[imatfaal]

Mike you would be better off reading some physics than flogging this dead horse.  That a unit of measurement is defined by reference to a physical constant does not mean that one is a function of the other.  You must learn that the metre and distance are not synonyms.

[MikeS]

Let me see if I understand this, you say "that distance is a function of the speed of light" but that the meter which is a unit of distance isn't.  Is that correct?

[imatfaal]

Let me see if I understand this, you say "that distance is a function of the speed of light" but that the meter which is a unit of distance isn't.  Is that correct?

Mike - are you being deliberately obtuse?  Here is what I said:

Mike just because the metre is now set by reference to the speed of light does not mean that distance is a function of the speed of light.

but the speed of light is so central to out physics that when it comes to measurement we use the speed of light to define the standard metre rule.

That a unit of measurement is defined by reference to a physical constant does not mean that one is a function of the other.

To take a phrase out of my post and quote it but remove the words "does not mean" and completely reverse the import of my post is completely out of line.  Which of the above quotes could possibly lead you to think that I had said what you have posted?

[MikeS]

Correct me if I am wrong but I have always maintained that the speed of light in a vacuum is a constant because the 'passage of time' is variable.  That is in full agreement with Einstein.

Actually, what Einstein would have claimed is that the speed of light is locally constant in an inertial reference frame in vacuum.  Therefore, observers in different reference frames do not agree when they compare lengths and time intervals.

This is quite a bit different from your claims that "the speed of light in a vacuum is a constant because the 'passage of time' is variable."

It's not different at all
E=mc2 says exactly that.  For the speed of light in a vacuum to remain a constant then either length or the'passage of time' have to be variable.  As we use the speed of light to define the length of a meter then 'time' itself is the variable.  In which case "the speed of light in a vacuum is a constant because the 'passage of time' is variable", is a perfectly reasonable statement.

Mike just because the metre is now set by reference to the speed of light does not mean that distance is a function of the speed of light.  Distance contracts AND time dilates - they do so that in a non-accelerating frame the speed of light will be measured as a constant.

Actually, what Einstein would have claimed is that the speed of light is locally constant in an inertial reference frame in vacuum.  Therefore, observers in different reference frames do not agree when they compare lengths and time intervals.

This is quite a bit different from your claims that "the speed of light in a vacuum is a constant because the 'passage of time' is variable."

I really don't see the difference. 
"the speed of light in a vacuum is a constant because the 'passage of time' is variable."
I could have added
"Therefore, observers in different reference frames do not agree when they compare lengths and time intervals."

Let me see if I understand this, you say "that distance is a function of the speed of light" but that the meter which is a unit of distance isn't.  Is that correct?

Mike - are you being deliberately obtuse?  Here is what I said:

Mike just because the metre is now set by reference to the speed of light does not mean that distance is a function of the speed of light.

but the speed of light is so central to out physics that when it comes to measurement we use the speed of light to define the standard metre rule.

That a unit of measurement is defined by reference to a physical constant does not mean that one is a function of the other.

To take a phrase out of my post and quote it but remove the words "does not mean" and completely reverse the import of my post is completely out of line.  Which of the above quotes could possibly lead you to think that I had said what you have posted?

Sorry I got it the wrong way around, please accept my apologies.


I have only just realised what I think is leading to the confusion.
Previously I wrote
"It seems to me that distance is precisely defined as a function of the speed of light".
Perhaps i should have said
"It seems to me that 'the meter as a unit of' distance is precisely defined as a function of the speed of light".

quote imatfaal
Mike just because the metre is now set by reference to the speed of light does not mean that distance is a function of the speed of light.  Distance contracts AND time dilates - they do so that in a non-accelerating frame the speed of light will be measured as a constant.

If I am reading this correctly I think you are saying that 'distance' (the concept) is not a function of the speed of light.  If that's the case I agree.

But I still don't see what made you take issue with me when I said
"the speed of light in a vacuum is a constant because the 'passage of time' is variable."
Would it have been acceptable to you if I had added
"the speed of light in a vacuum is a constant because the 'passage of time' 'in any reference frame" is variable."?

[imatfaal]

Sorry I got it the wrong way around, please accept my apologies.

No worries - Thanks.

"It seems to me that 'the meter as a unit of' distance is precisely defined as a function of the speed of light".

Yes - i would say "in terms of" rather than "as a function of" because any function no matter how complex of a constant is pretty boring.  Even the most natural unit of the length - the planck length has the speed of light in its definition - but then so does the planck time, mass, temperature and charge!

on the "passage of time" usage - it is non-standard; this is a highly non-intuitive and recondite area of physics and we cling to standard definitions and usage.   Why use a term that needs explanation when time dilation is easily used; passage of time (for me at least) brings in metaphysical questions. Philosophers since Augustine (and probably before) have pondered the passage and perception of time - it is important to remove experimental physics from abstract philosophy.

[JP]

And the meter is defined in terms of the speed of light precisely because the speed of light was found to be constant back when the meter was defined in terms of the size of the earth.