Light Speed question

[munion]

We went over this already — there are many processes that depend on the speed of light. If c changed, without a scaled change in all other physical constants (if that's even possible), something would be different, such as the strength of atomic or nuclear forces.

 

For the fine structure constant i have posted something for the others constants really i don't know what would happen may be remain the same ....

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Let's back up a bit. I think what you are really asking is "are the physical constants really constant with respect to time?" Physicists assume that the key physical constants are indeed constant in the theories they develop. Our current understanding of the universe cannot answer your question because it is a nonsense question in terms of that understanding: The constancy of the key physical constants is built-in to that understanding. One obvious consequence, however: Energy would not be conserved if the physical constants varied with time. Energy is conserved because the laws of physics are invariant with respect to time. Get rid of that invariance and you get rid of conservation of energy.

 

Because physicists do not like unwarranted assumptions, they test the heck out of these assumptions of the physical constants being constant. There are ways of looking back in time, a long ways back in time. For example, telescopes essentially see back in time. Another example are the Oklo deposits in Africa. Two billion years ago these formed a natural nuclear reactor. The decay products we see now from these two billion year old reactions demonstrate that the laws of physics have not changed over the last two billion years.

 

Here is one web site that tries to answer your question: http://www.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm. It starts with this personal preamble (emphasis mine):

As a child, I asked my parents "What if everything in the world had shrunk to half size overnight. How would we know? I'd be half as tall, but the ruler would be only half as long, so I couldn't tell." But this invited further questions: how long would it take to walk to school? If my half-length legs propelled me at half the speed, I wouldn't notice the change in the distance. Or perhaps shrinking all the molecules in my leg muscles would make the electrical forces stronger so I'd walk faster. Or maybe all the clocks would be sped up by a factor. Pendulums and planetary orbits would be shorter, and crystals would be stiffer (per unit area). Both gravitational and electric clocks would run fast. At the time, I didn't know about inverse square laws or quantum mechanics, but it seemed reasonable that the (electrical) muscular forces and gravitational forces should be changed, too.

Conclusion in retrospect? Starting from this point makes the question more complicated and confusing than it need be - one ends up going around in circles. It's easier to start logically and work up from the basics.

I think this same confusion is part of your problem. Read this article, see if it answers some questions.

 

Yes thank you about your answer....

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Dear DH I read more carefully the article and i have one notice it says:

 

"Is the speed of light constant?

What would it mean to say that c varied with time? Would it actually mean anything? In conventional units, the metre is defined as the distance that light travels in about 3 nanoseconds. (This is not quite the same thing as saying that the metre is the distance travelled in 1/c seconds.) Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler. According to the definition, we wouldn't say that the speed of light had fallen, but that the ruler had lengthened. How could that be? What would that mean?

 

Now the size of the ruler depends upon the size of atoms, which in turn is related (in our units) to quantum mechanical and electrical quantites. Could the atoms in the ruler have grown because electricity had faded, or because Planck's constant had increased? How would we know which?"

 

Obviously the guy is doing wrong here: if the speed of light slow down the clock that we are using to measure the time that the light travels the ruler tick slower so the marks on the ruler will be the same and the ruler will have the very same length as it has in the first measurement. I m suspecting that the very same thing is happening with the constants that the swansont has referred before. (Is something like the scale factor in FWR metric.). Is not the same but is about the same confusion....

 

 

PS: And one last thing if a constant varies does not meaning that the laws of physics are changing form

Edited September 8, 2009 by munion
Consecutive posts merged.

[kleinwolf]

I'm sorry to have confused some by my short-writing without a complete definition of the context, inducing a ???? reaction.

 

I maybe try to rewrite it more clearly.

 

Yes, all measurements of speed of light (in a vacuum) give a speed c, regardless of how fast the measuring equipment is moving. And atomic clocks get out of synch when one of them is riding in an airplane.

 

We could use a "formalism", either redefine a scope, or a new symbol for "speed" addition : like let say [math]+_r[/math], such that [math] c+_r v=c[/math] for all v, even for v=c.

 

Then why is this invariant speed a limit speed ? Because if you add 1km/h to c, it remains c, so you cannot go faster.

[munion]

Guys i would like your opinion about the post #53...

[iNow]

Guys i would like your opinion about the post #53...

 

I don't think it's specific enough, and I find it rather humorous.

[munion]

I don't think it's specific enough, and I find it rather humorous.

 

Tell me what do you want to clear out???

[insane_alien]

what he means is you got the post number wrong as post number 53 is the post you posted before iNows reply.

[munion]

what he means is you got the post number wrong as post number 53 is the post you posted before iNows reply.

 

Yes now i saw it .... i m feeling very ridiculous right now ..... #51 i was meaning (i think this time i got the right number)

[D H]

You apparently missed the point of the article, munion. The section marked Is the speed of light constant? is a lead-in to the rest of the article. That question at the end of this little section, "How would we know which," is a rhetorical question. The author proceeds to answer that vert question in the remainder of the article.

 

Your question, "What would happen if the speed of light changed," is a science fiction question. Physics cannot answer that question because the laws of physics assume the speed of light is constant. In the sense of what physics can describe, this is a non sequitur kind of question. It simply does not compute.

 

There is a very good reason why physics assumes the speed of light is constant. First there is direct observation. The speed of light is constant, as far as we can tell experimentally. Second, the speed of light is in a sense just an artifact of our definition of units. A better question is to poke at the dimensionless constants such as the fine structure constant. These are not artifacts of how we measure things. They are more fundamental than the speed of light. And as far as we can tell, constant.

[munion]

You apparently missed the point of the article, munion. The section marked Is the speed of light constant? is a lead-in to the rest of the article. That question at the end of this little section, "How would we know which," is a rhetorical question. The author proceeds to answer that vert question in the remainder of the article.

 

Your question, "What would happen if the speed of light changed," is a science fiction question. Physics cannot answer that question because the laws of physics assume the speed of light is constant. In the sense of what physics can describe, this is a non sequitur kind of question. It simply does not compute.

 

 

 

There is a very good reason why physics assumes the speed of light is constant. First there is direct observation. The speed of light is constant, as far as we can tell experimentally. Second, the speed of light is in a sense just an artifact of our definition of units. A better question is to poke at the dimensionless constants such as the fine structure constant. These are not artifacts of how we measure things. They are more fundamental than the speed of light. And as far as we can tell, constant.

 

"You apparently missed the point of the article" sorry for that but i don't have your intelligence.

Not again! This guy there it has a clear example and has omitted the fact that the clock slow down as the light speed slow down. The rest are simple excuses.... And finally if something rhetorical why mention this silly example???? This paragraph is the key to the writer to support that the SOL variation is sci fi but unfortunately for the writer is WRONG. You say "First there is direct observation" and i answer you CAN 'T do that even if SOL is changing. Again with the fine structure??? i have 3 post in this matter. The fine structure it WONT change (but there is some physicians that support that this constant also changing).

 

PS there is theories such as the joao magueijo (http://en.wikipedia.org/wiki/Jo%C3%A3o_Magueijo) that assumes the SOL changes by the time those guys are idiots by your opinion???

Edited September 9, 2009 by munion

[mooeypoo]

munion, D H is answering your question respectfully. There's no reason for you to take things personally and have the conversation turn to personal levels.

 

This is a debate, not a fist fight. Please be respectful.

[munion]

munion, D H is answering your question respectfully. There's no reason for you to take things personally and have the conversation turn to personal levels.

 

This is a debate, not a fist fight. Please be respectful.

 

Yes mooeypoo you have right but it makes me mad when he wrote that "You apparently missed the point of the article, munion". This article is erroneous and i least expect it to admit it. Now i m calm i want to express my apologies to D H if i insult him it wasn't in to my intentions .

Edited September 10, 2009 by munion

[D H]

The article is not erroneous. You objected to this:

What would it mean to say that c varied with time? Would it actually mean anything? In conventional units, the metre is defined as the distance that light travels in about 3 nanoseconds. (This is not quite the same thing as saying that the metre is the distance travelled in 1/c seconds.) Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler. According to the definition, we wouldn't say that the speed of light had fallen, but that the ruler had lengthened. How could that be? What would that mean?

 

That is exactly correct. Our current definition of the meter is "the distance travelled by light in free space in 1⁄299,792,458 of a second." This means the speed of light is constant by definition. If one conducted the experiment described by the author of that site, the only conclusion one could come to using our current definitions of time and distance is that the stick has gotten longer.

 

You are assuming that length is defined by marks on a stick. That is exactly how the meter used to be defined. There are a lot of problems with such a definition. In 1983 the standards committee dropped the old standard and adopted the definition quoted above.

 

The standards committee made this change for good reason. The speed of light is constant per accepted scientific theory and every measurement of the speed of light bears that assumption out.

 

Suppose someone did conduct the above experiment and found that the time it takes light to traverse the stick is increasing over time. The experimenters are going to try to find whether there are some hidden problems in their experiment. Suppose they find none. Are they going to assume the stick has grown longer just because it has per the current definitions of our units? No. They are going to poke, and poke and poke and poke, into this mystery. A result like that might well be worth a Nobel prize.

 

Ultimately it will come down to a change in one or more of the supposedly constant dimensionless constants, which is why we have been harruanging on those dimensionless constants.

 

What would such a change mean? We don't know. Science cannot answer that question because it assumes the speed of light is constant. It will stick to this assumption until some experiment shows the assumption to be wrong.

[munion]

The article is not erroneous. You objected to this:

What would it mean to say that c varied with time? Would it actually mean anything? In conventional units, the metre is defined as the distance that light travels in about 3 nanoseconds. (This is not quite the same thing as saying that the metre is the distance travelled in 1/c seconds.) Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler. According to the definition, we wouldn't say that the speed of light had fallen, but that the ruler had lengthened. How could that be? What would that mean?

 

That is exactly correct. Our current definition of the meter is "the distance travelled by light in free space in 1⁄299,792,458 of a second." This means the speed of light is constant by definition. If one conducted the experiment described by the author of that site, the only conclusion one could come to using our current definitions of time and distance is that the stick has gotten longer.

 

You are assuming that length is defined by marks on a stick. That is exactly how the meter used to be defined. There are a lot of problems with such a definition. In 1983 the standards committee dropped the old standard and adopted the definition quoted above.

 

The standards committee made this change for good reason. The speed of light is constant per accepted scientific theory and every measurement of the speed of light bears that assumption out.

 

Suppose someone did conduct the above experiment and found that the time it takes light to traverse the stick is increasing over time. The experimenters are going to try to find whether there are some hidden problems in their experiment. Suppose they find none. Are they going to assume the stick has grown longer just because it has per the current definitions of our units? No. They are going to poke, and poke and poke and poke, into this mystery. A result like that might well be worth a Nobel prize.

 

Ultimately it will come down to a change in one or more of the supposedly constant dimensionless constants, which is why we have been harruanging on those dimensionless constants.

 

What would such a change mean? We don't know. Science cannot answer that question because it assumes the speed of light is constant. It will stick to this assumption until some experiment shows the assumption to be wrong.

 

 

Whatever is the definition you are using to define to extract the measures is dependent from the speed of light.

You say " Suppose someone did conduct the above experiment and found that the time it takes light to traverse the stick is increasing over time. The experimenters are going to try to find whether there are some hidden problems in their experiment. Suppose they find none. Are they going to assume the stick has grown longer just because it has per the current definitions of our units? No. They are going to poke, and poke and poke and poke, into this mystery. A result like that might well be worth a Nobel prize."

I m saying that the time which the observer measures is the same and independent from the speed of light; not more not less and the stick has the same size; who said anything about length growth?. (except the writer of the article). Think about the inertia systems if you are an observer in one from that you say : i m not moving the rest around me are moving. If you have an acceleration and your speed increase to a value when this acceleration stop you will say the same thing that you are not moving and but the rest things around you. The very same thing i believe that is happening with the speed of light in 4D this time. Whatever changes you have (in the SOL "value") you are will always measuring the same value because everything scaled up or down by same amount.

I cant explain to you any better.....

 

 

Irrelevant but could be useful in order to be clear i m accepting all of the principles of special relativity and i hate aether theory.

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My english are going from the bad to worse...

Edited September 10, 2009 by munion

[D H]

I m saying that the time which the observer measures is the same and independent from the speed of light; not more not less and the stick has the same size; who said anything about length growth?. (except the writer of the article).

You are correct about time but not about length. As I said earlier, a meter is "the distance travelled by light in free space in 1⁄299,792,458 of a second." This means that

1. The speed of light is constant by definition.
   
2. By this definition of length, the only conclusion one can come to is that the ruler has gotten slightly longer.

 

You need to understand this before we can move on.

[munion]

You are correct about time but not about length. As I said earlier, a meter is "the distance travelled by light in free space in 1⁄299,792,458 of a second." This means that

1. The speed of light is constant by definition.
   
2. By this definition of length, the only conclusion one can come to is that the ruler has gotten slightly longer.

 

You need to understand this before we can move on.

 

 

Nope whatever is the definition that you are using the result will be the same because of the time in the first case the time will be 1⁄299,792,458 of a second; If the light speed change this time won't be different BUT your clock will go slower with everything else around you including the traveling ray of light and the result will be the same; by definition.

Edited September 10, 2009 by munion

[D H]

Light speed does not and can not change per the current definition of distance. You need to understand this before this discussion can move forward.

[munion]

Light speed does not and can not change per the current definition of distance. You need to understand this before this discussion can move forward.

 

The meter definition is the distance that cover the light in 1⁄299,792,458 of a second. Correct?

[D H]

Correct. That means the speed of light is 299,792,458 m/s and can not change -- at least using the current definition of a meter.

[munion]

Correct. That means the speed of light is 299,792,458 m/s and can not change -- at least using the current definition of a meter.

 

Then that means that even the SOL change (hypothetical) by the previous definition the length won't change. You will not notice any lengthen on your meter definition.

 

Let's do it step by step .

 

The 1⁄299,792,458 is an indication in the screen of your chronometer. Correct?

Edited September 11, 2009 by munion

[D H]

You will not notice any lengthen on your meter definition.

No! You are not reading the article.

 

Let's do it step by step .

 

The 1⁄299,792,458 is an indication in the screen of your chronometer. Correct?

Units! Always carry units in your calculations: 1 m / (299792458 m/s) = 3.33564095 nanoseconds.

 

The thought experiment to which you take objection starts with this as a basis. One step at a time:

1. Setup:
   1. 
      
   2. You have some device that enables you to measure the time it takes a light pulse to traverse the distance from a transmitter to a receiver.
      
   3. This is a "real" experiment; you cannot measure 3.33564095 nanoseconds. You can however measure down to the tenth of a picosecond, 3.336 nanoseconds, for example.
      
   4. You have a ruler that you want to calibrate with this device.

[*]Make a mark on the ruler corresponding to the location of the transmitter.

[*]Move the receiver along the ruler, measuring the transmission time as you do so.

[*]Stop moving the receiver when the transmission time is 3.3356 nanoseconds.

[*]Make a mark on the ruler corresponding to the location of the receiver.

You now have a calibrated ruler.

 

You missed the next part of the experiment. Suppose next year you use the device to measure the length between the calibrated scratch marks, but now you measure 3.3381 nanoseconds (for example).

 

What does this new measurement mean? (Your turn.)

Edited September 11, 2009 by swansont
fix quote tag

[munion]

You will not notice any lengthen on your meter definition.

No! You are not reading the article.

 

 

Units! Always carry units in your calculations: 1 m / (299792458 m/s) = 3.33564095 nanoseconds.

 

The thought experiment to which you take objection starts with this as a basis. One step at a time:

1. Setup:
   1. 
      
   2. You have some device that enables you to measure the time it takes a light pulse to traverse the distance from a transmitter to a receiver.
      
   3. This is a "real" experiment; you cannot measure 3.33564095 nanoseconds. You can however measure down to the tenth of a picosecond, 3.336 nanoseconds, for example.
      
   4. You have a ruler that you want to calibrate with this device.

[*]Make a mark on the ruler corresponding to the location of the transmitter.

[*]Move the receiver along the ruler, measuring the transmission time as you do so.

[*]Stop moving the receiver when the transmission time is 3.3356 nanoseconds.

[*]Make a mark on the ruler corresponding to the location of the receiver.

You now have a calibrated ruler.

 

You missed the next part of the experiment. Suppose next year you use the device to measure the length between the calibrated scratch marks, but now you measure 3.3381 nanoseconds (for example).

 

What does this new measurement mean? (Your turn.)

 

Nope again. The device that enables us to measure the time that the light goes from the transmitter to receiver will slow down. The ray of light also slow down and in 3.3356 nanoseconds you will have again your meter. The ONLY difference is that the procedure now is more "slow" if you can say that.

 

Please i m in work now and my boss are mad with me

Edited September 11, 2009 by swansont
fix quote tag

[Klaynos]

If length and time have both scaled relative to each other and there is no measurable difference between before and after NOTHING has changed.

[D H]

Nope again. The device that enables us to measure the time that the light goes from the transmitter to receiver will slow down.

You are misreading the article and you are quibbling with a proposition. The article says " Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler."

 

That light "takes longer than 3 ns to travel the length of the ruler" is a given condition in this (thought) experiment. Quibbling with this will get you nowhere other than confused.

 

 

You are throwing too many thoughts into the mix at once and all you are managing to do is to confuse yourself. Take it one step at a time. You are not taking your own advice.

 

munion, you are the one who asked "what if the speed of light changed". At least, I think that is your question. You used phrases such as the "4D speed". That doesn't quite make sense, so I reinterpreted your question to something that does make a bit more sense.

 

The question "what if the speed of light changed" doesn't quite make sense either, for the simple reason that the speed of light is currently defined to be a constant. The speed of light cannot change by definition.

 

This question is implying is that our definition of distance is not quite right, that distance has some deeper meaning than the one provided by our current definition of a meter. A better rendition of this question is "What if the speed of light changed (assuming some better definition of distance exists)".

 

Suppose our calibrated ruler has not truly changed in length. What has changed is the speed of light itself. The ruler will appear to have changed in length because we are using a faulty definition of distance.

[munion]

You are misreading the article and you are quibbling with a proposition. The article says " Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler."

 

That light "takes longer than 3 ns to travel the length of the ruler" is a given condition in this (thought) experiment. Quibbling with this will get you nowhere other than confused.

 

 

You are throwing too many thoughts into the mix at once and all you are managing to do is to confuse yourself. Take it one step at a time. You are not taking your own advice.

 

munion, you are the one who asked "what if the speed of light changed". At least, I think that is your question. You used phrases such as the "4D speed". That doesn't quite make sense, so I reinterpreted your question to something that does make a bit more sense.

 

The question "what if the speed of light changed" doesn't quite make sense either, for the simple reason that the speed of light is currently defined to be a constant. The speed of light cannot change by definition.

 

This question is implying is that our definition of distance is not quite right, that distance has some deeper meaning than the one provided by our current definition of a meter. A better rendition of this question is "What if the speed of light changed (assuming some better definition of distance exists)".

 

Suppose our calibrated ruler has not truly changed in length. What has changed is the speed of light itself. The ruler will appear to have changed in length because we are using a faulty definition of distance.

 

The article says " Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler." No you WONT find the next year that light takes longer than 3 ns this would be valid IF the time flow does not affected by the speed of light. Is that simple what is your objection here? Everything will flow slower and the result would be the same. The calibration in first year will be valid and the next. Except if you mean that in the second case the 3 ns is "more" than the 3 ns of the fist case. And yes i m confused i don t have a clear mind as yours.

[D H]

The article says " Suppose that we calibrate marks on a ruler using this definition one year, then next year find that light takes longer than 3 ns to travel the length of the ruler." No you WONT find the next year that light takes longer than 3 ns this would be valid IF the time flow does not affected by the speed of light. Is that simple what is your objection here?

You are quibbling with a supposition, and that is preventing you from moving on. Stop that!

 

There was no change if there is no change in what is measured, including everything that can be measured (i.e, the dimensionless fundamental constants). Arguing otherwise is akin to philosophers arguing about how many angels can dance on a pin.