No, the correct term is 'inertial reference frame' or IRF.
Their respective frames are close enough that the clocks will stay synced for the duration of the example, to at least the precision expressed in the example. If the frames were so different, they not be able to publish in a book the distance to AC from here in that <implied> frame.Because for all intensive purposes alpha centauri and earth could NEVER stay synced because they are both moving at different speeds, unless of course some human being arbitrarily wants to make the choice that they are in the same frame?
You do this a lot, asking if I'm saying what you're quoting of me. Yes, I indeed wrote those words. Are you suspecting that somebody else put their own words in my posts?Are you saying that traveling at the speed of light is not a technological limitation.Noax wrote:Traveling at lightspeed is a mathematical singularity and not describable. It is not a technological limitation.
No, it is reasonably stationary in Earth's frame and stays synced to the precision we're considering.That clock is only presumed to "dilate" or slow down compared to earth's frame, right?Noax wrote:AC's clock. It doesn't 'happen to be'. It will read 4.3 years when at the arrival event, and that clock takes a 3 day journey in traveler frame, so I subtracted.WHAT EVENT, and WHY does that event, on alpha centauri JUST HAPPEN TO BE 3 days short of time 4.3 years on "their" clock?
Also, who is "their"?
Contradictory, no.our answers appear to be contradictory and confusing.
I don't say that. I say everything is in every frame being considered here. They're just stationary in one of those, and moving in the other frames, but 'in' them all.How can any person KNOW what another clock is logging if they are, as you say, "in another frame"?
Sort of like asking if I stepped in front of the speeding bus and was struck by it, is being injured/killed what I imagine would happen, or what actually would happen. It seems both are the case. I imagine it that way, and it would actually happen.Is this all just what you imagine would happen, or do you believe that this is what actually would happen, or is it both?
Clocks being synced in some frame means 1) that the clocks have reasonably similar velocity, and 2) they read the same value in the frame in question. No adjustment from this 'same value'.Was alpha centauri clock synced the exact same, say for example as the exact same reading, or was alpha centauri clock adjusted in any other way from that reading.
If they don't have reasonably similar velocity, then they cannot be synced in this way. They can be synced instead to an event at which they are both present, meaning they read the same value at that event. Velocity matters not in this case.
No.So, ALL other frames in the Universe are the same, except for the "traveller's" frame, is that right?
The earth twin is not present at the u-turn event, and thus his age simultaneous with that event is frame dependent.However, you have missed the point. BEFORE you said, the clocks on earth would be logging slower from the "traveller's" frame, thus human beings and the "traveller's" brother would have aged "slower" because it was the "traveller's" frame that was "stationary" and the earth frame which was moving. But now you are saying when the u-turn takes place, the earth twin is already 8.6 years older than he was at the departure event. Now there is two questions, instead of just one;
1. Is the earth twin already 8.6 years at the u-turn event at alpha centauri or at the arrival event back on earth?
The traveler has two different frames, the outbound one and the return one. Different answers in different frames. The traveler is younger (having aged 140 days vs. 8.6 years) when the meet again at Earth.2. You said before the earth twin is younger than the "travelling" twin, from the "traveller's" frame, but now you are saying the the earth twin is older than the "travelling" twin, from the "traveler's" frame when the "travelling" twin is back on earth. So, which one is younger than the other when the "travelling" one is travelling AND when that one is back on earth at the arrival event?
First, there is no such thing as a 'certain position'. There are just events. 'Positions' are a reference to 3D space, not 4D spacetime. The earth twin ages slower in both outbound and return frames (about 3.1 days each) since that twin is moving fast in both frames.Are you saying that when a "traveler" moves AWAY from a 'certain position' that the clocks at that 'certain position' change slower and that things age slower there, from the "traveller's" frame, but the exact opposite happens when the "traveller" moves TOWARDS the same 'certain position, that is to say that the clocks and ageing process speed up doubly?Different frames order events differently. At the AC event (the U-turn), the Earth twin's age is 3 days in the outbound frame but 3 days short of 8.6 years in the return frame. Not magic, just a conceptual change about what time on Earth is simultaneous with some distant event that is not on Earth. It is real enough that the twin back home really is 8.6 years older in that return frame than he is in the outbound frame.Are you proposing some thing magical happened? Is the "travelers" frame magically completely erased and "come back" into earth's frame? Or, is there some purely logical reason for what happens here that you will now explain to us?
He doesn't age at that event. Just different frames put a different Earth event simultaneous with the u-turn event. The traveler being in that frame or not does not cause this. This is what it means that different frames order events differently.If so, then why does the earth twin age by 8.6 years at the u-turn event at alpha centauri, which is said to be a distance of 4.3 years away, and which takes the "traveler" about 4.3 years to travel there in earth's frame?
Suppose we wish to compare the altitude of two houses, on on the sea shore and the other on a mountain. Which is higher that the other depends on the arbitrary definition of which direction is 'up'. Yes, one direction is typically presumed, but actually any direction can be chosen, and if I consider a different direction to be 'up', then the house on the mountain can be the lower in altitude since the new direction orders the altitude of various points differently. No magic lifts the seaside house above the other. It is simply using a different designated direction that is 'up' and orders the altitude of different places differently.
It would be if I said that. I didn't.Did you not just say that the earth twin aged by 8.6 years, and in only one leg of the journey? If so, is this not contradictory?Noax wrote:Of course. That's why the Earth twin ages only 3 days during each leg of the journey, in the frame of the traveler.
The outbound trip does, yes.So, in earth's frame the time the trip takes is 4.3 years, right?
Compared to a greater precision.This supposed "two digits of precision" between alpha centauri and the solar system is compared or relative to what exactly?
That is the event which is simultaneous with the departure event in the outbound traveler frame.Why would alpha centauri clock read 3 days short of 4.3 years at departure time, in the "traveller" frame?
Zero.And, what did the alpha centauri clock read at departure time, in the earth frame?
Frame dependent, but the same as each other in Earth/AC frame.What was the reading on the clock on alpha centauri and on the clock on earth, which 'we' decided would be synced in the earth frame?
Frame dependent.And, is that the exact same reading at departure time?
The Earth and AC clocks are not synced in the traveler frames. The 'why' is because different frames order events differently.If so, and they are different from the "traveller" frame, at the departure time, then why so?
They stay in sync since they have negligibly different velocity.So, how "out of sync" now are earth clock and alpha centauri clock from each other, in earth/alpha centauri frame?
It was synced in Earth frame. It reads 4.3 years in the traveler frame. Different frames yield different answers.So, HOW did alpha centauri's clock end up being on 4.3 years at departure event, when it was synced with earth's clock at ZERO, at departure even?
We've said all along that they're synced in Earth frame.Also, do you think it might speed things up if you said in WHAT frame exactly clocks were synced, instead of just alluding to SOME frame?
Not in traveler frame, which differs from the other two by .999c.Okay. So, earth's clock and alpha centauri's clock are synced at ZERO, at departure event, in earth's frame, alpha centauri's frame, and in "traveller's" frame, is this right or wrong?
Yes and yes.So earth and alpha centauri's clocks are both are still synced in earth and alpha centauri's frame, is this right?
If yes, then that would mean that they both read 4.3 years, at arrival event, from earth and alpha centauri's frame, right?
Noax wrote:It was during time between the departure and arrival at AC events, in the traveler frame.And when you say both alpha centauri clock and earth clock have logged 75 hours, "in the traveler frame", is that while the "traveler" was in its own frame or when the "traveler" was present at the event of arrival on alpha centauri?
The AC clock is not present at that event, so is not synced to it. Instead it is synced to the Earth clock in the Earth frame. So in that Earth frame, yes, all 3 clocks read zero at that departure event. Without the frame specification, what the AC clock reads then is ambiguous.So, at departure event all three clocks, that is "traveller's" clock, earth's clock, and alpha centauri were synced at ZERO,
The traveler clock logs 70 days in the traveler frame.and somehow during the journey the "traveller's" clock, earth's clock, and alpha centauri's clock only logged 75 hours, from "travellers" frame,
In that AC frame, both AC clock and Earth clock read 4.3 years since they are synced in that frame and their clocks logged that much time during the trip, in said Earth/AC frame. Traveler clock reads 70 days, consistent with dilation of .999c over 4.3 years.but at arrival event on alpha centauri where "traveller" is now back in earth and alpha centauri's frame does the earth clock and alpha centauri's clock read 4.3 years and NOT 75 hours, and what does the "traveller's" clock read?
Body aging is a physical process just like any clock. It is a clock in fact, just not a very high precision one. It's why I suggested using pregnant women, which are far higher precision clocks.Also, does the age of the body of the "traveller" correspond with the "traveller's" clock, whatever that is, and do the ages of the bodies on earth and at alpha centauri correspond with the clocks on earth and at alpha centauri?
They're all right. None is defective.Also, if any of these clocks are different, then which one is RIGHT?
The traveler transitions (accelerates) to being stationary in a different frame when he executes the u-turn, or when he stops at AC if he doesn't want to come back. That acceleration, or more precisely, the "moment of acceleration" is the key transition. Moment of acceleration is a lot like moment of inertial or like torque where the effect is multiplied by the distance in question. The two twins could accelerate equally, but the one with the greater moment will age less .And, where and when does the actual transition from one so called "frame" to another supposed "frame" take place?
Frame dependent question as to which twin is moving, but to the 'traveler' who we say is taking the trip, it 'actually' takes 70 days.arth/alpha centauri frame was specified in relation to what earth clock reads, right? You also said, since the 'trip' took "that long". But how long did the actual 'trip', itself, take? A 'trip' is usually in relation to the object, human being or thing, taking the trip and NOT usually relative to the departure point, destination point, nor any thing else.
Any of them. If he stops there, then he accelerates and becomes stationary in the AC frame.What "frame" is the traveler in when they are at alpha centauri or earth?
This question makes no sense. The traveler is in neither place when making the trip.And, how long did the trip take for this traveler when they are at alpha centauri or back on earth?
Probably me.Was it you before who said some thing like that a human being can be "stationary" within a moving ship?
Frame dependent.But you also just said the twin back home had advanced by 4.3 years, so what did the earth clock advance by? 3 days or 4.3 years?
We've discussed the Earth/AC frame and the traveler frame, and perhaps the return frame. That's two or three at best that are relevant (not arbitrary) to the example.Seems like you have many different frames, which are again all arbitrary, correct?
2-4 are the same. 5 is the return frame if we want to consider the round trip. None other is relevant to the example.How about;
1. Traveler frame?
2. Earth frame?
3. Alpha centauri frame?
4. Earth/alpha centauri frame?
Is there any or many other frames that you can think of? If yes, how many and what are the name of some of them?
There is no plain simple answer. What a clock reads simultaneous with and event with which it is not present is always a frame dependent answer, despite your desire for there to be a frame independent one.I just asked a plain, simple question, which then seems to be unable to be answered by some people.
We've considered two or three, listed above.Okay so you want/need A "frame", HOW MANY different frames are there when the so called "traveler" is present at the arrival event at alpha centauri?
Simultaneously with AC (arrival or u-turn)event, Earth clock reads:Could you just provide the name for some of those "frames", and then just give the answer, to as many as those "frames" as you can?
Earth/AC frame: 4.3 years.
Traveler (outbound) frame: 75 hours
Traveler return frame: 8.6 years minus 75 hours.