# The Naked Scientists Forum

### Author Topic: Have the Pioneer anomalies also affected other probes?  (Read 25621 times)

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Have the Pioneer anomalies also affected other probes?
« Reply #75 on: 21/05/2011 14:44:33 »
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.

Your continual use of misleading terminology is very confusing and will stop many taking anything you say seriously.  If you mean time dilation then use the term that people know.  If it is an entirely new (or with different equations) then also say so.  By the way the time dilation side of einstein's theory has been tested to amazing exactness - AND it requires a length contraction to maintain speed of light constancy.  If you are maintaining that no distance contraction occurs then you need to explain how light speed constancy remains when the time dilation is the sole effect and we know experimentally that time dilation follows the equations einstein used.

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Have the Pioneer anomalies also affected other probes?
« Reply #76 on: 23/05/2011 07:26:39 »
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.

(1)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.  (2)Distance contracts AND time dilates - they do so that in a non-accelerating frame the speed of light will be measured as a constant.

(3)Your continual use of misleading terminology is very confusing and will stop many taking anything you say seriously.  If you mean time dilation then use the term that people know.  If it is an entirely new (or with different equations) then also say so.  By the way the time dilation side of einstein's theory has been tested to amazing exactness - (4)AND it requires a length contraction to maintain speed of light constancy.  If you are maintaining that no distance contraction occurs then you need to explain how light speed constancy remains when the time dilation is the sole effect and we know experimentally that time dilation follows the equations einstein used.

(1) The speed of light (meaning speed of light in vacuum), usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time.
http://en.wikipedia.org/wiki/Speed_of_light

It seems to me that distance is precisely defined as a function of the speed of light (and vice-versa).

(2) I thought the speed of light(in a vacuum)was constant in any inertial frame.

(3)Your continual use of misleading terminology is very confusing and will stop many taking anything you say seriously.
‘Passage of time’  Einstein, sometimes used the word passage.  'Passage of time', I believe is self descriptive and would be understood by everyone.  Time dilation only refers to time slowing down not speeding up so is imprecise as a term to explain time being variable.  The problem is the inadequacies of language, as we have already established dt/dt makes little sense.

(4)AND it requires a length contraction to maintain speed of light constancy.  If you are maintaining that no distance contraction occurs then you need to explain how light speed constancy remains when the time dilation is the sole effect and we know experimentally that time dilation follows the equations einstein used.
As I understand it, distance contraction only applies to objects traveling at relativistic speed.  Gravitational time dilation is not accompanied by an associated length contraction.  Therefore, length contraction is not required to maintain speed of light constancy.

Speed is distance divided by time.  As long as the arbitrary units defining length and time remain the same (299,792,458 metres per second) the speed of light will remain a constant.  However, the ‘length’ of a second and a meter can both change within that constraint.

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Have the Pioneer anomalies also affected other probes?
« Reply #77 on: 23/05/2011 10:36:56 »
No - a metre is defined in terms of the speed of light - there is a difference.  we have found that many measurements can be linked - ie they can be independently measured to a high degree of accuracy AND they can be calculated from other measurements taken from completely different experiments.  to make life easy we set constants in one and only one way - and that means that some measurements are done in terms of other things.  velocity is a function of distance - 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.

On your point on contraction - if you say distance contraction doesn't happen you must explain how relative velocity contraction/dolation works, not just find a circumstance in which it doesnt apply.

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Have the Pioneer anomalies also affected other probes?
« Reply #78 on: 23/05/2011 10:58:00 »
No - a metre is defined in terms of the speed of light - there is a difference.  we have found that many measurements can be linked - ie they can be independently measured to a high degree of accuracy AND they can be calculated from other measurements taken from completely different experiments.  to make life easy we set constants in one and only one way - and that means that some measurements are done in terms of other things.  velocity is a function of distance - 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.

Yes.  This is an important point.  The meter wasn't always defined in terms of the speed of light.  It was defined in terms of the size of the earth at one point.  The speed of light was experimentally found to be constant under this old definition.  As a result of this experimental evidence, the meter was redefined since the speed of light was apparently a universal constant.

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Have the Pioneer anomalies also affected other probes?
« Reply #79 on: 24/05/2011 07:55:57 »
quote from 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.

quote from MikeS
The speed of light (meaning speed of light in vacuum), usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time.
http://en.wikipedia.org/wiki/Speed_of_light
It seems to me that distance is precisely defined as a function of the speed of light (and vice-versa).

quote from imatfaal
No - a metre is defined in terms of the speed of light - there is a difference.

In your first quote above you say that distance isn't a function of the speed of light.
In your second quote above you say that distance is a function of the speed of light.
They can't both be correct.

quote imatfaal
By the way the time dilation side of einstein's theory has been tested to amazing exactness - AND it requires a length contraction to maintain speed of light constancy.
I was merely pointing out that in general relativity, gravitational time dilation does not require a length contraction.  Therefore, length contraction cannot be a pre-requisite for the speed of light to be constant.  I am not proposing anything new.

quote from imatfaal
velocity is a function of distance - 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.

Velocity is a function of distance and time.  As we use the speed of light to define the 'length' of the meter and length (distance) is a function of speed then it's a circular argument.  So when I said that "It seems to me that distance is precisely defined as a function of the speed of light (and vice-versa)." was reasonable.  To measure velocity (speed) we have to use distance but distance is defined from speed which means its a circular argument.

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Have the Pioneer anomalies also affected other probes?
« Reply #80 on: 24/05/2011 10:29:28 »
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

• Neilep Level Member
• Posts: 1044
##### Have the Pioneer anomalies also affected other probes?
« Reply #81 on: 24/05/2011 11:14:25 »
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

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Have the Pioneer anomalies also affected other probes?
« Reply #82 on: 24/05/2011 12:02:43 »
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:

Quote
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.
Quote
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.
Quote
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

• Neilep Level Member
• Posts: 1044
##### Have the Pioneer anomalies also affected other probes?
« Reply #83 on: 25/05/2011 09:11:04 »
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."
"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:

Quote
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.
Quote
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.
Quote
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."
"the speed of light in a vacuum is a constant because the 'passage of time' 'in any reference frame" is variable."?

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Have the Pioneer anomalies also affected other probes?
« Reply #84 on: 25/05/2011 11:52:14 »
Quote
Sorry I got it the wrong way around, please accept my apologies.
No worries - Thanks.

Quote
"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

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Have the Pioneer anomalies also affected other probes?
« Reply #85 on: 25/05/2011 11:56:29 »
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.

#### The Naked Scientists Forum

##### Have the Pioneer anomalies also affected other probes?
« Reply #85 on: 25/05/2011 11:56:29 »