a valid measurement. Velocity is displacement / time in a single reference frame. Your proposed scheme measures lab frame distance / spaceship time, w hich isn't a useful number and certainly isn't the ship's velocity.
if you travel at c, you arrive at the same time you left, by your own recko ning.
light does not age and does not experience time, from it's own perspective it leaves and arrives simultaneously.
Yes, if that were possible, I'd expect my speedo to show 'infinite', albeit for zero time. Is that wrong?
Yes. I reckon so.
Cheers
-- Syd
It is a reasonable question. If you were at either end of rod A-B length L then you would observe the mile posts as being 1/gamma apart and the same faster tick rate at both observing positions.
A----|----B -> v \ / A----|----B \ / A----|----B \ A----|----B
Hope the ascii art survives. The last one got mangled by auto tabs.
But the tick rates the observer in the middle sees would be faster from the front of the train and slower from the rear since the train is moving towards one emitting source and away from the other. The ticks are emitted at fixed distance intervals in the rest frame of the posts.
Light signals inside the train travel at c, the speed of light, but if the train is doing 0.9c then it has to travel a lot further to reach the observer in the middle of the train when starting from the rear.
Relativistic version of the Doppler shift for the .
Regards, Martin Brown
Thanks, does that the man in the middle would get more ticks from the front detector than from the rear? That would make my head explode.
Cheers
-- Syd
Time dilation depends only on the relative speeds of the two frames. There' s an offset, though, which depends on where the observer is sitting vis a v is the source.
Cheers
Phil Hobbs
I don't understand this. The observer is sitting in one frame and observes the other frame, yes? Where is the source?
How does he do that if the objects in the other frame don't emit anything?
Cheers
Phil Hobbs
[Scenario: Previously arranged mile markers in space. Ship travelling at 0.87c wrt these markers. Marker detectors at front and rear of mile-long ship. Man in middle of ship listening to ticks from both detectors.]
So man-in-the-middle would get the same frequency of ticks, front and rear, but with some time offset? I think he must.
And his simple speedometer, which times ticks, would show >c if he's moving at >0.87c relative to them? I think it must - at 0.87c he'll cover 1 light year as previously measured in 1 of his years as measured by his clock.
Cheers
-- Syd
You need to go back and read about Relativity again. Nothing will show that you have traveled at 1.25c. You are confusing the facts.
-- Rick C
Maybe I am, but that's not helpful.
If I travel at 0.87c for 1 year of my time as measured by my clock or my beard growth, how far will I have travelled?
Cheers
-- Syd
'
at 0.87c your time is dilatated by a factor of 2, so 1 of your years will b e 2 years here on Earth. It means that you'll travel 2 * 0.87c = 16.5 * 10^12 km = 1.74 ly (with some approximation).
Bye Jack
Your local clock is ticking slower. This is measurable on a jet liner (although a correction for the height of the aircraft and the influence of reduced gravitaional potential is also needed).
You should be able to work that out for yourself. Muons would not reach the ground if their lifetimes were not extended by time dilation.
ISTR that if you could accelerate a spaceship towards the centre of our galaxy at a steady 1g then you would arrive there in about 25 years.
There are some obvious practical problems with doing this.
Regards, Martin Brown
I thought I would have travelled 1 light year, however jack4747 makes it
1.74 light years. Either way ISTM that my mile marker counting speedometer would read either c or 1.74c and so far only John Devereux explicitly agrees. Will it?Cheers
-- Syd
no, your speedometer will read 0.87c, because it will give you the speed re spect the outside (that is not moving), so 0.87c.
In special relativity (but in general relativity too I think) the maximum s peed that you can reach or measure is c, nothing can go over it.
The most famous example is: you are on a train that is moving at c speed. Y ou shoot with a gun in the same direction that the train is moving, the pro jectile sill move at a speed equal to say v.
Common sense (and Newtons laws) will say seen from outside the projectile w ill move at a speed = c + v.
Not true. (never ever use common sense in physics)
From outside projectile speed will be c. You will see the projectile moving at speed = v.
That because, since you're moving at c speed, the time inside the train is slowed down to 0 (time is stopped). So from the outside even if common sense says the projectile should be movi ng faster than the train (that is a c speed), it will take a infinite time to reach the front of the train.
Think of a movie. A movie usually run at 30 frames per seconds. At relativi stic speed you slow down the fps to, let say, 1 frame per hour (or less). For you it will take forever to see the whole movie, but for the actors ins ide, the time will pass normally.
Bye Jack
I know that nothing can go faster than c. But my speedometer will
*show* >c if I pass more than 186282 of the mile markers I carefully set out earlier in 1 of my personal seconds because that is how speedos work.Please will someone agree?
Cheers
-- Syd
tto:
it
d respect the outside (that is not moving), so 0.87c.
um speed that you can reach or measure is c, nothing can go over it.
no, because if you measure the distance between the miles marker when you'r e moving at 0.87c, you will measure approximately 0.5 mile, and your speedo meter to be accurate has to take this into account and it will measure 0.87 c.
Bye Jack
I measured the distances when I laid them out. My speedo is a simple affair, doesn't know any better and will indicate >c.
Cheers
-- Syd
tto:
s it
ux
eed respect the outside (that is not moving), so 0.87c.
imum speed that you can reach or measure is c, nothing can go over it.
et
rk.
ou're moving at 0.87c, you will measure approximately 0.5 mile, and your sp eedometer to be accurate has to take this into account and it will measure
0.87c.yeah, sure, I really don't care what you think. You're wrong. If you can't see why, read a book or watch one of the dozens online lesson that universities put online.
I will not spend any more time on this subject with you.
Bye Jack
Who is doing the measuring? That is the issue. Who measures the year and who measures the distance?
Since you want to know what speed the traveler will perceive, the traveler is the relevant point of view.
Any school child can tell you that distance will be 0.87 light years... if both are measured by the traveler.
-- Rick C
If your mile marker is counting premeasured miles AND the traveler's speed is 0.87 as measured by an observer in the same frame of reference as the mile markers, then yes, the traveler will measure a speed other than 0.87c.
As someone else has already indicated, the traveler will measure the distance between the mile markers as being much less than a mile.
To answer your question you need to define the frame of reference you use to measure speed, distance and time.
-- Rick C
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