S.R. Defining the present

[ralfcis]

For all it's emphasis on RELATIVE motion, the first thing relativity does is assign absolute velocities. It says one frame is stationary and the other is moving. It says that's ok because either one can be considered stationary. But people ask, well has relativity considered all the infinite variations of other absolute velocities that make up the same relative velocity. Why aren't those drawn on their own STD's. I explored that here by showing no matter how you orient the axes of relative velocity to an intermediate common frame, the results between the axes were always the same. Setting one as moving or stationary had no effect on the results. Relativists say there's no need because it all works out. But that's not an answer, it's a guess and the wrong guess. That guess breeds fudge factors to mask over the deviation of the guess from the actual physics.

Relativity uses the lump sum fudge factor of relativity of simultaneity to get the right answers from any combination of absolute perspectives. Up until yesterday, I was introducing the fudge factor that while the stationary frame's time was pure time, the moving frame's time was a combination of time slowed by motion and a conversion of the space traveled into time. That fudge factor is the equation:

t'=t/Y where t' is the slowed time and
fudge factor time = t(1-1/Y). (the "moving" frame's distance traveled is converted into time)

But the problem is this; the fudge factor time is an endless series: ct/Yⁿ where n=0,1,2,3...For example, at .6c when t=5 for Bob, t'=4 for Alice. But Alice sees Bob moving from her perspective so t'=3.2 for Bob. But now t' for Alice is 2.56 and this continues until nothing is left. So you have to introduce a fudge factor to keep this from all dissolving in your hands like wet candy floss. There is no need for a fudge factor if you never introduce the concept of a stationary frame in the first place.

Relativity not only added the bandaid of relativity of simultaneity to mask the problem of unbalancing the perspectives, it also introduced a ban on looking under the hood of what's going on during reciprocal time dilation in order to solve the age difference problem. It then added acceleration as the differentiator. But then that introduced a whole slew of other problems (such as why that differentiator doesn't cause age difference at the start of a journey). It becomes an increasingly tangled web that any critical thinker looks at with suspicion and any believer is eager to accept because of how much faith is required.

The fact is both are aging slower relative to each other throughout the journey and there isn't an instantaneous correction to one's clock due to acceleration or clock handoff. Reciprocity can't be ignored because somehow it's cancelled out by a perspective you may not even be aware of. When Alice reaches that planet 4 ly away at .8c, she has really aged 2 years less than Bob whether she stops or not or whatever action Bob takes afterward. The messages she got from Bob do not suddenly fade away like a Marty McFly snapshot. Any change in velocity, not just stops, will create new relative reciprocal aging rates but it is the imbalance in reciprocal aging caused by the delay of light that causes age difference.

[BurtJordaan]

For all it's emphasis on RELATIVE motion, the first thing relativity does is assign absolute velocities. It says one frame is stationary and the other is moving. It says that's ok because either one can be considered stationary. But people ask, well has relativity considered all the infinite variations of other absolute velocities that make up the same relative velocity. Why aren't those drawn on their own STD's.

Ralf, you have made some wild statement here (and later on) and then seem to have convinced yourself later on that the truth lurks in the fact that there are no absolute velocities, just an infinite number of relative velocities - or better stated, an infinite number of inertial frames that are in relative motion and all equivalent.

This seems to be the pattern of the thread, and confusing as it might be to other members that are interested in relativity, as long as you eventually get to the right insight, it may be OK - or is it? There are perhaps too many contradictory statements in here.

I suggest that you wrap this up by a concise summary of the insights that you have reached (or still struggle with) and let's discuss those for correctness (or not). In the interest of the community, this thread should not ramble on along the current path, unless we move it to somewhere other than the physics section.

[ralfcis]

no absolute velocities, just an infinite number of relative velocities - or better stated, an infinite number of inertial frames that are in relative motion and all equivalent.

I don't know what you mean. I said every relative velocity can be made up of an infinite number of "absolute" velocities. The term absolute is wrong because there is no such thing, no aether, no CMB reference. However, the Earth, the LHC, the CMB and the "aether" or unicorns can all be used as intermediate reference frames to determine what share of the relative velocity each participant has. For example, if two ships are equidistant from earth and their relative velocity is .8c and they travel the same distance in the same time then their share is 50% of their relative velocity which works out to .5c each. This is how everyone seems to interpret "absolute velocity; as velocities relative to some "stationary" reference frame.

I clearly say all this is irrelevant. When you draw an STD with Bob at 0 velocity and Alice at .8c velocity, these are not relative velocities, they are "absolute" to a hidden stationary reference frame of Earth. That is painfully clear when Bob can take off from it and leave this implied stationary reference behind. I reject all that.

Bob's relative velocity is .8c and Alice's relative velocity is .8c Their network clocks are the basis for their own present. How they time events relative to their clock network is a separate reality. That's how relativity of simultaneity comes about. Two observers in relative motion will see the same events happen at different times according to their clock networks.

But what if Alice doesn't have a clock network following her. What if there's only an Earth clock network? Why would you care that if there was an Alice clock network that clocks reciprocal times to the Earth clock network eg according to the Earth clocks Bob is 5 and Alice is 3 and according to the Alice clocks Bob is 3 and Alice is 5? You don't care because they are different clock networks. All you have is the Earth clocks to measure the Earth based reality.

Every time Alice is passing near an Earth clock, a real measurement is being made. The time between approach and departure is 0 relative velocity and clocks can be compared; a real age difference has occurred in the Earth clock based reality. Yes, this is my latest departure from relativistic doctrine; I was dead set against this idea until now.

Alice just passes by the planet 4 ly away. According to relativity, no age difference has occurred because you don't know if Alice is passing the planet or the planet is passing the stationary Alice. But there is only relative motion. Each participant is experiencing his own reciprocal reality of time that are not mutually exclusive. They do not cancel each other out.

If Bob took off from Earth at .8c the precise moment Alice passed the planet (and you CAN determine that moment by applying relativity in post processing), would the reality suddenly switch to Bob being 3 and Alice being 5? I hope Relativity doesn't absolve itself from being able to make that call. It should yield the same result for Bob as it does for Alice stopping on the planet. Bob is essentially jumping into a 0 relative velocity frame with Alice the moment he takes off from Earth at .8c. Relativity seems to imply he is the one who broke the spell of constant relative motion being able to mask age difference. If Alice jumped into the 0 frame, she validates the Earth's clock network measurements relative to her on-board clock. If Bob does the jump then he validates Alice's clock network measurements so would he be suddenly 3 and Alice 5?

I'm saying I can make that call on the spot once I draw up the STD. I'm 99% sure that the STD will show that NO, reality doesn't suddenly swap and Bob is immediately 2 yrs younger than Alice. I'm saying once BoB takes off and Alice keeps going, he will see his view of Alice's relative velocity go to 0 while Alice will still see him going at .8c until the lTV signal from Bob reaches her and she sees the picture going at normal speed indicating that they are both at 0 relative velocity. For the time that Alice sees Bob still moving at .8c RELATIVE velocity, Bob continues aging slower than her as she had also been aging slower than him. Since Bob no longer sees Alice moving at .8c relative velocity, he must deduce she is no longer aging slower than him. So all during the time his TV signal has been propagating to her, Bob will be aging slower for longer and he will eventually end up aging 2 years less than Alice once his signal reaches her.

When Alice crosses the planet, she is already 3 and Bob is already 5 according to the earth clock network. So Bob takes off when he is 5. As Alice approaches 5, I can't see his age somehow regressing to 3. I'm pretty sure the result will NOT be that she is 5 and he is 3 but until I do the analysis I can't be 100% sure that my results will agree with what relativity says.

Of course, you're going to pull some sort of ace from your sleeve again and come up with a whole list of rules that allows relativity to come to the correct answer in the end. I hope so but it doesn't really matter because the simplest interpretation wins, not the one that's been around the longest. And you're going to counter that relativity is simpler so goodbye Ralf.

Anyways this is my wrap up of what I hope to prove in the next few months by providing proofs through STD examples of how this all works. I feel I've gone back to the purity of meaning of relativity being based on true relative motion. I'm sure you will not understand my last statement because I'm positive that you feel relativity has never deviated from the true concept of relative motion and that introducing stationary and moving frames was merely for mathematical convenience.

[BurtJordaan]

Ralf, I'm afraid that if this is the best that you can offer as a summary, then this thread does not belong in the physics section. It is so muddled with misconceptions that it does not serve the community for which the physics subforum was created - people who want to chat about mainstream physics in its standard forms.

Where would you prefer this thread to be moved to: beginner's science, philosophy of science or perhaps to private theories? Any other suggestions?

You are free to appeal to the forum administrators again, but I must inform you that the outcome may depend on your response to this request.

[ralfcis]

I figured as soon as I veered off from trying to understand how relativity defines the present I would be sent back to personal theories. I have no problems with that. I could reopen this question with a lot more focus and less exploration of possible explanations. I don't know who the relatively large numbers of people are who read my threads and what they get out of them if it is, as you say, nothing. But could you at least specifically address the topic of this thread and let me know where I have not represented relativity's view of the present correctly? Maybe, for once, instead of a general, "I don't know where to begin, you got it all wrong" you could at least return a paper full of x's where you believe I went wrong. Maybe relativity has a much more reasonable story than the one I've been exposed to. I still (even more so now) appreciate the fact I am able to get this far on this forum before I get kicked off for the same consistent reasons.

[BurtJordaan]

But could you at least specifically address the topic of this thread and let me know where I have not represented relativity's view of the present correctly?

Sure, but first give us the concise summary of your views of the pertinent points covered by the topic, as I requested above. It is hardly possible for any of us to distill it out of the pages full of prose that make up this thread so far.

[ralfcis]

Ok, I'll do that as quickly as I can.

[ralfcis]

I was working on the STD of when Bob takes off to be stopped relative to Alice. I can now see where I have misinterpreted relativity's terminology. I need some more time to get it straight.

[ralfcis]

Yup I totally misinterpreted what relativity was saying. I thought there were 2 competing but equal realities caused by reciprocal time dilation that as soon as one participant stopped, his reality became real and the other's just faded away. There is indeed a sudden shift of reality because the line of present suddenly swings from one time value to another depending on the direction. So when Bob takes off at t=5, his line of present suddenly swings from Alice being t'=3 to t'=8.2 or 8.5 (I need to calculate it). That time jump is made up of a sync offset lump sum added to the time dilation value. The jump is not caused by bob=5/Alice=3 jumping to Bob=3/Alice=5 as I had thought.

However, the part I got right is t=5 and t'=3 is real and not changed by anything Bob or Alice can do. Alice is younger than Bob at this point but Bob's move makes him suddenly younger than Alice. I haven't figured out by how much and what it really means when Bob's line of present is pointing to a future time for Alice. I mean she can't really be 8.5 when Bob=5 when just a second ago she was 3. I don't know how to interpret that.

[BurtJordaan]

This is not a complete reply, which will have to wait until you write your summary. But I must just correct the following gross misconception.

Alice is younger than Bob at this point but Bob's move makes him suddenly younger than Alice.

This is not what relativity says and has little bearing on reality. Age difference between twins can only accumulate over time if the twins take different paths through spacetime. A sudden change of paths relative to each other does not contribute to any difference - unless the different paths are sustained for some length of time.

And to have observable (real) age difference, they must be stationary in the same inertial frame at least once. But it does not depend on lines of simultaneity, just by the difference in paths through spacetime. You may benefit from reviewing my old thread: starting with the final post and working back as required.

[ralfcis]

Here is the STD showing what happens when either Alice stops or Bob stops. It shows how in both cases the person who stops at t=5 (t'=3) will immediately age 2 yrs less than the other. I'll go through the details when I have more time.

Anyways, relativity is correct, I understand how it defines "the present" as a swinging line during a velocity change, and I should have done this STD a long time ago.

[BurtJordaan]

Here is the STD showing what happens when either Alice stops or Bob stops. It shows how in both cases the person who stops at t=5 (t'=3) will immediately age 2 yrs less than the other.

Ralf, I have been telling you for ages that "will immediately age 2 yrs less than the other" is nonsense. Your STD shows only relative time dilation, as viewed reciprocally and in reality has no bearing on aging. You have to look at differences in spacetime paths and from that deduce propertime intervals between events, in order to determine any aging differences.

You are free to proceed on your line of argument, but frankly, you're wasting your time and maybe many other people's as well.

[ralfcis]

I have heard your words many times and I have struggled to incorporate them into something that I find satisfying. If I may just paraphrase your words back to you, maybe you could pin point where I go off the rails.

1. Two participants travel 2 different spacetime paths at a non-zero, mostly constant relative velocity between start and finish events.
2. A start and finish event is defined by both participants being in a 0 relative velocity frame whether they're co-located or separated by a distance.
3. The participant who's at both events (he has 0 proper distance separation from both) is the one who has traveled the shortest spacetime path and therefore in the least proper time so he has aged the least.
4. Each participant wears a pocket watch that is the source of a synchronized network of clocks that do not move relative to the pocket watch. So there is a sync'd clock network that is stationary for each participant.
5. The pocket watch measures proper time within the frame. The rate of the passage of time is the same within every frame so all age at the same rate.
6. The relative velocity through space between frames causes a reciprocal time dilation difference between pocket watch time and the opposing network clock time. Velocity through space is converted into time that subtracts from the proper time within a frame to result in relative time dilation between the frames.

So my STD is almost the same as the STD's in your book except the relative v=.8c instead of .6c and Alice and Bob both stop instead of Alice returning to Bob or Bob taking off from a stationary Earth frame to catch up with Alice.

Let's just consider Alice stopping at the 4 ly mark which is the end of the spacetime path. Her line of present at t'=3 aligns with Bob at 1.8 dilated time which is what her network clock co-located with Bob's pocket watch reads from his watch.

But then she stops. Her line of present swings to align with Bob's at Bob=5. From then on there is a 2 yr age difference between them even though Bob does not become aware of it until he hits 9. At 9 he can look back and figure out Alice has been 2 yrs younger than he for the past 4 yrs. Before that, they were aging at the same rate and seeing the same reciprocal time dilation (defined in 6.) of each other.

Now you're saying before the stop, Alice and Bob had both been aging the same. So when Alice hit 3, Bob was also 3. This means the same age line, (which I have defined previously in this thread) where both are 3, shifts just like the line of present from Bob=3 to Bob=5.

Now I have always been against this idea of sudden age shifts which I thought relativity was promoting. But now you're saying analysis of the spacetime path, which I assume is not depicted in my STD, shows that age difference does not happen abruptly. Please enlighten me because I can't see how smooth aging occurs in relativity from the STD analysis.

P.S. Wait, this may be where I go wrong. I'm swinging an age line and a line of present but in actual fact both were seeing the same time dilated aging of each other. Hence when the stop comes, the transition is smooth, not a discontinuity. Is this the answer?

[ralfcis]

No. It's an answer from Bob's perspective where he sees Alice's time smoothly dilating into the stop but Alice's perspective of Bob sees a sudden shift from Bob=1.8 to bob=5. Also notice that length contraction has no relevance to the discussion.

[BurtJordaan]

No. It's an answer from Bob's perspective where he sees Alice's time smoothly dilating into the stop but Alice's perspective of Bob sees a sudden shift from Bob=1.8 to bob=5. Also notice that length contraction has no relevance to the discussion.

You are very close! Just get rid of the idea that perspectives has anything to do with real aging. Aging differences accrue due to different spacetime paths lengths taken between events by different observers. And there is no 'rule' that can be defined: each case must be analyzed to determine the aging difference, if any.

Lastly, aging differences happen progressively, never at "frame jumps", but you have to consider the whole scenario.

[ralfcis]

Ok I think I see it now. I just need to verify with 4 STD's; two for Alice stopping and 2 for Bob stopping. The reciprocity happens before the speed change and that's where the perspective counts. After the change, the perspectives agree and are no longer reciprocal. The aging difference occurs before the change, it's smooth and it follows time dilation values. I need to verify with the STD's but I think this is how relativity handles age difference.

[ralfcis]

Nope, total failure. I just did the first STD of Alice stopping from Bob's and Alice's perspective. I can see from Bob's perspective, everything is smooth. He sees Alice age less in lock step with her accumulating time dilation seamlessly transitioning into their age difference after she stops.

Just to put some numbers to that from the left hand STD:

Bob's time /Alice's time
1.667 /1 Bob's perspective of Alice's time dilation
3 /1.8
5 /3 stop
6/4 Age difference
7/5

I had expected that from Alice's perspective, she could see Bob follow a reciprocal pattern but he does not. The fact that Alice is doing the stopping means there has to be a discontinuity in the progression from reciprocal time dilation to age difference. This is essentially what I've been saying from the beginning so we're back to square 1 again.

Here's Alice's perspective of Bob from the right hand STD:

Alice's time/Bob's time
1.667/1
3/1.8 huge sync offset discontinuity between 1.8 and stop
3/5 stop
4/6 age difference
7/5


I defined "sees" as post processing of the readings on Alice's pocket watch compared to Bob's distributed and sync'd clock network when the two are passing in close proximity. I assumed you had no disagreement with this definition as I had presented it in my paraphrasing of what I have understood thus far post. Do you have another definition because I can see no way that the person doing the stopping will not see a huge sync offset discontinuity.

As I showed in the previous post, nothing that Bob or Alice does after Bob's network clock at 5 reads Alice at 3 can change this reading. When relativity says from Alice's perspective, Bob's time is dilating the same as Alice and you can't determine age difference because of that, I disagree. That statement is comparing 2 different clock networks and the results from each have no bearing on the other. When Bob's network clock is 5, Alice's pocket watch is 3 and that fact is not changed by the fact that Alice's network clock is 5 and Bob's pocket watch is 3. I don't think you see what I've been saying all along because you assume I'm talking about something else and unless you acknowledge what is correct or not in my paraphrasing post, we'll never come to terms. I was hoping the results of this in-depth STD analysis would show me the same results from both perspectives but it does not.

[ralfcis]

Let's put this in the context of a story because trying to imagine Alice and her entire clock network having the entire universe whizz past her is just not realistic. Let's say Bob is coming toward the Earth at .8c and Alice is sitting there in control of the Earth clock network. They both set their clocks to 0 as Bob passes. Alice waits there 3 years and takes off towards Bob at .8c. This is her initiating a stop relative to Bob as the STD illustrates. Just before the stop, she is 3 and Bob is at 1.8. Just after the stop, she is 3 and Bob is suddenly 5 and thereafter Alice remains 2 yrs younger than Bob in age difference. Sure the numbers agree with the left hand STD analysis but I don't see how this sudden discontinuity sync offset explanation can be satisfactory to anyone. If you don't have a satisfactory explanation (like the mysterious spacetime path analysis for this specific example), I'll just go back to the personal theories section and continue with the rollout of ralfativity. It does not have any of these problems and has a much more satisfactory explanation for age difference.

[BurtJordaan]

I defined "sees" as post processing of the readings on Alice's pocket watch compared to Bob's distributed and sync'd clock network when the two are passing in close proximity. I assumed you had no disagreement with this definition as I had presented it in my paraphrasing of what I have understood thus far post. Do you have another definition because I can see no way that the person doing the stopping will not see a huge sync offset discontinuity.

I have read and agreed with your paraphrasing, except perhaps point 6, which is correct, but somewhat confusingly stated. I did not notice any definition of "sees" there. The definition that you have used above is also somewhat unclear. When Alice stops relative to Bob, she has only one clock to compare her clock to: a Bob-synchronized clock next to her, showing 5 years, while her clock shows 3 years (according to your scenario).

How does Alice know that this is a 'real' difference and not just a reciprocal one? Well in your scenario, she has started static in Bob's frame and became static in his frame again. So she immediately knows that it is an elapsed propertime difference. Even if she has not stopped, she could still read each of Bob's synchronized clocks as she passes them and immediately know that she are progressively experiencing less elapsed time than Bob's network.

If she did not start statically relative to Bob, but just flew past and set her clock to his value, she cannot really reach such a conclusion, because then she has had no information on the synchronization scheme that Bob has used for his network clocks. She will have to stop and then wait until two-way signals can be sent between between her and Bob to check their relative clock offsets.

And all this with no dependence on lines of simultaneity, slowing clocks, or any of those confusing things.

[ralfcis]

I can see now how critical it was to determine how SR defines the present; the purpose of this thread.

All those terms can be boiled down into one simple rule. Your age will either be Y his age or his age/Y at the frame jump depending on your perspective and on who initiates the frame jump. That's relativity in a nutshell and everything else is just useless talk.

I disagree with the asymmetry in the transition from reciprocal time dilation to age difference depending on perspective. Alice, as moving clock and frame jump initiator, has no discontinuity between her time slowing and aging less. But Bob has a huge discontinuity from the other perspective. Before Alice jumps, his clock is slowed relative to her network clock but then it suddenly flips to where she has aged less. There's no physics to back this discontinuity. It's a math trick to ensure the analysis agrees from both perspectives. Ralfativity has no asymmetry because there is no age difference independent of network clock at the frame jump. (however, relative to each network clock, the TV picture between the two is slowed suggesting slowed aging.) It gets settled during the propagation delay of the velocity change between participants.

I disagree you can't know the age difference relative to a network clock unless a frame jump has occurred. Alice has aged 2 yrs less than Bob comparing her pocket watch to Bob's network clock at the planet whether she stops or not. Reciprocal time dilation or any subsequent frame jump by either party cannot invalidate this fact.

I also disagree that determining age difference depends on 0 relative velocity. In ralfativity, any velocity change will result in age difference. There is nothing special about 0 relative velocity nor should there be from a physics standpoint.

How does all this not disprove relativity? If you have any questions I can go over any of these proofs again.

[BurtJordaan]

All those terms can be boiled down into one simple rule. Your age will either be Y his age or his age/Y at the frame jump depending on your perspective and on who initiates the frame jump. That's relativity in a nutshell and everything else is just useless talk.

That's 'Ralfitivity' in a nutshell, but the scenario is not properly defined. The devil is indeed in the details, so simple rules are bound to fail.

Let me rephrase the scenario's where Ralfitivity can work, using only observables. Let Bob's network have an outpost Charlie, 3 lyrs away, at rest in his frame with all network clocks synchronized. Here are 3 properly defined scenarios.

1. Alice is at rest with Bob, so she participated in the clock sync process, including her own. She then 'jumps' to a relative speed of v=0.6c, i.e. Y=1.25. We know it will take 5 years on Bob's network clocks for Alice to reach Charlie. It will take Alice 5/Y = 4 yrs on her clock. This is irrespective of whether she stops or just fly past.

2. Alice starts by just flying past Bob at Y=1.25, but she sets her clock to Bob's time at close range. She now has no observed knowledge of how Bob's network clocks has been synchronized, but she stops at Charlies and again find the elapsed time on Charlie's clock as 5 years and her own clock as 5/Y=4 years. Now she may have some uncertainty on Charlies clock sync with Bob, but she can consult Charlie's logs on the clock sync history and satisfy herself that Bob's clock is indeed in sync with Charlie's. If she has some doubt on the sync's integrity, she can wait until Bob's next scheduled clock sync signal arrives and she should be satisfied.

3. Alice again starts by just flying past Bob at Y=1.25 and again sets her clock to Bob's at close range. This time she does not stop, but just reads Charlie's clock on the fly (as 5 yrs), and her own as 5/Y=4 yrs. This time however, she was not and cannot be part of the sync process or examine it at first hand, because she is never stationary relative to Bob or Charlie. But the 5/Y still worked. Why?

We have been through this many times before. The 4 years is the propertime between the two events of interest and of the three partners, only inertial Alice was present at both events. The 4 years is unquestionably the propertime (and also Alice's aging) between the two events. So what is the 5 years?

If Alice knows relativity, she would have quickly answered that the coordinate time interval observed by Bob between the two events is 5 yrs and the coordinate distance between the events is 3 yrs, so Bob will also have aged yrs. She will be confident in this answer, because she also knows that inertial frames are equivalent, also in terms of the elapsed proper time (and aging of persons stationary in them).

If Alice did not know relativity, she might have been tempted into the false impression that Bob actually aged 5 years during her travel between the two events and that he hence must have "aged slower" that she did. This confuses coordinate time, as observed/measured by someone from a distance, with propertime or aging.

Any scenario that you can dream up in SR can be analyzed this way. This also what I understood that Ralfitivity says, but somewhere along the line, things apparently got confused.

[ralfcis]

Now that last part is very interesting. It's a part that I keep going back and forth on. In my latest iteration I say I only care that Alice's clock reads 4 and she reads Bob's network clock at 5 as she flies by at .6c. She therefore has aged 1 yr less, But in order to say that, I'm contradicting the concept that all frames in constant motion age at the same rate within the frame. In ralfativity, if no velocity change occurs, there is no delay of the notification of that change so no age difference can occur. This even extends to the scenario if a velocity change is an instantaneous pulse that quickly returns to the original constant relative velocity. Ralfativity states no age difference occurs.

But there's still the problem of two clocks being compared and a difference has been noted. In relativity, it gets calculated away. But if it's not a real age difference, what is it physically. I mean if you didn't know relativity and could calculate away its existence, it still exists as something.

[ralfcis]

I'm out of time but I forgot to mention a few things:

1. Ralfativity does not have clock sync problems because there are no clock networks. It depends on the universal accuracy of atomic clocks so it's not important to know if the clocks have been sync'd.

2. I think the resolution to whether a time dilation reading is a valid age difference reading even when there is no velocity change could be in the asymmetry between approach and separation. I need to think about this more. I know it's futile because no one has ever found this asymmetry. Maybe I should just drop it because ralfativity doesn't really care about this problem.

[ralfcis]

Ok, how about this rule for the marriage of age difference and time dilation without a frame jump. In cases where a common reference frame with a network of sync'd clocks is significantly more massive (such as the Earth, the CMB or the LHC) thereby not likely to initiate a frame jump , then its relatively moving smaller partner will age slower by the time dilation factor of Y (t massive = Yt moving). I mean we just can't ignore experimentally probable data just because it can't be verified and messes up our nice tidy theories; (unless of course there is a deeper reason for ignoring this data because recognizing it would contradict a fundamental truth of physics).

This result would be indirectly verifiable by knowing no experiment could possibly return a result where the clock value before the jump would theoretically have a large discontinuity with the time value after the jump. This horrible discontinuity is the flip side of the coin that prevents relativity from determining age difference without a frame jump. No physical proof is possible either way so why not err on the side that intuitively makes the most sense if any assumption really doesn't matter. Wow, this is one great idea albeit not strictly scientific.

P.S. I've been eating a lot of fish heads lately, never have things been so clear.

[ralfcis]

Mistake: these discontinuities also exist with frame jumps. They have no basis in physics. They do not describe a physical phenomenon except for Prof Brian Greene who uses them as proof that our future already exists and can be accessed by aliens riding a bike far away. I'll post the video of this claim if you want.

[ralfcis]

Thanks Jorrie, I got a good number of my questions answered here. I guess I'll go back to the personal theories thread and continue with ralfativity.

[ralfcis]

I went back to this and I still don't get it.

1. If Alice is stopped wrt Bob at either the start or end of the journey, the coordinate times match the proper times and Alice has aged 4 yrs and Bob 5 at the 3 ly mark.

2. If Alice is never stopped wrt Bob, his coordinate time is 5 but he has only really aged 4 even though his clock says 5. When Alice reaches the 3 ly mark, she can send a signal back to Bob that she aged 4 yrs between the time she zeroed her clock to Bob's. Bob could have told her at that point that his clock at the 3 ly mark is synced to his. Why would she need to witness this? When she passes that clock, she sends a signal back to Bob that his far clock read 5. He gets that signal when he's 8 and knows it took 3 yrs to reach him. So he knows 3 yrs ago he was 5 and Alice was 4. He also knew that Alice's clock is dilated wrt his so if her clock read 4, his would've had to have been 5.

3. In terms of reciprocal time dilation, when Alice was 4, she would have seen Bob's clock dilated wrt to hers and his time would've been 3.2. When she hit 5, his would've been 4 which is consistent with reciprocal time dilation. But in order for Alice's time to be 5 to her, Bob's time would have had to have been 6.25 and his dilated time wrt her clock would have been 4. But somehow his age is 5 regardless of what any clock says.

4. If Alice stopped at t'=4, his age would jump somehow to 5 (from t= 4?). If he jumped to .6c, stopping in relation to Alice, (when Alice is t'=4 and he was t=5), his line of present would swing to Alice =8 when he is 6.4.

Ok I'm just babbling now. How has Bob aged 4 when his clock says 5 and this is rectified if Alice comes to a full stop when she hits 4?

[BurtJordaan]

How has Bob aged 4 when his clock says 5 and this is rectified if Alice comes to a full stop when she hits 4?

In SR, everyone ages according to own clock readings. It is just that when they are moving relative to each other, they don't agree on which readings are simultaneous and which are not. When they are not moving relatively, they agree on simultaneity. Can you remember what I wrote here on "God's eye perspective"?

[ralfcis]

when they are moving relative to each other, they don't agree on which readings are simultaneous and which not.

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. If she starts with a fly-by, the answer changes to both have aged 4 despite what she reads on Bob's clock. Before this post, Alice had to have stopped at the 3ly mark for Bob to be 5 and Alice 4 (after waiting for the news to reach Bob). Before that, Alice had to turn around and return to Bob before any age difference determination could be made.

The new wrinkle here is she's moving and now 2 different determinations can be made on age difference based on how she started moving and one disagrees with the clock reading she sees when she passes the 3 ly mark. Your answer above says no determination can be made because they don't agree on simultaneity even though they both should because they know relativity.

[ralfcis]

Fun fact: This is essentially the same question that got me PERMANENTLY banned from the other physics forum all those years ago. Although,I must admit the question gets more and more specific every time I ask it (which is a lot).