Is time universal? NO (and its proof)

[Billy T]

Go back to the very instant after the "1 second acceleration phase" ceased and each were in different reference frames. You must analyze each frame one at a time. You appear to be analyzing them both at once. Let's call one A and the other B. when A stops accelerating, A would say that B has not accelerated yet. Now to B's frame. When B stop accelerating, B would say that A has not accelerated yet. this is the relativity of simultaneity that you are not accounting for. To see it explained in terms of the lorentz equations, follow my SR problem I posted awhile back here....

I don't do GR but know symetry when I see it. Whatever happens to A happens to B by symetry (or physics if you assume each has identicl rockets and each does identical burns, by the pre launch book/ flight plan.) The SRT point is that it is the 15 years of drifitn inertially, not the change frames for one second of clock changing frames with them that is important. In any case the GR analysis is the same for both as everything is symetric.

 

[Billy T]

Sorry guys for the frequent posts - I typically am away on Monday and return late tuesdays (Buillding house by myself - maily an excuse to get out of pSao Paulo Polution and get some exercise.) A lot hap[pened while I was gone and had to respond - going to bed now.

 

[Aer]

</em>
I don't do GR but know symetry when I see it.

Why does everyone tend to think GR has anything to do with flat spacetime that contains accelerations? IT DOES NOT! GR describes curved spacetime around massive bodies and nothing else. OK? Pete is the one that always brings up GR when talking about accelerations and he is incorrect to do so.

</em>
The SRT point is that it is the 15 years of drifitn inertially, not the change frames for one second of clock changing frames with them that is important. In any case the GR analysis is the same for both as everything is symetric.

No, the GR analysis simplifies to the SR equations because we are considering flat spacetime. What part of any problem, either here or in my SR problem page consists of curved spacetime that would require GR?

You do know the difference between GR and SR, do you not?

 

[MacM]

How many times need I say: "YES, SRT INCLUDES RECIPROCITY"? and then add: "Reciprocity is no problem (as you think it is) IF YOU UNDERSTAND:
"EVENTS SIMULTANEOUS IN ONE FRAME ARE NOT SIMULTANEOUS IN ANOTHER."

For examle, one twin can be IN HIS FRAME'S SIMULTANEIOUS 30 when his brother is 25 and his brother can also be 30 IN HIS FRAME'S SIMULTANEIOUS
when his brother is 25. Their "simultaneous" are different.

Sorry to see you buy into such nonsense but that is your perogative.

 

[Pete]

Why does everyone tend to think GR has anything to do with flat spacetime that contains accelerations? IT DOES NOT! GR describes curved spacetime around massive bodies and nothing else. OK? Pete is the one that always brings up GR when talking about accelerations and he is incorrect to do so.

Read a book. Or just-fucking-wikipedia-it.

GR makes predictions about non-inertial rest frames in flat space.

No, the GR analysis simplifies to the SR equations because we are considering flat spacetime. What part of any problem, either here or in my SR problem page consists of curved spacetime that would require GR?

Yes, the problem can be analysed in SR, because it's in flat space. But doing so requires using inertial frames only.
That's fine, and it can be done.

GR, however, allows the investigation of non-inertial frames, such as the frame in which Twin-One is always at rest.
This is also fine - and it gives different insights into the situation.

 

[James R]

Why does everyone tend to think GR has anything to do with flat spacetime that contains accelerations? IT DOES NOT!

Apart from anything else, SR is a subset of GR. Anything that can be done in SR is necessarily a part of GR, too.

And GR is not just about gravity.

 

[Billy T]

Sorry to see you buy into such nonsense but that is your perogative.

I don't "buy into it." - I believe it true that the speed of light is same for all inertail frames. From this, the equations of SR follow. To take your position (never defended by anything but assertions of your opinion, or at best by verbal arguments that reflect fact you don't understand that "events simultaneous in one frame are not simultaneous in another.") I would need to do one of three things:

1) Abandon belief that speed of light is same for all inertial frames - very hard to do as that means the measuremnet of vaccum dielectric constant and/or vaccum permability in different frames would need to be different. I.e. physics would be unique in Each frame. Since after six months, Earth is in a very different frame, going the opposite direction, even on Earth all data published in physics handbooks would be useless, except on the day when the Earth was again in the reference frame in which the data was measured. - Talk about ridiculious - this is so much so that I will not do (1) to join you in your belief.

2) Abandon mathematical logic and/or Maxwell's equations by which and from which SR's equations are derived. Recall Maxwell predicted electromagnet waves and their speed, BEFORE Hertz observed them and his equations are confirmed without exception experimentaly (even in the exchange of information between Earth and distant satelite or your often cited GPS with the correction for ionisphere refraction etc.)

3) Assume that my intution must be correct despite (1) and (2) being correct, and thus, on the strength of my intutive beliefs alone, postulate that SR is wrong in some way not yet known. I of course would not be able to show where the error in SR is but I could keep making unsuported assertions that it is in error and refuse to say were the error is in (1) and/or (2) that produces the error.

I don't believe MacM does either (1) or (2). Ergo, he must do (3).

 

[Billy T]

to Aer:
Pete & James R are correct in their statements about the SR and GR relationship, but perhaps the following will help you accept their truths:

1) I think you agree that locally gravity and acceleration are indistinguishable.
2) I think you accept that GR is required if space is not locally "flat."
3) In view of (1) & (2) if follows that locally in the presence of gravitating mass, one can adopt the view that there is no gravity but that space is not flat.

I.e. a local gravity field, or an accelerating frame, make GR manditory.

 

[Aer]

Apart from anything else, SR is a subset of GR. Anything that can be done in SR is necessarily a part of GR, too.

I said this, you didn't read my entire post GR analysis simplifies to the SR equations because we are considering flat spacetime.

And GR is not just about gravity.

True, but again, I was only talking about flat spacetime which is what the "Special" Relativity case is and flat spacetime is spacetime with no gravity.

 

[Aer]

Read a book. Or just-fucking-wikipedia-it.

Very well, I'll take your suggestion and provide wikipedia quotes for you.

GR makes predictions about non-inertial rest frames in flat space.

And the equations that make these predictions collapse into the Special Relativity equations because we are considering FLAT SPACETIME.

</em>(Spacetime has a non-Euclidean geometry. In special relativity, spacetime is flat.)

</em>In general relativity, the elegance of a flat spacetime and the ability to use a preferred coordinate system are lost (due to stress-energy curving spacetime and the principle of general covariance).

Yes, the problem can be analysed in SR, because it's in flat space. But doing so requires using inertial frames only.
That's fine, and it can be done.

So what is your problem? SR has elegant equation in which we obtain easy solutions. GR has ugly 5-6 page equations that are not so easy.

GR, however, allows the investigation of non-inertial frames, such as the frame in which Twin-One is always at rest.
This is also fine - and it gives different insights into the situation.

Using GR equations will not give you any better of a result, your 5-6 page equations will just have a lot of cancelling out and simplify to the SR equations. No insight added when spacetime is flat....

 

[Billy T]

I don't do GR but know symetry when I see it. ...

May seem strange to reply to myself, but I did not "know symetry" when I see it.

In the birthframe of the two twins, they are twins, but the sign of their accelerations for the second of acceleration (on their own clocks) is opposite. Thus, the equations that mix their great birthframe separation into time-like separations are different.

Because some of the purely space-like separation in the original birth frame is transformed in to time-like separation, DIFFERENTLY in their new different frames, they are no longer twins in their new frames. (Being "twins" is not something like being fat that you can take with you to a new frame. It is a relationship to the birthday of some one else.) That is, the day, which in the original birthframe that is simultaneous with twin A's birthday in the new A frame is not the day which is simultaneoous with twin B' birthday in his new frame. (Frame A has always existed before twin A enter it. So twin A has a birthday in new frame A. It is simultaneous with someday, but not the birthday in the birthframe. Likewise for twin in frame B, he has a day in the birthframe which is simultaneous with his date of birth in frame B.)

No problem with making a single pair of events simultaneous between two frames - just set t=0 ON CO-LOCATED clocks in both frames, but note that a second event, later, will not have the same date/time accumulated on clocks that are keeping "proper time" correctly.

I.e. B's new birthday in frame of birth is not the same day as either the original birthday in birth frame or the day which was simultaneous with A's birthday in the birthframe. Being twins is a relationship between two birthdays in the same frame (their birthframe in this case) but as they were born on different days which are simultaneous with the day of their birth in their new frames (A and B). I.e. they are no longer twins in frames A & B.

I know it is very intutive to think that "once twins," "always twins" but it ain't so. (Unlike being fat, they can't take their "twinness" with them to the new frames.) Their great space-like separtion in their birthframe was transformed differently into time-like spepartaion as they moved to frames A & B.

I thank Pete for helping me see my way thru this modified twin paradox. I hope he will post the drawings he made that show (in each of the three frames separately) exactly what is happening - the time they drift inertially back towards each other to have their photo taken with common flash is clearly seen to be different in these drawings. Each "inertial drift time" is time dilated wrt the proper time and simultaneity of the other, just as SR states.

 

[Aer]

to Aer:
Pete & James R are correct in their statements about the SR and GR relationship, but perhaps the following will help you accept their truths:

Yes! The only relationship they have claimed is that GR collapses into the SR equations for flat spacetime, if you had read my post before you would have seen that I stated this very same thing!

Using GR for flat spacetime is not going to tell you anything more meaningful than just using the SR equations.

1) I think you agree that locally gravity and acceleration are indistinguishable.
2) I think you accept that GR is required if space is not locally "flat."

All good - you've got it correct so far.

3) In view of (1) & (2) if follows that locally in the presence of gravitating mass, one can adopt the view that there is no gravity but that space is not flat.

No. You cannot assume "no gravity" with spactime not being flat - that is what gravity is in relativity! Non-flat spacetime.

I.e. a local gravity field, or an accelerating frame, make GR manditory.

Incorrect, and this is why Pete is wrong, an accelerating frame -in flat spacetime- does not require GR because SR is sufficient and GR tells you no more than SR.

 

[Aer]

In the birthframe of the two twins, they are twins, but the sign of their accelerations for the second of acceleration (on their own clocks) is opposite. Thus, the equations that mix their great birthframe separation (to put them into different new frames) are different.

Because some of the purely space-like separation in the original birth frame is transformed in to time-like separation, DIFFERENTLY in their new different frames, they are no longer twins in their new frames. (Being "twins" is not something like being fat that you can take with you to a new frame. It is a relationship to the birthday of some one else.)

And that is precisely what I told you in my posts. I told you several times, it is a result of the relativity of simultaneity. And you think I don't know what I am talking about? I will refer you to Pete

 

[Billy T]

And that is precisely what I told you in my posts. I told you several times, it is a result of the relativity of simultaneity. And you think I don't know what I am talking about? I will refer you to Pete

I read your old post, but it is a argument with Everneo that seems to have nothing to do with the current question (Perhaps you gave me the wrong reference?) If you said the same thing you did not do it clearly enought for me to recognize that they are no longer twins in frames A & B. - Like most everyone until Pete seet me straight, I thought "once twins, always twins"

Also I admit to some hesitance to take what you say almost unquestioningly as I do with Pete. I have nerver found him to be wrong (Even James R has made a few errors that I have pointed out to him and he has promplty acknowledged, but they were statements in an unstated contex as I recal and just "errors" because of this.) You and I have had several disagreements, as i recall.

I still think that it is somewhat a matter of choice whether or not one wants to "Bend a photon's path" while passing the sun by the sun's gravity, or by non flat space time, but I could be wrong on this. I will let Pete defend himself, he knows more than I do. I hope he finds time to post his drawings and chose to do that if his time is limited and he can not both reply to you and post those drawingswhich made me understand the strong paradox Neddy Bate and I evolved together.

 

[Aer]

I read your old post, but it is a argument with Everneo that seems to have nothing to do with the current question (Perhaps you gave me the wrong reference?)

everneo never entered the discussion in this thread. When I linked to the "SR Problem" thread, the problem was stated in the opening post only. All of James R's comments that you seem to take to heart in that thread were erroneous on his part because he didn't read the entire problem or understand it. Both Pete and Funkstar provided the correct answers to the questions with little difficulting. The problem is not difficult at all and only requires a few SR calculations. Then it easy to imagine the relativity of simultaneity.

Anyway, these are the post's I was refering to in which I said that, 1) it does matter who accelerates, because they change inertial frames, and 2) the change of inertial frames creates a "relativity of simultanetiy" issue in which the two only agree that they didn't accelerate simultaneous, but neither can agree as to who accelerated first.

</em>
It is not the length of acceleration that is the issue here, only the change of inertial frames. While the objects "accelerate" they are not in inertial frames. At the end of the acceleration, they are at rest in a new inertial frame different from the rest inertial frame in which they started. Their sense of "relativity of simultaneity" changes after the acceleration, so the two accelerating objects in the preceding example no longer agree that each accelerated simultaneously in the frame in which they meet and photograph each other as the same age and thus, they can say that the other's clock ticked slower than their own..

</em>
Go back to the very instant after the "1 second acceleration phase" ceased and each were in different reference frames. You must analyze each frame one at a time. You appear to be analyzing them both at once. Let's call one A and the other B. when A stops accelerating, A would say that B has not accelerated yet. Now to B's frame. When B stop accelerating, B would say that A has not accelerated yet. this is the relativity of simultaneity that you are not accounting for.

Hmm, I think I got the order switched on who accelerated first, but the general idea was correct Like I said, I was very tired when I wrote those posts.

Also I admit to some hesitance to take what you say almost unquestioningly as I do with Pete.

Very well, but Pete is wrong when he says that GR will describe anything more than SR in flat spacetime.

I have nerver found him to be wrong

The reason for this is obvious. IT is a result of your own self-admission which is that you do not fully understand general relativity.

Even James R has made a few errors that I have pointed out to him and he has promplty acknowledged

Funny, I asked James R once if he thought "relativistic mass" was meaningful and he essentially said no. This seems to be your biggest disagreement with me, I say it is useless and you say it is not.

I still think that it is somewhat a matter of choice whether or not one wants to "Bend a photon's path" while passing the sun by the sun's gravity, or by non flat space time

The words 'gravity' and 'non-flat spacetime' are synonymous in relativity, it is not a matter of choice.

 

[Prosoothus]

Billy T,

1) Abandon belief that speed of light is same for all inertial frames - very hard to do as that means the measuremnet of vaccum dielectric constant and/or vaccum permability in different frames would need to be different. I.e. physics would be unique in Each frame. Since after six months, Earth is in a very different frame, going the opposite direction, even on Earth all data published in physics handbooks would be useless, except on the day when the Earth was again in the reference frame in which the data was measured. - Talk about ridiculious - this is so much so that I will not do (1) to join you in your belief.

You are not taking into consideration that the Earth could be dragging the aether around with it. Even Einstein believed that the Earth is dragging spacetime around (frame-dragging). If the speed of light is only equal to c relative to Einstein's spacetime, then the measured omnidirectional speed of light on the surface of the Earth will always be equal to, or close to, c. This, however, does not mean that all inertial observers will measure the speed of light to be equal to c, only those that are stationairy relative to the aether, Einstein's spacetime, or whatever you want to call it.

Also, we know that air has certain physical properties that determine the speed that sound travels through it. If a person was moving through the air, the speed of sound in the air relative to that observer would change. This does not mean that the properties of air have changed, and that physics handbooks would become useless.

2) Abandon mathematical logic and/or Maxwell's equations by which and from which SR's equations are derived. Recall Maxwell predicted electromagnet waves and their speed, BEFORE Hertz observed them and his equations are confirmed without exception experimentaly (even in the exchange of information between Earth and distant satelite or your often cited GPS with the correction for ionisphere refraction etc.)

A physicist using the properties of the molecules in the air could determine, or predict, that the speed of sound in air is equal to 761 mph. An observer that is standing on the surface of the Earth can experimentaly confirm that the speed of sound in air is equal to 761 mph. But this DOES NOT mean that an observer that is moving through the air will measure the speed of sound to be equal to 761 mph.

 

[MacM]

I don't "buy into it." - I believe it true that the speed of light is same for all inertail frames. From this, the equations of SR follow.

Here is the root of your problem. You seem to believe the mathematical nonsense of SRT is the only answer and you are not considering any other alternatives as to why the speed of light "appears" invariant.

I've said it before and I will repeat it. The speed of light may "appear" invariant if you are not looking at the same photon when you have different velocities relative to the source.

A very sound theory of that principle has been put forth by Dr Dowdye, a NASA, Phd, Physicist, which he supports mathematically. Have you actually looked at such possiblity and understand the consequences are that you have the same observations and emperical test results but without any relativity at all?

You should.

 

[Pete]

At BillyT's request...
Modified Twin Paradox - Excel Spreadsheet

Graphs from the spreadsheet
Short explanation - in all frames, the twins meet after 30 years proper time for each twin (ie 30 candles on each cake).

For example, in Twin-One's after-acceleration rest frame:
Twin one moved at v=0.447c (gamma=1.118) for 16.771 years, which makes for a proper time of 15 years. Twin one then accelerated to rest, and stayed at rest for 15 years.
Twin two also moved at v=-0.447c (gamma=1.118) for 16.771 years, which makes for a proper time of 15 years. Twin two then accelerated, and moved at v=-0.745 (gamma=1.5) for 22.5 years, making another 15 years proper time.

 

[Pete]

Aer,
I'm not sure if we have a real difference of opinion or not.
My position is:

• Using SR only, it is not possible to use the frame of reference in which one of the twins is at rest throughout. Only non-accelerating frames can be used.
• Using GR, it is possible to use the frame of reference in which one of the twins is at rest throughout.
• Both models give the same prediction for this situation - the proper time between birth and photo is thirty years for each twin.

You agree with all that, right?

I disagree with nothing you've said about GR in this thread except your first comment:

Why does everyone tend to think GR has anything to do with flat spacetime that contains accelerations? IT DOES NOT! GR describes curved spacetime around massive bodies and nothing else.

It is clear that GR does say particular things about accelerating frames in flat space-time.
Yes, SR gives the same conclusions. So what? The reasoning leading to the conclusions is different - and that is interesting.

From the wikipedia page:

Acceleration effects

These effects occur in any accelerated frame of reference, and are therefore independent of the curvature of spacetime. (Note however that spacetime curvature usually is the source the causative acceleration when these effects are being observed.)

I just noticed this:

Very well, but Pete is wrong when he says that GR will describe anything more than SR in flat spacetime.

I think you've misread me. I don't think I ever said that.

 

[Pete]

I still think that it is somewhat a matter of choice whether or not one wants to "Bend a photon's path" while passing the sun by the sun's gravity, or by non flat space time

The words 'gravity' and 'non-flat spacetime' are synonymous in relativity, it is not a matter of choice.

This is interesting!

When using a curved-spacetime paradigm, it's not a matter of choice... but that's not the only paradigm available!

There's a great chapter in Kip Thorne's Black Holes and Time Warps (read it! everyone!) called What Is Reality. I have it in front of me now, because that little interchange inspired me to duck over to the library, grab it, and read it again.

Extremely briefly (too briefly.. really, find and read it!):
In the curved spacetime paradigm of GR, Perfect clocks and Perfect rulers accurately measure spacetime, which is curved by mass-energy.
In the flat spacetime paradigm of GR, spacetime is flat, but Perfect clocks and Perfect rulers are rubbery, their shapes and readings altered by gravitational fields. They don't always accurately measure spacetime.

Quotes:
"What is the real, genuine truth? Is spacetime really flat, or is it really curved? To a physicist like [Kip Thorne] this is an uninteresting question because it has no physical consequences. Both viewpoints give precisely the same predictions for any measurements performed with any kind of physical apparatus whatsoever... Moreover, physicists can and do use the two viewpoints interchangeably when trying to deduce the predictions of general relativity."

"This freedom carries power. That is why physicists were not content with Einstein's cured spacetime paradigm, and have developed the flat spacetime paradigm as a supplement to it."

Like I said, I don't pretend to understand this fully... so if you want to know more about it, I'll just point you to the book.