The invariance of c

[geordief]

19 minutes ago, Strange said:

Acceleration is different because it is not a relative phenomenon: you can tell if you are accelerating or not.

The speed of light would still be invariant: being under constant acceleration is indistinguishable from the effect of gravity. So, your local measurements of the speed of light would be the same. 

Suppose we accelerated into the Sun and visually recorded our trip,would we notice any difference from a similar recording when we only moved towards the Sun at a constant  velocity ?

(I think in the latter case we would see the Sun slowed down ** but cannot say how we would see it in the former case )

** compared to at zero velocity

1 hour ago, jajrussel said:

In your reference frame does Newton’s laws of motion still work? Here’s an article that probably oversimplifies things because my understanding of it is that if you are in a frame of reference where Newton’s laws of motion work then you are in an initial reference frame. If my understanding is correct how has your choice of direction removed  you from a frame of reference where Newton’s laws of motion work?  there is a possibility that I am completely wrong in my understanding of the article and, or in what you are saying? 🙂

https://newt.phys.unsw.edu.au/einsteinlight/jw/module1_Inertial.htm#IR

I would be a poor authority on this question but,I will try to give you an answer if you promise to take it with a pinch of salt...

Newton's laws apparently work  only as an  (extremely good) approximation at low relative speeds and low accelerations or gravity fields.

I should probably not say any more than that since the other people on this thread are far better equipped to give you helpful answers.

[studiot]

3 hours ago, geordief said:

I learned Galilean Relativity  at school and  it was a really satisfying  discovery.one that I have never questioned and which  seemed far reaching in its consequences in all sorts of contexts. 

I doubt it.

School relativity always has some kind of underlying 'absolute rest frame', even though it is not always explicitly stated.

Full blooded Galilean Relativity has no absolute rest frame.

They knew this, even in Newton's time, but chose not to go there.

 

Are you not speaking to me? I have posted several simplified answers for you to point you in the right direction.

 

As regards your discussion of 'the medium' and Swansont suggesting you consider the difference between sound waves and light (waves?)

Professor Beiser has written this little piece especially for people like you.

 

Note his version of the postulates is a modern professor version that I mentioned already.

The arrow denotes the beginning of the two boats scenarios in the first slide.

Edited October 21, 2019 by studiot

[Janus]

59 minutes ago, geordief said:

Suppose we accelerated into the Sun and visually recorded our trip,would we notice any difference from a similar recording when we only moved towards the Sun at a constant  velocity ?

(I think in the latter case we would see the Sun slowed down ** but cannot say how we would see it in the former case )

** compared to at zero velocity

 

In both cases you would visually record events on the Sun as occurring at a faster rate due to Relativistic Doppler shift. For the accelerating case, this increased rate would start out slow and then increase as your velocity with respect to the Sun increased.

What you would determine as actually happening to clocks on the Sun would be different.  At a constant velocity you would determine that the Sun's clock was running slow by a constant rate, due to your relative velocity.   With the acceleration you have two competing effects:   The normal relative velocity time dilation which starts out at zero ( if you started at rest with respect to the Sun) and has the Sun clock run slower and slower as your velocity towards the Sun increases.  The other effect is due to your measuring from an accelerated frame, where the Sun clock runs fast by a rate that is determined by the magnitude of the acceleration and the distance to the Sun. Greater accelerations and larger distances both lead to faster Sun clock rate.  Assuming a constant acceleration, the changing variable is distance.  So this effect would have the Sun clock running fastest when you are at the start of your trip and far away, and decreasing it rate as you got closer.   You have to compound the two above effects together to get the net result.  So the Sun clock could start off running fast and then transition to running slow during your trip.( though it will always turn out that more time will have past on the Sun clock during the trip than it did on yours.)*

 

* with a constant velocity, less time passes on the Sun clock, but it had a "head start" due to the relativity of simultaneity.

 

[jajrussel]

On 10/20/2019 at 5:38 PM, swansont said:

I’m not sure where you are getting “empty space” from, and how that applies to Newton’s first law, or how the first law implies invariance.

I’m sorry i missed this yesterday. Don’t know how. I guess i need to use a different device cause things seem to keep showing up haphazardly on my iPhone not to mention that it keeps changing words on me then i have to proof read with a fine tooth comb to try and find the errors the word inertial becomes initial and I reach the point where i can’t find the tree for the forrest, but in answer this this I can’t find it, and suddenly my search apps have become dumb to the point if i mention Einstein and vacuum in a sentence search i keep getting referred to Walmart, Target, and Amazon. If i ever run across the reference i will let you know, but for now I’m done. Thank you

[jajrussel]

On 10/20/2019 at 5:38 PM, swansont said:

I’m not sure where you are getting “empty space” from, and how that applies to Newton’s first law, or how the first law implies invariance.

Found this I think this were I got it from. Don’t remember what I was thinking when I read it now. Too many thoughts since then. I saw a connection. Maybe I read too much into it

[Mordred]

I would replace the empty space in that article with the term vacuum. You will never have a truly empty space.

Edited October 22, 2019 by Mordred

[swansont]

As Mordred says, they mean vacuum, and that's the condition for c having the value it does and being invariant. If it's in a medium, none of that holds for the speed you measure. You would not refer to it as c in a medium (the speed would be c/n. where n is the index of refraction of the medium)

And that has nothing to do with Newton's first law, which does not require a vacuum.

 

[studiot]

8 hours ago, jajrussel said:

Found this I think this were I got it from. Don’t remember what I was thinking when I read it now. Too many thoughts since then. I saw a connection. Maybe I read too much into it

 

Congratulations on looking at the 1905 paper itself.

Note that the route Einstein took was to start with consideration of time and thus simultaneity (not space, but separate from space).
This was the beginning of the development.
The few paragraphs leading up to this point you show are very important.

[geordief]

18 hours ago, studiot said:

 

Are you not speaking to me? I have posted several simplified answers for you to point you in the right direction.

I most certainly am . It is just that pressure of time ,allied with natural and increasing slowness/dullness of thought ,allied with similarly attributed obduracy  means that I have to give myself long periods of time to respond to some posts that require especially long attention.

 

You often seem to be able to drag up links that  go to what I have in mind in particular threads  and the last one (about Newton's law of reaction iirc is still, some two weeks later sitting on my desktop waiting for me to get round to it (there are 2 or 3 pages of Einstein's exposition to read...)

 

So ,thanks for your patient answers and directions  over the years ,, but there is the old adage about horse to water (it can just take me a very long time to  make my way to the trough  )

[jajrussel]

8 hours ago, Mordred said:

I would replace the empty space in that article with the term vacuum. You will never have a truly empty space.

Agreed  and understood. I called it a condition of no effect. Which is not always true. Things are happening but those things are not easily observed. Then it would be a condition of no apparent effect.

 

1 hour ago, swansont said:

Newton's first law, which does not require a vacuum.

Agreed and understand and accepted

 

1 hour ago, studiot said:

Congratulations on looking at the 1905 paper itself.

Thank you,  it is were i got the thought to begin with. I searched for the page you posted and started reading  note it was from that point that i started trying to explain a connection that seemed clear to me

from this point i don’t know how to continue to explain what  occurred to me while reading and thinking about this thread without it seeming like i want to argue. I would end up repeating myself, with slightly different rhetoric and i don’t want to do either. So I’ll go back to reading and thinking.

Edited October 22, 2019 by jajrussel
It needed doing

[jajrussel]

Note the 1905 paper is about the only Einstein paper were they still allow a download. Eventually I am going to have to assume some professor understands his work, or be prepared to pay around 89$ per volume for a printed version 89$ is what they were asking for volume 6... They were allowing all to be read freely online using their reader when I visited... but, no doubt that will change... this is way off topic but is in regard to a suggestion that was on topic... Thank you...

[Strange]

2 hours ago, jajrussel said:

Note the 1905 paper is about the only Einstein paper were they still allow a download.

I'm sure more is available.

Almost everything he wrote/published is available here: https://einsteinpapers.press.princeton.edu (a bit of background on the project here: https://www.aip.org/history-programs/news/einstein-papers-now-online)

Some available here: https://en.wikipedia.org/wiki/List_of_scientific_publications_by_Albert_Einstein

 

[studiot]

Good links, thanks. +1

[geordief]

On 10/21/2019 at 5:26 PM, studiot said:

 

 

As regards your discussion of 'the medium' and Swansont suggesting you consider the difference between sound waves and light (waves?)

Professor Beiser has written this little piece especially for people like you.

 

Note his version of the postulates is a modern professor version that I mentioned already.

The arrow denotes the beginning of the two boats scenarios in the first slide.

Thanks for that scenario which was new to me in its specificity and which I have now read carefully. Most  illuminating and very helpful.

I need to ask you though ,why you needed to  write"Professor Beiser has written this little piece especially  for people like you" ? (my bold)

What is my kind of people as per your judgement? 

[studiot]

8 hours ago, geordief said:

Thanks for that scenario which was new to me in its specificity and which I have now read carefully. Most  illuminating and very helpful.

I need to ask you though ,why you needed to  write"Professor Beiser has written this little piece especially  for people like you" ? (my bold)

What is my kind of people as per your judgement? 

It was a compliment.

People like you want to understand and are prepared to put in a substantial amount of effort, but lack the background for a fully rigourous mathematical route.

It is good to remember that the most advanced mathematics in the world only holds good so long as the premises upon which it is based are valid.

Proff Beiser says as much in introducing his boats and then basing his analysis on the stated (physical) postulates.

Einstein was one of those geniuses who could determine the (correct) underlying premises from which to develop the (applied) mathematics.
Of course he was also pretty good at mathematics.
But he also suffered from this (not saying you do) but it is a good article.

https://www.bbc.com/ideas/videos/why-smart-people-do-stupid-things/p07r0zdj

Edited October 23, 2019 by studiot

[geordief]

1 hour ago, studiot said:

It was a compliment.

People like you want to understand and are prepared to put in a substantial amount of effort, but lack the background for a fully rigourous mathematical route.

 

That is a relief. 

 

 

 

[Schmelzer]

On 10/1/2019 at 8:05 PM, geordief said:

Interesting  Maxwell's equations give  a speed  for em radiation without reference to any frame of reference.

There was at that time no need for specifying any frame of reference, because the reference was self-evident:  Absolute space and absolute time.

The theory did not have Galilean symmetry, so the issue of distinguishing absolute rest from inertial movement was a problem for Newtonian gravity, but not for EM theory.  

On 10/22/2019 at 7:49 PM, jajrussel said:

Note the 1905 paper is about the only Einstein paper were they still allow a download. Eventually I am going to have to assume some professor understands his work, or be prepared to pay around 89$ per volume for a printed version 89$ is what they were asking for volume 6... They were allowing all to be read freely online using their reader when I visited... but, no doubt that will change... this is way off topic but is in regard to a suggestion that was on topic... Thank you...

I see vol. 6 of Einstein collected papers for free, for example https://book4you.org/book/3343023/5642aa