# Light traveling as waves?

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## Main Question or Discussion Point

I'm having trouble understanding how light travels as waves and particles. I think it should be one or the other and not both. I'm thinking that light travels only as particles and only linear.

The fact that light wraps around things is due to the lensing effect that light does naturally. We can see this if you take a flashlight and point it at something solid that light cannot pass through and if you move the light source closer or farther to the object, the shadow changes, due to the lensing effect as a normal property that light has.

Wouldn't this mean that there is no such thing as gravitational lensing? That the redshift is just due to the lensing effect happening at high speed? There was an experiment that one guy did to show the redshift with rotating mirrors, but again isn't that just at high speed?

That would also be why light can be split or focused. If it were to travel as waves, and we tried to split it, it would then be split to nothing or focused to nothing.

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Orodruin
Staff Emeritus
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Nature does not care about what makes sense to you. Physics is about describing how Nature works based on experimental results.

davenn
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I'm having trouble understanding how light travels as waves and particles. I think it should be one or the other and not both. I'm thinking that light travels only as particles and only linear.
why ?
It depends on how you measure it ... measure it one way and it is obvious it behaves as a wave. Measure it another way
and it is seen to behave as particles .... there is no problem with this scenario

The fact that light wraps around things is due to the lensing effect that light does naturally. We can see this if you take a flashlight and point it at something solid that light cannot pass through and if you move the light source closer or farther to the object, the shadow changes, due to the lensing effect as a normal property that light has.
and there is the perfect example of why it behaves like a wave in that situation

Wouldn't this mean that there is no such thing as gravitational lensing? That the redshift is just due to the lensing effect happening at high speed? There was an experiment that one guy did to show the redshift with rotating mirrors, but again isn't that just at high speed?

again, why ? .... gravitational lensing and red shift are 2 very different situations
redshift is not caused by lensing, it is caused by motion.

That would also be why light can be split or focused. If it were to travel as waves, and we tried to split it, it would then be split to nothing or focused to nothing.

that statement doesn't make sense
light is split and refocussed on a regular basis in many lab experiments

Do you understand that light ... visible light is just a small section of the whole electromagnetic spectrum
that includes radio waves, infra-red, visible light, x-rays and gamma rays ??

Nature does not care about what makes sense to you. Physics is about describing how Nature works based on experimental results.
and as harsh as Orodruin's post may seem to you .... unfortunately for you, at this time, it is true

But don't give up, do some reading of some decent science literature ... first year university physics text books etc
and learn what it is really all about

regards
Dave

Drakkith
Staff Emeritus
Sorry to be blunt, but you are indeed incorrect. The wave-like nature of light has been known for centuries. Refraction and diffraction are both wave behaviors (you can get both from many types of waves, not just light). You cannot get diffraction or refraction from classical particles. The wave-like properties of light are part of its basic description and every single device used to generate, manipulate, or detect light depends on them either directly or indirectly. To not believe in these properties would be like not believing in momentum.

That would also be why light can be split or focused. If it were to travel as waves, and we tried to split it, it would then be split to nothing or focused to nothing.
Nonsense. You can easily see the splitting of waves in gravity waves (waves on the surface of water, not gravitational waves). One could then focus these waves with the appropriate setup. The same is true of all waves.

Orodruin
Staff Emeritus
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So, to expand, light is neither particles nor waves. Light is light. We have a fairly good description of how light behaves and according to this description it has some properties we would generally associate with a wave and some we would associate with a particle. Depending on what observations you perform, either the wave-like or particle-like properties might be more prominent.

One way to think of it is that the difficulty in classifying light with other phenomena comes from that those other phenomena have mass, and light does not. So it is actually in a category of it's own.

Although the single particle double-slit experiment is so suggestive of a wave interfering with another wave yet while there is only a single particle that it confuses me.

that statement doesn't make sense
light is split and refocussed on a regular basis in many lab experiments

Do you understand that light ... visible light is just a small section of the whole electromagnetic spectrum
that includes radio waves, infra-red, visible light, x-rays and gamma rays ??

My statement does make sense. It's kinda like when light hits a shiny sphere. It's reflected off into nothing. If light were waves then it wouldn't be able to be focused it would bounce into nothing.

I know light is split and focused all the time, that's the point I'm trying to make. It's not a wave.

Yes I understand that there is light that we cannot see but I think that radio waves shouldn't be included in that group.

Yes I believe that redshift is due to the lensing effect from an object that is in motion.

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that's the point I'm trying to make. It's not a wave.
And people here are saying that your point is totally wrong. You should read again what they said, its basic physics that you're trying to overthrow.

why ?
It depends on how you measure it ... measure it one way and it is obvious it behaves as a wave. Measure it another way
and it is seen to behave as particles .... there is no problem with this scenario

and there is the perfect example of why it behaves like a wave in that situation
I'm curious as to how it is so obviously behaves as a wave. Please explain.

and as harsh as Orodruin's post may seem to you .... unfortunately for you, at this time, it is true
It's not harsh at all. I think it's a bit naive considering he's listed here as a "mentor", but other than that; I can take it.

Sorry to be blunt, but you are indeed incorrect. The wave-like nature of light has been known for centuries. Refraction and diffraction are both wave behaviors (you can get both from many types of waves, not just light). You cannot get diffraction or refraction from classical particles. The wave-like properties of light are part of its basic description and every single device used to generate, manipulate, or detect light depends on them either directly or indirectly. To not believe in these properties would be like not believing in momentum.
For centuries people believed that the earth was the center of the universe. Pointing that out does nothing to explain what you mean.

I can see how diffraction is a wave behavior but not refraction. When light is refracted it comes out the other side unchanged (other than its direction). When sound waves pass through something different and are said to be "refracted", the waves change speed and wavelength. That would imply that they are not refracted the same as light and it is something different all together.

My eyes are devices to detect light. I can use a mirror to manipulate light. Still not seeing your point. With the universe constantly expanding there is no sitting still.

Nonsense. You can easily see the splitting of waves in gravity waves (waves on the surface of water, not gravitational waves). One could then focus these waves with the appropriate setup. The same is true of all waves.
Ok how about this? If the waves on the surface of water were to encounter something round would the waves really be "split", or would they just be diffracted?

Sound waves aren't split the same way light is. You can't make a different tone out of one sound.

And people here are saying that your point is totally wrong. You should read again what they said, its basic physics that you're trying to overthrow.
I know, isn't it wild?

Nugatory
Mentor
I'm curious as to how it is so obviously behaves as a wave. Please explain.
Diffraction, interference, and Doppler shift have all been observed in light. These phenomena can only be explained if light is a wave, as they are results of solving the wave equation under various initial conditions (you will encounter this equation and many of its implications in the second year of a undergraduate physics program - https://www.amazon.com/dp/0070048606/?tag=pfamazon01-20 is a good textbook at that level).

So we have almost five centuries of experiment and observation showing that light is a wave.

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Nugatory
Mentor
I know, isn't it wild?
That "snick" sound you just heard is the noise a thread makes when it is closed. Wild, isn't it?