Can Memory Invalidate the Symmetry in Special Relativity's Thought Experiments?

[phinds]

I have no idea why you say it's not right.

the train frame is not stationary in the station frame, that's clear, the train is stationary in its own frame.

What i say is that someone in the train frame interprets his own acceleration as what's keeping him stationary in his OWN frame.

Nothing is EVER necessary to keep something stationary in its own frame of reference. It is stationary there by definition.

 

[nearlynothing]

Nothing is EVER necessary to keep something stationary in its own frame of reference. It is stationary there by definition.

Lets not call it its own frame then, let's call it the non-inertial frame frame.

The train needs a force to stay stationary in this non-inertial frame, and interprets the station as "falling".

So the station is moving in this non-inertial frame as opposed to the train which is not, whereas the train is moving in the inertial frame of the station while the station itself is not.

 

[phinds]

Lets not call it its own frame then, let's call it the non-inertial frame frame.

The train needs a force to stay stationary in this non-inertial frame, and interprets the station as "falling".

So the station is moving in this non-inertial frame as opposed to the train which is not, whereas the train is moving in the inertial frame of the station while the station itself is not.

It doesn't matter whether or not YOU choose to call it "the frame of the train", it IS the frame of the train. You can call it green if you like, it is still the frame of the train (and yes, it is a non-inertial frame)

 

[nearlynothing]

It doesn't matter whether or not YOU choose to call it "the frame of the train", it IS the frame of the train. You can call it green if you like, it is still the frame of the train (and yes, it is a non-inertial frame)

All i am saying is that it's never possible to determine which is moving absolutely, no matter if you remember being accelerated or not.

I realize i phrased it wrong, i meant the train needs a force to stay in a non-geodesic path.

 

[bahamagreen]

Looks to me like the problem starts from remembering the acceleration, or looking at the printout of the accelerometer, or any other record keeping device or system that reveals a past real period of acceleration... prior to achieving the inertial reference frame.

... and the problem then comes from thinking that you were "still" before the acceleration, but now are "moving" as a result of it... shades of absolute space.

This is not a technical answer, but an inertial reference frame is "still" when it is yours no matter what history of previous accelerations might have been. In essence, an IRF has no "mechanical history" of accelerations (no lingering, ontological, causative, or otherwise potent effects). Another way to say it is that any and all possible acceleration histories are "equal" in their nonexistent effect after an IRF has been established - all IRF are physically identical despite any historical differences with respect to acceleration.

If you think about the implications of this, you will see that it never makes sense to say, "My IRF is moving and I know it because of this piece of evidence of past acceleration..."

As phinds often says, sort of, "You are moving and not moving at all possible speeds, depending on who is measuring and their relative motion, but do you feel any different?", or something like that... :)
Which means that to somebody somewhere in relative motion to your IRF, they might account for your relative motion to themselves by suggesting any and all possible combinations and configurations and durations of acceleration history to account for your observed relative velocity... each acceleration history unique, and all acting prior to your same final relative motion.

 

[PeterDonis]

I know that i had to startup the train from 0 km/h to start leaving the station.

No, you don't know this. All you know is that you had to start up the train from 0 km/h *relative to the station*. You don't know whether you started "moving" in any absolute sense when you started leaving the station, or if you were "moving" when you were in the station, and gradually stopped "moving" as you accelerated, until you reached a state of "rest" when the train stopped accelerating. You can't just assume that moving at 0 km/h relative to the station means you are "really at rest". (If you're inclined to say that you can, consider that the station is on a rotating Earth, which is moving relative to the Sun, which is moving relative to the galaxy, which is moving relative to other galaxies. The fact that the station *seems* to be at rest to you is not a good reason for claiming it is "really at rest" in any absolute sense.)

In other words, just knowing that you accelerated in the past doesn't show that you are "moving", because you don't know which state of motion is "really" at rest to begin with. All acceleration does is change your state of relative motion; it doesn't, and can't, let you determine which state of relative motion is "really moving" or "really at rest".

 

[Noa Drake]

Ok, thank you for these various comments, i am learning.

 

[phinds]

Excellent. That's what all the Science Advisors and Homework Helpers and Mentors here love to hear. They spend a lot of time here trying to do just that and it is sometime an underappreciate task. I, on the other hand, am just here to kibitz