Who is More "Relative"?

[RyanJ]

who is to say WHO is actualy moving' date=' what dictates the one whos time goes slower:confused:[/quote']

 

Read the books called "The Elegant Universe" and "The fabic of the cosmos" by Brian Greene - he dose a good job of explaining it through mst of the book is on multiple dimensions, M-theory and string theory

 

I'm not going to even try - I suck at explaining things but he does a good job

 

Its like two people accelerating towards eath other with no reference arround them, each can make an equally valid claim the other is moving...

 

Sorry I can't be of more help

 

Ryan Jones

[YT2095]

well yeah, this whole thread is basicly split into 2 main questions, the one you presented just, and the one about what makes the time alter?

 

if it has something to do with Speed, then 2 single bodies one moving one not, then who is who? what clock gets affected? all IS "relative" after all.

 

and what mechanism actualy affects these clocks? is it mechanical characteristic?, something we accept but don`t understand?, time gets lost but nothing`s out of Phase (another bag of questions there).

[RyanJ]

well yeah' date=' this whole thread is basicly split into 2 main questions, the one you presented just, and the one about what makes the time alter?

 

if it has something to do with Speed, then 2 single bodies one moving one not, then who is who? what clock gets affected? all IS "relative" after all.[/quote']

 

Thats the thing, becauses everything speed is relative to light they are both correct. One standing in space sees the other comming towards them and so does the other... both are correct from their relative perspective simply because you you need a reference from which to derive who is moving...

 

[/quote=YT2095]

and what mechanism actualy affects these clocks? is it mechanical characteristic?, something we accept but don`t understand?, time gets lost but nothing`s out of Phase (another bag of questions there).

 

This... I will see if I can exmplain itthe way I see it.

 

You old a ball in a container, assume this is a photon andthe upper and lower surfaces have the effect of being mirrors.

 

Put this ona table stationary and it will move up and down vertically. If wethen start moving it will move firther and firuther from the vertical, ineffect convering more space in the same time. So the direct effect of increased speed leads to a reduction of time from therelative respective.

 

 

there is also the one about two waring leaders sitting at a table (In a moing train and both refuse to sign the agreemnt first. A light is placed equally between them and the instnt they see the lightthey btoh ign, the same time.

 

Even though they agree on that the people outside the moving train will say that the person moving with the direction of the train would have seen it fractionally after the one moving in opposition to the trains motion. Who is correct, they both are from theirorn frame of reference

 

http://en.wikipedia.org/wiki/Time_dilation

 

If the best I can think of to hep you

 

Cheers,

 

Ryan Jones

[YT2095]

I understand how the frame thing works (I think), but with 2 guys in space with accurate watches, no gravity or other trivia involved, one moves away very fast in a circle around the other, each (to the other) will appear to be in motion, they eventualy meet up and their clocks are different, one will be faster than the others.

but which one, and Why?

[Severian]

if it has something to do with Speed' date=' then 2 single bodies one moving one not, then who is who? what clock gets affected? all IS "relative" after all.

[/quote']

 

It is symmetric. When the guy on the plane slows down to the Earth's rest frame, he sees that his clock is slow. But if the guy on the Earth speeds up to the plane's rest frame he will see that his clock is slow.

 

and what mechanism actualy affects these clocks? is it mechanical characteristic?, something we accept but don`t understand?, time gets lost but nothing`s out of Phase (another bag of questions there).

 

No time is lost. The time between the two events (synchronising clocks at the start and comparing them at the end) is genuinely different in the different frames. Just as flying from Glasgow to Warsaw with a change of plane in London is travelling a different distance from a flight from Glasgow to Warsaw via Paris.

[YT2095]

so how does speed affect clocks and things then?

 

it`s not Gravity, it`s not direction, it can`t be acceleration as decceleration would reset it again back to normal, they`re not out of phase in a rest frame as I doubt we`de even be able to see or interact with them.

what changes/causes it?

[Severian]

it`s not Gravity' date=' it`s not direction, it can`t be acceleration as decceleration would reset it again back to normal, they`re not out of phase in a rest frame as I doubt we`de even be able to see or interact with them.

what changes/causes it?[/quote']

 

It is direction - it is direction in space-time. If you think of time as being another direction, ie. so you count a component of the velocity as how fast an object is moving along the time direction, then everything has a velocity c in space-time. A 'stationary' object is moving with all of its velocity along the time axis. An object which moves in ordinary space is using up some of that velocity in the space directions so can't move in the time direction as fast, i.e. time passes more slowly. An object which moves at speed c in space (eg light) is stationary in the time direction.

[RyanJ]

so how does speed affect clocks and things then?

 

it`s not Gravity' date=' it`s not direction, it can`t be acceleration as decceleration would reset it again back to normal, they`re not out of phase in a rest frame as I doubt we`de even be able to see or interact with them.

what changes/causes it?[/quote']

 

Well.... gravity does affect time becaue gravity has the same effect as constant accelerated motion - just like you feel when something is accelerating.

 

And the slower things go the slower things move the faster time does actually move, in effect it is the reverse...

 

If I explained that wrong experts please correct me

 

Like I said I suck at explaining.. really read those books

 

Cheers,

 

Ryan Jones

[YT2095]

Severian, you`re Partly getting there in my way of understanding it, I Think I understand some of what your saying and it seems to make partial sense, all up until you make your way back to the initial frame you came from, why don`t the clocks all go back to normal again?

[RyanJ]

Severian, you`re Partly getting there in my way of understanding it, I Think I understand some of what your saying and it seems to make partial sense, all up until you make your way back to the initial frame you came from, why don`t the clocks all go back to normal again?

 

Because time time has been lost, only from a relative frame reference has anything actually changed...

 

Cheers,

 

Ryan Jones

[Severian]

Severian, you`re Partly getting there in my way of understanding it, I Think I understand some of what your saying and it seems to make partial sense, all up until you make your way back to the initial frame you came from, why don`t the clocks all go back to normal again?

 

You clock is measuring the time you have taken to get from event A to event B. That is a different time-length (if you see what I mean) for your journey than the time between A and B for the stationary person's journey. You have both travelled through space-time at 'c', but he used all of that velocity to travel from A to B along a direct route (not moving at all in space) while you used some of the 'c' moving through space so you weren't able to move as far in time as he was. Your clock is measuring the time you have spent moving between the two events, but his clock has measured the time he spent moving between them. Since you moved less (in the time direction) your clock should read less, even when you decelerate back into his frame.

[YT2095]

so from A to eventual B there is a change, that I agree with, and can also partly understand why

 

on the back from B to A (so we may compare our clocks) there may not be a change in time?

as in, if I were God and could see the guys clock at B, that said 11:59, and then magicaly jump instantly to the guy in position A and read his at 12:00.

then the guy at B travels back to A in say 10 minutes.

then both clocks will still be 1 minute appart in time as the "damage was done" so to speak when they were in 2 different postions A and B, and simply reversing your direction will have no affect at all?

 

other than being perhaps badly worded, does that sound about right?

[Saryctos]

so from A to eventual B there is a change' date=' that I agree with, and can also partly understand why

 

on the back from B to A (so we may compare our clocks) there may not be a change in time?

as in, if I were God and could see the guys clock at B, that said 11:59, and then magicaly jump instantly to the guy in position A and read his at 12:00.

then the guy at B travels back to A in say 10 minutes.

then both clocks will still be 1 minute appart in time as the "damage was done" so to speak when they were in 2 different postions A and B, and simply reversing your direction will have no affect at all?

 

other than being perhaps badly worded, does that sound about right?[/quote']

 

because, person1 accelerates to get to B, then accelerates again to return. The clocks would synchronize had person2 accelerated to meet you at B.

 

With that said, this thread does make me cry on the inside.(for the poor misunderstood relativity)

[Severian]

Bah, just accidentally deleted my response! Lets try again.....

 

Firstly I was intending events A and B to be at the same space point but at different times. So for example, plane guy sets off at event A: Earth N:52`32, W:002`04, Alt:492ft at 18:20 March 2, 2006, and arrives back at point B: Earth N:52`32, W:002`04, Alt:492ft at 18:20 March 16, 2006 (two weeks later).

 

You seem to be thinking of him setting off at A, travelling to B, where he turns round and comes back to arrive home at C. Notice that C is not equal to A because they are at different times.

 

With the God thing there is a problem. The whole reason that your clocks are travelling at different speeds is that you are defining your time diferently. Neither is wrong - they are just different. So when you say 'instantly' you have to state which time definition you mean (because whether or not events are 'simultaneous' depends on your frame).

 

I suspect from your wording that you want God to use the time direction as defined by the guy in the plane(?) In that case, he would read the guy on the Earth's clock as being slow. So it is actually the other way round from what you said. Plane guy's clock reads 12:00 while Earth guy reads 11:59.

 

Also, the trip back will have as much effect as the trip out, so when he gets home his clock will read 12:10 (if it took 10 minutes) while the guy on Earth's will read 12:08. At this point it looks like the Earth guy's clock is slow!

 

Actually there is no need for god-like powers - all you need is lots of little helpers standing stationary with respect to you at the turnaround point with a stopwatch.

[s pepperchin]

I understand how the frame thing works (I think)' date=' but with 2 guys in space with accurate watches, no gravity or other trivia involved, one moves away very fast in a circle around the other, each (to the other) will appear to be in motion, they eventualy meet up and their clocks are different, one will be faster than the others.

but which one, and Why?[/quote']

 

you can't use this as an example because if they both see the other one going around them then one of them must be travelling in a curcular path and that requires accelaration. So this would not happen one of them would feel that acceleration and they would know that they are the one that is moving.

[swansont]

That is a very 'practical' response. One could imagine, for the purposes of a thought experiment, that the Earth is not rotating (or only rotating very slowly compared to the planes velocity) and that the 'Earth' is so large that the acceleration (from the circular motion of the planes) is small enough to be neglected. Then your thought experiment can be handled purely with SR.

 

Actually you don't want a large earth, since the Sagnac time shift you'd get is proportional to the area enclosed. But the earth-centered-inertial (ECI) frame is convenient for a lot of analyses as long as you account for the noninertial terms.

[swansont]

and what mechanism actualy affects these clocks? is it mechanical characteristic?' date=' something we accept but don`t understand?, time gets lost but nothing`s out of Phase (another bag of questions there).[/quote']

 

It's not a physical mechanism that is affecting the clocks, i.e. it's not a mechanical effect, it's the nature of time. Time and distance are not absolute, though at speeds with which we are familiar we don't see this, so it seems very strange. Time and distance depend on the frame in which you measure them.

[Jacques]

Would it be more simple to say that acceleration slowdown the rate of clock ?

Speed does not slow the rate of the clock.

If true then gravity being an acceleration our clock on earth are all slowing down relative to a clock far far in space where gravity is weaker.

[Janus]

Would it be more simple to say that acceleration slowdown the rate of clock ?

Speed does not slow the rate of the clock.

No' date=' because it would not be correct to say so.

For example, I send two clocks off into space, accelerate them both up to the same speed with the same acceleration, let them coast for a while, and then bring them back, again with each clock experiencing the same acceleration.

The difference is that I let one clock coast for a longer period before bringing it back.

 

Then the clock that coasted for a longer period will read less when the clocks are brought back together

 

If true then gravity being an acceleration our clock on earth are all slowing down relative to a clock far far in space where gravity is weaker.

 

While a clock on the surface of the Earth does run slower than one in space it is not due to the local strength of gravity. It is due to a difference of potential between the two clocks.

 

For example, the Surface gravity of Uranus is less that that of the Earth's, but a clock on the surface of the Uranus will run slower than one on the surface of the Earth.

 

Another example would be two clocks at different heights in a uniform gravity field(one that does not change in strength between the two heights). The higher of the two clocks will run faster, even though it feels the same gravtitational force as the lower one.

[Jacques]

The difference is that I let one clock coast for a longer period before bringing it back.

OK but still it is not the speed that cause the clock to run slower. It is the acceleration who slows the clock. The rate of the clock stay the same at constant speed.

 

the Surface gravity of Uranus is less that that of the Earth's

 

Are you sure of that ? Uranus is a lot more massive than earth, but have a bigger diameter.

I think you would be crushed if you went on the surface of that planet but not 100% sure would need to do the calculation...

It is due to a difference of potential between the two clocks.

and you said

Another example would be two clocks at different heights in a uniform gravity field(one that does not change in strength between the two heights). The higher of the two clocks will run faster, even though it feels the same gravtitational force as the lower one.

Don't you se a contradiction ?

[Janus]

OK but still it is not the speed that cause the clock to run slower. It is the acceleration who slows the clock. The rate of the clock stay the same at constant speed.

 

If that were true then both clocks would read the same as they experienced the same accelerations. But they don't' date=' they record different times.

 

 

 

Are you sure of that ? Uranus is a lot more massive than earth, but have a bigger diameter.

I think you would be crushed if you went on the surface of that planet but not 100% sure would need to do the calculation...

 

mass of Uranus: 8.68e25 kg

Radius of Uranus 25,559,000 meters.

Formula for acceleration due to gravity:

[math]a_g = \frac{GM}{r^2}[/math]

plug the numbers in and you get 8.87 m/sec² for Uranus comapred to 9.8m/sec² for the Earth.

 

It is due to a difference of potential between the two clocks.

and you said

 

Another example would be two clocks at different heights in a uniform gravity field(one that does not change in strength between the two heights). The higher of the two clocks will run faster, even though it feels the same gravitational force as the lower one.

 

 

Don't you se a contradiction ?

 

No contradiction if you understand the difference between 'local force due to gravity' and 'gravitational potential'. If I drop the higher clock in the uniform field, it will fall, and as it falls it will gain speed. As it gains speed it gains kinetic energy. It can only gain kinetic energy by giving up potential energy. This potential energy is in the form of gravitational potential.

Thus the two clocks are at different Gravitational potentials and according to Relativity, it is the this difference in potential that acounts for the time rate difference between the two clocks, not the gravitational force felt by the clocks.

[s pepperchin]

Time dilation is caused by velocity the relativistic part of the equation is the [math]\gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}[/math] so it is the ratio of velocity to c that causes this effect.

[Jacques]

My point is that velocity is not the cause of the change in rate of the clock.

At constant speed the rate of the clock doesn't change. At v=.86 the rate of the clock is .5 and will always be .5 as long as v=.86

You are speaking of rate, I am speaking of change of rate. Can you reread my post and I think you will understand what I want to tell

Thanks

[Saryctos]

It's not a physical mechanism that is affecting the clocks, i.e. it's not a mechanical effect, it's the nature of time.

Time having an effect on an object has always been one of the things that turned me away from modernized physics.

Time is just a mechanism for evaluating changes relative to something else.

 

 

 

Example: You have a conveyor belt accelerating very fast(veeery fast), and on this you have a runner moving in the oposite direction at the same speed, you also have an observer who stands off the conveyor belt next to the runner. there is a watch on the runner, on the conveyor belt, and on the observer.

 

now, the question is, when the watch on the conveyor meets the runner and the observer on it's return(underside of the belt) what will the watches read relative to each other?

 

observer --> conveyor: the conveyor watch accelerated relative to the observer, and should read a different time.

runner --> conveyor: the runner accelerated relative to the conveyor watch, and should read a different time

observer--> runner: the runner did not accelerate relative to the observer, their watches should match.

 

Problem: The runner accelerated twice as fast relative to the conveyor when compaired to the observer. Therefore, the conveyor's time difference with the runner should not match the time difference of the observer.

 

If you were to take into account that acceleration affects the watches time keeping ability, and not time itself, then you can fix this problem. Unfortunately, what I've been told is that just isn't true.

[s pepperchin]

two objects in different frames do not have the same second.

 

as far as the observer, runner, belt cenario goes from the perspective of the observer the clock on the belt would be running slow while the clock on the runner is keeping time with the clock held by the observer. In the frame of the belt both of the other clocks would be running slower and the runner would see the same thing as the observer. This is because the observer and the runner are not moving RELATIVE to each other.