Some doubts on relativity

Oh! I see where is the problem with the example...

Thanx! I thought that we could make a kind of time-rate-map if we know all the objects and their velocity at the scene... and it would depend on the reference as we designated the zero-point in a metric... I see now that was not right...

And, in the example, now I see the motion-relation of D with the other galaxies must be knowed because it's unic... I have missed that point...

Lots of thanks for your help! I think I understand it now a little better!
 

wakeball32

To Nucleartear

Hi,
I am not a physics genius who has a degree specializing in relativity or anything, I just love the subject. Anyway, dealing with special relativity, just remember that nothing is absolute (i.e. time, velocity, etc,) because as your 1st post shows, all measurements are different with respects to different galaxies, hence none of them is absolute. Also, there is no such thing as simultaneity. Thats just some basics.
 
1,525
10
SR problems always lead to much debate and further questions - there are several explanations - Einstein took the position in his original publication that the turn around twin experinced acceleration and therefore the problem was not one that could be solved by SR per se - but there are other views and many proposed tests - the many tests that have verified SR also confirm Lorentz Ether Theory (actual time dilation and actual lenght contraction). These tests also cannot distinguish between one of the latest explanations of MMx experiment that proposes that the one way speed of light is constant in the earth centered system because the earths gravity modifies the local space (this is not an either drag hypothesis) and is distinquishable therefrom because distant sources such as the CBR and star light aberration will be detectable even though local over and back and one way light transmission will be isotropic. Finally, the notion that the twin problem gets explained because the turn around twin experiences forces - fails in the triplet thought experiment where there is no turn around - the outbound twin simply transfers his clock reading to an inbound brother who left years earlier - and this guy continues on back to earth with the info from the outbound brother - but the two clocks back on earth do not read the same. arrives back at the earth in th
 
499
1
Yogi, please read what you are saying. Any version of the twin situation, or triplet, or quadruplet situation matches up well. Why? Two situations.

1) Transfer of a physical clock. The outbound twin transfers the clock to the inbound twin. Seems nice and clean there for you doesn't it? But if I recall, is not a change in direction (remember velocity is a vector) an acceleration? Why yes it is. And wound not the clock experience quite a large acceleration when being transferred at such high velocities? Why yes, yes it would.

2)A signal is sent. This one is easier because the signal will be automatically shifted one way or the other depending on when it is sent. Remember even though c is constant, it will take some time for it to catch up with an object traveling a good fraction of c.
 

Janus

Staff Emeritus
Science Advisor
Insights Author
Gold Member
3,411
1,099
Originally posted by yogi
Finally, the notion that the twin problem gets explained because the turn around twin experiences forces - fails in the triplet thought experiment where there is no turn around - the outbound twin simply transfers his clock reading to an inbound brother who left years earlier - and this guy continues on back to earth with the info from the outbound brother - but the two clocks back on earth do not read the same. arrives back at the earth in th
This scenerio changes nothing, As it doesn't address the supposed "paradox" of the "Twin paradox"

If twin 1 stays on Earth and watches twin 2 travel at .866c for a distance of .866 ly, where he meets twin 3 inbound, he will say that 1 yr will have passed on his clock, while only .5 yr will have passed on twin 2's clock, due to time dilation.

Twin 2, upon meeting twin 3, will also say that .5 yr has passed on his clock. Because of length contraction, the distance between him and twin 1 at the time of meeting twin 3 is only .433 ly.

Thus all three twins agree as to the time shown on twin 2's clock when he transfers his clock reading to twin 3 and there is no paradox.

The "paradox" arises from the fact that Twin 2 should also see only .25 yr as having passed on Earth when he meets twin Three.

But this doesn't lead to a problem, either, as the only problem would be if twin 2 disagreed as to how much time had passed for twin 1 when twin 3 arrives with the time reading.

Assuming that Twin 3 is moving inward at .886 wrt to Twin 1.

That means according to Twin 1, 2 yrs will pass from the departure of Twin 1 to the Arrival of Twin 3.

Now the velocity of twin 3 to Twin 2 as measured by twin two is

(.866c+.866c)/(1+(.866c)²) = .9897c

This means, that measured by twin 2, twin 3's velocity wrt Twin 1 is

.9897c - .9=866c = .1237 c

Twin 3 was .433 ly from twin 1 when they met, so by twin 2's clock, it would take 3.499 years. Due to time dialtion, twin 2 would measure 1/2 this time as passing for twin 1 or 1.75 yr. add this to the .25 yrs, at the time of meeting, and twin 2 will say that 2 years will have passed for Twin 1, the same time that twin 1 measures. Again, no paradox.

The only other way to force a paradox is to have twin 1 watching the Twin 1 the whole time, and bring him back to the same frame as Twin 1 so that he can physically compare the time passed for twin 1 to the Time he Saw passing for twin1. On the outbound and Inbound trips, he would see less time pass for twin 1 than on his own clock. But the only way for there to be a paradox is if the two are brought back into the same frame and compared, (thus twin's 1 and 2 not moving relative to each other, are looking at the same clocks and both are seeing different readings, or each sees the other twin as being younger.)

But the only way for this to happen is for one twin to experience an acceleration, and this acceleration alters how he sees time pass on the the other twin's clock. It will cause him to see time as passing faster for his brother during this time of acceleration, to the extent that once the brother's are brought back together, he will agree that he aged less than his brother over the entire time period of separation.
 
1,525
10
Janus - Brad - we are not on the same page - to merely observe the outbound twins clock as he passes another space traveler (inbound) - and the space traveler (i called him the inbound triplet) sets his clock to the same reading as the outbound twin as they pass - and then the outbound twin continues to God knows where - and the inbound traveler's clock keeps accruing time until he returns to the earth (to meet the so called stay at home twin) - everyone seems to conclude there will be a difference in the two readings when the inbound travelers clock is compared to the stay at home twin's clock. Brad - the transfer of information as the outbound twin and the inbound traveler pass each other does not involve any acceleration. Janus - there are a number of experiments with centrifuges that verify there is no clock slowing due to acceleration per se - there is a clock slowing but it corresponds to the tangential velocity of the clock that is being centrifuged. There is a gravitational time dilation, but it is due to the G field - and there are many proposals as to why it is the G field that affects clocks and not acceleration due to ma - I am not purporting to be able to ad any ideas as to why there appears to be a difference between a G field time dilation and an ma centrifugal acceleration - but there is.
 
1,525
10
A little more to add to the above - Janus - your analysis is parallel to that given by Born in his book on SR - but if you go through Born's math you see he made a critical flaw in arriving at the time dilation for the turn around - he use a time period for the acceleration that corresponded with the total outward time interval- but this period did not involve an acceleration - that took place only during the turn around - you cannot make up for the acumulated loss of time that occurs with years of near c velocity travel with a short period of turn around acceleration (even if acceleration per se altered clock rates) - the formulas derived for the acceleration time dilation are typically based upon some metaphore like having a clock in the nose of an accelerating space ship and one in the tail - and both are subjected to the same acceleration field (they are both in the same vehicle) so there is a difference in the rate at which signals arrive from front to end and vice versa - this gives the correct formula for time dilation in a G field (somewhat surprizingly) but as I previously said - clocks subject to acceleration by some means other that a G field do not exhibit time dilation.
 
1,525
10
Brad - with regard to your post on the other forum re relativity ...to the effect that Einstein did not have doubts as to relativity - how would you explain the following quote from Einstein near the end of his life:

“There is no idea of which I would be sure that it would stand the
test of time, and I have doubts whether I am on the right way
In general ...feelings of dissatisfaction come from the inside.”

and another:
"The present position of science can have no lasting significance"


Einstein was forever evaluating his own work and correcting it - he would have been very distressed to have it canonized as gospel - as I said before - the last word has yet to be be written.
 

Janus

Staff Emeritus
Science Advisor
Insights Author
Gold Member
3,411
1,099
Originally posted by yogi
Janus - there are a number of experiments with centrifuges that verify there is no clock slowing due to acceleration per se - there is a clock slowing but it corresponds to the tangential velocity of the clock that is being centrifuged.

correct, but I never said that acceleration slowed the clock, only that the observer being accelerated will measure the other's clocks as running fast. Acceleration doesn't effect his clock, it effects how he measures other clocks.





There is a gravitational time dilation, but it is due to the G field - and there are many proposals as to why it is the G field that affects clocks and not acceleration due to ma - I am not purporting to be able to ad any ideas as to why there appears to be a difference between a G field time dilation and an ma centrifugal acceleration - but there is.
Again, it is not the G field that effects the clocks, but it is the clock's relative position within the field that effects how they measure each other. It is the amount of difference in their potential. This works perfectly with the centrifuge experiments, because, there too, the time measurement difference is related to potential.

There is no discrepency between the centrifuge experiments and gravitational time dialtion to be explained.
 
27
0
Hello hello... i'm a newbie here... see me pleaseee
may be i'm just not the right person to quote about these materials. (my modern physics score was "C")

Originally posted by nucleartear

You actually say that the time flows at the same velocity, but if we make a mesure of the time in the moving-object while we are at the static-reference we will detect it flows slower at the moving-object... (let me know if I'm wrong)
well... one argument about that..., what WE exactly measured was the flash of light which according to the famous Maxwell (i believe) has a great velocity that not even our most modern plane can compete. And Einstein said,(i don't feel i'm remembering it correctly) when two boats aproaching each other in a real dense fog, and blah blah...(i don't remember)--> their relative velocity to the light is c(i don't agree about this)(please don't angry to me if i'm wrong)

yes.. they are nearly equal to c. but for a velocity nearly equal to c, is the theory still really holds true.

plus... our beloved sun is emitting a continuous flow of light right..., and our earth would refract some of them right?... then, (i'm viewing the light as particles) what is the relative velocity of those particles? (when the sun-emitted particles move with the velocity of c, the refracted ones' would be minus c. i heard some said that the velocity of anything would not be greater than c. but this fact show that the velocity could be 2 times c.(am i right?) so how about it..., could anyone explain this misunderstanding of mine?

And the clocks of GPS satellites wouldn't need to be checked, and the celsius-clocks of the two-planes-experiment would have the same time, but one of them was delayed... [/B]

how about the fact? if i may know? experiment would always have better results than theories right?

thanks for reading. and, if i made a mistake, please forgive me and tell me the truth.
 

Janus

Staff Emeritus
Science Advisor
Insights Author
Gold Member
3,411
1,099
Originally posted by yogi
A little more to add to the above - Janus - your analysis is parallel to that given by Born in his book on SR - but if you go through Born's math you see he made a critical flaw in arriving at the time dilation for the turn around - he use a time period for the acceleration that corresponded with the total outward time interval- but this period did not involve an acceleration - that took place only during the turn around - you cannot make up for the acumulated loss of time that occurs with years of near c velocity travel with a short period of turn around acceleration (even if acceleration per se altered clock rates) - the formulas derived for the acceleration time dilation are typically based upon some metaphore like having a clock in the nose of an accelerating space ship and one in the tail - and both are subjected to the same acceleration field (they are both in the same vehicle) so there is a difference in the rate at which signals arrive from front to end and vice versa - this gives the correct formula for time dilation in a G field (somewhat surprizingly) but as I previously said - clocks subject to acceleration by some means other that a G field do not exhibit time dilation.
Again, no one is saying that acceleration effects clocks per se (or that velocity effects clocks per se either) We are saying that relative velocity effects how clocks measure each other, and acceleration felt by one clock effects how it measures others along the line of the acceleration it feels.

With the astronaut during turnaround, it is not only the strength of the acceleration he feels, but the distance and direction from him of the other clock he is measuring, that effects how he measures that other clock's rate.

Thus for an astronaut that has drifted at near c for years will be very far away from Earth, and the combined effect of this increased distance and the acceleration he feels during turnaround that will account for the speed up in time rate he sees for Earth. The longer he drifts, the further Away from Earth he is at turn around, and the greater the rate increase he sees in Earth's clock. So yes, a short turnaround can make up the difference.

So what happens is that from Earth the following is measured:

Twin 2 accelerates up to near c, coast for a while to some distance as measured form Earth, turns around and comes back. During this perod of The Earth observer will see twin 2's clock run slow for at varying rates due to the relative velocity of Twin 2 alone. (no additional time dilation is seen due to Twin 2's acceleration)

Twin 2 measures the following:

As he feels the acceleration and the distance between him and the Earth increase, he will measure the Earth's clock run slow due to the Increased relative velocity and the aceleration he feels at a changing rate. (since he is close to the Earth during this period, the acclerations effect on his measurements will be fairly small)

The force felt to acceleration is cut off, and now he measures only time dilation due to relative motion. The distance beween him and the Earth will increase unitl he reachs turnaround point. But because of length contraction, the distance between him and Earth will be less by his measurements than by the Earth's measurements. (If he coasted at .866c it will be just about 1/2 the distance as measured from Earth.)
Thus both he and the Earth will agree as what his clock reads at turnaround. (The Earth will say that he traveled a distance of x at .866c, and took T time to do so, but because twin 2 clock underwent time dilation it will only read 1/2 T. Twin 2 will say that the distance between the Earth and him increased to a distance of 1/2 x at .866c and it took, by his clock 1/2 T to do so. )

Up until now, twin 2 wil measure less time as passing on Earth than for him.

But now, as he feels the force due to turnaround, The Earth is in the opposite direction with respect to this force than it was earlier, and much further away. He will measure the Earth time rate as moving very fast during this period.

Once again, the force will stop and he will only measure the time dilation due to relative motion (earth clock running slow.)

The force of acceleration is felt again as he brakes, and he measures the combined effect of acceleration and relative velocity, both decreasing as the distance to earth decreases and the relative velocity lowers. This continues until twin 2 and Earth are at rest wrt each other again.

Due to the various measurments each made of each other clocks for the duration, each will agree who experienced less time and by how much. However, they won't agree as to how that time difference was reached. And neither is more correct than the other.
 
1,525
10
Good Post Janus - and I agree that one can arrive at the correct time discrepancy between the two clocks back on earth by this means - but you can also get to the same result by the much simplier hypothesis that velocity with respect to space alters the actual rate at which time passes - moreover, in the case where there is an inbound traveler who merely observes the outbound twin's clock - there is a discontinuity in the analysis - I know the standard (if there is such a thing) explanation of the lost time -

Take the case of the one way traveler - he passes earth at 0.8c and syncs his clock as he passes by - then continues at the same speed straight to Alpha Centuri - how much will he have aged when he arrives? - how much time will have accrued on the clock back on earth?
 

Janus

Staff Emeritus
Science Advisor
Insights Author
Gold Member
3,411
1,099
Originally posted by yogi
Good Post Janus - and I agree that one can arrive at the correct time discrepancy between the two clocks back on earth by this means - but you can also get to the same result by the much simplier hypothesis that velocity with respect to space alters the actual rate at which time passes

No, you don't get the exact same results. For example in relativity if an astronaut throws a ball forward, he only has to account for the ball's relative motion to him to determine its time dilation and length contraction wrt to hiim it doesn't matter how fast you consider the astronaut as moving himself. In the absolute motion to space notion you have to consider the ball's relative motion to space and the astronauts relative motion to space and compare the ratio. Thus if the astronaut is traveling very near the speed of light, even a small diference in velocity between him and the ball will cause a large difference in time rate between the two as measured by the astronaut). In Relativity a smal difference of velocity between the two would only cause a very small time rate difference between the two as measured by the astronaut.

A practical example is done everyday in particle accelerators. Particles are accelerated in opposite directions to near c and collided. If absolute motion wrt to space was the culprit, you would at times have the Earth's motion through space added to particles going in one direction and subtracted from those going in the other. This would produce an asymetry in the particles' time dilation and energy content. We never see this, we always get symetrical collisions no matter what time of day or year or what direction the accelerators are pointed.

In order for an "absolute motion to space" hypothesis to give the results we actually get, you have to create all kinds of ad-hoc explanations that don't naturally arise from the absolute motion hypothesis. (You to include additional hypotheses)

You then no longer have a "simpler" Theory.



moreover, in the case where there is an inbound traveler who merely observes the outbound twin's clock - there is a discontinuity in the analysis - I know the standard (if there is such a thing) explanation of the lost time -

What discontinuity?



Take the case of the one way traveler - he passes earth at 0.8c and syncs his clock as he passes by - then continues at the same speed straight to Alpha Centuri - how much will he have aged when he arrives? - how much time will have accrued on the clock back on earth?
He will have aged 3.225 yrs. By his reckoning because the distance from Earth to Alpha C is 2.58 ly( due to length contraction) and that's how long it takes to traverse this distance at .8c

By Earth's reckoning he will also have aged 3.225 yrs, because by Earth time he took 5.375 yrs to traverse 4.3 ly at .8c, but his time rate ran at .6 of Earth time.
 
1,525
10
Janus - Things appear to be symmetrical with respect to the earth centered reference system - one of the theories that has been advanced is that space is conditioned by the local gravitational field - I brought this up in one of my earlier posts - this explains why MMx and KT experiments fail to detect the earths motion relative to local space - but we can still detect the earths motion relative to distant light sources such as the CBR and starlight aberration. Gravitation conditioning of space is local - it differs from ether drag - which is disproven by aberration.

There are no experiments that I have come across that distinguish between Lorentz Ether theory and SR - they both lead to the same results - but in the former, time dilation is actual not observed - but the two theories rely opon exactly the same math (derived first as you know by Lorentz). The objection to Lorentz Ether Theory as originally propounded, is that it does require some actual physical deformation - which admittedly is hard to visualize and - as you and others would point out - makes the theory "not simple" But you can arrive at a free space result w/o the hypothesis of physical contraction - if time dilation is actual then length contraction is apparent (consequent to the fact that two observers in relative motion will measure the relative velocity between them as equal to v.


If the Alpha C traveler ages 3.2 years by his own calculation in his own environment (and I don't care what the earth guy calculates for the traveler). What I am saying is - if the traveler ages 3.2 years when he arrives -and the earth clock has logged 5 years or whatever when he arrives - how can time dilation not be actual? (The earth twin can determine when the traveler arrives on Alpha by having the traveler send a light signal and subtract 5 years off his clock when it arrives back at earth). This is the extended lifetime of the high speed muon problem, cloaked in astronomical fiction - I know its possible to weasel-word through it using SR - I am not unfamiliar with the many treatise on the subject - but they do not all agree and in fact there seems to be no official consensus

Several months ago there was a posting on these boards re data from clocks on board the space station. The applet depicted how the on- board clocks were observed to run at different speeds depending their velocity orientation vector as the station moved in its orbit about the earth. How say you on this.
 

Related Threads for: Some doubts on relativity

  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
2
Replies
29
Views
3K
Replies
1
Views
1K
Replies
2
Views
919
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
13
Views
2K
  • Last Post
Replies
8
Views
2K
Top