Lorentz contraction of box filled with gas

[AVentura]

well, no the gas wouldn't get extra pressure. because it's not the box that contracts, it's space itself. THe gas is in the box so both would undergo a lorentz contraction because both of them are in that local inertial frame.

is the space moving?

if not why would it contract?

if so what accelerated it?
how much force did that take?

 

[AVentura]

I have question for the people discussing the synchronization of clocks. What does this have to do with instantaneous transmission? it is easy to synchronize clocks over space. you measure the distance (d) from the master clock, and you subtract d/c from zero when you get your light pulse from it. the ability to lay synchronized clocks over space is a given.

am I missing something? obviously.

 

[granpa]

when an observer is moving he experiences a loss of simultaneity. this is simply because he is composed of atoms that are themselves interacting at the speed of light. as a result he perceives light pulses that are passing him by to be moving at c rather that c+-v.
because of this if he attempts to do as you say and synchronize clocks he will get a different result than a stationary observer. but of course as the twin paradox shows it is just an illusion that vanishes as soon as he stops.

 

[yuiop]

I have question for the people discussing the synchronization of clocks. What does this have to do with instantaneous transmission? it is easy to synchronize clocks over space. you measure the distance (d) from the master clock, and you subtract d/c from zero when you get your light pulse from it. the ability to lay synchronized clocks over space is a given.

am I missing something? obviously.

THe method you derscribe is the classic and accepted way to synchronise clocks in a frame and nothing is wrong with that. However, if all the clock in frame A are sychronised with each other and all the cloccks in frame B are synchronised with each other, then an obser in farm A would say the clocks in frame B are not synchronised and vice versa. Observers in frames A and B claim to be stationary and claim the other frame frame is moving, so in Special Relativity there is no notion of an absolute rest frame or absolute motion. Granpa was just making the point that if instantaneous transmission of information was possible (which it isn't) then an absolute rest frame could be determined.

 

[yuiop]

is the space moving?

if not why would it contract?

if so what accelerated it?
how much force did that take?

The space is not moving.

 

[AVentura]

when an observer is moving he experiences a loss of simultaneity. this is simply because he is composed of atoms that are themselves interacting at the speed of light. as a result he perceives light pulses that are passing him by to be moving at c rather that c+-v.
because of this if he attempts to do as you say and synchronize clocks he will get a different result than a stationary observer. but of course as the twin paradox shows it is just an illusion that vanishes as soon as he stops.

can the mover not see how fast she is moving relative to the master clock (by bouncing photons off it) and account for that?

 

[granpa]

what master clock? earlier we assumed the ability to communicate instantly and this led to the conclusion that we would have a single master clock somewhere. but in reality we can't communicate instantly.

in reality, all observers consider themselves to be at rest and no experiment can show which is really moving and which isnt.

he can determine his motion relative to another object. but which is moving? him or the master clock? its impossible to tell.

 

[yuiop]

when an observer is moving he experiences a loss of simultaneity. this is simply because he is composed of atoms that are themselves interacting at the speed of light. as a result he perceives light pulses that are passing him by to be moving at c rather that c+-v.
because of this if he attempts to do as you say and synchronize clocks he will get a different result than a stationary observer. but of course as the twin paradox shows it is just an illusion that vanishes as soon as he stops.

The twins paradox ceases to be an illusion when the twins come together at the end the age difference is real.

 

[granpa]

The twins paradox ceases to be an illusion when the twins come together at the end the age difference is real.

it ceases to be an illusion when he stops and begins to turn around.
remember the line of synchronized clocks? when he stops all the clocks are synchronized again. at that point he knows what time the stationary twins clocks says.

 

[AVentura]

what master clock? earlier we assumed the ability to communicate instantly and this led to the conclusion that we would have a single master clock somewhere. but in reality we can't communicate instantly.

in reality, all observers consider themselves to be at rest and no experiment can show which is really moving and which isnt.

I'm not saying that it is absolute time (or rest frame).

I am just saying that you can synchronize all clocks over space, moving or not. It's easy.

Some moving ones may need to run slower or faster than this arbitrary clock to stay in sync. But they can easily see by how much. And knowing zero time is even easier (zero-d/c)

 

[granpa]

yes. if we select one clock and call it the master clock then theoretically all clocks can be synchronized to it. but then clocks within your own frame will not be synchronized. which would make them rather pointless.

when people talk about clocks they are usually referring to the rate at which observers are aging.

 

[yuiop]

I'm not saying that it is absolute time (or rest frame).

I am just saying that you can synchronize all clocks over space, moving or not. It's easy.

Some moving ones may need to run slower or faster than this arbitrary clock to stay in sync. But they can easily see by how much. And knowing zero time is even easier (zero-d/c)

Hi AVentura,

there are ways to synchronise clocks that differ from Einstein's method (see this thread https://www.physicsforums.com/showthread.php?t=212171 ) but you usually end up with a system where clocks do not appear synchronised in your own frame or the speed of light is different in different in different frames or the one way speed of light is not isotropic and the maths generally gets more complicated.

Also, without instantaneous information transmission all clocks moving relative to the arbitary clock would initially appear to be running slower and have to be speeded up. (none would appear to be running faster).

 

[granpa]

there is only one way to synchronize the clocks within your own frame.

 

[AVentura]

when people talk about clocks they are usually referring to the rate at which observers are aging.

then you can't synchronize them for moving observers period.

 

[AVentura]

there is only one way to synchronize the clocks within your own frame.

no, you can use light, or snails.

you subtract d/c for light,

or d/s for snails (s=speed of snails)

 

[granpa]

then you can't synchronize them for moving observers period.

no you can't change the rate of aging

 

[granpa]

no, you can use light, or snails.

you subtract d/c for light,

or d/s for snails (s=speed of snails)

the results will be the same

 

[AVentura]

the results will be the same

the same results was the objective, i can think up more. they can all depart from this arbitrary master clock and add however much time they lost from dilation.

 

[granpa]

we were talking about synchronizing clocks within your own frame. not synchronizing all clocks moving or nonmoving to a master clock. post #188

 

[AVentura]

the results will be the same

we were talking about synchronizing clocks within your own frame. not synchronizing all clocks moving or nonmoving to a master clock. post #188

ok, I think see your point. to synchronize clocks in your own frame some signal must originate from the arbitrary master clock. is this what you meant?

 

[AVentura]

when an observer is moving he experiences a loss of simultaneity. this is simply because he is composed of atoms that are themselves interacting at the speed of light. as a result he perceives light pulses that are passing him by to be moving at c rather that c+-v.
because of this if he attempts to do as you say and synchronize clocks he will get a different result than a stationary observer. but of course as the twin paradox shows it is just an illusion that vanishes as soon as he stops.

you said "when an observer is moving"


now why must it be the same frame?

 

[granpa]

someone said something about there being different ways of defining synchronous. i simply pointed out that within anyone frame, at least, there is only one 'simultaneous'.

 

[granpa]

the confusion seems to be because some people are using clocks to refer to the rate at which natural process occur and others are using them to refer to arbitrary temporal measuring sticks.

how about using 'atomic clocks' to make it clear we are referring to rate of aging or rather the rate of atomic vibration.

 

[granpa]

ok, I think see your point. to synchronize clocks in your own frame some signal must originate from the arbitrary master clock. is this what you meant?

my point is that 2 events within a frame either are or are not synchronous. if 2 events occur simultaneously in china and new york the clocks in china may read differently than they do in new york but the events are still simultaneous.

 

[Mentz114]

granpa,

if 2 events occur simultaneously in china and new york the clocks in china may read differently than they do in new york but the events are still simultaneous.

You seem to be implying some kind of absolute simultaneity. Your statement above does not make sense unless you define 'simultaneous', and your definition will require some sort of clock synchronization, after which only some observers, not all, will agree that the events in NY and China were simultaneous.

 

[granpa]

my point is that 2 events WITHIN A FRAME either are or are not synchronous. if 2 events occur simultaneously in china and new york the clocks in china may read differently than they do in new york but the events are still simultaneous.

 

[Mentz114]

granpa,

'Synchronous' does not mean the same as simultaneous. The actual readings on the clocks are irrelevant. I repeat what I said above - even in a single frame you need to define simultaneity.

We are going into a recursive loop here - and we are hijacking this thread. I'm off.

M

 

[granpa]

i said the events were synchronous. not the clocks were synchronous. Main Entry:
syn·chro·nous Listen to the pronunciation of synchronous
Pronunciation:
\ˈsiŋ-krə-nəs, ˈsin-\
Function:
adjective
Etymology:
Late Latin synchronos, from Greek, from syn- + chronos time
Date:
1669

1: happening, existing, or arising at precisely the same time
2: recurring or operating at exactly the same periods
3: involving or indicating synchronism
4 a: having the same period; also : having the same period and phase b: geostationary
5: of, used in, or being digital communication (as between computers) in which a common timing signal is established that dictates when individual bits can be transmitted and which allows for very high rates of data transfer

 

[Mentz114]

granpa,
so, 'synchronous' has several possible meanings - which one do you mean ? Quoting dictionary definitions is no way to conduct a discussion.

1: happening, existing, or arising at precisely the same time

You've got to be joking. There is no such thing as 'precisely the same time' for spatially separated events. It depends on clock synchronisation, surely ?

I've forgotten what the argument is about, sorry, but you have a way of muddying the water.

 

[granpa]

There is no such thing as 'precisely the same time' for spatially separated events.

i think i know where the muddy waters are coming from and its not me. you might want to reconsider this position. i am not going to try to prove it to you though. you're going to have to work it out for yourself.

 

[Mentz114]

OK, I withdraw from that position. If our frame was a non-accelerating and non-rotating space-ship, we could synchronise clocks and distribute them (very slowly) around the ship. Then two events could be said to be simultaneous if they happened at six o'clock ( or whatever), as seen on the nearest clock.

 

[Austin0]

When they do that, a bunch of relativistic effects must always be included, and this includes the adjustments of the length of the bunch. In lab frame, the bunch length is always less than the bunch that we work with in the bunch frame. This manifest itself in our calculation of the space charge effects, for example.

_____________________________________________----
Hello Zapper The one thing I am unclear on is: When you say the space charge effects---does this mean that the contraction of the electrostatic effects make the electrons therefore bunch closer together or that the contraction, in effect ,opens up more space between them which is a problem if you want compact bunches?

Thanks [at least I hope that is the only thing I am unclear on]