For our Quantum Physicists amongst us...

[ian.settle1]

Saw QI the other day, the 'Does a falling tree in a deserted forest make a sound' question came up, which led on to when a beam of light passes in front of you, you can't see it. It's only when it hits your retina that one 'sees'.
So chatting down the pub about this (yes, not a single female in sight), we came up with the idea that everything one is not looking at, is in darkness? Which leads onto the question, if there are no observers does anything actually exist if there are no observees?

Sounds like you where all talking like women as the the beer had got to you all with asking questions like that

 

[Darkwood]

The 'does it still make a sound' is a lot more complex to answer because sound does not exist as such it just air pressure waves, it is not a sound until it hits an eardrum and is thus change from pressure waves into what our minds perceive as sound... the reason as well you may question why i haven't applied the same reasoning and explanation that i did to light in previous post is that light is a energy form in itself so the event happens whether your there to see it or not, where as sounds is a kind of kinectic energy and not an energy form in itself; it requires to hit an eardrum to be classed as sound if it dosn't then it is not sound and just a pressure wave.

 

[topquark]

Archy ive got shelfs of books on said subjects and the more you read them the more confusing they get, in reply to your query its just a matter of observation and event, if you are there when event happens and the radiation reflected at you is visible light then your brain will record the event, but its also a perception thing - different species have different light receptors and may not see the same thing as yourself but may see a differing event, either/or the event still happens but the knowledge it ever did is down to it been visible light and you receiving it. Basic example is the colour blind test if one of your colour receiving cones is faulty or missing you dont see the green no' in the blue pattern(example colours) but it is still there to those with full colour vision hence the green light still hits the retina the event happens (photon reflect to eye) but without the correct cone to register it you may be blind to it.

That's a great example DW.

 

[Kamikaze]

Me likes this thread :biggrin:, and just to add to darkwoods excellent posts. Sound waves rely on another medium like air or water to move from one place to another. For example through steel it is 15 times faster than through the air.
As to Archys falling tree in the deserted forest conundrum. I think that even if one can’t hear the sound the vibration of the sound wave from an observers point of view would indicate that a sound wave had been present.

 

[Darkwood]

Be careful Kam... regarding the tree falling to the ground in a forest, the forest floor would act like an accoustic damper as it will have a low density ratio unlike say steel and any vibrations would disipate faster than the pressure waves in the air so in this case its unlikely you would be made aware of the event through the ground but many factors do have a play in what will happen (temp, density, wind, obstacles, ground water content etc etc).

 

[Darkwood]

Think il retreat to nerdsville :vanish: lol

 

[Kamikaze]

Unless the falling tree and deserted forest are within a vacuum a sound will be created, however great or small that may be, that is for certain. So it all comes down to how good the observers sound detection is.
Archys question about whether anything actually exists has been bothering me. I shall return to my world between Tellytubby land and Middle Earth to ponder over that one.
:54:

 

[Darkwood]

Read my post regarding sound.... the falling tree will create pressure waves through the various mediums around it, it is not a sound until it hits the ear drum it is mearly a pressure wave so if their is no eardrums to translate the pressure wave into what is heard as sound then it has no sound, its just atoms bouncing together in a wave pattern.
Again dont try blend basic school physics with quantum theory or you'll just confuse matters, school teaches us about sound waves but they are not sound waves but pressure waves, sound waves dont exist in their own context of the word.
Example... close mouth and hold nose and blow, your ears will 'pop', this is because the pressure has change in the ear canal and the ear drum has changed shape in response hence you hear a pop; a sound!, now no 'sound wave' was ever created you just altered the pressure in you ear canals.
Its can be a hard concept to understand especially when you are taught about sound waves at school but these pressure waves can't be tagged with the term sound wave until they have been heard and even then its a misleading name as they are still pressure waves, you can usually translate these pressure waves easily through air and water, but consider solid steel that has vibration when you touch it yet you hear nothing, it is vibrating thus it has pressure waves running through or oscillating within it now you wouldn't normally call the vibration a sound wave but put it against your ear and and the vibrations (pressure wave) will be translated into sound if within 20hz -20khz frequency.

 

[topquark]

Read my post regarding sound.... the falling tree will create pressure waves through the various mediums around it, it is not a sound until it hits the ear drum it is mearly a pressure wave so if their is no eardrums to translate the pressure wave into what is translated as sound then it has no sound, its just atoms bouncing together in a wave pattern.
Again dont try blend basic school physics with quantum theory or you'll just confuse matters, school teaches us about sound waves but they are not sound waves but pressure waves, sound waves dont exist in their own context of the word.
Example... close mouth and hold nose and blow, your ears will 'pop', this is because the pressure has change in the ear canal and the ear drum has changed shape in response hence you hear a pop; a sound!, now no 'sound wave' was ever created you just altered the pressure in you ear canals.
Its can be a hard concept to understand especially when you are taught about sound waves at school but these pressure waves can't be tagged with the term sound wave until they have been heard and even then its a misleading name as they are still pressure waves, you can usually translate these pressure waves easily through air and water, but consider solid steel that has vibration when you touch it yet you here nothing, it is vibrating thus it has pressure waves running through or oscillating within it now you wouldn't normally call the vibration a sound wave but put it against your ear and and the vibrations (pressure wave) will be translated into sound if within 20hz -20khz frequency.

Spot on DW. I think that's one of the biggest problems with the way we teach, we seem to like paradigms. Like the old event/observer model to explain things, in practice an observer is nothing more than another event (it just happens to be in a sensory organ). But it's easier to explain that way.

Sound is just like light, it has no mass (supposedly....I'll come to that in a mo). It radiates out from a fixed point until it's quanta is released (either by an event ("colliding" with an object) or observer).

Now the quandry (latest thinking is a photon has no mass, it's just energy)....if light has no mass how come it is affected by the gravity of a black hole?

 

[Darkwood]

Gravity warps space time, light follows space time .... quickest way to answer that

 

[topquark]

Gravity warps space time, light follows space time .... quickest way to answer that

I take it you've been to the pub as well (not buying that one)

 

[Darkwood]

I take it you've been to the pub as well (not buying that one)

No! no beer for me tonight, its an often asked question in quantum physics but although at first its seems like it going to be a brain-buster it really is a straight forward concept, photon is like any other boson in that its a force carrier (excluding Higgs Boson as this is like a central piece linking quarks, leptons and bosons). The fabric of space time although still an unknown concept is affected by gravity and warped in some way, photons even though massless in the standard model still permiate through space time if the light travels long enough it also has red shift because over the billions of years the universe has expanded stretching space time and thus also stretching the waveform of the photon, this in itself hints that it is effected by anything that would stretch spacetime.

 

[Des 56]

You lads can't go off drinking beer at a time like this,I was just getting engrossed and educated by the sobriety of the thread

 

[Darkwood]

Browse the Quantum physics forum Des .... now even i get totally confused in there lol

 

[Des 56]

Browse the Quantum physics forum Des .... now even i get totally confused in there lol

The problem as I see it,I like this forum,so could I be in two places at one time ? lol