speed of light ?

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csmyth3025

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Re:

derekmcd":3cihl3fr said:
Replying to:The reason that you cannot understand it is because it is outside of your normal experience, and is not at all intuitive.  It took real genius to recognize the principles involved and work out the consequences.
Posted by DrRocket Real genius?  I had to laugh at that one.   I, certainly, lay no claims to be a genius, but you can be damned sure I can pick out the fake ones.  
"If something's hard to do, then it's not worth doing." - Homer Simpson
derekmcd - I'm not sure what you're laughing at, but I, too, feel that it took a real genius to appreciate the consquences of the constancy of the speed of light reqardless of the frame of reference of the observer.

Chris
 
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origin

Guest
Re: Re:

csmyth3025":1o2oxzwj said:
derekmcd":1o2oxzwj said:
Replying to:The reason that you cannot understand it is because it is outside of your normal experience, and is not at all intuitive.  It took real genius to recognize the principles involved and work out the consequences.
Posted by DrRocket Real genius?  I had to laugh at that one.   I, certainly, lay no claims to be a genius, but you can be damned sure I can pick out the fake ones.  
"If something's hard to do, then it's not worth doing." - Homer Simpson
derekmcd - I'm not sure what you're laughing at, but I, too, feel that it took a real genius to appreciate the consquences of the constancy of the speed of light reqardless of the frame of reference of the observer.

Chris

2 things:

why did you resurect this old post?

second - don't hold your breath for a response Derekmcd's last post was during the summer of 09.
 
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csmyth3025

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Re: Re:

origin":n5a10l0e said:
csmyth3025":n5a10l0e said:
derekmcd":n5a10l0e said:
Replying to:The reason that you cannot understand it is because it is outside of your normal experience, and is not at all intuitive.  It took real genius to recognize the principles involved and work out the consequences.
Posted by DrRocket Real genius?  I had to laugh at that one.   I, certainly, lay no claims to be a genius, but you can be damned sure I can pick out the fake ones.  
"If something's hard to do, then it's not worth doing." - Homer Simpson
derekmcd - I'm not sure what you're laughing at, but I, too, feel that it took a real genius to appreciate the consquences of the constancy of the speed of light reqardless of the frame of reference of the observer.

Chris

2 things:

why did you resurect this old post?

second - don't hold your breath for a response Derekmcd's last post was during the summer of 09.
Well - this was the last post on this subject and I thought that maybe someone else might be monitoring it. I just happened across as I was cruising through the forum.

Chris
 
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ramparts

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Chris - The last post on what? The speed of light? ;) What in particular are you trying to find out about?
 
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csmyth3025

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ramparts":gdlyotns said:
Chris - The last post on what? The speed of light? ;) What in particular are you trying to find out about?
The subject of the thread is "Speed of Light?". I understand that there are theoretical and observational reasons for believng that the speed of light has been constant throughout cosmological time and across cosmological distances. I'm always curious about the details for those reasons and I'm also interested in hearing reasoned arguments that might support dissenting views.

Chris
 
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Ishimura_

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Is it reasonable to draw this conclusion about light:

a) Light is energy and has no mass
b) Since light has no mass, it is not subject to acceleration
c) since light is not subject to acceleration, it always travels at the same speed in a vaccuum
d) that speed is the speed of light in a vaccuum (c)

Questions:

Does light have no mass or just no rest mass?
Via E=mc^2 could light ever be converted to matter?
 
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origin

Guest
Ishimura_":2d73meqe said:
Via E=mc^2 could light ever be converted to matter?
Light (actually higher energy E-M radiation) can be and is converted to matter - specifically it can be converted to a particle / anti-particle pair (typically a electron/positron pair).
 
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unclefred

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Ishimura_":1ft2gllc said:
Is it reasonable to draw this conclusion about light:

a) Light is energy and has no mass
b) Since light has no mass, it is not subject to acceleration
c) since light is not subject to acceleration, it always travels at the same speed in a vaccuum
d) that speed is the speed of light in a vaccuum (c)

Questions:

Does light have no mass or just no rest mass?
Via E=mc^2 could light ever be converted to matter?
Following your logic:
a) Sound is energy and has no mass. (Actually the same can be said about heat. neither have any mass.
b) Since sound has no mass, it is not subject to acceleration. As far as I know this is true. Sound travels a a distinct speed determined only by the properties of the media in which it is traveling. It instantly changes speed when entering a new media and does not accelerate (the same is true for light).
c) Since sound is not subject to acceleration, by your logic it should the travel at the same speed in a vacuum. Your logic is wrong. propogation in a vacuum has nothing to do with items a and b above.
 
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bellch87

Guest
Looking at the expansion of the universe, space itself can travel faster than the speed of light, right? So how could we use that to our advantage? If at all.
 
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origin

Guest
bellch87":1x59ofbn said:
Looking at the expansion of the universe, space itself can travel faster than the speed of light, right? So how could we use that to our advantage? If at all.
I see it as only a dissadvantage. As time goes on we will see less and less of the universe. As the universe expands our observable universe is shrinking....
 
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ramparts

Guest
bellch87":weumc9jh said:
Looking at the expansion of the universe, space itself can travel faster than the speed of light, right? So how could we use that to our advantage? If at all.
Well, not entirely. Space can expand such that two given points are moving away from each other faster than c, as far as they see, but that's not really space moving. On a local level (which is what matters) there's no travelling faster than c. In fact, there's really no motion at all :) The expansion of space is, well, different.
 
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nova_explored

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Does light have no mass or just no rest mass?
Via E=mc^2 could light ever be converted to matter?[/quote]
Following your logic:
a) Sound is energy and has no mass. (Actually the same can be said about heat. neither have any mass.
b) Since sound has no mass, it is not subject to acceleration. As far as I know this is true. Sound travels a a distinct speed determined only by the properties of the media in which it is traveling. It instantly changes speed when entering a new media and does not accelerate (the same is true for light).
c) Since sound is not subject to acceleration, by your logic it should the travel at the same speed in a vacuum. Your logic is wrong. propogation in a vacuum has nothing to do with items a and b above.[/quote]

Light carries its information on a photon, the idea behind a discrepancy between rest mass and mass, but that photon does not exhibit change, another proponent of a constancy, and no change over time. it also exhibits the properties of a wave (duality), which follows newtonian physics and inverse square law for distribution of energy, same as a radio wave, but that duality unique to the lightwave/photon pairing allows it to travel through ANY medium and while temp. slowed, instantly upon exiting a slower medium, resumes speed of C, with no acceleration.
This is known because- there is no change in information states, no change in energy states. Photon does not loose energy- another qualifier for a constant.

so, the 2, radio waves and light waves, while sharing properties, are nothing alike because of the particle aspect in a lightwave.
 
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origin

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nova_explored":1dv1av98 said:
it also exhibits the properties of a wave (duality), which follows newtonian physics and inverse square law for distribution of energy, same as a radio wave, but that duality unique to the lightwave/photon pairing allows it to travel through ANY medium and while temp. slowed, instantly upon exiting a slower medium, resumes speed of C, with no acceleration.

so, the 2, radio waves and light waves, while sharing properties, are nothing alike because of the particle aspect in a lightwave.
I am not sure what you are saying, but it sounds like you think there is some fundamental difference between a light wave and a radio wave. They are identical except for wavelength, or frequency if you like. What do you mean a light wave can travel through anything? Light can't travel through walls, but radio waves can travel through walls.

Light appears to travel more slowly through water because the photons are absorbed and reemited many times as it passes through the medium. So the photons really don't speed up when leaving the water they just stop 'running' into water molecules, so appear to speed up.
 
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nova_explored

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I am not sure what you are saying, but it sounds like you think there is some fundamental difference between a light wave and a radio wave. They are identical except for wavelength, or frequency if you like. What do you mean a light wave can travel through anything? Light can't travel through walls, but radio waves can travel through walls.

Light appears to travel more slowly through water because the photons are absorbed and reemited many times as it passes through the medium. So the photons really don't speed up when leaving the water they just stop 'running' into water molecules, so appear to speed up.[/quote]

Yeah, exactly. The photons can actually convert into another form and return to the properties of the photon. But that isn't the point.
A radio wave is not a point particle. A lightwave is. It is a massless particle that is also a wavefunction. A radio wave is not a particle.
Since both are EM radiation as a wave function does not make them the same thing. If you are making an experiment of the EM function of radiation then yes, they are the same family.

But if you are making an experiement of some quantum fluctuation with EM fields, they are different.
 
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origin

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A radio wave is not a point particle. A lightwave is. It is a massless particle that is also a wavefunction. A radio wave is not a particle.
You have a basic misunderstanding of the nature of EM radiation. All EM radiation is made of photons, whether microwaves, light or x-rays. Photons are generally used to describe EM radiation in the visible range but that is only by convention. Very high energy photons are called gama rays. They are the same thing, just different energies. All EM radiation can be looked at as massless particle that are also waves, this is the wave particle duality of EM radiation.
 
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nova_explored

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origin":olm8fj4d said:
A radio wave is not a point particle. A lightwave is. It is a massless particle that is also a wavefunction. A radio wave is not a particle.
You have a basic misunderstanding of the nature of EM radiation. All EM radiation is made of photons, whether microwaves, light or x-rays. Photons are generally used to describe EM radiation in the visible range but that is only by convention. Very high energy photons are called gama rays. They are the same thing, just different energies. All EM radiation can be looked at as massless particle that are also waves, this is the wave particle duality of EM radiation.
so a radio wave performs the same as a light wave with the double slit experiment?
 
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Mee_n_Mac

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nova_explored":1rpfwavk said:
origin":1rpfwavk said:
A radio wave is not a point particle. A lightwave is. It is a massless particle that is also a wavefunction. A radio wave is not a particle.
You have a basic misunderstanding of the nature of EM radiation. All EM radiation is made of photons, whether microwaves, light or x-rays. Photons are generally used to describe EM radiation in the visible range but that is only by convention. Very high energy photons are called gama rays. They are the same thing, just different energies. All EM radiation can be looked at as massless particle that are also waves, this is the wave particle duality of EM radiation.
so a radio wave performs the same as a light wave with the double slit experiment?
In a word ... yes. And it get even wierder. People have done the equivalent of the 2 slit experiment with atoms, buckyballs IIRC, and seen interference patterns as a result. So even large objects have wavelike properties.
 
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MeteorWayne

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nova_explored":2fo3b706 said:
so a radio wave performs the same as a light wave with the double slit experiment?
yes

Actually, had you done ths tiniest bit of research before you asked this question, you'd already know that.

Gimme a "U"
 
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dryson

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Light has mass, just not rest mass. If it had any finite rest mass at all, it would gain infinite mass and require infinte energy to get it to light speed.
This is interesting because if light did not have any mass then how would it achieve light speed velocities?

Here is an article that covers photons and gravity which seems to fit in with the discussion.

http://csep10.phys.utk.edu/astr162/lect ... khole.html
Here is a few paraphrases from the article:

Photons always travel at the speed of light, but lose energy when travelling out of a gravitational field.
The stronger the gravitational field, the more energy the photons lose.
which is built on the principle that the speed of light in a vacuum is constant.

Now the main parts that I read from this article were that when in a gravitational field the photon maintains a light speed velocity outside of the gravitational field the photon loses energy and when in a stronger gravitational field the photon also loses energy. The article also states that the speed of light is a constant speed when in a vacuum.So somewhere in this mix of gravitational wavelengths interacting with the photon there is an interaction between the two that creates the velocity of light speed. Otherwise if this were not fundamentally true then when the photon left a gravitational field or encountered a stronger gravitational field the photon should remain in the same phase but it doesn't So when we put the paraphrases together from the article it should actually read:

Photon's will always travel at the speed of light in a vacuum where gravity is present and causes an equal reaction upon the internal operations of the photon to force the photon to obtain a speed of light velocity. The photon will lose energy and not travel at the speed of light when traveling outside of the gravitational vacuum or when the photon encounters a stronger gravitational field in a vacuum the more energy the photon will lose relative to the same manner that the photon loses energy when it is outside of a gravitational vacuum thus causing the photon to dissipate or become invisible.

A gravitational field in a vacuum is the constant that sets the photon's speed of light velocity not that the speed of light in a vacuum is the constant.

The question is though if a photon is transformed into a redshift phase because of not being inside of a gravitationally vacuumed field or encounters a stronger gravitationally vacuumed field would and becomes invisible could the photon be changed back to it's phase of radiation by subjecting it to the appropriate wavelength at it's equilibrium? Could this be what dark matter is? Light that has passed out of the gravitational vacuum becoming invisible?
 
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MeteorWayne

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It is not permitted to make duplicate posts in multiple threads. Pick one, and I'll delete the other. Or I'll pick.

Moderator Meteor Wayne
 
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OleNewt

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Photon's will always travel at the speed of light in a vacuum where gravity is present and causes an equal reaction upon the internal operations of the photon to force the photon to obtain a speed of light velocity. The photon will lose energy and not travel at the speed of light when traveling outside of the gravitational vacuum or when the photon encounters a stronger gravitational field in a vacuum the more energy the photon will lose relative to the same manner that the photon loses energy when it is outside of a gravitational vacuum thus causing the photon to dissipate or become invisible.
So basically you are saying that the speed of light is not constant but we can't yet/never will detect the variations? This is going to make some horribly complex math even more complex. :mrgreen:
 
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Ishimura_

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Is it reasonable that light does have rest mass and we currently don't have the instrument discrimination to detect it? I'm thinking of string theory and that everything in string theory has a mass, since strings are one-dimensional and occupy some space and that light 'strings' have a mass close to the planck mass, but the vibrations cancel one another out to such an effect that the mass is below our detection threshhold (somewhere near 10^-27 grams for instance).

If this were the case, could light be the fastest thing we know of because it has the lightest mass of anything so far discovered and that there indeed may be something fast that light? For example, let's assume we discover something with a mass close to 10^-27 grams that travels at 1 billion meters per second. Could 'c' be readjusted to this value and still not violate relativity?

Purely a thought experiment here...
 
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ramparts

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Ishimura_":m8j46q00 said:
Is it reasonable that light does have rest mass and we currently don't have the instrument discrimination to detect it? I'm thinking of string theory and that everything in string theory has a mass, since strings are one-dimensional and occupy some space and that light 'strings' have a mass close to the planck mass, but the vibrations cancel one another out to such an effect that the mass is below our detection threshhold (somewhere near 10^-27 grams for instance).

If this were the case, could light be the fastest thing we know of because it has the lightest mass of anything so far discovered and that there indeed may be something fast that light? For example, let's assume we discover something with a mass close to 10^-27 grams that travels at 1 billion meters per second. Could 'c' be readjusted to this value and still not violate relativity?

Purely a thought experiment here...
If the photon did have a small but non-zero mass then c wouldn't change, it just wouldn't be the speed of light :) c is a fundamental constant of spacetime - it's the dimensional constant that links time and space dimensions, to be technical. One of the ways this manifests itself is as the speed limit of the universe, and another way it manifests itself is as the speed of massless particles. Since light is probably massless, it makes sense to call this the speed of light, but what's fundamental about c has nothing to do with light. c's connection with light is completely incidental.

Also, the constraints on the photon's mass are so small that even if it traveled somewhat slower than c, the "real value" of c would still be only negligibly larger than its present value of 300 million meters per second. A particle that travels at 1 billion meters per second is, sadly, ruled out.
 
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csmyth3025

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This discussion about the possibility that photons might have a non-zero mass raises a question that I'm not sure has been entirely resolved. Neutrinos are believed to have mass. The same Wikipedia article on neutrinos that makes this assertion also contains the following passage:

In the early 1980s, first measurements of neutrino speed were done using pulsed pion beams (produced by pulsed proton beams hitting a target). The pions decayed producing neutrinos, and the neutrino interactions observed within a time window in a detector at a distance were consistent with the speed of light. This measurement has been repeated using the MINOS detectors, which found the speed of 3 GeV neutrinos to be 1.000051(29) c. While the central value is higher than the speed of light, the uncertainty is great enough that it is very likely that the true velocity is not greater than the speed of light. This measurement set an upper bound on the mass of the muon neutrino of 50 MeV at 99% confidence.[18]

The same observation was made, on a somewhat larger scale, with supernova 1987a. The neutrinos from the supernova were detected within a time window that was consistent with a speed of light for the neutrinos. So far, the question of neutrino masses cannot be decided based on measurements of the neutrino speed.
The question that has me wondering is: If neutrinos have any mass - no matter how small - can they also travel at the speed of light?

Chris
 
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Mee_n_Mac

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csmyth3025":fm9vugqf said:
The question that has me wondering is: If neutrinos have any mass - no matter how small - can they also travel at the speed of light?

Chris

Nope, no can do.
 
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