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The Speed of Light, is it a relative thing?


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1 hour ago, Delasaurus said:

We know 'scientifically' that m varies around certain parts of the Earth, as does mass due to local gravitational changes

I’m struggling to find the scientific evidence for both your statements. Could you provide links.

To save you time, I’ve already checked the website of the Bureau International des Poids et Mesures and could not find anything.

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13 minutes ago, Filroden said:

I’m struggling to find the scientific evidence for both your statements. Could you provide links.

To save you time, I’ve already checked the website of the Bureau International des Poids et Mesures and could not find anything.

That's my understanding too. Mass doesn't change with gravity, weight does though.

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6 hours ago, SilverAstro said:

and ever so very tiny, (Tony) like a very very tiny Planck thing (/Baldrick), so how come it is now (perhaps) infinitely big,

maybe the period of exponential inflation never ended ?

The current view is that it was always infinite and continued to expand after inflation finished and is now expanding exponentially. 

Regards Andrew 

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1 hour ago, Filroden said:

I’m struggling to find the scientific evidence for both your statements. Could you provide links.

To save you time, I’ve already checked the website of the Bureau International des Poids et Mesures and could not find anything.

The 'definition' of the SI unit 'metre' has changed over certain periods;

At one point it was measured as the distance between Paris and somewhere else on the meridian, another time, it was measured against  Krypton -86.

It is now measured against the distance of the speed of light in a vacuum.

 

The best way I can point you to an excellent source of reference material for this kind of thing is The Open University Science course material, if you can get hold of it through E-bay. I think the updated version is S104. I studied in the old days of S101. The content is beautifully written and nicely laid out with plenty of 'workings out' for you to do. An astronomers dream!

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12 minutes ago, Delasaurus said:

The 'definition' of the SI unit 'metre' has changed over certain periods;

I know exactly how the metre is defined today and how a prototype measurement had to be used until a definition based on nature could be agreed. What I don't understand is how you can evidence that the metre varies in different parts of the world. Pointing at what things were in the past is not evidence. 

And just to be clear, even the historical definitions did not allow for the metre to be different in different parts of the world. They all produced a "standard" metre which was used as the benchmark everywhere. The fact that the methodology chosen could have given rise to many different definitions is irrelevant; they chose one particular method and used that to create a standard that was universal. So what evidence do you have that shows the metre varying based on location?

And you still haven't provided the evidence for how mass varies with gravity.

I don't need immediate answers. I appreciate these will need research and study and am happy to wait. The answer is important to me. As a surveyor and cartographer, I need to know if I've been practising my trade incorrectly.

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22 hours ago, saac said:

Not sure I'd agree with time being a mere concept - not entirely sure what you mean by that. As for infinity, I have always looked upon it as a mathematical concept rather than an absolute physical state.

Jim

Time varies, according to how we 'define' it. It is defined in science as the difference between any two  'events'.

That could be anything from when Micky Mouse arrives the next time on our TV's, the falling of leaves from trees from one season to another, or a heart beat or the cycles between the phases of the moon or the sun, or the ticking of a clock! Which is simply a mechanical tool that moves at certain periodic intervals.

But clocks tick at different rates do they not?

So, we needed something more accurate for scientific calculations, hence the invention of the atomic clock.

Time, in Medieval days however, was defined as being 1/84,000 part of a day.

And time, as we know, was a complete headache for the Railway networks whereby due to long distances, the train from London would not be at Paris say, at 10:00am as predicted, but at a different time if the chuffer maintained a constant speed. Therefore, adjustments in the speed of the train had to be made for it to actually arrive on time.

The problem in our busy modern life, is that we have forgotten that we have blindly signed up to an 'invention'. The invention that most of us have subscribed to, is the Atomic clock. That is NOT time, it is an invention of time that we belive is somehow 'real'.

Needless to say, I often wonder what exists between those two 'scientific' events?  Where does our time go to, if it never reaches the 2nd event?

 

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1 hour ago, Filroden said:

I know exactly how the metre is defined today and how a prototype measurement had to be used until a definition based on nature could be agreed. What I don't understand is how you can evidence that the metre varies in different parts of the world. Pointing at what things were in the past is not evidence. 

And just to be clear, even the historical definitions did not allow for the metre to be different in different parts of the world. They all produced a "standard" metre which was used as the benchmark everywhere. The fact that the methodology chosen could have given rise to many different definitions is irrelevant; they chose one particular method and used that to create a standard that was universal. So what evidence do you have that shows the metre varying based on location?

And you still haven't provided the evidence for how mass varies with gravity.

I don't need immediate answers. I appreciate these will need research and study and am happy to wait. The answer is important to me. As a surveyor and cartographer, I need to know if I've been practising my trade incorrectly.

'After Albert Einstein's special relativity, length can no longer be thought of being constant in all reference frames. Thus a ruler that is one meter long in one frame of reference will not be one meter long in a reference frame that is travelling at a velocity relative to the first frame. This means length of an object is variable depending on the observer. '

 

Check it out for yourself.

ps I've already corrected the mass/weight error.

Oh..and as we have Tectonic plate movement across the globe..we therefore have a velocity relative to the observer.  So I hope that clears matters for you.

;)

 

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Events are points in spacetime separated by an invariant spacetime interval. This interval has both spatial and temporal components which vary with reference frame. 

In relativity time is measured operationally by clocks and distance by meter sticks. While your clocks and meter sticks a appear to read differently when viewed from a different reference frame to you the spacetime interval remains constant.

Regards Andrew 

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59 minutes ago, Delasaurus said:

Time varies, according to how we 'define' it. It is defined in science as the difference between any two  'events'.

That could be anything from when Micky Mouse arrives the next time on our TV's, the falling of leaves from trees from one season to another, or a heart beat or the cycles between the phases of the moon or the sun, or the ticking of a clock! Which is simply a mechanical tool that moves at certain periodic intervals.

But clocks tick at different rates do they not?

So, we needed something more accurate for scientific calculations, hence the invention of the atomic clock.

Time, in Medieval days however, was defined as being 1/84,000 part of a day.

And time, as we know, was a complete headache for the Railway networks whereby due to long distances, the train from London would not be at Paris say, at 10:00am as predicted, but at a different time if the chuffer maintained a constant speed. Therefore, adjustments in the speed of the train had to be made for it to actually arrive on time.

The problem in our busy modern life, is that we have forgotten that we have blindly signed up to an 'invention'. The invention that most of us have subscribed to, is the Atomic clock. That is NOT time, it is an invention of time that we belive is somehow 'real'.

Needless to say, I often wonder what exists between those two 'scientific' events?  Where does our time go to, if it never reaches the 2nd event?

 

What you have largely described here is not time rather the instruments we use to measure time. There is absolutely no confusion nor doubt as to the unit of time or the definition of time. While different clocks as you say may "tick" at different rates , the unit they measure is fully described. Likewise, there is no "invention" that we have signed up to - time does not need our permission or acceptance. I certainly do not agree that those who have occasion to use atomic clocks have mistaken the clock itself for time.

Jim

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27 minutes ago, Delasaurus said:

'After Albert Einstein's special relativity, length can no longer be thought of being constant in all reference frames. Thus a ruler that is one meter long in one frame of reference will not be one meter long in a reference frame that is travelling at a velocity relative to the first frame. This means length of an object is variable depending on the observer. '

 

Check it out for yourself.

ps I've already corrected the mass/weight error.

Oh..and as we have Tectonic plate movement across the globe..we therefore have a velocity relative to the observer.  So I hope that clears matters for you.

;)

 

The relativistic effects you cite here are of course trivial and to all practical extents beyond measurement. For a bit of fun take the speed of plate tectonic movement use the Lorentz factor and calculate the contraction on 1m!  However, even if we suspend that notion, the definition and therefore the standards wouldn't change as the measurement would be taken within the same frame of reference. The laws of physics hold in either frame of reference (inertial) therefore the physical units are invariant.  Therefore  by definition, a metre remains a metre, a second remains a second to their own observer. As Andrew said earlier the space-time interval remains constant. Our standards are safe :) 

Jim

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25 minutes ago, saac said:

What you have largely described here is not time rather the instruments we use to measure time. There is absolutely no confusion nor doubt as to the unit of time or the definition of time. While different clocks as you say may "tick" at different rates , the unit they measure is fully described. Likewise, there is no "invention" that we have signed up to - time does not need our permission or acceptance. I certainly do not agree that those who have occasion to use atomic clocks have mistaken the clock itself for time.

Jim

So, you would agree then that it is a concept, Because as you say, it does not need our permission or acceptance?

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13 minutes ago, saac said:

The relativistic effects you cite here are of course trivial and to all practical extents beyond measurement. For a bit of fun take the speed of plate tectonic movement use the Lorentz factor and calculate the contraction on 1m!  However, even if we suspend that notion, the definition and therefore the standards wouldn't change as the measurement would be taken within the same frame of reference. The laws of physics hold in either frame of reference (inertial) therefore the physical units are invariant.  Therefore  by definition, a metre remains a metre, a second remains a second to their own observer. As Andrew said earlier the space-time interval remains constant. Our standards are safe :) 

Jim

They might be trivial, that is not to say they do not exist and therefore that makes m  a variable depending on your location.

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5 minutes ago, Delasaurus said:

So, you would agree then that it is a concept, Because as you say, it does not need our permission or acceptance?

This is difficult as all language is conceptual.  Thus it depends on your philosophical stance.  I believe in an objective world which is what it is. What we observe is in this sense is not our creation. However, we are constrained by our biology and we label things to allow us to think about them. In addition though I don't think we can do this in an arbitrary way if we want a coherent view of the world.

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6 minutes ago, Delasaurus said:

They might be trivial, that is not to say they do not exist and therefore that makes m  a variable depending on your location.

In SR some things are invariant and some are not. Rest msss is invariant,  kinetic energy is not but the energy momentum four vector is.

This is all well understood. Just to be clear a second is a second and a meter a meter in any inertial frame in which the clock or meter stick are at rest.

Regards Andrew 

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Drifting off topic again(?), but...

I was prompted to wonder about the (latest studies of) "Anisotrophy of the Fine Structure constant".  All set to irretrievably damage science a few years back? Or at least cause a slight rethink [teasing] of some theories! :D

I can understand those who might get fed up with science proselytisers publicists
and their crusades. There is now a separate discipline they call "Popular Science"? :p
And KUDOS to the grass roots scientists and conventional educators at all levels.

But I do feel sorry (exasperated and more) about the stuff (abuse) the National Labs
... NASA, CERN etc. have to suffer "for their science" on a daily (social media) basis. :(

Maybe we should adopt J.K.Rowling of "Science Publicist in Chief":

jkr.jpg.6dfd628235f477d10faac342d31ded67.jpg

"Go Jo!" And almost FIVE time the "followers" as other claimants! :evil4:

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6 hours ago, Delasaurus said:

which is why the 'standard' metric measure is kept under lock and key somewhere, in Belgium? Where all measurement is referred to it.

I think, but may be wrong ! all the standards used to be kept by the French standards people (in Paris perhaps ?) their equivalent of our NPL But now they are not reference standards, except for the Kg. All the others are now defined by atomic type thingies, frequency, oscillations, shell gap, only the Kg lump has a 'pick it up in your hands' type standard anymore.  And they are busy trying to count atoms sufficiently so as to do away with that lump as well, by invoking Avagadro etc.

So that funny number for the speed of light arose from trying to match it with the then existing stick that the French had at the time. What I was suggesting was that the stick should have been assumed to be wrong by a tiny little bit and it would have been a good opportunity to round it up to 300,000,000m/s by introducing a "leap mm" or fraction thereof ;) you see ? Think of leap seconds and the swap from Julian to Gregorian etc.

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18 minutes ago, Macavity said:

 they call "Popular Science"?

and that is a bit of a misnomer because amongst the popular populace it is difficult to find anyone with whom it (science) is popular ! One dictionary definition :  " liked, enjoyed, or supported by many people "  :icon_cry:

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1 hour ago, Delasaurus said:

They might be trivial, that is not to say they do not exist and therefore that makes m  a variable depending on your location.

Trivial in the mathematical sense. But no not variable, a second would still be a second as measured in the frame of reference of the event. What you are describing is dilation of time (SR) experienced by observers in different frames of reference - while they measure the event differently the definition of time and the unit of a second remains the same to both. In your spaceship moving at 0.99c a second is still a second just as it is on Earth.

Jim 

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3 minutes ago, SilverAstro said:

I think, but may be wrong ! all the standards used to be kept by the French standards people (in Paris perhaps ?) their equivalent of our NPL But now they are not reference standards, except for the Kg. All the others are now defined by atomic type thingies, frequency, oscillations, shell gap, only the Kg lump has a 'pick it up in your hands' type standard anymore.  And they are busy trying to count atoms sufficiently so as to do away with that lump as well, by invoking Avagadro etc.

So that funny number for the speed of light arose from trying to match it with the then existing stick that the French had at the time. What I was suggesting was that the stick should have been assumed to be wrong by a tiny little bit and it would have been a good opportunity to round it up to 300,000,000m/s by introducing a "leap mm" or fraction thereof ;) you see ? Think of leap seconds and the swap from Julian to Gregorian etc.

Yes, your right, I remember now, it was all kept in Paris. Is the NPL still going? I haven't been in there for yonks and yonks. They used to have an absolutely huge milling machine/lathe in there that was probably 50' long, which had a 3' cavity in the floor surrounding it. I remember saying that I suspected the cavity was to prevent vibration to all the other surrounding equipment, No! No!..the guy said. 'it's to protect all the other equipment from interfering with the lathe!

Fantastic place, In in the late 70's the Japanese, as they were becoming a 'serious' threat to UK manufacturing, sent the NPL a very fine piece of wire to show off how clever they were at extruding fine wire. And the NPL made a drill and drilled a hole right through the middle of it and sent it back to them, along with the drill. :)

Yeah, things have changed a lot from the temperature controlled standard 68 degree c lump of certified stainless steel.

Totally agree with you, why not make it 1,000,000,000 m/s to bring it up to date with metrification? ;)

 

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6 minutes ago, SilverAstro said:

and that is a bit of a misnomer because amongst the popular populace it is difficult to find anyone with whom it (science) is popular ! One dictionary definition :  " liked, enjoyed, or supported by many people "  :icon_cry:

I know what you mean but I'd suggest most folk are fans of science even if indirectly - how many would be willing to forgo their mobile phones? I would agree that a lot of people are put off science due to its nature - it deals with complicated and abstract concerns using a language that at times is impenetrable. What science does seam to attract perhaps like no other discipline (art, music etc) is an emotive reaction of  opposition/challenge. I don't know what fuels this but have often thought it is driven by the common misconception that science deals in absolutes and sets itself as "all knowing" and not to be challenged. Tall poppy syndrome perhaps, I don't know, maybe I have it wrong. 

 

Jim

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3 minutes ago, saac said:

I know what you mean but I'd suggest most folk are fans of science even if indirectly - how many would be willing to forgo their mobile phones? I would agree that a lot of people are put off science due to its nature - it deals with complicated and abstract concerns using a language that at times is impenetrable. What science does seam to attract perhaps like no other discipline (art, music etc) is an emotive reaction of  opposition/challenge. I don't know what fuels this but have often thought it is driven by the common misconception that science deals in absolutes and sets itself as "all knowing" and not to be challenged. Tall poppy syndrome perhaps, I don't know, maybe I have it wrong. 

 

Jim

I think that is exactly what I am trying to portray. I don't mean to be offensive to any one, but yes, science and physics puts itself out on the line as being untouchable, unchallengable and only open to those with some kind of higher intellect than others challenging it. The Art's on the other hand are constantly being challenged, shaped and reformed.

In the old days...ah the old days.. Science was part of the Arts. It had philosophical arguments as well. But today if we challenge science philosophically it seems that we are blithering idiots to the scientific community and don't know what we are talking about. So that makes us unworthy to talk to.

That is very, very, wrong. I think that the most common mistake is, as you say, people believing that science is the be all and end all and is absolute, it isn't.

 

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4 hours ago, andrew s said:

The current view is that it was always infinite

I was worried that someone would say something to that effect ! Cos I'd already asked myself if it could be infinite even when it was a tiny tiny thing less than the Planck thingie,  perhaps even down as small as a singularity (yes I know that is just a maths/equation fudge and may not be truly small)

Maybe the problem is with the word & concept "big".  Ie. we shouldnt think of the universe being 'infinitely big'  just infinite with no qualification ? Or perhaps "mathematically infinite" !

My head hertz.

 

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3 minutes ago, SilverAstro said:

I was worried that someone would say something to that effect ! Cos I'd already asked myself if it could be infinite even when it was a tiny tiny thing less than the Planck thingie,  perhaps even down as small as a singularity (yes I know that is just a maths/equation fudge and may not be truly small)

Maybe the problem is with the word & concept "big".  Ie. we shouldnt think of the universe being 'infinitely big'  just infinite with no qualification ? Or perhaps "mathematically infinite" !

My head hertz.

 

The problem is we can't see past the CMB so we don't know what it was like before that. Even inflation is a conjecture to explain what we see now. It may never have been at the Planck scale for all we know. 

Remember infinity is not the same as size/scale. There is an infinity of point in a mm or nm for that matter. We tend to think of infinity as big in common usage but that is not what it means in topology/mathematics. You can rescale any infinite quantity, up or down,  and it will still be infinite. 

Regards Andrew 

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