Relativity according to the observers in each frame

[Baby Astronaut]

If one person A is accelerating to (or traveling at) a very high speed relative to person B, do their views of each other work like this?...

 

Person A sees the actions of person B speeding up AND vice versa: person B sees the actions of person A speeding up.

 

Person B sees the aging process slowing down for person A, who in turn sees the aging process speeding up for person B.

 

So person A sees the other age quicker and move quicker.

While person B sees the other age slower and move quicker.

Edited November 24, 2011 by Baby Astronaut

[granpa]

http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

[swansont]

If at constant velocity, each will see the other's clock as running slow.

[Baby Astronaut]

To clarify fully, does that mean each person would see the other aging slower, when in reality just one of them is?

Edited November 25, 2011 by Baby Astronaut

[granpa]

it means you have to factor in relativity of simultaneity

 

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

 

each observer will also see the other one as shrunk.

 

this is possible because the length of an object is the distance from front to back at one simultaneous moment.

[Baby Astronaut]

I still don't get it. (What about my last question?)

[granpa]

how would we know?

[Mike-from-the-Bronx]

in Special Relativity:

 

To an inertial observer time for any inertially moving body or any accelerating body always runs SLOWER.

 

To an accelerating observer time for any inertially moving body always runs FASTER.

 

To an accelerating observer time for any other accelerating body may run FASTER or SLOWER. It's more complicated.

[between3and26characterslon]

If one person A is accelerating to (or traveling at) a very high speed relative to person B, do their views of each other work like this?...

 

Person A sees the actions of person B speeding up AND vice versa: person B sees the actions of person A speeding up.

 

Person B sees the aging process slowing down for person A, who in turn sees the aging process speeding up for person B.

 

So person A sees the other age quicker and move quicker.

While person B sees the other age slower and move quicker.

 

 

 

http://www.einstein-online.info/spotlights/dialectic

[swansont]

To clarify fully, does that mean each person would see the other aging slower, when in reality just one of them is?

 

They are both aging slower, according to the other observer. To break this symmetry, one of them has to accelerate. You can only say one of them is older/younger "in reality" if you have a single reference frame from which you can make the measurements. If they are both in inertial frames, you have two.

[granpa]

how would we know?

[IM Egdall]

how would we know?

 

If A and B meet and compare watches.

 

In one example, imagine person A remains in uniform motion but person B accelerates --that is she/he changes speed and /or direction so as to arrive where A is. They meet, compare watches, and find B's watch has run slower than A's. And B has aged less than A. Why? Because only B has experienced acceleration.

[granpa]

I created this thread specifically for beginners to relativity

 

http://www.physicsforums.com/showthread.php?t=314080

[Baby Astronaut]

In one example, imagine person A remains in uniform motion but person B accelerates --that is she/he changes speed and /or direction so as to arrive where A is. They meet, compare watches, and find B's watch has run slower than A's. And B has aged less than A. Why? Because only B has experienced acceleration.

Ah, that's where I've been making an error. I usually hear people traveling near c age slower, but in reality it's people who accelerate continually for a long time that would age slower. If they jumped directly into light speed (not accelerating once) they wouldn't age slower. Correct?

[swansont]

Ah, that's where I've been making an error. I usually hear people traveling near c age slower, but in reality it's people who accelerate continually for a long time that would age slower. If they jumped directly into light speed (not accelerating once) they wouldn't age slower. Correct?

 

Both observers would age slower, as measured by the other. Motion is what causes the clocks to run slow. Acceleration is what breaks the symmetry when they compare measurements.

[Baby Astronaut]

Both observers would age slower, as measured by the other. Motion is what causes the clocks to run slow. Acceleration is what breaks the symmetry when they compare measurements.

Ok, but when the moving person returns just one of them is going to be older (or more aged). So what the slower frame person observed had been an illusion.

[swansont]

Ok, but when the moving person returns just one of them is going to be older (or more aged). So what the slower frame person observed had been an illusion.

 

It's not an illusion. What you measure depends on your frame, and when you change frames, what you measure changes.

[granpa]

during the acceleration some strange things happen.

this is what lead to the idea general relativity.

 

read the thread that I gave a link to

[IM Egdall]

One way to see why the person who experiences acceleration is the one who ages more slowly is with the twins paradox. Swanson is correct. Both A and B see the other's time running more slowly. But the acceleration breaks this symmetry. This can be explained using time dilation and the doppler effect. See my write-up:

 

Click on http://marksmodernphysics.com/ then on Its Relative, Archives, The Twins paradox.

 

Hope it helps.

 

(For some reason the direct link below does not work)

http://marksmodernphysics.com/Mark's%20Modern%20Physics/Musings/index.html

Edited November 29, 2011 by IM Egdall