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BillyJoe · 30th June 2007, 01:38 AM

Originally Posted by Fredrik

OK, now I see four ASCII pictures and the description makes sense.

(Lots of smiles today!)

Originally Posted by Fredrik

The original diagram is a space-time diagram (even though it wasn't intended to be) with time increasing in the down direction and units such that c > 2.

So it is.

Paulhoff · 30th June 2007, 04:59 AM

Originally Posted by BillyJoe

(Yeah, KISS: Keep It Short and Simple.

)

I like my father's version better, Keep It Simple, Stupid.

As I have said before, humans just like to make things complicated. And some of them have a very overactive speech center in their brain.

Paul

robinson · 30th June 2007, 12:48 PM

Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain?

Paulhoff · 30th June 2007, 12:54 PM

Originally Posted by robinson

Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain?

What does you speech center tell you...........

Paul

BillyJoe · 30th June 2007, 02:13 PM

Originally Posted by robinson

Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain?

Apparently there are separate areas in the brain for generating speech and generating writing* but there is another area that formulates what you want to communicate that generates input for both of these areas.

*There are stroke sufferers who know exactly what they wish to say but are unable to say it, but they can write it down for you. (I assume they are able to type it as well)

illogical · 4th July 2007, 02:15 AM

when you read something, the vocal cords move. it's called subvocalization.

in linguistics, there is a theory that words are simply speech figures. obviously some languages like Chinese are closer to ideographic/logographic, while Romance languages are way different.

ynot · 7th July 2007, 03:07 PM

Before complete failure is declared, let me ask a “KISS” question . . .

Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A?

Ziggurat · 7th July 2007, 03:24 PM

Originally Posted by ynot

Before complete failure is declared, let me ask a “KISS” question . . .

Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A?

Yes.

ynot · 7th July 2007, 03:37 PM

Originally Posted by Ziggurat

Yes.

Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation?

Ziggurat · 7th July 2007, 04:07 PM

Originally Posted by ynot

Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation?

You're making an assumption that there's a single frame which you can label "A". But there isn't, and you cannot make that assumption. "A" changes reference frames. Here's a spacetime diagram of what you describe, as seen from three different reference frames:

The red line is earth. Green and blue are A and B, respectively. Panel 1 shows the earth reference frame. Panel 2 shows the reference frame in which B is stationary for the outbound journey. Panel 3 shows the reference frame in which A is stationary for the outbound journey. Note that if you consider the entire journeys, the A and B journeys are actually symmetric in all three reference frames (though the symmetry isn't as simple in panels 2 and 3). In panel 2, for example, both A and B will have time dilation for part of their journeys and no time dilation for part of their journeys, and which part comes first is different, but it's still symmetric (can you see why?). In fact, the journeys are symmetric for any reference frame, not just the three I picked. Therefore all obervers should agree that A and B experience the same amount of time. This is different from the twin paradox, where the journeys of the twins are not symmetric for any reference frame.

BillyJoe · 7th July 2007, 04:59 PM

I will attempt an explanation without the spacetime diagrams and without acceleration.

To avoid the problems associated with acceleration, we need four spaceships, A, B, X, and Y.
The analagous scenario would be as follows:

Firstly the setup:

A and B are moving towards each other at 0.8c.
They synchronise their clocks as they pass.
The Earth happens to be where A and B pass and an Earthling sychronises his watch with those of A and B.

The rest is analogous to the previous example:

Now A and B are moving away from each other at 0.8c
After a certain time interval as seen from Earth, A and B are passed by X and Y respectively, also at 0.8c
As X passes A, X synchronises his watch with A's watch.
As Y passes B, Y synchronises his watch with B's watch.
Eventually X and Y pass each other.
Symmetry demands that they pass at the Earth.
They compare the times on their clocks.
The symmetry of the situation demands that the times on the clocks of X and Y are the same.
The Earthling will confirm that the times on X and Y's clocks are less than on his own clock.

Thus both time dilation and it's independence on acceleration are confirmed.

Paulhoff · 7th July 2007, 05:40 PM

Originally Posted by ynot

Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation?

You asked if the time would be the same, and it is. There was time dilation, it was the same for both.

Paul

Fredrik · 7th July 2007, 06:03 PM

Originally Posted by ynot

Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A?

I have already answered this more than once. See e.g. #256.

Originally Posted by ynot

Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation?

No one says there wasn't. Time dilation is present in this scenario. But there's also a "simultaneity shift" when the rocket turns around. I have explained all of this already.

BillyJoe · 7th July 2007, 07:40 PM

Originally Posted by Fredrik

No one says there wasn't. Time dilation is present in this scenario. But there's also a "simultaneity shift" when the rocket turns around.

The way ynot figures it is that, in A's frame, B's clock should show less time has passed for B and, from B's frame, A's clock should show less time has passed for A.

Both the "shifting frames" and the "simultaneity shift" concepts are confusing for someone struggling with the basics.
I don't know if I will fare any better though.

Fredrik · 8th July 2007, 02:26 AM

Ynot, I'm answering BillyJoe, but you're the one who really needs to read this!

Originally Posted by BillyJoe

The way ynot figures it is that, in A's frame, B's clock should show less time has passed for B and, from B's frame, A's clock should show less time has passed for A.

Both the "shifting frames" and the "simultaneity shift" concepts are confusing for someone struggling with the basics.

I understand that of course, but there's no way that he (or anyone else) will ever understand time dilation without also understanding simultaneity.

To be more specific, there's no way that ynot will ever understand this unless he understands all of these three things:

1. The scenario is perfectly symmetrical, so any correct statement abut A and B will still be correct if A is replaced with B and vice versa. (This of course includes 2 and 3 below).

2. In both of A's frames, B is aging slower than A. (This is time dilation).

3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity).

Ynot seems to understand 1 and 2 already, so he needs to focus on 3.

BillyJoe · 8th July 2007, 03:21 AM

Originally Posted by Fredrik

3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity).

Ynot seems to understand 1 and 2 already, so he needs to focus on 3.

The problem is that "simultaneity shift" is really not possible. You can't go instantly from zero to 0.8c. Of course it works at any acceleration and final speed, but then it is less obvious that time dilation isn't caused by acceleration. I think ynot needs a leg up first before he tackles this, but I could be wrong.

Fredrik · 8th July 2007, 06:33 AM

Originally Posted by BillyJoe

The problem is that "simultaneity shift" is really not possible. You can't go instantly from zero to 0.8c. Of course it works at any acceleration and final speed, but then it is less obvious that time dilation isn't caused by acceleration. I think ynot needs a leg up first before he tackles this, but I could be wrong.

That stuff about how infinite acceleration isn't possible, is irrelevant, but you know that already. You may worry that others might not understand this, but I think it's pointless to worry about that, because anyone who can't get past a detail like that, has a lot to learn about physics in general before it makes sense to even begin to try to understand relativity. Newton's laws would be a better starting point.

I understand why you'd like to eliminate acceleration from these relativistic problems: You have noticed that some people incorrectly conclude that acceleration must be the cause of some "weirdness" in e.g. the twin "paradox" problem, and you have found a quick and easy way to prove them wrong. It's a good thing that you're able to prove them wrong without actually solving the problem, because now they don't have to understand the full solution to see that they're wrong. However, what you've said only explains why acceleration isn't a relevant part of these problems, and why A and B will be the same age.

That A and B will be the same age is implied by 1, and ynot already understands that. He understands both 1 and 2. His problem is that he thinks that 2 contradicts 1, and the only reason for that is that he doesn't understand 3.

3 is the reason why 2 doesn't contradict 1, so there's no way that anyone can understand this problem without understanding 3. (And that's true regardless of whether they consider ynot's formulation of the problem or yours).

Originally Posted by Fredrik

1. The scenario is perfectly symmetrical, so any correct statement abut A and B will still be correct if A is replaced with B and vice versa. (This of course includes 2 and 3 below).

2. In both of A's frames, B is aging slower than A. (This is time dilation).

3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity).

ynot · 9th July 2007, 10:20 PM

I’m feeling guilty that my busy life outside this forum doesn’t allow me to adequately read and respond to posts, let alone study the good information that has been provided. I understand how this can be annoying to those that have given this thread their time and effort (sorry). Rather than continue with “yeah-but” and “what-if” responses, I will study what has been provided when I get the time. Thanks to all for your help and patience. I might not “get it” yet but it certainly hasn’t been a total waste of time for me, and it seems it has been helpful to others.

BillyJoe · 10th July 2007, 05:10 AM

Actually, what I find really annoying is moving avatars!

You have no idea how many times I've watched that damn wheel go round.

robinson · 10th July 2007, 11:09 AM

What wheel?

Paulhoff · 10th July 2007, 11:52 AM

The perpetual motion machine that doesn’t work.

Paul

ynot · 10th July 2007, 01:33 PM

Originally Posted by Paulhoff

The perpetual motion machine that doesn’t work.

Paul

Whadaya mean “doesn’t work”!!??

Do you deny the evidence before you?

I offer further indisputable proof . . .

Now how am I going to spend that million bucks?

schlitt · 3rd February 2008, 04:50 PM

Hey ynot, did you ever sort out your dilemma regarding this issue?

I had been pondering relativity lately, found this thread and started reading it with a completely compatible opinion of your first post.
Midway through the first page it suddenly struck me, and i think i understand the concept now.

The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space.

Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective.

(please anyone, correct me if i am wrong here)

BillyJoe · 4th February 2008, 03:22 AM

Originally Posted by schlitt

Midway through the first page it suddenly struck me, and i think i understand the concept now.

The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space.

Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective.

(please anyone, correct me if i am wrong here)

Yes, unfortunately, you are wrong.

What is really happening is what is happening from the point of view of someone at the point in space where it is actually happening. Everyone else sees something different happening, but that is only what seems to be happening from their point of view, not what is really happening. However, they can find out what is really happening by using the math derived from relativity theory to calculate what is happening at the point in space where it is actually happening.

I hope that makes sense....

....because it is a serious answer.

regards,
BillyJoe

schlitt · 4th February 2008, 11:50 AM

Originally Posted by BillyJoe

Yes, unfortunately, you are wrong.

What is really happening is what is happening from the point of view of someone at the point in space where it is actually happening. Everyone else sees something different happening, but that is only what seems to be happening from their point of view, not what is really happening. However, they can find out what is really happening by using the math derived from relativity theory to calculate what is happening at the point in space where it is actually happening.

I hope that makes sense....

....because it is a serious answer.

regards,
BillyJoe

OK, I understand what you are saying. But surely the person who is "at the point in space where it is actually happening" as you put it, is still merely seeing the event relative to themselves. The fact they are closer gives less dilation, but still some nevertheless? (unless everything were 100% static?)

Time comes from the measurement of movement through space, so those viewing a moving object at distance are not "wrong", in their measurements, they simply need to be adjusted for in relation to measurements taken at the source of the event measured (or anywhere else for that matter), due to the time measurement at that point being different. Given the parameters, this can be done mathematically.

Does that sound right?

Tumbleweed · 4th February 2008, 12:38 PM

Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously

Ziggurat · 4th February 2008, 02:42 PM

Originally Posted by Tumbleweed

Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously

No. Only one reality exists. The traveling twin will be younger when they reunite, they will both agree on that. The difficulty many newcomers to relativity have with the problem is the fact that superficially it seems like it should be symmetric, but it isn't, and any complete analysis of the problem will reveal that asymmetry.

Fredrik · 4th February 2008, 03:19 PM

Originally Posted by schlitt

The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space.

Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective.

(please anyone, correct me if i am wrong here)

I don't know if you're wrong, but I also don't quite understand what you're saying. What I do know is that you need to consider at least two events to find any disagreement between different observers.

Fredrik · 4th February 2008, 03:26 PM

Originally Posted by Tumbleweed

Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously

What Ziggurat said.

If you want to understand this problem, you will have understand the space-time diagram in post #239, so I suggest you start there.

Paulhoff · 4th February 2008, 03:43 PM

Originally Posted by Tumbleweed

Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously

The one that traveled is younger.

Paul

Tumbleweed · 4th February 2008, 03:48 PM

Oh I fully agree that there is one final reality - that the twins are indeed of separate age, but they traveled different realities - or frames of reference- to get to the new frame of reference/reality. And I get that it got that way because distance was being traded, basically for time. V still equals d/t in each frame of reference
And I agree that the time dilation is one way and not symmetrical. In other words, the rocket is speeding away from the Earth and not also vice versa

Tumbleweed · 4th February 2008, 04:09 PM

Here's a puzzle that has always bugged me. You have two objects headed towards each other at the speed of light. They acheive this by each approaching a fixed point in a straight line in space at half the speed of light.
Taking the twins thingie and relativity's time/distance differential to the extreme, would not the distance between the two objects shrink to zero (for them only) no matter how many light years they are said to be apart as judged by a third observer? Or looking at it another way, would the elapsed time clock on each space ship read zero (as well as the odometer) when they met, again regardless of how many light years they appear to be apart by an independent observer. Or even regardless as to ANY outside observation, not within their frame of reference

sol invictus · 4th February 2008, 04:19 PM

Originally Posted by Tumbleweed

Here's a puzzle that has always bugged me. You have two objects headed towards each other at the speed of light. They acheive this by each approaching a fixed point in a straight line in space at half the speed of light.
Taking the twins thingie and relativity's time/distance differential to the extreme, would not the distance between the two objects shrink to zero (for them only) no matter how many light years they are said to be apart as judged by a third observer?

No.

Velocities don't add like that in relativity. Each object will see the other moving towards it at 4/5 the speed of light.

http://en.wikipedia.org/wiki/Velocity-addition_formula

schlitt · 4th February 2008, 04:32 PM

Originally Posted by Fredrik

I don't know if you're wrong, but I also don't quite understand what you're saying. What I do know is that you need to consider at least two events to find any disagreement between different observers.

Yes, i agree.

The discrepancy between the two events is real, due to time being linked with the observer. The concept that there is no absolute time is what i think throws a lot of people.

Tumbleweed · 4th February 2008, 04:36 PM

Originally Posted by sol invictus

No.

Velocities don't add like that in relativity. Each object will see the other moving towards it at 4/5 the speed of light.

http://en.wikipedia.org/wiki/Velocity-addition_formula

Okay assuming its only .8 the speed of light. It would still take far less time for them to meet as far as their clocks are concerned, as compared to an outside observors calculations using Newtonian physics would have calculated, right? The inference being that the vast distances to the galaxies might be not be that, the distance depending on relative velocity instead of Newtonian calculations

Tumbleweed · 4th February 2008, 04:43 PM

Here'a another puzzle. You have the Earth and a fixed point way out in space. You took a tape measure and measured the exact distance to that fixed point. THe point is moving in harmony with the earth through the cosmos, so the distance is always the same
Various and sundry objects pass throught that fixed point all at different speeds and angles. As they pass through that point, they each measure the exact distance to Earth, Do ANY of their calculations agree with either your measurement or anyone elses. Or will they all be different

Paulhoff · 4th February 2008, 04:51 PM

Originally Posted by Tumbleweed

Here'a another puzzle. You have the Earth and a fixed point way out in space. You took a tape measure and measured the exact distance to that fixed point. THe point is moving in harmony with the earth through the cosmos, so the distance is always the same
Various and sundry objects pass throught that fixed point all at different speeds and angles. As they pass through that point, they each measure the exact distance to Earth, Do ANY of their calculations agree with either your measurement or anyone elses. Or will they all be different

If I am not mistaken, the only ones that will be the same, are those that travel at right angles to the earth thru that point.

>>>>>>>>>.>>>>>>>>>> the period is the fixed point

__________"E"arth

Paul

Fredrik · 4th February 2008, 04:56 PM

Originally Posted by Tumbleweed

Oh I fully agree that there is one final reality - that the twins are indeed of separate age, but they traveled different realities - or frames of reference- to get to the new frame of reference/reality.

Please don't use the word reality here. It looks horrible. Even if we remove that word, that sentence still looks strange. The traveling twin changed his frame of reference by changing his velocity, not by changing his position.

Originally Posted by Tumbleweed

And I agree that the time dilation is one way and not symmetrical. In other words, the rocket is speeding away from the Earth and not also vice versa

No, time dilation is symmetrical here. If both of the twins say "my brother's aging slower than me", they're both right. The reason why this symmetry doesn't cause a paradox is that something else entirely happens when the rocket turns around. It's not a physical effect. It's just a change of coordinates. I explained these things earlier in the thread (starting with post #239, near the end of page 6).

(And it's just as correct to say that the Earth is speeding away from the rocket. That's just the same set of events described from a different inertial frame).

robinson · 4th February 2008, 05:03 PM

Originally Posted by Fredrik

The traveling twin changed his frame of reference by changing his velocity, not by changing his position.

Please don't say things like that.

Tumbleweed · 4th February 2008, 05:09 PM

Originally Posted by Paulhoff

If I am not mistaken, the only ones that will be the same, are those that travel at right angles to the earth thru that point.

>>>>>>>>>.>>>>>>>>>> the period is the fixed point

__________"E"arth

Paul

So if no one can agree on how far away something is, except for those in the same frame of reference, velocity-wise, Einstein did indeed screw up the whole universe

30th June 2007, 01:38 AM	#281
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Originally Posted by Fredrik OK, now I see four ASCII pictures and the description makes sense. (Lots of smiles today!) Originally Posted by Fredrik The original diagram is a space-time diagram (even though it wasn't intended to be) with time increasing in the down direction and units such that c > 2. So it is.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

30th June 2007, 04:59 AM	#282
Paulhoff You can't expect perfection. Join Date: May 2005 Location: South Florida Posts: 12,575	Originally Posted by BillyJoe (Yeah, KISS: Keep It Short and Simple. ) I like my father's version better, Keep It Simple, Stupid. As I have said before, humans just like to make things complicated. And some of them have a very overactive speech center in their brain. Paul
	__________________ For our money "IN WHICH GOD DO YOU TRUST" Much worse than the Question not asked, is the Answer not Given Don't accept an answer that can't be questioned - God is Surperfluous A society fails when ignorance outweighs knowledge Science doesn’t know everything, but religion doesn’t know anything Life is so horrent and also so beautiful, but without it there is nothing

30th June 2007, 12:48 PM	#283
robinson Banned Join Date: Aug 2006 Posts: 6,136	Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain?
robinson Banned Join Date: Aug 2006 Posts: 6,136

30th June 2007, 12:54 PM	#284
Paulhoff You can't expect perfection. Join Date: May 2005 Location: South Florida Posts: 12,575	Originally Posted by robinson Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain? What does you speech center tell you........... Paul
	__________________ For our money "IN WHICH GOD DO YOU TRUST" Much worse than the Question not asked, is the Answer not Given Don't accept an answer that can't be questioned - God is Surperfluous A society fails when ignorance outweighs knowledge Science doesn’t know everything, but religion doesn’t know anything Life is so horrent and also so beautiful, but without it there is nothing

30th June 2007, 02:13 PM	#285
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Originally Posted by robinson Is the speech center the same as the part of the brain that makes us type words? Or is that a different part of the brain? Apparently there are separate areas in the brain for generating speech and generating writing* but there is another area that formulates what you want to communicate that generates input for both of these areas. *There are stroke sufferers who know exactly what they wish to say but are unable to say it, but they can write it down for you. (I assume they are able to type it as well)
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

4th July 2007, 02:15 AM	#286
illogical Thinker Join Date: Jun 2007 Posts: 178	when you read something, the vocal cords move. it's called subvocalization. in linguistics, there is a theory that words are simply speech figures. obviously some languages like Chinese are closer to ideographic/logographic, while Romance languages are way different.
illogical Thinker Join Date: Jun 2007 Posts: 178

7th July 2007, 03:07 PM	#287
ynot Illuminator Join Date: Jan 2006 Location: New Zealand Posts: 4,731	Before complete failure is declared, let me ask a “KISS” question . . . Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A?
	__________________ Rumours of a god’s existence have been greatly exaggerated. My post are all (IMO) unless stated otherwise.

7th July 2007, 03:24 PM	#288
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,285	Originally Posted by ynot Before complete failure is declared, let me ask a “KISS” question . . . Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A? Yes.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

7th July 2007, 03:37 PM	#289
ynot Illuminator Join Date: Jan 2006 Location: New Zealand Posts: 4,731	Originally Posted by Ziggurat Yes. Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation?
	__________________ Rumours of a god’s existence have been greatly exaggerated. My post are all (IMO) unless stated otherwise.

7th July 2007, 04:07 PM	#290
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,285	Originally Posted by ynot Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation? You're making an assumption that there's a single frame which you can label "A". But there isn't, and you cannot make that assumption. "A" changes reference frames. Here's a spacetime diagram of what you describe, as seen from three different reference frames: The red line is earth. Green and blue are A and B, respectively. Panel 1 shows the earth reference frame. Panel 2 shows the reference frame in which B is stationary for the outbound journey. Panel 3 shows the reference frame in which A is stationary for the outbound journey. Note that if you consider the entire journeys, the A and B journeys are actually symmetric in all three reference frames (though the symmetry isn't as simple in panels 2 and 3). In panel 2, for example, both A and B will have time dilation for part of their journeys and no time dilation for part of their journeys, and which part comes first is different, but it's still symmetric (can you see why?). In fact, the journeys are symmetric for any reference frame, not just the three I picked. Therefore all obervers should agree that A and B experience the same amount of time. This is different from the twin paradox, where the journeys of the twins are not symmetric for any reference frame.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

7th July 2007, 04:59 PM	#291
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	I will attempt an explanation without the spacetime diagrams and without acceleration. To avoid the problems associated with acceleration, we need four spaceships, A, B, X, and Y. The analagous scenario would be as follows: Firstly the setup: A and B are moving towards each other at 0.8c. They synchronise their clocks as they pass. The Earth happens to be where A and B pass and an Earthling sychronises his watch with those of A and B. The rest is analogous to the previous example: Now A and B are moving away from each other at 0.8c After a certain time interval as seen from Earth, A and B are passed by X and Y respectively, also at 0.8c As X passes A, X synchronises his watch with A's watch. As Y passes B, Y synchronises his watch with B's watch. Eventually X and Y pass each other. Symmetry demands that they pass at the Earth. They compare the times on their clocks. The symmetry of the situation demands that the times on the clocks of X and Y are the same. The Earthling will confirm that the times on X and Y's clocks are less than on his own clock. Thus both time dilation and it's independence on acceleration are confirmed.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it. Last edited by BillyJoe; 7th July 2007 at 05:02 PM.

7th July 2007, 05:40 PM	#292
Paulhoff You can't expect perfection. Join Date: May 2005 Location: South Florida Posts: 12,575	Originally Posted by ynot Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation? You asked if the time would be the same, and it is. There was time dilation, it was the same for both. Paul
	__________________ For our money "IN WHICH GOD DO YOU TRUST" Much worse than the Question not asked, is the Answer not Given Don't accept an answer that can't be questioned - God is Surperfluous A society fails when ignorance outweighs knowledge Science doesn’t know everything, but religion doesn’t know anything Life is so horrent and also so beautiful, but without it there is nothing

7th July 2007, 06:03 PM	#293
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Originally Posted by ynot Synchronised clocks A and B travel away from the Earth in opposite directions, at the same speed and for the same distance, then turn around and return to Earth. In other words, everything about their trips are exactly the same, except that they are in opposite directions. When the clocks are back on Earth again, would A observe that B still showed the same time as A? I have already answered this more than once. See e.g. #256. Originally Posted by ynot Thanks. I don‘t understand why the answer isn‘t “No”. From the frame of A, B travelled at a different speed so why was there no time dilation? No one says there wasn't. Time dilation is present in this scenario. But there's also a "simultaneity shift" when the rocket turns around. I have explained all of this already.
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912

7th July 2007, 07:40 PM	#294
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Originally Posted by Fredrik No one says there wasn't. Time dilation is present in this scenario. But there's also a "simultaneity shift" when the rocket turns around. The way ynot figures it is that, in A's frame, B's clock should show less time has passed for B and, from B's frame, A's clock should show less time has passed for A. Both the "shifting frames" and the "simultaneity shift" concepts are confusing for someone struggling with the basics. I don't know if I will fare any better though.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

8th July 2007, 02:26 AM	#295
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Ynot, I'm answering BillyJoe, but you're the one who really needs to read this! Originally Posted by BillyJoe The way ynot figures it is that, in A's frame, B's clock should show less time has passed for B and, from B's frame, A's clock should show less time has passed for A. Both the "shifting frames" and the "simultaneity shift" concepts are confusing for someone struggling with the basics. I understand that of course, but there's no way that he (or anyone else) will ever understand time dilation without also understanding simultaneity. To be more specific, there's no way that ynot will ever understand this unless he understands all of these three things: 1. The scenario is perfectly symmetrical, so any correct statement abut A and B will still be correct if A is replaced with B and vice versa. (This of course includes 2 and 3 below). 2. In both of A's frames, B is aging slower than A. (This is time dilation). 3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity). Ynot seems to understand 1 and 2 already, so he needs to focus on 3.
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912

8th July 2007, 03:21 AM	#296
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Originally Posted by Fredrik 3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity). Ynot seems to understand 1 and 2 already, so he needs to focus on 3. The problem is that "simultaneity shift" is really not possible. You can't go instantly from zero to 0.8c. Of course it works at any acceleration and final speed, but then it is less obvious that time dilation isn't caused by acceleration. I think ynot needs a leg up first before he tackles this, but I could be wrong.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

8th July 2007, 06:33 AM	#297
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Originally Posted by BillyJoe The problem is that "simultaneity shift" is really not possible. You can't go instantly from zero to 0.8c. Of course it works at any acceleration and final speed, but then it is less obvious that time dilation isn't caused by acceleration. I think ynot needs a leg up first before he tackles this, but I could be wrong. That stuff about how infinite acceleration isn't possible, is irrelevant, but you know that already. You may worry that others might not understand this, but I think it's pointless to worry about that, because anyone who can't get past a detail like that, has a lot to learn about physics in general before it makes sense to even begin to try to understand relativity. Newton's laws would be a better starting point. I understand why you'd like to eliminate acceleration from these relativistic problems: You have noticed that some people incorrectly conclude that acceleration must be the cause of some "weirdness" in e.g. the twin "paradox" problem, and you have found a quick and easy way to prove them wrong. It's a good thing that you're able to prove them wrong without actually solving the problem, because now they don't have to understand the full solution to see that they're wrong. However, what you've said only explains why acceleration isn't a relevant part of these problems, and why A and B will be the same age. That A and B will be the same age is implied by 1, and ynot already understands that. He understands both 1 and 2. His problem is that he thinks that 2 contradicts 1, and the only reason for that is that he doesn't understand 3. 3 is the reason why 2 doesn't contradict 1, so there's no way that anyone can understand this problem without understanding 3. (And that's true regardless of whether they consider ynot's formulation of the problem or yours). Originally Posted by Fredrik 1. The scenario is perfectly symmetrical, so any correct statement abut A and B will still be correct if A is replaced with B and vice versa. (This of course includes 2 and 3 below). 2. In both of A's frames, B is aging slower than A. (This is time dilation). 3. When A turns around, he goes from a frame where B is younger to a frame where B is older. (This is not time dilation, it's relativity of simultaneity).
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Last edited by Fredrik; 8th July 2007 at 06:44 AM.

9th July 2007, 10:20 PM	#298
ynot Illuminator Join Date: Jan 2006 Location: New Zealand Posts: 4,731	I’m feeling guilty that my busy life outside this forum doesn’t allow me to adequately read and respond to posts, let alone study the good information that has been provided. I understand how this can be annoying to those that have given this thread their time and effort (sorry). Rather than continue with “yeah-but” and “what-if” responses, I will study what has been provided when I get the time. Thanks to all for your help and patience. I might not “get it” yet but it certainly hasn’t been a total waste of time for me, and it seems it has been helpful to others.
	__________________ Rumours of a god’s existence have been greatly exaggerated. My post are all (IMO) unless stated otherwise.

10th July 2007, 05:10 AM	#299
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Actually, what I find really annoying is moving avatars! You have no idea how many times I've watched that damn wheel go round.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

10th July 2007, 11:09 AM	#300
robinson Banned Join Date: Aug 2006 Posts: 6,136	What wheel?
robinson Banned Join Date: Aug 2006 Posts: 6,136

10th July 2007, 11:52 AM	#301
Paulhoff You can't expect perfection. Join Date: May 2005 Location: South Florida Posts: 12,575	The perpetual motion machine that doesn’t work. Paul
	__________________ For our money "IN WHICH GOD DO YOU TRUST" Much worse than the Question not asked, is the Answer not Given Don't accept an answer that can't be questioned - God is Surperfluous A society fails when ignorance outweighs knowledge Science doesn’t know everything, but religion doesn’t know anything Life is so horrent and also so beautiful, but without it there is nothing

10th July 2007, 01:33 PM	#302
ynot Illuminator Join Date: Jan 2006 Location: New Zealand Posts: 4,731	Originally Posted by Paulhoff The perpetual motion machine that doesn’t work. Paul Whadaya mean “doesn’t work”!!?? Do you deny the evidence before you? I offer further indisputable proof . . . Now how am I going to spend that million bucks?
	__________________ Rumours of a god’s existence have been greatly exaggerated. My post are all (IMO) unless stated otherwise.

3rd February 2008, 04:50 PM	#303
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Hey ynot, did you ever sort out your dilemma regarding this issue? I had been pondering relativity lately, found this thread and started reading it with a completely compatible opinion of your first post. Midway through the first page it suddenly struck me, and i think i understand the concept now. The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space. Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective. (please anyone, correct me if i am wrong here)
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Last edited by schlitt; 3rd February 2008 at 04:51 PM.

4th February 2008, 03:22 AM	#304
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Originally Posted by schlitt Midway through the first page it suddenly struck me, and i think i understand the concept now. The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space. Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective. (please anyone, correct me if i am wrong here) Yes, unfortunately, you are wrong. What is really happening is what is happening from the point of view of someone at the point in space where it is actually happening. Everyone else sees something different happening, but that is only what seems to be happening from their point of view, not what is really happening. However, they can find out what is really happening by using the math derived from relativity theory to calculate what is happening at the point in space where it is actually happening. I hope that makes sense.... ....because it is a serious answer. regards, BillyJoe
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

4th February 2008, 11:50 AM	#305
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Originally Posted by BillyJoe Yes, unfortunately, you are wrong. What is really happening is what is happening from the point of view of someone at the point in space where it is actually happening. Everyone else sees something different happening, but that is only what seems to be happening from their point of view, not what is really happening. However, they can find out what is really happening by using the math derived from relativity theory to calculate what is happening at the point in space where it is actually happening. I hope that makes sense.... ....because it is a serious answer. regards, BillyJoe OK, I understand what you are saying. But surely the person who is "at the point in space where it is actually happening" as you put it, is still merely seeing the event relative to themselves. The fact they are closer gives less dilation, but still some nevertheless? (unless everything were 100% static?) Time comes from the measurement of movement through space, so those viewing a moving object at distance are not "wrong", in their measurements, they simply need to be adjusted for in relation to measurements taken at the source of the event measured (or anywhere else for that matter), due to the time measurement at that point being different. Given the parameters, this can be done mathematically. Does that sound right?
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Last edited by schlitt; 4th February 2008 at 12:10 PM.

4th February 2008, 12:38 PM	#306
Tumbleweed Muse Join Date: Dec 2006 Location: Port Orchard, WA Posts: 555	Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously

4th February 2008, 02:42 PM	#307
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,285	Originally Posted by Tumbleweed Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously No. Only one reality exists. The traveling twin will be younger when they reunite, they will both agree on that. The difficulty many newcomers to relativity have with the problem is the fact that superficially it seems like it should be symmetric, but it isn't, and any complete analysis of the problem will reveal that asymmetry.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law Last edited by Ziggurat; 4th February 2008 at 02:43 PM.

4th February 2008, 03:19 PM	#308
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Originally Posted by schlitt The problem comes with viewing an event as happening with one true timeframe. When in reality, time does not work like this, time is created by the relative viewer, in relation the the event in space. Once you abandon the idea that there is one true measure for a single event, you see how everyone's relative perspective is the only thing that matters, and this means their perspectives have to be adjusted for, if you are relying in information to be synchronized between each perspective. (please anyone, correct me if i am wrong here) I don't know if you're wrong, but I also don't quite understand what you're saying. What I do know is that you need to consider at least two events to find any disagreement between different observers.
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912

4th February 2008, 03:26 PM	#309
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912	Originally Posted by Tumbleweed Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously What Ziggurat said. If you want to understand this problem, you will have understand the space-time diagram in post #239, so I suggest you start there.
Fredrik Graduate Poster Join Date: Jun 2004 Posts: 1,912

4th February 2008, 03:43 PM	#310
Paulhoff You can't expect perfection. Join Date: May 2005 Location: South Florida Posts: 12,575	Originally Posted by Tumbleweed Lets get back to the twins again. Once they are reunited back on earth, which one is going to tell the other that, despite appearances, there can be only one reality and they are both in fact the same age. Or are both realities existing simultaneously The one that traveled is younger. Paul
	__________________ For our money "IN WHICH GOD DO YOU TRUST" Much worse than the Question not asked, is the Answer not Given Don't accept an answer that can't be questioned - God is Surperfluous A society fails when ignorance outweighs knowledge Science doesn’t know everything, but religion doesn’t know anything Life is so horrent and also so beautiful, but without it there is nothing

4th February 2008, 03:48 PM	#311
Tumbleweed Muse Join Date: Dec 2006 Location: Port Orchard, WA Posts: 555	Oh I fully agree that there is one final reality - that the twins are indeed of separate age, but they traveled different realities - or frames of reference- to get to the new frame of reference/reality. And I get that it got that way because distance was being traded, basically for time. V still equals d/t in each frame of reference And I agree that the time dilation is one way and not symmetrical. In other words, the rocket is speeding away from the Earth and not also vice versa

4th February 2008, 04:09 PM	#312
Tumbleweed Muse Join Date: Dec 2006 Location: Port Orchard, WA Posts: 555	Here's a puzzle that has always bugged me. You have two objects headed towards each other at the speed of light. They acheive this by each approaching a fixed point in a straight line in space at half the speed of light. Taking the twins thingie and relativity's time/distance differential to the extreme, would not the distance between the two objects shrink to zero (for them only) no matter how many light years they are said to be apart as judged by a third observer? Or looking at it another way, would the elapsed time clock on each space ship read zero (as well as the odometer) when they met, again regardless of how many light years they appear to be apart by an independent observer. Or even regardless as to ANY outside observation, not within their frame of reference

4th February 2008, 04:19 PM	#313
sol invictus Philosopher Join Date: Oct 2007 Location: Nova Roma Posts: 8,435	Originally Posted by Tumbleweed Here's a puzzle that has always bugged me. You have two objects headed towards each other at the speed of light. They acheive this by each approaching a fixed point in a straight line in space at half the speed of light. Taking the twins thingie and relativity's time/distance differential to the extreme, would not the distance between the two objects shrink to zero (for them only) no matter how many light years they are said to be apart as judged by a third observer? No. Velocities don't add like that in relativity. Each object will see the other moving towards it at 4/5 the speed of light. http://en.wikipedia.org/wiki/Velocity-addition_formula

4th February 2008, 04:32 PM	#314
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Originally Posted by Fredrik I don't know if you're wrong, but I also don't quite understand what you're saying. What I do know is that you need to consider at least two events to find any disagreement between different observers. Yes, i agree. The discrepancy between the two events is real, due to time being linked with the observer. The concept that there is no absolute time is what i think throws a lot of people.
schlitt Graduate Poster Join Date: Jun 2007 Posts: 1,081	Last edited by schlitt; 4th February 2008 at 04:32 PM.

4th February 2008, 04:36 PM	#315
Tumbleweed Muse Join Date: Dec 2006 Location: Port Orchard, WA Posts: 555	Originally Posted by sol invictus No. Velocities don't add like that in relativity. Each object will see the other moving towards it at 4/5 the speed of light. http://en.wikipedia.org/wiki/Velocity-addition_formula Okay assuming its only .8 the speed of light. It would still take far less time for them to meet as far as their clocks are concerned, as compared to an outside observors calculations using Newtonian physics would have calculated, right? The inference being that the vast distances to the galaxies might be not be that, the distance depending on relative velocity instead of Newtonian calculations