Speed of light is a universal constant

[aura]

I wonder that speed of light is a universal constant but why its so that it doesn't change wrt observers in different ref frames. an object moving with some velocity V1 wrt another object will be at rest wrt a third object (that is also moving with a velocity V1). but speed of light will be same be we on Earth or on moom irrespective of their motions.Does anybody ever thought of the same thing or has anything to say about this?

ps-i tried to post it in general forum but couldn't access that hence posting here.

 

[HallsofIvy]

I don't know that anyone can say "why" the speed of light is independent of frame of reference- the fact that it is constant is confirmed by experiment.

One way to look at it is this: Force equals mass time acceleration and we "feel" forces. If we were in a closed box moving at a constant speed no (mechanical) experiment could tell us the speed since there is no acceleration to give a force.
BUT the force due to a magnetic field on a charge DOES depend on speed. We could do some kind of electro-magnetic experiment (i.e. light) to determine speed! That's exactly what the Michaelson-Morley experiment was designed to do- and it gave a null result. The only way to reconcile those is to postulate that the speed of light is independent of the reference frame.

 

[OlderDan]

I wonder that speed of light is a universal constant but why its so that it doesn't change wrt observers in different ref frames. an object moving with some velocity V1 wrt another object will be at rest wrt a third object (that is also moving with a velocity V1). but speed of light will be same be we on Earth or on moom irrespective of their motions.Does anybody ever thought of the same thing or has anything to say about this?

ps-i tried to post it in general forum but couldn't access that hence posting here.

Certainly people have thought about it. For a long time most people assumed there had to be some medium that light traveled through (the ether) at constant speed, and that if you were moving through that medium you would see light traveling at a different speed wrt to yourself. Experiments were performed to measure the speed of the Earth through this ether. The novel thought that the speed could be the same to everyone regardless of their state of motion is a relatively recent idea, and the foundation of special relativity.

Imagine a universe where light could be caught by an observer, or even passed. Suppose photons carried with them little snapsots of some event, and you could catch up to and collect photons that left that event and traveled off into space. As you collected and viewed them, you would be seeing the event in reverse time order, like running a movie film backwards. What's more, as far as you know the event took place at some point in front of you instead of behind you. Rather preposterous isn't it? At least as preposterous as the idea that everyone sees light traveling at the same speed. Of course photons do not carry snapshots, and from a wave perspective light behaves very differently from what I described, but the idea of traveling faster than, or catching up to light always leads to a rather preposterous view of the universe.

 

[StatusX]

Newtonian physics is actually inconsistent with Maxwell's electrodynamics. Imagine you have a uniform line charge of positive charge per legth \lambda, and there is a positive test charge nearby. The charge feels some repulsive force F. Now switch to a frame where the wire and charge are moving along the direction of the wire. The line charge is the same (according to Newton), so the E field is the same. But there is also a magnetic field which pulls the charge in. The force is different, and thus the movement of the particle depends on the frame you're in, which is clearly wrong. I'm suprised this wasn't a bigger deal back in the 19th century, but they probably had all kinds of ad hoc explanations to patch up the holes.

Relativity made electrodynamics consistent again, and in fact showed how electricity and magnetism are two aspects of the same thing. For this particular situation, the resolution is that length contraction compresses the wire, making the charge per unit length increase. This increases the repulsive electric force just enough to counter the attractive magnetic force and yield the same particle trajectory in all frames.

 

[aura]

I don't know that anyone can say "why" the speed of light is independent of frame of reference- the fact that it is constant is confirmed by experiment.

One way to look at it is this: Force equals mass time acceleration and we "feel" forces. If we were in a closed box moving at a constant speed no (mechanical) experiment could tell us the speed since there is no acceleration to give a force.
BUT the force due to a magnetic field on a charge DOES depend on speed. We could do some kind of electro-magnetic experiment (i.e. light) to determine speed! That's exactly what the Michaelson-Morley experiment was designed to do- and it gave a null result. The only way to reconcile those is to postulate that the speed of light is independent of the reference frame.

what you are saying is there is no means to measure the speed when we are in the system that's true but every system in motion has its own velocity and the velocity of any other object will depend on the vel of the ref frame of observer but the same is not true incase of light though this holds good for sound then why light is only ruled out?In Michaelson-Morley experiment, change in speed was not detected as the shortenning of one arm of the interferometer just canceled the fringe shift...can there be SOME basic problem that gives this const theory of light[i am sounding wierd, i know]

Certainly people have thought about it. For a long time most people assumed there had to be some medium that light traveled through (the ether) at constant speed, and that if you were moving through that medium you would see light traveling at a different speed wrt to yourself. Experiments were performed to measure the speed of the Earth through this ether. The novel thought that the speed could be the same to everyone regardless of their state of motion is a relatively recent idea, and the foundation of special relativity.

Imagine a universe where light could be caught by an observer, or even passed. Suppose photons carried with them little snapsots of some event, and you could catch up to and collect photons that left that event and traveled off into space. As you collected and viewed them, you would be seeing the event in reverse time order, like running a movie film backwards. What's more, as far as you know the event took place at some point in front of you instead of behind you. Rather preposterous isn't it? At least as preposterous as the idea that everyone sees light traveling at the same speed. Of course photons do not carry snapshots, and from a wave perspective light behaves very differently from what I described, but the idea of traveling faster than, or catching up to light always leads to a rather preposterous view of the universe.

your 1st para is michaelson morley experiment...just seriously think how light can violate the principles that every other object follows..what is there in light that makes it so diff. i already gave the example of sound wave

statusX i will reply to u...

 

[aura]

Newtonian physics is actually inconsistent with Maxwell's electrodynamics. Imagine you have a uniform line charge of positive charge per legth \lambda, and there is a positive test charge nearby. The charge feels some repulsive force F. Now switch to a frame where the wire and charge are moving along the direction of the wire. The line charge is the same (according to Newton), so the E field is the same. But there is also a magnetic field which pulls the charge in. The force is different, and thus the movement of the particle depends on the frame you're in, which is clearly wrong. I'm suprised this wasn't a bigger deal back in the 19th century, but they probably had all kinds of ad hoc explanations to patch up the holes
Relativity made electrodynamics consistent again, and in fact showed how electricity and magnetism are two aspects of the same thing. For this particular situation, the resolution is that length contraction compresses the wire, making the charge per unit length increase. This increases the repulsive electric force just enough to counter the attractive magnetic force and yield the same particle trajectory in all frames.

well this is the description of what the principle of relativity states...but again as EM wave holds good is nothing of much significance as light is a form of EM wave...so well i reiterate that why its so that the properties of this particular wave does not change while they do for all other. is it because we perform experiments with eyes and it can't catch the change in the medium (light here) on which the observation is based on..i can see only this difference in light and other waves that sound wave's perception is by our other sensory organ i,e ears and not light!(eyes) and hence we can measure the change by observing objectively..r u getting what i am trying to say? then we will never be able to find the change in its speed as the thing we are using for doing so itself depends on light...i am weird ..don't take it seriously

 

[StatusX]

c is the universal speed limit. Anything traveling at c in one reference frame will travel at c in all others. This is just the way the universe works, and it would be so even if there was no such thing as electromagnetism or light or eyes. The reason light happens to travel at c is because photons are massless, and relativity predicts that all massless particles will travel at c.

 

[matt grime]

why is this in homework?

anyway, no theories give a causal explanation of the phenomenon; it just is (as far as we can tell).

sound waves are not the same as light waves. light exhibits wave particle duality for a start and the wave portion is latitudinal, whereas sound waves, which require a medium in which to propogate (unlike light) are longitudinal, though i find it hard to understand what you're saying here.

 

[aura]

well i just meant that is it not possible that our observation is limiting ourselves somewhere? anyway it has been in a lot in disussion so i am not quite enthusiastic abt discussing it all over again.only wanted to know other's opinions here. i will have this curiosity if not others that why its so...i know its the principle on what universe works that is of no concern...i am not discussing its implications...i don't want to say anything and i don't think that i should at least not at this stage ...may be i am wrong and also may be its 99.99999999...9% correct that i am wrong but i want to explore the .000000....1% genuinity of what i think[not in this particular matter but everything]...i couldn't get any proper view and its fine as its not expected also...

why is this in homework?

anyway, no theories give a causal explanation of the phenomenon; it just is (as far as we can tell).

sound waves are not the same as light waves. light exhibits wave particle duality for a start and the wave portion is latitudinal, whereas sound waves, which require a medium in which to propogate (unlike light) are longitudinal, though i find it hard to understand what you're saying here.

can you link your explanation to the Q asked..please stick to the topic...its known to every XII th std student what light and sound waves are...please don't undermine the question (don't digress from topic) well forget it ...

ps-where it should be? i don't know..i am new here...

 

[matt grime]

is it because we perform experiments with eyes and it can't catch the change in the medium (light here) on which the observation is based on..i can see only this difference in light and other waves that sound wave's perception is by our other sensory organ i,e ears and not light!(eyes) and hence we can measure the change by observing objectively..:

"can you link your explanation to the Q asked..please stick to the topic...its known to every XII th std student what light and sound waves are...please don't undermine the question (don't digress from topic) well forget it ..."

i replied to your own question. not that it hjas a question mark to indicate where it ends. as i said, it is difficuilt to decipher what you mean; try writing more clearly before accusing others of wandering off topic.

wrong? right? who knows, so far I've not been able to ascertain what it is you're saying. nor do i care now.

 

[rbj]

I don't know that anyone can say "why" the speed of light is independent of frame of reference- the fact that it is constant is confirmed by experiment.

i think i have a feel for why the speed of E&M propagation should be the same for all inertial reference frames. it really just comes from Maxwell's Eqs. and the knowledge that there is no ether medium that E&M is propagated in (that's what the Michaelson-Morley experiment null result really meant). i mean, how do we tell the difference between a moving vacuum and a stationary vacuum? if we can't, if there really is no difference between a moving vacuum and a stationary vacuum, that such a concept is really meaningless, then whether the light that you are measuring originated from a flashlight mounted on a rocket moving past you at c/2 or from a stationary flashlight, how does that change the fact that a changing E field is causing a changing B field which is causing a changing E field, etc.? that propagation of an E field and B field disturbance, which has velocity 1/ \sqrt{ \epsilon_0 \mu_0 }, how is this propagation different whether you are moving with whatever device initiated it or moving relative to that device (after this E&M disturbance has moved away from that device)? whether you are holding the flashlight or moving past it at high velocity, Maxwell's Equations say the same thing regarding the nature of E&M in the vacuum.

... the force due to a magnetic field on a charge DOES depend on speed. We could do some kind of electro-magnetic experiment (i.e. light) to determine speed!

the force due to a magnetic field on a charge is a psuedoforce that is really a manifestation of electrostatic forces but with the effects of special relativity tossed in.

That's exactly what the Michaelson-Morley experiment was designed to do- and it gave a null result. The only way to reconcile those is to postulate that the speed of light is independent of the reference frame.

the null result of the Michaelson-Morley experiment really meant that there was no ether that was a medium of absolute reference for light or any other E&M wave to propagate in. sound has air, but light has no counterpart to air for it to propagate in. the null result was a surprise for them. they tried the experiment at different times of the year expecting the Earth to be moving through the ether at some time as it revolved around the sun. and the speed of the Earth moving through space was a sufficient fraction of the speed of light that the interference fringe shift in the experiment should have been noticeable (and it was not noticeable).

not meaning to dispute anything, Halls, just wanted to add another POV.

r b-j

 

[aura]

"can you link your explanation to the Q asked..please stick to the topic...its known to every XII th std student what light and sound waves are...please don't undermine the question (don't digress from topic) well forget it ..."

i replied to your own question. not that it hjas a question mark to indicate where it ends. as i said, it is difficuilt to decipher what you mean; try writing more clearly before accusing others of wandering off topic.

wrong? right? who knows, so far I've not been able to ascertain what it is you're saying. nor do i care now.

My question is in my first post if you care to read that...i am not supposed to repeat that again and again in every post. my posts are well linked to my original Q but your ans doesn't have any correlation with the original Q..thats why i said so...try finding your fault rather than just blaming others...u find lack of clarity in my language but i find lack of connectivity in your suggestions and what is asked for..lets forget it...you must have obtained more than me in AWA but not more than point 1 i am sure well i didn't get what i expected as the topic i chose was not known to me that much ...i know least abt politics but i chose that as it was having morality in it which i didn't want to leave

cyao

ps- well everyone here is just repeating the michaelson moreley experiment but not trying to find the why behind the ans...as i told ether couldn't be detected as the fringe shift was nullified by the contraction of one arm of interferometer and that happenned as we were in the system...anyway thanks for all answers...

 

[aura]

wow i just noticed that someone called madness also had posted this sometimes before...i have read relativity and i have solved problems considering C a const as that is the fundamental law of relativity but still i am not convinced ahy its a const as only einstein said was that (i am para phrasing)if the vel of light were not a universal const then the principle of relativity would fail and a special inertial frame would be singled out(the one at rest in the ether) but the form of maxwell's eqns as well as failure of any experiment to detect motion through ether, suggests that the speed of light is constant independent of the motion of the source. absence of ether preserved the simplicity of the principle of relativity.

BUT this is no explanation of the reason behind the phenomenon.his argument was based on the fact that vel of light predicted by elctromagnetic theory involves no reference to a medium and hence c MUST be a constant...thats all..NO reasonings

 

[matt grime]

My question is in my first post if you care to read that...i am not supposed to repeat that again and again in every post. my posts are well linked to my original Q but your ans doesn't have any correlation with the original Q..thats why i said so...try finding your fault rather than just blaming others...u find lack of clarity in my language but i find lack of connectivity in your suggestions and what is asked for..lets forget it...you must have obtained more than me in AWA but not more than point 1 i am sure well i didn't get what i expected as the topic i chose was not known to me that much ...i know least abt politics but i chose that as it was having morality in it which i didn't want to leave

you posted more than one question and i was answering what seemed like another question, a question that i quoted back when you asked what i was respondng to (is it... then something about light and sound and sensory organs... , is it generally indicates a question) which apparently asked about the diffrence between light and sound. and now we've wasted yet more posts on it.

I have no idea what AWA is, and no interest in comparing "scores" with you.

as hallsofivy (or was it hurkly) said in the very first post we have no "why" explanation (it is a postulate), as for a great many things in science.

 

[aura]

you posted more than one question and i was answering what seemed like another question, a question that i quoted back when you asked what i was respondng to (is it... then something about light and sound and sensory organs... , is it generally indicates a question) which apparently asked about the diffrence between light and sound. and now we've wasted yet more posts on it.

I have no idea what AWA is, and no interest in comparing "scores" with you.

as hallsofivy (or was it hurkly) said in the very first post we have no "why" explanation (it is a postulate), as for a great many things in science.

i posted ONE question and what you told was just the explanation of something that i asked to illustrate my point in original question.so your every answer should relate to the first question even if u are answering the 2nd one...sound waves are longitudinal and requires medium in no way associates as to why its change in speed can be detected while change in speed of light cannot be? my illustration does include the fact that light is the medium that we are using for detecting the change in speed of light or in other words we are using a medium to detect the change in the medium only...if you couldn't see the question in my post which was

well this is the description of what the principle of relativity states...but again as EM wave holds good is nothing of much significance as light is a form of EM wave...so well i reiterate that why its so that the properties of this particular wave does not change while they do for all other. is it because we perform experiments with eyes and it can't catch the change in the medium (light here) on which the observation is based on

yes i forgot to put Q mark and if u couldn't get because of that then may be i am wrong, don't know!...

and yes i don't have any interest to argue on this matter with you.answer it if you know else don't...else try to find the reasons and then answer.i also don't want to compare my scores with you as you are no way my compettitor[stick to the topic]...don't want any further argument here..if u want u can pm me...lets stick to the topic here ..better say that "einstein didn't mention any why to it!" not that there is "no why" to this as neither you nor i can say that...have you read about the quarks in quantum mechanics...my reasoning for this Q lies near to some logic similar to one of its properties...but i won't discuss it anymore...reason-you can and should understand...all the best and thanks a lot...

Regards

 

[russ_watters]

Well, I can answer one question for you: we do not perform experiments with our eyes. Our eyes are only used to read the results, not to make the actual measurements.

As for the "why" - "why" is not a question adequately dealt with by science. For that, you may need religion because eventually the long string of "why"s will have to end with either 'God made it that way' or 'it just is'.

 

[Doc Al]

...just seriously think how light can violate the principles that every other object follows..what is there in light that makes it so diff.

Actually all objects and light follow the same rules, at least as far as their measured speeds go. What's different about light is that its speed happens to equal the universal speed limit.

 

[Danger]

All laws of nature appear to be random consequences of the specific conditions of the Big Bang. In another universe (parallel to ours, or if ours had formed differently, or preceding ours), c could be 50,000,000 kph, Planck's Constant could be 6, Avagadro's Number 14.8, etc. This just happens to be the one that we live in. To know why any of these things are as they are, we would have to know every single detail of the initial conditions. It's extremely unlikely, if not impossible, that we ever will.

 

[Danger]

i had just posted 1 sentence...don't know how that vanished...i had posted that i do not believe in big bang!...

You have every right not to, but I'm sticking with it until something better comes along. So far 'Steady State' has been disproven, and the alternative is something supernatural. If evidence leads to a different scientifically derived theory, I'll give it equal credence.

 

[panthera]

You have every right not to, but I'm sticking with it until something better comes along. So far 'Steady State' has been disproven, and the alternative is something supernatural. If evidence leads to a different scientifically derived theory, I'll give it equal credence.

do you know some stars have shown a blue shift instead of red shift? and scientists always refute this fact..i had once attended a lecture of jayant narlikar in IUCAA and he was much convincing and it did strengthen my perspective.

 

[Doc Al]

Let's not turn this into a debate over the Big Bang. Please stick to the topic.

 

[rbj]

Well, I can answer one question for you: we do not perform experiments with our eyes. Our eyes are only used to read the results, not to make the actual measurements.

As for the "why" - "why" is not a question adequately dealt with by science. For that, you may need religion because eventually the long string of "why"s will have to end with either 'God made it that way' or 'it just is'.

actually, Russ, i don't totally agree. we don't have all the answers (and i'll admit we never really will, because the more we learn, the more new questions that crop up) to the "why" questions, but if we ask the right questions, maybe someday we'll get answers to them.

we do perform crude experiments without eyes and ears and skin and other senses. this fancy equipment of ours is really an extension of those senses. we judge distances relative to approximately the size of our bodies and we judge time relative to approximately the rate that our brains can perform simple compare-like operations (i heard, when we're about 16, we can do about 40 per second). it is no accident that a meter is roughly how tall we are and a second is roughly how long a heartbeat is. this is a "natural" anthropocentric result.

now the speed of light is simply what it is, but its numerical value depends solely on the anthropocentric units we have decided to use to measure it (the meter and the second). the gravitational constant and Planck's constant and the Coulomb force constant and Boltzmann constant are also simply what they are, but again, the numerical values they take on have to do with the anthropocentric units we have sort of arbitrarily decided to use.

if you want to get away from those man-made units, then you need to use Planck units (or something very similar) and then the speed of light is just naturally equal to 1. same for Planck's constant and G and \epsilon_0 and k.

the dimensionful numerical values they take on is just because of the size we happen to be (that is close to the meter) relative to the Planck length l_P and the way we experience time (which is in the ballpark of a second) relative to the Planck time t_P.

now, i don't know why an atom's size is approximately 10^{25} l_P, but it is, or why biological cells are about 10^{5} bigger than an atom, but they are, or why we are about 10^{5} bigger than the cells, but we are and if any of those dimensionless ratios changed, life would be different. but if none of those ratios changed, nor any other ratio of like dimensioned physical quantity, we would still be about as big as 10^{35} l_P, our clocks would tick about once every 10^{44} t_P, and, by definition, we would always perceive the speed of light to be c = \frac{1 l_P}{1 t_P} which is the same as how we do now, no matter how some "god-like" manipulator might change it.

so the questions to ask are not "why is the speed of light what it is?", but is why we are as big as we are relative to the Planck length, why we think as slow as we do relative to the Planck time, and why things we deal with weigh as much as they do relative to the Planck mass. if we answer those questions, then we can answer why light travels 299792458 of these lengths we call "meters" in the time elapsed in one of these periods we call "seconds". the speed of light, Planck's constant, the graviational constant, and Coulomb's constant merely define, in our already established unit system, where the scaling or tick marks of nature are. once we look at these quantities from the perspective of nature's scaling, they're all naturally just 1 unit large. then it's like asking "why is it that a Newton of force is just the right amount that will accelerate a kilogram of mass at 1 meter/sec^2? why don't we measure it to be some other amount of force?"

best,

r b-j

 

[aura]

i don't understand how people can correlate size of atoms with speed of light...size of anything is not a variable whereas speed can be variable...i am getting agitated sorry..its purely underestimating the question...how can 1 compare size and planks const etc etc with speed of light? the consts terms were found after the expression came into being but light exists in itself! i see no point in the argument...see i am not a fool and have discussed this issue with many famous physicists so i can't tolerate this..it seems people have 0 knowledge or simply trying to stiffle the discussion...

 

[aura]

What is light?

Its having both wave and particle nature. Hard core facts---- it consists of certain particles which we named as photons and the quantum physics has proved its existence.Then optical phenomenon like diffraction, interference, refraction,polarization etc have proved its wave nature…they are TRUE properties of light but cannot be quantified. Speed of light is NOT its internal property like the size or mass of any particle…it is something which is a variable quantity that is different from the constituents of light..it’s a PHENOMENON…a phenomenon is changeable but the internal properties are not…I don’t consider the speed of light as its intrinsic property as no object’s speed is considered so.well I better term it as velocity. For a moment forget about relativity.velocity of any particle in an atom need not be const always.it depends on the energy the particle posseses.we can see from the tunneling effect itself that more the number of attempts a particle makes, more is the probability of its emission[any particle] and the K.E in every case is diff which in turn implies that velocities are different…so while the SIZE(mass here) of the emitted particle remains same every time its emitted[ we have given fixed numerical values to every particle even to the degenerated ones, so mass is fixed], it can travel with diff velocities depending on the KE in diff cases. So velocity is something which VARIES…so its not comparable with quantities as size or color etc….Now considering relativity every objects vel is relative and there is NO SPACE for “absolute” in relativity.then why the vel of light is NOT relative…I hope atleast I could make the diff between size and velocity[meaningless!]

i don't know better ans than this for the above post...

 

[russ_watters]

we do perform crude experiments without eyes and ears and skin and other senses.

Well, maybe I should have said scientific experiments. There is very little, if anything, left up to the senses in a laboratory experiment.

And yes, units are arbitrary, but that has nothing to do with my post.

i don't understand how people can correlate size of atoms with speed of light...size of anything is not a variable whereas speed can be variable

Size is variable. The size of an object (distances) depends on the frame of reference of the observer.

There are a great many other misconceptions in your other post as well. I know its strange when you hear about it the first time but the universe really does work the way people are describing it. The evidence is incontrovertible.

 

[aura]

Well, maybe I should have said scientific experiments. There is very little, if anything, left up to the senses in a laboratory experiment.

And yes, units are arbitrary, but that has nothing to do with my post. Size is variable. The size of an object (distances) depends on the frame of reference of the observer.

There are a great many other misconceptions in your other post as well. I know its strange when you hear about it the first time but the universe really does work the way people are describing it. The evidence is incontrovertible.

i think you didn't care to read the line where i wrote forget about relativity for time being as i knew someone will insert it to prove useless things not related to my explanation...here people are so indulged in finding error that they are talking useless..if you are so interested in finding my fault than looking at the reasons then u will never be able to understand anything...size is not a variable when seen from one ref frame BUT vel is...now someone can raise the issue of mass-energy conversion as they are so ignorant that they think inserting complex equations and theories would prove that they know so much but they have 0 knowledge of fundamentals...read my post...i will not argue anymore as its worthless...i have misconceptions! then u are the first person to say this...my explanation is acepted by scientists though there are limitations and i have given a talk regarding this...if people don't know abt the aubject matter, why they argue so much..its like an adament kid who never tries to listen to what others say instead always push his undeveloped theories...

 

[russ_watters]

i think you didn't care to read the line where i wrote forget about relativity for time being as i knew someone will insert it to prove useless things not related to my explanation...

Catch-22, aura - even if you discard relativity, you still have to deal with reality and time dilation and length contraction are a reality. They are not just a consequence of some esoteric equations, they are directly observed.

if you are so interested in finding my fault...

The purpose of this forum is not to find fault but to teach. And there is a lot you can learn if you choose to. We really are trying to help.

 

[aura]

Catch-22, aura - even if you discard relativity, you still have to deal with reality and time dilation and length contraction are a reality. They are not just a consequence of some esoteric equations, they are directly observed. The purpose of this forum is not to find fault but to teach. And there is a lot you can learn if you choose to. We really are trying to help.

well i am writing in cool manner...first time dilation and length contraction are part of relativity which i am NOT discarding...i am talking of a single ref frame...say Earth (as an isolated system) in that ref frame when we measure size of a stationary atom, it remains same but speed need not be if its moving and that depends on the energy its having. now both this const and variable i,e length/mass and vel resp. change wrt some other ref frame...but remember that vel can be variable even in the ref frame where the length is not ...so length/mass and vel are NOT comparable


bye

 

[rbj]

listen, aura. so you want fundamentals? you ask "what is light?" here's an answer (i've posted this before):

suppose you're holding an object that is negatively charged and I'm facing you about 5 meters away holding a positively charged object of about the same amount of charge. being opposite polarity, the charges attract each other so we are restricting the movement the charges to only left-right and up-down motion. so i raise my charge up and what does your charge do? if you allow free up-down motion, then your charge goes up. if i move mine down, then yours goes down.

what happens if i move mine up and down repeatedly? yours does the same. that is an electromagnetic wave and my driven charge can be thought of as a transmitting antenna and yours as a receiving antenna. if i move mine up and down a million times per second, you can tune it in on your AM radio. if i move mine up and down 99.9 million times per second, you can tune it in on your FM radio. if i move mine up and down 500,000,000,000,000 times per second, you will see it as a blur of orange light.

does that answer your question? (not to imply that there ain't particle-like properties of light or E&M also.)

r b-j

 

[rbj]

All laws of nature appear to be random consequences of the specific conditions of the Big Bang. In another universe (parallel to ours, or if ours had formed differently, or preceding ours), c could be 50,000,000 kph, Planck's Constant could be 6, Avagadro's Number 14.8, etc. This just happens to be the one that we live in. To know why any of these things are as they are, we would have to know every single detail of the initial conditions. It's extremely unlikely, if not impossible, that we ever will.

Danger, not meaning to pick a fight (more so to pick nits), but the values of c or \hbar or N_A or G or k or any dimensionful constants are not determined by properties of the universe at all. they are human constructs. the only fundamental numbers that the universe or nature give us are dimensionless numbers. with the Standard Model and the Cosmological Constant and whatever else, i think the count is 25 or 26 fundamental numbers.

again, if we were to measure things in Planck units, then c = 1, \hbar = 1, \frac{1}{4 \pi \epsilon_0} = 1, G = 1. N_A is whatever we want it to be (we just have to decide how much a "mole" of carbon weighs or whatever unit we'll call it). that's a real human construct and the universe doesn't really give a rat's ass about it.

a good example of a dimensionless number that nature is telling us is the Fine-structure constant \alpha = \frac{e^2}{\hbar c 4 \pi \epsilon_0} which is about 1/137.03599911 .

r b-j

 

[Danger]

Danger, not meaning to pick a fight (more so to pick nits)

It's not even nit-picking, m'man; we're referring to different aspects of the same things. The values, as I employ the term, are fundamental aspects of space-time. The numerical definitions of those values are completely fabricated. Light speed can be 286,282 mps or 300,000 kps or 1,9435,354.45 kurps per mlank (if you're a Rigel 7 mud-tumbler). No matter what anyone calls it, it doesn't change the physical aspects of it.

 

[Dr.Brain]

What is light?

Its having both wave and particle nature. Hard core facts---- it consists of certain particles which we named as photons and the quantum physics has proved its existence.Then optical phenomenon like diffraction, interference, refraction,polarization etc have proved its wave nature…they are TRUE properties of light but cannot be quantified.

Speed of light is NOT its internal property like the size or mass of any particle…it is something which is a variable quantity that is different from the constituents of light..it’s a PHENOMENON…a phenomenon is changeable but the internal properties are not…

Basically, what you are trying to imply is that we need to forget relativity for the timebeing and believe in your facts.

Your text says that (forgetting relativity) , light's speed or infact velocity of any particle is not intrinsic property at all, not depending on its internal features.

In a particular inertial reference frame , no doubt the size of an object remains same (but different from the original size in a stationary frame of reference), but the velocity is variable and it does not depend on its internal features is certainly not quite digestible.

Lets say we are in a particular fixed stationary reference frame and we are observing a phenomena:

Take for example, a light ray in vacuum with velocity 'c' , it enters into a medium ,for example glass , now the photons are no doubt form the internal features of light, these photons are traveling at the speed of light in vacuum , now the light enters into a glass slab, now the photons in the glass will still move at the same speed 'c' but they are being obstructed every now and then , due to frequent collisions with the atoms of the medium and as a result it seems to us that light ray as a whole has slowed down a bit, so light ray slows down in a medium due to obstructed motions of the photons , which are ofcourse internal.

I might have agreed to you if you had said that 'light can have two different speeds at two different instants due to change in medium in the same inertial reference frame" , but I certainly do not agree that 'velocity is variable and
mass remains constant.Mass is a quantity which changes with velocity if we take into consideration one particular particle/object.

 

[Kazza_765]

i am talking of a single ref frame...say Earth (as an isolated system) in that ref frame when we measure size of a stationary atom, it remains same but speed need not be if its moving and that depends on the energy its having. now both this const and variable i,e length/mass and vel resp. change wrt some other ref frame...but remember that vel can be variable even in the ref frame where the length is not ...so length/mass and vel are NOT comparable

Length and mass are only constant if velocity is constant. If an atom is at rest relative to your reference frame, ie. the Earth in your post, then we will measure its length as being X. If it is moving relative to the Earth we will measure its length as Y. We measure the highest value for length when the atom is stationary, the lowest value for mass, and the lowest value for velocity (0). Velocity can't change without length/mass changing also.

 

[aura]

Length and mass are only constant if velocity is constant. If an atom is at rest relative to your reference frame, ie. the Earth in your post, then we will measure its length as being X. If it is moving relative to the Earth we will measure its length as Y. We measure the highest value for length when the atom is stationary, the lowest value for mass, and the lowest value for velocity (0). Velocity can't change without length/mass changing also.

Do you know that there is something called as " rest mass" which remains constant even if the particle moves and is the intrinsic property of the particle.As the numeric const of the size was compared with velocity, i gave this example.i already mentioned the word "stationary" while commenting on "mass" and a person who knows a bit of basic should know that it refers to the rest mass of the particle.Now the sentence"rest mass of a stationary atom" is meaningless at least to me.



I don't want to comment on other's concepts.They may go ahead.There is always a possibility that someone misses something while arguing and it's not unusual that someone missed to think about "rest mass"[that i was talking about] and i am not like a person who will infer from this, that the one doesn't know what is "rest mass" but i want people to admit when there is some reasonable matter and instead of crossing that, i want them to think about it and its not a debate so if they find my queries justified and if, ever they have also thought similarly, they can also give facts in favour of the matter.That will in no way harm anybody.I just don't like arguments which are forceful rather than convincing.Here we are not standing for or against the motion so there is no harm to support any perspective and to try to find the reason. I think this is enough.

ps- i will not answer anymore and since i am a bit busy will not be able to visit either.

bye

 

[Kazza_765]

Do you know that there is something called as " rest mass" which remains constant even if the particle moves and is the intrinsic property of the particle.As the numeric const of the size was compared with velocity, i gave this example.i already mentioned the word "stationery" while commenting on "mass" and a person who knows a bit of basic should know that it refers to the rest mass of the particle now the sentence"rest mass of a stationery atom" is meaningless at least to me.

Why would I mention that mass is at a minimum when stationary in your reference frame if I didn't know there is a rest mass. You don't seem to be making any sense.

say Earth (as an isolated system) in that ref frame when we measure size of a stationary atom, it remains same but speed need not be if its moving

I think this is where your problem lies. If an atom is stationary it has a measurable size and velocity, which remain constant. From what I can tell you go on to say that in our reference frame - Earth - a stationary atom has a constant mass/size but a variable velocity.

but remember that vel can be variable even in the ref frame where the length is not

If the velocity of the atom changes it is no longer stationary. You are correct in that the mass/size of an atom stationary in our reference frame is constant, but so is its velocity. Its when you change the speed of the atom relative to you, that you also change its size. You can't change one without the other, either it is stationary and mass/size/velocity is constant, or it is moving relative and mass/size/velocity are transformed.

 

[aura]

If the velocity of the atom changes it is no longer stationary. You are correct in that the mass/size of an atom stationary in our reference frame is constant, but so is its velocity. Its when you change the speed of the atom relative to you, that you also change its size. You can't change one without the other, either it is stationary and mass/size/velocity is constant, or it is moving relative and mass/size/velocity are transformed.

rest mass remains const even if the atom moves! even if vel during its motion changes!...Mo remains const so does Lo

M=Mo/sqrt(1-vsqr/csqr)

Mo always remain const irrespective of whether the particle moves or not...its M that changes but i am talking about Mo..vel is not any intrinsic property as the rest mass, it changes when the atom moves[say initially it was 0 while at rest and while in motion its x m/s but Mo will be Mo both when the atom is at rest and is in motion, only what changes is M but i am talking of Mo(rest mass)].Now please i think this is going too far and i am getting tired of explaining ..don't make me answer again and again...its a request...

thanks

 

[Doc Al]

I think this thread has gone on long enough.