Just a question about light speed

[guitarguru11]

Just joined today, so, hi everyone!

And please, forgive me and point me in the right direction if this has been answered/discussed etc...

I'm pretty much an armchair physics kinda guy, and understand the whole concept of speed of light.. But what I can't really find an explanation for, is what exactly is the 'light' that is referenced to in the "speed of light."

Is this ALL forms of any kind of 'light?' ie: our light spectrum, Gamma, Xrays etc..
And their Hz don't depict how fast they travel through space and or time?
Do they all travel at tthe same speed, it's just their intensity is different?
Kind of like driving a Ford Focus into a wall @ 60mph vs. an Abrams tank through the same wall at the same speed? Where the Ford represents our visible light, and the tank represents Gamma rays?

Or am I totally and completely off here?
Thanks in advance for any and all replies!

 

[bcrowell]

Yep, you've got it right. They all travel at the same speed, regardless of frequency and intensity.

 

[guitarguru11]

Yep, you've got it right. They all travel at the same speed, regardless of frequency and intensity.

Thanks for that quick reply!

But, what about sound waves vs light waves?

Are sound waves actually traveling at 'c' , are at a lower frequency, and are thus just 'slowed down' by the median their in? ie: air, water, stone?

Meaning: I know a voice can't travel through a brick wall the same way a wi-fi signal can, even though they are both waves of some sort. Being that the wi-fi signal is more closely 'repeated' (crests/troughs being closer together), it's going to penetrate with more force. Is that the same for light?
Is all that right? It at least sounds right in my head...

If I am right, which I'm probably not... Can we, or do we, have a median that slows down light, in the same sense that brick slows down sound?

 

[JesseM]

Thanks for that quick reply!

But, what about sound waves vs light waves?

Are sound waves actually traveling at 'c' , are at a lower frequency, and are thus just 'slowed down' by the median their in? ie: air, water, stone?

Meaning: I know a voice can't travel through a brick wall the same way a wi-fi signal can, even though they are both waves of some sort. Being that the wi-fi signal is more closely 'repeated' (crests/troughs being closer together), it's going to penetrate with more force. Is that the same for light?
Is all that right? It at least sounds right in my head...

If I am right, which I'm probably not... Can we, or do we, have a median that slows down light, in the same sense that brick slows down sound?

Sound waves are vibrations in the particles of a medium (not 'median' by the way) such as air or water, where the particles are bumping each other back and forth in a rhythmic way, see the animations http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html (and pick out an individual dot to watch, note that it just goes back and forth rather than traveling along with the wave). Sound waves don't travel at c, and their speed varies depending on what inertial frame you're analyzing them from (although in the 'rest frame of the medium' where the average momentum of the particles is zero, sound waves from different sources and going in different directions all have the same speed in the coordinates of this frame). Light is not today thought to be a vibration in a physical medium made of particles like this, although 19th century physicists imagined it was (their name for this unseen medium was the luminferous aether, but the theory of relativity predicted that all experiments to try to detect the 'rest frame of the aether', like the Michelson-Morley experiment, would fail, and so the idea fell out of favor)

 

[bobc2]

If I am right, which I'm probably not... Can we, or do we, have a median that slows down light, in the same sense that brick slows down sound?

Actually, I think sound might travel faster through brick than through air. The speed of sound through a solid medium is expressed through the equation (if I'm remembering it correctly): v = SQRT(E/p), where E is the modulus of elasticity and p is the mass density.

So, the more massive (per unit volume), the slower the wave. But, the higher the modulus (related to how stiff--how difficult to compress), the faster the wave travels. Again, I haven't really done the calculation for brick (maybe someone knows the answer on that), but for example, the speed of sound is much higher in metals like aluminum and steel than it is in air.

For light to propogate through the aether medium at 186,000 mi/sec, that medium would have to have an incredibly high modulus so to speak and low inertia effects. But as JesseM has pointed out, physicists don't think in those terms at all in thinking about light waves. In fact light is perhaps mostly thought of as particles having curious quantum electrodynamic properties, i.e., photons.

There is a really good book you would like: "QED - The Strange Theory of Light and Matter" by Richard P. Feynman. I always see it on the shelf every time I go to Borders Book Store.

 

[Drakkith]

Are sound waves actually traveling at 'c' , are at a lower frequency, and are thus just 'slowed down' by the median their in? ie: air, water, stone?

Meaning: I know a voice can't travel through a brick wall the same way a wi-fi signal can, even though they are both waves of some sort. Being that the wi-fi signal is more closely 'repeated' (crests/troughs being closer together), it's going to penetrate with more force. Is that the same for light?

As said before, a sound wave is the result of a large number of particles moving in a certain way. Light is NOT like this. Light ACTS like a wave and it also ACTS like a particle depending on how you observe it. A Photon is a single Quanta of light. The key here is that the Photon itself IS the wave. You don't have 1,000 photons moving together like a wave, they actually are each their own wave. Light is composed of an electric and magnetic field that oscillate with each other, we call this an Electromagnetic Wave. Each field causes the other field to exist and propagate. You cannot separate these fields or break a photon into smaller pieces. Thats what Quanta means. One singular amount of energy or momentum that cannot be broken up.

A Wi-Fi signal is an electromagnetic wave. It is light but with a lower frequency. How EM radiation penetrates objects is NOT like a sound wave.