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Offline McQueen

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What is the speed of light really?
« on: 16/05/2016 12:25:23 »
There seems to be a lot of confusion about the speed of light. For instance some die hard Quantum Mechanics adherents, still believe that the speed of light follows Galilean transformations:
Depending on what you mean you could be wrong. If you mean that if, in the inertial frame S, a beam of light was moving from along the x-axis in the positive direction with speed c and another beam was moving along the same x-axis in the negative direction with speed c then their relative speed of the two beams is 2c. What SR states is that that will be the same in any inertial frame of reference.

This statement indicates such an extremely poor understanding of  special and general relativity, that it is quite depressing to realize that the most eager supporters of Quantum Mechanics, the ones who are willing to stand up for it no matter what, are the ones who do not realize that Quantum Mechanics does not claim to yield answers that satisfy ‘reality’.  This is true regardless of whether one is thinking in terms of multiple dimensions, or of the invariance of the speed of light in a vacuum. Supporters of the type I refer to will insist that it is not dimensions that are in question but “degrees of freeedom’. In the same  way these supporters will also argue about the speed of light being constant, in the terms quoted above, Apart from this they are extremely abusing and lofty in their self regard and disparaging of those who try to state the facts as they exist. He following are examples:

Quote from: McQueen
 This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good. This was extremely puzzling,

Quote
PmbPhyThat's because you have a misunderstanding of the invariance of c postulates of relativity.

Having pointed out this seeming unwillingness on the part of certain QM supporters to accept the fact that the very definition of Quantum Mechanics is that nothing can be defined in the classical sense of the term, it is time to return to the question of what does the term speed of light as constant mean ?

I had demonstrated  earlier by mathematical examples , how the speed of sound is invariant in a given medium provided the medium does not undergo a change:
For instance take the example of two cars; car (a) at 60 kmh and car (b) at 30 kmh  approaching each other from opposite directions at a distance of 10 Km. Their combined speed would be 60kmh + 30 kmh = 90 kmh. This can easily be verified by calculating at what point the two cars would meet if they maintain the same constant speeds. Since the distance between them is 10 Km, it will take 10/90 = 0.111 hours for the two cars(a) and (b) to meet. During this time Car (s) would have travelled 3.33 Km and  car (a) would have traveled = 6.6666 Km  Thus the time taken for  the two cars meet is the time calculated according to their combined velocities 60 kmh and 30 kmh = 90 kmh.  The same kind of relationship holds true in general for any two bodies moving with respect to each other.  If two people (a) and (b) are walking towards each other from an initial starting distance of 1 km and their speeds respectively are 5 kmh and 3 kmh, then their speed with respect  to each other is 8 kmh and to verify this it is found that if they continue to maintain these same speeds that they will meet after 7.5 minutes, during this time (a) would have travelled 0.625 Km, and (b) would have travelled  0.375 Km. making a total of 1 Km.

 Yet coming back to the first example take car (a) travelling at 60 kmh is 1 km distant from car (b) travelling at 30kmh. Suppose that at this time car(a) activates a siren and also suppose that the speed of sound is  340m/s . At what time will the sound reach car(b) supposing that car(a) and car(b) continue to approach each other at the same speeds.  Would Galilean transformations apply and the combined speed with which car(a) and car(b) together with siren sound be 16.6m/s + 340m/s + 8.3m/s = 365m/s approx and they would meet at 1000/365 = 2.75 seconds. The answer is NO. Because the speed of sound is invariant in a medium it means that it does not obey Galilean transformations, thus the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs. During this time car (b) would have travelled 24.5 m approx.  This is a completely unexpected result, until one realizes that light also exhibits such invariance:

That is, if two beams of light were approaching each other  they would not follow Galilean transformations and have a combined speed of 600,000 km per second but each beam of light would have a constant speed of 300,000 km per second. This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good.

 The natural conclusion that one comes to on witnessing this circumstance, is, that the invariance that light demonstrates as it travels through a vacuum could very well be because it is travelling through a medium whose presence has thus far managed to elude us. The point being that this ( to some) is a more acceptable explanation than to believe in time dilation or the fact that objects shrink as they approach close to the speeds of light. The irony being that these physical properties may very well manifest themselves, even if a medium (aether) for light to travel through does exist. But they would manifest themselves not because the speed of light is a constant but because an aether exists.
« Last Edit: 16/05/2016 18:47:27 by chris »


 

Offline alancalverd

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Re: What is it with the speed of light …?
« Reply #1 on: 16/05/2016 17:19:42 »
Light and sound are very, very different. You can't use one as an analogy of the other.
 

Offline arcmetal

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Re: What is the speed of light really?
« Reply #2 on: 16/05/2016 20:17:22 »
There seems to be a lot of confusion about the speed of light. For instance some die hard Quantum Mechanics adherents, still believe that the speed of light follows Galilean transformations:

This statement indicates such an extremely poor understanding of  special and general relativity, ...

 Yet coming back to the first example take car (a) travelling at 60 kmh is 1 km distant from car (b) travelling at 30kmh. Suppose that at this time car(a) activates a siren and also suppose that the speed of sound is  340m/s . At what time will the sound reach car(b) supposing that car(a) and car(b) continue to approach each other at the same speeds.  Would Galilean transformations apply and the combined speed with which car(a) and car(b) together with siren sound be 16.6m/s + 340m/s + 8.3m/s = 365m/s approx and they would meet at 1000/365 = 2.75 seconds. The answer is NO. Because the speed of sound is invariant in a medium it means that it does not obey Galilean transformations, thus the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs. During this time car (b) would have travelled 24.5 m approx.  This is a completely unexpected result, until one realizes that light also exhibits such invariance:

That is, if two beams of light were approaching each other  they would not follow Galilean transformations and have a combined speed of 600,000 km per second but each beam of light would have a constant speed of 300,000 km per second. This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good.

 The natural conclusion that one comes to on witnessing this circumstance, is, that the invariance that light demonstrates as it travels through a vacuum could very well be because it is travelling through a medium whose presence has thus far managed to elude us. The point being that this ( to some) is a more acceptable explanation than to believe in time dilation or the fact that objects shrink as they approach close to the speeds of light. The irony being that these physical properties may very well manifest themselves, even if a medium (aether) for light to travel through does exist. But they would manifest themselves not because the speed of light is a constant but because an aether exists.

Thank you for this, I am liking this explanation.  If I have it straight, this is simply saying that a wave's speed is dependent on the properties of the medium in which it travels and not on the speed of the craft that caused it.

I can see the confusion happens when examples are given in which the people in the moving cars are tossing bullets at each other (so if car (a) shoots a bullet from a gun at 200 m/s, and car (b) shoots a bullet from a slingshot at 20 m/s... and so on)  The combined speeds of the bullets will follow Galilean transformations since the effects of the medium (the air) on the bullets is negligible.... Therefore, one shouldn't compare speeding bullets flying through the air shot from fast moving cars with the speed of siren sounds, or of lasers, shot from the same moving cars.

« Last Edit: 16/05/2016 20:20:34 by arcmetal »
 

Offline lightarrow

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Re: What is the speed of light really?
« Reply #3 on: 17/05/2016 07:42:30 »
There seems to be a lot of confusion about the speed of light. For instance some die hard Quantum Mechanics adherents, still believe that the speed of light follows Galilean transformations:
Depending on what you mean you could be wrong. If you mean that if, in the inertial frame S, a beam of light was moving from along the x-axis in the positive direction with speed c and another beam was moving along the same x-axis in the negative direction with speed c then their relative speed of the two beams is 2c. What SR states is that that will be the same in any inertial frame of reference.

This statement indicates such an extremely poor understanding of  special and general relativity, that it is quite depressing to realize that the most eager supporters of Quantum Mechanics, the ones who are willing to stand up for it no matter what, are the ones who do not realize that Quantum Mechanics does not claim to yield answers that satisfy ‘reality’.  This is true regardless of whether one is thinking in terms of multiple dimensions, or of the invariance of the speed of light in a vacuum. Supporters of the type I refer to will insist that it is not dimensions that are in question but “degrees of freeedom’. In the same  way these supporters will also argue about the speed of light being constant, in the terms quoted above, Apart from this they are extremely abusing and lofty in their self regard and disparaging of those who try to state the facts as they exist. He following are examples:

Quote from: McQueen
 This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good. This was extremely puzzling,

Quote
PmbPhyThat's because you have a misunderstanding of the invariance of c postulates of relativity.

Having pointed out this seeming unwillingness on the part of certain QM supporters to accept the fact that the very definition of Quantum Mechanics is that nothing can be defined in the classical sense of the term, it is time to return to the question of what does the term speed of light as constant mean ?

I had demonstrated  earlier by mathematical examples , how the speed of sound is invariant in a given medium provided the medium does not undergo a change:
For instance take the example of two cars; car (a) at 60 kmh and car (b) at 30 kmh  approaching each other from opposite directions at a distance of 10 Km. Their combined speed would be 60kmh + 30 kmh = 90 kmh. This can easily be verified by calculating at what point the two cars would meet if they maintain the same constant speeds. Since the distance between them is 10 Km, it will take 10/90 = 0.111 hours for the two cars(a) and (b) to meet. During this time Car (s) would have travelled 3.33 Km and  car (a) would have traveled = 6.6666 Km  Thus the time taken for  the two cars meet is the time calculated according to their combined velocities 60 kmh and 30 kmh = 90 kmh.  The same kind of relationship holds true in general for any two bodies moving with respect to each other.  If two people (a) and (b) are walking towards each other from an initial starting distance of 1 km and their speeds respectively are 5 kmh and 3 kmh, then their speed with respect  to each other is 8 kmh and to verify this it is found that if they continue to maintain these same speeds that they will meet after 7.5 minutes, during this time (a) would have travelled 0.625 Km, and (b) would have travelled  0.375 Km. making a total of 1 Km.

 Yet coming back to the first example take car (a) travelling at 60 kmh is 1 km distant from car (b) travelling at 30kmh. Suppose that at this time car(a) activates a siren and also suppose that the speed of sound is  340m/s . At what time will the sound reach car(b) supposing that car(a) and car(b) continue to approach each other at the same speeds.  Would Galilean transformations apply and the combined speed with which car(a) and car(b) together with siren sound be 16.6m/s + 340m/s + 8.3m/s = 365m/s approx and they would meet at 1000/365 = 2.75 seconds. The answer is NO. Because the speed of sound is invariant in a medium it means that it does not obey Galilean transformations, thus the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs. During this time car (b) would have travelled 24.5 m approx.  This is a completely unexpected result, until one realizes that light also exhibits such invariance:

That is, if two beams of light were approaching each other  they would not follow Galilean transformations and have a combined speed of 600,000 km per second but each beam of light would have a constant speed of 300,000 km per second. This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good.

 The natural conclusion that one comes to on witnessing this circumstance, is, that the invariance that light demonstrates as it travels through a vacuum could very well be because it is travelling through a medium whose presence has thus far managed to elude us. The point being that this ( to some) is a more acceptable explanation than to believe in time dilation or the fact that objects shrink as they approach close to the speeds of light. The irony being that these physical properties may very well manifest themselves, even if a medium (aether) for light to travel through does exist. But they would manifest themselves not because the speed of light is a constant but because an aether exists.
Which movie have you seen recently?

--
lightarrow
 

Offline McQueen

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Re: What is the speed of light really?
« Reply #4 on: 17/05/2016 08:35:20 »
The original title of this post was “What is it with the speed of light …..?” which unfortunately has been changed to: “What is the speed of light really ? “ a title more apropros of lightarrow and his understanding  apparently. Anyway, yes arcmetal did make some interesting points. For instance if a car moving at 40m/s fires of a bullet that has a velocity of 100 m/s then to a person in the car the bullet would appear to have a velocity of 100m/s , but to an observer the bullet would appear to travel at 140m/s i.e., the velocity of the car plus the velocity of the bullet and if the bullet hit an object  it would hit  that object with a velocity of 140m/s and not with a velocity of 100m/s as would have been the case if the bullet had been fired from a stationary position. If on the other hand it was a sound that had been emitted instead of a bullet that was fired from the car then if the speed of sound in that medium ( air ) is approx. 340 m/s, then that is the speed at which the sound of the siren will travel it will not travel at 340m/s plus 40 m/s or at 380 m/s but at 340 m/s. The same scenario would apply if it was a beam of light, although in that case the velocity would be 300,000 km/s.
 

Offline PmbPhy

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Re: What is the speed of light really?
« Reply #5 on: 17/05/2016 13:31:00 »
Quote from: McQueen
This statement indicates such an extremely poor understanding of  special and general relativity, ...
Actually I have an extremely good understanding of relativity. That's why a relativity professor at MIT whom I know referred to me when someone approached him seeking a relativity tutor. What I just explained to you in that post is what a freshman in physics learns in the PHY I course that is required in college. In fact its so easy to prove that a chimp could prove it. In fact its so easy to prove that what I said is sufficient to someone who's intelligent enough to comprehend it.

Since you only seem to post rude comments when people prove that you're wrong, and since you have such a poor reputation, you will never see my respond to your posts again. I have better things to do with my time than to respond to the nonsense you've been posting since you've gotten here. I heard you were bad but I didn't understand why until you posted that very ignorant response.
 

Offline McQueen

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Re: What is the speed of light really?
« Reply #6 on: 17/05/2016 13:40:41 »
Since you only seem to post rude comments when people prove that you're wrong, and since you have such a poor reputation, you will never see my respond to your posts again. I have better things to do with my time than to respond to the nonsense you've been posting since you've gotten here. I heard you were bad but I didn't understand why until you posted that very ignorant response.

Don't worry you are a paradigm of politeness ! In any case at least the statement you made about chimps seems to be correct and I do believe that they would catch on faster than you that the speed with which a wave propagates depends on the medium through which it propagates and not on some archaic highly suspect mathematics, a chimp might just accept that fact faster than you can, Mr MIT physics professor consultant. Incidentally you never said but do you still hold to your statement that:
Quote
Depending on what you mean you could be wrong. If you mean that if, in the inertial frame S, a beam of light was moving from along the x-axis in the positive direction with speed c and another beam was moving along the same x-axis in the negative direction with speed c then their relative speed of the two beams is 2c. What SR states is that that will be the same in any inertial frame of reference.

I'll make it easy for you, you claim that two beams of light travelling towards each other on the same axis will have a cumulative speed of 2C or 600,000 km/s. Right or wrong ? If that is what you taught the physics freshman then goodluck to him!

How can I explain to someone who believes that they know what special relativity and general relativity are. That above all they are theories, all that I was trying to do was to explain why those particular choices, (i.e.,  to postulate the speed of light as invariant in a vacuum but not to explain why or how that could be) were made. I strongly feel that since the originator of both special relativity and General relativity, namely Albert Einstein, could not explain mathematically or otherwise why the speed of light is constant in a vacuum, for other ( hopefully admittedly) less talented or intellectually endowed persons to attempt to do so, is naturally ludicrous.
« Last Edit: 17/05/2016 14:00:22 by McQueen »
 

Offline Prophet12

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Re: What is the speed of light really?
« Reply #7 on: 21/05/2016 15:47:53 »
The simple answer is the true speed of light is variable....... light/it is energy or a result of energy/mass (E+mc2) so it has weight and can be externally effected by such and in so, is variable based on influences....even a vacuum which has an influence comparatively...
DS
 

Offline Colin2B

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Re: What is the speed of light really?
« Reply #8 on: 23/05/2016 19:06:37 »
Quote from: McQueen
This statement indicates such an extremely poor understanding of  special and general relativity, ...
Since you only seem to post rude comments when people prove that you're wrong, and since you have such a poor reputation, you will never see my respond to your posts again. I have better things to do with my time than to respond to the nonsense you've been posting since you've gotten here. I heard you were bad but I didn't understand why until you posted that very ignorant response.
Wise decision, the conclusions reached here are flawed
http://www.thenakedscientists.com/forum/index.php?topic=66803.0
 

Offline McQueen

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Re: What is the speed of light really?
« Reply #9 on: 24/05/2016 05:59:39 »
Wise decision, the conclusions reached here are flawed
http://www.thenakedscientists.com/forum/index.php?topic=66803.0

Talking through your hat as usual...!
 

Offline McQueen

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Re: What is the speed of light really?
« Reply #10 on: 24/05/2016 06:01:41 »
The simple answer is the true speed of light is variable....... light/it is energy or a result of energy/mass (E+mc2) so it has weight and can be externally effected by such and in so, is variable based on influences....even a vacuum which has an influence comparatively...
DS

Actually, Prophet12, that is quite an insightful statement.
 

Offline Colin2B

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Re: What is the speed of light really?
« Reply #11 on: 25/05/2016 14:56:56 »
Wise decision, the conclusions reached here are flawed
http://www.thenakedscientists.com/forum/index.php?topic=66803.0

Talking through your hat as usual...!

Really?


If we take this post of yours:
Would Galilean transformations apply and the combined speed with which car(a) and car(b) together with siren sound be 16.6m/s + 340m/s + 8.3m/s = 365m/s approx and they would meet at 1000/365 = 2.75 seconds. The answer is NO. Because the speed of sound is invariant in a medium it means that it does not obey Galilean transformations, thus the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs. During this time car (b) would have travelled 24.5 m approx.  This is a completely unexpected result, until one realizes that light also exhibits such invariance

You state that the speed of the soundwave and the car do not obey Galilean transformations and hence come to a false result that "the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs"

Well, if I am talking through my hat so are all the physics departments in Universities, physics lecturers, textbook authors, Encyclopedias etc, and I find it hard to believe that you are the only one to get it right. Sounds like delusions of grandeur to me.

Perhaps I might quote Advanced Physics - Tom Duncan, which is a secondary school textbook.


Or University of California lecture notes


I could also mention any Acoustics textbook by Tom Rossing Emeritus Professor at Stanford, among many, many others.

Perhaps it is you talking through somewhere much darker than the inside of my hat - as usual
« Last Edit: 25/05/2016 15:01:26 by Colin2B »
 

Offline Colin2B

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Re: What is the speed of light really?
« Reply #12 on: 01/06/2016 16:37:26 »
Even more misunderstanding:
But The wave's speed depends only on the medium. Adding energy to the wave doesn't speed it up, it just increases its amplitude. A water wave, unlike many other types of wave, has a speed that also depends on its shape: a broader wave moves faster.  This means that just like electromagnetic radiation the speed of sound and of waves in water are invariant, they do not follow the laws of  Galilean transformations.
If energy is added to a water wave, either by an increase in wind speed or by increasing the speed of a boat creating waves, then the wave will increase in speed and consequently wavelength.

 

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Re: What is the speed of light really?
« Reply #12 on: 01/06/2016 16:37:26 »

 

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