How fast am i traveling???

del88

I've been reading a bit about einstein and can't get my head around something.......
How fast am i traveling....if i was to take of in a space ship i would be moving away from the earth at a given speed....lets say 2000mph....after a week i would only be moving away from the earth at that speed...all other objects is the universe would be moving at diffrent speeds..some towards,some at the same speed....at that point ....how fast am i traveling.
Einstein talks about traveling at close to the speed of light and how time slows....but How would he measure that speed ? Is it measured from the original fixed point in space/time??

Professor_Fink

del88 wrote: »

I've been reading a bit about einstein and can't get my head around something.......
How fast am i traveling....

The whole point of relativity is that there is no preferred reference frame, and hence no absolute velocity. What matters is relative velocity. Different observers will see you moving at different speeds depending on their velocities relative to one another. The only reason one twin ages faster than the other in the twin paradox is because the symmetry is broken because only one twin accelerates.

caffrey

Fink is correct, it is all relative, even if you are not "moving" on earth you are actually still moving, the earth is rotating etc etc. even if you consider that there was nothing but you and the earth in existance and you were floating in space and "not moving" and the earth was also "not moving", who is to say that you both arent rotating and you just dont seem to be so because you are in geosynchronous orbit, insert an observer somewhere else and he/she recognises your rotation.

del88 wrote: »

Einstein talks about traveling at close to the speed of light and how time slows....but How would he measure that speed ? Is it measured from the original fixed point in space/time??

There are only 2 things assumed by eisteins theory of special relitivity.

1. The laws of physics are the same in all reference frames and
2. The speed of light in a vacuum is a constant.

there is an extensive article on wikipedia I am sure

Morbert

caffrey wrote: »

Fink is correct, it is all relative, even if you are not "moving" on earth you are actually still moving, the earth is rotating etc etc. even if you consider that there was nothing but you and the earth in existance and you were floating in space and "not moving" and the earth was also "not moving", who is to say that you both arent rotating and you just dont seem to be so because you are in geosynchronous orbit, insert an observer somewhere else and he/she recognises your rotation.





There are only 2 things assumed by eisteins theory of special relitivity.

1. The laws of physics are the same in all reference frames and
2. The speed of light in a vacuum is a constant.

there is an extensive article on wikipedia I am sure

A small caveat: Special relativity only covers the lorentz group of transformations, so the laws of physics are the same in all inertial reference frames. You have to go to General Relativity to say the laws of physics are the same in all reference frames.

del88

So let me get this straight.......to me I'm never really moving...everything else is moving either away or towards me at different speeds and different rates of time as observed by me....ok
so my mass is always the same to me..... but if i could observe the mass of the traveling object it would increase to ME as it accelerates ...but to itself it would remain the same....but if it where to look back at me i would be to the one whose mass is increasing....i think..
Still thinking here.....dose that mean we would have the combined mass from the big bang caused by the acceleration from that point as viewed from that point in space time???
cheers for the replies...it's a very interesting idea..

Morbert

del88 wrote: »

So let me get this straight.......to me I'm never really moving...everything else is moving either away or towards me at different speeds and different rates of time as observed by me....ok
so my mass is always the same to me..... but if i could observe the mass of the traveling object it would increase to ME as it accelerates ...but to itself it would remain the same....but if it where to look back at me i would be to the one whose mass is increasing....i think..
Still thinking here.....dose that mean we would have the combined mass from the big bang caused by the acceleration from that point as viewed from that point in space time???
cheers for the replies...it's a very interesting idea..

Relativistic mass does increase with relative velocity, though I am not a fan of that formalism. I prefer to think of momentum as increasing "relativistically" with velocity. This leaves mass invariant (i.e. the same for all observers). This invariant mass is the mass found in the equation.

E^2 = p^2c^2 + m^2c^4

Gurgle

Professor_Fink wrote: »

The only reason one twin ages faster than the other in the twin paradox is because the symmetry is broken because only one twin accelerates.

I think I've confused myself un-neccessarily with this:

Twin paradox:

#1 accelerates away from #2, #1 experiences time dilation relative to #2 and ages more slowly.

From the point of view of #1 it's #2 who accelerates away... so #2 should experience time dilation relative to #1. But the opposite is the case, #2 experience time contraction relative to #1.

Or is time dilation an effect of acceleration?
That would seem to contradict the equivalence of gravity and acceleration.

del88

Gurgle wrote: »

I think I've confused myself un-neccessarily with this:

Twin paradox:

#1 accelerates away from #2, #1 experiences time dilation relative to #2 and ages more slowly.

From the point of view of #1 it's #2 who accelerates away... so #2 should experience time dilation relative to #1. But the opposite is the case, #2 experience time contraction relative to #1.

Or is time dilation an effect of acceleration?
That would seem to contradict the equivalence of gravity and acceleration.

Ye thats true......both of them are accelerating in refrence to each other.....
If me and gurgle where in space and i accelerated away from him woudln't he be effectivly accelerating away from me in aqual but oppiste way.......so if we are both accelerating away from each other in relation to our own frame of refrence then shouldn't time dialation effect us both the same way ....effectivly cancelling it's effect out???? hmm

Morbert

del88 wrote: »

Ye thats true......both of them are accelerating in refrence to each other.....
If me and gurgle where in space and i accelerated away from him woudln't he be effectivly accelerating away from me in aqual but oppiste way.......so if we are both accelerating away from each other in relation to our own frame of refrence then shouldn't time dialation effect us both the same way ....effectivly cancelling it's effect out???? hmm

This is why it's called the twin 'paradox'. If the laws of physics are the same in all reference frames, then why doesn't special relativity tell us that both twins witness time dilation? Each twin should witness themselves grow older than the other twin, but they clearly don't.

The paradox does have a solution: Special relativity says the laws of physics are invariant in all inertial reference frames. General relativity is needed if we wish to consider the laws of physics invariant in all reference frames, accelerated or inertial. In general relativity, there is a time dilation effect associated with acceleration. When the travelling twin accelerates, he experiences a uniform potential field equivalent to a gravitational field. Clocks in different locations in such a field will tick at different rates, so the travelling twin concludes that the earth twin's clock ticked faster in the presence of this field, and hence, the earth twin aged much more than the travelling twin. The earth twin experiences no such field, so the paradox is removed.

del88

Morbert wrote: »

General relativity is needed if we wish to consider the laws of physics invariant in all reference frames, accelerated or inertial. In general relativity, there is a time dilation effect associated with acceleration. When the travelling twin accelerates, he experiences a uniform potential field equivalent to a gravitational field. Clocks in different locations in such a field will tick at different rates, so the travelling twin concludes that the earth twin's clock ticked faster in the presence of this field, and hence, the earth twin aged much more than the travelling twin. The earth twin experiences no such field, so the paradox is removed.

ahhh
So it's the energy that is used by the accelerating twin (ie rocket boost) that differentiates between the two.....and that difference means that time dialation only applies to him (our her)....so in E=MC2 the enegy that is used by the accelerating twin is proportional to the amout of time dialation observed over a given time to the twin on they earth and likewise for the accelerating twin.....
Now it's a bit clearer...cheers

Morbert

del88 wrote: »

ahhh
So it's the energy that is used by the accelerating twin (ie rocket boost) that differentiates between the two.....and that difference means that time dialation only applies to him (our her)....so in E=MC2 the enegy that is used by the accelerating twin is proportional to the amout of time dialation observed over a given time to the twin on they earth and likewise for the accelerating twin.....
Now it's a bit clearer...cheers

If we do the calculations in the earth twin's reference frame, then we only need to consider the kinematics of the travelling twin. i.e. The specific forces experienced by the space twin aren't important, and only its velocity is. From the perspective of the space twin, the strength of the uniform potential field is important if we want to explicitly calculate "gravitational time dilation". This potential field is proportional to the force experienced by the space twin, but in an odd way no energy has been used on him because he is still technically stationary in his reference frame.

And the strange thing is neither twin's viewpoint is "more correct". It is just as correct to say the earth twin's clock ticked at a constant rate as it is to say the space twin's clock ticked at a constant rate, provided you specify the reference frame you are using.

Professor_Fink

Gurgle wrote: »

I think I've confused myself un-neccessarily with this:

Twin paradox:

#1 accelerates away from #2, #1 experiences time dilation relative to #2 and ages more slowly.

From the point of view of #1 it's #2 who accelerates away... so #2 should experience time dilation relative to #1. But the opposite is the case, #2 experience time contraction relative to #1.

Hi Gurgle,

There is a subtlety you seem to be missing here. Acceleration isn't relative in the same way velocity is. If you are in an accelerating frame, you experience a fictitious force, which you do not experience in a non-accelerating frame. So, only one twin experiences the fictitious force. This is what determines the difference in time dilation experienced. It's also the basis of for the equivalence principal in general relativity.

Gurgle wrote: »

Or is time dilation an effect of acceleration?
That would seem to contradict the equivalence of gravity and acceleration.

It is an effect of acceleration. Actually, it in no way contradicts the equivalence principal, since a gravitational field of equivalent strength to the fictitious force causes equal time dilation.

Gurgle

Professor_Fink wrote: »

It is an effect of acceleration. Actually, it in no way contradicts the equivalence principal, since a gravitational field of equivalent strength to the fictitious force causes equal time dilation.

Ah, thats the bit I was missing.
But wouldn't that mean that continuous exposure to a gravitational field would cause time to keep slowing, in the same way as continuous acceleration?

Professor_Fink

Gurgle wrote: »

Ah, thats the bit I was missing.
But wouldn't that mean that continuous exposure to a gravitational field would cause time to keep slowing, in the same way as continuous acceleration?

Yes, that's exactly what it means. In fact it is the reason for black holes, since the event horizon is the point where time has essentially stopped running from the perspective of an outside observer.

So time ticks slower for us than is we were floating freely in space, but only by a small amount.

del88

So acceleration is the opposite to gravity...

Professor_Fink

del88 wrote: »

So acceleration is the opposite to gravity...

No, acceleration and gravity are in some sense equivalent, rather than opposite.

Morbert

del88 wrote: »

So acceleration is the opposite to gravity...

You're very close to a cornerstone of relativity. An accelerating reference frame is equivalent to an inertial reference frame in a uniform gravitational field. This relationship means we can describe gravity in terms of spacetime curvature.

del88

Morbert wrote: »

You're very close to a cornerstone of relativity. An accelerating reference frame is equivalent to an inertial reference frame in a uniform gravitational field. This relationship means we can describe gravity in terms of spacetime curvature.

So their the same thing to a degree....they both have a simmilar effect on spacetime....
Thanks for the patience in trying to explain this to me lads .....