Question about light

Sorry I have a question, I have found an answer but... not quite understanding the answer..

Ok so the question I was thinking to myself was, If sound waves can travel through walls why can't light.

I found this answer..Phys answer


But the answer was roughly, because light is on the same wavelength and frequency as the wall (or other matter) which to me doesn't make sense. I just can't see how a wall could have a wavelength similar to light.
I am assuming that there has to be an interaction on a quantum level.

Oh well someone shed some light on the subject please.

I'm terrible at explaining things, though the answer you linked to isn't bad. It's a decent answer so aslong as you re-read it to try understand it better, isn't much else I can say

reply to post by KingAtlas


I think the most basic, easy to understand answer is that sound waves cause matter to vibrate and create new sound waves on the other side from the vibrations. The denser the material the less vibration and the fewer sound waves created on the other side.

Light waves are reflected by matter and do not cause any effect. Some matter reflects less light so light can pass through it (Glass for example) and some matter will reflect 100% of the light waves and be completely reflected. Note the light isn't actually disappearing it is reflecting and dispersing.

Now is there something going on at the quantum level? Of course there is! I just don't know what it is and nobody knows for certain but I bet there are quite a few theories out there.

light is made of photons, an actual partical, so it hits the material and reflects/deflects of.

there is no sound partical, it is simply collision after collision of particals into each other. sound travels faster in denser objects because particals are closer together.

ok ... so it's the doppler effect then creating the sound on the other side.?

as for the light photon explanation, the problem i have with thtat is that a photon is both partice and wave or
wave particle, and therefor your saying that the
waveparticle is reflecting because it has a particle,
but i can't see that being the reason,
because even if it were a wave particle "bouncing off" the other particles,
then that would insinuate that a wave particle would have to have a "mass",
because with out the mass the wave particle would not "bounce off" the other particles... but as far as I understand if a wave particle had any mass it couldn't possibly travel at the speeds at which it does.

Ok so the question I was thinking to myself was, If sound waves can travel through walls why can't light.

Some frequencies of light can pass through walls such as infra red (heat) and x rays (extremely high frequency). As with sound, the thickness of the wall and the strength of the light/sound makes a difference as to if it can pass through or not.

I just can't see how a wall could have a wavelength similar to light.

Each specific colour is at a specific wavelength. The fact that you can see a colour indicates that you can see the wall. The colour of the wall alters the lights photons wavelength as it bounces of the wall and enters your eye. It is pretty tricky how different compounds alter the wavelengths of the photons that bounce of them. While it may not always be easy to understand, there is always a reason why.

the problem i have with that is that a photon is both partice and wave

A lot of people and science in general is still having a problem with it. With a photon being mass less is part of it, according to the theory of relativity it should also be frozen in time travelling at the speed of light. But different substances to alter the speed that light travels. It does get tricky.

reply to post by kwakakev

Good answer kawkakev!

I'd just clarify the photon always travels at the speed of light. The only reason we measure slower speeds in some substances is due to delays caused from photons being absorbed and re-emitted. But when the photons are moving they are moving at the speed of light even in substances where we measure the speed of light as slower.

Here's a thermal image of a house where infrared has been converted to visible light so we can see what light is going through the walls in the infrared range:

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