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Collector
Posts: 4685
Joined: August 21st, 2001, 12:37 pm

### Time dilation

when the observers come back to each other also make discussion much simpler, because as rmax is pointing out when traveling away from each other and then tryng to compare observations then we also have to do with signal speed, that in special relativity is limited to speed of light.but if observers also do not return to each other we also get into a lot of tricky questions that are hard to test out and can lead to a lot of discussions if (in particular with people not well read on the topic). Because the observers then in addition need to communicate by signals over long distances. Is the speed of light really isotropic, this again will depend on how you measure time and speed, but yes under Einstein's assumptions of how to measure speed and time, light is isotropic, but there exist other variants of relativity theory that look at this slightely differently, but still is consitent with experiments.But yes time dilation is a fact it looks like, and when observers returning to same frame we have very strong reasons of what frame had highest velocity etc. In other examples things get quickly quite complicated.
Last edited by Collector on January 31st, 2011, 11:00 pm, edited 1 time in total.

Richyiee
Topic Author
Posts: 57
Joined: September 2nd, 2008, 5:20 pm

### Time dilation

if the frame of reference was the rocket wouldnt its velocity and acceleration be 0.

Collector
Posts: 4685
Joined: August 21st, 2001, 12:37 pm

### Time dilation

QuoteOriginally posted by: Richyieeif the frame of reference was the rocket wouldnt its velocity and acceleration be 0.Take a ride on your motorbike, you are moving at the same velocity as your harley, but do you not feel accelration. If you not feel acceleration then time toreplace the engine!
Last edited by Collector on January 31st, 2011, 11:00 pm, edited 1 time in total.

tagoma
Posts: 18363
Joined: February 21st, 2010, 12:58 pm

### Time dilation

if i understand well the the speed-of-light rocket explanation, the cosmetic industry could make its revolution in sending its don't-wanna-look-old clients travelling on a high-speed rocket. am i right?well, i wonder about possible collateral damages. could plastic boobs resist to speed acceleration ?? is anyone aware of scientific research on this peculiar topic ?
Last edited by tagoma on January 31st, 2011, 11:00 pm, edited 1 time in total.

Richyiee
Topic Author
Posts: 57
Joined: September 2nd, 2008, 5:20 pm

### Time dilation

you keep on coming back to this "feeling acceleration", its just not very convincing ;p . If there only existed 2 things in the universe, tom and jim, and we observe the distance between tom jim was getting shorter, you could say tom was accelerating towards jim, or you could say jim was accelerating towards tom , or they are both accelerating towards each other, why do you keep insisting on one being the prefered frame of reference

Collector
Posts: 4685
Joined: August 21st, 2001, 12:37 pm

### Time dilation

QuoteOriginally posted by: Richyieeyou keep on coming back to this "feeling acceleration", its just not very convincing ;p . If there only existed 2 things in the universe, tom and jim, and we observe the distance between tom jim was getting shorter, you could say tom was accelerating towards jim, or you could say jim was accelerating towards tom , or they are both accelerating towards each other, why do you keep insisting on one being the prefered frame of referenceif you are thinking about that the acceleration of the space-ship leaving earth is looking different from the perspecitive of the earth observer and the space-ship observer then you are right. How big the accelration was as measured by different observers is another discussion. A person moving at a constant velocity will not observe accelration in her own frame, but someone accelerating will observe accelration in own frame, this they can both agree on when comparing measurments when coming back together. In other words both can agree on assymetric situation and on the direction of the assymetry, both will not claim they felt acceleration. With feeling accelration I should possibly say as measured by very accurate instruments. As soon as you move away from the example of both starting in same frame and then coming back to each other in same frame things get much more complicated. In your example above when do both observer starts their clocks to compare if they not start in the same frame? do they send light signals to each other etc, then agian you have to discuss lots of other aspects of relativity theory. Try to understand the "simple" examples first.
Last edited by Collector on January 31st, 2011, 11:00 pm, edited 1 time in total.

rmax
Posts: 6080
Joined: December 8th, 2005, 9:31 am

### Time dilation

QuoteOriginally posted by: Richyieeyou keep on coming back to this "feeling acceleration", its just not very convincing ;p . If there only existed 2 things in the universe, tom and jim, and we observe the distance between tom jim was getting shorter, you could say tom was accelerating towards jim, or you could say jim was accelerating towards tom , or they are both accelerating towards each other, why do you keep insisting on one being the prefered frame of referenceIncorrect. There is no preferred frame of reference. The usual example is if you are in a lift travelling at a constant speed, you cannot tell if you are moving or not (i.e. there is no experiement you can perform without opening the doors and seeing if the floors are zipping by). When the lift accelerates you cannot tell if it is gravity that has increaed or whether the lift is now accelerating (again no experiement is available to explain what is causing the acceleration). Hence all frames of reference at a constant speed are equal, all frames of reference at a constant acceleration (regardless whether it is gravity of an energy input) are equal. However I can perform an experiment that shows if one lift is experiencing an acceleration or not. Hence acclerating frames and no accelerating frames are different and hence need to be treated differently. Neither is preferred but is shows that the twins paradox is only a paradox because for the paradox to exist an acceleration must have occured, hence the frames of reference are not identical.In terms of your tom/jim example - a distance getting shorter is comparing two frames of reference (via a Lorentz transformation) - and means that there is a velocity, NOT an acceleration (dv/dt). EDIT: Unskyld Collector - cross posting!
Last edited by rmax on January 31st, 2011, 11:00 pm, edited 1 time in total.

Richyiee
Topic Author
Posts: 57
Joined: September 2nd, 2008, 5:20 pm

### Time dilation

my point in the tom/jim example is that there are many velocities combinations for tom and jim which can describe the observation that they are getting closer.if we change it abit so that tom and jim are accelerating towards each other, then again there are many combinations of accelerations for tom and jim which describe the same obseration. e.gWe observe the distance between tom and jim is decreasing by 1m/s, we can describe this by saying [tom's velocity is 1m/s towards jim,jims velocity is 0] or [toms velocity is 0, jims velocity is 1m/s towards tom] e.g2 We observe tom and jim accelerating towards each other at1m/s/s, we can describe this by saying [tom's velocity is 1m/s/s towards jim,jims velocity is 0] or [toms velocity is 0, jims velocity is 1m/s/s towards tom] In the case of the lift, by saying that you are accelerating you are implying that the building floor is still, (Because your acceleration describes the observation that the distance between you and the building floor is increasing/decreasing) thus you implicity state your prefered reference frame (the building floor), but as in the tom/jim example you could also describe this observation by saying the floor is accelerating away from the lift that is still.
Last edited by Richyiee on January 31st, 2011, 11:00 pm, edited 1 time in total.

Richyiee
Topic Author
Posts: 57
Joined: September 2nd, 2008, 5:20 pm

### Time dilation

http://mb-soft.com/public2/twinspar.htmlthis guys suggests when the twins meet again they are the same age

farmer
Posts: 13477
Joined: December 16th, 2002, 7:09 am

### Time dilation

Can we accelerate someone in a circle, so that the swollen side of his head is younger than the numb side?

Posts: 23951
Joined: September 20th, 2002, 8:30 pm

### Time dilation

If I come upon two objects traveling at fixed high velocities relative to each other and query observers on each object, I can't predict which object's observer will claim to have the "slow clock" relative to the other object unless I know the unobserved, historical accelerations between them. Did object 1 accelerate away from object 2 or did object 2 accelerate away form object 1?The acceleration interpretation seems quite intriguing because it says relative velocity, by itself, is insufficient to predict which object experiences time dilation. One must know the entire history of past accelerations to estimate the time dilation.

trackstar
Posts: 27445
Joined: August 28th, 2008, 1:53 pm

### Time dilation

QuoteOriginally posted by: farmerCan we accelerate someone in a circle, so that the swollen side of his head is younger than the numb side?If you spun him so that the swollen side of his head was facing inward, you might have a certrifuge effect and the swelling would go down.Would have to spin him pretty fast, but that's ok.I have a few candidates in mind...(they are not on this thread, so we will have to go and get them). Some educational videos:Extreme Raw Power Centrifuge and actually astronauts and fighter pilots have to go through this kind of training:Centrifuge Training One, two, BREATH. Looks fun to me!
Last edited by trackstar on January 31st, 2011, 11:00 pm, edited 1 time in total.

Richyiee
Topic Author
Posts: 57
Joined: September 2nd, 2008, 5:20 pm

### Time dilation

if you only have two points of reference, the only meaningful measure is the distance between the two objects at each point in time, how can you say which is accelerating away from which when you only have a scaler measure

Posts: 23951
Joined: September 20th, 2002, 8:30 pm

### Time dilation

Acceleration due to gravity or due to induced forces (e.g., elevator or rocket) does have one distinct difference. A person at the North pole will feel a constant 1-G acceleration in one direction whilst a person at the South pole will feel 1-G acceleration in the opposite direction but neither object will experience the increasing time dilation effects that a 1-G rocket would.

ExSan
Posts: 4570
Joined: April 12th, 2003, 10:40 am

### Time dilation

what is a vortex ?

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