 but in 1965 the biological clock of the hibernating guy would have made him look 40 while the other guy looked 60. At this point, 2 different clocks are being compared but in a way they have been brought together at the same coordinate time, started at the same age, lived the same number of years but had aged differently.

Ralfativity has the same "problem" as relativity but for a different reason. Age difference in ralfativity occurs during the time it takes for info of a change in relative velocity to reach the other guy. If no change has occurred, then there can be no age difference even though Alice would see a difference between her clock and Bob's network clock as she flew by. If she stopped, that clock difference would become an age difference after the news of the stop reached Bob. If she slowed down or sped up, ralfativity allows one to calculate what percentage of the clock difference becomes permanent age difference. How she started, whether from a stop or a fly-by, would have no effect on determining age difference from clock difference.

The thing that nags at me is that clock difference will eventually become age difference one way or another. If Alice just kept on going forever, the idea that she will permanently be the same age as Bob becomes academic and useless info as that scenario's results can either never happen or no one will care if they do. So my original question still stands. No one cares if they're the same age on a flyby, the clock difference matters as a concrete point in establishing the eventual age difference between the two. Those clock readings are real and can't be undone by any future action taken by Bob or Alice. The perspective of either is also academic as no one cares what spacetime looks like from Alice's perspective as she has no clock network deployed. So let's just cut all the fat out of relativity and just leave the useful parts.
Last edited by ralfcis on October 5th, 2017, 5:26 am, edited 3 times in total.
ralfcis
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### Re: S.R. Defining the present

ralfcis » 04 Oct 2017, 19:33 wrote:Alice is moving when she flys by the 3 ly mark but if she started from a stop, she's 4 and Bob is 5 at the 3 ly mark.

Correct for Alice, but how would she know that Bob's clock reads 5 years at the moment that she reads her clock? And how would Bob know when to read his own clock? Your issue lurks in a misunderstanding of the relativity of simultaneity. And making up 'rules' for what each clock will read for each specific scenario for each event has lead you down the garden path now for some 8+ years, I think. (?)

I'm not going to add to the confusion by describing some fancy scenario. I think you need to go back to basics. The classical 'twin paradox' was for a round trip, where there is absolutely no confusion on the outcome. Alice and Bob are together in the same inertial frame when Alice sets off towards a turning point, after which she travels back and docks with Bob again.

The final result is only known after the docking. For your values, Alice's clocks read 0, 4 yrs at turnaround and finally 8 yrs. After all she was present at each event. Bob can only directly read Alice's clock at the beginning and end as 0 and 10 yrs. That much is absolute, directly observable and not depending on any theory - it is just the outcome of the test.

Bob's knowledge of the clock readings at the turnaround is indirect, but he can actually deduce it without knowledge of relativity: simply divide the total elapsed times by two. So Bob can reasonably deduce that Alice's clock read 4 yrs at the turnaround and his clock 5 yrs. A more direct, but relativity-reliant conclusion about the turnaround point can be made by Alice and Bob. Alice simply transmits her position and time at turnaround to Bob. Bob gets it when his clocks reads 8 yrs, subtracts the propagation delay for 3 lyrs and get 5 yrs, as expected.

The round-trip 'twin-paradox' solution was not proposed by Einstein. His original scenario (paraphrased) was one-way: Alice takes off from inertial Bob and flies at high speed to a distant location, where she 'stops', to be stationary in Bob's inertial frame again. She would have aged less than Bob. Let's say Alice traveled our usual distance of 3 lyrs in Bob's frame at v =0.6c. If, after her arrival, Alice and Bob checked their clock sync again (both ways), they will unequivocally find Alice's clock one year behind Bob's. This an absolute aging difference, not frame dependent. And it only required half of the later "twin paradox" scenario.

This result was originally controversial and many physicist tried to prove it false on the grounds of inconsistency, or claiming that it shows a paradox in SR. This resulted in many variants of the Einstein scenario, essentially stretching it past its limits of validity, especially on the basis of aging of the partners. There is only one variant of the Einstein scenario that I know of to be equally valid. Alice can simply fly by Bob, where they both start their stopwatches. Then she stops at the agreed distance, without stopping her stopwatch. At their leisure, they can send each other their stopwatch times, compensate for the propagation delay of the other's signal and so determine that there is an absolute time difference of one year.

This is true because they could start their stopwatches when they were together and compare them (via two-way TV signals, if you like) when they are relatively stationary again, with a common definition of simultaneity. The variant where Alice sits inertial with Bob and then flies away, but never stops at the agreed distance, does not work. Now they never have a common simultaneity in which to compare their clocks again. And if they try while relatively moving, they will get reciprocal values - each will think the other has aged less. And what's more, the reciprocal difference will grow larger and larger with subsequent observations, as the separation increases.

Ralf, I urge you to study the named scenarios carefully and see if it makes sense to you. Please ask questions on these scenarios, because it contains the truth about relativity. Once you are comfortable with this, we can discuss some of the "why's", but if you are just going to throw in other fanciful scenarios, we are both wasting our time. Over the years, it has probably been those types of scenarios that prevented you from getting a deep insight into the relativity of simultaneity.

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### Re: S.R. Defining the present

This is fun but work is making it impossible for me to have a fluid conversation. I edited my post since you replied. I will reply to your post in pieces throughout the day.
ralfcis
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### Re: S.R. Defining the present

how would she know that Bob's clock reads 5 years at the moment that she reads her clock? /quote]

She passes by Bob's far clock, which Bob assured her was sync'd to his as she flew by Bob, reads it and her clock simultaneously because they are right next to each other in galactic terms. Simultaneity is assured by short distances.

And how would Bob know when to read his own clock?[

All Bob's clock reading is done in post processing. She sends her info to Bob. He receives her info when he's 8. He then knows that since she is 3 ly away, her info is delayed by 3 yrs. He subtracts 3 from 8. So when he was 5, she was 4 and she read his far clock as 5.
ralfcis
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### Re: S.R. Defining the present

The classical 'twin paradox' was for a round trip, where there is absolutely no confusion on the outcome.

No point in discussing something we agree on. Relativity can handle this simple scenario but it's every other scenario that, well, you know my opinion on that.

The final result is only known after the docking.

Docking? Not just docking, docking or flyby. Oops the pandora's box opens again. Flybys, acceleration, when does either cause age difference and a slew of other questions that have been asked and never answered in 8+ years. The evidence that they have not been answered is that you want to limit discussion to the simplest scenario where none of these questions come out.
ralfcis
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### Re: S.R. Defining the present

That much is absolute, directly observable and not depending on any theory

I'm not like the other relativity deniers on this forum. I fully accept all the facts of relativity. It's Einstein's THEORY I have huge problems with, the explanation of those facts. I've been trying to get the theory's side of the story. In the meantime I've come up with my own theory which satisfactorily answers all my questions (and it's already a side part of the theory anyway). I'm still open to see if Einstein's theory of relativity has something to say but getting the answers takes years and years of asking. It's not that I'm not understanding the answers, there are very few answers that have been given. There's a lot of semantics, stalling, context misdirection and general vague answers to specific questions involved. Unfortunately there doesn't seem to be anyone on here that can back up my opinion of how things are. Kudos to the life scientists for trying to keep up though.
Last edited by ralfcis on October 5th, 2017, 9:40 am, edited 1 time in total.
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### Re: S.R. Defining the present

Oh it's 9:35. I have 2 and a half more hours of fun to look forward to.
ralfcis
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### Re: S.R. Defining the present

And if they try while relatively moving, they will get reciprocal values - each will think the other has aged less.

The reciprocal values are not so reciprocal when you look at the facts behind them. When Bob is 5 and "sees" Alice as 4 doesn't happen with the same clocks, at the same time or even at the same point in space as when Alice is 5 and "sees" Bob as 4 (a yr later and 3/4ly away.

When they're viewing each others TV signal and see the other moving in half speed slow motion, it doesn't mean their time is dilating at half speed any more than if they were approaching each other and their mutual TV picture was fast forwarding at double speed that now they were aging faster than the other. No one cares what a sub-atomic particle's view of the universe is just as no one cares what Alice's reciprocal view is (see my post a few posts back). Once she travels 3 ly, whether she stops or not, she will eventually be proven under any scenario to have aged 1 yr less that Bob. Bob can initiate a stop wrt Alice at that time as Alice keeps going but he will have a yr deficit to overcome before he eventually comes out as having aged 1 yr less than Alice because he initiated the stop. These are the facts of the case and they remain undisputed except in the 1 example where no one stops and that is a don't care scenario.

The variant where Alice sits inertial with Bob and then flies away, but never stops at the agreed distance, does not work.

It depends on your definition of works. I will show in a series of STD's that relativity makes predictions of age difference without any of it having actually happened. This is when Bob takes off at .6c at t=4 and his line of present swings up to Alice's age as t'=5 even though that hasn't happened yet. Brian Greene chimes in as this is a proof that the past, present and future are concurrent since Alice's future is on the same line of present as Bob's present. Anyway since that projection is "valid", I'm saying it's equally valid to project that Bob's line of present at t=5 says Alice is 4 whether she's moving or not because she will eventually will be proven to have been 4 at that time once someone makes a velocity change.
ralfcis
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### Re: S.R. Defining the present

ralfcis » 05 Oct 2017, 14:51 wrote:
Jorrie wrote:how would she know that Bob's clock reads 5 years at the moment that she reads her clock?

She passes by Bob's far clock, which Bob assured her was sync'd to his as she flew by Bob, reads it and her clock simultaneously because they are right next to each other in galactic terms. Simultaneity is assured by short distances.

I presume that you talk about the case where Alice does not 'stop'. This is where your troubles start and we should not talk about anything else, unless you agree on the basics principles.

Yes, she can read Bob's remote clock that she flies by, but no matter how much Bob assured her, she has an own, well defined definition of what is simultaneous and what not in her own inertial frame. According to her definition, that remote clock is not in sync with Bob's clock. According to her knowledge of relativity and according to her own frame's measurements, Bob's clock reads only 3.2 yrs at the moment hers reads 4 yrs, when Bob's remote clock reads 5 yrs.

This is the crux of the relativity of simultaneity. It is inertial frame dependent and you have to agree and understand that - else, forget about understanding relativity, ever.

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### Re: S.R. Defining the present

Yup but again there are 4 clocks (not just 2) involved.
1. There is Bob's atomic pocket watch with Bob on Earth.
2. There is Alice's on-board atomic clock.
3. There is Bob's network of sync'd clocks, one of which is right beside Alice as she passes the 3 ly mark
4. There is Alice's network of sync'd clocks, one of which is flying by Bob on earth (at Alice's speed) just as Alice is passing the 3ly mark.

Alice's network clock at 4 will read Bob's pocket watch at 3.2
Alice's on-board clock at 4 will read Bob's network clock at the 3 ly mark as 5.

These are 2 unrelated readings and we spent about a year to come to an agreement on this. Should I dig up where this started or ended because part of the problem is I think we have an agreement and then sometime later not only don't we have one but the subject was never discussed in the first place.

P.S. Again this whole misunderstanding stems from Einstein's clock sync method which I avoid completely. The idea that Alice's on-board clock and network clock are the same clock just because they're Einstein sync'd is false. Because they are separated by 3 ly they are not simultaneous and the readings at Alice =4 happen at two different points in space and time involving 2 different pairs of clocks. Einstein's clock sync method is the problem.
ralfcis
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### Re: S.R. Defining the present

If you reject Einstein's clock sync method, you are not talking relativity, because clock sync and SR's simultaneity are essentially the same thing. If you want to talk about some theory that is in conflict with that, then I cannot help you. Also, that would not qualify it to remain under this Physics subforum. Your choice.

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### Re: S.R. Defining the present

ralfcis » May 8th, 2017, 8:42 am wrote:Sorry mitchellmckain, can I respond to your post in 5 months. I'm just trying to write down what's in my backlog before I forget it all. Also my threads get shut down if I take too long completing them.

As of today, 5 months have passed since I posted my explanation in response to your question, so here is a reminder accordingly. You have 3 more days before it is 5 months after your response quoted above. I am teasing you of course, because you are certainly free to respond or not to any post as you choose.

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### Re: S.R. Defining the present

You're not reading what I write.. I don't need his clock sync method and my last post is exactly his method. We spent a year discussing this and whatever. I need to move on with other threads. Just another tactic to shut down discussion. So you're denying there are 4 clocks involved in Einstein's method.? Wow.
ralfcis
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### Re: S.R. Defining the present

When I saw Mitchellmccain's post I went ballistic. 5 months have passed and I'm still no closer to even starting my goal than I was 5 months ago. And here was Jorrie again asking me to explain simultaneity for the umpteenth time. Well on Friday I thought I could blow out a quick post that wouldn't delay me too much and show I understand everything about simultaneity. It took me all day to draw up a complex colored STD but as I looked deeply into it I realized there were huge cracks in my understanding. I don't have that STD with me but here are the cracks:

1. The hyperbolic propertime line joins all the points that Alice=4 simultaneously at any velocity. This means if Alice was chopped up and sent from Earth at the same time on ships travelling various velocities and a piece was left with Bob on Earth, the line of simultaneous rot of all the pieces would be that hyperbolic line. If the piece beside Bob had only rotted 4 yrs then Bob had only aged 4 yrs, the same amount of time as the piece of Alice on the .6c spaceship.

2. Yet Bob has a line of present extending horizontally across the STD where all clocks on that line are Einstein sync'd to t=4. That line intersects Alice's slanted line of present when her meat had only aged 3.2 yrs, not 4. I could prove they were in the same present because if she sent out a signal to Bob saying what she read off his network clock and what she read off her on-board clock and that she was at the 2.4 ly marker in space when this happened, Bob would get the signal 2.4 yrs later when he was 6.4 and he could subtract 2.4 from 6.4 and indeed confirm he was 4 when Alice was 3.2. This contradicts the line of rot.

3. But now from Alice's stationary perspective, she sees Earth receding from her. (This sudden switch from moving to stationary is probably where the relativity of simultaneity slips in but I couldn't prove it.) She has her own network of clocks stationary with respect to her. Earth will intersect the line of clocks that are sync'd to 3.2 when Bob's pocket watch says 2.56.
This is not possible, Alice's present cannot reach back in time to be simultaneous with Bob's past. So we need to set up a scenario where we predict a mathematical network clock from the future will intersect the Earth clock at 2.56 and send a signal out to Alice to see if she had had a real network clock there at that time, would it have read 3.2, the same as her on-board clock time. My STD confirmed this was true except for one horrible thing, the speed of light had to halved from Bob to Alice in order for this to be true.

4. I tried other speeds and every time for the speed of light travelling from Bob to Alice, the speed of light had to be multiplied by the doppler ratio. So at .8c, the speed of light had to be multiplied by 1/3. I forgot the ratios for the other speeds I tried but they were all the doppler ratio for that speed. It was as if the speed of light was different for Alice's spacetime, the same thing I found when converting Minkowski STD's to Epstein Std's. The behavior of c seems to change with spacetime type.

Looks like trying to explain this is going to slow me up some more so mitchellmccain, can I put off my response for another 12 months? I'll post my colored STD when I get back to work Monday.
ralfcis
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### Re: S.R. Defining the present

Ralf, may it not perhaps be more fruitful if you first learn what the relativity of simultaneity really means, before spending all the time writing about it?

The relativity of simultaneity is normally the very first thing that should be learned in relativity - it is exactly where Einstein started his 1905 SR paper (Section I).

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### Re: S.R. Defining the present

I'll post what it really means tomorrow and you'll probably close down the thread for heresy but I've finally figured out the answers to all my questions above. You're again offering a general answer to specific questions. The specific answers are quite surprising, I hope you'll hear them out.
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### Re: S.R. Defining the present

If it is simply not mainstream, the worst that can happen is a shift to the private theory subsection. Closure usually happens when posts contain attacks on members or on the scientific community at large.

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### Re: S.R. Defining the present

Here is the Minkowski-STD of .6c.

The blue area represents spacetime that Bob and Alice see of their own frame. The overlapping red area is what Bob's perspective of Alice's spacetime in motion is. Instead of a square grid, it's a rhombic grid. Alice also sees Bob's frame as a rhombic grid but it's off to the left. But so far as each is concerned, their own spacetime is a normal square grid.

The square grid has a ct vertical axis while the rhombic grid has a corresponding ct'=ct/Y axis whose slope is the inverse of the relative velocity between the two. An Epstein-STD depiction of spacetime is made by simply interchanging the ct and ct' axes.

The x and x'-axes represent space coordinates but they also represent lines of present where all clocks on the space coordinates are Einstein sync'd to the same time that the line intersects the ct or ct' axis. That all clocks on the same line share the same clock reading simultaneously can be verified by comparing the clock reading transmitted to the clock reading received minus the signal transit delay. For example Alice would send a signal to Bob form the 3 ly mark which would reach Bob at t=8. 8-3=5 which confirms Bob is 5 when Alice is 4. (Later calculations will show different results.)

The blue horizontal line from t=5 to t'=4 is the line of present for Bob t=5. Every point on that line through space has been sync'd to simultaneously read 5 from Bob's perspective. There is a point at the 3 ly mark that has one of Bob's network clocks that says t=5 just as Alice is crossing that same point at .6c with her ct' clock saying t'=4. Alice and Bob's clocks started from the same point at the same time and now Alice's clock does not read the same as Bob's network clock.

Alice has rhombic coordinates from Bob's perspective so he will see her line of present (orange line at t'=4) at an angle to his line of present (blue line at t=5). Her orange line represents a line of clocks all Einstein sync'd to t'=4 through space. The intersection of Bob's network clock and Alice's on-board clock happens in the same present for both of them. This is a very strong present as it's at the same point in space because the two are colocated. However this present is competing with other types of present as we shall see.

Alice also has a stationary perspective of Bob moving away from her. You can take her rhombic grid and unfold it to a square grid thereby folding Bob's square grid into a rhombic one or you can do the analysis with Alice's grid remaining rhombic. Her line of present at 4 will intersect Bob's t-axis at t=3.2. So how can Alice be 4 and Bob be both 3.2 and 5. The answer is Alice's perspective has changed and different clocks are being compared.

Let's first verify that Bob's time t=3.2 is valid. This is much more difficult this time because Alice's line of present intersects Bob's past which is physically impossible. However, we mathematically calculate that Bob should send his light signal at t=3.2 to see if Alice's clock will be 4. The signal takes 4.8 yrs to reach Alice when she's 6.4. The math doesn't work out unless you multiply 4.8 by the doppler ratio of 1/2 (for .6c). So now subtract 6.4-2.4 and Alice is indeed 4 when Bob =3.2.

We'll get back to why the doppler ratio must be used but the terminology of the result is misleading. The first result of Bob=5 when Alice =4 is the time comparison between Bob's network clock and Alice's on-board clock in the present for both from Bob's stationary perspective. The second comparison of Alice = 4 when Bob = 3.2 is the time comparison between Alice's virtual network clock and Bob's on-earth clock with Bob's past being brought into Alice's present from Alice's stationary perspective. What could be more apples and oranges than that?

The doppler ratio for the speed of light comes in because we maintained Alice's rhombic grid but that disappears once we unfold it into a square grid and fold Bob's into a rhombic one. But now a new wrinkle appears that Alice=4 means two different times from each perspective. This is where the relativity of simultaneity comes in.

The t'=4 hyperbolic line in the graph represents Alice=4 at any relative velocity. What this means, in terms of clock comparisons, is the time comparison between Bob's on-earth clock and Alice's on-board clock.

There is a final set of clock comparisons that deal with the relativity of simultaneity which is the circled area in the STD. The RoS or sync offset = vx = .6 *3 =1.8 as circled. It is the clock comparison between Bob's network clock (t=5) and Bob's on-board clock (t=3.2) for Alice's on-board and virtual network clocks =4. But since Alice's clocks are separated by different perspectives, RoS is actually a sum of the clock differences between Alice's on-board clock and Bob's network clock from Alice's moving perspective (5-4=1) and Bob's on-board clock and Alice's network clock from Alice's stationary perspective (4-3.2=.8) for a total RoS of 1.8.

It's pretty clear to me from the above analysis that the only useful clock comparison during relative motion is Bob's network clock and Alice's on-board clock. Alice would just not have a bunch of network clocks following her around at her speed throughout space and in no way can her and Bob's on-board clocks be physically compared unless they're both stationary.

Next we'll look at the Epstein STD version of this analysis and then the STD of .6c made up of Bob and Alice leaving earth at .33c (which makes their relative velocity .6c according to the velocity combo law).
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### Re: S.R. Defining the present

Ralf, the diagram is quite confusing, but essentially correct. Your description is super-confusing and here and there very far from valid. But, knowing the futility of trying to correct it piece by piece, how about we leave you to discover the errors on your own?

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### Re: S.R. Defining the present

Just give me one part you find wrong because "here and there" doesn't sound like the usual "it's all wrong". Maybe you're talking about the new idea where I break up total RoS into 2 separate parts. The only confusing part I see is in keeping track of the 4 clocks and how they get compared. I'm pretty sure relativity only considers comparisons between the two on-board clocks. So the source of my "errors" is from adding the 2 network clocks.

If our differences stem from a disagreement of how many clocks are involved, then that disagreement is fundamental. I believe I have derived the correct results using a 4 clock explanation. I think the ball is in your court to prove 2 clocks can explain all the time paradoxes that I listed. Would you like me to list them in point form?
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ralfcis
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### Re: S.R. Defining the present

ralfcis » 09 Oct 2017, 21:22 wrote:Just give me one part you find wrong because "here and there" doesn't sound like the usual "it's all wrong".

Ralf wrote:The first result of Bob=5 when Alice =4 is the time comparison between Bob's network clock and Alice's on-board clock in the present for both from Bob's stationary perspective. The second comparison of Alice = 4 when Bob = 3.2 is the time comparison between Alice's virtual network clock and Bob's on-earth clock with Bob's past being brought into Alice's present from Alice's stationary perspective. What could be more apples and oranges than that?

I think that this paragraph contains the core of your problems.What makes you think that Alice's clock network is more 'virtual' than Bob's? The lines of simultaneity on any form of spacetime diagrams are no more than an infinite set of 'virtual' sync'd clocks and rulers, specific to each inertial frame of reference.

Nothing stops us from populating both frames with real sync'd clocks and rulers - it is just not necessary, because Einstein gave us the theory to predict what each comparison will yield.

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### Re: S.R. Defining the present

.What makes you think that Alice's clock network is more 'virtual' than Bob's?

Bob's t=5 line of present intersects Alice's t'=4 line of present in the present from Bob's stationary perspective. Alice therefore reaches 4 after Bob has reached 3.2 from Bob's perspective. Alice has to have a virtual clock to reach from her present to Bob's past. But if you consider Alice being the stationary perspective from the start and her having her own clock network following her around can Bob be 3.2 in the same present when Alice is 4. When will a space traveler ever have her own clock following her 3 ly behind at .6c? Never. The results of no experiment are affected by this so an inconvenient moving clock network can be ignored. The problem results in relativity's insistance that the reciprocal time dilation makes the choice of network clock invalid. Please show me a scenario where that's true. Show me some change either Bob or Alice can make that will immediately overturn the fact that Bob's clock reads 5 and Alice's clock reads 4. As I stated before, if Bob makes the stop by accelerating to Alice's speed, he will need extra time to overcome the deficit of Alice having aged 1 year less than Bob at the time Bob makes his change.

So as you said relativity gives us the tools to not worry about considering Alice's clock as the network. Even if you did it wouldn't affect the outcome. Show me any scenario where it could except for the one that would never happen when Alice nor Bob ever come to a mutual stop. Choosing the larger entity for the clock network, which I don't even need, will yield correct results.

I guess what you're objecting to is I'm saying switching perspectives in mid-stream unbalances the reciprocity. Yes it forces Alice to have a virtual clock network as opposed to no clock network.
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### Re: S.R. Defining the present

Ok, here's the clincher: there is only 1 possible scenario where Bob's network clock is 5 and can be compared physically to Alice's on-board clock = 4. That comparison can be messaged to Bob who can calculate that his age was simultaneously 5 when Alice's was 4 when Alice was the moving frame. You try to do the reverse analysis where Alice is stationary and Bob's on-board clock will be less than her network clock, always. Bob's network clock will go virtual just like Alice's did in the 1st analysis so it can't be physically compared and messaged. Yikes am I getting mixed up? I need to do a full reverse analysis to make sure.
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### Re: S.R. Defining the present

ralfcis » 09 Oct 2017, 22:38 wrote:When will a space traveler ever have her own clock following her 3 ly behind at .6c? Never.

Why then do you allow Bob to have a clock leading him by 3 lyr? Your Minkowski is for all-inertial Alice and Bob, so we are forced to treat them exactly the same. No one is "the space traveler", they just travel relative to each other. Their clocks run at the same rate, but different observers read them differently.

The results of no experiment are affected by this so an inconvenient moving clock network can be ignored. The problem results in relativity's insistance that the reciprocal time dilation makes the choice of network clock invalid.

Relativity simply tells you that when you make a coordinate dependent observation, every different coordinate system will give a different result. When you make a coordinate independent observation, like the time difference at the end of an "out and back" scenario, all coordinate systems will agree on the result.

Please show me a scenario where that's true. Show me some change either Bob or Alice can make that will immediately overturn the fact that Bob's clock reads 5 and Alice's clock reads 4. As I stated before, if Bob makes the stop by accelerating to Alice's speed, he will need extra time to overcome the deficit of Alice having aged 1 year less than Bob at the time Bob makes his change

The scenario that we are discussing is presumably your Minkowski diagram, where I see no frame jumps. Just two inertial frames in relative motion. All you can say then is that when Alice's clock 4, Bob's local network clock (at 3 lyr in his coordinates) reads 5. Change the view to Alice's coordinates and when Bob is at -3 lyr in her coordinates, his clock will read 4 and Alice's network clock will read 5. Completely reciprocal. Most of the confusing calculations that you have done above tells you nothing of value - apart from how confusing it can be.

Things will change if Alice makes a stop at Bob's local clock. But the same can be said for when Bob would make a stop at Alice's local network clock. Then the final outcome will depend on who made the stop, as you well know.

Like the Scottish sang to King Edwards army: "... send them homeward to think again". Change "homeward" to "homework", which is: draw the Minkowski with Alice as the reference frame. Same distances and relative speed, just leftward.

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### Re: S.R. Defining the present

Here is the side by side STD.

As you can see the orange and blue lines, although connecting the same nominal values are not the same. The order is reversed; orange is on top for Bob with Alice stationary and on the bottom with Bob stationary. The events are not even happening in the same present and completely different clocks are being compared. The orange line is virtual because it joins a line of present to the past as if it was also present. Bob's virtual orange line connects his network clock to Alice's on-board clock from the past so it is not physically comparable.

So my statement is correct :

there is only 1 possible scenario where Bob's network clock is 5 and can be compared physically to Alice's on-board clock = 4.

Now you're trying to discount the significance of that statement but saying my M-std is all virtual. It is not, it represents physical reality when clocks can be compared and mathematical modeling when they can't.

Our terminology problems are vast, I'd say insurmountable. But what's worse is when you won't answer direct and specific questions and even when I think you have, you won't stick to it. So again I ask, are you doing your analysis with 2 or 4 clocks. Because if you're only comparing on-board clocks well then of course clock comparisons between moving clocks are physically impossible. That's why relativity is forced to wait until the two clocks are stopped to make a determination of age difference. So until you answer the question, we have no common ground for discussion. Once you do, we can work on a dictionary or a glossary of terms that will allow you to translate what I'm saying.
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### Re: S.R. Defining the present

ralfcis » 10 Oct 2017, 13:32 wrote:So my statement is correct :

there is only 1 possible scenario where Bob's network clock is 5 and can be compared physically to Alice's on-board clock = 4.

Yes, but what do you think it tells Alice about Bob's own clock reading at the moment when she reads her own clock? In her frame, that network clock is not sync'd to Bob's clock.

Our terminology problems are vast, I'd say insurmountable. But what's worse is when you won't answer direct and specific questions and even when I think you have, you won't stick to it. So again I ask, are you doing your analysis with 2 or 4 clocks.

I would say our understanding of the terminology is vastly different. BTW, you don't seem too good on answering direct questions either; or sticking to your conclusions, for that matter... ;)

The answer to you question is: neither. I use SR equations for analysis, not clocks. When convenient for discussion, I stick in as many physical clocks as required - absolutely no limit.

Now to your side by side STD. Didn't you notice the elephant in the picture?

You have two inertial observers who's spacetime paths are perfectly symmetrical relative to the origin. Yet you stick two asymmetrical time comparisons on the diagram, as if the observers were somehow different. They are not. Whatever you want to call it, there is no justification for the asymmetry.

You can obviously repair the diagram by sticking in two more red lines, so that it all becomes symmetrical again. And then contemplate what it means in terms of the relativity of simultaneity, which still seems to be your Achilles heel.

BTW, this type of diagram has its place in relativity teaching. It is called the Loedel diagram.

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### Re: S.R. Defining the present

In her frame, that network clock is not sync'd to Bob's clock.

I don't care about how two rows of sync'd clocks see each others row as unsync'd when in relative motion. I use the light signal method. Alice at t=4 reads Bob's network clock as 5 and sends the news back to Bob. He subtracts the time delay to get the signal and he knows in the present when he was 5, Alice was 4. No sync scenario can undo that fact.

you don't seem too good on answering direct questions either; or sticking to your conclusions, for that matter..

If that's how you feel, feel free to call me out on it as many times as I do you. Do you have any examples where you asked me a question and I didn't go out of my way to answer it? Certainly this thread disproves your assertion. True, though, I change my conclusions when I come up with better ones; it's called science.

I use SR equations for analysis, not clocks.

I must have missed your equations because all you've been talking about is comparing clocks and I kept asking which specific clocks are you comparing. Don't you think it weird that you kept insisting that Bob and Alice were the same age because their on-board clocks read the same. That fact is irrelevant because those 2 clocks can only be physically compared when stopped (and that's a separate discussion). I instead focused on looking for a real comparison between those clocks and the network clocks which yielded measurable and irreversible results during relative motion. We were arguing 2 completely different things.

Please show me your 2 red lines so I can consider (and refute) your correction because I know you're still working with only 2 clocks. My contention was :

there is only 1 possible scenario where Bob's network clock is 5 and can be compared physically to Alice's on-board clock = 4.

Show me where to add the lines where this would no longer be true. My lines are where Bob is 5 and Alice is 4 and a real physical clock comparison can be made (and that only happens in 1 place so far as I know).
ralfcis
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### Re: S.R. Defining the present

ralfcis » 10 Oct 2017, 16:58 wrote: I don't care about how two rows of sync'd clocks see each others row as unsync'd when in relative motion. I use the light signal method. Alice at t=4 reads Bob's network clock as 5 and sends the news back to Bob. He subtracts the time delay to get the signal and he knows in the present when he was 5, Alice was 4. No sync scenario can undo that fact.

What this says to me is that you don't care about relativity, because those "two rows of sync'd clocks" are what the relativity of simultaneity is all about. As a matter of fact, 99% of the issues that people have with SR can be distilled down to not understanding the relativity of simultaneity.

Your "light signal method" can only be used to compare two spatially separated clocks that are not moving relative to each other (for long enough so that they can send light signals both ways). Otherwise, like in your scenario, it is a coordinate system dependent comparison and it will always be reciprocal. In other words, it is not a proper comparison. The number of physical clocks does not change this fact.

I think you know all this, so what is the argument really about?

Please show me your 2 red lines so I can consider (and refute) your correction because I know you're still working with only 2 clocks.

Rather reconsider the above and I'm sure that you can figure out the two lines yourself.

PS: Confrontational discussions are not very fruitful. I think your issues have been answered and if it is does not quickly converge, this thread has had its run.

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### Re: S.R. Defining the present

Your "light signal method" can only be used to compare two spatially separated clocks that are not moving relative to each other (for long enough so that they can send light signals both ways).

If I respond to this the thread it gets moved into the limbo zone where no one will ever see it again. The two clocks ( Bob's network clock at the 3 ly mark and Alice's on-board clock moving past it)are not spatially separated at the 3ly mark. That alone makes their relative motion irrelevant. In the classic twin paradox, two co-located clocks do not have to be relatively stopped for their on-board clocks to be validly compared. Alice can return to Bob and whiz right past him.

In my case it is Bob's network clock and Alice's on-board clock that are briefly co-located in the moment between approach and separation which also qualifies as stopped. Sync'd clock networks are a valid part of relativity but you seem to object to the new way I'm using them. You're saying that new way is faulty but it's the elephant in the room and can't really be discussed.

You think I know better and am playing some evil manipulative game corrupting young impressionable minds on this forum. No and I will stop posting on this thread if I can save it from oblivion as you've banished almost all my threads there so far. I had hoped to do the Epstein- STD analysis as well as the special case of relative velocity combined from symmetrical motion. But if that also gets thrown out, I'm just wasting my time. Maybe you'd let me start a new thread for those analyses.
ralfcis
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### Re: S.R. Defining the present

ralfcis » 11 Oct 2017, 02:29 wrote:The two clocks ( Bob's network clock at the 3 ly mark and Alice's on-board clock moving past it)are not spatially separated at the 3ly mark. That alone makes their relative motion irrelevant. In the classic twin paradox, two co-located clocks do not have to be relatively stopped for their on-board clocks to be validly compared. Alice can return to Bob and whiz right past him.

Correct, but the two above scenarios are different. I have never said clocks that are co-located, even momentarily, cannot be validly compared. It is about getting either an absolute or a relative clock difference (elapsed time). In the full 'twins' scenario, the two clocks are compared twice when co-located and you get an immediate and absolute elapsed time difference for the two-way trip.

In a case where Alice stops at Charlie for long enough so that a two-way light signal can propagate between her and Bob, this counts for the second compare. Hence we get a delayed, but absolute elapsed time difference. In the case where Alice just flies past Charlie, she and Charlie can read each others clocks momentarily as a first comparison, but a second comparison is now not possible. Hence, the elapsed time can only be calculated in a relative way (non-absolute), meaning that Alice and Bob gets different values.

Since one is not allowed by relativity to discriminate between inertial frames, it is easy to prove that the situation is reciprocal, using 4 clocks, with the 4th one Alice's buddy Dawn, flying by Bob. Or rather, Bob flying by Dawn, since we should now use Alice's inertial frame as reference. And for equivalence, we must place Dawn 3 lyrs behind Alice. Now you will get the exact reciprocal situation. Bob will pass Dawn when his clock reads 4 yrs and Dawn's 5 yrs. But these elapsed time are still relative, because only one direct comparison between each two clocks is possible.

Now I'm going to ask again: please put the two other lines on your STD above. It may be an eye-opener when you have worked it out.

If you would preach this sort of relativity to young impressionable minds, there is no problem, even if you make mistakes that we talk about and you correct them. My problem is that your fairly good knowledge of relativity seems to be somewhat contaminated by your "Ralfitivity" and then parts of proper relativity seem to fly out the window.

BTW, have you noticed that many of the Personal Theory threads far outscore the Physics threads in views? So you fear of 'view degeneration' seems to be unfounded. One issue may be that the members that can really help you may quickly unsubscribe from the thread. Another issue is that while you will here be confronted by only one theory (SR), there you may encounter a diverse set of personal theories that compete with yours for attention.

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