Wondering about SR postulate

  • Thread starter Noa Drake
  • Start date
  • Tags
    Sr
In summary: Because, as phinds pointed out, this is the central point of SR - that ALL inertial frames are equally valid. It's not "either/or" it's "as well as." So, if the station is moving away from you but you are not accelerating (i.e. you are in an inertial frame), then you can say that you are not moving and that the station IS moving away from you. You can say it, but so could someone on the station. The point is that both statements are equally valid. And this is the central point of SR.EDIT: PS: you can also say that the station is stationary and that you are moving away
  • #1
Noa Drake
5
0
Hello, i am new here.
I have been studying SR en GR for a while on a hobby level,
and i keep pondering on the following :



Consider the following situation :


A train with a person on it leaves the station.

SR says that while moving with constant velocity, the trainguy cannot tell the difference between him
riding out of the station or the station leaving him, relatively to each other. ok.

It is also understood that no experiment can be used to distinguish between these two possibilities.
By extention, no current technology can make the distiction. ok.



>> What about this 'experiment' ?

I am trainguy (and i also drive the train), and i have to figure it out :

I know that i had to startup the train from 0 km/h to start leaving the station.
For this i had to accellarate for a while first, and then gradually lower the power again to approach a constant speed, until indeed i have reached a constant speed. then maintaining the same level of power.



How can i now distinguish between the station leaving me and the train, or me and the train leaving the station ?
('Now' = while going at constant speed, after the accellaration has terminated.)

> I simply consult my memory , and if i don't suffer any rare medical condition such as instant Altzheimer
from the moment on where accellaration turned into constant speed,

then i can safely conclude that :

-It was definitely me starting up the train and performing the necessary handlings to get to a constant speed.
-It was definitely not the station that was 'started up' in any way.

-And so it was definitely me and the train moving away from the station,
the station that was set in motion in any way.

I don't experience it, i know it.



>>>>

So me and the train are moving away from the station, not vice versa.
I know this by consulting my memory ,
although i may not experience the difference, or detect the difference with a device.


So i simply know the situation is not symmetric, i doesn't matter anymore wether or not i can distinguish between the two by experience, observation, or device detection.




Is this a valid thought experiment ?
 
Physics news on Phys.org
  • #2
Accelerating frames are not inertial. By inserting a non-inertial frame and making it part of the experiment, you have left SR. It is well understood that acceleration is NOT relative and can be determined, thus your experiment adds nothing to SR/GR.

EDIT: by the way, welcome to the forum :smile:
 
  • #3
Noa Drake said:
SR says that while moving with constant velocity, the trainguy cannot tell the difference between him
riding out of the station or the station leaving him, relatively to each other. ok...

I am trainguy (and i also drive the train), and i have to figure it out :

I know that i had to startup the train from 0 km/h to start leaving the station.
For this i had to accellarate for a while first, and then gradually lower the power again to approach a constant speed, until indeed i have reached a constant speed. then maintaining the same level of power.

You start off OK by talking about constant velocity, and then all of a sudden you're accelerating from 0 to whatever. Not only that, but you're driving the car! How are you supposed be objective when you're driving the car? Of course you're going to know that it's you leaving the station.

So, as phinds pointed out, the thought experiment ends right there. The "train" analogy/example goes back to the early 20th century mentality before we started using rocket ships as the relative vehicles, simply because at that time everyone was familiar with trains. Even if you weren't driving the train, you'd have to take into account the psychophysiological effects on your vestibular semicircular canals of the influences of gravitation, inertial acceleration of the train car, and friction of the tracks into your thought experiment. That's why most of the SR thought experiements are done in intergalactic space these days.
 
  • #4
@ phinds and DiracPool

Ok, i understand that accellaration is not relative and can be determined, whereas moving with constant speed in the above context is not.

But SR does not stipulate how this constant speed has to be achieved, it does not stipulate that the constant motion cannot be predecessed by an accellaration.

Hence why would the above experiment be unusable ?

If the original SR thought experiment limits the picture to the constant speed, then it has left out an important part of reality : You can never obtain any constant speed without prior accellaration.
Hence predictions made from the limited experiment , must stay confined to this limited thought experiment situation.

In other words, logically speaking, the predictions cannot consist of extrapolations to reality.

No ?
 
  • #5
Noa Drake said:
No ?

No.

But SR does not stipulate how this constant speed has to be achieved, it does not stipulate that the constant motion cannot be predecessed by an accellaration.

Exactly, and it makes no pretensions otherwise. That's why it's called the "special" theory of relativity.

Hence why would the above experiment be unusable ?

It would be unusable mostly because your thesis that, "I simply consult my memory...", etc. is not a factor that plays into the equation. SR is not influenced by your memory.

In other words, logically speaking, the predictions cannot consist of extrapolations to reality.

I don't know what that means.
 
  • #6
I understand why you are confused. It seems like this is a matter of interpreting correctly what SR is "trying to say."

You are absolutely correct when you say that since you refer to your own memory and you do not suffer from any mental illnesses, you can conclude that it was indeed you and the train that left the train station and not the station itself (of course, you make this conclusion once you've finally reached a constant speed at which point you are in a valid inertial frame). This is true!

However, SR says that you could also claim that the station is moving AWAY from you. This claim is also true and completely valid.

Why is the latter true also? Because Albert Einstein postulates in SR that the laws of physics are the SAME in ALL inertial frames of reference. Since you are moving away from the station at a constant speed (after you have accelerated to that speed), yes you are in a valid inertial frame of reference. Now, since you can't feel any type of acceleration or changes in your motion (the reason why constant velocity is required for an inertial frame), you could also imagine that it is the train that is stationary and that the train station is moving away from YOU at that same constant velocity (since you can't feel any type of acceleration). Since the station is also moving away from you at a constant velocity, this is ALSO an inertial frame of reference for you. And since the laws of physics are the same in all inertial reference frames, this must be a completely valid perspective.

So it is not that SR is trying to tell you that you aren't moving away from the train station. You ARE moving away from the train station! But SR is telling you that it is ALSO true that the station is moving away from you.
 
Last edited:
  • #7
Noa Drake said:
A train with a person on it leaves the station.

SR says that while moving with constant velocity, the trainguy cannot tell the difference between him
riding out of the station or the station leaving him, relatively to each other. ok.
While even Einstein thought that was true when he wrote the special theory of relativity (SR). How SR applies to inertial frames and thus to situations in the absence of gravity. I tried this myself and found it to be true. What happens is that there is a cross term in the metric of the form dtdx which causes particles falling down to be deflected. Therefore you can tell which is moving. However if instead of using train stations we used space stations and thus inertial frames then we're back to SR again and what you said is true again.
 
  • #8
Noa Drake said:
Hello, i am new here.
I have been studying SR en GR for a while on a hobby level,
and i keep pondering on the following :



Consider the following situation :


A train with a person on it leaves the station.

SR says that while moving with constant velocity, the trainguy cannot tell the difference between him
riding out of the station or the station leaving him, relatively to each other. ok.

It is also understood that no experiment can be used to distinguish between these two possibilities.
By extention, no current technology can make the distiction. ok.



>> What about this 'experiment' ?

I am trainguy (and i also drive the train), and i have to figure it out :

I know that i had to startup the train from 0 km/h to start leaving the station.
For this i had to accellarate for a while first, and then gradually lower the power again to approach a constant speed, until indeed i have reached a constant speed. then maintaining the same level of power.



How can i now distinguish between the station leaving me and the train, or me and the train leaving the station ?
('Now' = while going at constant speed, after the accellaration has terminated.)

> I simply consult my memory , and if i don't suffer any rare medical condition such as instant Altzheimer
from the moment on where accellaration turned into constant speed,

then i can safely conclude that :

-It was definitely me starting up the train and performing the necessary handlings to get to a constant speed.
-It was definitely not the station that was 'started up' in any way.

-And so it was definitely me and the train moving away from the station,
the station that was set in motion in any way.

I don't experience it, i know it.



>>>>

So me and the train are moving away from the station, not vice versa.
I know this by consulting my memory ,
although i may not experience the difference, or detect the difference with a device.


So i simply know the situation is not symmetric, i doesn't matter anymore wether or not i can distinguish between the two by experience, observation, or device detection.




Is this a valid thought experiment ?
You are considering two Inertial Reference Frames (IRF's):

1) The rest frame of the station in which the trainguy starts out at rest.

2) The rest frame of the trainguy after he accelerates.

Both of these IRF's are equivalent (as well as a million others) but you have to include the same things in all of them.

In IRF 1, the station remains at rest while the trainguy accelerates to a final velocity.

In IRF 2, both the station and the trainguy start off traveling at some negative speed but the trainguy decelerates to a stop while the station continues moving.
 
  • #9
Noa Drake said:
Hello, i am new here.
I have been studying SR en GR for a while on a hobby level,
and i keep pondering on the following :
Consider the following situation :A train with a person on it leaves the station.

SR says that while moving with constant velocity, the trainguy cannot tell the difference between him
riding out of the station or the station leaving him, relatively to each other. ok.

It is also understood that no experiment can be used to distinguish between these two possibilities.
By extention, no current technology can make the distiction. ok.
>> What about this 'experiment' ?

I am trainguy (and i also drive the train), and i have to figure it out :

I know that i had to startup the train from 0 km/h to start leaving the station.
For this i had to accellarate for a while first, and then gradually lower the power again to approach a constant speed, until indeed i have reached a constant speed. then maintaining the same level of power.
How can i now distinguish between the station leaving me and the train, or me and the train leaving the station ?
('Now' = while going at constant speed, after the accellaration has terminated.)

> I simply consult my memory , and if i don't suffer any rare medical condition such as instant Altzheimer
from the moment on where accellaration turned into constant speed,

then i can safely conclude that :

-It was definitely me starting up the train and performing the necessary handlings to get to a constant speed.
-It was definitely not the station that was 'started up' in any way.

-And so it was definitely me and the train moving away from the station,
the station that was set in motion in any way.

I don't experience it, i know it.
>>>>

So me and the train are moving away from the station, not vice versa.
I know this by consulting my memory ,
although i may not experience the difference, or detect the difference with a device.So i simply know the situation is not symmetric, i doesn't matter anymore wether or not i can distinguish between the two by experience, observation, or device detection.

Is this a valid thought experiment ?

You could also conclude that while your engines were accelerating you, you remained stationary in space, and that there was an interaccion deviating you from geodesic motion, while it was the station that failed to remain stationary in space.

So even though you remember you started off the engine yourself you can't tell just which is moving away from which in an absolute manner. These are frame dependent notions.
 
  • #10
nearlynothing said:
You could also conclude that while your engines were accelerating you, you remained stationary in space, and that there was an interaccion deviating you from geodesic motion, while it was the station that failed to remain stationary in space.

So even though you remember you started off the engine yourself you can't tell just which is moving away from which in an absolute manner. These are frame dependent notions.

"stationary in space" is a meaningless concept. All motion is relative. "stationary" is a form of motion and is only meaningful when stated as being relative to something. "space" is not something in that sense.
 
  • #11
PhysicistMike said:
... However if instead of using train stations we used space stations and thus inertial frames then we're back to SR again and what you said is true again.

HUH? What difference does it make if you use train stations or space stations? If one of them accelerates, the passengers/driver/whatever can TELL that they are the ones accelerating. As I have already pointed out, the error in his logic was not in using a train instead of something in space, it was in using something that accelerates and expecting SR to be applicable.
 
  • #12
phinds said:
"stationary in space" is a meaningless concept. All motion is relative. "stationary" is a form of motion and is only meaningful when stated as being relative to something. "space" is not something in that sense.

I didnt refer to a coordinate system, but of course there would have to be a coordinate system, either one in which the train is at rest or where the station is at rest.

So my statement would be that they're stationary in the space of one of these frames, defined according to some simultaneity convention.
 
  • #13
phinds said:
HUH? What difference does it make if you use train stations or space stations? If one of them accelerates, the passengers/driver/whatever can TELL that they are the ones accelerating. As I have already pointed out, the error in his logic was not in using a train instead of something in space, it was in using something that accelerates and expecting SR to be applicable.

SR is perfectly applicable for accelerated motion.
 
  • #14
nearlynothing said:
I didnt refer to a coordinate system, but of course there would have to be a coordinate system, either one in which the train is at rest or where the station is at rest.

So my statement would be that they're stationary in the space of one of these frames, defined according to some simultaneity convention.

Exactly. And if they then move apart there is some acceleration going on, which is my point.
 
  • #15
nearlynothing said:
SR is perfectly applicable for accelerated motion.

And does that lead you to the conclusion that the OPs original logic is sound?
 
  • #16
@Kyle.Nemeth (post 6) :

I see that you understood what i intended with the thought experiment, thank you .

Then you said this :
"However, SR says that you could also claim that the station is moving AWAY from you. This claim is also true and completely valid.
Why is the latter true also? Because Albert Einstein postulates in SR that the laws of physics are the SAME in ALL inertial frames of reference."

> Using the postulate as a defense against an argument that tries to illustrate that we cannot extrapolate things about THE laws of physics from a very limited thought experiment (were essential parts of reality are not allowed to exist), is not very fair.

You could never obtain the constant speed without at some point in the past having accellarated to some degree.
It is like saying let us imagine an experiment were a guy is hanging in the air, and exclude the rest of reality.
Being that he must have been jumping first, or perhaps have fallen out of a plane etc.
It is cutting a shorter clip from the entire scene.

>What validity does the original SR thought experiment have if you deliberately handicap the observer (trainguy is not allowed to use his memory) and omit essential information ? How could any predictions about the laws of physics in general be correct, when derived from this limited and unreal situation ?


(I understand now that maybe i had better posted this under phylosophy.)
 
  • #17
phinds said:
Exactly. And if they then move apart there is some acceleration going on, which is my point.

This acceleration brings nothing new into play, i think maybe you're not getting my point.

The passenger in the train can define a frame in which he is at rest, regardless of his acceleration.
This frame can't be inertial if he is accelerating, but that doesn't matter here.
His acceleration can be measured locally, with accelerometers, so this can be defined in absolute terms, with no reference to coordinates. Now in this frame he sees the station failing to remain stationary, he interprets his own acceleration as a means to remain stationary in that frame.

If looked at from the point of view of someone in the station, this person can also define a frame in which he is at rest, this frame can be inertial. Now he interprets the acceleration of the train as causing a change in velocity of the train in this frame of reference.

Both points of view are valid and so you can't say which is moving in a frame-independent manner even though the passenger would clearly remember the engines being working and accelerating the train.The only thing you can say absolutely is that there is an interaction deviating the particles composing the train from geodesic motion.
 
Last edited:
  • #18
phinds said:
And does that lead you to the conclusion that the OPs original logic is sound?

Well i don't see a logic flaw there, the point is he doesn't know yet how to interpret the tought eperiment in the context of relativity.
 
  • #19
Noa Drake said:
You could never obtain the constant speed without at some point in the past having accellarated to some degree.
It is like saying let us imagine an experiment were a guy is hanging in the air, and exclude the rest of reality.
Being that he must have been jumping first, or perhaps have fallen out of a plane etc.
It is cutting a shorter clip from the entire scene.

That's actually wrong. You can forget about the "past" and care about the present in order to determine the future.
 
  • #20
Noa Drake said:
@Kyle.Nemeth (post 6) :

I see that you understood what i intended with the thought experiment, thank you .

Then you said this :
"However, SR says that you could also claim that the station is moving AWAY from you. This claim is also true and completely valid.
Why is the latter true also? Because Albert Einstein postulates in SR that the laws of physics are the SAME in ALL inertial frames of reference."

> Using the postulate as a defense against an argument that tries to illustrate that we cannot extrapolate things about THE laws of physics from a very limited thought experiment (were essential parts of reality are not allowed to exist), is not very fair.

On the contrary, it is completely fair. The postulates are accepted as facts characteristic of our universe. If one hasn't accepted them as facts, then they are not justified in discussing anything about SR because then you are just saying that the theory is wrong. Anyone that claims such a theory is incorrect, their argument is not very strong without theoretical and experimental proof.

Noa Drake said:
@Kyle.Nemeth (post 6) :

You could never obtain the constant speed without at some point in the past having accellarated to some degree.
It is like saying let us imagine an experiment were a guy is hanging in the air, and exclude the rest of reality.
Being that he must have been jumping first, or perhaps have fallen out of a plane etc.
It is cutting a shorter clip from the entire scene.

Suppose we do want to imagine an experiment where some guy is suspended in air on earth. Because we omit the fact of where he came from or how he got there does NOT imply that we are omitting reality itself. The fact of the matter is that he is there and a certain set of rules (physical laws) will apply to him. How he got there actually may not matter at all, depending on what we are trying to determine.

For example, If we want to know how long this guy has been suspended in free fall then we might want to know how exactly he got there in the first place. If, say, we wanted to know his acceleration (if indeed he is in AIR on earth), we could immediately say that it is 9.8 m/s2. We can assume this because we have accepted this value of the Earth's gravitational acceleration near the surface of the Earth as FACT. Thus, we need not know ANY details about how he got there.

If we accept the postulates of SR as facts, we can make assumptions that my seem confusing but are valid.

Noa Drake said:
@Kyle.Nemeth (post 6) :

>What validity does the original SR thought experiment have if you deliberately handicap the observer (trainguy is not allowed to use his memory) and omit essential information ? How could any predictions about the laws of physics in general be correct, when derived from this limited and unreal situation ?

Handicapping an observer is not a main feature of the SR thought experiments. However, many demonstrations of said thought experiments do have this feature to make for simpler understanding of the underlying CONCEPT.

If you remember that it was you who accelerated away from the train station to a constant speed because you operated the train yourself, SR is not implying that you must forget that ever happened in order to understand the perspective of the other inertial frame.

Once you finally reach your constant speed, you are then in an inertial frame because you can NOT feel any changes in your motion or acceleration. When we claim you are now in an inertial frame, we are not implying that everything that happened before you reached the inertial frame didn't happen. Obviously, all of that stuff DID happen and you remember, so you KNOW that it was you who sped up the train to some constant speed. SR isn't contradicting these facts.

SR claims that the notion of the train station moving away from YOU at a constant speed, rather than you moving away from it, is completely vaild regardless of whether it is ACTUALLY you who is moving. The reason it is completely fine to assume this validity is because we have accepted the postulates as facts (justifiably so).

I'd like to recommend this website:

WorldscienceU.com

This website offers a course in SR, taught by Brian Greene, professor of physics at Columbia University. He does an outstanding job and not to mention it is a fun course.
 
  • #21
@Nearlynothing

You said :
"His acceleration can be measured locally, with accelerometers, so this can be defined in absolute terms, with no reference to coordinates. Now in this frame he sees the station failing to remain stationary, he interprets his own acceleration as a means to remain stationary in that frame."

An interesting angle, i'll have to let that sink in for a while.
 
  • #22
nearlynothing said:
SR is perfectly applicable for accelerated motion.

SR is NOT applicable at all for accelerated motion. In fact, the reason for being in an inertial frame is that you are NOT accelerating and thus can not PHYSICALLY distinguish whether it is you and the vehicle who is moving, or the world around you that is moving.
 
  • #23
Kyle.Nemeth said:
SR is NOT applicable at all for accelerated motion. In fact, the reason for being in an inertial frame is that you are NOT accelerating and thus can not PHYSICALLY distinguish whether it is you and the vehicle who is moving, or the world around you that is moving.

But SR is not limited to inertial frames at all.
 
  • #24
nearlynothing said:
But SR is not limited to inertial frames at all.

Actually, it is. SR is based on inertial frames.

Gamma is the "fudge factor," so to speak, that explains the difference in coordinates between perspective frames of reference.

Time dilation is the notion of time that observers experience with respect to other observers/objects frames of reference.

Length contraction is a phenomenon observed with respect to observers/objects frames of reference.

Lorentz transformations are equations recognized by Einstein (not originally formulated by him) that allow for one to transform coordinates from one reference frame to another.

A perspective in which one is accelerating is not an inertial frame, this is even stated by Newton's First Law of Motion, or the Law of Inertia.
 
  • #25
Kyle.Nemeth said:
Actually, that is what SR is all about.

Not quite, SR does stress the equivalence of all inertial frames, but it's not at all a theory confined to them. You can define frames that are not inertial in minkowski space, nothing about space-time is changed by the use of these coordinates
 
  • #26
Noa Drake said:
@Nearlynothing

You said :
"His acceleration can be measured locally, with accelerometers, so this can be defined in absolute terms, with no reference to coordinates. Now in this frame he sees the station failing to remain stationary, he interprets his own acceleration as a means to remain stationary in that frame."

An interesting angle, i'll have to let that sink in for a while.

Well, that's not right. He is clearly NOT staying stationary in that frame. Since it is moving away from him, he is moving away from it. What his acceleration does is keep him from being dragged along with that frame, since without acceleration, he is stationary in that frame.

From HER frame of reference, the guy on the train is stationary and the train station is accelerating away from both of them.Here's another way of looking at it:

Take a frame of reference and grid it as XY coordinates. In that frame, there is a pretty girl at 0,0.

At 10,0 there is a train station and a train.

Through some means that we don't care about, the train station, in our XY frame of reference, begins accelerating in the negative Y direction. The guy on the train doesn't want to lose sight of the pretty girl, so he has to accelerate to stay on the X axis while the train station moves away from him. From HIS frame of reference, he is moving relative to the train station but NOT moving relative to the girl, he is maintaining his position is her frame of reference.
 
  • #27
Kyle.Nemeth said:
Actually, it is. SR is based on inertial frames.

Because this misunderstanding has been so widely propagated in the pop-sci press, because so few first-year courses try to correct it, and because Einstein himself back in 1905 did not fully appreciate what he had wrought, people can be forgiven for believing that SR is based on inertial frames.

But it's not - it works for all frames in flat space-time. Whether the frame is inertial or not is just a simple coordinate transformation as long as the space-time is flat (that is, described by the Minkowski metric in ##x,y,z,t## coordinates). For a good example of a purely SR treatment of a non-inertial frame in flat space-time, google for "Rindler coordinates", and note that the Rindler coordinates are just a transformation of the Minkowski coordinates.
 
  • Like
Likes 1 person
  • #28
nearlynothing said:
Not quite, SR does stress the equivalence of all inertial frames, but it's not at all a theory confined to them. You can define frames that are not inertial in minkowski space, nothing about space-time is changed by the use of these coordinates

I agree.

For the sake of trying to help @NoaDrake understand the idea, I thought it was necessary to remain within the elementary context of SR. But you are correct in the context of a Minkowski Space.
 
  • #29
phinds said:
Well, that's not right. He is clearly NOT staying stationary in that frame. Since it is moving away from him, he is moving away from it. What his acceleration does is keep him from being dragged along with that frame, since without acceleration, he is stationary in that frame.

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.
 
  • #30
Kyle.Nemeth said:
I agree.

For the sake of trying to help @NoaDrake understand the idea, I thought it was necessary to remain within the elementary context of SR. But you are correct in the context of a Minkowski Space.


Yeah I agree non-inertial frames can be more tricky. But they are needed in this scenario, I don't think simply saying that the thought experiment goes beyond the range of applicability of SR is enough.
 
  • #31
nearlynothing said:
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.
 
  • #32
phinds said:
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.
 
Last edited:
  • #33
nearlynothing said:
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)
 
  • #34
phinds said:
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.
 
Last edited:
  • #35
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.
 
<h2>What is the SR postulate?</h2><p>The SR postulate, or Special Relativity postulate, is a fundamental principle in physics that states that the laws of physics should appear the same to all observers in uniform motion, regardless of their relative velocities.</p><h2>Why is the SR postulate important?</h2><p>The SR postulate is important because it forms the basis of Einstein's theory of Special Relativity, which has revolutionized our understanding of space and time. It also has significant implications for our understanding of the behavior of objects at high speeds.</p><h2>What evidence supports the SR postulate?</h2><p>There is a wealth of evidence that supports the SR postulate, including numerous experiments that have been conducted over the past century. One of the most famous examples is the Michelson-Morley experiment, which showed that the speed of light is constant regardless of the observer's frame of reference.</p><h2>Can the SR postulate be proven?</h2><p>The SR postulate is a fundamental principle in physics and as such, it cannot be proven in the traditional sense. However, the predictions and implications of the postulate have been extensively tested and confirmed through numerous experiments and observations.</p><h2>Are there any exceptions to the SR postulate?</h2><p>So far, all experimental evidence supports the SR postulate. However, there are some theoretical models, such as Quantum Mechanics, that may suggest some deviations from the postulate at very small scales. These are still areas of active research and have not been definitively proven or disproven.</p>

What is the SR postulate?

The SR postulate, or Special Relativity postulate, is a fundamental principle in physics that states that the laws of physics should appear the same to all observers in uniform motion, regardless of their relative velocities.

Why is the SR postulate important?

The SR postulate is important because it forms the basis of Einstein's theory of Special Relativity, which has revolutionized our understanding of space and time. It also has significant implications for our understanding of the behavior of objects at high speeds.

What evidence supports the SR postulate?

There is a wealth of evidence that supports the SR postulate, including numerous experiments that have been conducted over the past century. One of the most famous examples is the Michelson-Morley experiment, which showed that the speed of light is constant regardless of the observer's frame of reference.

Can the SR postulate be proven?

The SR postulate is a fundamental principle in physics and as such, it cannot be proven in the traditional sense. However, the predictions and implications of the postulate have been extensively tested and confirmed through numerous experiments and observations.

Are there any exceptions to the SR postulate?

So far, all experimental evidence supports the SR postulate. However, there are some theoretical models, such as Quantum Mechanics, that may suggest some deviations from the postulate at very small scales. These are still areas of active research and have not been definitively proven or disproven.

Similar threads

Replies
17
Views
2K
  • Special and General Relativity
Replies
10
Views
982
  • Special and General Relativity
Replies
7
Views
951
  • Special and General Relativity
Replies
15
Views
1K
  • Special and General Relativity
Replies
21
Views
523
  • Special and General Relativity
5
Replies
167
Views
6K
  • Special and General Relativity
2
Replies
52
Views
4K
  • Special and General Relativity
2
Replies
44
Views
3K
  • Special and General Relativity
Replies
13
Views
1K
Replies
14
Views
774
Back
Top