light is a wave...right?

[spikerz66]

sound is a wave. the inner ear detects sound by the vibrations on the eardrum from the sound wave. light is a wave also. does the moving of the eardrum to make a vibration imply that the sound wave has a mass and is pounding against the eardrum? wouldnt this mean that the wave has a mass? if light to is also a wave using this analogical thinking wouldnt this to imply that light waves have a mass?

 

this doesent make sence why light is so different from sound of there both a wave- you cant get very much simpler defintion of the two than a wave-

 

now so you dont think im retarded i do realise that light has no mass bc if it would every time we step out of the dark we would be turned into swiss cheese from the "mass" of the photons.

 

what im trying to get at is are there a differnt definition of a wave than i dont know of?

[Sisyphus]

Ok, a few things. First, sound: It is a wave, yes, a compressive wave through a medium of matter. It does not in itself have mass. It is a successive, "chain-reaction" movement of the matter it moves through, which does have mass. Just like a wave through water: it's the water that has the mass, the wave is a just a motion.

 

Now, light. Light is NOT a wave in the same sense. It does, more or less, move like a wave when it's travelling. However, there are important differences. For one thing, there is no medium through which it moves, so it's not a compressive wave like sound. Second, it only hits things in one location, as a particle, a "photon." What this means, in an extremely over-simplified way, is that you can statistically predict where the photon will go based on the same mathematics you would use to describe a wave like sound, but, when that photon actually shows up, it can only be at a single point, not a whole wave-front.

 

Basically, "wave" and "particle" are both inaccurate descriptions of what light actually IS, but are useful translations into concepts we have some grasp of and which share some of light's properties. Actually, EVERYTHING is both/neither a wave and a particle, but the wave aspects are unnoticable in all but the smallest beings, like photons and electrons.

 

As for whether it has mass, that is also not really a simple answer. General relativity says that an objects mass as perceived by us is dependent on both it's "rest mass" (how massive it is with a relative velocity of zero) and it's relative velocity. It says that the mass of an object moving at light speed relative to us (like, for example, light), must have an infinite mass if it has any "rest mass" at all. Since photons obviously do not have infinite mass, they have no rest mass, which is what is meant by "mass" most of the time.

 

HOWEVER, they DO have "inertia:" it does exert pressure and put holes in things. Its inertia is very small and proportional to the "frequency" of the "light wave." But it does exist.

[jackson33]

think the confusion may be in Electromagnetic Energy and other forms of energy. a quick google on EME, will give you charts and figure for these. the range is from radio to gamma, all of which travel at C in space, contain photons and require a source for production, which are charged reactions, so to speak. there are some studies into thought waves, still controversial, but some do suggest instant or at minimal C speed.

[spikerz66]

Thanks for the very imformative post Sisyphus it was very helpful to me but while reading it a few points popped into my head.

 

Ok, a few things. First, sound: It is a wave, yes, a compressive wave through a medium of matter.

 

The medium that sound passes through being mostly, in our case on earth Air right?

 

For one thing, there is no medium through which it moves, so it's not a compressive wave like sound.

 

If a sound wave can traverse through air as a medium, than why cant light? We do not live in a vacuum. Therefore there HAS to be something for in which light to travel. Isnt this a medium?

 

On another note, wouldnt there be no sound if there is no medium for it to pass through? Using this logic does this mean that there is no light in space (a vacuum) if theres nothing for it to travel through?

 

 

Basically, "wave" and "particle" are both inaccurate descriptions of what light actually IS, but are useful translations into concepts we have some grasp of and which share some of light's properties.

 

HOWEVER, they DO have "inertia:" it does exert pressure and put holes in things. Its inertia is very small and proportional to the "frequency" of the "light wave." But it does exist.

 

This to me is very important. I cannot agree with you more on this. I cannot though think of any examples though in which light can exert pressure on thing, maybe im not thinking hard but i really would like more info on this.

If anyone knows anything onit then PLEASE tell me.

[spikerz66]

I apologise for the double post but another thing just went through my head.

When light is travelling through the vacuum of space its moving at C whouldnt it slow down if it enters a medium? Such as.....Earths atmosphere? Does this mean that the speed of light on earth is actually slowed down unless its in a complete vacuum?

[swansont]

Yes, light slows when it enters a medium with a higher index of refraction, but it can propagate through vacuum, whereas sound cannot. Light propagates through air, but the air isn't required.

 

Note also that sound is a longitudinal wave, while light is a transverse wave.

 

Light exerts pressure on things; it's the basis of laser cooling, which won the Nobel Prize for Chu, Cohen-Tannoudji and Phillips in 1997. Atoms are being trapped with light pressure in my lab at this very moment. It's not normally noticed because it's such a small force once you get above atomic mass scales.

[spikerz66]

Thank you swansont im just curious what more exactly are you doing in your lab now? How else can light exert pressure on it?

 

So this means that in our atmosphere light speed isnt a constant? its slowed down slowly?

[Sisyphus]

The medium that sound passes through being mostly, in our case on earth Air right?

 

Yup. Though it can travel through any matter of all but the least density, and travels better through more dense media, like water or rock. What we hear is mostly through air, though, because our ears are generally in air, and sound doesn't transfer too well between media of different densities.

 

If a sound wave can traverse through air as a medium, than why cant light? We do not live in a vacuum. Therefore there HAS to be something for in which light to travel. Isnt this a medium?

 

As Swansont said, light can travel through air, but that air is just a hindrance, it's not a medium. Light travels best through vacuum.

 

On another note, wouldnt there be no sound if there is no medium for it to pass through? Using this logic does this mean that there is no light in space (a vacuum) if theres nothing for it to travel through?

 

You are correct that there would be no sound without a medium for it to travel through. However, that is not the case with light, which is why it's an entirely different sort of "wave" altogether.

 

This to me is very important. I cannot agree with you more on this. I cannot though think of any examples though in which light can exert pressure on thing, maybe im not thinking hard but i really would like more info on this.

If anyone knows anything onit then PLEASE tell me.

 

You wouldn't notice it in everyday life, just because it's such a small effect compared with all the other forces we continually deal with. However, under special circumstances, it's quite observable:

 

http://en.wikipedia.org/wiki/Light_sail

 

So this means that in our atmosphere light speed isnt a constant? its slowed down slowly?

 

No, it doesn't slow down. It's just slower than it would be in empty space.

[swansont]

Thank you swansont im just curious what more exactly are you doing in your lab now? How else can light exert pressure on it?

 

I trap atoms for use in an atomic clock (Rubidium Fountain)

[spikerz66]

wow i cant believe i forgot about the sagan light sail.