TIME DILATION. WHY do clocks that are

[Denius1704]

In a last effort to try and understand your explanations of relativity i will put the "paradox" in an example and i would like to "hear" from you what the exact explanation from the point of view of relativity will be.

The one twin is sitting on Earth, the other one is moving away at certain speed (let's use the half the speed of light example). So from the point of view of the twin on Earth, the moving one is aging two times slower than him and when he comes back to Earth he will be much younger, but... From the point of view of the moving twin, the one sitting on Earth will also be aging two times slower, because well... according to him, it is his brother that is moving away not him. So when he comes back to Earth, his brother would be much younger. Now if we assume that the time dilation happened, then both brothers would have aged less, equally... which will put them at the same age when they meet up with each other. So from what point of view would have the time dilation actually happened? From the perspective of a third observer? How would they be able to distinguish that time actually slowed down for any of them?

Or... Does the time dilation happen only for the "moving" brother, but not for the one sitting on Earth? And if so then how come the moving brother experiences only an illusion of the one sitting on Earth aging slower than him, without the actual time dilation, but the one sitting on Earth doesn't?

I know you said that this "paradox" is a paradox only to the people not using Relativity properly so i am asking how would one use Relativity properly to explain it and rule it out as an actual paradox?

 

[Dale]

I know you said that this "paradox" is a paradox only to the people not using Relativity properly so i am asking how would one use Relativity properly to explain it and rule it out as an actual paradox?

There are many ways to explain the twin paradox: http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

My favorite way is the spacetime diagram approach, but you should read them all and pick the one you like the best.

 

[ghwellsjr]

In a last effort to try and understand your explanations of relativity i will put the "paradox" in an example and i would like to "hear" from you what the exact explanation from the point of view of relativity will be.

The one twin is sitting on Earth, the other one is moving away at certain speed (let's use the half the speed of light example). So from the point of view of the twin on Earth, the moving one is aging two times slower than him and when he comes back to Earth he will be much younger, but... From the point of view of the moving twin, the one sitting on Earth will also be aging two times slower, because well... according to him, it is his brother that is moving away not him. So when he comes back to Earth, his brother would be much younger. Now if we assume that the time dilation happened, then both brothers would have aged less, equally... which will put them at the same age when they meet up with each other. So from what point of view would have the time dilation actually happened? From the perspective of a third observer? How would they be able to distinguish that time actually slowed down for any of them?

Or... Does the time dilation happen only for the "moving" brother, but not for the one sitting on Earth? And if so then how come the moving brother experiences only an illusion of the one sitting on Earth aging slower than him, without the actual time dilation, but the one sitting on Earth doesn't?

I know you said that this "paradox" is a paradox only to the people not using Relativity properly so i am asking how would one use Relativity properly to explain it and rule it out as an actual paradox?

I can see you like round numbers. Unfortunately, your example is flawed. You would have to go to a speed of 0.866c to get each twin to age two times slower than his twin, so with your permission, I'd like to illustrate what happens at a different speed, 0.6c because it makes the arithmetic come out in nice easy numbers.

At a speed of 0.6c the time dilation factor is 0.8. So let's assume that both twins are going to watch the other one age during the trip. There are many ways we could do this but let's just say that each twin has a blinking light that flashes exactly once per second and they each count the other one's flashes during the trip. As soon as the traveler starts out at 0.6c, they will each observe the other one flashing at exactly one have the rate of their own. This is a combination of time dilation and the delay in the light travel time.

Let's say that after many days, the traveler turns around. He will immediately now see the flashes from his Earth bound twin come in at double his own rate. But what will the Earth bound twin see? Well, he won't see anything different until several days later because the sight of his twin turning around is subject to the delay in the light travel time. Eventually though, he will see the light flashes coming from his twin suddenly go from one half his rate to double his rate. But this will happen near the end of the trip. It is this imbalance in the ratio of the observed rates by each twin of the other twin's flashes that accounts for the difference in the total count that each one makes of his twin's flashes and thus the amount that each one has aged during the trip.

Look up Relative Doppler for more details.

 

[sisoev]

The delay is proportional to the distance (delay=dist/c). Assuming that the U-turn maintains a constant distance to the observer then there is a delay, but it is constant during the turn. Despite the fact that the delay is not changing, time dilation is observed. This is known as the transverse Doppler effect, and has been experimentally measured.

This is not correct. As I said above, this has been experimentally measured. Both with the frequency of emitted radiation as well as with the lifetime of unstable particles. I.e. both clocks based on EM and clocks based on the strong and weak nuclear forces demonstrate time dilation.

I cannot find any reason of why the delay will be proportional to the distance.
It makes more sense to say that it is proportional to the light shift, because the light shift represents the distance.

I cannot also imagine that the light from a moving in circle object will be red shifted.
It is probably an error.
Since we do the measurements, the light travels in our frame of reference and since there is no difference in the distance, it MUST not show shift to red or blue, otherwise we will observe a paradox.

The red shift claim for circular moving object is very much like the explanation of the http://en.wikipedia.org/wiki/Ladder_paradox" ; it says that although both doors open simultaneously the ladder will see that the closer door opens first.
That's wrong, because the ladder sees the doors as light reflection and since the back door opens simultaneously with the front door, there will not be door at the back, to reflect a ligh which will travel to the lader and show a presence of a door.
To imagine it in easy way, we can put light source on the inside of the back door, and the switch to turn the light on we place on the front door when it opens completely.
If they open simultaneously, the ladder will never see the light beam from the back door, because new paradox will emerge; we will have two light beams, one directed to the ladder and one perpendicular down from the opened back door.

What do you say about that, DaleSpam?

Same is with the red shift of the light from a moving in circle clock.
If we say that we observe red shift, the clock will still see its own reflection from a mirror on "our side" as not shifted in any direction light. I put "Our side" between quotation marks, because we are actually a mirror in the clock's frame of reference.
In that case we will end up with two different wave lengths for same light, measured on same distance in two frames of reference.

 

[Denius1704]

I can see you like round numbers. Unfortunately, your example is flawed. You would have to go to a speed of 0.866c to get each twin to age two times slower than his twin, so with your permission, I'd like to illustrate what happens at a different speed, 0.6c because it makes the arithmetic come out in nice easy numbers.

As i stated in my first post i am not a physicist and the last time i used higher math was 12 years ago, so my use of numbers was just abstract to illustrate my point.

Let's say that after many days, the traveler turns around. He will immediately now see the flashes from his Earth bound twin come in at double his own rate. But what will the Earth bound twin see? Well, he won't see anything different until several days later because the sight of his twin turning around is subject to the delay in the light travel time. Eventually though, he will see the light flashes coming from his twin suddenly go from one half his rate to double his rate. But this will happen near the end of the trip. It is this imbalance in the ratio of the observed rates by each twin of the other twin's flashes that accounts for the difference in the total count that each one makes of his twin's flashes and thus the amount that each one has aged during the trip.

Look up Relative Doppler for more details.

So from what i understand it is the turnaround that gives the difference. What i don't understand is how come only the Earth bound twin takes into account this turnaround? I mean, the moving brother might not see the Earth bound one turn around, but from his point of view he would have stopped moving away from him, so for that amount of time the flashes would come at the same rate as his own flashes going out. But the same should be said for the Earth bound brother. He should see a transition from the 1/2 rate to 1 rate to 2 (double rate). It was even said in a previous post that time delay would change during a half circle turnaround. So basically both brothers should still experience the same changes.

Or it would be even simpler if we take out the whole turnaround event. Since this is purely theoretical example we can put an event of instant turnaround where the moving brother goes through one portal and comes out another at exactly the same distance but moving in reverse direction (towards Earth). That way the Earth bound brother won't have the turnaround event to mess things up for him. What happens in that situation then?

DaleSpam i opened that page you linked, and i still find it difficult to agree with the explanations. I take into consideration the fact that i don't understand most of the math in there, but still... the example that you prefer with the graph still takes into account only the POV of the Earth bound and does its math only from there. I opened another explanation which thankfully didn't have any math in it and the way they used to explain it there was with the whole inertial frame missing from the one brother. But even there they write that a possibility of the moving brother not experiencing any acceleration and gravitational forces with an instant turnaround could be considered and the explanation of that was left to the "reader". I take that as a failure to explain the problem fully and explaining it only when certain conditions are met and others aren't.

 

[ghwellsjr]

As i stated in my first post i am not a physicist and the last time i used higher math was 12 years ago, so my use of numbers was just abstract to illustrate my point.

The math in Special Relativity is very simple. If you have a calculator with a square root function, that's all you need. General Relativity, which involves gravity, requires very complex math. So please be content to leave gravity out of the discussions until you have mastered SR.

So from what i understand it is the turnaround that gives the difference. What i don't understand is how come only the Earth bound twin takes into account this turnaround? I mean, the moving brother might not see the Earth bound one turn around, but from his point of view he would have stopped moving away from him, so for that amount of time the flashes would come at the same rate as his own flashes going out. But the same should be said for the Earth bound brother. He should see a transition from the 1/2 rate to 1 rate to 2 (double rate). It was even said in a previous post that time delay would change during a half circle turnaround. So basically both brothers should still experience the same changes.

If you want the traveler to stop first and then turn around and start his journey home, then yes, there would be the transitions from 1/2 rate to the 1 rate to the double rate, and you are correct that the traveler sees this as soon as he stops and turns around. And the Earth twin will see exactly the same thing but not at the moment it happens because he has to wait for the flashes in travel over a very great distance to reach him which will take a long time.

Or it would be even simpler if we take out the whole turnaround event. Since this is purely theoretical example we can put an event of instant turnaround where the moving brother goes through one portal and comes out another at exactly the same distance but moving in reverse direction (towards Earth). That way the Earth bound brother won't have the turnaround event to mess things up for him. What happens in that situation then?

If I'm understanding you correctly, this is essentially what I was describing originally, that is, I didn't worry about how the traveling twin actually got turned around, I just assumed that he instantly changed from going away from the Earth (seeing 1/2 flash rate) to going toward the Earth (double flash rate).

So the bottom line is that the traveler counts the half-rate flashes from the Earth twin for the same amount of time that he counts the double-rate flashes, but the Earth twin counts the low-rate flashes from the traveler for most of the trip and doesn't start counting the high-rate flashes until near the end so he ends up with a much smaller count than the traveler does. And remember, they are each counting the one-second flashes from the other twin.

 

[sisoev]

........
And the Earth twin will see exactly the same thing but not at the moment it happens because he has to wait for the flashes in travel over a very great distance to reach him which will take a long time.
.........
So the bottom line is that the traveler counts the half-rate flashes from the Earth twin for the same amount of time that he counts the double-rate flashes, but the Earth twin counts the low-rate flashes from the traveler for most of the trip and doesn't start counting the high-rate flashes until near the end so he ends up with a much smaller count than the traveler does. And remember, they are each counting the one-second flashes from the other twin.

ghwellsjr, both brothers will see absolutely the same in a mirror turned image and will count flashes in absolutely the same ratio, since they are at same distance with same velocity relative to each other.
You'll eventually need to include the acceleration of the flying brother, but I don't see how that would resolve the time difference, because the brother on Earth (or in a motionless space craft) also sees himself as accelerating away. If the G-force during the acceleration helps somehow, then you will be right :)

 

[Dale]

DaleSpam i opened that page you linked, and i still find it difficult to agree with the explanations.

Well, the question was how relativity would explain it. All of those explanations are valid under relativity. It sounds like you do not understand relativity. Unfortunately for you, the experimental evidence is overwhelming. There is no avoiding relativity.

the explanation of that was left to the "reader". I take that as a failure to explain the problem fully and explaining it only when certain conditions are met and others aren't.

I think this is a little unfair to call a "failure". It is not possible for any document to cover everything. So any document must make a choice about what to cover and what not to cover. Then everything else is left to the reader or to other documents.

 

[ghwellsjr]

ghwellsjr, both brothers will see absolutely the same in a mirror turned image and will count flashes in absolutely the same ratio, since they are at same distance with same velocity relative to each other.
You'll eventually need to include the acceleration of the flying brother, but I don't see how that would resolve the time difference, because the brother on Earth (or in a motionless space craft) also sees himself as accelerating away. If the G-force during the acceleration helps somehow, then you will be right :)

The ratios that I'm talking about are not the 1/2 and double rates but rather the length of time that each twin sees those rates coming from the other twin. I will be 50-50 for the traveler and 80-20 for the Earth twin.

Earlier in this thread you have been asking about the light travel time but now you seem to believe that it is non-existent. Are you saying that when the traveler is far away from the Earth twin, the Earth twin will still see him change direction half way through the trip and he won't have to wait for the light from that action to reach him? If you believe this, then you are believing in action-at-a-distance or an infinite speed for light. Are you sure you want to maintain this position?

 

[sisoev]

The ratios that I'm talking about are not the 1/2 and double rates but rather the length of time that each twin sees those rates coming from the other twin. I will be 50-50 for the traveler and 80-20 for the Earth twin.

Earlier in this thread you have been asking about the light travel time but now you seem to believe that it is non-existent. Are you saying that when the traveler is far away from the Earth twin, the Earth twin will still see him change direction half way through the trip and he won't have to wait for the light from that action to reach him? If you believe this, then you are believing in action-at-a-distance or an infinite speed for light. Are you sure you want to maintain this position?

ghwellsjr with the twin brothers example you better think of the speed as of velocity, because in absence of a third object the speed is irrelevant.

Now try to imagine what happens to both brothers and you'll see no difference for both of them. One of them will do the real traveling, but the other will see himself as traveling the same path with the same acceleration, speed, turning around and arriving back.

When the "brother in motion" turns back, he will keep seeing the flashes sent to him before he turned back, and some time latter he will start seeing the flashes sent after he turned around.
Same for the other brother; he will see himself as turning around some time later after the "real turn" was made from his brother.

I do not imply limitless light speed in this example, for there is no space for such suggestion.

 

[Dale]

I cannot find any reason of why the delay will be proportional to the distance.
It makes more sense to say that it is proportional to the light shift, because the light shift represents the distance.

Your comment here does not make sense. Do you understand that a light pulse travels a distance of \Delta d = c \Delta t therefore the distance is proportional to the time and vice versa.

I cannot also imagine that the light from a moving in circle object will be red shifted.

A failure of imagination on your part does not change the facts. The light from an object moving in a circle, or tangentially to you, is red shifted. Did you not read the link I posted?

The red shift claim for circular moving object is very much like the explanation of the http://en.wikipedia.org/wiki/Ladder_paradox" ; it says that although both doors open simultaneously the ladder will see that the closer door opens first.
That's wrong, because the ladder sees the doors as light reflection and since the back door opens simultaneously with the front door, there will not be door at the back, to reflect a ligh which will travel to the lader and show a presence of a door.

Again, you are under the misapprehension that SR is about visual appearances. The light delay is accounted for. SR is about what happens after accounting for the delay due to the finite speed of light.

we will end up with two different wave lengths for same light, measured on same distance in two frames of reference.

What do you mean by this? The wave lengths are different in different frames of reference, but I am not sure what you mean by the qualifier "measured on the same distance".

 

[ghwellsjr]

ghwellsjr with the twin brothers example you better think of the speed as of velocity, because in absence of a third object the speed is irrelevant.

OK, then let the Earth be that third object and change every occurrence of "speed" to "velocity" in my previous explanations.

Now try to imagine what happens to both brothers and you'll see no difference for both of them. One of them will do the real traveling, but the other will see himself as traveling the same path with the same acceleration, speed, turning around and arriving back.

When the "brother in motion" turns back, he will keep seeing the flashes sent to him before he turned back, and some time latter he will start seeing the flashes sent after he turned around.
Same for the other brother; he will see himself as turning around some time later after the "real turn" was made from his brother.

So much of what you say is true and I don't see why you aren't grasping this simple concept: There is a big difference between what the two brothers see. A brother that actually turns around will immediately see a difference in the other brother's flash rate whereas the other brother won't see it til the pattern of flashes gets transmitted from his distant brother to him.

If you don't agree with this can you please explain where you think I'm wrong?

I do not imply limitless light speed in this example, for there is no space for such suggestion.

Good.

 

[dumbperson]

I have a question about time too.

Sorry if this is a dumb question:

if there's a moving train with a mirror in it, and an observer(guy1) inside the train shines a light into it and measures the time it takes for it to get to the mirror and come back. He will measure a shorter time than an observer(guy2) outside of the train that is standing still. So the observer(guy2) says the time goes slower inside the train because its moving, but can the observer(guy1) in the train not say that time is going slower for the guy2 because in guy1's restframe guy 2 is moving? if so can someone explain this to me?

sorry if this is a dumb question, I am just curious

 

[sisoev]

Your comment here does not make sense. Do you understand that a light pulse travels a distance of \Delta d = c \Delta t therefore the distance is proportional to the time and vice versa.

The same distance can be traveled by light sent from approaching source, from departing source or from still source. Then same distance will be covered respectively by blue, red shifted, or unchanged light.
You'll probably ask me how this change anything.

Few posts earlier I asked you the question "what do we consider as light and how do we measure its speed". One photon is not light and its speed should not represent the speed of light.
The speed of light should be represented by the frequency with which we meet every successive wave. The faster we move through the waves the faster we meet every next one thus changing the frequency, respectively the "speed of light". This way we will see that the speed of light depends on the speed of the observer and on the speed of the source.
If you accept this, the theory of relativity will start to make no sense.

Again, you are under the misapprehension that SR is about visual appearances. The light delay is accounted for. SR is about what happens after accounting for the delay due to the finite speed of light.

No, I'm not under such misapprehension, but SR should take into account that some things work only one way and no relativity can be applied to them.
The example with the two garage doors treats overlapping simultaneous events to which you cannot apply simultaneity for the simple reason that you cannot observe them as two events; you see only one of them and you should treat them as one.
The fact that you KNOW about the second event does not make it present to work with it and to apply values to it for later use.
Ignoring this will create paradoxes like the example I gave you with the two light beams from the back garage door.

What do you mean by this? The wave lengths are different in different frames of reference, but I am not sure what you mean by the qualifier "measured on the same distance".

The wave length depends on the speed of the source and it cannot be different if the distance to the observer is not changed, but please ignore this for now.

 

[sisoev]

OK, then let the Earth be that third object and change every occurrence of "speed" to "velocity" in my previous explanations.

Ha-ha :)
Sometime I also need to adjust the environment and the events to my way of thinking, and then I know that I'm somewhere wrong.

So much of what you say is true and I don't see why you aren't grasping this simple concept: There is a big difference between what the two brothers see. A brother that actually turns around will immediately see a difference in the other brother's flash rate whereas the other brother won't see it til the pattern of flashes gets transmitted from his distant brother to him.

If you don't agree with this can you please explain where you think I'm wrong?

The trick for the right comprehension is to think for both brothers as symmetrically placed for the events in time.
If the departing brother measures x distance, the other will measure it as x as well, and if one of them measure n velocity it is n for the other as well.
Both of them observe the other with the same delay since they are symmetrically placed from the point in time where the events started.

 

[Dale]

The speed of light should be represented by the frequency with which we meet every successive wave. The faster we move through the waves the faster we meet every next one thus changing the frequency, respectively the "speed of light". This way we will see that the speed of light depends on the speed of the observer and on the speed of the source.

Pure nonsense. The units are not even correct. Frequency is in units of 1/time and speed is in units of distance/time. The frequency cannot possibly be the speed of light.

If you accept this, the theory of relativity will start to make no sense.

Good thing I don't accept it then.

No, I'm not under such misapprehension, but SR should take into account that some things work only one way and no relativity can be applied to them.

There are indeed many things that are invariant under the Lorentz transform. SR does take those into account. In fact, in some sense SR is primarily the study of these invariant quantities.

The wave length depends on the speed of the source and it cannot be different if the distance to the observer is not changed, but please ignore this for now.

OK, but it is wrong.

Please study this page, you seem to be under some severe misconceptions about how things work: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

 

[ghwellsjr]

The trick for the right comprehension is to think for both brothers as symmetrically placed for the events in time.
If the departing brother measures x distance, the other will measure it as x as well, and if one of them measure n velocity it is n for the other as well.
Both of them observe the other with the same delay since they are symmetrically placed from the point in time where the events started.

How can you think that both brothers are symmetrically placed from the point in time where the events started when one of them is causing the event to happen (he's turning around) and the other one is observing it from afar?

 

[sisoev]

Pure nonsense. The units are not even correct. Frequency is in units of 1/time and speed is in units of distance/time. The frequency cannot possibly be the speed of light.

I said "represented" not "measured", DaleSpam

Pardon me, but the rest of your answer seams very much like a dodging.
The fact that SR takes into account "many things that are invariant under the Lorentz transform" does not answer how do you see the "overlapping simultaneous events" (the two garage doors)
Not mentioning that my note puts in doubt an important part of SR.
I guess I have to wait until someone else comes with explanation.

I can imagine how annoying a guy like me can be in the midst of a company like you guys.
Later these days I'll post a thought experiment with graphics and after your answer I'll stop bothering you :)

I wish you a great weekend :)

 

[sisoev]

How can you think that both brothers are symmetrically placed from the point in time where the events started when one of them is causing the event to happen (he's turning around and the other one is observing it from afar?

The "turning around" event has no special meaning in the experiment, ghwellsjr
It is "experienced" from the other brother the same way as the brother who executes the event. The only difference is that if the real turn is to right, the other brother sees it as to left.
Once they start approaching each other in straight line, the tings are the same.
Both of them will observe the events with the same rate ratio.

 

[Dale]

I said "represented" not "measured", DaleSpam

You will have to explain the difference and the relevance then. How do you transform from the frequency "representation" to the actual speed?

Not mentioning that my note puts in doubt an important part of SR.

The only thing in doubt is your understanding of physics.

Later these days I'll post a thought experiment with graphics

I will look forward to it. Your description of the garage door paradox is unclear, so a picture would be useful.

 

[sisoev]

You will have to explain the difference and the relevance then. How do you transform from the frequency "representation" to the actual speed?

This will come with the experiment I intend to present with graphics.

I will look forward to it. Your description of the garage door paradox is unclear, so a picture would be useful.

DaleSpam, talking to you is like talking to my teacher and I appreciate your patience. I really do.

I cannot add more to the way I see the ladder experiment.
My point is that we cannot treat an overlapping simultaneous events like a simultaneity since the light from them brings information only for one of them.
To elaborate; if the simultaneous events are aligned with the observer, there will not be light information for the back event, because it is simultaneous with the front.
We know about the back event, but we cannot deal with its light information because it is absent for us.
If we take this into account, we will see that the explanation for the ladder paradox fails.
Therefore the rod contraction is false too.
Hence, the theory of relativity stands incorrect.

 

[Dale]

The "turning around" event has no special meaning in the experiment, ghwellsjr
It is "experienced" from the other brother the same way as the brother who executes the event.

This is factually incorrect. An accelerometer carried by one brother detects the g-forces of the turnaround, and an accelerometer carried by the other does not. The frequency of the pulses from the other brother changes immediately for one brother (the same one that detects the g-forces) and not for the other. The experiences of the two brothers are not the same.

 

[Dale]

My point is that we cannot treat an overlapping simultaneous events like a simultaneity since the light from them brings information only for one of them.

What do you even mean by the phrase "overlapping simultaneous events"?

 

[sisoev]

What do you even mean by the phrase "overlapping simultaneous events"?

Aligned with the observer.

 

[Dale]

How is an event aligned with anything, let alone an observer? When I use the word "aligned" I mean that two things which have some associated direction or axis are parallel. Events do not have a direction or an axis. Do you mean something like the event is on the observer's worldline?

 

[sisoev]

How is an event aligned with anything, let alone an observer?

Well, an event is actually light information for an observer.
Now, align the light information for the two simultaneous events with the observer and you'll have the information only for the front event.

 

[Dale]

Well, an event is actually light information for an observer.

No, an event is a given place at a given time. I.e. the airplanes crashed at an altitude of 2 miles, at lattitude 45º, longitude 30º, at 3:00 pm. That is an event. The light emanating from that event forms a light cone with the origin at the event. The event is a 0-dimensional set, the light cone is a 3-dimensional set.

Now, align the light information for the two simultaneous events with the observer and you'll have the information only for the front event.

Are you simply saying something to the effect that opaque objects (like garage doors) absorb light so you lose information about things on the other side of the object? If so, then simply make the doors out of glass.

 

[sisoev]

This is factually incorrect. An accelerometer carried by one brother detects the g-forces of the turnaround, and an accelerometer carried by the other does not. The frequency of the pulses from the other brother changes immediately for one brother (the same one that detects the g-forces) and not for the other. The experiences of the two brothers are not the same.

The g-force doesn't only change the frequency of the emitted signals, but also the frequency of the perceived ones.

 

[Dale]

The g-force doesn't only change the frequency of the emitted signals, but also the frequency of the perceived ones.

Do you agree that only one of the twins measures g-forces?

 

[Denius1704]

I think he is trying to say that how can we see any light reflected from the back door (so as to give the perception of it opening later than the front door) if that said back door opened at exactly the same time as the front one. Where would the information of that back door opening be carried and how would we perceive it? That is if I'm understanding his argument correctly.

 

[sisoev]

No, an event is a given place at a given time. I.e. the airplanes crashed at an altitude of 2 miles, at lattitude 45º, longitude 30º, at 3:00 pm. That is an event. The light emanating from that event forms a light cone with the origin at the event. The event is a 0-dimensional set, the light cone is a 3-dimensional set.

No, an event is a light information.
No light information - no observation of an event.
If we don't observe an event we cannot measure its values.
You can set a values for non-observed event, like in the explanation of the ladder paradox but that holds the risk to create new paradox, and I think that SR has already enough of them ;)

Are you simply saying something to the effect that opaque objects (like garage doors) absorb light so you lose information about things on the other side of the object? If so, then simply make the doors out of glass.

What I am saying is that if you turn two book pages at once you'll see the first and the third.
Hope that this is easy enough to picture it out :)

 

[sisoev]

Do you agree that only one of the twins measures g-forces?

Yes, how couldn't I :)

 

[Denius1704]

This is factually incorrect. An accelerometer carried by one brother detects the g-forces of the turnaround, and an accelerometer carried by the other does not. The frequency of the pulses from the other brother changes immediately for one brother (the same one that detects the g-forces) and not for the other. The experiences of the two brothers are not the same.

When i suggested the example i thought we all agreed that there is no turnaround event, so what g-forces are we talking about now?

Imagine the guy from Earth was watching the one moving away and then the next second moving towards him. Why would the light need more time to reach the Earth guy all of a sudden if it was reaching him just fine until the last moment of moving away? If we are imagining an uninterrupted flow of light from the moment of departure to the moment the moving brother switches directions, i imagine the image the Earth brother would receive would be a sudden shift from the 1/2 rate to the 2 rate. And the same thing would occur for the moving brother as well, like a "mirror" as sisoev suggested.

Now, apparently my imagination is very wrong and the logic i am using as well, otherwise SR would not exist today. What i am asking for is not answers such as "you are wrong" and "well that doesn't happen because it's been accounted for", but instead to be shown where my logic breaks, at which point? I am not asking for mathematical equations, because when a client comes to me to explain to him a problem with the software i don't start talking to him in 0's and 1's, but instead i try and talk his language, the one he understands. Otherwise we will be sitting on this thread for weeks everyone saying the same things not understanding the others.

And for the sake of eliminating any kind of G-Force let's imagine both brother in space in their own respective space ships, with the moving ship being equipped with inertial dampeners (or whatever they call them in the movies these days) so that if there is ANY kind of change in acceleration it will not be felt at all by either the ship or the person in the ship.

 

[Dale]

No, an event is a light information.
No light information - no observation of an event.
If we don't observe an event we cannot measure its values.
You can set a values for non-observed event, like in the explanation of the ladder paradox but that holds the risk to create new paradox, and I think that SR has already enough of them ;)

No, this is incorrect. An event is something which happens at a given place at a given instant of time:
http://en.wikipedia.org/wiki/Event_(relativity )
http://www.colvir.net/prof/richard.beauchamp/rel-an/rela.htm
http://www.hep.uiuc.edu/home/g-gollin/relativity/p112_relativity_7.html

What I am saying is that if you turn two book pages at once you'll see the first and the third.
Hope that this is easy enough to picture it out :)

Sure, pages are opaque. No big deal, just make the garage doors partially transparent.

 

[Dale]

Yes, how couldn't I :)

Since you agree that one twin measures the g forces and the other twin does not then it is clear that the twins experience the turnaround differently. So your earlier claim is not correct:

The "turning around" event has no special meaning in the experiment, ghwellsjr
It is "experienced" from the other brother the same way as the brother who executes the event.

The brother who executes the turn experiences g forces, the other does not. It is not experienced the same way.

 

[Dale]

When i suggested the example i thought we all agreed that there is no turnaround event, so what g-forces are we talking about now?

Sorry, I thought we were talking about the standard twins paradox. If there is no turnaround/no g-forces then the twins never reunite so there is no way to unambiguously compare their ages.

Imagine the guy from Earth was watching the one moving away and then the next second moving towards him. Why would the light need more time to reach the Earth guy all of a sudden if it was reaching him just fine until the last moment of moving away? If we are imagining an uninterrupted flow of light from the moment of departure to the moment the moving brother switches directions, i imagine the image the Earth brother would receive would be a sudden shift from the 1/2 rate to the 2 rate. And the same thing would occur for the moving brother as well, like a "mirror" as sisoev suggested.

If there are no g-forces then there will be no shift in rate at all. The rate will be permanently 1/2.

Now, apparently my imagination is very wrong and the logic i am using as well, otherwise SR would not exist today. What i am asking for is not answers such as "you are wrong" and "well that doesn't happen because it's been accounted for", but instead to be shown where my logic breaks, at which point? I am not asking for mathematical equations, because when a client comes to me to explain to him a problem with the software i don't start talking to him in 0's and 1's, but instead i try and talk his language, the one he understands. Otherwise we will be sitting on this thread for weeks everyone saying the same things not understanding the others.

I think we first need to clarify what scenario we are talking about. Do you want to have two perpetually inertial observers (no reunion, no unambiguous comparison of ages, no change in signal rate, perfectly symmetrical) or do you want to have one of the twins be non-inertial (g-forces, asymmetrical)? You cannot have it both ways.

And for the sake of eliminating any kind of G-Force let's imagine both brother in space in their own respective space ships, with the moving ship being equipped with inertial dampeners (or whatever they call them in the movies these days) so that if there is ANY kind of change in acceleration it will not be felt at all by either the ship or the person in the ship.

That cannot be done in flat spacetime, and if you are struggling with the twins paradox then we definitely do not want to go to curved spacetime as that cannot be done effectively without some rather hairy math.

 

[sisoev]

No, this is incorrect. An event is something which happens at a given place at a given instant of time:
http://en.wikipedia.org/wiki/Event_(relativity )
http://www.colvir.net/prof/richard.beauchamp/rel-an/rela.htm
http://www.hep.uiuc.edu/home/g-gollin/relativity/p112_relativity_7.html

I'm not even considering reading the links :)
The argument takes philosophical turn.
We couldn't talk about given place and given time if we didn't observe the event at given place and given time.
So "given place" and "given time" are properties of known event.
It becomes known through observation.
Observation becomes such through light information delivered to conscious mind or apparatus which will deliver the recorded information for the event to a conscious mind.

Sure, pages are opaque. No big deal, just make the garage doors partially transparent.

That won't change anything, DaleSpam :)
It is not the front door that prevents you to see the delayed opening of the back door.
It is the simultaneity of the aligned with you events which does not leave information except for the front event (the one which is closed to you)

Earlier I tried to explain it with light attached to the inside of the back door.
The light turns on by a switch on the front door when it is completely open.
Since the events are simultaneous, the light will be directed down when the back door is opened.
If you insist that you'll see the front door open and the back door closed, then you'll have to see the light from the source attached on the back door (the front door is opened and switched it on).
Because we cannot have two 90 degree positioned light beams from one light source, we end up with new paradox, which does not help solving the ladder paradox.

 

[Dale]

I'm not even considering reading the links :)

You do not appear to be interested in learning physics. You seem to be a crackpot with an anti-relativity agenda. That is not permitted on this forum. If you become interested in learning relativity then I would be glad to help. If you just want an anti-relativity soapbox then I suggest sciforums instead.

The fact is that the term "event" has a clearly defined meaning in relativity and it is very distinct from the concept you are describing. The concept you are describing is called a "light cone" in relativity.

It is not the front door that prevents you to see the delayed opening of the back door.
It is the simultaneity of the aligned with you events which does not leave information except for the front event (the one which is closed to you)

How does simultaneity block the information? Simultaneity is not opaque. If the doors are transparent then the fact that they are closed doesn't stop any information.

 

[sisoev]

You do not appear to be interested in learning physics. You seem to be a crackpot with an anti-relativity agenda. That is not permitted on this forum.

If you become interested in learning relativity then I would be glad to help. If you just want an anti-relativity soapbox then I suggest sciforums instead.

That is not good attitude, DaleSpam :)
I showed gratitude and respect to you.
I can say that I'm not considering to read something only if I have enough knowledge about the subject.
You should not treat me as completely ignorant person.
I may know a little bit more than you in some fields of the science and philosophy.
Have that in mind and don't lose your nerves ;)

 

[sisoev]

How does simultaneity block the information? Simultaneity is not opaque. If the doors are transparent then the fact that they are closed doesn't stop any information.

Read again two posts back.
It appears that simultaneity is "opaque" when the events are aligned with the observer.
Comment on my explanation and I'll know how to clear it for you.

 

[PAllen]

Read again two posts back.
It appears that simultaneity is "opaque" when the events are aligned with the observer.
Comment on my explanation and I'll know how to clear it for you.

This has no meaning for anyone who has studied physics. To try to get at what you might mean, consider the following:

I have a 1 meter stick. In the middle I have red light that flashes every second. At the far end I have blue light that flashes every second. I am at the 'near' end. All synchronization of clocks done by slow transport. I see blue flashes arrive a tiny bit later than red flashes. Accounting for light speed, I conclude the emission events were simultaneous. Where is the opaqueness of simultaneity?

[Dalespam is not being rude for reminding you of forum rules. These forums are intended to discuss physics, specifically defined as peer reviewed theories in established journals. There are other places on the web to discuss theology, 'alternative science', or whatever. But when you register here you agree to discuss mainstream science. ]

 

[ghwellsjr]

When i suggested the example i thought we all agreed that there is no turnaround event, so what g-forces are we talking about now?

Imagine the guy from Earth was watching the one moving away and then the next second moving towards him. Why would the light need more time to reach the Earth guy all of a sudden if it was reaching him just fine until the last moment of moving away? If we are imagining an uninterrupted flow of light from the moment of departure to the moment the moving brother switches directions, i imagine the image the Earth brother would receive would be a sudden shift from the 1/2 rate to the 2 rate. And the same thing would occur for the moving brother as well, like a "mirror" as sisoev suggested.

Now, apparently my imagination is very wrong and the logic i am using as well, otherwise SR would not exist today. What i am asking for is not answers such as "you are wrong" and "well that doesn't happen because it's been accounted for", but instead to be shown where my logic breaks, at which point? I am not asking for mathematical equations, because when a client comes to me to explain to him a problem with the software i don't start talking to him in 0's and 1's, but instead i try and talk his language, the one he understands. Otherwise we will be sitting on this thread for weeks everyone saying the same things not understanding the others.

And for the sake of eliminating any kind of G-Force let's imagine both brother in space in their own respective space ships, with the moving ship being equipped with inertial dampeners (or whatever they call them in the movies these days) so that if there is ANY kind of change in acceleration it will not be felt at all by either the ship or the person in the ship.

OK, we'll make sure the moving ship has inertial dampeners so that no change in direction will be felt by the traveling twin.

You and sisoev are so close to understanding this, I think the best way to help you is to use an analogy to sound Doppler. We're all familiar with the shift in the pitch of an emergency vehicle's siren as it passes by us going from a higher rate to a lower rate. To make things easier, let's assume that the siren is putting out a single frequency sound instead of the typical siren that is modulated all over the place, and let's assume that it is very loud so we can hear it from a great distance away. Once that vehicle has passed us and we are hearing the lower rate sound, it will stay at that same low rate as long as the vehicle maintains a constant speed. But let's suppose that after it has gone a mile from us, the vehicle shuts off its emergency lights and its siren at the same time. What will we see and hear? Well, even kids know that it takes about five seconds for the sound to travel a mile so it will take five seconds for us to hear the sound drop out after the lights turn off, correct? But now let's suppose that instead of turning off the siren, the vehicle turns around very quickly, in a fraction of a second, what will we see and hear? Well, again, about five seconds after we see it turn around, we will hear the pitch change from its lower rate to the higher rate, correct? And it will stay at the higher rate until it reaches us, I'm sure you will agree.

Now let's consider a slightly different situation where the emergency vehicle is stopped with its siren blaring out a loud constant frequency. Then suppose we are in a vehicle approaching it. No matter how far away we are, we will hear the higher rate sound, and just like before, as we pass it the sound will drop from the higher rate to the lower rate, correct? But then suppose a mile down the road, we make a quick turn around. What will we hear? If you give it a little thought, I think you will conclude that we immediately hear the pitch go from the lower rate to the higher rate, don't you agree? If you don't agree, then when will we hear the switch from the lower rate to the higher rate, because remember, when we get to the siren and pass it, the pitch has to pass from the higher rate to the lower rate.

So what have we learned? When we are colocated with the source of the sound, we immediately hear the change in the rate of the sound's pitch but when we are located a distance from the source of the sound, we will hear the pitch change immediately if we're the one changing speed but we will hear it sometime later if the source of the sound is changing speed.

Now, is there anything in this analogy that you don't understand or don't agree with?

 

[sisoev]

This has no meaning for anyone who has studied physics. To try to get at what you might mean, consider the following:

I have a 1 meter stick. In the middle I have red light that flashes every second. At the far end I have blue light that flashes every second. I am at the 'near' end. All synchronization of clocks done by slow transport. I see blue flashes arrive a tiny bit later than red flashes. Accounting for light speed, I conclude the emission events were simultaneous. Where is the opaqueness of simultaneity?

[Dalespam is not being rude for reminding you of forum rules. These forums are intended to discuss physics, specifically defined as peer reviewed theories in established journals. There are other places on the web to discuss theology, 'alternative science', or whatever. But when you register here you agree to discuss mainstream science. ]

Imagine that you observe red light and blue light behind it. I don't know what mixture of color will be your observation, but when the lights simultaneously stop, you'll not see blue light coming to you.

I know the rules.
What I did not expected was to be forced to agree or to leave the forums.
Further more, the moderator can decide to close the topic if he/she decides that it becomes meaningless.
I am learning in discussion.
You guys have the chance to answer my arguments and convince me otherwise.
That will be the best way to educate me :)

 

[Denius1704]

Now, is there anything in this analogy that you don't understand or don't agree with?

Thank you ghwellsjr, i do understand the analogy and i do see the whole problem a bit clearer now, it helped.

Basically that would also mean that in a system of only two bodies, one moving and one stationary, even without the effect of an acceleration being felt we would still be able to say which one is moving and which one isn't, because of this effect? Am i right in assuming this?

Thanks again for the lengthily explanation.

 

[Dale]

That is not good attitude, DaleSpam :)
I showed gratitude and respect to you.

It has nothing to do with gratitude and respect. It has to do with the rules of the forum, which you agreed to when you signed up for your account. Please click on the link labeled "Rules" at the top of the page and re-read the section on Overly Speculative Posts.

We welcome students who have a question and come hear to learn, we do not welcome crackpots who have an agenda and come here to argue. You have shown signs of the latter (claims that contradict experimental observations) and you have not shown signs of the former (willingness to learn when information is provided).

I can say that I'm not considering to read something only if I have enough knowledge about the subject.
You should not treat me as completely ignorant person.

But you are ignorant of relativity. You do not even know the definition of very basic terms in relativity like "event". What is worse, you are deliberately ignorant and unwilling to learn, even when the information is spoon-fed to you. Ignorance is fine and easily overcome, but unwillingness to learn is not.

I may know a little bit more than you in some fields of the science and philosophy.
Have that in mind and don't lose your nerves ;)

If we were discussing those fields then that would be relevant and I would seek to learn from you and I would read the links you provided in order to better educate myself and overcome my ignorance in those fields. But we are not discussing those fields, we are discussing relativity.

 

[Dale]

the light will be directed down when the back door is opened ... Because we cannot have two 90 degree positioned light beams from one light source

Do you mean that the lights on the door are lasers or other tightly-collimated sources that only point in one direction rather than spherical waves that point in all directions? If so, then just use standard light bulbs that radiate spherically.

You seem to be trying to come up with specific tiny details that avoid the essence of the physics. The usual formulation of the ladder paradox never even mentions any lights. The existence and position of any light bulbs and the material of the door are irrelevant to whether or not the door is open or closed at a given time. Turning on or off the lights will not prevent you from crashing into a closed door nor will it make you crash into an open door.

IMO, the lights are just a red herring, but if you insist on having them for some reason then simply make them spherical-wave sources and make the doors transparent.

 

[PAllen]

Imagine that you observe red light and blue light behind it. I don't know what mixture of color will be your observation, but when the lights simultaneously stop, you'll not see blue light coming to you.

That is absurd. You will see a moment of pure red light, then a mixture of red and blue, then pure blue light. Even though each flash's start and stop are simultaneous, one emitter is further away.

If you deny this, there is no point of discussion - forget relativity, you are denying observable reality.

 

[ghwellsjr]

Thank you ghwellsjr, i do understand the analogy and i do see the whole problem a bit clearer now, it helped.

Basically that would also mean that in a system of only two bodies, one moving and one stationary, even without the effect of an acceleration being felt we would still be able to say which one is moving and which one isn't, because of this effect? Am i right in assuming this?

Thanks again for the lengthily explanation.

No, it's not a matter of which one is moving, it's a matter of which one is changing speed or direction and where the two are in relation to each other when this happens.

So let's extend the analogy a little bit to include your question:

Suppose you are stopped and the vehicle with the siren passes you and you hear the sound drop in pitch from the high rate to the low rate and after it is a mile down the road, you take off after it at the same speed it is going. Now you will hear the pitch go from the low rate to the actual pitch of the siren, won't you? So there you both are separated by a mile, both moving and it's just like you were both stationary in terms of what you are hearing. But now if you increase your speed, you will immediately hear the pitch go higher, right? But instead of that, suppose the other vehicle slows down, will you immediately hear the pitch get higher? No, not until five seconds goes by.

Once you grasp the idea that distance causes a delay in what you observe if the other person changes speed but no delay if you are the one that changes speed, then you can easily understand the Twin Paradox with no math, no equations, no formulas.

Does this make perfect sense to you now?

 

[sisoev]

That is absurd. You will see a moment of pure red light, then a mixture of red and blue, then pure blue light. Even though each flash's start and stop are simultaneous, one emitter is further away.

If you deny this, there is no point of discussion - forget relativity, you are denying observable reality.

You are building your experiment on wrong analogy, PAllen.

Imagine that sometime in the past a red light (in the front) and blue light (behind the red) were mixed for you.
Now we deal with two different information (red and blue) mixed into one information (let say purple)
Now imagine that both information(colors) are simultaneously extracted.
What will be left?
Non.

Taking this to a transparent doors (red and blue) you'll see a purple door which opens.
Behind it we will see what ever is behind the blue door

 

[Denius1704]

No, it's not a matter of which one is moving, it's a matter of which one is changing speed or direction and where the two are in relation to each other when this happens.

So let's extend the analogy a little bit to include your question:

Suppose you are stopped and the vehicle with the siren passes you and you hear the sound drop in pitch from the high rate to the low rate and after it is a mile down the road, you take off after it at the same speed it is going. Now you will hear the pitch go from the low rate to the actual pitch of the siren, won't you? So there you both are separated by a mile, both moving and it's just like you were both stationary in terms of what you are hearing. But now if you increase your speed, you will immediately hear the pitch go higher, right? But instead of that, suppose the other vehicle slows down, will you immediately hear the pitch get higher? No, not until five seconds goes by.

Once you grasp the idea that distance causes a delay in what you observe if the other person changes speed but no delay if you are the one that changes speed, then you can easily understand the Twin Paradox with no math, no equations, no formulas.

Does this make perfect sense to you now?

Thanks for extending the explanation, but those are just variations of the same principle. My last question about two objects in a system was just to satisfy a philosophical question and you did answer it (albeit i didn't formulate the question as properly as it was in my head :) ). In the extended example you give, if those two cars are isolated in a system with just themselves, when they are both moving with the same speed that would be equal to being stationary, so when the one "slows" down as it is in your example that would translate that it is actually accelerating towards the other "stationary" car. Doesn't mattet, i get the example :)