flashprogram

OK, if earth is not going to define the frame in which time is absolute, and now you think there is something very strange about this frame, you need to tell us exactly how you are going to identify this frame. Saying that the future as well as the past and present are cast in concrete, doesn't help, you need tell us where is this frame. How fast is the earth or the solar system moving through it and in which direction?

In your example, you didn't tell us the speeds of the ships with respect to this absolute frame, you just took a relativistic approach and said there was a difference in speed. And you didn't define the time at which the twins popped into existence in terms of an absolute time frame. You've got to decide if you want to promote an absolute time realism or a relativistic one. Please be specific. Tell us how you are going to identify the absolute time reference frame. No more fuzzy ideas--that won't get us anywhere.
Imagine instead of ships we have identical chunks of radioactive material moving at constant but different speeds in straight lines, no one knows exactly how fast they're moving relative to each other. Clearly if the difference in speed is great time dilation will seemingly notably affect half lifes. After a time their composition should thus measurably differ in such a way that it would be possible to order them in terms of speed differences, and to tell which rock was the slowest amongst them all.

If they were on a collision course the nature of the collision would be affected not just by differences in speed but via the differing composition. Reaching the same destination at different speeds should thus result in different stuff*(compositionally) arriving at the destination. IF the stuff was originally identical, the one receiving it will be able to note compositional change and thus be able to tell and compare the speed at which it came.

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ghwellsjr

Gold Member
More fuzzy idea that aren't getting us anywhere. I'm sure you think your ideas are clear as a bell and they make perfect sense to you but you aren't describing precisely what you are proposing and it is so open to interpretation.

Also, you keep changing your apparatus, I suppose, because you think it buttresses your position. You can keep it simple. Just describe how you think two identical clocks would work in your proposed concept of "realism" with absolute time. You don't need to embellish your story with spontaneously generated twins, radioactive rocks, colliding tombstones or anything else. Please keep it simple and describe exacly and precisely what your idea is and what would happen from start to finish.

All you have to do is say a clock has this time on it at this location and is traveling at this speed in this direction and another clock has this other time on it at this other location traveling at this other speed in this other direction and then describe what happens and how that proves your position.

flashprogram

More fuzzy idea that aren't getting us anywhere. I'm sure you think your ideas are clear as a bell and they make perfect sense to you but you aren't describing precisely what you are proposing and it is so open to interpretation.

Also, you keep changing your apparatus, I suppose, because you think it buttresses your position. You can keep it simple. Just describe how you think two identical clocks would work in your proposed concept of "realism" with absolute time. You don't need to embellish your story with spontaneously generated twins, radioactive rocks, colliding tombstones or anything else. Please keep it simple and describe exacly and precisely what your idea is and what would happen from start to finish.

All you have to do is say a clock has this time on it at this location and is traveling at this speed in this direction and another clock has this other time on it at this other location traveling at this other speed in this other direction and then describe what happens and how that proves your position.
The problem is, taking any two arbitrary objects, letting some time elapse... and measuring the rate at which their clocks differ should be practically possible. If we have a collection of objects, we can take any two arbitrary objects and do so, thus looking at how they differ relatively to each other. Trying to expand this so that we can relate all objects to each other probably presents some serious problem. The problematicity of this is probably in some way similar to what occurs with gravity, in the http://en.wikipedia.org/wiki/N-body_problem" [Broken].

As you asked: putting the two things simultaneously in two objects, even if impractical is either impossible or it is possible. The question is can we relate one instant on one object with one instant or sets of instances in the other? I don't see why not, why should it be impossible to relate moments in one to one or more moments in the other? but I honestly cannot tell how this would be represented.

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JesseM

As you asked: putting the two things simultaneously in two objects, even if impractical is either impossible or it is possible. The question is can we relate one instant on one object with one instant or sets of instances in the other? I don't see why not, why should it be impossible to relate moments in one to one or more moments in the other? but I honestly cannot tell how this would be represented.
Are you familiar with the idea of the relativity of simultaneity?

ghwellsjr

Gold Member
Flashprogram, here is what I was trying to get you to do:

Suppose we have two clocks, A and B, that are separated by 1 light year. A is stationary and B is traveling at a speed of .5c toward A and they start out with the same time on them, which clock will have elapsed more time when they meet? The answer is A and can you see that I have implied a specific frame for this scenario?

On the other hand, you have proposed scenarios such as:

Suppose we have two clocks, A and B, that are separated by 1 light year. They are traveling toward each other with a relative speed of .5c and they start out with the same time on them, which clock will have elapsed less time when they meet? The answer is indeterminate because you have not stated or implied a frame in which to describe or analyze your scenario.

Do you see the difference between these two scenarios? The second one, typical of your scenarios, is not specific enough, it has no frame. It could be interpreted like the first scenario or it could be interpreted like the first one but with the clocks, A and B, interchanged. So the answer could be either A or B if we had more information.

Now you are supposing that nature has an answer to the question for your type of scenario; all we have to do is wait until the clocks meet and we will see which one has elapsed more time and that will determine which one was traveling slower and that will establish a preferred frame for nature.

And therein lies the problem: you are defining scenarios without frames and then talking as if nature is also defining scenarios but with a frame. You can't have it both ways. Either you get to define specifically what you want to consider happening in a scenario OR you have to let nature do whatever it wants and you draw whatever conclusions are valid from the measurements you can make.

So let's go back and see what's wrong with your combination of your partially defining a scenario and letting nature define the other part: When you say that two separated real clocks start out with the same time on them, you are saying something that we cannot know by making a measurement until those two clocks with a known relative speed and a known relative distance between them come together and we compare their times. After that happens, we can pick a frame, calculate backwards and determine, in that frame, what the times were on the two clocks when they were separated by a given distance. But it is totally arbitrary. We could pick a different frame and calculate backwards and show that the two clocks had totally different times on them when they were separated by a given distance.

So it is not legitimate for you to claim that two clocks start off with the same time on them without specifying a frame and then making the claim that you can determine the correct frame by waiting until they unite to compare their elapsed times and assuming that the choice of frame is determined by nature and not by you.

flashprogram

JesseM, I've heard of it. The order of non-causally related events can vary between observers, even be reversed or interpreted as simultaneous, iirc.

So it is not legitimate for you to claim that two clocks start off with the same time on them without specifying a frame and then making the claim that you can determine the correct frame by waiting until they unite to compare their elapsed times and assuming that the choice of frame is determined by nature and not by you.
Even if the clocks have different arbitrary times at the outset, all we have to do is establish a causal relation between the two objects, with this causal relation information can be exchanged, and on the basis of such exchanges, it can be determined that from that moment assuming all else remains constant, the clocks in the two objects differ in rate by a measurable proportion... and from such measure difference in speed can be inferred.

ghwellsjr

Gold Member
You are a master at making fuzzy statements. I can't tell what you are talking about. It would help if you would define your terms. What do you mean by causal relation--is that when two observers with a relative speed between them finally arrive together at the same location just long enough to exchange information?

yogi

If two clocks A and B travel at a constant relative velocity, which clock runs slow is a meaningless question. A second clock in the frame of A can be used to measure the time lapse of B clock and it will always appear to run slower when measured by the two clocks in the A frame, and the same is true for a second clock introduced in B frame to measure clocks in the A frame - as pointed out on a previous post, which clock runs slow depends upon in which frame the measurement is made. This is not an aging difference and therefore is not a paradox - there can be no age difference because the situation is symmetrical. Age difference only occurs when acceleration is involved somewhere during the time differential that defines the beginning and end of the experiment The pion in the lab is an example of real age difference because it has been accelerated from a rest position in the lab to near c velocity. This is a shrunk example of the one way twin paradox - you have acceleration following the initial synchronization of the pion clock in the lab frame (the pion changes from the lab frame to another frame in a jiffy or so) - but because the pion decay time is already known for at rest pions - only the lab clock and the distance before decay are needed to calculate the age of the traveling entity.

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flashprogram

If two clocks A and B travel at a constant relative velocity, which clock runs slow is a meaningless question. A second clock in the frame of A can be used to measure the time lapse of B clock and it will always appear to run slower when measured by the two clocks in the A frame, and the same is true for a second clock introduced in B frame to measure clocks in the A frame - as pointed out on a previous post, which clock runs slow depends upon in which frame the measurement is made. This is not an aging difference and therefore is not a paradox - there can be no age difference because the situation is symmetrical. Age difference only occurs when acceleration is involved somewhere during the time differential that defines the beginning and end of the experiment The pion in the lab is an example of real age difference because it has been accelerated from a rest position in the lab to near c velocity. This is a shrunk example of the one way twin paradox - you have acceleration following the initial synchronization of the pion clock in the lab frame (the pion changes from the lab frame to another frame in a jiffy or so) - but because the pion decay time is already known for at rest pions - only the lab clock and the distance before decay are needed to calculate the age of the traveling entity.
But we've already seen the difference in clock rates will have measurable effects on things like half life, which will alter the composition of radioactive rocks or ships composed of such. Surely the physical composition of the ships cannot be frame dependent.

In previous posts related on this issue, others have commented that acceleration and deceleration need not be involved for effects to be measurable, for us to tell that clocks differ in rate of measuring time, and thus objects that are at constant speed and remain at such constant speed will experience different rates of 'aging'(passage of time) even while remaining at constant speed, if their speed differ.(example suppose we know the routes of the two ships, and put 2 messages with equal spacing along each such route. Between message one and message two of each route, the number of events in the two ships, say number of birthdays will vary between the two ships.)

Spontaneously created matter within a ship moving at high speed, close to C speed, if radioactive, will experience half life at a different rate(passing of time) as compared to the same matter created similarly in a slower ship.

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yogi

But we've already seen the difference in clock rates will have measurable effects on things like half life, which will alter the composition of radioactive rocks or ships composed of such. Surely the physical composition of the ships cannot be frame dependent.

Spontaneously created matter within a ship moving at high speed, close to C speed, if radioactive, will experience half life at a different rate(passing of time) as compared to the same matter created similarly in a slower ship.
Measurements of half lives in the B frame made by clocks in the A frame will indicate a slower rate of decay in the B frame. Measurments of half lives in the A frame made by clocks in the B frame will indicate a slower rate of decay in the A frame

ghwellsjr

Gold Member
But we've already seen the difference in clock rates will have measurable effects on things like half life, which will alter the composition of radioactive rocks or ships composed of such. Surely the physical composition of the ships cannot be frame dependent.

In previous posts related on this issue, others have commented that acceleration and deceleration need not be involved for effects to be measurable, for us to tell that clocks differ in rate of measuring time, and thus objects that are at constant speed and remain at such constant speed will experience different rates of 'aging'(passage of time) even while remaining at constant speed, if their speed differ.(example suppose we know the routes of the two ships, and put 2 messages with equal spacing along each such route. Between message one and message two of each route, the number of events in the two ships, say number of birthdays will vary between the two ships.)

Spontaneously created matter within a ship moving at high speed, close to C speed, if radioactive, will experience half life at a different rate(passing of time) as compared to the same matter created similarly in a slower ship.
Flashprogram, one problem with using radioactive rocks is that the radiation they give off is proportional to their initial size so determining their age or their aging rate from just the radiation is almost impossible so let's consider another object, totally imaginary, something like a pulsar except much smaller, that gives off a very bright flash of light at a regular interval, say once per second. And let's imagine that two exactly identical such objects exist and that one of them is traveling at 60% of the speed of light directly toward the other one which is stationary. Now let's also consider that each one can see the flashes from the other one and have been doing so for a very long time and that they are still very far apart from each other. Isn't this very much like the scenarios that you have been devising?

Now here's the question for you: How will each object observe the rate of the flashes from the other object compared to their own flash rate?

flashprogram

Now here's the question for you: How will each object observe the rate of the flashes from the other object compared to their own flash rate?
It would seem that one would see a higher number of flashes than the other, unless I'm missing something. It would seem that if you sped the object up arbitrarily close to C, it will experience the passage of time at a very slow rate during any interval of travel.

Say the following, we can put an even simpler example:

Two ships are headed to pass a destination say X.X lightyears away, they start from the same origin, and they're both covering the same distance(as previously measured by stationary observers at the origin and destination points). One ship is traveling at .9c, the other is traveling arbitrarily close to C(e.g. .999999999999....c). As they pass the destination they leave a message of what happened during the trip(a log of activities.).

It can be seen that as the two ships were traveling very close to C, from the observers at the destination's perspective they covered the distance within a similar span of time.

The log shows that on one ship the traveler only managed to view a single episode of 'LOST', the other ship shows a year's worth of activities in the log. How can there be any argument regarding which ship had more events and thus had faster rate of the passage of time, and which had a slower rate?

ghwellsjr

Gold Member
It would seem that one would see a higher number of flashes than the other, unless I'm missing something. It would seem that if you sped the object up arbitrarily close to C, it will experience the passage of time at a very slow rate during any interval of travel.
No, they would each measure the other one's flashes as occuring at exactly double the rate of their own. This is an example of Relativistic Doppler. And the faster the one ship is going, the higher the ratio they both measure of the other one's flashes compared to their own.
Say the following, we can put an even simpler example:

Two ships are headed to pass a destination say X.X lightyears away, they start from the same origin, and they're both covering the same distance(as previously measured by stationary observers at the origin and destination points). One ship is traveling at .9c, the other is traveling arbitrarily close to C(e.g. .999999999999....c). As they pass the destination they leave a message of what happened during the trip(a log of activities.).

It can be seen that as the two ships were traveling very close to C, from the observers at the destination's perspective they covered the distance within a similar span of time.

The log shows that on one ship the traveler only managed to view a single episode of 'LOST', the other ship shows a year's worth of activities in the log. How can there be any argument regarding which ship had more events and thus had faster rate of the passage of time, and which had a slower rate?
This is correct in your implied stationary rest frame (except maybe for your statement about them both covering the distance in a similar span of time, since one of them is very close to C while the other one is only .9c, but I don't think this adversely affects your scenario).'

By the way, you have finally specified a scenario with enough details to unambiguously interpret what is going on. Good for you.

However, in the rest frame of the "faster" ship, the destination is traveling toward him at almost the speed of light and wasn't very far away (because of length contraction) and it only took one hour to get to him, whereas the other ship is traveling away from him and is "running away" from the approaching destination so even though the "faster" ship sees the "slower" ship as having time-dilated clocks, it still takes a year of the "slower" ship's time for the destination to catch up to him.

And from the rest frame of the "slower" ship, the destination is traveling toward him at .9c and takes a year to get to him but the "faster" ship is traveling at almost the speed of light toward the destination and even though the "slower" ship sees the "faster" ship's clock as running slower than his own, it still takes one hour of the "faster" ship's clock to reach the approaching destination.

So the issue of which had more events is different from the issue of the rate of the passage of time because you are overlooking the effect of length contraction. In a given frame, a clock can be running at a normal rate but the distance covered is very short and so the number of events can be very small.

flashprogram

Hmmm...

That relativistic doppler effect is very strange, almost like an escape clause. Yeah while you traveled a million light years from a distant galaxy, and your flashing machine which flashes each frame you manage to watch of a single 'lost' episode to us(you just managed to finish just a single episode during all this travel), and earth has been using the identical flashing machine to loop the episode for a million years... there's this weird effect, and tada gotcha relativistic doppler effect meddles in and you got nothing.

So the issue of which had more events is different from the issue of the rate of the passage of time because you are overlooking the effect of length contraction. In a given frame, a clock can be running at a normal rate but the distance covered is very short and so the number of events can be very small.
The length contraction while a true phenomena I'd heard about, is still a bit tricky to picture, how about the following:

What happens if we imagine that instead of empty space, this is a very long road with identical houses at equal distances along the way(say a large neighborhood), and instead of spaceships we have very fast runners(same .9c and .9999...c). One runner breaks the mailboxes on the left and the other the mailboxes on the right. The runners reach house number 1 Trillion, and drop a message*(the message says the point at which they got while watching an identical video on their ipad.).

They each broke 1 Trillion mailboxes and passed along one trillion houses, yet at house 1T, one managed to see the whole video while the other did not. By measure of houses passed by and broken mailboxes, it would seem the length is the same even if the runners measure the road contracted to different extents.

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ghwellsjr

Gold Member
I think you're catching on.

flashprogram

The effect of acceleration is proportional to the distance between the twins. At the start and end of the trip, this distance is zero.
if this is so instantaneous travel could land you anywhere and would require a practically infinite energy source, good luck finding that! Since antiquity it has been searched, and no one is supposed to have found it hence, the red queen dilemma.... constant progress while appearing to show zero progress.

Mueiz

Hi,

I've seen many variations of explanations of the twin paradox using special relativity, but i haven't yet seen an explanation that bothers to take into account the initial acceleration of the travelling twin away from planet Earth. Is it safe to say that this can be neglected? And, also, if the travelling twin were to accelerate away from Earth and then decelerate onto the distant planet and then stay there without coming back, would he still be younger than his twin at home?

Thanks for any help that anyone can provide!
acceleration and deceleration effects can not be the resolution of the so called twin paradox because we can make the interval of uniform motion long enough to neglct the effects of acceleration and deceleration.
There is no twin paradox if we look from one frame of reference...each of the twin will see that the other is younger ..when we ask ''who is younger?'' we must chose a frame .

ghwellsjr

Gold Member
Hi,

I've seen many variations of explanations of the twin paradox using special relativity, but i haven't yet seen an explanation that bothers to take into account the initial acceleration of the travelling twin away from planet Earth. Is it safe to say that this can be neglected? And, also, if the travelling twin were to accelerate away from Earth and then decelerate onto the distant planet and then stay there without coming back, would he still be younger than his twin at home?

Thanks for any help that anyone can provide!
acceleration and deceleration effects can not be the resolution of the so called twin paradox because we can make the interval of uniform motion long enough to neglct the effects of acceleration and deceleration.
There is no twin paradox if we look from one frame of reference...each of the twin will see that the other is younger ..when we ask ''who is younger?'' we must chose a frame .
This is true, we must choose a frame to decide who is younger, but if we limit ourselves to the frame in which they both started out at rest and both ended up at rest, then the twin that traveled to the distant planet will be younger and they will both eventually see and agree that he is younger although while he is traveling, they will both see the other one as younger.

While traveling, due to relativistic doppler, they will both symmetrically see the other one as aging at a younger rate. When the traveling twin stops on the distant planet, he immediately begins to see his twin age at the same rate as himself but his twin back on earth will continue to see the traveling twin aging at the same lower rate until he eventually sees that his twin has stopped traveling and begins aging at the same rate as himself. Since they are now both stationary in the same frame, according to Special Relativity, we can compare their ages and the traveling twin will be younger in that frame.

HarryWertM

From Meir Achuz' post no. 4....
The effect of acceleration is proportional to the distance between the twins.
Huh?? Meir [or anybody], can you show equations or web sites to support this statement?

PAllen

From Meir Achuz' post no. 4....

Huh?? Meir [or anybody], can you show equations or web sites to support this statement?
This sounds like a distorted version of one way of talking about differential aging. In a real gravitational field, the further apart two clocks are in the gravity gradient, the larger the difference in their aging. If one uses a non-inertial frame, with metric modeling inertial force as gravity, you also see that the further apart two observers are (in the direction of acceleration), the greater the difference in clock rate. It is possible to explain almost all twin variants this way, but I don't find it the most natural way (personally).

Ich

can you show equations or web sites to support this statement?
If you have the traveling twin at distance d change her velocity by dv, the "simultaneous" event at the origin shifts by dt = -dv*d, which is the essence of Meir Achuz' statement.
You can derive this from the Lorentz transformations by first solving for t' at the event t=0, x=d, then solving for t at the event t', x=0.

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